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154 Cards in this Set
- Front
- Back
What genera are included in the Micrococcaceae family
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1. Staphhylococcus
2. Micrococcus |
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Describe the cellular morphology of members of the Micrococcacae family (Staphylococcus, micrococcus)
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gram positive cocci that commonly occur in clusters
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Where do Stahylococci species colonize the normal human
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-skin
-mucous membranes |
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What is the coagulase reaction of Staphylococcus aureus
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S. aureus is coagulase positive
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What is the coagulase reaction of Staphylococcus epidermidis and S. saprophyticus
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S. epidermidis and S. saprophyticus are coagulase negative
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What is coagulase? What does it do? What is its function in vivo
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-A bacteria made protein that has a prothrombin like activity
-It converts fibrinogen to fibrin resulting in the formation of a visible clot -In vivo, it is thought to form a fibrin barrier at the site of staphylococcal infection, localizing the organism into abscesses |
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What differentiation is the coagulase test used for?
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Coagulase differentiates Staphylococcus aureus (positive) from other staphylococci and micrococci
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List some Staphylococcus aureus associated human diseases
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-cutaneous infections (boils, furuncles, carbuncles, impetigo, folliculitis, surgical and stich wounds
-toxin mediated diseases (food intox, toxic shock, scalded skin syndrome) -bacteremia, bone, organ infection |
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T/F Staphylococcus aureus is part of the normal flora of a healthy human
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True. S. aureus may apper chronically or intermittently in the nares of on the hands of healthy people (carriers)
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T/F coagulase negative staphylococci (S. epidermidis, S. saprophyticus) are pathogenic
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Sort of true. They are opportunistic pathogens. S. epidermidis can infect catheters, grafts, prostethis, and implants leading to endocarditis. S. saprophyticus can lead to acute UTI in young females
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Where do Micrococcus species colonize the normal human
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transient flora of the skin
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What is the catalase result of micrococcaceae (Staphylococcus and Micrococcus)
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catalase positive
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How can Micrococcus species be differentiated from Staphylococcus species (3 ways)
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-cellular morphology (Staph is bigger, Micrococcus usually appears in tetrads)
-Oxidase (Micrococcus is positive, Staph is negative) -bacitracin (Micrococcus is suceptible, Staph is resistant |
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Describe the pigments produced by Staphylococci
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the pigments are lipochromes (insoluble in water but soluble in organic solvents) S. epidermidis and S. saprophyticus each produce a white to gray pigmented colony. Many S. aureus strains produce a golden yellow pigment but some are white
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T/F most coagulase negative streptococci produce strong zones of beta hemolysis
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false, most coag negative streptococci do not show a strong zone of beta hemolysis
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What does the novobiocin test differentiate
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it is used to identify coagulase negative streptococci, S. saprohyticus is resistant, S. epidermidis is sensitive
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Describe mannitol salt agar. How is it selective? How is it differential?
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Mannitol salt agar is used to select and differentiate staphylococci species.
Selectivity- 7.5% salt concentration supresses growth of most bacteria except Staphylococci and Enterococci. Differerntial-manitol fermenting bacteria such as S. aureus and S. saprophyticus produce a yellow halo, indicating the productiong of acid from mannitol fermentation. Phenol red is the pH indicator |
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What is the principle test used for the identification of S. aureus?
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coagulase. S. aureus is coagulase positive
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What are the two forms of coagulase produced by S. aureus
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1. cell bound aka clumping factor
2. free |
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Describe the steps of the coagulase test
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1.A drop of water and a drop of plasma are placed on a slide
2. A colony is removed with a wooden stick and mixed into the water, another is placed in the plasma 3. Look for clumping to indicate a positive reaction |
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What is the negative control in the coagulase test
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the colony is transfered into water
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Describe what is occuring biochemically during a positive coagulase test
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the cell bound clumping factor acts on fibrinogen binds it so that it aggregates
free coagulase causes the conversion of fibrinogen to fibrin and leads to the formation of a fibrin clot |
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T/F a slide coagulase detects free coagulase
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False. The slide test detects only bound coagulase, a tube test must be used to detect both free and bound coagulase
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What is the purpose of doing a tube coagulase test
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The tube coagulase test detects both free and bound coagulase. It is more sensitive than the slide test btu requires more time.
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how is a tube coagulase test carried out
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Colonies are emulsified in a tube containing 0.5 ml rabbit plasma. The tube is incuabted for 4 hours, checked and then incuabted overnight if negative (just in case fibrinolysin is present) A positive test is the formation of a clot
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What does the oxidase test detect? How is the test preformed
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It detects the presence of cytochrome oxidase
A colony is swabed and if it contains oxidase, the substrate 1% tetramethyl-p-phenylenediamine dihydrochloride is oxidized to a purple color |
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What two situations could give a false positive oxidase test result
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1. Using a colony that was growing on selective media
2. Using a colony that was growing on glucose containing media |
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how can a strain of S. aureus be slide coagulase negative but tube coagullase positive
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If the slide coag test is negative the strain does not have bound clumping factor. If the tube test is positive the strain has free coagulase
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What test would differentiate S. aureus from S. epidermidis
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coagulase
S. aureus is positive S. epidermidis is negative |
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What test would differentiat S. epidermidis from S. saprophyticus
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novobiocin
S. epidermidis is susceptible S. saporphyticus is resistant |
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What test differentiates Staphylococcus species from streptococcus species
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catalase
Staphylococcus are positive Streptococcus are negative |
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describe the SCV (small colony variant) of S. aureus
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It is a slower growing strain that causes persistant infections. It is resistant to antibiotics due to its slow metabolism
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Define opportunistic pathogen
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causes an infection in a compromised host. Can also occur if a huge number infect a healthy person
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Define noscomial infection
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hospital aquired
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define bactermia
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bacteria in the blood
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define Iatrogenic
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infection due to procedure or treatment (IV, cathetar, etc)
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Define Endocarditis
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inflamation/ infection of heart valve/heart lining, usually occurs with artificial valave
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define tropism
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affinity for
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What are the 3 mucous membranes that are most important when considering infection
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1. respiratory tract
2. gastrointestinal tract 3. genitourinary tract |
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What is they oxygen relationship of Staphyloccus species
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falcultative
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describe staphylococcus gram stain and morphology
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gram positive clusters, division on more than one plain leads to clustering (contrast to planer divison that gives tetrads and strepping)
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Define fomite
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inaniment surface where bacteria (esp. staph) colonize eg. bedding, clothing, keyboard, etc
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Where are Staphylococcus species normally found
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nasal (nares), skin, mucous membranes
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Describe the steps of biofilm formation
How do they affect antibiotic efficacy |
1. plantonic (free floating cells)
2. attachment 3. cell-cell adhesion and proliferation 4. maturation 5. detachment Need 1000x higher antimicrobial dose, usual the device has to be removed |
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What is quarum sensing
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the ability of bacteria to communicate and coordiante behavior via chemical signaling molecules
When the molecule binds to the receptor, it activates transcription of various genes including signal molecule synthesis, when the bacterial reach a threshold density a positive feedback loop is engage for signaling molecule and the receptor becomes fully activated. This can up regulate other genes like virulence or biofilm formation |
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What disease is associated with S. Saprophyticus (where does it have a tropism)
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urinary tract infection usually in young, sexually active women
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what disease is associated with S. epidermidis
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Infections of surgical implants, catheters, prosthetic heart valves, can lead to endocarditis
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What does Staphylococcus epidermidis secrete that helps it adhere to implants
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EPS (extracellular polymeric substance)
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What are some virulence factors produced by S. aureus
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cytolytic toxins, enzymes, coagulase, cell wall protein A
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What diseases are caused by S. aureus
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Skin wound infections which can progress to osteomyelitis, lesions (furuncles, carbuncles, stich wounds, impetigo)
Pneumonia, UTI |
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Describe the food INOTOXICATION (not infection) caused by S. aureus
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Some toxins produce a preformed enterotoxin that can cause sickness within 1-12 hours. Foods invovled include processed meat, salted ham, creme filled pastries, custards, mayonaise. An outbreak can be ID if >10^5 CFU/ml are detected in unheated food, the heat stable toxin can be detected
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What diseases are associated with the exotoxins produces by S. aureus
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Toxic shock syndrome, scalded skin syndrome
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Which two strains of Staphylococcus are resistnat to mehicillin
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S. aureus and S. epidermidis
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define pyrogenic
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fever producing (cytokines lead to fever)
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define pyogenic aka. suppurative
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pus producing
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What type of hemolysis do Staphylococcus species produce
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beta hemolysis due to cytolytic toxin or hemolysin
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What tests differentiates Micrococcaceae from Streptococcus and Enterococcus
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The micrococcaceae (staphylocuccus and micrococcus) are all catalase positive. Staphylococcus and enterococcus are catalase negative
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What is detected in the tube coagulase test? Slide
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tube= free coagulase
slide= bound coagulase |
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Which Staphylococcus species is suceptible to novobiocin
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S. epidermidis is suceptible, S. saprophyticus is resistant
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What is being detected when using the latex agglutination test to identify S. aureus
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bound clumping factor and protein A, The Fc of Ig molecues (which are boudn to the latex) binds protein A and pulls the latex together giving a visible matrix. IF bound coagulase is also present, the will be strands of fibrin
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Describe the morphology of Streptococcus and Enterococcus species
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non-motile gram positive cocci
they can have spherical, oval, or elongated shapes |
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Why do Streptococcus and Enterococcus species usually form pairs or chains
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the cocci divide in one plane
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What is the colony morphology of streptococus and enterococcus species
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very small, various colors
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What are the catalase and oxiase results for streptococcus and enterococcus species
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catalase negative (differentiate from staphylococcus)
oxidase negative (differentiate from Neisseria) |
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Describe alpha hemolysis
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production of a greenish discoloration on BAP due to incomplete lysis of RBCs
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describe beta hemolysis
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colonies are surounded by a clear zone due to complete lysis of RBC and breakdown of hemoglobin
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What are the two hemolysins that can be produced by group A streptococci?
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Streptolysin O- antigenic, oxygen labile
Strepolysin S- non anitgenic, oxygen stable |
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Why is it necessary to stab the agar of a BAP if trying to test for Beta hemolytic streptococci
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streptolysin O is oxygen labile and will only produce hemolysis if it is in the low oxygen environment beneth the agar
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What are lancefield groups
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a classification system for human infection streptococci and enterococci based on group specific cell wall antigens. Some species do not react (viridans strep and S. pnuemoniae)
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S. pnuemoniae does not react with lancefield group antisera, how can it be identified antigenically?
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capsular polysaccharide antigens
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Considering Streptococcus pyogenes...
Lancefield group? Normal Flora location? Disease? |
Streptococcus pyogenes is in Lancefield group A.
Normal flora-low numbers by carriers 2-20% on skin and URT Disease-pharyngitis, skin infections, scarlet fever |
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What are two types of sequelae that can follow an infection with Streptococcus pyogenes
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1.rheumatic fever
2. acute glomerularnephritis |
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If a patient presents with rheumatic fever or acute glomerularnephritis, what test should be done to identify the cause?
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an ASO antibody titer to detect antibodies to streptolysin O. A positive test would confirm a previous infection with S. pyogenes or another member of streptococcal group A
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In terms of Streptococcus agalactiae
Lacefield group normal flora location Disease |
Streptococcus agalactiae is in lancefield group B
It normally colonizes in low numbers the female genital tract or URT disease- neonatal infections (sepsis and meningitis) aquired in utero/delivery (early onset) or post delivery (late onset), can infect compromised adults and causes mastitis in cows |
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Streptococcus bovis
lancefield group normal flora? disease |
lancefield group B
can be normal flora in some humans disease-carcinoma of the colon and endocarditis |
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Enterococcus faecalis, E. faecium
normal flora disease |
normal flora of GI tract can be found up to 10^8 CFU/ gram feces
Disease- nosocomial infections, UTI, bacterimia, endocarditis, wounds |
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Streptococcus pnemoniae
normal flora disease |
normal-URT of carriers, nasopharynx in low numbers, several serological types
disease- bacterial pneumonia, menigitis, otitis media, sinusitis, pathogenicity is dependent on antiphagocytic properties of capsule, capular antigens provide the basis for serological differentiation (over 80 serotypes) |
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What are viridans strep
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alpha hemolytic strep
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Viridans (alpha hemolytic) strep
normal flora disease |
normal flora- universally present on surfaces of teeth, tounge, cheeks, saliva.
disease- subacute bacterial endocarditis, S. mutans causes tooth decay |
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Bacitracin sensitivity can be used to make a presumptive differentiation between the beta hemolytics group A and groups B and C strep. Which is suceptible and which is resistant?
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Group A strep are suceptible to bacitracin, Groups B and C are resistant
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Describe the CAMP test
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Group B streptococci produce CAMP factor which enhances staphylococcal Beta lysin activity. When the two are overlayed on a BAP, enhanced hemolysis is observed. S. aureus is streaked down the middle of the plate as a source of a weak B lysin, a streak of the test strain is palced near it (do not overlap!) Incubate overnight at 37 w/o CO2 and look for enhanced hemolysis
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What species could serve as a positive control for a CAMP test?
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Any group B streptococcus such as S. agalactiae
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Why can't a CAMP plate be incubated with CO2
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CO2 incubation can result in a false positive reaction with other beta hemolytic species
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What is the CAMP test used for?
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To distinguish group B streptococci (like S. agalactiae) from other beta hemolytic streptococci
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What is the optochin test used for
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to differentiate S. pneumoniae (suceptible) from other alpha hemolytic Streptococci (resistant)
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What is optochin
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it's a detergent like compound that messes up the cell membrane
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What does a positive bile esculin test look like?
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growth, the media turns to form a dark brown or black complex
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What is the Bile esculin test used for
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for alpha hemolytic gram positive cocci, it differentiates enterococcus and group D (+) from the viridans strep and nonhemolytic strep (-)
note that some group D and enterococcus are alpha hemolytic and some are non hemolytic so the bile esculein test is used in both places. For alpha hemolytic, the optochin test is done first to separate out S. pneumonaie |
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What is the salt broth test used for
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to differentiate enterococcus from group D strep (S. bovis)
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What is the purpose of using a 2 swap method for identification of throat infections
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The first swab can be used to do a rapid latex agglutination test for group A strep. If the test is negative, the 2nd swab is used for culture on BAP and identification by traditional methods
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What type of identification is lancefield grouping
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definitive
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How is the RADT (rapid antigen identification test) preformed?
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1. extraction procedure to expose the cell wall antigen
2. Antigen is detected with group specific antibodies using latex agglutination or coagglutination |
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What is the gram stain mophology of S. pneumoniae
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gram + lancet shapped diplococci
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How do you differentiate the alpha hemolytic Enterococcus faecalis from strep pneumoniae
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optochin disk test
Enterococcus is resistant, strep pneumo is suceptible |
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How do you differentiate enterococcus species from streotococcus bovis (group D)
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PYR or salt broth test
enterococcus is positive group D is negative |
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describe the PYR disk test
what groups can it identify? How does it work? |
rapid and presumptive test for identifying group A strep (s. pyogenes) and enterococci. Both have an enzyme that can hydrolyse PYR and form a product that makes a red complex, requres culture in log phase growth 18-24 hr
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define pyoderma
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strep infection of the skin leading to pus production
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What is the oxidase test result for
Neisseria Micrococcus Streptococcus Staphylococcus |
Nessieria and micrococcus are positive
Streptococcus and Staphylococcus are negative |
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What type of antigens are used for lancefield grouping of beta hemolytic strep? group D strep?
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beta hemolytic- carbohydrate antigens
group D- lipoteichoic acid |
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what organism causes mastitis in cows
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S. agalactiae
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T/F group C strep are usually vetrinary pathogens
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True but they can infect humans also
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What are the presumptive tests for identifying group A strep? Definitive
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presumptive= bacitracin, PYR
definitive= Lancefield grouping |
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What are the presumptive tests for identifying S. pyogenes (group A) vs. S. agalatiae (group B)
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bacitracin -S. pyogenes (group A) is suceptible, S. agalactiae is suceptible (group B)
CAMP- S. agalactiae is positive |
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Which organism has the unique concave or "doughnut" shaped colony
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S. pneumoniae
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What it the seletive component of the bile esculin test? differential
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selective- bile
differential- esculin (hydrolysed to form dark brown/ black complex) |
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What are 3 ways to do antigen detection tests
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1. latex agglutination
2. coagglutination 3. ELISA |
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What genera make up the gram positive non spore forming bacilli
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Corynebacterium, Listeria, Lactobacillus
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Describe the gram stain morphology of corynebacterium
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gram positive
diptheroid/club shaped bacillus exhibiting palisade (acute angle chinese character) arrangemetns due to the snapping of dividng cells |
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Describe L monocytogens
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-intreacelluar parasite
-widely distributed in the environment -found in imporpery handeld dairy, meat products |
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Which human populations are most suceptible to Listeria monocytogenes infection
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pregnant women, newborns, immunocompromised host
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What are some manifestations of listeriosis
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septicemia, gastroenteritis
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Describe the two forms of fetal infection with L. monocytogenes
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1. early onset- aquire infection in utero resulting in still birth or early onset of disease
2. Late onset-exposure at/ after birth resulting in septicemia and/or menigitis |
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Both Listeria monocytogenes and group B strep (S. agalactiae) produce weak beta hemolysis on BAP. How can these groups be differentiated?
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1. catalase- listeria is positive, group B strep negative
2. umbrella motility 3. cold enrichment 4. gram stain- Listeria is a rod, group B strep is a cocci |
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What are the normal flora sites of Lactobacillus
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low numbers in oral cavity, large numbers in GI and female genital tract
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Describe the genus bacillus
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gram positive spore forming rods, that form endospores and grow aerobically. Found in nature
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How do humans become infected with B. anthracis
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handling infected food. animals, or animal products (usually causes anthrax in sheep, cattle, and horses)
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What two toxins does B. cereus make and how to they differ
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1. emetic, preformed, heat stable toxin, causes intoxcation in 1-6 hrs, common in rice dishes
2. diarrheal, heat labile toxin, 10-12 hrs until sxs, contaminates, meat, veggies |
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We studied two organisms that produce toxins in food. What were they?
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B. cereus- emetic and diarreal toxin,
S. aureus preforemd enterotoxin and exotoxin |
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What two organisms that we studied are particularly dangeous to newborns
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listeria monocytogenes and group B strep
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What rapid test will distinguish L. monocytogenes from S. agalactiae
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catalase, Listeria is positive, Strep agalactiae is negative
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How can you differentiate lactobacillus and streptococcus
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gram stain cell morphology
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In addition to food poisoning, B. cereus can cause opportunistic infections. Where/how?
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trauma, implantation, IV drug use, catheter, ocular
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What types of infections can result from B. anthracis
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pulmonary, cutaneous (eschar lesion), gastrointestinal
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Describe the unique colony and gram stain morphology of B. anthracis
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granular, dry, nonhemolytic (hard to pick)
gram stain- long chains of gram positive bacilli, non motile |
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Describe Neisseria gram stain
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small gram negative cocci that grow in pairs with adjacent sides flattened
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Which two rapid tests are positive for all Neisseria spp.
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oxidase and catalase
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Neisseria subflava, N. lactamica, and N. sicca are nonpathogenic Neisseria species. Where do they inhabit
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URT, genital tract
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The only known rerservoir for meningococcus (N. meningitidis) is the nasopharynx of carrier adults. What diseases are cased when someone is infected?
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septicemia
meningitis |
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How can gonorrhea be diagnosted in a male
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-finding gram negative, kidney bean shaped diplococci within PMNs in a purulent urethral exudate
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Why is a gram stain revealing gram negative kdney bean shpaed diplococci within PMNs in an exudate from a female not a definitive diagnosis of gonorrhea for a female
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Non pathogenic species of resident flora may ave similar cell morphology. To confirm Dx, N. gonorrhoeae must be isloated and identified
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N. gonorrhoeae and N. meningitids are obligate parasites of man so they must be grown in very specific conditions. This usually helps distinguish them from nonpathogenic strains expect for________ which can only be distinguished by biochemical tests
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Nesseria lactamica
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where is Moraxella catarrhalis usually a pathogen and where is it normal flora
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it is a common inhabitant of the URT but it can cause opportunistic infections such as otitis media, sinusitis, an pneumonia
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What media does N. gonorrhoeae require for growth. Describe how its made
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N. gonorrehhoeae requires Modified Thayer Martin (MTM) media and a 5% CO2 atmosphere, MTM is chocoalte agar made by adding partially lysed RBCs with additional antifungal and antibacterial agents. It also contains selective agents to select against normal mucosal flora Nesseria spp.
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Normal flora N. lactamica grows on selective/ differential MTM media. How then can it be differentiated from N. gonorreaheae
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Use CTA carbohydrate utilization tests
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What is the basis of the oxidase test
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Neisseria (and others) produce oxidase enzyme that in the prescence of oxygen, cytochrome C and an oxidizing reagent, oxidizes the reagent and forms a dark purple color
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How must Neisseria spp. be transported after a sample is taken
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need room temperautre selective GC media with CO2
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define capnophilic
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CO2 loving
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What one rapid test will differnetiate Neissiera from Staph and Strep
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Oxidase
Neisseria is positive staph and strep are negative |
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Besides the common infections sites as a result of sexual transmission (oral, anal, genital) where can N. gonorrhoeae be found
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-ascending infection to upper reproductive tract of women
-dissemination to joints -ocular infections in newborsn and clinical microbiologists |
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Describe the special steps that must be taken to obtain a sample for isolation of GC
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-specail swab, no wood or cotton
-can't tolerate temperature changes -need ~%5 CO2 |
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Does GC grow on BAP with CO2?
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No but normal flora Neisseria species do
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what is an endogenous disease
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a disease caused when a normal flora bacteria gets into the wrong location
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What are some benefits to normal flora
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-prevent colonization by pathogenic bacteria
-help synthesize vitamin K -immune stimulation |
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How should a throat culture be obtained
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-patient opens mouth and says "ah"
-tounge is depressed -glide swab over tounge into the posterior phayrnx -the mucosa behind the uvula and between and including the tonsillar pillars is swabbed with a gentle back and forth sweeping motino |
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How should a nasopharyngeal sample be obtained
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insert swab into nostril and press swap tip on the mucosal surface of the midinferior portion of the inferior turbinate
-rub several times across the mucosal surface |
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what is the most perdominate oraganism in a throat culture (healthy)
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viridans strep
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What organisms on a BAP plante would indiaation a URT infection
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-beta hemolytic group A strep
-brops B and C strep -S. pnuemoniae -pure culture of any gram negative bacilli -pure culture of Staphylococcus species |
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What are the sterile sites of the body
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blood, CSF, urine, virius of the eye, sinovial fluid, peritoneal and pleural cavity
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what are bacteriocins
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secreted by MOs, toxic to others usualy of similar species
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What are the innate defenses of the upper respiratory tract URT
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nasal turbinates and hair, mucus and cell sloughing, reflexes, antibacterial substances, phagocytes, normal flora
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Does the lower respiratory tract (trachea, bronchi, alveolar spaces) have normal flora
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NO!
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How can a sample be collected frm the LRT
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-sputum
-brochial brush (BB) -lung biopsy or fine needle aspirate -brochocalverlar lavage (BAL) -bronchial wash (BW) |
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What two gram positive organisms are likely to cause infections in newborns
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L. monocytogenes S. agalactiae (group B strep)
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What two organisms that are arranged as diplococci can cause meningitis
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S. pneumonaie, N. menigititis
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