Microbiology Quiz # 1 - Staph & BH Strep

Microbiology Quiz # 1 - Staph & BH Strep Microbiology For Medical Lab Science
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Describe the appearance of staphylococci on a smear? (gram +/- and what arrangement)
 
gpc, pr, cl
Describe the appearance of micrococci on a smear? (gram +/- and what arrangement, size)
 
gpc, TETRADS!!! (this distinguishes micrococci from staphylococci), they are also larger than staph.
Describe the appearance of staphylococci on BAP (poss colors, poss hemolyses)
 
cream, golden, white, BH or NH, op
Describe the appearance of micrococci on BAP (color)
 
stable pigment, can be carotenoid (yellow or red) esp at lower temps
What kind of atmosphere do staph. require? (ie. what are they in terms of oxygen/carbon tolerance/use)
 
Facultative ANAEROBE
What kind of atmosphere do micrococci require? (ie. what are they in terms of oxygen/carbon tolerance/use)
 
AEROBES
What are the results for staph when a lysostaphin and modified oxidase test are performed?
 
Lysostaphin = Sensitive MO = Negative
What are the results for micrococci when a lysostaphin and modified oxidase test are performed?
 
Lysostaphin = Resistant MO = Positive
Are staph considered pathogenic? Are micrococci considered pathogenic?
 
Staph are pathogenic. Micrococci are not usually.
Describe the appearance of staph. aureus on BAP (size, hemolysis, color)
 
med-lg, BH (NH) golden, cr, wh
What are the results for TC, SC, DNase and Novobiocin tests when run on staph. aureus; which is the most important test for this organism?
 
TC pos, SC pos, DNase pos, Novobiocin S TC is the most important 'gold standard'
Describe the appearance of staph. epidermidis on BAP (hemolysis, size, color)
 
NH (BH), sm-med, wh-gr
Describe the appearance of staph. saprophyticus on BAP (hemolysis, size, color)
 
NH, lg, chalk-wt, possibly yellow or orange
What are the results for staph. epidermidis when TC, SC, DNase, and novobiocin tests are run?
 
TC neg, SC, neg, DNase neg, Novobiocin Sens
What are the results for staph. saprophyticus when TC, SC, Dnase, and novobiocin tests are run?
 
TC neg, SC neg, DNase neg, Novobiocin Resistant
Describe the principle of the TC test (and what positive and negative results appear as)
 
Detect primarily free coagulase. Coagulase binds w CRF. Complex reacts w fibrinogen forms fibrin clot.+ = clotted
Describe the principle of the SC test (and what + and - results appear as)
 
Detects bound coag. Coag interacts w fibrinogen forms fibrin clot.+ = agglut & background clearing; - = remains cloudy; rapid screen for aureus only
Describe the principle of the DNase test (toluidine blue)
 
Dye complex interacts with intact DNA. When DNA hydrolyzed, dye turns pink = +ve. -ve if still blue
Describe the principle of the DNase test (HCl flood plate)
 
DNA in media when intact ppts (see cloudiness). If hydrolyzed, see clearing around organism.
What plates can you run a Novobiocin test on?
 
MH, or TS
Describe the latex agglutination test for s. aureus
 
Protein A of s. aureus binds with the IgG on the latex molecule. Also can use to detect PbP2a (MRSA)
When do staph strains need to be typed (in what kind of cases)? (2)
 
Nosocomial infection or food poisoning
List 3 methods for epidemiological studies of s. aureus
 
PCR (molecular), bacteriophage/plasmid typing, antibiogram
Describe the main mechanisms of pathogenicity of staph.
 
Toxins: Hemolysins, enterotoxins Enzymes: coagulase, fibrinolysin, thermonuclease; Adherence: biofilm Drug resistance
Skin infections due to staph (5)
 
folliculitis, furuncle (boil), carbuncle, impetigo, abscess
Name 2 diseases of the respiratory system that staph. can cause
 
aspiration pneumonia (intubation) and hematogenous pneumonia
Name 3 diseases caused by disseminated toxins due to staph.
 
toxic shock syndrome (TSST-1), scalded skin syndrome (exfoliative toxin), food poisoning (heat stable enterotoxin)
Name 1 disease of the heart that staph can cause
 
Endocarditis (heart valves). can lead to DIC "bleeding out"
Are CNS pathogenic? If no, what are they and how do they gain entry?
 
No, opportunistic. Gain through medical indwelling devices.
Name 1 disease of the heart that CNS can cause
 
Prosthetic heart valve endocarditis
Name 1 disease of the brain/spinal cord that CNS can cause as a result of contamination during a specimen collection
 
Meningitis from CSF shunt
What diease is staph. saprophyticus most usually assoc with?
 
UTIs
What is the name of the enzyme that enables staph to become resistant to penicillins?
 
Penicillinase (type of B-lactamase)
If a staph tests 'S' to penicillin can you report this immediately?
 
no, must run another test to check for inducible resistance.
What drug was developed to 'beat out' the resistance to penicillins; is this effective on MRSA
 
Oxacillins; no MRSA are resistant
How are MRSA penicillin resistant
 
They have an altered PBP site (PBP2a)
What is the drug of choice for treating MRSA?
 
Vancomycin
What does heteroresistance mean? Which bacteria (scientific name) exhibit this trait?
 
Sensitive and resistant cells within the same culture; MRSA
What can be done to enhance the recovery of MRSA (enable it's detection in the lab) - 3 things
 
Increase salt, lower temperature, increase incubation time
Staph. lugdunensis can be found where on the body? What are the results for SC and PYR?
 
groin, PYR pos, SC pos
Staph. schleiferi is becoming a problem for what type of infection? What are the results for SC and PYR?
 
Nosocomial (from medical indwelling devices) SC pos, PYR pos
How are strep different than staph? (appearance)
 
Strep are smaller, translucent
What type of atmosphere do strept require (oxygen/carbon usage/tolerance)
 
Facultative anaerobe, also fermentative
What are the results for oxidase and catalase for strep
 
neg and neg (catalase neg differentiates them from staph which are cat +)
Describe the appearance of BH strep groups ACG on BAP and on slide
 
wide band BH, small colony, (A may be 'pushy') translucent; gpc pr, ch
Describe the appearance of BH strep group B on BAP and on slide
 
narrow band BH, lg colony, transl, may be orange; gpc pr, ch (string of pearls poss from broth)
Where are strep groups CG normally found?
 
as normal flora in URT, GIT
Is group A considered normal flora?
 
no, 'carrier' if it's present.
Where are strep group B usually found
 
as normal flora in GIT and female RT
Describe latex agglutination (acid)
 
acid + test isolate + neutralizer + ab-latex pos if agglutin & background clearing; neg if cloudy; tests for ABCFG; fast
Describe latex agglutination (enzyme)
 
enzyme (pronase B) + test isolate; incubate; pos if agglut and bg clearing; can test for ABCDFG but must wait for incub.
List at least 2 drugs held in reserve to treat MRSA
 
Daptomycin, Linezolid, Synercid, Ortavancin
What are the 2 hemolysins that Group A strep can have?
 
Streptolysin O = oxygen labile (dies from O2 exposure) Streptolysin S = oxygen stabile
What tests would you perform to ID a group A strep? and what is the organism's scientific name if IDed biochemically?
 
Catalase neg, (see wide band BH), bacitracin (S), PYR (+) or can do lancefield latex agglu at end to confirm; s. pyogenes
Name 5 mechanisms of pathogenicity of strep group A
 
toxins (hemolysins O,S; pyogenic - flesh eat, erythrogenic - scarlet fever); enzymes, adherence, capsule (hyaluronic acid), mimicry
Name some clinical manifestations as a result of strep gr A infection
 
pharyngitis, cellulitis, erysipelas, impetigo, necrotizing fascitis, 2 sequelae (rheumatic fever, acute glomerulonephritis)
What is the name of the test that can detect for a strep gr A infection (usually for post infection)
 
Antistreptolysin O
What class of abx are most strep gr A sensitive to.
 
penicillins
What is the (general) principle of the PYR test
 
detects an enzyme. if pos, see pink
How does bacitracin work (mechanism against bacteria)? how is it administered?
 
Works on cell wall; topical use only; too toxic for ingestion
How can you detect/grow gr A strep containing streptolysin O?
 
Stab media to provide anaerobic environment.
What tests would you run to ID a group C or G strep?
 
Cat neg, (wide band BH), bacitracin R, latex CG
What are the clinical implications of strep gr C and G? how is it similar to group A? how is it different?
 
same as group A but doesn't cause 2 sequelae; considered pathogenic when predominant in throat swab
Are group C/G strep pathogenic? If not what are they?
 
No, opportunistic
What tests would you run to ID a group B strep?
 
Cat neg, (narrow band BH), CAMP pos
Name 2 other tests that can be run to ID a group B strep
 
Hippurate Columbia agar deep (pos if see orange pigment in stab lines; starch user)
Describe the CAMP test
 
CAMP produced by gr B strep interacts with staph hemolysin and causes hemolysis. pos if see arrowhead pointing to staph streak.
Describe the hippurate test
 
Na-hippurate + isolate; incubate (gr B produces glycine); ninhydrin + glycine = purple = pos
What are the clinical manifestations of group B strep
 
Affects newborns; can cause pneumonia
What class of abx are strep gr B resistant to?
 
aminoglycosides
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