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