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Micro ch 9 part one
Staph and other catalase positive GPC
| Question | Answer |
|---|---|
| All staph species are catalase ____ | positive |
| All strep species are catalase ____ | negative |
| Which are the clinically significant species of staph? | S. aureus, S. epidermidis, S. haemolyticus, S. lugdunensis, and S. saprophyticus |
| Name three general characteristics of all staph species (with exceptions, of course) | GPC in clusters, catalase +, modified oxidase negative |
| In a catalase test, bubbles indicate a ____ reaction. | positive |
| What two groups of species are catalase positive? | Saphylococcus and Micrococcus |
| What patients are most likely to be infected by Micrococci? | immunocompromised patients |
| What is the most commonly isolated Micrococcus species? | M. luteus |
| What is the most common test to differentiate Staph from Micrococcus? | oxidase test |
| In a bile solubility test, what is a positive reaction? | flattening of colonies on plate, or decrease in turbidity in tube |
| In a PYR test, what is a positive reaction? | red |
| In a salt tolerance test, what is a positive reaction? | turbidity is positive for growth |
| Why does a catalase-positive GPC not necessarily mean it is a species of staph? | Micrococcus spp are also catalase + GPC and can look like staph on a Gram stain |
| What is the clinical significance of S. aureus? | small amount of indigenous flora, causes "staph infections", major cause of infections of skin, soft tissue, respiratory, bone, joint, endovascular and wounds, one of 4 most common causes of nosocomial infections |
| What is the most common cause of toxic shock syndrome 1? | S. aureus |
| List virulence factors of S. aureus. | exfoliative toxin, panton-valentine toxin, enterotoxin A and D, exoenzymes, protein A (antiphagocytic), toxic shock syndrome |
| What is one of the most common causes of food poisoning? | enterotoxin A and D from S. aureus |
| What drug is most S. aureus resistant to? | penicillin |
| What is MRSA treated with? | vancomycin, linezolid (Zyvox), or quinupristin-dalfopristin (Synercid) |
| What are intermediately vancomycin-resistant strains of S. aureus treated with? | high doses of vancomycin, but some are completely resistant (VRSA) |
| Describe the colony morphology of S. aureus. | grows on BAP and can be white to yellow, large, smooth, entire, raised and opaque, most have multiple zones of beta-hemolysis |
| What can be used to screen for S. aureus carriers? | mannitol salt agar (MSA) |
| Name two lab tests for S. aureus | coagulase test, agglutination tests |
| What is the principle behind the coagulase test? | coagulase causes clot formation and is produced by S. aureus, but not by most other spp of staph |
| What is a name for coagulase negative spp of staph? | CONS |
| Describe the coagulase test. | a drop of water is placed on slide, colony mixed in, followed by drop of rabbit plasma. observed immediately for clumps |
| What indicates a positive reaction in a coagulase test? | clumps |
| What does a positive coagulase test mean? | the organism is most likely S. aureus,b ut can be one of 3 other spp, which are not commonly isolated from clinical specimens |
| What does a negative coagulase test mean? | the organism is most likely not S. aureus, however some strains do not produce clumping factor |
| What test can be done on organisms that test negative for coagulase? | tube coagulase |
| What is the tube coagulase test? | it detects free coagulase that is not bound to the outside of cells |
| What does a positive coagulase tube test indicate? | S. aureus |
| What does a negative coagulase tube test indicate? | a CONS |
| What test has largely replaced the coagulase test? | agglutination tests |
| What is the hemagglutination test? | detects clumping factor using sheep RBCs coated with fibrinogen |
| What is the latex agglutination test? | uses latex particles coated with fibrinogen, IgA, and antibodies to capsular antigens |
| What is a positive result in an agglutination test? | agglutination |
| What species does a positive agglutination test indicate? | S. aureus |
| Give the presumptive ID for S. aureus. | white to yellow, creamy, opaque colonies on BAP; GPC in clusters; catalase + ; coagulase + |
| What are CONS? | coagulase negative staphylococci |
| When are CONS speciated? | only if isolated from a normally sterile site, or if repeatedly isolated from a site of infection |
| What are the 4 most commonly isolated spp of CONS (in order)? | S. epidermidis, S. haemolyticus, S. lugdunensis, S. saprophyticus |
| What is the clinical significance of S. epidermidis? | indigenous skin flora, opportunistic pathogen; associated with postsurgical infections, UTIs, infections of prosthetic devices |
| What are the drug resistances of S. epidermidis? | MRSE strains are multi-drug resistant |
| What is the colony morphology of S. epidermidis? | cannot be used to ID because often it is almost identical to S. aureus |
| What are lab tests for S. epidermidis? | Coagulase negative, commercial systems can differentiate between other CONS |
| What is the clinical significance of S. haemolyticus? | associated with various infections |
| What is the colony morphology of S. haemolyticus? | larger than S. epidermidis and S. aureus |
| What are lab tests for S. haemolyticus? | commercial systems |
| What is the clinical significance of S. lugdunensis? | can cause endocarditis and associated with other infections |
| What is the colony morphology of S. lugdunensis? | not much help except colonies are glossy |
| What are lab tests for S. lugdunensis? | differentiated from S. epidermidis by pyrrolidonyl arylamidase (PYR) test |
| What does a positive PYR test indicate? | S. lugdunensis |
| What does a negative PYR test indicate? | S. epidermidis |
| What is the clinical significance of S. saphrophyticus? | common cause of UTIs, especially in young, sexually active females |
| What is the colony morphology of S. saphrophyticus? | larger and more convex than other CONS |
| What is S. saphrophyticus resistant to that most other species of staph are sensitive to? | novoviocin |
| What is a positive result in a novovicin resistance test? | no zone is positive (this is unusual because most antibiotic disk tests are positive when there IS a zone) |
| What are lab tests for S. saphrophyticus? | novoviocin resistance, commercial systems |
| The main point of table 9-1 on page 216 is that Staphylococci and Micrococci have this relationship? | everything that Staph is resistant to, Micro is susceptible to, and vice-versa |
| What are some other catalase-positive GPC, that is not staph? | Alloiococcus, Kocuria, Kytococcus, and Rothia (they are indigenous flora of skin, mucosa, and oropharynx, but are opportunistic pathogens) |
| What is a positive reaction in a modified oxidase test? | purple |
| What is the next step after you have identified your organism as a GPC? | perform catalase test |
| What are the likely suspects if your catalase test is positive? | micrococcus or staphylococcus |
| What is the next step after you have a positive catalase test? | Differentiate micrococcus from staphylococcus with one of the methods in table 9-1 (bacitracin sensitivity, furazolidone sinsitivity, oxidase production, lysostaphin) |
| What do you do after identifying Micrococcus spp? | that is usually sufficient |
| What do you do after identifying staphylococcus spp? | perform slide coagulase test |
| If your catalase test is negative, your organism is probably? | Streptococcus sp or Enterococcus sp |
| What do you do if you get a positive slide coagulase result? | report S. aureus |
| What do you do if you get a negative slide coagulase result? | perform tube coagulase test |
| What do you do if you get a positive tube coagulase result? | report S. aureus |
| What do you do if you get a negative tube coagulase result? | report 'coagulase-negative Staph' |
Created by:
robinly1