Staphylococci Flashcards
What temperature is used for staph cultivation?
37C
What type of air requirements are needed for staphylococci?
Facultative anaerobes
What types of staph are spore forming?
Clostridium & bacillus
What can subspecies be classified as?
Phage groups
Ribotypes
Strains
How are staph encountered as?
Commensals
Pathogens
How do staph gram stain as?
Gram positive cocci
Staph are catalase positive or negative?
Positive
What do staph ferment?
Sugars
Are they motile or nonmotile?
Non motile
Air requirements include what?
Aerobic
Facultative anaerobes
What are they similar to?
Micrococcus
Staph aureus (halo) produces what?
Boils Folliculitis Furuncles Carbuncles Purulent abcesses
S. aureus can cause infections including what?
Skin, wound, blood, & toxin related diseases
What are 3 types of cutaneous staph infections?
Folliculitis
Furuncle
Carbuncle
What is folliculitis?
Infection of the hair follicles
What are furuncles?
An acute, round, firm tender, circumscribed, perifollicular staph pyoderma that usually ends in central suppuration
What are carbuncles?
Two or more confluent furuncles with separate heads
Infection is deeper
May cause fever/chills
What is bullous impetigo?
Skin infection caused by staph that is highly infectious
By contact with patient, fomites, autoinnoculation
What are some staph toxin related diseases?
Scalded skin syndrome
Toxic shock syndrome
Food poisoning
Can staph cause food poisoning?
Yes
Staph food poisoning is what?
An enterotoxin
How is staph food poisoning gotten?
Contaminated food kept at a temp that allows bacterial growth & toxin release
Reheating food may kill bacteria but the toxin is heat stable
Symptoms occur 1-6 hours after ingestion
Self limit at 24 hours
Toxic shock syndrome is caused by what toxin?
TSST-1 toxin 1
What is toxic shock syndrome?
Rare potentially fatal multi-system disease with sudden fever, chills, vomiting, diarrhea, muscle aches, & desquamating rash
What is desquamating rash?
Rash that can lead to hypotension & shock
When was TSS originally described?
1978 - associated with highly absorbent tampon use
TSS is what kind of infection?
Localized infection
Caused by systemic toxin
Scalded skin syndrome is more common in what?
Infants
What type of toxin is involved in scalded skin syndrome?
Epidermolytic toxin
What does epidermolytic toxin do?
Dissolves skin
What is scaled skin syndrome also known as?
Ritter disease
What are the characteristics of scalded skin syndrome?
Lesion has purulent material
Then cutaneous erythema followed by peeling of the epidermis
Lasts 2-4 days & spontaneously heals
What are gram positive bacteria treated with & why?
Treated with cell wall inhibitors
Beta lactams & vancomycin
What are cell wall components for structural integrity?
b-lactams
Penicilins
Cephalosporins
Vancomycin
What are some 50S inhibitors?
Erythromycin
Clindamycin
Chloramphenicol
What are beta lactam antibiotics?
Naturally occurring
Synthetic
Semi-synthetic
What do cell walls do for organisms?
Helps organisms resist changes in osmotic conditions
How do b-lactams inhibit cell wall synthesis?
B-lactams are structural analogs to acyl D-alanyl-D-alanine
Inhibit the transpeptidation reactions
What are types of b-lactams?
Penicillins
Cephalosporins
Monobactams
Cabapenems
What is vancomycin (glycopeptide)?
A narrow spectrum, limited to gram positive
Cannot penetrate outer cell membrane of gram negative
Links to peptide substrate to prevent transportation
Beta lactams interfere with cell wall synthesis - what are their characteristics?
Look like the next building block for cell wall synthesis
If they are inserted by the penicillin binding proteins into the cell wall - cell wall synthesis will stop
What is MRSA?
A major nosocomial infection - HA-MRSA
When acquired in the community - CA-MRSA
What is SCCmec cassette in MRSA?
MRSA strains with a large insertion into the chromosome that brings several genes
Usually antibiotic resistance & virulence genes
All have mecA gene
What gene do SCCmec cassette MRSA strains have?
mecA gene
What does mecA code for?
An alternate penicillin binding protein - PBP2a
Methicillin resistant staph are what?
Penicillin resistant strains can be treated with nfacillin or oxacillin - resistant to effects of penicillinase
What is MRSA resistant to?
Any penicillin drug
Why is MRSA resistant to penicillin drugs?
Due to the presence of the methicillin resistance gene (mecA) on the chromosome
mecA codes for PBP2a
PBP2a doesn’t bind to penicillins
What is oxacillin used for?
To detect methicillin resistance
A plate with high salt & polymixin make the media select for staph
What does CLSI recommend using for methicillin resistant staph?
Cefotoxin plates to induce the mecA gene because MR can show heteroresistance
How is staph resistant to vancomycin?
Vancomycin interferes with cell wall synthesis but is not a beta lactam
What are two vancomycin resistant staphs?
VISA
VRSA
What is VISA?
Vancomycin intermediate S. aureus
Can arise from vancomycin overuse
What is VRSA?
Resistant S. aureus
How can you find out if it is vancomycin resistant staph?
Screening by a vancomycin agar plate
How are staph resistant to macrolide?
Macrolide antibiotics that inhibit protein synthesis at the level of the ribosome - 50s
What are two examples of macrolide resistant staph?
Clindamycin & erythromycin
What do clindamycin & erythromycin do?
Usually don’t have the same susceptibility pattern
When they don’t, it could be because the organisms can be induced to be resistant once the patient starts to take the antibiotic
What is used to test inducible macrolide resistance?
D test
How does the D test work?
Places clindamycin & erythromycin in close proximity to each other on a Kinky Bauer plate
Erythromycin makes the bacteria around it express its erm gene
This demonstrates its resistance to the clindamycin
What does the D test do?
Determines in advance if the organism will respond to clindamycin
If the test is positive - report all macrolides as resistant
What color will MRSA turn a mannitol salt plate?
Pink
What happens when MRSA is on a chromagar plate?
Has color
What are rapid detection tests in positive blood cultures for MRSA?
PCR
Fluoresenct in situ hybridization for mecA & staph aureus
What are virulence factors of staph aureus?
Enterotoxins TSST-1 Exfoliative toxin Cytolytic toxin Enzymes Protein A binds to Fc portion of antibody, blocks phagocytosis
What are types of cytolytic toxins?
alpha toxin beta toxin panton valentine - kills WBC leucocidin delta toxin
What does S. aureus gram stain as & what shape?
Gram positive cocci in clusters
What do S. aureus colonies look like on blood agar and what type of hemolysis do they have?
Smooth white creamy colonies with beta hemolysis
Are S. aureus catalase positive or negative?
Positive (virulence factor) that causes the release of oxygen (bubbles) from H2O2
Are S. aureus coagulase positive or negative?
Positive (virulence factor) that clumps plasma - clumping factor
May be on the bacterial surface & agglutinate immediately
May be secreted as extracellular staphylocoagulase which takes longer, & is demonstrated in a tube
What are characteristics of S. epidermidis?
Commensal
Pathogen
What makes S. epidermidis a commensal?
Found on skin
Common contaminant of wound, blood cultures
What makes S. epidermidis a pathogen?
Slime/biofilm
Endocarditis - in blood stream
Nosocomial UTI
What is the result of catalase test for S. epidermidis?
Positive
What is the result of coagulase test for S. epidermidis?
Negative
What is the bacitracin test result for S. epidermidis?
Resistant
Negative
What is the novobiocin test result for S. epidermidis?
Positive
Susceptible
What is S. saprophyticus?
A saprophyte
What is a saprophyte?
An organisms that grows on & derives its nourishment from dead or decaying organic matter
What is an example of S. saprophyticus?
Honeymoon cystitis - UTI from sex
Results of coagulase test for S. lugdunensis?
Negative with tube test
Positive with agglutination test
What types of infections does S. lugdunensis cause?
CA - community acquired
HA - hospital acquired
S. lugdunensis may contain what gene?
mecA gene
Why has S. lugdunensis been confused with S. aureus?
Can identified as PYR positive & ornithine decarboxylate positive
What is the microdase (oxidase) test result for micrococcus?
Positive
What type of fermenter is micrococcus?
Nonfermenter - staph ferment
What type of response to sugars does micrococcus give?
Asacchrolytic - no response
Is micrococcus susceptible to lysozyme?
Yes
Is micrococcus susceptible or resistant to lysostaphin?
Resistant
What is the bacitracin (A disk) test result of micrococcus?
Sensitive/Positive
Is micrococcus susceptible or resistant to Furazolidone?
Resistant
Stomatococcus mucilaginous is what?
Normal flora
What does is the colony morphology of Stomatococcus mucilaginous?
Medium white colony
What type of hemolysis is stomatococcus mucilaginous?
Nonhemolytic
What is the transmission of Stomatococcus mucilaginous?
Same as micrococcus
Seen in bone marrow & malignancies
What is the result of A disk test for Stomatococcus mucilanginous?
Negative
Micrococcus is positive