Gram Pos Aerobic Cocci Flashcards
What should the plates be incubated at?
35 degrees C
Which Staph species is most virulent?
S. aureus
Since staph spp. are apart of normal flora, how do the organisms gain access to atypical?
Cuts, abrasions, and trauma
Most human disease are ____ infections.
Endogenous- those caused by a persons microbial flora that spread to sites where they can cause disease.
What are exogenous infections?
Diseases caused by organisms from outside sources (influenza virus, Neisseria gonorrhoeae)
ID for Staph spp.
Non-motile
Non-spore forming
Facultative anaerobes
Gram +, pairs, tetrads, or grape - like clusters
What is Staph spp. resistant to?
Bacitracin
What can Staph aureus cause?
Ritter disease
Caused by the release of exfoliative toxins
Blisters- culture neg
No scarring
Most neonates are capable of fighting off disease themselves.
Describe Staph Toxic Shock Syndrome
Fever, erythematosus rash, hypotension, multiple organ system involvement, and associated with tampon use.
Treatment is antibiotics and fluids.
List and describe the type of pyogenic cutaneous infections from Staph aureus.
Folliculitis- infection of hair follicles.
Stye- infection of hair follicle on eye lid.
Furuncles (boils)- extension of folliculitis; raised, painful, red nodules that now also involve skin surrounding hair follicles.
Carbuncles- occur when furnucles come together.
What does Staph aureus also cause?
Food poisoning
Bullous impetigo- blisters are culture pos
Bacteremia- catheters
Endocarditis- can be nosocomial
ID for Staph aureus
Creamy yellow colonies
Beta- hemolysis
Opaque
Medium to large
What are 3 purposes of bacterial enzymes and toxins?
To convert host tissue into nutrients the bacteria can utilize.
To evade host immune defenses.
Gain entry to sites allowing them to establish infections.
What are Staph aureus’s extracellular enzymes and toxins?
Coagulase- converts fibrinogen to fibrin.
Staphylokinase- dissolves fibrin/clot enabling infection to spread.
Leukocidins- lysis of neutrophils and macrophages inhibiting phagocytosis.
Hemolysins- alpha, beta, gamma, delta- all lyse RBCs- alpha, gamma, delta may lyse WBCs.
Hyaluronidases- hydrolyze hyaluronic acid in connective tissue- spreads infection.
Lipase- hydrolyzes plasma and skin lipids- enables organism to colonize certain body areas
Exfoliatins- hydrolyze tissue-staph scalded skin syndrome.
Protein A- binding IgG molecules at the Fc region and Fab region of B cell receptors, impairs opsonization and phagocytosis.
Beta lactamase- inactivates penicillin
How do beta-lactamases work?
They’re enzymes produced by some bacteria that bind to beta- lactam rings in antibiotics and make them ineffective.
Beta-lactam antibiotics include:
Penicillins, cephalosporins, carbapenems, and monobactams.
ID for Staph epidermis
Gram + Catalase + Coagulase - Colonies are opaque gray-white Produces biofilm Gamma hemolysis Small to medium size
ID for Staph saprophyticus
Gram + Catalase + Coagulase -
Bright white, creamy colonies, gamma hemolysis
Associated as 2nd most common cause of UTI’s in young females. behind UPEC
How did MRSA develop?
Overuse of antibiotics
What organism contains a mecA gene which imparts a wide range of antibiotic resistance?
Methicillin resistant Staph aureus (MRSA)
Micrococcus spp. are strictly ____
Aerobic
ID for Micrococcus spp.
Gram + Catalase + Coagulase - Microdase +
Tetrads
Rarely a disease; contaminant
Small to medium size
Opaque, convex
Gamma hemolysis
Various colors: white, tan, yellow, orange, to pink.
What media is selective and differential for Staph spp?
Mannitol salt agar
How is Mannitol salt selective?
Increased NaCl concentration
Also contains sugar alcohol Mannitol and pH indicator phenol red.
What media is selective and differential for MRSA?
BBL CHROM agar MRSA II
What is in BBL CHROM agar MRSA II that makes the media selective/ differential?
Cefoxitin- makes selective. Inhibits growth of gram neg organisms and yeasts.
Chromagen additives- differentiation
MRSA hydrolyzes chromagen- MAUVE colored colonies are produced.
Growth of mauve colonies within 24 hrs- definitive ID. Growth after 48 hrs with mauve colonies- presumptive. Need additional tests.
What organism is resistant to novobiocin? Sensitive?
Resistant: Staph saprophyticus
Sensitive: Staph epidermis
What does catalase convert?
H2O2 into water and oxygen (bubbles)
What does the Microdase (modified oxidase test) differentiate?
Staph spp from Micrococcus spp.
How does the Microdase test work?
Detects presence of oxidase enzyme
If pos, turn blue (Micrococcus). If neg, disk will stay original color (Staph spp.)
What does the Coagulase slide test for?
Only bound factor. Can yield false negatives.
Anytime slide test is neg, confirm with a tube test. Tube test contains both free and bound factor, so more sensitive.
What does Lysostaphin sensitivity differentiate?
Staph spp. from Micrococcus spp
Micrococcus-resistant
Staph spp.- susceptible
What antibiotics are used to treat MRSA?
Macrolides like clindamycin or vancomycin
Which antibiotics are tested in MRSA susceptibility testing?
Oxacillin and cefoxitin
