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Staphylocococcus

Microbiology ppt 3 - Staphylococcus & Micrococcus

QuestionAnswer
Micrococcus spp. general characteristics Gram positive cocci - tetrads & clusters -Normal flora of human skin, mucosa & oropharynx. -In clinical samples - usually considered contaminant -Aerobic
Diseases associated with Micrococci Rarely associated with infections except if the host is immunocompromised. Usually a normal flora.
Micrococcus spp colony morphology & Gram stain BA: usually white/yellow or orange colonies, small-medium, gamma hemolytic, opaque and convex Gram stain: GPC in tetrads or clusters.
Micrococcus spp testing identifiers -Catalase positive -Bacitracin susceptible -Microdase positive -Lysostaphin resistant
Micrococcus luteus appearance YELLOW, small to medium colonies. Gamma hemolytic, opaque and convex.
CHROM agar tests for MRSA
CNA media selective for.. Gram positive bacteria, also used in place of PEA
CONS Colony Morphology BA: White, gray-white, gold or creamy yellow opaque colonies are mostly gamma(γ) hemolytic. Exception is S. haemolyticus which is β-hemolytic
Catalase tests differentiates between.. Staphylococcus and streptococcus
Catalase test false positives -Gouge the agar and put it with the colony. The RBC's from the agar can produce a false positive. -Enterococcus can produce a few bubbles which can be percieved as a pseudopositive/or a weak positive by accident.
Is S. aureus a NF? Yes of the nose, nasopharynx, skin, perineum and mucosa
Virulence factors of S. aureus -Has a polysaccharide capsule which allows it to evade phagocytosis. -Peptidoglycan activates complement and Interleukin1 -Has cytotoxins and exotoxins. -Penicillinase (breaks up beta lactamase)
Infections associated with S. aureus -Localized skin and soft tissue infections like impetigo, folliculitis, furuncles or carbuncles. -Wound infections -Scalded skin syndrome in neonates. -TSS
Staphylococcus epidermidis (CONS) related infections -NF of the skin, can cause endogenous infections -Infections associated with prosthetic devices -CSF Shunt Infections Virulence factors: Exopolysaccharide(slime layer")and delta toxin
Tube coag is also known as Free coagulase
Slide coag is also known as Bound coagulase
S. Saprophyticus can cause... UTI in women of child bearing age, otherwise it's a normal flora.
Identification of S. aureus BA: Creamy yellow, gold/white, opaque, β-hemolytic. MSA: Yellow halo Tube coag/free coag positive
Which bacterias can give false positives on slide coagulase S. Lugdunensis & S. schleiferi
Why must tube coag's be checked at the 4 hour mark? Clots can form and then be dissolved by staphylokinase, this would make a false negative at 24h.
Latex Agglutination (Eg. Staphaurex) tests for the presence of.. Clumping factor + Protein A (Some kits produce false negatives with MRSA) (May see false positives with S. haemolyticus, S. hominis and S. saprophyticus.
Are CONS NF? NF of skin and mucous membranes (We don't routinely speciate except for specific circumstances, eg-CSF, some blood cultures, UTE from a person who is a biological female
If you want to rule out S. lugdunensis from other CONS, which tests would you run? PYR -> pos Ornithine -> pos
Novobiocin tests for which bacteria? S. Saprophyticus, is resistant to novobiocin
Detection of methicillin resistance? Cefoxitin disc diffusion
Most commonly used cell wall active agent that retains activity and is alternative drug of choice for infections with resistant strains Vancomycin
When testing for S. intermedius, we use which test PYR, S. intermedius is PYR positive
Created by: moreandmore
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