Unit 5: Staphylococcus

Staphylococcus

GPC in pairs, tetrads, and clusters; means 'bunch of grapes'; catalase positive; reduce nitrates to nitrites; aerobic or facultative anaerobic; non-motile; cytochrome oxidase negative.

Streptococcus

Gram-positive cocci that is catalase negative.

Neisseria

Gram-negative cocci

Gram-positive cocci

Thick peptidoglycan wall; stain purple.

Gram-negative cocci

Thin peptidoglycan layer; stain pink/red.

Catalase Positive

Ability to break down hydrogen peroxide, indicated by bubble formation.

Coagulase

Enzyme that converts fibrinogen to fibrin to form a visible clot; can be bound (slide test) or free (tube test).

DNase Test

Extracellular enzyme that breaks down DNA into smaller units; positive reaction indicated by color change with methyl green or toluidine blue.

Mannitol Salt Agar

Selective medium for isolation of pathogenic staphylococci; staphylococci can grow in high concentrations of NaCl.

Staph aureus

Normal flora of nose & skin; mannitol fermenting bacteria; shows beta-hemolysis; can cause a range of infections.

Staph epidermidis

Normal flora of skin and mucous membranes; sensitive to novobiocin.

Staph saprophyticus

Found in genital tracts of young women; resistant to novobiocin.

Novobiocin Disk

Antibiotic used to differentiate Staph epidermidis (sensitive) from Staph saprophyticus (resistant).

Beta-Hemolysis

Type of hemolysis shown by S. aureus on blood agar.

Gamma Hemolysis

Type of hemolysis shown by S. epidermidis and other CoNS on blood agar.

Aerobic

Capable of producing energy through aerobic respiration.

Facultative Anaerobic

Capable of switching back to anaerobic respiration depending on oxygen availability.

Non-motile

Organisms that do not move on their own.

Cytochrome oxidase negative

Characteristic of staphylococci.

Methyl green indicator

Used in DNase test; colorless positive reaction.

Toluidine blue

Used in DNase test; pink positive reaction.

Methicillin-resistant Staphylococcus aureus (MRSA)

Very pathogenic because it acquired the mecA gene that makes it resistant to antibiotics.

Cefoxitin

Antibiotic used to detect MRSA in lab; better indicator than oxacillin since it induces mecA more efficiently.

Cefoxitin Resistant

≤ 21 mm (Methicillin Resistant S. aureus).

Cefoxitin Sensitive

≥ 22 mm (Methicillin Sensitive S. aureus).

SOFTPAINS

Mnemonic for diseases caused by Staphylococcus aureus: Skin Infections, Osteomyelitis, Food poisoning/gastroenteritis, Toxic shock syndrome, Pneumonia, Acute endocarditis, Infective arthritis, Necrotizing fasciitis, Sepsis and Staphylococcal scalded skin syndrome (SSSS).

Staph haemolyticus

Healthcare Associated; resistant to multiple antibiotics.

Staph lugdunensis

Catalase positive, coagulase negative but on Staph latex it's weakly positive; causes bacteremia, wound infections, endocarditis, septic arthritis, vascular catheter infections, UTI.

Staph slide Latex Test

Agglutination assay for the qualitative detection of coagulase.

Micrococcus

Appears similar to Staph; Gram-positive cocci, catalase-positive, occurs in clusters, non-pathogenic, found on skin.