Loys 6/7

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Natural habitats of Gram-positive cocci
Skin
Mucous membranes
Intestines
Most Important Human Pathogens
Staphylococcus aureus
Streptococcus pyogenes
Streptococcus agalactiae
Streptococcus pneumoniae
Enterococcus faecalis and E. faecium
Staphylococcus
Catalase-producing
Aerobic or facultative anaerobic
Nonmotile
Non-spore-forming glucose fermenters
Staphylococcus
Greek words: staphule (bunches of grapes) and kokkos (berries)
Microscopic Morphology of Staphylococcus
Gram-positive cocci in clusters described as “grape-like”
Clinical Manifestations of S. aureus
Skin infections
Septic arthritis
Bacteremia
Spinal epidural abscess
Toxin-mediated diseases
Food poisoning
UTI
Osteomyelitis
Pathogenic Determinants of S. aureus
Staphylokinase
Coagulase
Hyaluronidase
Lipase
Exfoliatin
Protein A
Toxic shock syndrome toxin (TSST-1)
Enterotoxins A–E
Hemolysin
Leukocidin
Methicillin-resistant S. aureus (MRSA) is a strain resistant to antibiotics such as methicillin, nafcillin, and oxacillin
MRSA is acquired after prolonged stay in the hospital, close contact with carriers, and broad-spectrum antibiotics
Coagulase-Negative Staphylococci (CoNS) 
S. epidermidis
S. capitis
S. haemolyticus
S. hominis subsp. hominis
S. lugdunensis
S. saccharolyticus
S. warneri
Staphylococcus epidermidis
Resistant flora of the skin/mucous membrane
Blood culture contaminant
Opportunistic pathogen
Distinct predilection for foreign bodies
Staphylococcus saprophyticus
Normal flora of skin and urethra
Common cause of UTI in young sexually active women
2nd most common cause of UTI in young women
Family Micrococcaceae
Micrococcus
Arthrobacteria
Kocuria
Micrococcus spp.
Opportunistic pathogens
Grows on 5% NaCl but not on 7.5% NaCl
LAB Diagnosis for Staphylococcus
Coagulase test
Catalase test
DNAse test
Novobiocin susceptibility test
Polymyxin B susceptibility test
Modified oxidase test
Culture Media for Staphylococcus
Blood agar plate (BAP)
Tellurite Lysine Agar
Mannitol Salt Agar (MSA)
Colistin-nalidixic acid (CNA)
Phenylethyl alcohol (PEA)
Gram stain
Staphylococci are Gram-positive
Arrangement: Staphylococcus – grape-like
Micrococcus – tetrads
Sarcinae – cuboidal
Catalase is an enzyme that decomposes hydrogen peroxide (H2O2) to water and ground-state oxygen
Coagulase test is the most useful single criterion for ID of S. aureus
DNAse test determines if an organism can produce DNAse (hydrolyzes DNA)
Novobiocin susceptibility test differentiates S. epidermidis (susceptible) from S. saprophyticus (resistant)
Incubate for 4 hours @ 35°C
If (-) for 4 hours incubate for another 24 hours @RT
Coagulase-positive Staphylococcus
S. hyicus
S. intermedius
S. lutrae
S. delphini
S. schleiferi subsp. coagulans
DNAse Test 
Determines if an organism can produce DNAse (hydrolyzes DNA)
Reagents for DNAse Test
DNAse agar with methyl green
toluidine blue as indicator
(+) result for DNAse Test
Clearing of media (methyl green)<|>Blue into rose pink (toluidine blue)
Organisms with (+) DNAse Test
S. aureus
Moraxella
Serratia
Reagent for Novobiocin Susceptibility Test
5 ug Novobiocin
sheep BAP
Positive result for Novobiocin Susceptibility Test 
ZOI >16mm
S. aureus is resistant to Polymyxin B
Other staph are sensitive to Polymyxin B
Staphylococcus saprophyticus is resistant to novobiocin, indicated by the lack of a zone of inhibition around the disk
Modified Oxidase Test 
Rapid method to differentiate Staphylococcus (-) from Micrococcus (+)
Reagent for Modified Oxidase Test
Tetramethyl-p-phenylenediamine dihydrochloride in dimethyl sulfoxide
(+) result for Modified Oxidase Test 
Blue color
Oxidation Fermentation Test 
Determines if an organism is an oxidizer or fermenter
Components of Oxidation Fermentation Test
Glucose in OF tubes
Open tube
Closed tube sealed with vaspar, vasellin and paraffin
Indicator for Oxidation Fermentation Test 
Bromthymol blue
Color of media is green. If pH becomes acidic it turns yellow.