Microbiology Chapter 7
Staphylococcus, Gemella, Macrococcus, Salinococcus
Gram positive cocci that appear as tetrads and are usually larger than Staphylococcus. Obligate aerobes and Catalase positive. colonies are yellow
Gram positive cocci that appear as clusters or tetrads. Facultative anaerobes and Catalase positive
Hydrogen peroxide is added to bacterial colony. Rapid bubbling indicates a positive reaction
Mannitol Salt Agar (MSA)
Contains 7.5%-10% NaCl, mannitol, phenol red indicator. Isolates salt tolerant bacteria like staphylococcus. Yellow indicates mannitol fermentation
Coagulase is most reliable method of identification. Growth and fermentation on MSA, DNAse positive, and sometimes exhibits beta hemolysis
Contains DNA and the dyes toluidine blue and methyl green. Activity detected by clearing of the green color when DNA is degraded.
Fibrinogen is converted into a fibrin clot. Performed on both slide (Bound) and in tube (Free)
Latex agglutination test
Carrier particles coated with human fibrinogen and IgG will react with clumping factor and protein A of S. aureus
Isolate and identify staphylococci by inhibiting other bacteria and utilizing chromogens that bind with specific enzymes and form colored compounds.
A chromogenic agar that will form deep pink to fuchsia colored colonies if populated with S aureus.
Specimens are collected from wounds, sputum, blood, urine, and abscess and are isolated on Sheep blood agar and Colistin-nalidixic acid (CNA).
S. aureus pathogenicity
Production of many extracellular toxins and compounds, antibiotic resistance, and ubiquitous. Invades tissues and can disseminate through blood to tissues and organs.
Toxic-Shock syndrome, food-borne illnesses, pneumonia, and septicemia. Causes folliculitis, boils, furuncles, impetigo in skin and soft tissues
S. aureus virulence factors
Protein A inhibits complement fixation and phagocytosis, Capsular polysaccharide enables organism to resist phagocytosis. Peptidoglycan and techoic acid permits organism to sustain environmental stress
S.aureus extracellular toxins (Exotoxins)
Coagulase, Fibrinolysin-Staphylokinase, Lipase, Hyaluronidase, Nucleases, Exfoliatins.
Fibrin formation, antiphagocytic property
Lyses and dissolves fibrin clots; enables infections to spread
Hydrolyzes lipids in plasma and skin; allows for colonization and initiation of skin infections
Lyse hyaluronic acid and spreads infection
Deoxyribonuclease (DNase); degrades DNA
Hydrolyze tissue; Staphylococcal Scalded Skin Syndrome
S. aureus superantigens
Enterotoxins and other pyrogenic toxin such as toxic-shock syndrome toxin 1 (TSST-1); promote cytokine release and progression of toxic shock syndrome
S. aureus antibiotic resistance
Beta lactamase (penicillinase), methicillin resistance, and vancomycin resistance
Beta lactamase (penicillinase)
Enzyme that provides resistance to penicillin and other beta lactam antibiotics. Can be detected with iodometric, acidometric, or chromogenic assays
Methicillin Resistant S. aureus (MRSA)
Isolated with Cefoxitin screen tests, chromogenic agars, and latex agglutination for PBP2a
Coagulase negative Staph (CoNS) species
S. epidermidis, S. saprophyticus, S. hominis, S. hemolyticus
Coagulase negative Staph (CoNS) characteristics
Catalase positive, GPC clusters, growth on Mannitol Salt Agar, but do not ferment mannitol, DNase negative, and coagulase negative
Normal flora on skin and mucous membrane. Increasingly being found as and opportunistic pathogen in health care associated infections
S. epidermidis characteristics
Gram-positive cocci in clusters, nonhemolytic, positive growth on CNA, Growth on MSA but no fermentation, coagulase negative, DNase negative, and susceptible to novobiocin
Associated with urinary tract infections (UTI), resistant to novobiocin, coagulase negative, DNase negative, grows on MSA with variable fermentation
Used to differentiate S. epidermis (susceptible) from S. saprophyticus (resistant).