Lec.1 Genus: staphylococcus Some are members of the normal flora of the skin and mucous membranes of human, others cause suppuration, abscess formation, a variety of pyogenic infections, and even fatal septicemia. Genus staphylococcus has at least 35 species. The three main species of clinical importance are: Staphylococcus aureus (pyogen). Staphylococcus albus (epidermidis). Staphylococcus citreus (saprophyticus).

cultural characteristics. Morphology and identification Microscopical : Micrococcus. resemble staphylococci, found free-living in the environment, form regular pakets of four or eight cocci. Their colonies can be yellow, red or orange . cultural characteristics. Colonies on solid media are round, smooth, raised and pigmented. Staph. aureus usually forms golden yellow colonies. Staph. epidermidis forms white colonies. Staph. saprophyticus. forms lemon yellow colonies.

Growth characteristics produce catalase. relatively resistant to drying, heat (50°C for 30min.), and 9% sodium chloride, inhibited by certain chemicals e.g. 3% hexachlorophene. sensitive to many antimicrobial drugs. Resistance falls into several classes: β-lactamase production is common, under plasmid control, makes the organism resistant to many penicillins . Resistance to nafcillin, methicillin and oxacillin, is independent of β- lactamase production, under chromosomal control through special gene known as mec A gene which resides on bacterial chromosome. The resistance is related to the lack of certain penicillin binding proteins (PBPs) in the organisms.

Vancomycin resistant staph Vancomycin resistant staph. susceptible to vancomycin if the minimum inhibitory concentration (MIC) is ≤ 2µg/ml; intermediate susceptibility if the MIC is 4-8µg/ml; resistant if the MIC is ≥ 16 µg /ml. After 2002 in USA, new vancomycin-resistance Staph isolated due to presence of Van resistance gene that acquired from enterococci and nafcillin resistance gen(mec A). Plasmid-mediated resistance to tetracyclines, erythromycins, aminoglycosides and other drugs. Tolerance

Antigenic structure Peptidoglycan Teichoic acid Protein A Capsule Clumping factor (coagulase)

Toxins and Enzymes Toxins Exotoxins includes several toxins. Leukocidin Exofoliative toxins Toxic Shock Syndrome toxin 1- (TSST-I) Enterotoxins

Enzymes Catalase All staphylococci produce catalase. Coagulase Staph. aureus produce coagulase Staphylokinase resulting in fibrinolysis. Lipases. Hyaluronidase (spreading factor). β- Lactamase Proteinases.

Pathogenesis S. epidermidis, are members of the normal flora of human skin and respiratory and gastrointestinal tracts. Nasal carriage of S. aureus occurs in 20-50% of human. Staphylococci are also found regularly on clothing, bed linens, and other fomites in human environment. The pathogenic capacity of S. aureus is the combined effect of extracellular factors and toxins together with the invasive properties of the strain. Pathogenic, invasive S. aureus produce coagulase and tend to produce a yellow pigment and to be hemolytic. Nonpathogenic, noninvasive Staphylococci as S. epidermidis are coagulase negative and tend to be nonhemolytic. Such organism rarely produce suppuration but may infect orthopedic or cardiovascular prostheses or cause disease in immunocompromised persons. Staph. saprophyticus is typically novobiocin resistant, and non-hemolytic, it cause urinary tract infection in young women.

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