Staphylococcus Aureus - Morphology, Infections, and Treatment - PDF

Gram positive cocci Stapylococci Streptococci Enterococci Staphylococci  Staphylococci Gram positive cocci, 1u in diameter, arranged in grape like clusters, Non capsulated, non motile and non spore forming..  Classification Staph. aureus :...

Gram positive cocci Stapylococci Streptococci Enterococci Staphylococci  Staphylococci Gram positive cocci, 1u in diameter, arranged in grape like clusters, Non capsulated, non motile and non spore forming..  Classification Staph. aureus : The most important pathogen Coagulase Positive Staph. Epidermidis and Staph. Saprophyticus : ✓Coagulase negative. ✓They are normal human flora. ✓Sometimes cause human infection.  1. Staphylococcus aureus ❑Morphology: ▪ Gram positive cocci arranged in irregular grape -like clusters, ▪ Non motile and non-sporing. ❑Culture: ❖ Facultative anaerobes ❖grow on most bacteriologic media, at 37°C ❖ Grows on nutrient agar : produce golden yellow colonies. ❖ Grows also on blood agar: o Staph. aureus produces complete hemolysis Blood agar complete hemolysis ❖Mannitol salt agar o Selective medium containing 7.5% NaCl for isolating Staph. aureus from contaminated samples. o Staph. aureus give yellow color because of mannitol fermentation. Mannitol salt agar ❑ Biochemical reactions: Staph. aureus is -Catalase test: -Coagulase test: POSITIVE -DNAase test: -ferments mannitol - causes gelatin liquefaction  Phathogenesis, antigenic structure and virulence factors Invasion Extracellular (antigenic enzymes structure) ▪ Peptidoglycan ▪ Teichoic acids Toxins ❑ Catalase ▪ Protein A ❑ Toxic shock syndrome ❑ Coagulase ▪ Surface toxin (TSST – 1) test receptors ❑ Enterotoxins ❑ Clumping ❑ 3-Exfoliative toxins. factor ❑ Other ❑Antigenic structure Staph. aureus has several important cell wall antigens: Peptidoglycan: ✓A polysaccharide polymer. ✓It elicits production of interleukin-1 (endogenous pyrogen). ✓It is a chemoattractant for polymorphonuclear leukocytes and has endotoxin like activity.  Teichoic acids.: ✓ Polymers of ribitol phosphate, are linked to peptidoglycan. ✓ adherence of the staphylococci to mucosal cells Protein A: ✓ binds to the Fc portion of IgG molecules so the Fab portion of IgG is free to combine with a specific antigen; ✓ prevent complement activation. Surface receptors for specific bacteriophages: permit the "Phage typing" for epidemiologic purposes. ❑Enzymes: Catalase: converts hydrogen peroxide into H2O and O2. Differentiates the Staphylococci (positive) from the Streptococci (negative). Coagulase: enzyme- like protein that clots citrated plasma by converting fibrinogen into fibrin which when deposited around the lesion cause Staphylococci to become more resistant to phagocytosis. Most infections caused by Staph. aureus are localized due to coagulase production.  Clumping factor: ✓on Staph. aureus cell wall surface & binds to fibrinogen, ✓yielding aggregation of the bacteria and promoting their attachment to blood clots. ✓It is distinct from coagulase. Other enzymes: ✓Hyaluronidase, staphylokinase, ✓ proteinases, lipases and β-lactamase. ❑Toxins: 1- Toxic shock syndrome toxin (TSST – 1): Causes shock in: - Tampon-using menstruating women - individuals with wound infections - patients with nasal packing used to stop bleeding from the nose. The toxin is produced locally in the vagina, nose, or other infected site, then enters the bloodstream, causing toxemia. This toxin is a superantigen and causes toxic shock by stimulating the release of large amounts of IL-1, IL-2, and tumor necrosis factor (TNF). 2- Enterotoxins: They act as superantigens. It causes food poisoning with prominent vomiting (caused by cytokines which stimulate the enteric nervous system to activate the vomiting center in the brain) and watery diarrhea. Enterotoxin is heat-resistant and not inactivated by brief cooking. It is resistant to stomach acid and enzymes. There are many types (A–E, G-I, K-M). 3-Exfoliative toxins: Two types of proteins A and B. They yield the desquamation seen in staphylococcal scalded skin syndrome (peeling of the skin). They are superantigens. 4- Leukocidins: are toxins that kill leucocytes and cause necrosis of tissues. Panton- Valentin leukocidin (PVL): is produced by recently isolated community- associated CA-MRSA and is associated with severe necrotizing pneumonia in children.  Diseases caused by Staph. Aureus A. Pyogenic diseases: ✓Superficial infections: are localized infections in the form of carbuncle, boils, impetigo, wound infection and abscess formation. ✓Deeply seated infections: if Staph. aureus disseminates and bacteremia Osteomyelitis, Meningitis, Pneumonia, Urinary tract infections Endocarditis may occur. B. Toxigenic diseases: Food poisoning: Caused: by ingestion of enterotoxin in food that is improperly cooked and kept unrefrigerated for some Incubation period: is short (1-8 hours) WHY?. time. The source of infection: is the nose and hands of cookers or food handlers. The type of food: is carbohydrate rich food e.g., cakes, koskosi, and pastry, milk and milk products Symptoms: it is characterized by nausea, vomiting, diarrhea, no fever.  Toxic shock syndrome In response to TSST-1 ✓ is manifested by an abrupt onset of high fever. ✓ vomiting, diarrhea, myalgia. ✓ Macular & sun burn-like rash that goes on to desquamate. ✓ Hypotension with cardiac and renal failure in the most severe cases. Scalded skin syndrome (SSS) in response to the presence of exfoliative toxin. in which the superficial layers of the epidermis slough ❑ Laboratory diagnosis of Staphylococcus aureus infections: ❖ Specimen according to the site of infection ▪ blood for blood culture in septicaemia, bacteraemia and endocarditis. ▪ swabs from lesions (pus) e.g. in superficial pyogenic infecions. ▪ CSF in cases of meningitis. ▪ urine in UTI. ▪ vomitus, stool, food remanants in food poisoning. ▪ Joint aspirate in arthritis. ▪ Sputum in Pneumonia. ❖Direct Gram stained smear: Gram +ve cocci arranged in grape like clusters among pus cells ❖Culture: at 37 degree for 24 hours Nutrient agar blood agar Mannitol salt agar  Gram stained film: o Gram positive cocci arranged in grape like clusters.  Biochemical reactions: Positive catalase test Positive coagulase test positive DNAase test  Phage typing: o To determine the source of infection in : Epidemiological tracing of outbreaks in hospitals. Samples from wounds, nose and nail bed of doctors, nurses and from fomites are tested. Outbreaks of food poisoning, the organism isolated from food, vomitus, stool, and from nose and nail bed of food handlers. Serological identification: o By latex agglutination test. Molecular identification: o PCR or DNA probes. Antibiotic sensitivity testing:  Diagnosis of Staphylococcal food poisoning: Specimen vomitus, stools or food remnants Isolation and identification as mentioned above using mannitol salt agar Demonstration of enterotoxin: by precipitation (gel diffusion) method. Bacteriophage typing to trace the source of infection in outbreaks of food poisoning.  Treatment 1-90% of S. aureus strains produce β-lactamase by transmissible plasmids. 2- They are often susceptible to β-lactamase -resistant penicillins: (e.g. methicillin or oxacillin), cephalosporins, or vancomycin. 3- 20% of S. aureus strains are "methicillin"-resistant (MRSA). The drug of choice for these Staphylococci is vancomycin. 4- Newer antimicrobial agents such as linezolide and daptomycin are now available.  Prevention Cleanliness. Frequent handwashing. Aseptic management of lesions help to control spread of Staph aureus. Persistent colonization of the nose by Staph aureus can be reduced by intranasal mupirocin, but is difficult to eliminate completely. Shedders may have to be removed from high-risk areas e.g., operating rooms and newborn nurseries.  Diseases caused by coagulase negative Staph. 1-Staph. epidermidis (opportunistic pathogen) It is part of the normal human flora on the skin and mucous membranes Predisposing factors: It can enter the bloodstream (bacteremia) especially at the site of IV catheters, prosthetic implants (prosthetic heart valves, vascular grafts, and prosthetic joints) due to the production of glycocalyx. A major cause of sepsis in neonates It causes peritonitis in patients undergoing peritoneal dialysis. 2- Staph. saprophyticus: Staph. saprophyticus causes: urinary tract infections, particularly in sexually active young women. This organism is second to Escherichia coli as a cause of community-acquired urinary tract infections in young women. Coagulase negative Staphylococci: S. epidermidis S. saprophyticus Colonial White non hemolytic Variable colored non morphology hemolytic Mannitol negative negative fermentation Dnase test negative negative Novobiocin sensitive resistant sensitivity  Most important staphylococcus species Species Coagulase Typical hemolysis Important features production Staph. aureus + ve Beta Protein A on cell surface, suppurative lesions Staph. - ve None Sensitive to novobiocin, common member epidermidis of skin flora Staph. - ve None - Resistant to novobiocin; sometimes cause saprophyticus urinary tract infections - It is normal flora of skin. Thank You