Staphylococcus Notes

NOTES NOTES STAPHYLOCOCCUS MICROBE OVERVIEW ▪ Staphylococcus: genus of Gram-positive bacteria responsible for many diseases ▪ Aerobic, facultative anaerobic ▪ Frequent skin colonization: up to half of population Genetic material ▪ All staphylococci are catalase-positive Taxonomy ▪ Staphylo-: cluster; -coccus: berry Morphology ▪ Organized in grape-like clusters ▪ Gram stain: round, Gram-positive (purple) bacteria; thick peptidoglycan cell wall Antibiotic resistance mechanisms ▪ β-lactamase: hydrolysis of β-lactam antibiotics; some β-lactam antibiotics are resistant to the enzyme (e.g. oxacillin, nafcillin, flucloxacillin) ▪ mecA gene → penicillin binding protein (PBP2a) → reduced affinity for β-lactam antibiotics; present in methicillin-resistant strains ▪ vanA gene → modifies cell wall peptidoglycans → vancomycin cannot bind to bacteria STAPHYLOCOCCUS AUREUS osms.it/staphylococcus-aureus PATHOLOGY & CAUSES ▪ Staphylococcus aureus: common bacterium, causes infections in most organ systems ▪ Aureus: golden colonies in mannitol salt agar, due to mannitol fermentation ▪ Skin colonization: approx. 30% of population ▫ Primary colonization site: nostrils ▪ Pathogen transmission: direct contact, fomites Virulence factors ▪ Cytolysins: alpha-toxin, Panton–Valentine leukocidin (PVL); both destroy neutrophils ▫ PVL related to severe skin, lung infections 548 OSMOSIS.ORG ▪ Hemolysins: form pores in host cells (e.g. erythrocytes, macrophages, lymphocytes) ▪ Superantigens: enterotoxins, toxic shock syndrome toxin-1 (TSST-1) ▫ Superantigens stimulate activation of excessive amount of T-cells → increased production of cytokines → uncontrolled inflammation ▪ Epidermolytic toxins A and B: skin blistering ▪ Coagulase: activates prothrombin → coagulation ▪ Bacterial spread: protease degrades proteins; lipase degrades lipids ▪ Protein A: inactivates immunoglobulins → phagocytosis evasion ▪ Can form biofilms ▫ Biofilm: adherence of cells to polymer

Chapter 98 Staphylococcus surfaces (e.g. catheters) ▫ Properties allow immune evasion CAUSES ▪ Common cause of infections and toxinmediated diseases acquired from community/healthcare environment ▫ Endocarditis, ocular infections, pneumonia, meningitis, osteomyelitis, septic arthritis, prosthetic device infections, catheter-associated infections Skin/soft tissue infections ▪ E.g. surgical site infections, abscesses, impetigo, cellulitis, erysipela, fasciitis, mastitis Toxic shock syndrome (TSS) ▪ Mediated by toxic shock syndrome toxin-1; commonly caused by growth of S. aureus in vagina/surgical sites → multiple organ dysfunction Staphylococcal scalded-skin syndrome (Ritter disease) ▪ Mediated by epidermolytic toxins A and B Foodborne illness ▪ Caused by ingestion of S. aureus endotoxins SIGNS & SYMPTOMS Skin/soft tissue infections ▪ Erythema, swelling, warmth, localized warmth/fever ▫ Staphylococcal scalded-skin syndrome (Ritter disease): fever, erythema, fluidfilled bullae on the skin → skin loss Systemic infections ▪ Joint pain, abdominal pain, headache, CVA tenderness, new onset heart murmur TSS ▪ Fever, hypotension, rash, coagulopathy, tissue necrosis (site of infection) Foodborne illness ▪ Nausea, vomiting, diarrhea, abdominal pain DIAGNOSIS LAB RESULTS ▪ Culture-based observation ▫ Clustered golden Gram-positive cocci ▫ Catalase-positive; coagulase-positive ▪ Polymerase chain reaction (PCR) amplification ▪ May be guided by further studies depending on site of infection RISK FACTORS ▪ Immunosuppression, IV drug use, recent invasive procedure, foreign material in body (e.g. prosthetics, catheters, sutures), dialysis COMPLICATIONS ▪ Sepsis, bacteremia, invasive infection ▪ Antibiotic resistance: all strains resistant to penicillin G; some strains resistant to methicillin (MRSA) or vancomycin (VRSA); some strains have intermediate resistance to vancomycin (VISA) ▫ Resistant strains are common pathogens in nosocomial infections Figure 98.1 Staphylococcus takes on a golden colour when cultured with mannitol containing media. OSMOSIS.ORG 549

TREATMENT MEDICATIONS Topical antibiotics ▪ Superficial skin infections Oral/IV antibiotics ▪ Treatment based on the pathogen’s antibiotic susceptibility ▫ Oxacillin/nafcillin/cefazolin ▫ MRSA: vancomycin/trimethoprimsulfamethoxazole ▫ VRSA: linezolid SURGERY ▪ Abscess drainage (if applicable) ▪ Foreign material removal in body (if applicable) STAPHYLOCOCCUS EPIDERMIDIS osms.it/staphylococcus-epidermidis PATHOLOGY & CAUSES ▪ Staphylococcus epidermidis: bacteria commonly associated with infections of surgical sites, indwelling catheters, and prosthetic devices ▪ Part of skin and mucous membrane natural flora ▪ Does not produce exotoxins CAUSES ▪ Skin/mucous colonization → barrier rupture → infection ▪ Can form biofilms on foreign materials in body; biofilm properties allow immune evasion ▪ Polymer surface adhesion → extracellular matrix production → polysaccharide intercellular adhesin (PIA) secretion → multi-layered bacteria ▪ Common S. epidermidis infections: catheter-associated infection, intravascular catheter infection, prosthetic joint infection, endocarditis (frequently associated with prosthetic valves), surgical site infection RISK FACTORS ▪ Immunosuppression, neonates, recent invasive procedure, foreign material in the body (e.g. prosthetics, catheters), dialysis 550 OSMOSIS.ORG COMPLICATIONS ▪ Sepsis, bacteremia ▪ Neonates: pneumonia, urinary tract infections, meningitis, enterocolitis, omphalitis SIGNS & SYMPTOMS Local ▪ Pain, tenderness, swelling, warmth, erythema, drainage at incisional site Systemic ▪ Fever, hypotension, leukocytosis DIAGNOSIS LAB RESULTS Culture-based observation ▪ Blood, urine, synovial fluid, surgical site ▫ Clustered Gram-positive cocci ▫ Catalase-positive; coagulase-negative; novobiocin-sensitive PCR amplification

Chapter 98 Staphylococcus TREATMENT MEDICATIONS SURGERY ▪ Remove foreign material from body (if applicable) Oral antibiotics ▪ Empiric treatment: vancomycin ▪ If proven methicillin sensitivity: oxacillin/ nafcillin; may be combined with rifampicin, gentamicin ▪ Fusidic acid for skin infections (if available) STAPHYLOCOCCUS SAPROPHYTICUS osms.it/staphylococcus-saprophyticus PATHOLOGY & CAUSES SIGNS & SYMPTOMS ▪ Staphylococcus saprophyticus: bacteria that commonly produces urinary tract infections (UTI) in young, biologicallyfemale individuals ▪ Frequently part of vagina’s natural flora ▪ Tropism for urinary tract: surface fibrillar protein (Ssp) and hemagglutinin/adhesin allow pathogen’s adherence to uroepithelial cells ▪ Does not produce exotoxins ▪ Etiologic agent: community-acquired UTIs (occasionally) ▪ Usually presents as symptomatic cystitis (bladder inflammation) ▪ Dysuria (painful urination), urinary urgency, increased urinary frequency, suprapubic pain, occasional hematuria RISK FACTORS DIAGNOSIS LAB RESULTS Urinalysis ▪ Presence of leukocytes, erythrocytes, bacteria, negative urine nitrate Culture-based observation ▪ Clustered Gram-positive cocci ▪ Catalase-positive; coagulase-negative; novobiocin-resistant ▪ Biologically-female (shorter urethra), recent sexual activity (“honeymoon cystitis”), diabetes, immunosuppression, indwelling urinary catheter Quantitative PCR COMPLICATIONS MEDICATIONS ▪ Pyelonephritis TREATMENT ▪ Oral antibiotics ▪ Symptomatic therapy (e.g. phenazopyridine) OSMOSIS.ORG 551