Staphylococcus
Staphylococus aureus routes of transmission
Inhalation - aerosols Direct contact Ingestion of preformed toxin Endogenous
What to use for non-beta-lactamase producing S. aureus (methicillin-susceptible)
Penicillinase-resistant synthetic penicillins: methicillin, nafcillin, oxacillin, dicloxacillin
Staphylococcus transmission
Person to person Self - colonizing,strain gains entrance through trauma or wound Directly through surgical procedures
Stomatococcus
Rarely clinically significant
Treatment of Staphylococcus aureus
Wound drainage Pull indwelling device Antimicrobial agents: Penicillin Erythromycin Vancomycin Discontinue antibiotics Enterocolitis only
Toxin production of Staphylococus aureus
Alpha toxin Hemolyzes red cells, destroys platelets, kills leukocytes, and causes necrosis of skin (dermonecrosis) Leukocidin or Panton-Valentine factor Lethal to PMN's by partially disrupting their membranes Component most responsible for production of pus in Staph infections Enterotoxins Ingestion of food containing one of these preformed enterotoxins results in staphylococcal food poisoning Exfoliatinsoxins An exotoxin that leads to separation and loss of the most superficial layers of the epidermis Toxic Shock Syndrome Toxin (TSST-1) Appears to be capable of producing widespread organ damage through other yet poorly defined mechanisms - end result of which is toxic shock.C
Types of virulence factors
Anatomical Toxin production Enzyme production
biochemical tests for staphylococcus
Catalase Oxidativ-fermentations of carbohydrates (turns media from green to yellow) mannitol fermentative (S. aureus ONLY) Coagulase (S. aureus ONLY) Novobiocin susceptibility
Deep lesions of Staphylococus aureus
Cellulitis Osteomyelitis Disease of growing bones - occurs in children under 12 Arthritis Organ tissue abscesses Endocarditis common in intravenous drug users Pneumonia Enterocolitis Manifestations include high fever and profuse diarrhea - can be life threatening Infection of wounds S. aureus major cause of wound infections
Predisposing conditions that can cause stapylococcus infection
Chronic infections • Indwelling devices • Skin injuries • Immune response defects
Types of Staphylococus aureusdiseases
Cutaneous infection Deep lesions Disease due to toxin production
Describe coagulase test
Detects enzyme coagulase cell-bound "clumping factor" converts fibrinogen to fibrin extracellular enzyme "free coagulase" thrombokinase-like acton clots fibrinogen in the presence of plasma
Methicillin-resistant Staphylococcus aureus (MRSA)
Due to presence of mec gene Alters the site at which methicillin binds to kill the bacteria Causes the same infections as susceptible bacteria Can colonize a host without causing illness (increasing transmission)
Cutaneous Staphylococus aureus infections
Folliculitis • Inflammatory condition of a hair follicle Furuncle (boil) • A superficial infection that develops in a hair follicle, sebaceous gland, or sweat gland - deeper than in folliculitis Carbuncle • Spread of furuncle to subcutaneous tissues with development of one or more abscesses Impetigo • Acute and highly communicable • Characterized by large blisters in superficial layers of skin Seen most often in infants and children
S. aureus epidemiology
Found Worldwide colonizes anterior nares and sometimes other skin sites about 30% of population are persistent carriers 20-30% of population are intermittent carriers up to 60% are non-carriers - carrier rate may be higher in hospitals considered normal flora of intestine Most common in hospitals and nursing homes Usual sites of colonization are nostrils, skin, groin and wounds
Micrococcus
Free living saprophytes
Microscopic examination of staphylococcus
Gram positive cocci Pairs and clusters Numerous polymorphonuclear cells
Staphyloccocus common reservoirs
Health-care staff Patients Inanimate objects
Hemolysin toxins
Hemolyzes RBCs Alpha: platelets/WBCs/tissue Beta: sphingomyelin of RBCs GammaL host cell membranes Delta: less lethal
Staphylococus aureus extracellular enzymes
Hyaluronidase: Connective tissue, enhance invasion and survival in tissues Staphylokinase: Fibrinolysin Coagulase: Virulance marker Lipase: Allows colonization Penicillianse: Confers resistance
Current and Future Concerns of staphylococcus aureus
Increasing frequency Community-acquired MRSA Resistance to a wider range of antibiotics VISA strains: vancomycin intermediate susceptibility S. aureus
Organisms similar to Staphylococcus
Micrococcus Planococcus Stomatococcus
Anatomical features to diagnose staphylococcus
Non motile No spores
Characteristics of Staphylococcus
Normal flora of the skin and mucous membrane Asymptomatic, chronic carriage 32 species gram positive cocci clusters (can be in singles or pairs) Non-motile Non-spore forming Non-fastidious facultative anaerobe yellow or white colonies w/ regular conves morphology Catalase positive
Planococcus
Not clinically significant
Coagulase-positive staphylocci
S. aureus - Human Pathogen Animal species S. intermedius S. hyicus S. delphini S. schleiferi
Less common staph species to cause disease
S. hemolyticus S. hominis S. simulans
Novobiocin response in Staph
Sensitive: All other Staph spp resistant: S. saprophyticus
Types of Staphylococus aureus clinical infections
Skin and wound Food poisoning scalded skin syndrome Toxic shock syndrome Respiratory Bacterima Osteomyelitis
Cultural characteristics of Coagulase negative staphylococci
Smooth, creamy, white small-to-medium sized usually non-hemolytic
Diseases caused by toxin production of Staphylococcus aureus:
Staphylococcal Scalded Skin Syndrome Exfoliatin-producing strains Most common in young children Food Poisoning Foods commonly involved are meats, salads, creams Vomiting or diarrhea Incubation period = 1 - 5 hours Duration = 1 -3 days Toxic Shock Syndrome Most common in young women Causes fever, vomiting, diarrhea, sore throat and muscle pain Can lead to hypotension and organ damage TSST-1 toxin release
Most common staph species to cause disease
Staphylococcus aureus Staphylococcus epidermidis Staphylococcus saprophyticus
Most common CNS isolated
Staphylococcus epidermidis
Non routine tests for Staph
TSST-1 production Serology Phage typing DNA probes
Anatomical features of Staphylococus aureus
Teichoic acid: component of cell wall that mediates adherence of organism to host and contributes to initiation of infection • Protein A: coats surface of aprox. 90% Staph. aureus strains o Has strong affinity for Fc portion of IgG molecules o blocks phagocyte receptor sites on IgG molecules inhibiting phagocytosis
Characteristics of Staphylococcus aureus
The most virulent Staphylococcus species The only human Staph species that produces coagulase The most common species of Staph involved in human infections Common cause of necrotic skin infections and abscesses Tolerant to high salt concentrations Ferments mannitol Hemolysis (beta-hemolytic)
Genus Staphylococcus
resemble members of Micrococcaceae family 14 to 17 species associated with humans Several veterinary pathogens Key test to differentiate species is the coagulase test
Colony morphology of staphylococcus
small, white to yellowish, CREAMY S.aureus may produce hemolysis on blood agar
Cultural characteristics of S. saprophyticus
smooth, creamy, may produce a yellow pigment usually not hemolytic
Describe the catalase test
tests for enzyme catalase H2O2------->H2O + O2 bubbling = positive No bubbling - Negative ( streptococci and other lactic acid bacteria, no @s generated)
What to use for methicillin -resistant S. aureus (MRSA) and methicillin-resistant S. epidermidis (MRSE)
vancomycin combined with rifampin or gentamicin
characteristics of Coagulase-negative staphylocci (CNS)
• Habitat o Skin and mucous membranes • Approximately 35 species • Common human isolates o S. epideremidis, S. saprophyticus, S. haemolyticus • Less virulent than S. aureus • Common nosocomial infections • Usually involved with implantation of medical devices • Ubiquitous • Normal flora o usually contaminants in clinical specimens
Staphylococcus epidermidis epidemiology
• Habitat: skin and mucous membranes • Cell wall: glycerol-teichoic acids • Virulence factor: "slime" • Mode of transmission: implantation of medical devices such as catheters, shunts, and prosthetic devices • Infections are acquired nosocomially • Serious infections among immunosuppressed patients may occur
Staphylococcus saprophyticus epidemiology
• Habitat: skin and mucous membranes • Cell wall: glycerol-teichoic acids • Virulence factor: "slime" • Mode of transmission: implantation of medical devices such as catheters, shunts, and prosthetic devices • Infections are acquired nosocomially • Serious infections among immunosuppressed patients may occur
diseases caused by Staphylococcus epidermidis
• Nosocomial infections particularly in immunocompromised or neutropenic patients Associated with implantation of prosthetic devises • Endocarditis seen most commonly in drug addicts • Bacteremia (contamination) Must show repeated isolation Usually occurs is extremely compromised individuals can be life threatening
Common human isolates that are CNS
• S. epidermidis Nosocomial infections Endocarditis bacteremia • S. saprophyticus Urinary tract infections (UTI)
Other gram-positive cocci
• S. haemolyticus associated with wound infections, bacteremia, and endocarditis • S. lugdunensis and S. schleiferi are also found to be opportunists • Habitat: skin and mucous membranes • Rarely implicated in infections
Treatmentss of CNS
• Wound drainage • Pull line (line sepsis) • Antimicrobics o erythromycin or vancomycin used when patient allergic to penicillin or when organism is resistant to penicillin • Discontinuation of antimicrobial therapy (enterocolitis only)