Staphylococci

• Staphylococci


  • Stain darkly gram(+)
  • Round and tend to occur in bunches like grapes
  • Require supplementation with various amino acids and other growth factors, cultured on enriched media
  • Facultatively anaerobic
  • Produce catalase (+) (streptococci is catalase-negative)
  • S. aureus - most virulent specie secrete coagulase, an enzyme that causes citrated plasma to clot
  • Other species that occasionally cause disease and lack coagulase are often referred to as coagulase-negative staphylococci
• Staphylococci

  • Resistant to heat and drying, and thus can persist for long periods on fomites (inanimate objects)
  • Frequent hand-washing before and after contact with food or potentially infected individuals decreases the transmission
• Staphylococcus

  Generally, significant host compromise is required like: break in the skin or insertion of a foreign body, obstructed hair follicle, compromised immune system
• Disease caused by Staphylococcus

  1. Largely or wholly the result of actual invasive infection, overcoming host defense mechanisms, and the production of extracellular substances which facilitate invasion<|>2) A result of toxins in the absence of invasive infection ("pure" toxinoses)<|>3) A combination of invasive infection and intoxication

  
• Localized skin infections caused by Staphylococcus aureus

  • Small, superficial abscesses involving hair follicles (folliculitis) or sweat or sebaceous glands
  • Sty (external hordeolum) - eyelash
  • Furuncle (boil) – subcutaneous abscess (neck, face, axilla, buttocks)
  • Carbuncle – larger, deeper skin infections
  • Impetigo – localized, superficial, spreading crusty skin lesion in children

  
• Deep, localized infections caused by Staphylococcus aureus

  • Metastatic from superficial infections
  • Most common cause of acute and chronic bone marrow infection
  • Most common cause of acute infection of joint space in children (septic joint) – emergency because pus can rapidly cause irreparable cartilage damage
• Staphylococcus infections do not elicit strong or long-lasting immunity, as demonstrated by the continuing susceptibility of individuals to S. aureus infections throughout life
• Coagulase-negative Staphylococci


  Of 12 species recovered as normal commensals of human skin and anterior nares, the most abundant and important is S. epidermidis<|>The second most important coagulase-negative staphylococcus is S. saprophyticus<|>Important agents of hospital-acquired infections associated with the use of implanted prosthetic devices and catheters

  
• Staphylococcus epidermidis

  Present in large numbers as part of the normal flora of the skin<|>Frequently recovered from blood cultures, generally as a contaminant from skin<|>Despite its low virulence, it is a common cause of infection of implants such as heart valves and catheters<|>Acquired drug resistance by S. epidermidis is even more frequent than by S. aureus<|>Produces an extracellular polysaccharide material called polysaccharide intercellular adhesin (sometimes called "slime"), that facilitates adherence to bioprosthetic material surfaces, such as intravenous catheters, and acts as a barrier to antimicrobial agents

  
• Staphylococcus saprophyticus


  Frequent cause of cystitis in women, probably related to its occurrence as part of normal vaginal flora<|>It tends to be sensitive to most antibiotics, even penicillin G<|>Distinguished from S. epidermidis and most other coagulase-negative staphylococci by its natural resistance to novobiocin

  
• Staphylococcus is a genus of Gram-positive bacteria in the family Staphylococcaceae in the order Bacillales. Under the microscope, they appear spherical (cocci), and form in grape-like clusters. Staphylococcus species are facultative anaerobic organisms (capable of growth both aerobically and anaerobically).

  
• The name was coined in 1882 by Scottish surgeon and bacteriologist Alexander Ogston (1844-1929), following the pattern established five years earlier with the naming of Streptococcus. It combines the prefix "staphylo-" ('bunch of grapes'), and suffixed by the Modern Latin: coccus, lit. 'spherical bacterium' ('grain, seed, berry').
• Staphylococcus includes at least 40 species. Of these, nine have two subspecies, one has three subspecies, and one has four subspecies. Most are harmless and reside normally on the skin and mucous membranes of humans and other organisms. Staphylococcus has been found to be a nectar-inhabiting microbe. Found worldwide, they are a small component of soil microbial flora.

  
• Acute endocarditis


  Generally associated with IV drug abuse by injection of contaminated preparations or needles. Also colonizes skin around the injection site, and if the skin is not sterilized before injection, bacteria can be introduced into soft tissues and the bloodstream, even when a sterilized needle is used
• Septicemia

  Generalized infection with sepsis or bacteremia that may be associated with a known focus (for example, a septic joint) or not (an occult focus)
• Infections caused by Staphylococcus aureus

  • Acute endocarditis
  • Septicemia
  • Pneumonia
  • Nosocomial infections - hospital-associated infections, often of wounds (surgical, decubital) or bacteremia associated with catheters
• Toxinoses


  Diseases caused by toxins produced by bacteria
• Toxic shock syndrome

  • High fever
  • Rash resembling a sunburn, with diffuse erythema followed by desquamation
  • Vomiting
  • Diarrhea
  • Hypotension
  • Multi-organ involvement (especially GI, renal, and/or hepatic damage)
• Staphylococcal gastroenteritis

  Ingestion of food contaminated with enterotoxin produced by Staphylococcus aureus
• Staphylococcal gastroenteritis


  Caused by ingestion of food contaminated with enterotoxin
• Staphylococcal gastroenteritis


  • Food is protein rich (egg salad or cream pastry) or salty, like ham, and improperly refrigerated
  • Nausea, vomiting, and diarrhea are acute following a short incubation period (< 6 hrs) because toxin in the food has already been formed before food is ingested
• Scalded skin syndrome


  • Superficial bullae resulting from the action of an exfoliative toxin that attacks the intercellular adhesive of the stratum granulosum, causing marked epithelial desquamation
  • The bullae may be infected or may result from toxin produced by organisms infecting a different site