Staphylococcus

S. aureus

• Structural components

  • Capsule: inhibits chemotaxis and phagocytosis; inhibits proliferation of mononuclear cells

  • Protein A: inhibits antibody-mediated clearance by binding lgG1, lgG2, and lgG4 Fc receptors; leukocyte chemoattractant; anticomplementary

S. spidermidis

• Biology

  • Normal microbiome of skin

  • Catalase positive

  • Coagulase negative staphylococci

  • Low virulence

  • An opportunistic pathogen

S. saprophyticus

• Biology

  • Gram-positive 

  • Catalase positive

  • Coagulase negative

  • Non hemolytic

• Resistant to Novobiocin

Streptococcus normal flora and pathogens

• Normal flora

  • Oropharynx/upper respiratory tract

  • Skin (some species)

  • Gastrointestinal tract (limited species)

• Can be pathogens at

  • Throat (strep throat)

  • Lungs (pneumonia)

  • Blood (bacteremia, sepsis)

  • Heart valves (endocarditis)

  • Skin and soft tissue (cellulitis)

Enterococcus normal flora and pathogens

• Normal flora

  • Gastrointestinal tract **main site

  • Genitourinary tract (especially perineal area)

• Can be pathogens at

  • Urinary tract (UTIs)

  • Blood stream (bacteremia, sepsis)

  • Heart (endocarditis)

  • Wounds and surgical sites

Strep

throat and skin

Enterococcus

gut and urine

S. aureus infections

• Toxin mediated (food poisoning, scalded skin syndrome, and toxic shock syndrome)

• Cutaneous infections (carbuncles, folliculitis, furuncles, impetigo, and wound infections)

• Other (bacteremia, endocarditis, pneumonia empyema, osteomyelitis, and septic arthritis)

S. epidermidis infections

Bacteremia; endocarditis; surgical wounds; opportunistic infections of catheters, shunts, and prosthetic devices

S. saprophyticus infections

UTIs

Methicillin-resistant Staphylococcus aureus (MRSA) information

• Causative agent of serious infections in hospitalized patients and outside the hospital in previously healthy children and adults

• First discovered in 1961

• First case in US in 1980s

• Now resistant to methicillin, amoxicillin, penicillin, oxacillin, and other common antibiotics

• Bacterial resistance to methicillin and related penicillins and cephalosporins is mediated by acquisition of a gene (mec A and mec C) that codes for a penicillin-binding protein with low affinity to penicillin

• Hospital acquired

• Community associated

• Most common cause of community-acquired skin and soft tissue infections

• Skin infections

  • Appear as wounds that are red, swollen, painful, have pus or other drainage