Staphylococcaceae and Micrococcaceae

• Staphylococcus species


  Formerly under the family Micrococcacceae but now classified under family Staphylococcacceae
• Staphylococci


  • Staphylococcus aureus
  • Staphylococcus epidermis
  • Staphylococcus saprophyticus
• Staphylococci found in animals only

  • Staphylococcus hyicus
  • Staphylococcus chromogenes
  • Staphylococcus intermedius
  • Staphylococcus delphini
  • Staphylococcus felis
  • Staphylococcus schleiferi subsp. Coagulans
  • Staphylococcus lutrae
  • Staphylococcus pseudointermedius
• Staphylococci


  • Gram positive cocci in grape-like clusters
  • 0.5-1.5 um in diameter
  • Nonmotile
  • Non-spore forming
  • Facultative anaerobic, predominantly aerobic
  • Grow most rapidly in 37 C
  • Halotolerant
  • Catalase positive
  • Nitrate reduction (+)
• Staphylococcus aureus


  • Coagulase (+)
  • DNase (+)
  • Mannitol fermenter
• Habitat of Staphylococcus aureus

  • Human nose and skin (main)
  • Nasopharynx
  • Perineum
  • Axillae
  • vagina
• Transmission of Staphylococcus aureus

  • Via contaminated hands
  • Mostly acquired endogenously from colonized anterior nares or by direct contact like touching the face or nose picking
• Factors that can cause a person to acquire S. aureus infections

  • Wounds in the mucosal or cutaneous surfaces
  • Presence of foreign bodies or implants
  • Prior infection with other agents like virus
  • Underlying disease with defects in cellular or humoral immunity, defects in opsonization of antibodies, hypogammmabulinemias, complement component deficiencies
  • Chronic underlying disease
  • Therapeutic or prophylactic antimicrobial administration
• Cutaneous diseases caused by Staphylococcus aureus

  • Folliculitis
  • Hidrodenitis supparativa
  • Furuncle
  • Carbuncle
  • Impetigo
• Toxigenic diseases caused by Staphylococcus aureus

  • Staphylococcal Food Poisoning
  • Staphylococcal Scalded Skin Syndrome (SSSS)
  • Staphylococcal Toxic Shock Syndrome (TSS)
• Miscellaneous Systematic Infections caused by Staphylococcus aureus

  • Osteomyelitis
  • Pneumonia
  • Bacteremia
• Virulence Factors of Staphylococcus aureus

  • Microcapsule
  • Protein A
  • Catalase
  • Coagulase
  • Deoxyribonuclease (DNase)
  • Hyaluronidase
  • Lipase
  • Staphylokinase
  • Phosphatidylinositol-specific phospholipase C
• Protein A

  Not able to bind to Fc receptor on phagocytes anymore
• Protein A

  • Blocks complement fixation
• Catalase


  Inactivates toxic hydrogen peroxide and free radicals formed by the myeloperoxidase system in the phagocytic cell
• Aggresin


  Blocks phagocytosis and immune response (antigenic disguise)
• Coagulase


  Converts fibrinogen to fibrin, forms fibrin coat in the bacterial cell
• Deoxyribonuclease (DNase)


  Hydrolyzes DNA, liquefies and decreases viscosity of abscess materials
• Hyaluronidase


  Hydrolyzes the intracellular matrix of acid mucopolysaccharides (hyaluronic acid) in tissue, spreads organism to adjacent areas in tissue
• Lipase


  Hydrolyzes lipids, helps spread organism in cutaneous and subcutaneous tissues
• Staphylokinase


  Plasminogen activator, causes fibrinolysis, dissolves fibrin clot, spreads to contiguous tissue
• Phosphatidylinositol-specific phospholipase C


  Affects tissue of host, destruction of complement components and products
• Beta-lactamase


  Exotoxin, under plasmid control, transmitted by transduction and conjugation, provides resistance to beta-lactam antibiotics (penicillin, penicillin derivatives, cephalosporins)
• Blood Cell Toxins (Hemolysin and Leukocidins)


  • Hemolysins lyse RBCs by disrupting cell membranes, leukocidin lyse neutrophils and macrophages, incapacitate host's phagocytic line of defense
• Alpha-Hemolysin


  Heterogenous protein, forms pores on target cell membrane, causes osmotic swelling and rupture, lyses RBCs, damages monocytes, macrophages, lymphocytes, skeletal muscle, heart, renal tissue, active against thrombocytes, contributes to septic thrombotic events during bacteremia
• Beta-hemolysin


  Exotoxin, sphingomyelinase, degrades sphingomyelin, cytotoxic to human RBCs and monocytes, inactive against granulocytes, lymphocytes, and fibroblasts
• Delta-hemolysin


  Small peptide, surfactant or detergent-like, interacts with cell membrane and forms channels which causes leakage of cellular contents, has a role in S. aureus diarrheal diseases
• Gamma-hemolysin


  Leukocidin, composed of protein S and F, causes pore formation which increases cation permeability, degranulation of cytoplasm, cell swelling, and lysis, causes release of inflammatory mediators leading to necrosis and severe inflammation
• Panton-Valentine Leukocidin (PVL)


  Pore forming toxin, active against neutrophils, causes tissue necrosis, has S and F proteins, works together with gamma toxin
• Toxic Shock Syndrome Toxin (TSS-1)


  Superantigen, promotes manifestation of toxic shock syndrome, found in 20% of S. aureus
• Exfoliative Toxins/Exofoliatins


  Epidermolytic toxins, facilitate dissolution of the hyaluronic acid of the stratum granulosum of epidermis, intraepithelial splitting of cellular linkages, seen in Staphylococcal Scalded Skin Syndrome, has 2 proteins that are both superantigens: Exfoliative toxin A (ET-A) and Exfoliative toxin B (ET-B)
• Enterotoxins A-E, G-J, K-R, and U, V


  Toxins in the intestines, heat stable exotoxins, responsible for staphylococcal food poisoning, superantigens, found in 50% of S. aureus
• Penicillinase is a specific type of beta-lactamase that has specificity for penicillin, it was the first beta-lactamase to be identified
• Superantigens


  Stimulate T cells non-specifically without normal antigenic recognition, directly cross-link T-cell receptor to MHC class II on APCs outside of antigen-binding sites, releases cytokines in large amounts causing overwhelming inflammatory response
• MRSA


  Strains of S. aureus that are resistant to methicillin and related beta-lactam antibiotics, resistant due to presence of altered penicillin-binding protein (PBP2a/PBP2') due to acquisition of mecA located in SCCmec (staphylococcal cassette chromosome), includes health care-associated MRSA (HA-MRSA) and community-associated MRSA (CA-MRSA)
• MRSA infections can be prevented by cleanliness, hygiene, and aseptic management of lesions, application of topical antiseptics like mupiracin to nasal or perineal carriage sites, surveillance of anterior nares colonization among staff, strict adherence to infection control policies, and chemoprophylaxis in surgical procedures
• Staphylococcus epidermidis


  Coagulase (-), DNase (-), non-mannitol fermenter, most commonly encountered staphylococcal species, 99% of the normal flora of the skin, opportunistic pathogens but less virulent than S. aureus, associated with nosocomial infections due to use of contaminated medical devices
• Staphylococcus saprophyticus


  Coagulase (-), DNase (-), urease (+), mannitol fermentation (variable), primarily a saprophyte, primary site of colonization is the gastrointestinal tract, normal flora of female genitourinary tract, 2nd most common cause of community-acquired UTI in young, sexually active females
• Micrococcus species


  • Gram positive cocci in tetrads, larger (0.5-3.5 um in diameter), some are pigmented bacteria (Micrococcus luteus, Micrococcus roseus)
• Micrococcus species are found free-living in the environment (soil, air, extreme environments, food) and as part of the normal flora of skin, mucosa, and oropharynx in humans, they are rarely implicated in human infection, commonly in immunocompromised hosts