Gram Positive Cocci Flashcards
Main Gram-Positive Cocci
staphylococcus, streptococcus, and enterococcus
Staphylococcus
large gram-positive cocci, seen as grape-like clusters. Commensals of skin and exposed mucosa of animals and humans. Numerous species survive well in the environment. Classic opportunistic bacteria colonizing skin and mucous membranes
Virulence of Staphylococcus classification
classified based on the enzyme coagulase that converts fibrinogen to fibrin and result in the formation of a clot
Coagulase positive staphylococcus
virulent:
S. aureus, S. hyicus, S. schleiferi subsp. coagulans,
S. intermedius group
S. pseudintermedius, S. intermiedius, S. delphini
Staphylococcus Pathogenesis
- invade broken skin or mucous membrane
- overcome innate immune response
- inflammation, destruction of neutrophils, pus formation
- wound infections, systemic infections, pyoderma, mastitis, folliculitis
Toxin mediated diseases in humans caused by the effect of superantigens
staphylococcal toxic shock syndrome, staphylococcal food poisoning, staphylococcal scalded skin syndrome in humans
Coagulase negative staphylococcus
rarely cause disease in immunocompetent animals. A common cause of nosocomial infections. Urinary tract infections, colonize indwelling catheters and implants and forms biofilms and may cause bacteraemia and endocarditis.
Laboratory diagnosis of Staphylococcus infection
- cytology or gram-staining- gram positive cocci in clusters and evidence of inflammation with abundance of neutrophils is highly suggestive of infection
- culture- routing aerobic culture
- molecular detection using PCR
Staphylococcus Treatment
identify underlying disease states or predisposing factors. Choice of therapy depends on infection site and severity.
Antimicrobial resistance of Staphylococcus
clindamycin resistance
Staphylococcus Infection Control
prevent transmission (contact precautions, hygiene, awareness of increased risk, isolation of animals, counselling owners of potential risk)
Streptococcus
gram positive catalase negative cocci in chains. Do not survive well in the environment. Causes pyogenic infections. Causes local and/or systemic infections. Infection with streptococci may be endogenous or exogenous. Some species are contagious. Pathogenic streptococci tend to be host-adapted
Streptococcus equi subsp. equi
abscess formation in the regional lymph nodes in the head and neck
Streptococcus equi subsp equi (group c)
causes strangles, a contagious respiratory tract disease in horses. Equids are the only known hosts. High morbidity and low mortality. Transmission through contact with horses shedding bacterium and contaminated environments. Weaned foals and yearlings are most susceptible.
Strangles Virulence Factors
hyaluronic acid capsule, M protein, IgG Fc binding proteins, DNAases, streptococcal pyrogenic exotoxins, antiphagocytic capsule, lytic enzymes- hyaluronidase, streptokinase, toxins, superantigens
Strangles Clinical Signs
clinical signs appear 3-14 days after exposure. Infected animals present with fever, depression, anorexia, dysphagia, and moist cough, purulent nasal discharge. Lymph node abscess within 2 weeks of initial signs
Strangles Potential Complication
guttural pouch empyema, spread from retropharyngeal lymph nodes into guttural pouches through lymphatic drainage and rupture into pouch. Metastatic/disseminated strangles.
Guttural Pouch Chondroids
accumulation of soft or hard concentrations in one or both guttural pouches. Associated with chronic empyema
Strangles Diagnosis
- staining and detection from smears.
- culture- abscess swab, nasal, swab, pus, lavage fluid
- serology- ELISA for antibodies to M protein
- PCR- for diagnosis and detection of asymptomatic carriers
Strangles Treatment
most animals recover spontaneously. In symptomatic animals, relieve pain and hasten recovery. Infected animals usually recover after abscesses mature and rupture
When are antibiotics effective for strangles?
if given soon after exposure and before abscess formation and indicated in cases of disseminated infection.
Strangles Control
most animals have strong immunity after recovering. Vaccinate with killed S. equi vaccines in pregnant mares and foals to maintain high levels of anti M protein opsonizing antibodies. Live, intranasal vaccine is used to stimulate mucosal immunity as well as serum opsonizing antibodies
Strangles Phases
- Incubatory- nasal shedding begins 4-7 days after exposure with or without clinically evident nasal discharge
- Clinical- shedding from affected sites, nasal, pharynx, lymph nodes, guttural pouch
- Convalescent- nasal shedding for up to 6 weeks after recovery
- Long Term- 5-7 months or more, mostly from guttural pouch
