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J. Sykes1
1University of California- Davis,
Department of Medicine & Epidemiology, Davis, USA
Streptococci and enterococci are gram-positive cocci that occur in pairs and chains. They are facultative to strict anaerobes. Over 40 species of Streptococcus exist that vary in host tropism and virulence properties. β-hemolytic streptococci cause complete lysis of red blood cells and result in a zone of clearing around
the colony on blood agar. α-hemolytic streptococci reduce hemoglobin, causing a green discoloration
of the agar around bacterial colonies. γ-hemolytic or non-hemolytic streptococci do not produce hemolysis. Pyogenic streptococci are β-hemolytic streptococci that belong to Lance eld groups A (Streptococcus pyogenes), B (Streptococcus agalactiae), C (includes Streptococcus dysgalactiae and Streptococcus equi subsp. zooepidemicus) and G (includes Streptococcus canis). Viridans streptococci are often non-hemolytic or α-hemolytic and are often commensal organisms that have low virulence. Many Group D streptococci have now been classi ed as Enterococcus.
Streptococci typically invade tissues opportunistically when there is a breach in normal host barriers and cause a variety of disease manifestations, such as pyoderma, pneumonia, endocarditis, arthritis, osteomyelitis, meningoencephalitis, cellulitis and UTIs. Severe and life-threatening manifestations of streptococcal infection include necrotizing fasciitis (NF) and streptococcal toxic shock syndrome (STSS). STSS is any streptococcal infection associated with the sudden onset of shock
and organ failure. Shock and organ failure results from elaboration of pyrogenic exotoxins by streptococci, which cause fever and act as superantigens. Superantigens stimulate T cell responses by binding to, and cross-linking, the MHC class II complex of antigen- presenting cells, and the T cell receptor, which bypasses normal MHC-restricted antigen processing. This leads to massive cytokine release, with signs of fever, vomiting, and hypotension, together with tissue damage, DIC, and multiple organ dysfunction. Death can occur within 48 hours after the onset of illness.
NF is a bacterial infection of the deep subcutaneous tissues and fascia, characterized by extensive necrosis and gangrene of the skin and underlying tissues (‘ esh-
eating bacteria’), which can begin as a small wound
and progress rapidly over 24 to 72 hours, sometimes accompanied by STSS. Lesions usually involve a
limb, and are intensely painful, with accumulation of exudate along fascial planes that requires drainage and debridement. Outbreaks of NF, arthritis, sinusitis and meningitis caused by S. canis have been reported in cats in shelters and breeding colonies.
Streptococcus canis
S. canis is the most frequently isolated streptococcal species from dogs and cats. It colonizes the skin, genital and gastrointestinal tracts of healthy dogs and cats. Infection with S. canis may be associated with neonatal bacteremia, pharyngitis, cervical lymphadenitis, bacteremia and endocarditis, UTIs, wound infections, otitis externa, bronchopneumonia, pyometra or metritis, meningoencephalitis, NF, STSS, necrotizing sinusitis, pyothorax, discospondylitis, arthritis, osteomyelitis, mastitis, cholangiohepatitis and peritonitis. Although opportunistic infections with S. canis occur sporadically, outbreaks of Group G streptococcal infection have
been reported in group-housed animals, which have suggested spread of virulent strains.
Severe manifestations of S. canis infection, such as STSS and NF, have been increasingly described in dogs and cats in recent years, sometimes in the absence
of obvious immunosuppressive underlying conditions
or wounds. Little is known about virulence factors of
S. canis. A protein analogous to M protein, a major virulence factor of S. pyogenes, has been identi ed in S. canis.
Streptococcus equi subspecies zooepidemicus
S. equi subsp. zooepidemicus is a commensal of the upper respiratory and lower genital tracts of horses, and can cause disease in dogs and cats. Different strains of S. equi subsp. zooepidemicus exist. Infected horses may have been a source of infection for some dogs.
Several outbreaks of S. equi subsp. zooepidemicus hemorrhagic,  brinosuppurative, and necrotizing pneumonia have been described in group-housed
dogs. The pneumonia can progress rapidly and been accompanied by signs suggestive of STSS. In some dogs, death occurs within 48 hours of the onset of respiratory signs. Other infected dogs have shown
only mild signs of upper respiratory disease. Chronic lymphoplasmacytic rhinitis, sometimes with turbinate lysis in association with S. equi subsp. zooepidemicus infection has also been described in several dogs, which resolved after speci c antimicrobial treatment. Outbreaks of pneumonia, rhinosinusitis and meningoencephalitis have also occurred in cats.
An Urban Experience

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