Streptococcus and Enterococcus Infections

Streptococci are commensal and pathogenic bacteria that colonize the nose, mouth, intestine, genital tract, and skin. Pathogenic streptococci produce beta hemolysin and polysaccharide surface antigens that can be differ­entiated serologically into Lancefield groups.

Systemic streptococcal infections can occur as a cause of sporadic disease or outbreaks of disease in both immu­nocompetent and immunocompromised mice. Group A Streptococcus has been isolated from bacteremic Swiss mice that were inoculated with sterile endotoxin. The mice were found to carry Streptococcus in their pharyn- ges, and affected animals had cervical lymphadenitis, with bacteria isolated from multiple organs. Group B Streptococcus has been associated with meningo­encephalitis, ependymitis, and periventriculitis in nude mice. Infection of the brain was presumed to arise by extension from the nose, where bacteria were isolated from subclinical carriers. Group B S. agalactiae has been associated with an epizootic in a barrier colony of DBA/2 mice, which had ascending pyelonephritis with subse­quent bacteremia resulting in suppurative lesions in a variety of organs, including heart, kidneys, spleen, and liver, and less commonly in uterus, thorax, lymph nodes, and lungs.

Systemic disease due to alpha hemolytic S. viridans has been noted in irradiated SCID and SCID-beige mice. Mice were severely ill, with splenomegaly and pulmo­nary congestion. Massive numbers of Gram-positive bacteria were present in vessel lumina, with virtually no host response, particularly in glomerular capillaries (Fig. 1.80). A similar syndrome has been seen by the authors in irradiated SCID mice infected with E. faecalis.

An alternative form of streptococcal disease in mice is ulcerative dermatitis, which resembles the syndrome associated with Staphylococcus. Group G Streptococcus has been incriminated in an epizootic of necrotizing dermatitis. Ulcerative lesions were present on the dorsal

FIG. 1.80. Kidney from an irradiated SCID/beige mouse with disseminated alpha-hemolytic streptococcal infection. Numerous bacterial colonies are present in glomerular vessels.

thoracic or lumbar regions, with progressive spread to the shoulder and pelvic regions. Underlying tissue had vasculitis and thrombosis, with bacterial invasion of subcutaneous tissue. The bacterium was isolated from the oropharynx and spleens of many of the mice.