159 - Miscellaneous Gram-Positive Organisms

Summary

PEDIOCOCCUS SPECIES

Pediococci are gram-positive cocci that grow in pairs and tetrads. Normal inhabitants of the gastrointestinal tract, they are used extensively in industry to ferment cheese and other dairy products, soy products, and alcoholic beverages. Eight species of pediococci are recognized, but only the closely related Pediococcus acidilactici and Pediococcus pentosaceus have been identified as human pathogens. In recent years, these organisms have been increasingly recognized as a cause of bacteremia and pneumonitis in the immunocompromised host. These organisms have also been isolated from intra-abdominal infections such as peritonitis and hepatic abscesses. Risk factors for Pediococcus infections include prior antibiotic therapy, abdominal surgery, and gastric feeding.

Diagnosis is made by isolation and identification of the organism from cultures of blood or other body fluids. As one of the lactic acid bacteria associated with foods, Pediococcus species may be difficult to distinguish from enterococci and Leuconostoc species. Approximately 95% of clinical isolates will cross-react with group D streptococcal antisera. Tests that aid in distinguishing pediococci from other organisms include a negative pyrrolidonylarylamidase (PYRase) test and the absence of gas production from glucose. With newer application of molecular genetic techniques to determine relatedness of food-associated lactic acid bacteria, reorganization of the genus with novel morphologic or phenotypic differentiation of Leuconostoc species from Pediococcus species is being studied.

Pediococci are intrinsically highly resistant to vancomycin and other glycopeptides. Most strains are moderately susceptible to penicillin and ampicillin. Minimum inhibitory concentrations (MICs) are variable for cephalosporins.