Biochemical, Enzymatic, and Serological Differentiation of Peptococcus indolicus (Christiansen) Sørensen from Peptococcus asaccharolyticus (Distaso) Douglas

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Peptococcus indolicus (formerly Micrococcus indolicus) is an asaccharolytic anaerobic coccus that is frequently isolated from udder secretions from cases of heifer and dry-cow mastitis (summer mastitis). To facilitate better identification and its differentiation from Peptococcus asaccharolyticus, a variety of biochemical, enzymatic, and serological properties were studied. Seventy-nine strains of P. indolicus of bovine origin and 10 strains of P. asaccharolyticus of human origin were examined using the API 20A and API-ZYM test kit systems. In addition, production of extracellular enzymes by using sensitive substrate-containing agar plate tests, production of peptocoagulase (a plasma-clotting factor), hemolytic properties, metabolic end products by gas chromatography, and serological characteristics with a set of P. indolicus typing antisera were investigated. P. indolicus and P. asaccharolyticus were not satisfactorily differentiated solely by the API 20A system. P. indolicus differed from P. asaccharolyticus in producing H2S, reducing nitrate to nitrite, producing peptocoagulase, possessing alkaline phosphatase, and producing large amounts of propionate from lactate. Moreover, none of the strains of P. asaccharolyticus was typable with the P. indolicus typing antisera. The majority (88%) of P. indolicus strains also gave weak hydrolysis of ribonucleic acid, and 6 out of 79 produced deoxyribonuclease. All strains in this study were sensitive to metronidazole (5 μg) by disk diffusion tests.

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