SUMMARY Gram-positive anaerobic cocci (GPAC) are a heterogeneous group of organisms defined by their morphological appearance and their inability to grow in the presence of oxygen; most clinical isolates are identified to species in the genus Peptostreptococcus. GPAC are part of the normal flora of all mucocutaneous surfaces and are often isolated from infections such as deep organ abscesses, obstetric and gynecological sepsis, and intraoral infections. They have been little studied for several reasons, which include an inadequate classification, difficulties with laboratory identification, and the mixed nature of the infections from which they are usually isolated. Nucleic acid studies indicate that the classification is in need of radical revision at the genus level. Several species of Peptostreptococcus have recently been described, but others still await formal recognition. Identification has been based on carbohydrate fermentation tests, but most GPAC are asaccharolytic and use the products of protein degradation for their metabolism; the introduction of commercially available preformed enzyme kits affords a physiologically more appropriate method of identification, which is simple and relatively rapid and can be used in routine diagnostic laboratories. Recent reports have documented the isolation in pure culture of several species, notably Peptostreptococcus magnus, from serious infections. Studies of P. magnus have elucidated several virulence factors which correlate with the site of infection, and reveal some similarities to Staphylococcus aureus. P. micros is a strongly proteolytic species; it is increasingly recognized as an important pathogen in intraoral infections, particularly periodontitis, and mixed anaerobic deep-organ abscesses. Comparison of antibiotic susceptibility patterns reveals major differences between species. Penicillins are the antibiotics of choice, although some strains of P. anaerobius show broad-spectrum β-lactam resistance.

Summary.A collection of 256 clinical strains and 40 reference strains of gram-positive anaerobic cocci (GPAC) was studied, to characterise the recognised species more fully and to define groups of strains which might correspond to previously undescribed species. The methods used were: gas-liquid chromatography (GLC) for the detection of volatile fatty acids (VFAs) ; determination of the pre-formed enzyme profile with a commercially available kit, ATB 32A ; microscopic appearance; colonial morphology; and antibiotic sensitivity tests. Strains were placed in one of five VFA groups according to their GLC profile; 96% of strains were further assigned to 12 groups by their enzyme profile. There was ~9 9 % agreement between the two methods.Of 11 1 clinical strains in the VFA-negative group, 110 gave one of three distinct enzyme profiles corresponding to Peptostreptococcus magnus, P. micros and P . heliotrinreducens. The assignment of strains to groups based on their microscopic appearance and colonial morphology agreed well with groupings according to enzyme profile. Identification of butyrate-producing GPAC was unsatisfactory because it relied heavily on the enzyme profile; testing for indole production was of limited discriminative value. Most strains of P . asaccharolyticus and P . indolicus were very similar in enzyme profile, microscopic appearance and colonial morphology, but a sub-group of P . asaccharolyticus could be distinguished. A further indole-positive group corresponding to Hare group I11 was also noted. Strains of P. prevotii and P. tetradius were very similar, but easily distinguished from other butyrateproducing GPAC. However, 45% of the butyrate-producing cocci could not be assigned to recognised species; most of these were assigned to one of two new groups, the ADH group and the bGAL group, by their enzyme profile, microscopic appearance and smell. Four strains that produced a terminal VFA peak of isovaleric acid formed a new group designated 'ivoricus'. Reliable features for the identification of P . anaerobius were GLC (all GPAC that produced isocaproic acid were identified as P . anaerobius), enzyme profile and sensitivity to SPS. Two clinical strains that produced caproic acid were identified as Hare group VIII; they were distinguished from Peptococcus niger by their enzyme profile and colonial morphology.A phenotypic classification based on GLC and enzyme profile is presented, with a method for the identification of most strains of GPAC within 48 h of primary isolation.

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Summary.The clinical importance of the gram-positive anaerobic cocci (GPAC) isolated in 1987 at St Bartholomew's Hospital, London, is assessed. Of about 800 anaerobic isolates, 209 (27 YO) were GPAC, of which 67 (32%) were from abscesses and 22 (11 YO) were in pure growth. Four species comprised 77% of the 168 isolates available for study: Peptostreptococcus magnus (55 isolates, 33 YO), P. micros (23, 14 YO), P. asaccharolyticus (24, 14 Yo) and P. anaerobius (27, 16 YO). Different species were associated with different sites, from P. magnus (usually skin-associated sites ; normally cultured with aerobes, infrequently with other anaerobes), P. asaccharolyticus (distributed widely) and P. anaerobius (usually genitourinary and gastrointestinal; always below the diaphragm) to P. micros (always deep sites with other anaerobes). P. magnus was isolated from 15 abscesses and was obtained in pure culture from 11 specimens, six of them abscesses developing from infected sebaceous cysts. P. micros was usually isolated from soft tissue abscesses, never from the skin, and with a characteristic mixed flora consisting of " Streptococcus milleri" and anaerobic gram-negative rods. P. heliotrinreducens was a rare isolate from similar specimens. P. asaccharolyticus was cultured from a wide variety of sites, typically mixed with both aerobes and anaerobes, and frequently from abscesses. Most isolates of P. anaerobius came from gastrointestinal or female genitourinary specimens, never from above the diaphragm and rarely from the skin; cultures were usually heavily mixed. Isolates of P. vaginalis and the " bGAL" group made up 11 YO of strains and were usually cultured from superficial sites, P. vaginalis often from post-operative wound infections with Staphylococcus aureus. There were only two isolates of P. hydrogenalis, three of P. tetradius and none of P. barnesae, P. prevotii, P. lacrimalis, P. lactolyticus, P. productus or Peptococcus niger. GPAC are a heterogeneous group associated with a wide variety of infections, particularly abscesses, and are frequently isolated in pure culture. They deserve further study.

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