Description of Two Morphotypes of Peptostreptococcus micros

Abstract

Peptostreptococcus micros is often isolated from abscesses in several parts of the human body. The oral cavity is considered the natural habitat for the species, which has been implicated as a periodontal pathogen. In plaque samples from periodontitis patients we observed the presence of a rough morphotype of P. micros in addition to the previously recognized smooth morphotype. The rough morphotype has not been described previously. Both morphotypes are frequently isolated simultaneously from the same patient. In this paper strains of both morphotypes are described. The smooth morphotype, represented by the type strain, grew as small, dome-shaped, bright white, nonhemolytic colonies. The rough morphotype grew as equally white dry colonies which were hemolytic and had wrinkled edges. DNA-DNA reassociation studies revealed homology at the species level between the two morphotypes; in addition, no differences in physiological characteristics were observed when the organisms were tested with API-32A and API-ZYM kits. The rough cells had long, thin fibrillar structures outside the cell envelope when they were stained negatively for electron microscopy. In the smooth morphotype these structures were not present. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of whole-cell extracts were different for the two morphotypes. In xylene-water phase partition studies, the smooth morphotype was found to be hydrophobic, whereas the rough morphotype was found to be relatively hydrophilic. The distinct morphotypes were stable on blood agar; however, the rough morphotype changed to a nonfibrillar type with a smooth colony morphology after repeated subculturing in broth.Gram-positive anaerobic cocci are commonly found on mucous membranes of the oral cavity, the intestines, and the vagina. These bacteria are isolated from a variety of human abscesses as well. Frequently, the strains isolated belong to the genus Peptostreptococcus. The presence of Peptostreptococcus micros is not restricted to a particular part of the human body. Polymicrobial pulmonary and cerebral abscesses (9, 12, 24), as well as female genital tract infections (7), can contain high percentages of P. micros. It is thought that the natural habitat of this species is the oral cavity (14). Plaque of healthy individuals contains low percentages of this bacterium. It is isolated more often and in increased percentages from patients with periodontitis (18). A correlation in patients has been reported between poor response to periodontal therapy and the percentage of P. micros present in the total cultivable anaerobic flora (17). Furthermore, the presence of the microorganism has been related to active sites of periodontitis (4, 30), to endodontic lesions, and to human immunodeficiency virus-related periodontitis (3, 25, 26, 36). For these reasons P. micros has been implicated as a periodontal pathogen (27).P. micros usually forms smooth colonies. In samples obtained from periodontitis patients, we frequently isolated a rough morphotype of P. micr...

Characterization of Smooth and Rough Morphotypes of Peptostreptococcus micros

“…Previously, van Dalen et al (32) have described two phenotypically different types of P. micros, the Sm type and the Rg type, which prevalence study performed in our laboratory (33), the Rg morphotype could be isolated only from patients that were also infected with Sm type P. micros. As the Rg type was found to be unstable in broth culture, changing to Rgs"-type colonies, we determined whether the existence of Rg and Sm morpho- Fig.…”

“…These two morphotypes are serologically distinguishable; the Sm morphotype represents serotype a, while the Rg morphotype represents serotype b (34). Both morphotypes can be isolated from subgingival plaque samples; the Rg type is always isolated in association with the Sm type, whereas the Sm type can also be isolated alone (33).…”

“…ELISAs were performed as described previously (33). After the bacteria were harvested and washed once in PBS, 100 p, 1 of a bacterial suspension in PBS (OD,,,, 0.1; -1O'bacteria) was added to each well of a 96-well flat-bottom plate (catalog no.…”

“…Recent work in our laboratory revealed the existence of the following two morphotypes of P. micros (32): a smooth-colony (Sm) morphotype, which is recognizable by white, domeshaped, mucous colonies; and a rough (Rg) morphotype, which produces dry white colonies with wrinkled edges. These two morphotypes are serologically distinguishable; the Sm morphotype represents serotype a, while the Rg morphotype represents serotype b (34).…”

“…van Dalen et al (32) described the instability of the Rg morphotype in broth culture; the Rg morphotype readily changed to a Sm variant (Rg'"). Phase variation is uncommon in gram-positive bacteria and has been reported previously only for Streptococcus species (36) and Corynebacterium species (8, 13).…”