Serological studies of peptostreptococci using an indirect fluorescent antibody test

Members of the genus Peptostreptococcus are frequent isolates from periodontal lesions. A study was undertaken for determination of the serological relationships of oral and non-oral strains of several species of this genus. Eighty-nine strains of peptostreptococci representing seven species were tested by means of an indirect fluorescent antibody technique (IFA), with rabbit antisera to Peptostreptococcus anaerobius ATCC 27337, Peptostreptococcus micros VPI 2618-A, and Peptostreptococcus productus ATCC 27340. Each antiserum showed positive fluorescence when reacted with homologous cells. When anti-P. micros VPI 2618-A serum was added to suspensions of P. micros ATCC 33270 and clinical isolates of P. micros in the IFA, positive fluorescence was observed to a titer of 1:64 with 26 out of 29 strains. Positive fluorescence was also seen when P. anaerobius VPI 5737 and clinical isolates of P. anaerobius were tested with anti-P. anaerobius ATCC 27337 serum; a titer of at least 1:64 was observed in 10 out of 14 strains. These results support the presence of two serological groups of P. anaerobius, rabbit anti-P. anaerobius ATCC 27337 serum reacting with Group II organisms. No interspecies cross-reactivity was observed except with four strains of Peptostreptococcus magnus, which reacted with several antisera as well as with normal rabbit serum and the saline controls. These results indicate that rabbit antisera and the use of an IFA are useful in the identification of P. anaerobius and P. micros from oral lesions.