Applications of bacteriocin-like inhibitory substance (BLIS) typing in a longitudinal study of the oral carriage of beta-haemolytic streptococci by a group of Dunedin schoolchildren.

A longitudinal study of the distribution of oral beta-haemolytic streptococci in 103 children (ages 5-6 y) attending three Dunedin schools was initiated in February 1987. A total of 858 paired pharyngeal and saliva specimens were obtained in nine principal sampling sessions, the last being in May 1989. The detection rate of Lancefield group A streptococci in directly plated pharyngeal cultures (19.8%) was considerably higher than in the corresponding saliva cultures (5.1%). By contrast, Lancefield group F and serologically non-groupable beta-haemolytic Streptococcus anginosus tended to be more prevalent in saliva (10.9% positive) than in pharyngeal specimens (7.1%). Group A streptococci were recovered at least once from 59 (57.3%) of the subjects. Representative beta-haemolytic streptococcus isolates were typed according to their production of bacteriocin-like inhibitory substances (BLIS) and by traditional serological techniques. The epidemiological value of BLIS typing was particularly evident in that both BLIS-positive and BLIS-negative strains could be differentiated within serotypes M1, M12 and M22 and also the serologically not typable group A streptococcus isolates. Ten children consistently had small numbers of group A streptococci present in their pharyngeal cultures, for periods of at least 12 months. In six of these subjects the carried strain was M-type 4/BLIS-type 655. This study has shown that in young schoolchildren long-term carriage of a variety of species of beta-haemolytic streptococci with little associated clinical evidence of infection may be common.