Streptococcus pneumoniae serogroups and colony morphology: a look back.

From 1985 to 1987, Streptococcus pneumoniae isolates were collected from children under 5 years of age in the Asaro Valley, Papua New Guinea as part of a study on bacterial colonization and respiratory tract infections. Data on serogroup and colony morphology were collected to survey serogroups and associated colony morphologies present in the area and to assess whether colony morphology can be indicative of serogroup. In total, 5989 colonies were examined; serogroups 6, 10, 14, 15, 19, 23, 33, 34, 35 and nonserotypeable strains were the most common and accounted for 77% of all the colonies, with serogroups 6, 19 and 23 accounting for 48%. The majority of colonies displayed the typical draughtsman morphology, though serogroup 10 and non-serotypeable isolates most often displayed a raised colony morphology. Of the 15 mucoid colonies identified 73% were serotype 3, though only 29% of serotype 3 isolates were mucoid. Thus colony morphology is of limited value in identifying the pneumococcal serogroup/serotype apart from mucoid colonies, which are likely to be serotype 3.