Pulsed-field gel electrophoresis used to investigate genetic diversity of Haemophilus influenzae type b isolates in Australia shows differences between Aboriginal and non-Aboriginal isolates

We used pulsed-field gel electrophoresis to study the epidemiology and popu lation structure of Haemophilus influenzae type b, DNAs from 187 isolates r ecovered between 1985 and 1993 from Aboriginal children (n = 76), non-Abori ginal children (n = 106), and non-Aboriginal adults (rr = 5) in ut ban and rural regions across Australia H-ere digested with the SmaI restriction end onuclease. Patterns of 13 to 17 Hell-resolved fragments (size range, simila r to 8 to 500 kb) defining 67 restriction fragment length pol morphism (RFL P) types were found, Two types predominated. One type (n = 37) accounted fo r 35 (46%) of the isolates from Aboriginals and 2 (2%) of the isolates from non-Aboriginals, and the other type (n = 37) accounted for 2 (3%) of the i solates from Aboriginals and 39 (35%) of the isolates from non-Aboriginals. Clustering revealed seven groups at a genetic distance of similar to 50% s imilarity in a tree like dendrogram. Ther included two highly divergent gro ups representing 50 (66%) isolates from Aboriginals and 6 (5%) isolates fro m non-Aboriginals and another genetically distinct group representing 7 (9% ) isolates from Aboriginals and 81 (73%) isolates from non-Aboriginals. The results showed a heterogeneous clonal population structure, with the isola tes of two types accounting for 42% of the sample. There was no association between RFLP type and the diagnosis of meningitis or epiglottitis, age, se s, date of collection, or geographic location, but there Has a strong assoc iation between the origin of isolates from Aboriginal children and RFLP typ e F2a and the origin of isolates from non-Aboriginal children and RFLP type A8b. The methodology discriminated Hell among the isolates (D = 0.91) and will be useful fur the monitoring of postvaccine isolates of H. influenzae type b.