Molecular Epidemiology of Unrelated Clusters of Multiresistant Strains of Haemophilus influenzae

Abstract

Three epidemiologically unrelated clusters of Haemophilus influenzae resistant to ampicillin, chloramphenicol, and tetracycline were studied. The biotypes and cell-envelope protein patterns were determined for 17 nonencapsulated strains, 6 from Dundee and 11 from Cheltenham, and for 6 type b encapsulated strains from Guildford. After mobilization by conjugation, large 32- to 36-MDa plasmids were purified from all the strains. The restriction fragment patterns of the plasmids were determined by ethidium bromide staining of digested purified plasmid or by Southern hybridization of digested total cellular DNA of the parent strains, probed with purified plasmid. Evidence is presented for a chromosomal location of the plasmids in the parent strains, the spread in nature of a plasmid between distinguishable strains of H. influenzae, the person-to-person spread of a strain within a cluster, and a high degree of sequence homology between distinguishable plasmids, implying their close relatedness.

Transferable Antibiotic Resistance Elements in Haemophilus influenzae Share a Common Evolutionary Origin with a Diverse Family of Syntenic Genomic Islands

“…Briefly, the whole sequence was derived from a random library generated from purified extrachromosomal closed circular ICEHin1056, an element harbored by the ampicillin-, tetracycline-, and chloramphenicol-resistant organism H. influenzae type b strain 1056 (3,10). The sequences were assembled by using Pred and Phrap (17,18,21) and were viewed and edited with the Staden (50) suite of programs.…”

“…It was recognized that this antibiotic resistance was transferred by conjugation and was encoded by 40-to 60-kb related mobile elements (10,14,15,25,(31)(32)(33). Transposons, inserted at separate sites into the conjugative element, contained the resistance genes.…”

“…The ␤-lactamase gene encoding Ap r formed part of Tn3, and the genes encoding tetracycline and chloramphenicol resistance resided in a Tn10-like compound transposon (14,15,25,26). Surprisingly, free plasmids could not be easily detected in clinical isolates (10,52). However, extrachromosomal plasmids could be isolated from transconjugants (10,52).…”

“…Surprisingly, free plasmids could not be easily detected in clinical isolates (10,52). However, extrachromosomal plasmids could be isolated from transconjugants (10,52). It is now recognized that these related resistance elements not only conjugate but integrate site specifically into H. influenzae tRNA Leu (11).…”

“…Homologies for most of these islands have recently been reported by other workers (24,27,41,58), but the evolutionary implications of these homologies were not studied. The starting point of this investigation, however, was a bioinformatics study of the complete sequence of a large conjugative Haemophilus resistance element, ICEHin1056, which was previously referred to as p1056 (3,10,11,35). Identification of homologous sequences in ICEHin1056 and elements or genomic islands found in ␤-and ␥-Proteobacteria indicated the presence of a syntenic core element with a shared evolutionary origin.…”