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Summary: The tetracycline-resistant Haemophilus influenzae strains lu121 and fr16017, recently isolated in West Germany, each harbour a plasmid; that of the former (pLU121) has a mol. wt of 31.5 x 106 and that of the latter (pFR16017) has a mol. wt of 33 x 106. Conjugation and DNA-DNA hybridization studies have shown that both plasmids are self-transmissible and carry tetracycline-resistance genes. The purified plasmid DNA of H. influenzae strain lu121 transformed a sensitive Escherichia coli strain to tetracycline resistance. The two R factors are closely related to the H. influenzae plasmid specifying ampicillin resistance (pKRE5367). Electron microscope DNA heteroduplex analysis indicated that pLU121 and pFR16017 probably carry the tetracycline-resistance transposon TnD and that pKRE5367 probably carries the ampicillin-resistance transposon TnA. There is more than one integration site for the insertion which probably represents TnD in pFR16017. All three plasmids have a similar plasmid core and could have a common evolutionary origin.

The ampicillin-resistant Haemophilus influenzae strain Ve445 which caused purulent meningitis and septicaemia in a newborn child in Germany contained a 4.4 megadalton (Mdal) plasmid (pVe445) and produced a TEM type beta-lactamase. The transformation to ampicillin resistance of a sensitive Escherichia coli strain with isolated pVe445 DNA proved that the structural gene for the beta-lactamase resided on this plasmid genome. Molecular DNA-DNA hybridization studies and electron microscope DNA heteroduplex analysis indicated that pVe445 probably contained 38 to 41% of the ampicillin translocation DNA segment (TnA) found on R factors of enteric origin. The TnA fragment present in pVe445 most likely does not contain both of the inverted repeat sequences of TnA. DNA-DNA polynucleotide sequence studies indicated that the 4.4 Mdal plasmid pVe445 was unrelated to the 30 to 38 Mdal H. influenzae R plasmids but was closely related to the 4.1 Mdal ampicillin resistance specifying H. influenzae plasmid RSF0885 isolated in the U.S.A. The H. influenzae plasmid pVe445 shared 91% of its base sequences with the beta-lactamase specifying Neisseria gonorrhoeae plasmid pMR0360 (4.4 Mdal) and had 85% of its base sequences in common with the beta-lactamase specifying N. gonorrhoeae plasmid pMR0200 (3.2 Mdal). All of the four 3.2 to 4.4 Mdal beta-lactamase specifying R plasmids of H. influenzae and N. gonorrhoeae investigated probably have a common evolutionary origin.

The ampicillin-resistant isolate Haemophilus influenzae KRE5367 which produced a TEM type β-lactamase contained a 30 megadalton (Mdal) plasmid (pKRE5367) with a copy number of approximately 2 per chromosomal equivalent and a mole fraction guanine plus cytosine content of 0.39. Ampicillin resistance was transferred by cell-to-cell contact, and the transformation to ampicillin resistance of a sensitive Escherichia coli strain with isolated pKRE5367 DNA proved that the structural gene for the TEM type β-lactamase resided on the plasmid genome. It was shown by molecular hybridization that pKRE5367 probably contained the ampicillin translocation DNA segment (TnA) found on some R factors of enteric origin. The H. influenzae plasmid pKRE5367 had most of its polynucleotide sequences in common with other R factors recently isolated from H. influenzae. DNA-DNA hybridization studies indicated that pKRE5367 shared about 70% base sequence homology with the two tetracycline-resistance R plasmids pLU 121 (31.5 Mdal) and pFR 16017 (33 Mdal) recently isolated in W. Germany. In addition, pKRE5367 had nearly 100% of its polynucleotide sequences in common with the 30 Mdal ampicillin-resistance R plasmid RSF007, isolated in the U.S.A.; it shared 70% base sequence homology with the 31.5 Mdal tetracycline-resistance plasmid pUB701, isolated in the U.K.; and it had 65% of its polynucleotide sequences in common with the 38 Mdal tetracycline- and chloramphenicol-resistance R plasmid pR1234 isolated in the Netherlands. Despite the broad geographical range, the R plasmids of H. influenzae appeared to be closely related.