Haemophilus parainfluenzae isolates recovered from patients with respiratory diseases were studied for their ability to undergo genetic transformation by isogenic DNA. Two chromosomal markers, streptomycin resistance and nalidixic acid resistance, were tested for transformation efficiencies in H. parainfluenzae recipients from three biotypes. Most efficient in transformation was biotype II, followed by biotype I, while biotype III was nontransformable. Lack of transformation was not owing to poor donor activity of DNA, but to inability of the cells to develop competence. Strains that formed clumps in liquid media were nontransformable. Since the transformable biotype II is one of the prevalent biotypes world wide, one can speculate that DNA transformation probably plays a major role in the spread of drug resistance in H. parainfluenzae.
The location of the genes coding for NAD independence in four unusual clinical isolates of Haemophilus puruinfluenzae was determined by transferring these genes to plasmid-free Haemophilus influenza Rd by transformation and analysing transformants for the presence of plasmids by agarose gel electrophoresis. All NADindependent transformants were found to carry a single plasmid species. The plasmids, originally harboured by the four H. puruinfluenzue isolates recovered from unrelated sources, were of the same size (5.25 kb). Spontaneous reversion to NAD dependence occurred with a low frequency (0.1 to 0.2 % of the progeny of a single clone) in both H. puruinfluenzae and H. influenzae Rd. The revertants had lost this small plasmid. Mitomycin C exhibited a plasmid 'curing' effect with a frequency of 'curing' of between 1 and 6% of the surviving clones. It was concluded that the genes conferring NAD independence were located on the small 5-25 kb plasmid.
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