Lymphadenopathy and non-suppurative meningo-encephalitis in calves experimentally infected with bovine immunodeficiency-like virus (FL112) |
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Authors: | R Munro R Lysons C Venables M Horigan M Jeffrey M Dawson |
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Affiliation: | Institute for Medical Microbiology and Epidemiology, Leipzig University, Germany. |
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Abstract: | At least 10% of spontaneous chromosomal antibiotic resistant mutants of bacteria express a strain-dependent graded reduction of virulence; this correlates linearly with a prolonged generation time. Occasionally, these mutants are temperature sensitive or/and auxotrophe. The work described in this paper provides evidence that in such strains the resistance and the accompanying markers exist only as a functional genetic unit. In a series of transduction experiments with a pathogenic strain of Salmonella typhimurium, it was found that without exception, the resistance and the additional markers were 100% simultaneoulsy transferred. Furthermore, antibiotic-resistant Escherichia coli mutants with prolonged generation time, were isolated from faecal samples; it is thus indicated that, such innocuous mutants occur at any time in the intestine. It is concluded that concerns connecting such mutants to the possibility of resistance dissemination are unfounded; furthermore, even if transfer of resistance occurred, only attenuated strains would be disseminated. |
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