Gentamicin-Resistant cultures of have been reported from many countries since 1975. Although specific epidemics have been associated with bacteria of uniform properties, many distinct strains, as indicated by differences in phage-typing pattern and sensitivity to other antibiotics, have been concerned (Soussy , 1975; Shanson, Kensit and Duke, 1976; Speller , 1976; Warren and Roberts, 1976; Bint , 1977; Wyatt , 1977; Lewis and Altemeier, 1978; Michel, Stessman, and Sacks, 1978; Naidoo and Noble, 1978; Buckwold , 1979; Faden , 1979; Greenhood , 1979).

The sudden appearance of gentamicin resistance in a wide variety of cultures after a 10-year period in which the resistance was exceedingly rare resembles the sequence of events with neomycin resistance in this organism (Lacey, 1971, 1975), and could be explained by the spontaneous transfer of a plasmid or plasmids between cultures Gentamicin resistance in is attributable to the production of inactivating enzymes (Bint , 1977; Dowding, 1977; Scott , 1978), as is usually the case with plasmid-mediated resistance. Plasmid DNA has been identified in gentamicin-resistant strains by Soussy (1975) and by Wood, Carter and Best (1977), but in neither case was it established that this DNA was responsible for the resistance, because the plasmid DNA was not isolated after transduction of the trait. Although transduction of gentamicin resistance has been achieved by a few workers, the frequencies have been low (Porthouse , 1976; Bint , 1977), and several others have been unable to transduce the resistance at all (e.g., Naidoo and Noble, 1978; Greenhood , 1979). Naidoo and Noble (1978) showed that gentamicin resistance could be transferred, at rather low frequency, between cultures seeded on to murine or human skin. Recently de Saxe and Porthouse (1979) described the isolation of plasmid DNA after transduction of gentamicin resistance. However, the transduction occurred at rather low frequency and mixed-culture incubation also resulted in transfer of resistance at low frequency.

Thus, as Greenhood (1979) have pointed out, there is strong epidemiological evidence for the occurrence of transfer of gentamicin resistance in nature, but experiments have not reproduced these postulated events. This paper describes some experiments relevant to this problem.


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