Anaerobic R factor transfer in Escherichia coli.

R factor mediated transfer of antibiotic resistance between Enterobacteriaceae has been reported to occur in the mammalian gastrointestinal tract (Kasuya, I 964; Reed, Sieckmann & Georgi, 1969; Guinie, 1970; Wiedemann, Knothe & Doll, 1970) where conditions are mainly anaerobic as demonstrated by the abundance of obligate anaerobic bacteria such as Bacteroides species (Moore, Cat0 & Holdeman, 1969) and direct studies of intestinal gas composition (Askevold, I 956). However, most laboratory investigations of the incidence of R factors and their transfer frequencies have been performed under aerobic conditions using faecal facultative strains. The only investigation of resistance transfer under anaerobic conditions in vitro is that of Mitsuhashi (1965), who reported complete inhibition of transfer of an R factor from a ShigellaJtexneri donor to an Escherichia coli recipient. On the basis of this result, it may be questioned whether in vivo R factor transfer is in fact possible (Chabbert, Baudens & Bouanchaud, 1969). Fisher (1957) reported restriction of chromosomal transfer by an Escherichia coli Hfr strain under anaerobic conditions in various minimal media. However, it has recently been shown by Stallions & Curtiss (1972) that anaerobic chromosomal transfer by an E. coli Hfr strain can occur at a high frequency provided that the mating medium is nutritionally rich. This gives rise to a contradiction, since Mitsuhashi (1965) used brain heart infusion broth, a rich medium, yet found inhibition of R factor transfer. This puzzling situation prompted a re-examination of R factor transfer under anaerobic conditions by facultative faecal E. coli strains in a rich medium. Fisher (1957) and Mitsuhashi (1965) obtained anaerobic conditions by evacuation. Stallions & Curtiss (1972) flushed with N, for the duration of the mating. In this investigation, both mating and selection of recombinants were performed under stringent anaerobic conditions using methods developed for the isolation of obligate anaerobes (Hungate, I 969) to obtain a degree of anaerobiosis similar to that found in vivo.