Some aspects of transmissible drug resistance in animals and their human contact - abstract

ABSTRACT

The use of antibiotics in animal feeds and in Veterinary Medicine is believed to select for antibiotic-resistant organisms in the normal gut flora of animals. Such resistant organisms may be passed to human contacts; if the resistance is due to transferable resistance factors, then the normal flora in the gut of human contact may become resistant to antibiotics. The purpose of this study was to ascertain the incidence of multiple drug resistance in the gut flora of pigs, to measure the transferability of these resistances to sensitive organisms and in addition to compare these patterns with those of the human contacts of the pigs. Faecal samples were collected from 110 pigs known to have received antibiotics (penicillin, di-hydrostreptomycin, oxytetracyline, chlortetracyline and sulfamethazine) and from 42 human contacts (handlers and relatives). Faecal samples were also collected from 72 pigs, not known to have received any antibiotics, and from 28 human contacts. Specimens were plated to MacConkey agar and antibiotic "Multodiscs" applied. Multiply-resistant organisms were mated with a multiply-sensitive recipient, in a modified version of the technique of Schroeder et al (1968). Antibiotic-resistant recombinants were recovered by plating the mixture on MacConkey agar containing nalidixic acid and/or streptomycin/tetracycline. Antibiograms were repeated on the recombinants. 96 percent of the faecal specimens from the test pigs yield multiply-resistant (more than 3 antibiotics) coliforms. This contrasted with 25 percent from the control pigs. 65 percent of the multiply-resistant organisms while none of the human contacts of the control pigs yielded multiply-resistant organisms. Only 27 percent of the multiply-resistant organisms in the human contact of the test pigs could tranfer some of all of the resistance factors. In all cases, resistance was greatest to streptomycin, tetracycline and sulfonamide. The high incidence of antibiotic resistance in the test pigs indicates the effect of prior antibiotic exposure on the selection of antibiotic resistant strains. The similarity of resistance patterns between the test pigs and their handlers suggests the transmission of organisms from pigs to man. The low frequency of transmissible drug resistance in the human contacts suggests instability of the transfer factor in the human intestine.(AU)