Resistance plasmids in gram negative bacteria isolated at the University Hospital of the West Indies, Jamaica

One hundred and sixty-five multiply resistant gram negative bacteria isolated at UHWI were tested for their ability to transfer their antibiotic resistance to a recipient Escherichia coli K12 strain J53-2. The isolates were representatives of 9 diferent genera. The majority of the isolates (68) were from urine, 48 isolates were Salmonella ohio strains from stools, and the remaining 53 isolates were from blood, pus, burn swabs and other sources. 82.8 percent of the 169 isolates tested transferred part of all of their resistance determinants to strain J53-2 at 37§C. The incidence of transferable resistance was found to differ according to the genera considered with quite high frequencies in some genera, e.g. S. ohio (100 percent), E. coli (80.9 percent) and Klebsiella pneumoniae (72.3 percent), and lowest incidence in Acinetobacter (20 percent). A higher frequency (80.9 percent) of transferable resistance was demonstrated in urine than non-urine (69.8 percent) isolates. In addition, particular genera (E. coli, K. pneumoniae, Proteus and Enterobacter) had a higher incidence of transferable resistance when organisms were isolated from urine than when isolated from non-urine specimens. The incidence of resistance to trimethoprim (Sxt), tetracycline (Te), cephaloridine (Cf) and ampicillin (Am) was higher than that of resistance to gentamicin (Gm), amikacin (AN) and tobramycin (NN). Similarly, transfer of resistance to Sxt, Te Cf and Am occurred with higher frequency than transfer of resistance to Gm, AN and NN. Simultaneously resistance to 3, 4 and 5 antibiotics was more prevalent (accounting for 72.8 percent of the positive isolates) than was simultaneous resistance to 1, 2, 6 and 7 antibiotics (27.2 percent of the positive isolates). Transfer of resistance to 1, 2, 3 and 4 antibiotics occurred more frequently than transfer of resistance to 5, 6 and 7 antibiotics. Experiments were done to validate the method used to detect transferable resistance. The biochemical characteristics, nutritional requirements and antibiotic resistance of E. coli K12 strain J53-2 exconjugants obtained from transfer experiments indicated that the method used was a valid one for detection of transferable resistance. Filtrates of multiply resistance donor isolates did not transfer resistance to E. coli K12 strain J53-2. Transfer of resistance by whole cell cultures of the donors to J53-2, was unaffected by the presence of deoxyribonuclease I in the medium used for mating. Of the 29 isolates that did not transfer resistance to E. coli K12 strain J53-2 at 37§C, 13 (44.8 percent) were able to do so at 30§C, 4 (13.8 percent) were able to transfer resistance because they produced a colicin that was active against J53-2 and 5 (17.2 percent) possessed nonconjugative R plasmids which could not be transferred to J53-2 unless another "intermediate" host, E. coli K12 strain NH4104 was present. Three of the twenty-nine isolates were lost during storage. Two of the seven isolates, an E. coli and a Serratia marcescens isolate, tested for curing of antibiotic resistance by use of acridine orange and/or ethidium bromide demonstrated curing of part or all of their antibiotic resistance. Results of the curing experiments were inconclusive. Taking into account transferable resistance at 37§C and 30§C, the presence of nonconjugative R plasmids and loss of donors in storage this study provided evidence for the occurrence of R plasmids in 91.8 percent of 169 gram negative bacteria isolated from UHWI during the period May 1983 to March 1984. For two of the isolates with transferble resistance demonstration of curing of antibiotic resistance provided further evidence for plasmid encoded resistance (AU)

Transmissible drug resistance among E. coli strains isolated from pig and human specimens

Resistance factors, the transmissible genetic elements which confer drug resistance on members of the Enterobacteriaceae, are frequently found in isolates from human specimens. It was suggested that farm animals which receive antibiotics might harbour these R factors and infect the human community by way of the farm workers who handle them. In this study, a total of 252 faecal specimens were collected - 152 from pigs and employees on a farm using antibiotics, and 100 from pigs and employees on control farms using no antibiotics. An E. coli culture was selected from each specimen and examined for resistance to: Ampicillin, Sulphonamide, Streptomysin, Chloramphenicol, Tetracycline, Nalidixic Acid. Resistance cultures were further examined for the ability to transfer drug resistance to sensitive bacteria. 1. 110 faecal specimens were collected from the test pigs which had been given antibiotics. All the specimens yielded multiply resistance E. coli of which 94 (86 percent) were able to transfer all or part of their resistance pattern to a suitable sensitive recipient. 2. 42 humans in contact with the test pigs were examined in the same manner. 86 percent of the isoaltes were resistant to one or more of the drugs and 48 percent transferred drug resistance. 3. Specimens were collected from 72 pigs in the control group. 68 (94 percent) contained drug resistant E. coli of which 16 (22 percent) transferred their resistance. 4. 20 out of 28 humans (i.e. 72 percent) in the control group yielded resistant E. coli and six (21 percent) transferred their resistance. The results indicate that: I. Those pigs exposed to antibiotics harboured coliforms with R factors more frequently than pigs not exposed to antibiotics. II. The control human group also had a lower occurrence of transmissible drug resistance than the group who worked with the antibiotic-treated pigs. III. The relatives of the farm employees excreted more transmissible drug resistant strain (43 percent) than the human control group (21 percent). IV. The highest incidence of transmissible drug resistant strains was among individuals who were taking antibiotics at the same time the specimens were collected. Pigs which had not been given antibiotics for some months showed a lower yield of transmissible drug resistant strains than those currently taking antibiotics at the time the specimens were collected. V. The humans from the test farm, although they were not currently taking antibiotics, yielded drug resistant strains at a rate comparable to the test pigs. However, only 48 percent of these transferred drug resistance, compared with 86 percent of the test pigs. VI. Drug resistant bacteria were found in the majority of specimens from all groups, but the ability to transfer these resistances varied widely (Summary)