Drug-resistant Escherichia coli and Klebsiella-Enterobacter in healthy adults in Thailand and the effect of antibiotic administration

Antibiotic resistance and its transfer among clinical and nonclinical Klebsiella strains in botanical environments

A total of 183 isolates of Klebsiella from drinking water, market vegetables, wood, sawdust, industrial effluents, and human and animal origin were examined for susceptibility to 10 antibacterial agents. Incidence of resistance to two or more antibiotics tested was: 65% of the human clinical isolates, 59% among bovine mastitis, and 24% among the nonclinical isolates. The five different multiple resistance patterns among nonclinically derived Klebsiella were also found among the human and bovine mastitis isolates. Statistical analyses revealed that patterns of resistance among Klebsiella isolates from drinking water, market vegetables, and industrial effluents were highly correlated with each other and with resistance patterns of human clinical isolates. Antibiotic resistance was transferred between Klebsiella growing in two habitat-simulated environments (growing radish plants and aqueous sawdust suspensions). Transconjugants were detected in 5 of 21 and 6 of 21 mating pairs, respectively. Average transconjugants/donor ranged from 10(-3) to 10(-6) in Penassay broth, from 10(-6) to 10(-7) on radish plants, and from 10(-5) to 10(-8) in sawdust suspensions. Although antibiotic resistance transfer under simulated environmental conditions can occur, regrowth of clinical strains is probably the major cause for the widespread occurrence of antibiotic-resistant Klebsiella in the nonclinical environment.

Microbial development of drug resistance: mechanisms and clinical significance

Bacteria have demonstrated a disconcerting ability to develop resistance to antimicrobial agents nearly as quickly as new compounds become available. During the past two decades the molecular bases of several types of resistance have been elucidated. Mechanisms of resistance include the transference of genetic material either through conjugation (involving direct contact between microorganisms), or indirectly through transduction (involving bacteriophages). In addition to this "infectious" drug resistance, genetic mutations which permit the utilization of new metabolic pathways, and the production of enzymes which can inactivate the antimicrobic have been described. One particularly complex problem has been the ability of many Enterobacteriaceae to develop resistance to multiple antimicrobials simultaneously. The possible effect of such an occurrence is illustrated by the recent epidemic of multiply resistant Salmonella typhi in Mexico. Because the typhoid bacilli shared an identical resistance pattern to an epidemic Shigella dysenteriae type 1 the in vivo interspecies transmission of resistance has been postulated. Understanding the various mechanisms of resistance development should allow more rational use of antimicrobial agents.