Flow of resistance genes in the environment and from animals to man

Abstract

Some antibiotic-resistant bacteria occur naturally in the environment but many arise by contamination with human and animal excreta in sewage, slurry and manure. These may be ingested as contaminants of water, animal feeds and cultivated foods or, in the case of animals, by licking their environment. Gene transfer has been demonstrated in voided calf faeces and the resultant transconjugants, subsequently ingested, colonized the calf gut. Identified strains of antibiotic-resistant Escherichia coli have been traced from the gut contents of pigs, calves and chickens to carcasses at slaughter and ultimately shown to colonize the gut of a human volunteer handling and eating the meat. Similarly, antibiotic-resistant strains of Salmonella typhimurium phage type DT204c, have been isolated from calves and humans indicating a possible zoonotic spread. The significance of these observations is discussed.

The prevalence and genetics of resistance to commonly used antimicrobial agents in faecal Enterobacteriaceae from children in Bangladesh

“…Similar multiresistant strains of S. typhi have also been reported from other countries [7][8][9]. Vibrio cholerae resistant to commonly used antibiotics have been reported from Philippines [10], Thailand [ 11], Tanzania [12] and Kenya [13]. In Bangladesh several studies have demonstrated the extensive problems of multiple resistance in shigellae [14][15][16].…”

“…These were selected to ensure that isolates for each month and each village were included. Of these 65 were E. coli, 12 resistance pattern to be transferred was Ap Tm Cm Tc Su Sm, from 28 isolates followed by Ap Cm in 9 strains. Table 3 shows the resistance patterns transferred by different plasmids.…”

“…Resistance in gut flora may arise from the wide-spread, indiscriminate use of antimicrobials [19] and from environmental spread of resistant enteric flora [20]. Several reports have indicated a relatively high prevalence of antimicrobial resistance in enteric flora in children in tropical countries [21][22].…”

Ecological aspects of the antimicrobial resistence in bacteria of importance to humn infections

“…Strains resistant to antimicrobials may, under certain conditions, transfer genes by means of plasmids (19) to other strains that are resistant to other antibiotics, and this process can generate strains resistant to a larger group of antibiotics than formerly. Plasmids (self-replicating DNA molecules), which in many situations can carry genes for resistance to antimicrobials (5,15), are potentially transferable among bacteria (31).…”

“…The occurrence of strongly selective environments for antimicrobials such as hospitals, industries, and veterinary activities (where large quantities of antimicrobials are used to promote growth and to prevent and treat infections) leads to an increase in the frequency of resistance bacterial genes. Degraded sanitation in communities may lead to the establishment of routes for dissemination of microorganisms (19,22) and genetic elements such as plasmids, which can amplify the problem by contributing to the increase of multi-resistant bacteria.…”