Evidence of increased spread and establishment of plasmid RP4 in the intestine under sub-inhibitory tetracycline concentrations

Abstract

The consequences of using anti-microbial agents in a complex ecosystem like the animal intestine can be difficult to predict. We have looked at effects of modulations in growth of competing intestinal bacteria on transfer and establishment of new genetic elements in the intestinal microflora. For this purpose, we used tetracycline, which gradually reduces the growth rate of tetracycline-sensitive bacteria, as the concentration of this drug is increased. The effect of tetracycline on transfer and establishment of the plasmid RP4, which encodes resistance to this drug, in populations of Escherichia coli BJ4 colonizing the intestine was investigated. A tetracycline-sensitive E. coli BJ4 strain was allowed to establish in the gastrointestinal tract of mice, where after an isogenic E. coli BJ4 carrying RP4 was given to the mice per os. Tetracycline in the drinking water given to the animals was kept in concentrations that allowed the sensitive recipient strain to colonize the gut. A given 'window' between the highest and the lowest antibiotic doses tested was shown to be optimal for the establishment of transconjugants in the intestine. These observations are important for the evaluation of the effect of a given drug on the intestinal ecosystem. A reduced potential for growth of a given bacterial species, caused by the presence of sub-inhibitory concentrations of a bacteriostatic antibiotic, will facilitate establishment of competing (i.e. closely related) organisms, which have acquired resistance genes and therefore grow well in the presence of the drug.

Effect of Tetracycline on Transfer and Establishment of the Tetracycline-Inducible Conjugative Transposon Tn 916 in the Guts of Gnotobiotic Rats

“…Supported by a few previous publications from our laboratories (18,20), this challenges the hypothesis that isogenic strains in the gut, like in a chemostat, are not able to coexist due to the highly competitive intestinal environment (11,17,19,31). Chemostat predictions show that the cells must grow fast enough to compensate for the continuous washout of bacteria with feces and faster than other bacterial species competing for the same nutrients in order to persist in the dynamic system (12).…”

Impact of Therapeutic Treatment with β-Lactam on Transfer of the bla CTX-M-9 Resistance Gene from Salmonella enterica Serovar Virchow to Escherichia coli in Gnotobiotic Rats

“…The control group of five animals received drug-free water by gavage. Fresh fecal samples were collected from each rat by provoked defecation on days 0, 1,7,8,14,15,16,17,18,19,20,21,22,27,29,31, and 34. The samples were homogenized by whirly mixing in sterile water (10%).…”

“…Hypotheses, such as gene inactivation or silencing, have been put forward, but no conformational experiments have been conducted. Although antibiotic selective pressure has been shown to increase the proportion of antibiotic resistance genes in vivo, most experiments have been conducted with subinhibitory antibiotic concentrations (13,27,32,33). In our study, we investigated modulation of the transfer during a therapeutic antibiotic treatment.…”

Antibiotic Susceptibility of Probiotic Bacteria

“…Previously, in vivo transfer between LAB has only been shown in the gastrointestinal tracts of gnotobiotic rats (Jacobsen et al, 2007) and mice (McConnell et al, 1991;Morelli et al, 1988). The transfer frequencies have been observed to increase when the animals have received the antibiotic in question at subtherapeutic levels (Igimi et al, 1996;Licht et al, 2003;Salyers & Shoemaker 1996) in their drinking water or feed, suggesting that increasing the antibiotic pressure can amplify the transfer of antibiotic resistance between bacterial species. All of these above studies indicate that antibiotic resistant factors may be transferred from food related bacterium species (LAB) to other, potentially pathogenic species.…”