The effect of chlortetracycline treatment and its subsequent withdrawal on multi-resistant Salmonella enterica serovar Typhimurium DT104 and commensal Escherichia coli in the pig

Abstract

Aims:To investigate the effect of a therapeutic and sub-therapeutic chlortetracycline treatment on tetracyclineresistant Salmonella enterica serovar Typhimurium DT104 and on the commensal Escherichia coli in pig. Methods and Results: Salmonella Typhimurium DT104 was orally administered in all pigs prior to antibiotic treatment, and monitored with the native E. coli. Higher numbers of S. Typhimurium DT104 were shed from treated pigs than untreated pigs. This lasted up to 6 weeks post-treatment in the high-dose group. In this group, there was a 30% increase in E. coli with a chlortetracycline minimal inhibitory concentration (MIC) > 16 mg l )1 and a 10% increase in E. coli with an MIC > 50 mg l )1 during and 2 weeks post-treatment. This effect was less-pronounced in the low-dose group. PCR identified the predominant tetracycline resistance genes in the E. coli as tetA, tetB and tetC. The concentration of chlortetracycline in the pig faeces was measured by HPLC and levels reached 80 lg g )1 faeces during treatment. Conclusion: Chlortetracycline treatment increases the proportion of resistant enteric bacteria beyond the current withdrawal time. Significance and Impact of the Study: Treated pigs are more likely to enter abattoirs with higher levels of resistant bacteria than untreated pigs promoting the risk of these moving up the food chain and infecting man.

Effect of Tetracycline Dose and Treatment Mode on Selection of Resistant Coliform Bacteria in Nursery Pigs

“…In accordance with the findings of a previous study (14), we observed a significantly higher number of tetracycline-resistant E. coli bacteria right after treatment in the group receiving the highest dose, but in contrast to the findings described in the previous publication, the concentration and proportion returned to the starting levels within 3 to 4 weeks. The proportions of resistant coliforms at T 4 , corresponding to the time shortly before slaughter and, thus, the time when the pigs entered the food chain, was significantly below the level before treatment.…”

“…A possible reason for the minimal selective effect of dose in our study may have been the very high starting concentrations of resistant bacteria. While this is representative of the proportions of tetracycline-resistant commensal E. coli bacteria in pigs in Denmark (25), it is much higher than the 1 to 10% chlortetracycline-resistant E. coli strains detected by Delsol et al (14) prior to their experiment. Our results may thus not be representative of those for farms with an initial lower concentration of tetracycline-resistant bacteria.…”

“…Apart from the treatment regimen (flock treatment versus individual treatment), the selection of antibiotic-resistant bacteria is influenced by factors such as the treatment dose (14,15), the number of animals housed together (16), and other management factors (17)(18)(19)(20)(21). Among these factors, mathematical modeling suggests that dose may play a particularly important role in the selection of resistant coliform bacteria following tetracycline treatment (22).…”

Impact of Three Ampicillin Dosage Regimens on Selection of Ampicillin Resistance in Enterobacteriaceae and Excretion of bla TEM Genes in Swine Feces

“…Tenfold serial dilutions of the filtrate were prepared, and 100-l samples of the dilutions were spread on MacConkey plates (AEB 151602; AES, Ker Lann, France) containing 0 and 16 g/ml of ampicillin. MacConkey agar is classically used for selective growth of Enterobacteriaceae (7,8,11,30). Enterobacteriaceae growing in the presence of 16 g/ml of ampicillin were classified as resistant.…”

Comparison of pulsed-field gel electrophoresis patterns of antimicrobial-resistant Escherichia coli and enterococci isolates from the feces of livestock and livestock farmers in Japan

“…bacteria from intestinal microflora of food animals will contaminate carcasses at slaughter in the same way as zoonotic bacteria (Delsol et al, 2003). Therefore, the emergence of resistant bacteria in food animals has created public health concern because of the possibility of transmission via the food chain from animals to humans (van den Bogaard and Stobberingh, 1999;Wegener, 2003).…”