The use of antibiotics in pig farms may endanger public health? Study of the emergence of resistance.

One of the negative consequences of the extensive use of antimicrobials in human and veterinary medicine is the appearance of bacteria resistant to antimicrobials. In those cases of severe infections, or when the patient suffers immune depression, the presence of antimicrobial resistant bacteria can increase the morbidity or mortality of the patient. For this reason, the World Health Organization (WHO) has classified some antimicrobial drugs as critically important in human medicine, since they are the last option to treat some infectious diseases. Third generation cephalosporin and macrolides are some of these antimicrobials.
Additionally, the majority of the antimicrobials used in veterinary medicine are structurally similar to those used to treat human infections. Therefore, the emergence of antimicrobial resistant bacteria in livestock may pose a risk to human health if resistant bacteria reaches the consumer via the food chain.
In Spain, betalactam antimicrobials (penicillins and cephalosporins) and macrolides (tulathromycin and tildipirosin) are the most commonly prescribed drugs during the suckling period. For this reason the aim of this study was:

  1. To evaluate if treatment with ceftiofur is a risk factor for the emergence of cephalosporin resistant Escherichia coli (CR E. coli) during the nursing period in conventional pig farms.
  2. To assess if these farms are a reservoir of resistant bacteria that can persist and enter the food chain.

The study was conducted at eight conventional pig farms; four for each treatment with ceftiofur or tulathromycin. At each farm, seven-day-old piglets were divided into two groups: a control group and a treatment group. Faecal samples were collected on day 0 and on days 2, 7 and 180 post-treatment for microbiological studies. Sows were also sampled on day 0. Pigs were fed using a standard nutritional program set by the companies, which included use of different prophylactic antimicrobials during the nursery period (amoxicillin, apramycin, tiamulin, oxytetracycline, and finally in one of the farms colistin sulfate). This treatment commenced after the administration of ceftiofur or tulathromycin (from 21 to 70 days of age).

On five farms, 7-day-old piglets excreted CR E. coli before treatment associated with the presence of CR E. coli in sows. It appears that these bacteria were circulating in the farms prior to farrowing. Those farms where the sows were negative, offspring were also negative, and they remained like that the whole production cycle, independently of the treatment. Accordingly, intervention strategies aiming at improving biosecurity, cleaning and disinfection will most likely reduce the circulation of these bacteria in the farm.

placa cultiu

Treatment with ceftiofur resulted in a transitory increase of CR E. coli after 48 h. Out of the eight farms, five were positive for CR E. coli, however, the occurrence of CR E. coli positive animals decreased with the age of the animals. In three farms, pigs departed to the abattoir excreting CR E. coli representing a public health concern. Although a reduction in counts of resistant bacteria is expected during meat processing, some processes at the slaughterhouse may contribute to contamination of meat with resistant bacteria or to the cross-contamination of clean animals. As a consequence, CR E. coli contaminated meat may reach the consumer. Strategies to control CR E. coli in the sows may prevent colonization of piglets by resistant bacteria at the beginning of the life cycle, which appears to be the critical point in time to reduce occurrence at slaughter. Any effort contributing to reduction of the load of antimicrobial resistant bacteria in primary production will have an impact in the final product, and therefore in protecting human health.

This study was funded by a national research grant form the Spanish government MINECO (AGL2011-28836)  and has been recently published in the scientific journal The Veterinary Journal:

Shedding of cephalosporin resistant Escherichia coli in pigs from conventional farms after early treatment with antimicrobials Karla Cameron-Veas, Miguel A. Moreno, c, Lorenzo Fraile, Lourdes Migura-Garcia doi:10.1016/j.tvjl.2016.02.017

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