TDK conference 2019

One of the most prevalent foodborne zoonotic disease worldwide is salmonellosis. In humans it most frequently causes acute gastroenteritis and bacteraemia, in animals more often chronic asymptomatic carriage is present. In the European Union, due to mandatory Salmonella control strategies in poultry flocks over the last decade, member states have succeeded in significantly reducing the number of Salmonella carriers at poultry farms. Some of the European countries (e.g. Sweden, Norway, Finland, Denmark) are already applying control programs also in swine herds, but in the EU, there is currently no regulation for mandatory control programs to find Salmonella carriers. As a result, there is not enough information about the presence of Salmonella spp. in pigs, neither of the chance of meat becoming infected during the slaughtering process.

In this study, our aim was to explore antimicrobial resistance in bacteria belonging to the Salmonella genus isolated from asymptomatic carrier pigs. A total of 100 pigs were sampled during slaughtering in an abattoir at the southern part of Hungary. We collected ileocaecal lymph nodes and samples with cotton swabs from the intestinal mucosa of the ileum. Salmonella was identified in 14 lymp nodes and in 33 intestinal samples (40% of the pigs). Beside these samples, seven additional Salmonella isolates collected from clinical cases were investigated.

We performed in vitro antibiotic susceptibility testing with the microdilution method in 96-well microplates with five antibiotics: enrofloxacin, ceftiofur, colistin, gentamicin and amoxicillin. For the first four antibiotics, all of the isolates were susceptible, while towards amoxicillin from the total of 54 tested samples 47 isolates showed 64 µg/ml or higher minimal inhibitory concentration (MIC-) values. According to CLSI (Clinical and Laboratory Standards Institute) breakpoints, bacteria showing 16 µg/ml or higher MICs are considered resistant towards amoxicillin. In addition, in vivo it is practically impossible to attain such high concentrations in the intestinal tract and liver of pigs, so thus our results basically show that these bacteria were resistant to amoxicillin.