Monitoring of AMR (Antimicrobial Resistance) in a large pig production system in Italy

Extended-spectrum penicillins have a similar spectrum of activity to 2nd and 3rd generation cephalosporins and they include aminopenicillins such as amoxicillin and ampicillin and amoxicillin in combination with clavulanic acid. Bacterial resistance to extended-spectrum penicillins has evolved rapidly in recent years specially in Enterobacteriaceae because these bacteria could carry beta-lactamases capable of hydrolyzing important beta-lactam antimicrobials (EMA, 2015). It has also been assessed by the EMA in 2015 that the veterinary use of aminopenicillins might have the ability to facilitate the spread of antimicrobial resistance similarly to 3rd and 4th-generation cephalosporins.

In order to monitor a possible change of sensitivity in time of amoxicillin, ampicillin, amoxicillin-clavulanic acid and ceftiofur (3rd generation cephalosporin) in a large production system in Italy during years 2011-2015, we gathered data from the automatic Disc Diffusion susceptibility tests micro-reader SIRSCAN Micro TM (I2A, France) database. These data were obtained from swine bacterial strains isolated from field clinical cases and namely enteric pathogens belonging to the Enterobacteriaceae family (haemolytic Escherichia coli – HEC), respiratory pathogens (Pasteurella multocida – PM) and Streptococcus suis (SS). AMR was determined using the Kirby-Bauer disk diffusion technique on Mueller-Hinton agar (OXOID, UK) following CLSI guidelines.

From 2011 to 2015, 1714 bacterial strains were tested for AMR (731 HEC, 226 PM and 757 SS). HEC maintained a constant and high level of susceptibility to ceftiofur ranging from 73,46% in 2015 to 86,23% in 2013 with an average of the 78.06%. In contrast, the lack of efficacy for amoxicillin and ampicillin was documented by a lower number of susceptible strains (9,50% and 9,44 respectively). Amoxicillin and clavulanic acid susceptibility was also less than ceftiofur and ranged from 34,56% in 2013 but increasing up to 54,79% in 2015. PM and SS showed more than 90% of susceptibility to all antimicrobials tested but ceftiofur that, for the latter, reached an average of 75,57% in the 5-year period.

In spite of a rather common usage of aminopenicillins and their combination with beta-lactamase inhibitors, in the 5-year period 2011-2015, SS and PM are still highly susceptible to these antibiotics and to 3rd generation cephalosporins as ceftiofur. On the other hand, in the same period of time, HEC, causative agent of the swine post-weaning diarrhea, reveals resistance to these first substances but still maintaining a high level of susceptibility to ceftiofur without an increase of level of resistance.

Disclosure of Interest: None Declared.