Validation of an antimicrobial susceptibility testing protocol for Brachyspira hyodysenteriae and Brachyspira pilosicoli in an international ring trial.

Brachyspira hyodysenteriae and Brachyspira pilosicoli cause economically important enteric disease in pigs. Treatment of these infections often includes antimicrobial administration, which can be most effective when therapeutic options are informed by antimicrobial susceptibility testing data. Here we describe a method for broth dilution antimicrobial susceptibility testing of these bacteria, both of which are difficult to culture in vitro. The protocol was evaluated for its fitness for use in an inter-laboratory ring trial involving eight laboratories from seven countries, and employing eleven test strains (5 Brachyspira hyodysenteriae including the type strain B78T and 6 Brachyspira pilosicoli) and six antibiotics. Overall intra- and inter-laboratory reproducibility of this method was very good (>90 % MICs at mode +/- 1 log2). Whole genome sequencing revealed good correspondence between reduced susceptibility and the presence of previously defined antimicrobial resistance determinants. Interestingly, lnu(C) was identified in B. pilosicoli isolates with elevated MICs of lincomycin, whilst tva(B) was associated with elevated MICs of pleuromutilins in this species. We designated two new control strains with MICs lying within currently tested ranges, including for the pleuromutilins, in contrast to the control strain B. hyodysenteriae B78T. These were deposited at the DSMZ-German Collection of Microorganisms and Cell Cultures GmbH. The validation of a standard protocol and identification of new control strains facilitates comparisons between studies, establishment of robust interpretative criteria, and ultimately contributes to rational antimicrobial use when treating infected livestock.

Impact of ceftiofur injection on gut microbiota and Escherichia coli resistance in pigs.

Resistance to extended-spectrum cephalosporins (ESCs) is an important health concern. Here, we studied the impact of the administration of a long-acting form of ceftiofur on the pig gut microbiota and ESC resistance in Escherichia coli. Pigs were orally inoculated with an ESC-resistant E. coli M63 strain harboring a conjugative plasmid carrying a gene conferring resistance, bla CTX-M-1. On the same day, they were given or not a unique injection of ceftiofur. Fecal microbiota were studied using quantitative PCR analysis of the main bacterial groups and quantification of short-chain fatty acids. E. coli and ESC-resistant E. coli were determined by culture methods, and the ESC-resistant E. coli isolates were characterized. The copies of the bla CTX-M-1 gene were quantified. After ceftiofur injection, the main change in gut microbiota was the significant but transitory decrease in the E. coli population. Acetate and butyrate levels were significantly lower in the treated group. In all inoculated groups, E. coli M63 persisted in most pigs, and the bla CTX-M-1 gene was transferred to other E. coli. Culture and PCR results showed that the ceftiofur-treated group shed significantly more resistant strains 1 and 3 days after ESC injection. Thereafter, on most dates, there were no differences between the groups, but notably, one pig in the nontreated group regularly excreted very high numbers of ESC-resistant E. coli, probably leading to a higher contamination level in its pen. In conclusion, the use of ESCs, and also the presence of high-shedding animals, are important features in the spread of ESC resistance.

Bacterial pathogens associated with lung lesions in slaughter pigs from 125 herds.

Relationships between macroscopic lesions and Polymerase Chain Reaction (PCR) detection of Mycoplasma hyopneumoniae (Mhp), Pasteurella multocida (Pm), Actinobacillus pleuropneumoniae (App), Haemophilus parasuis (Hps) and Streptococcus suis (Ssuis) of the lungs of 3731 slaughter pigs from 125 herds were assessed in France. Pneumonia and pleuritis were the most frequent lesions (69.3% and 15% of the lungs, respectively). Mhp, Pm, App, Ssuis and Hps were detected in 69.3%, 36.9%, 20.7%, 6.4% and 0.99% of the lungs, respectively. Mhp and Pm were associated with pneumonia at both the pig and herd levels. Pleuritis was not associated with any pathogen at the pig level, but was associated with a high percentage of pigs PCR-positive for App at the herd level. Measures focused on control of Mhp, Pm and App should significantly reduce the occurrence of both pneumonia and pleuritis.

Longitudinal study of respiratory infection patterns of breeding sows in five farrow-to-finish herds.

A longitudinal study was carried out in five French farrow-to-finish herds differently affected by respiratory diseases to describe the carrying and infection patterns of batches of sows to various respiratory pathogens during gestation and lactation. An entire batch of sows was followed during two successive reproduction cycles. Nasal, tonsillar and oro-pharyngeal swabs and blood samples were taken from each sow 9 and 4 weeks before farrowing and 1 and 4 weeks after farrowing. Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, Pasteurella multocida, Haemophilus parasuis and Streptococcus suis were detected from swab samples using PCR assays. Blood samples were tested for antibodies against M. hyopneumoniae, A. pleuropneumoniae serotypes 1-9-11 and 2, Porcine Circovirus type-2 (PCV-2) and Porcine Reproductive and Respiratory Syndrome virus (PRRSV) by ELISA tests. Antibodies against H(1)N(1), H(1)N(2) and H(3)N(2) Swine Influenza Viruses (SIV) of European lineages were tested by hemagglutination inhibition assay. The results indicated that S. suis is widespread among sows (67.1% of PCR-positive sows). A. pleuropneumoniae, P. multocida, and H. parasuis were detected by PCR in 30.9%, 24.6% and 23.4% of the sows, respectively. Antibodies against M. hyopneumoniae were recovered from more than 55% of the sows in all herds whereas the micro-organism was detected in 2.4% of the sows. Although PCV-2 and SIV infections were highly prevalent, the PRRSV infection patterns ranged from no infection in farms mildly affected by respiratory diseases to active circulation in more severely affected herds. The sow population thus constitutes a reservoir for a continuous circulation of respiratory pathogens and needs to be properly considered in control strategies.