Deletions of ttrA and pduA genes in Salmonella enterica affect survival within chicken-derived HD-11 macrophages.

In mammals, enteric salmonellas can use tetrathionate (ttr), formed as a by-product from the inflammatory process in the intestine, as electron acceptor in anaerobic respiration, and it can fuel its energy metabolism by degrading the microbial fermentation product 1,2-propanediol. However, recent studies have shown that this mechanism is not important for Salmonella infection in the intestine of poultry, while it prolongs the persistence of Salmonella at systemic sites in this species. In the current study, we show that ΔttrApduA strains of Salmonella enterica have lower net survival within chicken-derived HD-11 macrophages, as CFU was only 2.3% (S. Enteritidis ΔttrApduA), 2.3% (S. Heidelberg ΔttrApduA), and 3.0% (S. Typhimurium ΔttrApduA) compared to wild-type strains after 24 h inside HD-11 macrophage cells. The difference was not related to increased lysis of macrophages, and deletion of ttrA and pduA did not impair the ability of the strains to grow anaerobically. Further studies are indicated to determine the reason why Salmonella ΔttrApduA strains survive less well inside macrophage cell lines.

Competitive exclusion products as an antimicrobial alternative to control Salmonella Heidelberg in broilers.

Intestinal infections caused by non-typhoidal Salmonella spp., along with antimicrobial resistance spread are a major food safety concern worldwide. Here, we evaluate the potential of competitive exclusion products developed by anaerobic or aerobic conditions to control systemic infection, cecal colonization, fecal excretion, and improve the intestinal health in broilers challenged by Salmonella Heidelberg (SH). A total of 105 day-old chickens were randomly distributed into three experimental groups: A (untreated control), B (treated with anaerobic culture), and C (treated with aerobic culture). During 21 days, morphometric parameters of the small intestine were analyzed using microscopy, fecal excretions by cloacal swabs, systemic infection, and cecal colonization by colony-forming unit counts (CFU/g). The results indicated the lowest number of positive swabs (45.33%) recovered from Group C, followed by Group B (71.8%) and Group A (85.33%). The bacterial enumeration revealed the lowest amounts in Group C at the necropsy realized in 5-, 7-, and 14-days post-infection (DPI) (P = 0.0010, P = 0.0048, and P = 0.0094, respectively). Statistical differences between intestinal morphometrics were observed in the Group C at 21 DPI. Our results suggest that the product developed under aerobic conditions can improve intestinal health, protecting birds against SH.

In vitro conjugation of IncB/O-plasmid: Minimum inhibitory concentration of ß-lactams increases 16-fold in Salmonella enterica compared with Escherichia coli.

The use of antimicrobials in poultry leaves residues in the litter, favoring the emergence of antimicrobial-resistant pathogens and making it a source of contamination. An in vitro 4 × 4 factorial trial was performed to investigate the influence of four treatments, consisting of antimicrobial sub-concentrations, on the transference of IncB/O-plasmid through conjugation in four groups. Each group was composed of one plasmid donor bacterium (Escherichia coli H2332) and a recipient bacterium (Escherichia coli J62 or Salmonella enterica serovars, Enteritidis, Typhimurium, or Heidelberg). Our results showed a little decrease in the conjugation frequency in almost all treatments between the two bacterial species, which varied according to each strain. The MIC test revealed an increase of up to 4096-fold in resistance to beta-lactams in Salmonella serovars after plasmid acquisition. This finding suggests that some genetic apparatus may be involved in increased antimicrobial resistance in Salmonella serovars after the acquisition of primary resistance determinants.

Low temperatures do not impair the bacterial plasmid conjugation on poultry meat.

Conjugation plays an important role in the dissemination of antimicrobial resistance genes. Besides, this process is influenced by many biotic and abiotic factors, especially temperature. This study aimed to investigate the effect of different conditions of temperature and storage (time and recipient) of poultry meat, intended for the final consumer, affect the plasmid transfer between pathogenic (harboring the IncB/O-plasmid) and non-pathogenic Escherichia coli organisms. The determination of minimal inhibitory concentrations (MIC) of ampicillin, cephalexin, cefotaxime, and ceftazidime was performed before and after the conjugation assay. It was possible to recover transconjugants in the poultry meat at all the treatments, also these bacteria showed a significant increase of the MIC for all antimicrobials tested. Our results show that a non-pathogenic E. coli can acquire an IncB/O-plasmid through a conjugation process in poultry meat, even stored at low temperatures. Once acquired, the resistance genes endanger public health especially when it is about critically and highly important antimicrobials to human medicine.