A. Martel

Intestinal mucus protects Campylobacter jejuni in the ceca of colonized broiler chickens against the bactericidal effects of medium-chain fatty acids

Campylobacter jejuni is the most common cause of bacterial-mediated diarrheal disease worldwide. Because poultry and poultry products are a major source of C. jejuni infections in humans, efforts should be taken to develop strategies to decrease Campylobacter shedding during primary production. For this purpose, the efficacy of medium-chain fatty acids (MCFA) as feed additives to control C. jejuni colonization in broiler chickens was analyzed. First, the antimicrobial activity of the MCFA caproic, caprylic, and capric acid on C. jejuni was evaluated in vitro. Minimal inhibitory concentrations were 0.25 mM for caproic and 0.5 mM for caprylic and capric acids at pH 6.0 and 4 mM for all 3 compounds at pH 7.5. Time-kill curves revealed strong bactericidal properties of the tested compounds toward C. jejuni at pH 6.0. Concentrations as low as 4 mM caprylic and capric acids and 16 mM caproic acid killed all bacteria within 24 h. Capric acid had the highest activity, with concentrations of 4 mM killing all bacteria within the hour. Together these data show a profound bactericidal, dose-dependent activity of the tested MCFA toward C. jejuni in vitro. For this reason, the effect of these 3 MCFA on C. jejuni was evaluated in vivo. The addition of any of the acids to the feed, from 3 d before euthanization, was not capable of reducing cecal Campylobacter colonization in 27-d-old broilers experimentally infected with C. jejuni at 15 d of age. Using a cecal loop model, sodium caprate was not able to reduce cecal Campylobacter counts. When time-kill curves were conducted in the presence of chick intestinal mucus, capric acid was less active against C. jejuni. At 4 mM, all bacteria were killed only after 24 h. Thus, despite the marked bactericidal effect of MCFA in vitro, supplementing these acids to the feed does not reduce cecal Campylobacter colonization in broiler chickens under the applied test conditions, probably due to the protective effect of the mucus layer.

Molecular analysis of human, porcine, and poultry Enterococcus faecium isolates and their erm(B) genes.

ABSTRACT Fifty-nine erm(B)-positive Enterococcus faecium strains isolated from pigs, broilers, and humans were typed using multilocus sequence typing (MLST), and the coding sequence of the erm(B) gene was determined. Identical erm(B) gene sequences were detected in genetically unrelated isolates. Furthermore, genetically indistinguishable strains were found to contain different erm(B) alleles. This may suggest that horizontal exchange of the erm(B) gene between animal and human E. faecium strains or the existence of a common reservoir of erm(B) genes might be more important than direct transmission of resistant strains.

Macrolide and Lincosamide Resistance in the Gram-Positive Nasal and Tonsillar Flora of Pigs

Macrolide and lincosamide resistance phenotypes and the presence of the erm(A), erm(B), erm(C), and mef(A) genes were determined in 344 bacterial strains belonging to 34 species and nine genera, isolated from the tonsils and nasal cavities of 2-week- and 6-week-old piglets, derived from four different farms. These piglets had never before been treated with macrolides or lincosamides. Macrolide and lincosamide resistance was most frequently present in Streptococcus and Enterococcus strains, of which over two-thirds were resistant. These genera were followed in decreasing order of resistance frequency by Lactobacillus, Rothia, Staphylococcus, Arcanobacterium, Actinomyces, Pediococcus strains. Only five infrequently occurring species did not show resistance. This high frequency of resistance in nontreated piglets indicates that resistant strains circulate in the herds. In streptococci, enterococci, and Lactobacillus strains, resistance was most often encoded by the erm(B) gene and in staphylococci by erm(A) or erm(C). The erm(B) gene was sporadically detected in other bacterial genera (Actinomyces, Rothia, Aerococcus, Pediococcus). The sequence of the erm(B) gene of 29 strains of 11 pigs originating from the four different farms was determined. This sequence was identical in 12 strains and only differed by 1-6 nucleotides in the other strains, indicating that exchanges of resistance genes might occur between bacterial species and genera belonging to the nasal or tonsillar flora of piglets.

Endothelial Binding of Beta Toxin to Small Intestinal Mucosal Endothelial Cells in Early Stages of Experimentally Induced Clostridium Perfringens Type C Enteritis in Pigs

Beta toxin (CPB) is known to be an essential virulence factor in the development of lesions of Clostridium perfringens type C enteritis in different animal species. Its target cells and exact mechanism of toxicity have not yet been clearly defined. Here, we evaluate the suitability of a neonatal piglet jejunal loop model to investigate early lesions of C. perfringens type C enteritis. Immunohistochemically, CPB was detected at microvascular endothelial cells in intestinal villi during early and advanced stages of lesions induced by C. perfringens type C. This was first associated with capillary dilatation and subsequently with widespread hemorrhage in affected intestinal segments. CPB was, however, not demonstrated on intestinal epithelial cells. This indicates a tropism of CPB toward endothelial cells and suggests that CPB-induced endothelial damage plays an important role in the early stages of C. perfringens type C enteritis in pigs.

Salmonella Enteritidis universal stress protein (usp) gene expression is stimulated by egg white and supports oviduct colonization and egg contamination in laying hens

Salmonella enterica subspecies enterica serovar Enteritidis has caused a worldwide egg-associated pandemic since the mid 1980s. The exact mechanisms causing this egg tropism are still largely unknown, and only a few Salmonella genes have been implicated in the interaction with the oviduct or eggs. A in vivo expression technology screening performed previously, identified the uspA and uspB genes as being highly expressed in the chicken oviduct and in eggs. Here, we demonstrate that uspA and uspB gene expression is indeed induced after contact with egg white. Intra-oviduct inoculation of Salmonella Enteritidis uspB and uspBA mutant strains showed that the mutants had a decreased ability to colonize the magnum and isthmus of the oviduct, the organs that produce the egg white and eggshell membranes, respectively, at 7 days post-inoculation. Intravenous challenge showed that a Salmonella Enteritidis uspBA mutant strain had a decreased ability to contaminate eggs. Analogous to the function of universal stress proteins A and B in other bacterial species, we hypothesize that the Salmonella uspA and uspB genes are involved in long term persistence of Salmonella Enteritidis in harmful environments, such as in the oviduct and eggs, by conferring resistance against compounds that damage the bacterial cell membrane and DNA.

Microarray-Based Detection of Salmonella enterica Serovar Enteritidis Genes Involved in Chicken Reproductive Tract Colonization

ABSTRACT Salmonella enterica serovar Enteritidis has developed the potential to contaminate table eggs internally, by colonization of the chicken reproductive tract and internalization in the forming egg. The serotype Enteritidis has developed mechanisms to colonize the chicken oviduct more successfully than other serotypes. Until now, the strategies exploited by Salmonella Enteritidis to do so have remained largely unknown. For that reason, a microarray-based transposon library screen was used to identify genes that are essential for the persistence of Salmonella Enteritidis inside primary chicken oviduct gland cells in vitro and inside the reproductive tract in vivo. A total of 81 genes with a potential role in persistence in both the oviduct cells and the oviduct tissue were identified. Major groups of importance include the Salmonella pathogenicity islands 1 and 2, genes involved in stress responses, cell wall, and lipopolysaccharide structure, and the region-of-difference genomic islands 9, 21, and 40.