Improvement and validation of RAPD in combination with PFGE analysis of Salmonella enterica ssp. enterica serovar Senftenberg strains isolated from feed mills

Persistence of microbiological hazards in food and feed production and processing environments

Listeria monocytogenes (in the meat, fish and seafood, dairy and fruit and vegetable sectors), Salmonella enterica (in the feed, meat, egg and low moisture food sectors) and Cronobacter sakazakii (in the low moisture food sector) were identified as the bacterial food safety hazards most relevant to public health that are associated with persistence in the food and feed processing environment (FFPE). There is a wide range of subtypes of these hazards involved in persistence in the FFPE. While some specific subtypes are more commonly reported as persistent, it is currently not possible to identify universal markers (i.e. genetic determinants) for this trait. Common risk factors for persistence in the FFPE are inadequate zoning and hygiene barriers; lack of hygienic design of equipment and machines; and inadequate cleaning and disinfection. A well-designed environmental sampling and testing programme is the most effective strategy to identify contamination sources and detect potentially persistent hazards. The establishment of hygienic barriers and measures within the food safety management system, during implementation of hazard analysis and critical control points, is key to prevent and/or control bacterial persistence in the FFPE. Once persistence is suspected in a plant, a 'seek-and-destroy' approach is frequently recommended, including intensified monitoring, the introduction of control measures and the continuation of the intensified monitoring. Successful actions triggered by persistence of L. monocytogenes are described, as well as interventions with direct bactericidal activity. These interventions could be efficient if properly validated, correctly applied and verified under industrial conditions. Perspectives are provided for performing a risk assessment for relevant combinations of hazard and food sector to assess the relative public health risk that can be associated with persistence, based on bottom-up and top-down approaches. Knowledge gaps related to bacterial food safety hazards associated with persistence in the FFPE and priorities for future research are provided.

Characterization and Evaluation of a Salmonella enterica Serotype Senftenberg Mutant Created by Deletion of Virulence-Related Genes for Use as a Live Attenuated Vaccine

Natural infections of chickens with Salmonella enterica subsp. enterica serovar Senftenberg (S. Senftenberg) are characterized by low-level intestinal invasiveness and insignificant production of antibodies. In this study, we investigated the potential effects of lon and cpxR gene deletions on the invasiveness of S Senftenberg into the intestinal epithelium of chickens and its ability to induce an immune response, conferring protection against S Senftenberg infection. With the allelic exchange method, we developed JOL1596 (Δlon), JOL1571 (ΔcpxR), and JOL1587 (Δlon ΔcpxR) deletion mutants from wild-type S Senftenberg. Deletion of the lon gene from S Senftenberg produced increased frequency of elongated cells, with significantly greater amounts of exopolysaccharide (EPS) than in the cpxR-deleted strain and the wild-type strain. The in vivo intestinal loop invasion assay showed a significant increase in epithelial invasiveness for JOL1596 (Δlon) and JOL1587 (Δlon ΔcpxR), compared to JOL1571 (ΔcpxR) and the wild-type strain. Furthermore, the S Senftenberg wild-type and mutant strains were internalized at high levels inside activated abdominal macrophages from chicken. The in vivo inoculation of JOL1587 (Δlon ΔcpxR) into chickens led to colonization of the liver, spleen, and cecum for a short time. Chickens inoculated with JOL1587 (Δlon ΔcpxR) showed significant increases in humoral, mucosal, and cellular immune responses specific to S Senftenberg antigens. Postchallenge, compared to the control group, the JOL1587 (Δlon ΔcpxR)-inoculated chickens showed not only lower persistence but also faster clearance of wild-type S Senftenberg from the cecum. We conclude that the increased intestinal invasiveness and colonization of internal organs exhibited by JOL1587 (Δlon ΔcpxR) led to the establishment of immunogenicity and conferred protective efficacy against S Senftenberg infections in chickens.

The application of genetics methods to differentiation of three Lactobacillus species of human origin

In recent decades, the interest in probiotics as diet supplements or drugs has increased. In order to determine a specific bacterial isolate to be probiotic, it is necessary to describe precisely its probiotic characteristics and taxonomic properties, including the strain level. Most of the well-known genotyping methods were designed for the commonly-found pathogenic bacteria. The objective of this study is to undertake an attempt at standardization of FISH, RAPD and PFGE methods to genotype and identify the bacteria belonging to Lactobacillus fermentum, L. gasseri and L. plantarum species. The FISH probes have been designed and tested for Lactobacillus fermentum, L. gasseri and L. plantarum species and an endeavor has been made at standardization of RAPD and PFGE methods for these bacterial species. Moreover, the MLST method was applied to differentiate Lactobacillus plantarum strains. L. plantarum isolated from humans could not be genetically diversified with the use of RAPD, PFGE or MLST methods; only the strains originating from plants have displayed diversification among themselves and have been different from the strains of human origin.

Persistence of Salmonella Senftenberg in poultry production environments and investigation of its resistance to desiccation

Most Salmonella serovars, including Salmonella enterica subsp. enterica serovar Senftenberg (S. Senftenberg), are tolerant to desiccation and able to colonize and persist in feed mills. In addition, they may survive cleaning and disinfection procedures used on poultry farms. The present study was conducted to investigate the survival of S. Senftenberg in broiler parent stock farms and broiler farms. The isolates from one of the parent stock farms investigated only differed by a single band in fluorescent amplified fragment-length polymorphism analysis and had identical pulsed-field gel electrophoresis profiles, indicating that a S. Senftenberg clone had persisted for more than 2 years, despite cleaning, disinfection, desiccation and depopulation, and was subsequently able to infect Salmonella-free layers. Isolates from the same house on a different broiler parent stock farm were found to be identical by amplified fragment-length polymorphism analysis and pulsed-field gel electrophoresis although the farm tested negative for Salmonella 55 times over a period of 18 months between the two positive samplings. An assay was developed to investigate the survival of 34 S. Senftenberg isolates during desiccation at approximately 38% relative humidity. On average, the viability of S. Senftenberg isolates decreased by 1000-fold over 35 days. The persistent clones were no more resistant to desiccation than the other isolates investigated. However, S. Senftenberg was more resistant to desiccation than an isolate of Pantoea agglomerans commonly found on poultry feed-processing lines. This study demonstrates the risk of persistence of feed-associated serovars such as S. Senftenberg.