Pathogenicity Islands and Host Adaptation of Salmonella Serovars

Embracing Diversity: Differences in Virulence Mechanisms, Disease Severity, and Host Adaptations Contribute to the Success of Nontyphoidal Salmonella as a Foodborne Pathogen

Not all Salmonella enterica serovars cause the same disease. S. enterica represents an incredibly diverse species comprising >2,600 unique serovars. While some S. enterica serovars are host-restricted, others infect a wide range of hosts. The diseases that nontyphoidal Salmonella (NTS) serovars cause vary considerably, with some serovars being significantly more likely to cause invasive disease in humans than others. Furthermore, while genomic analyses have advanced our understanding of the genetic diversity of these serovars, they have not been able to fully account for the observed clinical differences. One overarching challenge is that much of what is known about Salmonella's general biology and virulence strategies is concluded from studies examining a select few serovars, especially serovar Typhimurium. As targeted control strategies have been implemented to control select serovars, an increasing number of foodborne outbreaks involving serovars that are less frequently associated with human clinical illness are being detected. Harnessing what is known about the diversity of NTS serovars represents an important factor in achieving the ultimate goal of reducing salmonellosis-associated morbidity and mortality worldwide. In this review we summarize the current understanding of the differences and similarities among NTS serovars, highlighting the virulence mechanisms, genetic differences, and sources that characterize S. enterica diversity and contribute to its success as a foodborne pathogen.

The dynamics of gut-associated microbial communities during inflammation

Our intestine is host to a large microbial community (microbiota) that educates the immune system and confers niche protection. Profiling of the gut-associated microbial community reveals a dominance of obligate anaerobic bacteria in healthy individuals. However, intestinal inflammation is associated with a disturbance of the microbiota-known as dysbiosis-that often includes an increased prevalence of facultative anaerobic bacteria. This group contains potentially harmful bacterial species, the bloom of which can further exacerbate inflammation. Here, we review the mechanisms that generate changes in the microbial community structure during inflammation. One emerging concept is that electron acceptors generated as by-products of the host inflammatory response feed facultative anaerobic bacteria selectively, thereby increasing their prevalence within the community. This new paradigm has broad implications for understanding dysbiosis during gut inflammation and identifies potential targets for intervention strategies.

Molecular characterisation of Salmonella strains by an oligonucleotide multiprobe microarray

A DNA microarray has been developed for the simultaneous characterisation and typing of Salmonella enterica subsp. enterica isolates. One-hundred and nine 35-40 mer oligonucleotides probes detect flagellar and somatic antigen encoding genes (serogroup or serotype specific), important virulence genes located within or outside the pathogenicity islands, phage-associated genes and antibiotic resistance determinants. The probes were printed on glass slides and whole genomic Cy5-labelled Salmonella DNA was hybridised to the substrate. A set of 19 different Salmonella strains and one Escherichia coli strain has been selected as positive and negative controls for each probe. The validity of the results is confirmed by gene-specific PCRs or phenotypic methods (serotyping, MIC determination for various antimicrobial agents). Of 2071 data points generated, an agreement of 97.4% has been obtained between microarray and PCR/phenotypic results. Twenty-six data points (1.3%) were classified as uncertain and, similarly, 1.3% showed a discordant result. The microarray described here is a new tool to study the epidemiology of Salmonella strains on the genotypic level and might become a powerful method in risk assessment studies.