The combination of virulence gene and antimicrobial resistance gene typing using DNA arrays is a recently developed genomics-based approach to bacterial molecular epidemiology. We have now applied this technology to 523 Salmonella enterica subsp. enterica strains collected from various host sources and public health and veterinary institutes across nine European countries. The strain set included the five predominant Salmonella serovars isolated in Europe (Enteritidis, Typhimurium, Infantis, Virchow, and Hadar). Initially, these strains were screened for 10 potential virulence factors (avrA, ssaQ, mgtC, siiD, sopB, gipA, sodC1, sopE1, spvC, and bcfC) by polymerase chain reaction. The results indicated that only 14 profiles comprising these genes (virulotypes) were observed throughout Europe. Moreover, most of these virulotypes were restricted to only one (n = 9) or two (n = 4) serovars. The data also indicated that the virulotype did not vary significantly with host source or geographical location. Subsequently, a representative subset of 77 strains was investigated using a microarray designed to detect 102 virulence and 49 resistance determinants. The results confirmed and extended the previous observations using the virulo-polymerase chain reaction screen. Strains belonging to the same serovar grouped together, indicating that the broader virulence-associated gene complement corresponded with the serovar. There were, however, some differences in the virulence gene profiles between strains belonging to an individual serovar. This variation occurred primarily within those virulence genes that were prophage encoded, in fimbrial clusters or in the virulence plasmid. It seems likely that such changes enable Salmonella to adapt to different environmental conditions, which might be reflected in serovar-specific ecology. In this strain subset a number of resistance genes were detected and were serovar restricted to a varying degree. Once again the profiles of those genes encoding resistance were similar or the same for each serovar in all hosts and countries investigated.

This review evaluates the current literature based on the impact of antibiotics on the intestinal microbiota and the critical role of intestinal bacteria in controlling infection and subsequent clinical disease caused by STEC and Salmonella, and the transmissibility of these important pathogens.A number of studies have indicated that antibiotic therapy could result in unexpected changes in the clinical picture of disease. This is observed, for example, in the case of infections associated with Shiga-toxin-producing Escherichia coli (STEC), when antibiotics used in treatment of the disease may increase the risk of hemolytic uremic syndrome (HUS) and thus fatal outcomes. In the case of such infections, treatment with antibiotics is usually discouraged. The use of antibiotics could cause also undesirable changes in the intestinal microbial flora and prolonged pathogen shedding, which is observed in the case of Salmonella infections. Inappropriate antibiotic therapy can result in Salmonella remaining in the host's cells (intracellular) and thus resulting in further asymptomatic carriage and a further complication is the development of resistance.

Implementation of control measures in line with European Commission regulations has led to a decrease in salmonellosis in the European Union since 2004. However, control programmes do not address laying hens whose eggs are produced for personal consumption or local sale. This article reports an investigation of a salmonellosis outbreak linked to home-produced eggs following a family event held in a farm in September 2011 near Warsaw, Poland. In the outbreak, 34 people developed gastroenteritis symptoms. Results from a cohort study indicated a cake, prepared from raw home-produced eggs, as the vehicle of the outbreak. Laboratory analysis identified Salmonella enterica serotype Enteritidis (S. Enteritidis) in stool samples or rectal swabs from 18 of 24 people and in two egg samples. As no food items remained, we used phage typing to link the source of the outbreak with the isolated strains. Seven S. Enteritidis strains analysed (five from attendees and two from eggs) were phage type 21c. Our findings resulted in culling of the infected laying hens and symptomatic pigeons housed next to the hens. Salmonella poses as a public health problem in Poland: control measures should not forget home-produced eggs, as there is a risk of infection from their consumption.

Two molecular biology methods were used to differentiate Salmonella enterica 1,4,[5],12:i:- strains: “Salmonella Check&Trace microarray” (CT) and multiplex PCR (mPCR). For 92 strains in CT result “Salmonella 1,4,[5],12:i:-“ were obtained. Those strains were confirmed in mPCR as monophasic fljB-lack Salmonella Typhimurium. For 17 strains, which in CT assay were recognized as Salmonella Typhimurium, the same identification was obtained in mPCR. Reference Salmonella strains: Lagos, Agama, Tsevie, Glocester and Tumodi in CT were recognized as Salmonella genovar, in mPCR – as Salmonella O:4, H:i other than Salmonella Typhimurium, the same like Salmonella Farsta, recognized incorrectly in CT as Salmonella Typhimurium.

In the Salmonella antigenic pattern, more than one phase of flagellar antigen is observed. The phase of flagellar antigen depends of the gene which encodes the protein building the filament of flagella. The fliC gene encodes the 1st phase of flagellar antigen and the fljB gene encodes the 2nd phase of flagellar antigen. The third phase of flagellar antigen is encoded by one of the genes localized on the plasmid. Expression of the fljB gene (part of the hinfljBA operon) is regulated by a mechanism of DNA fragment sequence inversion. The hin gene, which encodes Hin invertase, flanked by two regions - hixL and hixR - is inverted by Hin invertase together with Fis protein. This process turns on or turns off of the hinfljBA operon. When this operon is turned on, FljB protein is produced (structural protein of flagella filament), and also FljA protein, which is a transcriptional repressor of the fliC gene. This means that one Salmonella cell could have only one phase flagellar antigen--1st or 2nd phase. Sometimes, due to mutation in one of the mentioned genes, naturally diphasic Salmonella strains have the ability to produce only one phase of flagellar antigen. Mostly monophasic Salmonella with an active fliC gene are observed. In recent years such a strain, Salmonella enterica with the antigenic formula 1,4,[5],12: i: -, is one of the most often isolated strains from human cases in many European countries.