Non-typhoidal Salmonella is the most common foodborne bacterial pathogen in most countries. It is widely present in food animal species, and therefore blocking its transmission through the food supply is a prominent focus of food safety activities worldwide. Antibiotic resistance in non-typhoidal Salmonella arises in large part because of antibiotic use in animal husbandry. Tracking resistance in Salmonella is required to design targeted interventions to contain or diminish resistance and refine use practices in production. Many countries have established systems to monitor antibiotic resistance in Salmonella and other bacteria, the earliest ones appearing the Europe and the US. In this chapter, we compare recent Salmonella antibiotic susceptibility data from Europe and the US. In addition, we summarize the state of known resistance genes that have been identified in the genus. The advent of routine whole genome sequencing has made it possible to conduct genomic surveillance of resistance based on DNA sequences alone. This points to a new model of surveillance in the future that will provide more definitive information on the sources of resistant Salmonella, the specific types of resistance genes involved, and information on how resistance spreads.

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Antimicrobial Resistance in Nontyphoidal Salmonella.

Shigella species and Shiga toxin-producing Escherichia coli (STEC) are agents of bloody diarrhea that may progress to potentially lethal complications such as diarrhea-associated hemolytic uremic syndrome (D+HUS) and neurological disorders. The bacteria share the ability to produce virulence factors called Shiga toxins (Stxs). Research over the past two decades has identified Stxs as multifunctional toxins capable of inducing cell stress responses in addition to their canonical ribotoxic function inhibiting protein synthesis. Notably, Stxs are not only potent inducers of cell death, but also activate innate immune responses that may lead to inflammation, and these effects may increase the severity of organ injury in patients infected with Stx-producing bacteria. In the intestines, kidneys, and central nervous system, excessive or uncontrolled host innate and cellular immune responses triggered by Stxs may result in sensitization of cells to toxin mediated damage, leading to immunopathology and increased morbidity and mortality in animal models (including primates) and human patients. Here, we review studies describing Stx-induced innate immune responses that may be associated with tissue damage, inflammation, and complement activation. We speculate on how these processes may contribute to immunopathological responses to the toxins.

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Roles of Shiga Toxins in Immunopathology

Antibiotic resistance and class 1 integron patterns of non-typhoidal human Salmonella serotypes isolated in Hungary in 2002 and 2003.

The ability of Shigella to invade, colonize, and eventually kill host cells is influenced by many virulence factors. However, there is no analysis of related genes in Jiangsu Province of China so far. Shigella flexneri was collected from 13 cities of Jiangsu Province through the provincial Centers for Disease Control (CDC) for analysis of distribution of major virulence genes (ipaH, ipaBCD, ial, virF, virB, sigA, set1A, sepA, sat, pic, set1B and sen) detected by PCR technology. A total of 545 isolates received were confirmed as S. flexneri which belongs to 11 serotypes of S. flexneri, among which serotype 2a was the most predominant (n = 223, 40.9%). All isolates were positive for ipaH gene, followed by sat (94.1%), sigA (78.9%), set1B (78.0%), pic (77.6%), set1A (74.5%), virF (64.8%), sepA (63.5%), sen (56.9%), ipaBCD (50.5%), ial (47.0%) and virB (47.0%). The presence of virulence genes in different serotypes was distinct. The existence of virulence genes of serotype 1b was generally lower than other serotype-the positive rate for virulence genes was between 0.0 and 14.1% except for ipaH and sat. In addition, virulence genes also fluctuated in different regions and at different times in Jiangsu province. The result of analysis on the relationship between virulence genes of S. flexneri showed that the existence of virulence genes of Shigella could be well represented by multiplex PCR combination ipaH + ial + set1A, which had a high clinical value. The present study was designed to explore the prevalence of 12 S. flexneri-associated virulence genes. The data showed high diversity of virulence genes with regard to periods, regions and serotypes in Jiangsu Province of China.

/pdf/low-distribution-of-genes-encoding-virulence-factors-in-2o2j6w0icn.pdf

Low distribution of genes encoding virulence factors in Shigella flexneri serotypes 1b clinical isolates from eastern Chinese populations

Distribution and characterization of Shiga toxin converting temperate phages carried by Shigella flexneri in Hispaniola

Comparison of phage types (PTs) determined by Felix and Callow's and Anderson's methods was performed testing 99 human strains of S. enterica serotype Typhimurium (S. typhimurium) isolated in Hungary. PT2 and PT2c--according to Felix-Callow--corresponded with Anderson's DT104 in case of 39 strains out of 40. Among 59 isolates belonging to other Felix-Callow's PTs only one strain was found which was DT 104. Similar unambiguous equalities could not be established between any other PTs comparing the two methods. The PTs of 17,877 human strains isolated between 1988 and 1999 were determined using Felix-Callow's method. On the basis of the above equality the emergence of DT104 could be followed retrospectively by means of the rate of PT2 and PT2c. The increase of DT104 began already in 1989, emerging first PT2c then PT2. It predominated since 1991 and it reached its maximum (78.3%) in 1999. The incidence of multiresistance among one of the groups of DT104 strains (Felix-Callow's PT2) was significantly higher in 1998 than the average of non-DT104 strains. The predominant R-type was ACST.

The spread and antibiotic resistance of Salmonella enterica serotype typhimurium DT104 in Hungary.

The integron content of 52 DT104/U302 phage type strains and 53 non-DT104/U302 strains of Salmonella enterica serotype Typhimurium (S. Typhimurium) was studied in PCR experiments using a 5'-CS/3'-CS primer pair (Levesque et al., 1995). Forty-three out of 44 streptomycin- and/or ampicillin-resistant DT104 and related phage type strains were found to carry a 1 kb and/or 1.2 kb long integron. The other resistance markers did not affect the number and size of integrons; no integron-free multidrug-resistant (MDR) DT104 strains were found. The two large groups of DT104 strains (Felix-Callow's phage types 2 and 2c) proved to be identical in respect of integron patterns (IPs), supporting the views of those authors who consider DT104 a single clone. Strains of human and animal origin did not differ from each other in their IPs. Within the non-DT104 phage types, ampicillin- and/or streptomycin-resistant, integron-free MDR strains were also found. Based on amplicons varying between 290 and 3500 bp an IP system was suggested. The commonest amplicon sizes in non-DT104 strains were 1450 and 2050 bp. The IPs of DT104 strains and of non-DT104 strains containing an integron of 1 and 1.2 kb size were stable. In contrast, the IPs of other non-DT104 strains showed a varying degree of instability. Integron loss was frequently associated with spontaneous plasmid elimination and changes of R-type among the descendants of a given strain.

Integron content of Salmonella enterica serotype Typhimurium strains isolated in Hungary in the years 1997-1999

By PCR using the ant(3”)-Ia primer pair the aadA gene was detected in 34 streptomycin- and spectinomycin-resistant Salmonella enterica serotype Typhimurium strains. Out of them 12 belonged to DT104 and 22 to non-DT104 phage type. Using different primer combinations it was demonstrated that this gene was integron-associated in all cases: in the DT104 strains it was generally contained by a 1 kb integron while in the majority of the non-DT104 strains by a 2.05 kb (less often by a 1.9 or 1 kb) integron. In the case of integrons carrying multiple cassettes the cassette containing the aadA gene was located closer to the 3' end of the integron. The aadA genes of DT104 and non-DT104 strains were different: in the former group the aadA2 gene, while in the latter group (constituted by strains of five different phages types as well as unclassifiable and untypable strains) the aadA1 gene could be identified. The RH50/RH51 primer pair described by Collis and Hall (1992) proved to be suitable for rapid discrimination ...

Analysis of gene cassettes of streptomycin-spectinomycin resistance of Hungarian Salmonella enterica serotype Typhimurium strains

Diagnostic value of multiplex polymerase chain reaction (PCR) was examined by using three primer pairs, specific for the common conserved region of stx1 and stx2, eae and an enterohaemolysin A gene (ehxA). The sensitivity in respect of each amplicon decreased with three exponents comparing to the individual PCR reactions. These PCR reactions were partially inhibited by the presence of certain additional primers. This inhibitory effect was template-concentration dependent, and was partially balanced by usage of increased amount of dNTP. Taq DNA polymerase in a range of 0.3-1.25 U/reaction did not influence the inhibition. The same inhibition was detected if the annealing temperature was changed from 48 degrees C to 57 degrees C. Pairs of EHEC primers inhibited a Salmonella enteritidis virulence-plasmid specific gene amplification, as well. Theoretical inhibiting effects were predicted by Primer Premier software but our observations can be sufficiently explained neither by the competitions between the specific and aspecific amplifications nor by the inhibition caused by dimerization of primers.

Partial inhibition of amplifications by primers of EHEC genes.

Antimicrobial susceptibility, integron carriage, genetic relationship and presence of some important virulence genes of the integron-carrier strains of Shigella sonnei (n = 230) and Shigella flexneri (n = 22) isolated from stool samples of patients in Hungary between 1998 and 2008 were investigated. Sixty-seven per cent (168/252) of the strains were resistant to sulfamethoxazole/trimethoprim (SxT) followed by streptomycin (S, 47 %), ampicillin (A, 32 %) and tetracycline (Tc, 28 %). Thirty-six per cent (90/252) exhibited multidrug resistance, mostly showing SSxTTc or ASSxTc, ASSxTTc resistance patterns. An S. sonnei strain of imported origin was resistant to cefotaxime and harboured a bla
CTX-M-55-type extended-spectrum β-lactamase gene. Altogether 33 % of the S. sonnei (n = 75) and 14 % of the S. flexneri (n = 3) strains had either class 1 or class 2 integrons or both. The variable regions encoded aadA1 or dfrA1-aadA1 genes for the class 1 and dfrA1-sat2-aadA1 or dfrA1-sat2 genes for the class 2 integrons. Pulsed-field gel electrophoresis analysis revealed that those strains that have different integron types represented different genetic clusters. The Shiga toxin (stx1) gene was identified in one S. sonnei strain and the cdtB gene was detected in an S. flexneri strain. The results reveal the high incidence of antibiotic resistance among Shigella isolates and the presence of the stx1 gene in S. sonnei and the cdtB gene in S. flexneri. The genetic diversity of Shigella spp. isolated recently in Hungary was also demonstrated.

Antimicrobial resistance and genetic characteristics of integron-carrier shigellae isolated in Hungary (1998-2008).

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