Search

Objectives: Plasmid-mediated mobilized colistin resistance is currently known to be caused by phosphoethanolamine transferases termed MCR-1, MCR-2, MCR-3 and MCR-4. However, this study focuses on the dissection of a novel resistance mechanism in mcr-1-, mcr-2- and mcr-3-negative d-tartrate fermenting Salmonella enterica subsp. enterica serovar Paratyphi B (Salmonella Paratyphi B dTa+) isolates with colistin MIC values >2 mg/L., Methods: A selected isolate from the strain collection of the German National Reference Laboratory for Salmonella was investigated by WGS and bioinformatical analysis to identify novel phosphoethanolamine transferase genes involved in colistin resistance. Subsequently PCR screening, S1-PFGE and DNA-DNA hybridization were performed to analyse the prevalence and location of the identified mcr-5 gene. Cloning and transformation experiments in Escherichia coli DH5α and Salmonella Paratyphi B dTa+ control strains were carried out and the activity of MCR-5 was determined in vitro by MIC testing., Results: In this study, we identified a novel phosphoethanolamine transferase in 14 mcr-1-, mcr-2- and mcr-3-negative Salmonella Paratyphi B dTa+ isolates with colistin MIC values >2 mg/L that were received during 2011-13. The respective gene, further termed as mcr-5 (1644 bp), is part of a 7337 bp transposon of the Tn3 family and usually located on related multi-copy ColE-type plasmids. Interestingly, in one isolate an additional subclone with a chromosomal location of the mcr-5 transposon was observed., Conclusions: Our findings suggest that the transfer of colistin-resistance-mediating phosphoethanolamine transferase genes from bacterial chromosomes to mobile genetic elements has occurred in multiple independent events raising concern regarding their variety, prevalence and impact on public health., (© The Author 2017. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

A total of 36 contemporary human, animal, and environmental (+)-tartrate-fermenting (dT+) Salmonella enterica serovar Paratyphi B isolates, formerly called Salmonella serovar Java, and five related monophasic S. enterica serovar 4,5,12:b:- isolates from Belgium, Germany, the Netherlands, and the United Kingdom were investigated for clonality and antimicrobial resistance profiles, as well as their virulence and resistance gene repertoire. Two major clonal lines, which could be phenotypically differentiated by the expression of the O:5 antigen, were identified. All O:5 antigen negative strains were multidrug resistant and originated (with two exceptions) from Belgian, Dutch, or German poultry. Strains exhibiting the O:5 antigen encoded by the oafA gene revealed a more heterogeneous group including multidrug-resistant and susceptible strains. Compared to O:5 antigen negative isolates, Salmonella Paratyphi B dT+ O:5 positive strains possessed additional virulence determinants. The Salmonella genomic island 1 was only found in O:5 positive strains. Five monophasic Salmonella 4,5,12:b:- lacking the phase-2 flagellar antigen were assigned to Salmonella Paratyphi B dT+ isolates of the O:5 positive group. The conclusion of the analysis is that Salmonella Paratyphi B dT+ O:5 negative and O:5 positive isolates evolved from a different lineage. Salmonella Paratyphi B dT+ O:5 positive strains possess additional fimbrial and virulence genes that probably enable this clone to interact with a broader range of hosts and the environment. Salmonella Paratyphi B dT+ O:5 negative continuously persists in poultry across Western Europe, especially Belgium, the Netherlands, and Germany.

Salmonella serotype Paratyphi B isolates obtained from shellfish and human infections in Galicia (northwest Spain) from 1998 were investigated by different phenotypic and genetic methods to evaluate their systemic or enteric nature. Isolates were investigated for D-tartrate fermentation, presence of genes encoding the effector proteins sopE1 and avrA, pulsed-field gel electrophoresis profile, and antimicrobial susceptibility. Systemic variant strains (dT-) were the dominant among the marine environment isolates. All dT- isolates were sopE1 positive and avrA negative, presented an indistinguishable electrophoresis profile, and were grouped in a single cluster. More electrophoresis heterogeneity was observed among dT+ isolates. Only two isolates showed resistance to any of the 16 antibiotics included in our panel. The present study identified the marine environment as a potential natural source of systemic variant isolates of Salmonella Paratyphi B. The presence of systemic variant isolates of Salmonella Paratyphi B in the marine environment is of notable public health significance as a result of the potential risk of acquiring enteric fever linked to the consumption of raw shellfish.

This study was conducted to investigate the occurrence of multiple-antibiotic resistance among 261 clinical isolates of Salmonella enterica serotype Paratyphi B strains collected between 2000 and 2003 through the network of the French National Reference Center for Salmonella. The 47 multidrug-resistant (MDR) isolates identified (18%), were characterized on the basis of the presence of several resistance genes (bla(TEM), bla(PSE-1), bla(CTX-M), floR, aadA2, qacEdelta1, and sul1), the presence of Salmonella genomic island 1 (SGI1) by PCR mapping and hybridization, and the clonality of these isolates by several molecular (ribotyping, IS200 profiling, and pulsed-field gel electrophoresis [PFGE]) and phage typing methods. The results of PCR and Southern blot experiments indicated that 39 (83%) of the 47 S. enterica serotype Paratyphi B biotype Java MDR isolates possessed the SGI1 cluster (MDR/SGI1). Among these 39 MDR/SGI1 isolates, only 3 contained variations in SGI1, SGI1-B (n = 1) and SGI1-C (n = 2). The 39 MDR/SGI1 isolates showed the same specific PstI-IS200 profile 1, which contained seven copies from 2.6 to 18 kb. Two PstI ribotypes were found in MDR/SGI1 isolates, RP1 (n = 38) and RP6 (n = 1). Ribotype RP1 was also found in two susceptible strains. Analysis by PFGE using XbaI revealed that all the MDR/SGI1 isolates were grouped in two related clusters, with a similarity percentage of 82%. Isolation of MDR/SGI1 isolates in France was observed mainly between the second quarter of 2001 and the end of 2002. The source of the contamination has not been identified to date. A single isolate possessing the extended-spectrum beta-lactamase bla(CTX-M-15) gene was also identified during the study.

An epidemiological investigation of a calf rearing premises and a closely associated dairy herd was carried out after the isolation of Salmonella enterica serovar Paratyphi B variant Java phage type 3b variant 2 from clinically diseased calves on the premises. The isolate was resistant to ampicillin, chloramphenicol, streptomycin, sulphonamides, tetracyclines, trimethoprim and cefoperazone. The organism was widespread on the calf unit and was also recovered from the dairy premises, mainly from groups of weaned calves. The investigation was extended to 10 epidemiologically linked farms but no S Java was isolated from any of the 40 to 60 samples collected from each premises. Molecular studies showed that the S Java isolates were genetically most similar to isolates from cases of human disease associated with ornamental fish tanks or feed. Long PCR and resistance gene profiling identified a resistance island which was indistinguishable from the human 'fish tank' strain of S Java and animal and human epidemic strains of S Typhimurium DT104. The isolates were clearly distinguished from multi-resistant S Java strains commonly associated with continental poultry. This is the first report of S Java with this resistance pattern in Great Britain.

We document an increase in the number of multidrug-resistant Salmonella enterica serovar Paratyphi B dT+ identified in Canada. Most of these strains harbor Salmonella genomic island 1 (SGI1). Further studies are needed to determine factors contributing to the observed emergence of this multidrug-resistant strain.

A total of 4801 Salmonella strains of 67 serovars isolated from various sources in 1968-1982 were studied for their sensitivity to 12 drugs. The Salmonella strains of groups A, B, C, D and E amounted to 0.8, 84.6, 6.4, 5.8 and 2.0 per cent, respectively. The Salmonella strains of the other groups amounted to 0.4 per cent. During the 5-year periods, the number of the antibiotic resistant Salmonella strains increased from 57.7 to 93.4 per cent. The conjugative drug resistance was detected in 16 out of the 67 serovars. The Salmonella strains usually resistant to 4-10 drugs were the donors of this conjugative drug resistance. The strains of S. typhimurium responsible for the hospital infections were characterized by the highest levels of the antibiotic polyresistance and the greatest variety of the conjugative R plasmids. The structure of the multiple and conjugative drug resistance of the organisms causing salmonellosis was more frequently defined by the conjugative plasmids of the antibiotic resistance of the S. typhimurium serovar. The Salmonella R plasmids determined various levels of the antibiotic resistance. The highest resistance levels were observed to benzylpenicillin, chloramphenicol and erythromycin and the lowest resistance levels to tetracycline.

The pathogenicity level of antibiotic sensitive and streptomycin resistant strains of S. typhimurium, S. paratyphi B and S. kottbus changed under the effect of identical R plasmids more frequently in contrary directions. The conjugative plasmids of antibiotic resistance widened the ranges of the virulence changes in the Salmonella serovars for albino mice. It was found that 7 out of 8 plasmids studied significantly decreased and increased the virulence of the antibiotic sensitive Salmonella strains. As a rule, R plasmids of various origin decreased the virulence of all the tested streptomycin chromosome resistant causative agents of salmonellosis.