Lack of efflux mediated quinolone resistance in Salmonella enterica serovars Typhi and Paratyphi A.

International audienceSalmonella enterica serovars Typhi and Paratyphi A isolates from human patients in France displaying different levels of resistance to quinolones or fluoroquinolones were studied for resistance mechanisms to these antimicrobial agents. All resistant isolates carried either single or multiple target gene mutations (i.e., in gyrA, gyrB, or parC) correlating with the resistance levels observed. Active efflux, through upregulation of multipartite efflux systems, has also been previously reported as contributing mechanism for other serovars. Therefore, we investigated also the occurrence of non-target gene mutations in regulatory regions affecting efflux pump expression. However, no mutation was detected in these regions in both Typhi and Paratyphi isolates of this study. Besides, no overexpression of the major efflux systems was observed for these isolates. Nevertheless, a large deletion of 2334 bp was identified in the acrS-acrE region of all S. Typhi strains but which did not affect the resistance phenotype. As being specific to S. Typhi, this deletion could be used for specific molecular detection purposes. In conclusion, the different levels of quinolone or FQ resistance in both S. Typhi and S. Paratyphi A seem to rely only on target modifications

The genome sequence of Brucella pinnipedialis B2/94 sheds light on the evolutionary history of the genus Brucella

International audienceBackground: Since the discovery of the Malta fever agent, Brucella melitensis, in the 19th century, six terrestrial mammal-associated Brucella species were recognized over the next century. More recently the number of novel Brucella species has increased and among them, isolation of species B. pinnipedialis and B. ceti from marine mammals raised many questions about their origin as well as on the evolutionary history of the whole genus. Results: We report here on the first complete genome sequence of a Brucella strain isolated from marine mammals, Brucella pinnipedialis strain B2/94. A whole gene-based phylogenetic analysis shows that five main groups of host-associated Brucella species rapidly diverged from a likely free-living ancestor close to the recently isolated B. microti. However, this tree lacks the resolution required to resolve the order of divergence of those groups. Comparative analyses focusing on a) genome segments unshared between B. microti and B. pinnipedialis, b) gene deletion/fusion events and c) positions and numbers of Brucella specific IS711 elements in the available Brucella genomes provided enough information to propose a branching order for those five groups. Conclusions: In this study, it appears that the closest relatives of marine mammal Brucella sp. are B. ovis and Brucella sp. NVSL 07-0026 isolated from a baboon, followed by B. melitensis and B. abortus strains, and finally the group consisting of B. suis strains, including B. canis and the group consisting of the single B. neotomae species. We were not able, however, to resolve the order of divergence of the two latter groups

DNA polymorphism analysis of Brucella lipopolysaccharide genes reveals marked differences in O-polysaccharide biosynthetic genes between smooth and rough Brucella species and novel species-specific markers

Background: The lipopolysaccharide is a major antigen and virulence factor of Brucella, an important bacterial pathogen. In smooth brucellae, lipopolysaccharide is made of lipid A-core oligosaccharide and N-formylperosamine O-polysaccharide. B. ovis and B. canis (rough species) lack the O-polysaccharide. Results: The polymorphism of O-polysaccharide genes wbkE, manA(O-Ag), manB(O-Ag), manC(O-Ag), wbkF and wbkD) and wbo (wboA and wboB), and core genes manB(core) and wa** was analyzed. Although most genes were highly conserved, species- and biovar-specific restriction patterns were found. There were no significant differences in putative N-formylperosamyl transferase genes, suggesting that Brucella A and M serotypes are not related to specific genes. In B. pinnipedialis and B. ceti (both smooth), manB(O-Ag) carried an IS711, confirming its dispensability for perosamine synthesis. Significant differences between smooth and rough species were found in wbkF and wbkD, two adjacent genes putatively related to bactoprenol priming for O-polysaccharide polymerization. B. ovis wbkF carried a frame-shift and B. canis had a long deletion partially encompassing both genes. In smooth brucellae, this region contains two direct repeats suggesting the deletion mechanism. Conclusion: The results define species and biovar markers, confirm the dispensability of manB(O-Ag) for O-polysaccharide synthesis and contribute to explain the lipopolysaccharide structure of rough and smooth Brucella species

Ciprofloxacin-resistant Salmonella Kentucky in Travelers

Ciprofloxacin-resistant Salmonella Kentucky in travelers</p

Genomic comparisons of Brucella spp. and closely related bacteria using base compositional and proteome based methods

<p>Abstract</p> <p>Background</p> <p>Classification of bacteria within the genus <it>Brucella </it>has been difficult due in part to considerable genomic homogeneity between the different species and biovars, in spite of clear differences in phenotypes. Therefore, many different methods have been used to assess <it>Brucella </it>taxonomy. In the current work, we examine 32 sequenced genomes from genus <it>Brucella </it>representing the six classical species, as well as more recently described species, using bioinformatical methods. Comparisons were made at the level of genomic DNA using oligonucleotide based methods (Markov chain based genomic signatures, genomic codon and amino acid frequencies based comparisons) and proteomes (all-against-all BLAST protein comparisons and pan-genomic analyses).</p> <p>Results</p> <p>We found that the oligonucleotide based methods gave different results compared to that of the proteome based methods. Differences were also found between the oligonucleotide based methods used. Whilst the Markov chain based genomic signatures grouped the different species in genus <it>Brucella </it>according to host preference, the codon and amino acid frequencies based methods reflected small differences between the <it>Brucella </it>species. Only minor differences could be detected between all genera included in this study using the codon and amino acid frequencies based methods.</p> <p>Proteome comparisons were found to be in strong accordance with current <it>Brucella </it>taxonomy indicating a remarkable association between gene gain or loss on one hand and mutations in marker genes on the other. The proteome based methods found greater similarity between <it>Brucella </it>species and <it>Ochrobactrum </it>species than between species within genus <it>Agrobacterium </it>compared to each other. In other words, proteome comparisons of species within genus <it>Agrobacterium </it>were found to be more diverse than proteome comparisons between species in genus <it>Brucella </it>and genus <it>Ochrobactrum</it>. Pan-genomic analyses indicated that uptake of DNA from outside genus <it>Brucella </it>appears to be limited.</p> <p>Conclusions</p> <p>While both the proteome based methods and the Markov chain based genomic signatures were able to reflect environmental diversity between the different species and strains of genus <it>Brucella</it>, the genomic codon and amino acid frequencies based comparisons were not found adequate for such comparisons. The proteome comparison based phylogenies of the species in genus <it>Brucella </it>showed a surprising consistency with current <it>Brucella </it>taxonomy.</p

Emergence of Multidrug-resistant Salmonella Paratyphi B dT+, Canada

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

Variant Salmonella Genomic Island 1 Antibiotic Resistance Gene Cluster in Salmonella enterica Serovar Albany

Salmonella genomic island 1 (SGI1) contains an antibiotic resistance gene cluster and has been previously identified in multidrug-resistant Salmonella enterica serovars Typhimurium DT104, Agona, and Paratyphi B. We identified a variant SGI1 antibiotic-resistance gene cluster in a multidrug-resistant strain of S. enterica serovar Albany isolated from food fish from Thailand and imported to France. In this strain, the streptomycin resistance aadA2 gene cassette in one of the SGI1 integrons was replaced by a dfrA1 gene cassette, conferring resistance to trimethoprim and an open reading frame of unknown function. Thus, this serovar Albany strain represents the fourth S. enterica serovar in which SGI1 has been identified and the first SGI1 example where gene cassette replacement took place in one of its integron structures. The antibiotic resistance gene cluster of serovar Albany strain 7205.00 constitutes a new SGI1 variant; we propose a name of SGI1-F

Major primary bile salts repress Salmonella enterica serovar Typhimurium invasiveness partly via the efflux regulatory locus ramRA

Bile represses Salmonella enterica serovar Typhimurium (S. Typhimurium) intestinal cell invasion, but it remains unclear which bile components and mechanisms are implicated. Previous studies reported that bile inhibits the RamR binding to the ramA promoter, resulting in ramA increased transcription, and that ramA overexpression is associated to decreased expression of type III secretion system 1 (TTSS-1) invasion genes and to impaired intestinal cell invasiveness in S. Typhimurium. In this study, we assessed the possible involvement of the ramRA multidrug efflux regulatory locus and individual bile salts in the bile-mediated repression of S. Typhimurium invasion, using Caco-2 intestinal epithelial cells and S. Typhimurium strain ATCC 14028s. Our results indicate that (i) major primary bile salts, chenodeoxycholate and its conjugated-derivative salts, cholate, and deoxycholate, activate ramA transcription in a RamR-dependent manner, and (ii) it results in repression of hilA, encoding the master activator of TTSS-1 genes, and as a consequence in the repression of cellular invasiveness. On the other hand, crude ox bile extract and cholate were also shown to repress the transcription of hilA independently of RamR, and to inhibit cell invasion independently of ramRA. Altogether, these data suggest that bile-mediated repression of S. Typhimurium invasion occurs through pleiotropic effects involving partly ramRA, as well as other unknown regulatory pathways. Bile components other than the bile salts used in this study might also participate in this phenomenon