Development of quinolone resistance and prevalence of different virulence genes among Shigella flexneri and Shigella dysenteriae in environmental water samples

Characterization of Shigella flexneri Serotype 6 Strains Isolated from Bangladesh and Identification of a New Phylogenetic Cluster

A significant cause of shigellosis in Bangladesh and other developing countries is Shigella flexneri serotype 6. This serotype has been subtyped, on the basis of the absence or presence of a group-specific antigen, E1037, into S. flexneri 6a and 6b, respectively. Here, we provided rationales for the subclassification, using several phenotypic and molecular tools. A set of S. flexneri 6a and 6b strains isolated between 1997 and 2015 were characterized by analyzing their biochemical properties, plasmid profiles, virulence markers, pulsed-field gel electrophoresis (PFGE) results, and ribotype. Additionally, the genomic relatedness of these subserotypes was investigated with global isolates of serotype 6 using publicly available genomes. Both subserotypes of S. flexneri 6 agglutinated with monoclonal antiserum against S. flexneri (MASF) B and type VI-specific antiserum (MASF VI) and were PCR positive for O-antigen flippase-specific genes and virulence markers (ipaH, ial, sen, and sigA). Unlike S. flexneri 6a strains, S. flexneri 6b strains seroagglutinated with anti-E1037 antibodies, MASF IV-I. Notably, these two antigenically distinct subserotypes were clonally diverse, showing two distinct PFGE patterns following the digestion of chromosomal DNA with either XbaI or IceuI. In addition, hybridization of a 16S rRNA gene probe with HindIII-digested genomic DNA yielded two distinguishing ribotypes. Genomic comparison of S. flexneri subserotype 6a and 6b strains from Bangladesh indicated that, although these strains were in genomic synteny, the majority of them formed a unique phylogroup (PG-4) that was missing for the global isolates. This study supports the subserotyping and emphasizes the need for global monitoring of the S. flexneri subserotypes 6a and 6b. IMPORTANCE Shigella flexneri serotype 6 is one of the predominant serotypes among shigellosis cases in Bangladesh. Characterization of a novel subserotype of S. flexneri 6 (VI:E1037), agglutinated with type 6-specific antibody and anti-E1037, indicates a unique evolutionary ancestry. PFGE genotyping supports the finding that these two antigenically distinct subserotypes are clonally diverse. A phylogenetic study based on single-nucleotide polymorphism (SNP) data revealed that these two subserotypes were in genomic synteny, although their genomes were reduced. Interestingly, a majority of the S. flexneri 6 strains isolated from Bangladesh form a novel phylogenetic cluster. Therefore, this report underpins the global monitoring and tracking of the novel subserotype.

Detection of human pathogenic bacteria in rectal DNA samples from Zalophus californianus in the Gulf of California, Mexico

Human intrusions into undisturbed wildlife areas greatly contribute to the emergence of infectious diseases. To minimize the impacts of novel emerging infectious diseases (EIDs) on human health, a comprehensive understanding of the microbial species that reside within wildlife species is required. The Gulf of California (GoC) is an example of an undisturbed ecosystem. However, in recent decades, anthropogenic activities within the GoC have increased. Zalophus californianus has been proposed as the main sentinel species in the GoC; hence, an assessment of sea lion bacterial microbiota may reveal hidden risks for human health. We evaluated the presence of potential human pathogenic bacterial species from the gastrointestinal (GI) tracts of wild sea lions through a metabarcoding approach. To comprehensively evaluate this bacterial consortium, we considered the genetic information of six hypervariable regions of 16S rRNA. Potential human pathogenic bacteria were identified down to the species level by integrating the RDP and Pplacer classifier outputs. The combined genetic information from all analyzed regions suggests the presence of at least 44 human pathogenic bacterial species, including Shigella dysenteriae and Bacillus anthracis. Therefore, the risks of EIDs from this area should be not underestimated.

Small RNAs as Fundamental Players in the Transference of Information During Bacterial Infectious Diseases

Communication shapes life on Earth. Transference of information has played a paramount role on the evolution of all living or extinct organisms since the appearance of life. Success or failure in this process will determine the prevalence or disappearance of a certain set of genes, the basis of Darwinian paradigm. Among different molecules used for transmission or reception of information, RNA plays a key role. For instance, the early precursors of life were information molecules based in primitive RNA forms. A growing field of research has focused on the contribution of small non-coding RNA forms due to its role on infectious diseases. These are short RNA species that carry out regulatory tasks in cis or trans. Small RNAs have shown their relevance in fine tuning the expression and activity of important regulators of essential genes for bacteria. Regulation of targets occurs through a plethora of mechanisms, including mRNA stabilization/destabilization, driving target mRNAs to degradation, or direct binding to regulatory proteins. Different studies have been conducted during the interplay of pathogenic bacteria with several hosts, including humans, animals, or plants. The sRNAs help the invader to quickly adapt to the change in environmental conditions when it enters in the host, or passes to a free state. The adaptation is achieved by direct targeting of the pathogen genes, or subversion of the host immune system. Pathogens trigger also an immune response in the host, which has been shown as well to be regulated by a wide range of sRNAs. This review focuses on the most recent host-pathogen interaction studies during bacterial infectious diseases, providing the perspective of the pathogen.