Genetic characteristics and phylogenetic analysis of Brazilian clinical strains of Pseudomonas aeruginosa harboring CRISPR/Cas systems

Unravelling complex transposable elements surrounding blaGES-16 in a Pseudomonas aeruginosa ExoU strain

OBJECTIVES

We characterised the complex surrounding regions of bla_GES-16 in a Pseudomonas aeruginosa exoU+ strain (P-10.226) in Brazil.

METHODS

Species identification was performed by MALDI-TOF MS, and the antimicrobial susceptibility profile was determined by broth microdilution based on European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints. The whole genome sequencing (WGS) of P-10.226 strain was performed using both short-read paired-end sequencing on the Illumina MiSeq platform as well as the long-read Oxford Nanopore MinION.

RESULTS

WGS analysis showed that P-10.226 carried bla_GES-16, which was found as a gene cassette inserted into a novel class I integron, In1992 (aadB-bla_OXA-56-bla_GES-16-aadB-aadA6c), whose 3'-CS was truncated by a nested transposable element, IS5564::ISPa157. The structure was even more complex since IS6100-ΔIS6100 structure and a TnAs2-like harbouring the operon merRTPADE was found downstream In1992. Fragments of TnAs3 harbouring 25-bp imperfect inverted repeats were identified bordering the intl1 of In1992 and also flanking IS6100-ΔIS6100, which might be genetic marks of its previous presence in the genome. Interestingly, In1992 also shows a distinct cassette array from In581 (bla_GES-16-dfrA22-aacA27-aadA1), which was previously reported in Serratia marcescens strains recovered in Brazil. Finally, exoU gene, which encodes a potent cytotoxin of type III secretion systems (T3SS) effector proteins from P. aeruginosa and is associated to severe infections, was also detected.

CONCLUSION

We described the novel In1992 carrying bla_GES-16 surrounded by complex transposition events in a XDR P. aeruginosa strain. The identification of many sets of direct repeats adjacent to TnAs3 fragments indicates a major past of transposition events that shaped the current genetic environment of In1992.

Comparative genomics of Nocardia seriolae reveals recent importation and subsequent widespread dissemination in mariculture farms in the South Central Coast region, Vietnam

Between 2010 and 2015, nocardiosis outbreaks caused by Nocardia seriolae affected many permit farms throughout Vietnam, causing mass fish mortalities. To understand the biology, origin and epidemiology of these outbreaks, 20 N. seriolae strains collected from farms in four provinces in the South Central Coast region of Vietnam, along with two Taiwanese strains, were analysed using genetics and genomics. PFGE identified a single cluster amongst all Vietnamese strains that was distinct from the Taiwanese strains. Like the PFGE findings, phylogenomic and SNP genotyping analyses revealed that all Vietnamese N. seriolae strains belonged to a single, unique clade. Strains fell into two subclades that differed by 103 SNPs, with almost no diversity within clades (0–5 SNPs). There was no association between geographical origin and subclade placement, suggesting frequent N. seriolae transmission between Vietnamese mariculture facilities during the outbreaks. The Vietnamese strains shared a common ancestor with strains from Japan and China, with the closest strain, UTF1 from Japan, differing by just 220 SNPs from the Vietnamese ancestral node. Draft Vietnamese genomes range from 7.55 to 7.96 Mbp in size, have an average G+C content of 68.2 % and encode 7 602–7958 predicted genes. Several putative virulence factors were identified, including genes associated with host cell adhesion, invasion, intracellular survival, antibiotic and toxic compound resistance, and haemolysin biosynthesis. Our findings provide important new insights into the epidemiology and pathogenicity of N. seriolae and will aid future vaccine development and disease management strategies, with the ultimate goal of nocardiosis-free aquaculture.

OUP accepted manuscript

Bacteria and archaea use the CRISPR-Cas system to fend off invasions of bacteriophages and foreign plasmids. In response, bacteriophages encode anti-CRISPR (Acr) proteins that potently inhibit host Cas proteins to suppress CRISPR-mediated immunity. AcrIE4-F7, which was isolated from Pseudomonas citronellolis, is a fused form of AcrIE4 and AcrIF7 that inhibits both type I-E and type I-F CRISPR-Cas systems. Here, we determined the structure of AcrIE4-F7 and identified its Cas target proteins. The N-terminal AcrIE4 domain adopts a novel α-helical fold that targets the PAM interaction site of the type I-E Cas8e subunit. The C-terminal AcrIF7 domain exhibits an αβ fold like native AcrIF7, which disables target DNA recognition by the PAM interaction site in the type I-F Cas8f subunit. The two Acr domains are connected by a flexible linker that allows prompt docking onto their cognate Cas8 targets. Conserved negative charges in each Acr domain are required for interaction with their Cas8 targets. Our results illustrate a common mechanism by which AcrIE4-F7 inhibits divergent CRISPR-Cas types.

CRISPR Element Patterns vs. Pathoadaptability of Clinical Pseudomonas aeruginosa Isolates from a Medical Center in Moscow, Russia

Pseudomonas aeruginosa is a member of the ESKAPE opportunistic pathogen group, which includes six species of the most dangerous microbes. This pathogen is characterized by the rapid acquisition of antimicrobial resistance, thus causing major healthcare concerns. This study presents a comprehensive analysis of clinical P. aeruginosa isolates based on whole-genome sequencing data. The isolate collection studied was characterized by a variety of clonal lineages with a domination of high-risk epidemic clones and different CRISPR/Cas element patterns. This is the first report on the coexistence of two and even three different types of CRISPR/Cas systems simultaneously in Russian clinical strains of P. aeruginosa. The data include molecular typing and genotypic antibiotic resistance determination, as well as the phylogenetic analysis of the full-length cas gene and anti-CRISPR genes sequences, predicted prophage sequences, and conducted a detailed CRISPR array analysis. The differences between the isolates carrying different types and quantities of CRISPR/Cas systems were investigated. The pattern of virulence factors in P. aeruginosa isolates lacking putative CRISPR/Cas systems significantly differed from that of samples with single or multiple putative CRISPR/Cas systems. We found significant correlations between the numbers of prophage sequences, antibiotic resistance genes, and virulence genes in P. aeruginosa isolates with different patterns of CRISPR/Cas-elements. We believe that the data presented will contribute to further investigations in the field of bacterial pathoadaptability, including antimicrobial resistance and the role of CRISPR/Cas systems in the plasticity of the P. aeruginosa genome.