Population Structure of Pseudomonas aeruginosa from Five Mediterranean Countries: Evidence for Frequent Recombination and Epidemic Occurrence of CC235

Abstract

Several studies in recent years have provided evidence that Pseudomonas aeruginosa has a non-clonal population structure punctuated by highly successful epidemic clones or clonal complexes. The role of recombination in the diversification of P. aeruginosa clones has been suggested, but not yet demonstrated using multi-locus sequence typing (MLST). Isolates of P. aeruginosa from five Mediterranean countries (n = 141) were subjected to pulsed-field gel electrophoresis (PFGE), serotyping and PCR targeting the virulence genes exoS and exoU. The occurrence of multi-resistance (≥3 antipseudomonal drugs) was analyzed with disk diffusion according to EUCAST. MLST was performed on a subset of strains (n = 110) most of them had a distinct PFGE variant. MLST data were analyzed with Bionumerics 6.0, using minimal spanning tree (MST) as well as eBURST. Measurement of clonality was assessed by the standardized index of association (IA S). Evidence of recombination was estimated by ClonalFrame as well as SplitsTree4.0. The MST analysis connected 70 sequence types, among which ST235 was by far the most common. ST235 was very frequently associated with the O11 serotype, and frequently displayed multi-resistance and the virulence genotype exoS −/exoU +. ClonalFrame linked several groups previously identified by eBURST and MST, and provided insight to the evolutionary events occurring in the population; the recombination/mutation ratio was found to be 8.4. A Neighbor-Net analysis based on the concatenated sequences revealed a complex network, providing evidence of frequent recombination. The index of association when all the strains were considered indicated a freely recombining population. P. aeruginosa isolates from the Mediterranean countries display an epidemic population structure, particularly dominated by ST235-O11, which has earlier also been coupled to the spread of ß-lactamases in many countries.

Detection of Exotoxins and Antimicrobial Susceptibility Pattern in Clinical Pseudomonas Aeruginosa Isolates

“…In addition, previous studies were shown that the presence of the TTSS effector genotypes, especially exoU genotype, correlate with increasing the virulence and resistance to one or more antibiotics. In a study by Agnello et al, they were found that the presence of exoU gene was significantly correlated with flouroquinolones-resistance (4 (23,26). In present study 81.7% and 88.6% of isolates were resistant to ciprofloxacin and levofloxacin; respectively.…”

“…Notably, in our study the percent of exoU + /exoS + isolates were relatively high (20.6%) compared to other studies. Even though exoS and exoU genes are located in different location in P. aeruginosa genome, the simultaneous carriage of both genes less have been reported (23). A possible explanation is that both of the ExoU and ExoS proteins are important for P. aeruginosa survival.…”

“…A possible explanation is that both of the ExoU and ExoS proteins are important for P. aeruginosa survival. However each of them shows different activity in a specific environment and situation (23,24). Therefore, the exotoxins genotype of a clinical isolate may be indicated of particular environmental reservoir of that isolate.…”

Molecular Detection of the VirulentExoUGenotype ofPseudomonas aeruginosaIsolated from Infected Surgical Incisions

“…Proper surveillance for the emergence of the cytotoxic and MDR P. aeruginosa isolates would be essential for preventing serious P. aeruginosa outbreaks in surgical wards. In fact, further studies are needed to evaluate the clinical outcome of surgical site infections with isolates showing cytotoxic and MDR traits [41].…”

Divergence of a strain of Pseudomonas aeruginosa during an outbreak of ovine mastitis

“…MLST analysis showed that PSE305 belonged to the subtype, ST-244. This subtype has been identified in a collection of human wound isolates from the Mediterranean, and in cases of bacteraemia in Asia (Maatallah et al, 2011;Woo et al, 2011). Hence, it is likely that the two isolates compared in this study are derived from the same outbreak.…”