Genotypic diversity and virulence parameters variation within samples of nosocomial populations of Pseudomonasaeruginosa

Abstract number: 1134_04_169

Fonseca A.P., Correia P., Fonseca A.F., Tenreiro R., Sousa J.C.

Objectives:  

The objective of this study was to evaluate the differences in genotypic diversity between sources and among several virulence parameters, namely adhesion to polystyrene, hexadecane and silicone, initial biofilm formation and motility. A total of 96 strains of P. aeruginosa collected at a Portuguese Central Hospital and isolated from 5 different sources were examined: Urine (U), Bronchial Secretion (BS), Catheter (C), Exudate (E) and Reference Strains (R).

Methods:  

A combination of two genomic typing systems, the minisatellite-primed PCR (MSP-PCR) and the enterobacterial repetitive consensus sequence PCR (ERIC-PCR), was used to discriminate the 96 strains. The data were analysed using BioNumerics software. Bacterial adhesion (2 h) and initial biofilm formation (6 h) were studied by growing bacteria in LB in a modified microtiter-plate assay. Strains were screened for their capacity to adhere to hydrophobic biomaterials such as silicone and hexadecane using a biphasic separation method. The opportunistic P.aeruginosa were also screened for their capacity to swim (flagella) and twitch (pili). All tests were run in triplicate. For quantitative comparisons of genotypic diversity among samples, Stoddart's and Simpson's indices were used.

Results:  

Our results show that genotypic groups including several sources and clusters of source-specific genotypes are dispersed throughout the phenogram, regardless of isolation source. In 96 strains, 59 (61%) correspond to genotypic groups that include strains from all 5 sources; the other genotype groups were shared by strains from 2 to 4 of the 5 sources and accounted for a total of 28 isolates (29%); the remaining 9 isolates (9%) were included in genotypes with only one source (BS or U or R). Both diversity measures yielded similar results; the population from R and BS had the highest diversity. In general, all the pairwise differences in genotypic diversity between sources were not statistically significant (P > 0.05), except the pairwise difference between BS and C sources. None of the pairwise differences in all the parameters tested between sources were statistically significant (P > 0.05).

Conclusions:  

There were no significant differences in genotypic diversity among samples from the 5 different sources. Strains from each of the 5 sources exhibited wide variations in the virulence parameters tested.

Acknowledgments:  

This study was supported by a research grant from Fundação Calouste Gulbenkian.