Impact of heavy metals on the selective phenotypical markers of Pseudomonas aeruginosa

The aim of this study was to characterize the impact of heavy metals on phe notypical markers of Pseudomonas aeruginosa. Twenty-two isolates of P. aeru ginosa, either clinical (20) or secondary treated wastewater (2), were used to inoculate micro-ecosystems of sterile distilled water or secondary wast e effluent in the presence of subminimal inhibitory concentrations of a var iety of heavy metals commonly encountered in the aquatic naturally habitat (Ca2+, Co2+, Cr3+, Cu2+, Hg2+, Ni2+, Zn2+). Micro-ecosystems were exposed t o visible light at laboratory temperature and individual strains were reiso lated after a 1-, 3-, or 6-month period. The re-isolates (129) were charact erized using hierarchical classification analysis in order to define affini ties among variants of P. aeruginosa. Subsequently, discriminant analysis w as used to detect eventual relationships among the different phenotypical m arkers studied. Results of the hierarchical classification, based on qualit ative or quantitative approaches, showed clearly that incubation of P. aeru ginosa in the presence of heavy metals altered the studied phenotypical mar kers, namely serotype, phage type, MIC of metals, and pyocin type. Discrimi nant analysis showed that the studied phenotypical markers could be classif ied into four clusters: C1 (L1 and L2 phage types, Hg tolerance and/or resi stance, S2 serotype), C2 (P2 pyocin type, Cd tolerance and/or resistance, S 1 serotype), C3 (Co and Cr tolerance and/or resistance) and C4 (P1 pyocin t ype, Ni, Zn, and Cu tolerance and/or resistance).