Heterogeneity among infecting strains of Pseudomonas aeruginosa in diversedepartments of a large Tunisian hospital

Clinical isolates of Pseudomonas aeruginosa were obtained during a half-yea r screening period of five different nards of the La Rabta Hospital (Tunis) . Distinct clinical isolates (N=82) were obtained from patients, 40 (48%) o f which originated from the Department of Otolaryngology. In order to defin e the local epidemiology of this opportunistic organism, all strains were s erotyped, analysed for pyocin production and genetically characterized with the help of pulsed-field gel electrophoresis (PFGE). The data show that, d espite the frequent occurrence of identical serotypes, most of the isolates represent unique pyocin types (N=53) and genotypes (N=64). A combination o f the pyocin and PFGE data showed that nearly all strains were of unique ty pes, except for two pairs of strains. A limited number of strain clusters n as observed on the basis of DNA typing data alone. This involved eight geno types, some of which were clustered with respect to clinical environment or time. Genotype 22 occurred most frequently (6/83, 7%) and independently of time and locale, indicating that it ma? represent either a clonal type con stituting a major fraction of all P. aeruginosa isolates in the region or a more prevalent organism. Despite a relatively-high incidence of P. aerugin osa infections, the polyclonality of these strains shows that, in La Rabta Hospital. pseudomonal infections are not primarily due to excessive spread of a single bacterial genotype. (C) 2001 The Hospital Infection Society.