The metabolically versatile Gram-negative bacterium Pseudomonas aeruginosa inhabits terrestrial, aquatic, animal-, human-, and plant-host-associated environments and is an important causative agent of nosocomial infections, particularly in intensive-care units. The population genetics of P. aeruginosa was investigated by an approach that is generally applicable to the rapid, robust, and informative genotyping of bacteria. DNA, amplified from the bacterial colony by circles of multiplex primer extension, is hybridized onto a microarray to yield an electronically portable binary multimarker genotype that represents the core genome by single nucleotide polymorphisms and the accessory genome by markers of genomic islets and islands. The 240 typed P. aeruginosa strains of diverse habitats and geographic origin segregated into two large nonoverlapping clusters and 45 isolated clonal complexes with few or no partners. The majority of strains belonged to few dominant clones widespread in disease and environmental habitats. The most frequent genotype was represented by the sequenced strain PA14. Core and accessory genome were found to be nonrandomly assembled in P. aeruginosa. Individual clones preferred a specific repertoire of accessory segments. Even the most promiscuous genomic island, pKLC102, had integrated preferentially into a subset of clones. Moreover, some physically distant loci of the core genome, including oriC, showed nonrandom associations of genotypes, whereas other segments in between were freely recombining. Thus, the P. aeruginosa genome is made up of clone-typical segments in core and accessory genome and of blocks in the core with unrestricted gene flow in the population. bacterial evolution ͉ chip technology ͉ population genetics P seudomonas aeruginosa is a metabolically versatile Gramnegative bacterium, which inhabits terrestrial, aquatic, animal-, human-, and plant-host-associated environments (1). This opportunistic pathogen is the most dominant bacterium causing chronic infections in the cystic fibrosis (CF) lung (2) and has emerged as an important causative agent of nosocomial infections, particularly in intensive-care units (3).The P. aeruginosa genome is a mosaic of a conserved core and variable accessory segments (4). The core genome is characterized by a conserved synteny of genes, a low average nucleotide divergence of 0.5%, and multiple alleles at a few loci that are subject to diversifying selection (4-6). The accessory genome consists of a variable set of genomic islets and genomic islands, most of which belong to an ancient tRNA-integrated island type (4, 7-11). Genome size ranges from 5.2 to 7 Mbp in the P. aeruginosa population (4).Typing informative traits allows identification of bacterial isolates to the strain level and provides basic information about the evolutionary biology, population biology, taxonomy, ecology, and genetics of bacteria. Typically, strains of bacteria, including P. aeruginosa, have been differentiated on the basis of specific phenotypic traits or anonymous ...

Pseudomonas aeruginosa has a wide ecological distribution that includes natural habitats and clinical settings. To analyze the population structure and distribution of P. aeruginosa, a collection of 111 isolates of diverse habitats and geographical origin, most of which contained a genome with a different SpeI macrorestriction profile, was typed by restriction fragment length polymorphism based on 14 single nucleotide polymorphisms (SNPs) located at seven conserved loci of the core genome (oriC, oprL, fliC, alkB2, citS, oprI, and ampC). The combination of these SNPs plus the type of fliC present (a or b) allowed the assignment of a genetic fingerprint to each strain, thus providing a simple tool for the discrimination of P. aeruginosa strains. Thirteen of the 91 identified SNP genotypes were found in two or more strains. In several cases, strains sharing their SNP genotype had different SpeI macrorestriction profiles. The highly virulent CHA strain shared its SNP genotype with other strains that had different SpeI genotypes and which had been isolated from nonclinical habitats. The reference strain PAO1 also shared its SNP genotype with other strains that had different SpeI genotypes. The P. aeruginosa chromosome contains a conserved core genome and variable amounts of accessory DNA segments (genomic islands and islets) that can be horizontally transferred among strains. The fact that some SNP genotypes were overrepresented in the P. aeruginosa population studied and that several strains sharing an SNP genotype had different SpeI macrorestriction profiles supports the idea that changes occur at a higher rate in the accessory DNA segments than in the conserved core genome.

Abstractlung transplant recipients in our clinic infected with Pseudomonas aeruginosa acquired new Background -The source of airway colonisation with Pseudomonas aeruginosa strains or retained their strains which they harboured before lung transplantation. Methods -Seventy four P aeruginosa isol-were different from those carried before the H von der HardtPreoperative isolates were retrieved from (Thorax 1997;52:318-321) sputum samples and postoperative isolates