Genome Diversity of Pseudomonas aeruginosa Isolates from Cystic Fibrosis Patients and the Hospital Environment

Abstract

Pseudomonas aeruginosa is a gram-negative rod that is ubiquitous in nature. P. aeruginosa is also the quintessential opportunistic pathogen, causing a wide variety of infections in compromised hosts. In cystic fibrosis patients, P. aeruginosa is the leading cause of death. In this study, the evolutionary genetic relationships among 17 P. aeruginosa isolates were examined by comparative sequence analysis of the housekeeping gene encoding malate dehydrogenase and the chaperone groEL. The P. aeruginosa isolates examined included the sequenced strain PAO1, 11 strains recovered from cystic fibrosis patients in Ireland, 4 environmental isolates recovered from a hospital environment, and 1 isolate recovered from a plant rhizosphere. Phylogenetically, clinical and environmental isolates clustered together with one another on the mdh gene tree. At the groEL locus, among the 17 isolates examined, only two polymorphic sites were observed, highlighting the close genetic relationship between isolates from these different environments. Phenotypic analysis of 12 traits among our isolates, however, found that only clinical isolates produced phenazines and elastase. Furthermore, molecular analysis of the distribution of 15 regions associated with virulence showed that two of the environmental isolates examined lacked the majority of regions. Among the clinical isolates examined, the 15 virulence regions were variably present. The distribution of two prophages (Bacto1, Pf1) was also determined, with most isolates encoding both these regions. Of the four genomic islands (the flagellum island and PAGI-1, -2, and -3) examined, only two isolates contained the flagellum island, and PAGI-1, -2, and -3 were absent from all isolates tested. Our data demonstrate the significant role horizontal gene transfer and recombination, together with gene loss, play in the evolution of this important human pathogen.The remarkable ability of Pseudomonas aeruginosa to adapt and thrive in a wide variety of environments is due in part to its extensive genetic versatility, which contributes significantly to its potential as a pathogen. P. aeruginosa is an opportunistic pathogen that is a common cause of hospital-acquired infections, particularly infecting patients with predisposing factors, such as burn victims, immunocompromised hosts, or those with metabolic disorders. In cystic fibrosis (CF) patients, P. aeruginosa is believed to be a major contributory factor to chronic lung infections and is thought to form biofilms and to adhere to human mucin in the lower respiratory tract (46, 53). Once P. aeruginosa colonizes the CF patient's lung, it cannot be eradicated even by the most aggressive antibiotic therapy. It is likely that as part of colonization, invasion, and survival in the human host, P. aeruginosa utilizes a unique range of genes; however, the precise repertoire of virulence genes required is unclear.Several studies have examined the genetic diversity of P. aeruginosa isolates from CF patients (9,13,30,40,44,49). In these studies, it was deter...

Molecular Detection of the VirulentExoUGenotype ofPseudomonas aeruginosaIsolated from Infected Surgical Incisions

“…The low incidence of the multi-substrate protease (27%) in this study was in agreement with Finnan et al [33].…”

“…The frequency of the ExoU gene (18%) was similar to that obtained by Feltman et al [31] and Bradbury et al [32], however, it was relatively lower than that reported by Mitov et al [30] with a frequency of 30%. Moreover, the proportion of isolates (9%) having both genes was in agreement with Finnan et al [33] and Mitov et al [30], suggesting that the isolates with dual expression of both genes are increasing compared with earlier studies that showed a low number of such isolates (down to one isolate from a total of 115 isolates) [31]. ExoS is known to modify bacterial invasion while ExoU is recognized for inducing cytotoxicity and is more detrimental than ExoS toxin [31,34], thus, the presence of strains producing both toxins found in this study could indicate the emergence of highly virulent strains with mixed invasive-cytotoxic genotype.…”

Genotypic and Phenotypic Variation in Pseudomonas aeruginosa Reveals Signatures of Secondary Infection and Mutator Activity in Certain Cystic Fibrosis Patients with Chronic Lung Infections

“…Five PAO1 transcription factors were also absent, two having the lysR family signature (PA0207 and PA2220) and one, vqsM (PA2226), with 47% similarity to the essential quorum-sensing regulator OruR. As a group, therefore, all nine strains isolated from these two patients share attributes seen as characteristic of CRI in the cystic fibrosis lung (20,22,80): loss of certain genes whose products, by virtue of being secreted from or situated at the cell surface, offer targets for the immune system and loss of others whose products help mediate quorum sensing.…”

Filamentous Bacteriophage Produced by Pseudomonas aeruginosa Alters the Inflammatory Response and Promotes Noninvasive InfectionIn Vivo

“…When studied in vitro, some of the most highly transcribed genes in P. aeruginosa biofilms belong to a filamentous Pf1-like bacteriophage (Pf phage) (5,6). The Pf prophage is also prevalent among clinical P. aeruginosa isolates from people with CF (7)(8)(9)(10)(11)(12)(13), and approximately 10 7 Pf phage per ml has been detected in the sputum of people with CF, where they interact with host polymers, such as mucin, to increase viscosity (14). These observations suggest that Pf phage may play a role in infection pathogenesis.…”