Genetic Characterization Indicates that a Specific Subpopulation of Pseudomonas aeruginosa Is Associated with Keratitis Infections

Abstract

Pseudomonas aeruginosa is a common opportunistic bacterial pathogen that causes a variety of infections in humans. Populations of P. aeruginosa are dominated by common clones that can be isolated from diverse clinical and environmental sources. To determine whether specific clones are associated with corneal infection, we used a portable genotyping microarray system to analyze a set of 63 P. aeruginosa isolates from patients with corneal ulcers (keratitis). We then used population analysis to compare the keratitis isolates to a wider collection of P. aeruginosa from various nonocular sources. We identified various markers in a subpopulation of P. aeruginosa associated with keratitis that were in strong disequilibrium with the wider P. aeruginosa population, including oriC, exoU, katN, unmodified flagellin, and the carriage of common genomic islands. The genome sequencing of a keratitis isolate (39016; representing the dominant serotype O11), which was associated with a prolonged clinical healing time, revealed several genomic islands and prophages within the accessory genome. The PCR amplification screening of all 63 keratitis isolates, however, provided little evidence for the shared carriage of specific prophages or genomic islands between serotypes. P. aeruginosa twitching motility, due to type IV pili, is implicated in corneal virulence. We demonstrated that 46% of the O11 keratitis isolates, including 39016, carry a distinctive pilA, encoding the pilin of type IV pili. Thus, the keratitis isolates were associated with specific characteristics, indicating that a subpopulation of P. aeruginosa is adapted to cause corneal infection.Pseudomonas aeruginosa is a common infective cause of corneal ulceration (bacterial keratitis) (14,32,54). P. aeruginosa keratitis is frequently associated with contact lens wear (54), because hypoxia and trauma from the contact lens allows bacterial adhesion, and as the bacterium is a common contaminant of moist areas such as a contact lens case, the exposure of the ocular surface to the bacterium can easily occur. Subsequently, a combination of P. aeruginosa virulence factors and damage to host ocular defenses allows infection to develop. The host immune and inflammatory responses then contribute both to the elimination of the bacteria and to associated damage to tissues (14). P. aeruginosa is an opportunistic pathogen that is capable of causing a range of infections (16, 38), and it carries an impressive array of virulence factors. The virulence factors implicated in keratitis include twitching motility associated with type IV pili (63), flagella (13), a type III secretion system (22), and quorum-sensing regulated exoproducts (58).The genome of P. aeruginosa consists of core genes (approximately 90%) and accessory genes (approximately 10%) (40).The core genome, carried by all strains of P. aeruginosa, includes many of the recognized virulence genes (61). However, some strain-variable virulence-associated genes also occur, often clustered within genomic islands (3,33,47,50,60,61)....

Complete Sequence of pOZ176, a 500-Kilobase IncP-2 Plasmid Encoding IMP-9-Mediated Carbapenem Resistance, from Outbreak Isolate Pseudomonas aeruginosa 96

“…3. Other close homologs include RepAs of genomic islands of P. aeruginosa PACS171b, 39016, PA2192, and PA7 (38,40,43,44).…”

Characterization of protease IV expression in Pseudomonas aeruginosa clinical isolates

“…These mobile genetic elements can contribute to virulence in a combinatorial manner with other accessory genome 'modules', resulting in strain-specific virulence (Lee et al, 2006). There are 45 specific genome modules that tend to be associated in MK strains (Stewart et al, 2011). The similarity of the piv gene sequence of strain Pear17 to those of strains possessing the exoU gene rather than the exoS gene, corresponding to increased virulence of this low-protease-containing strain, suggests that the piv gene might be part of a genomic island containing other virulence factors that combine with genome modules within this strain to increase virulence.…”

H-NS Plays a Role in Expression of Acinetobacter baumannii Virulence Features

“…Expression of these phenotypes varies between strains and to a degree between clonal groups, such as the conserved expression of twitching motility by isolates in the international clone I group (3). Although motility has been associated with increased biofilm formation and virulence in other bacteria, such as Pseudomonas aeruginosa and Dichelobacter nodosus (13)(14)(15)(16)(17)(18), the significance of motility in the virulence potential of A. baumannii remains to be confirmed.…”