Abstract
P. aeruginosa is the most common Gram-negative organism causing bacterial keratitis. Pseudomonas utilizes various virulence mechanisms to adhere and colonize in the host tissue. In the present study, we examined virulence factors associated with thirty-four clinical P. aeruginosa isolates collected from keratitis patients seeking care at L V Prasad Eye Institute, Hyderabad. The virulence-associated genes in all the isolates were genotyped and characteristics such as antibiotic susceptibility, biofilm formation, swarming motility, pyoverdine production and cell cytotoxicity were analyzed. All the isolates showed the presence of genes related to biofilm formation, alkaline proteases and elastases; however, there was a difference in the presence of genes related to the type III secretion system (T3SS). A higher prevalence of exoU+ genotype was noted in the drug-resistant isolates. All the isolates were capable of forming biofilms and more than 70% of the isolates showed good swarming motility. Pyoverdine production was not associated with the T3SS genotype. In the cytotoxicity assay, the presence of exoS, exoU or both resulted in higher cytotoxicity compared to the absence of both the genes. Overall, our results suggest that the T3SS profile is a good indicator of P. aeruginosa virulence characteristics and the isolates lacking the effector genes may have evolved alternate mechanisms of colonization in the host.
Highlights
P. aeruginosa, a Gram-negative bacterium, is ubiquitous in nature and a major opportunistic human pathogen
alkaline protease (AprA) has been shown to impede bacterial clearance by host cells by preventing complement mediated phagocytosis, LasB degrades mucins and surfactant proteins that aids in bacterial clearance [17,18]
Subedi et al reported that levofloxacin, ciprofloxacin and amikacin were the most effective drugs for ocular infections [23]. They found that the antibiotic resistance rates in ocular isolates have been stable [24] a recent report from Das et al found a significant decrease in susceptibility in Pseudomonas spp. isolated from keratitis patients to a fourth generation fluoroquinolone, moxifloxacin [25], suggesting a rise in antibiotic resistance in Pseudomonas spp
Summary
P. aeruginosa, a Gram-negative bacterium, is ubiquitous in nature and a major opportunistic human pathogen. P. aeruginosa causes acute or chronic infections in patients with cystic fibrosis, cancer or extensive burns [6] It has a repertoire of virulence factors such as presence of flagellin and type IV pili along with secreted exotoxins, proteases and elastases. The T3SS regulon consists of five operons including pscL and pscU that encodes components of secretion machinery [11] Another virulence associated factor is the swarming ability which is attributed to its rotating polar flagellum. Pyoverdine, a siderophore produced by Pseudomonas spp., is known to contribute to its virulence This plays an important role in chelating iron from the host or the environment and imparts a green fluorescence [22]. They found that the antibiotic resistance rates in ocular isolates have been stable [24] a recent report from Das et al found a significant decrease in susceptibility in Pseudomonas spp. isolated from keratitis patients to a fourth generation fluoroquinolone, moxifloxacin [25], suggesting a rise in antibiotic resistance in Pseudomonas spp
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