Detection of virulence factors in Pseudomonas aeruginosa strains isolated from contact lens-associated corneal ulcers.
OBJECTIVE
In microbial keratitis associated with contact lens use, Pseudomonas is the most common etiologic agent. The purpose of this study was to report on the microbiological findings of 8 P. aeruginosa strains isolated from contact lens-associated corneal ulcers.


METHODS
Scrapings from contact lens-related corneal ulcers were inoculated for culture. Identification and antibiotic susceptibility testing were performed by using the Vitek system (bioMérieux). The Pseudomonas' ability to form biofilm; produce gelatinase, elastase, and alkaline protease; and adhere to and invade human corneal epithelial cells was studied. Polymerase chain reaction with enterobacterial repetitive intergenic consensus primers (ERIC-PCR) was used to establish clonal relationship between the different isolates.


RESULTS
All the strains showed multiple antibiotic resistance (resistance to 4 or more antibiotics), but all were susceptible to aminoglycosides and fluoroquinolones. Biofilm production was weak in 5 cases and absent in the remaining 3 cases. All isolates were able to produce alkaline protease and gelatinase but not elastase. Adherence to human corneal epithelial cells was poor (0-15 bacteria/cell) in 5 cases and medium (16-60 bacteria/cell) in 3 cases. Five isolates were found to be efficient invaders (>1000 CFU/mL). ERIC-PCR showed 8 different genetic patterns.


CONCLUSIONS
Because multiresistant Pseudomonas isolates are common, we recommend antibiotic susceptibility testing in all cases of Pseudomonas keratitis so that, if there is no response to initial empiric treatment, antibiotics can be modified according to susceptibility results. The ability to produce alkaline protease and gelatinase and invade the corneal epithelium may play a major role in the pathogenesis of contact lens-related P. aeruginosa keratitis. Also, ERIC-PCR seems to be an inexpensive, fast, reproducible, and discriminatory DNA typing tool for effective epidemiologic surveillance of P. aeruginosa isolates potentially transmissible between patients with ocular infections.
Pinna
Antonio
A
Institute of Ophthalmology, Section of Experimental and Clinical Microbiology, University of Sassari, Sassari, Italy. apinna@uniss.it
Usai
Donatella
D
Sechi
Leonardo A
LA
Molicotti
Paola
P
Zanetti
Stefania
S
Carta
Arturo
A
D000293:Adolescent; D000328:Adult; D001422:Bacterial Adhesion / Q000502:physiology; D001426:Bacterial Proteins / Q000378:metabolism; D015373:Bacterial Typing Techniques; D018441:Biofilms; D015169:Colony Count, Microbial; D003261:Contact Lenses / Q000382:microbiology*; D003320:Corneal Ulcer / Q000382:microbiology*; D024881:Drug Resistance, Bacterial; D024901:Drug Resistance, Multiple, Bacterial; D010450:Endopeptidases / Q000378:metabolism; D015818:Eye Infections, Bacterial / Q000382:microbiology*; D005260:Female; D018093:Gelatinases / Q000378:metabolism; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D010196:Pancreatic Elastase / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011552:Pseudomonas Infections / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000145:classification / Q000302:isolation & purification / Q000502:physiology*; D014774:Virulence; D037521:Virulence Factors / Q000378:metabolism*
D001426:Bacterial Proteins; D037521:Virulence Factors; D010450:Endopeptidases; D010196:Pancreatic Elastase; D018093:Gelatinases; C087822:alkaline protease