Cytotoxic clinical isolates of Pseudomonas aeruginosa identified during the Steroids for Corneal Ulcers Trial show elevated resistance to fluoroquinolones.
BACKGROUND
To determine the relationship between type three secretion genotype and fluoroquinolone resistance for P. aeruginosa strains isolated from microbial keratitis during the Steroids for Corneal Ulcers Trial (SCUT) and for two laboratory strains, PA103 and PAO1.


METHODS
Confirmed P. aeruginosa isolates from the SCUT were divided into exoU(+) or exoU(-). The exoU(+) strains contained the gene encoding ExoU, a powerful phospholipase toxin delivered into host cells by the type three secretion system. Isolates were then assessed for susceptibility to fluoroquinolone, cephalosporin, and aminoglycoside antibiotics using disk diffusion assays. Etest was used to determine the MIC of moxifloxacin and other fluoroquinolones. Laboratory isolates in which the exoU gene was added or deleted were also tested.


RESULTS
A significantly higher proportion of exoU(+) strains were resistant to ciprofloxacin (p = 0.001), gatifloxacin (p = 0.003), and ofloxacin (p = 0.002) compared to exoU(-) isolates. There was no significant difference between exoU(+) or exoU(-) negative isolates with respect to susceptibility to other antibiotics except gentamicin. Infections involving resistant exoU(+) strains trended towards worse clinical outcome. Deletion or acquisition of exoU in laboratory isolates did not affect fluoroquinolone susceptibility.


CONCLUSIONS
Fluoroquinolone susceptibility of P. aeruginosa isolated from the SCUT is consistent with previous studies showing elevated resistance involving exoU encoding (cytotoxic) strains, and suggest worse clinical outcome from infections involving resistant isolates. Determination of exoU expression in clinical isolates of P. aeruginosa may be helpful in directing clinical management of patients with microbial keratitis.
Durga S
DS
Borkar
Nisha R
NR
Acharya
Chelsia
C
Leong
Prajna
P
Lalitha
Muthiah
M
Srinivasan
Catherine E
CE
Oldenburg
Vicky
V
Cevallos
Thomas M
TM
Lietman
David J
DJ
Evans
School of Optometry, University of California, 688 Minor Hall, 94720 Berkeley, CA, USA. fleiszig@berkeley.edu.
Suzanne M J
SM
Fleiszig
D000368:Aged; D003315:Cornea / Q000382:microbiology* / Q000473:pathology; D003320:Corneal Ulcer / Q000188:drug therapy / Q000382:microbiology* / Q000473:pathology; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial; D015818:Eye Infections, Bacterial / Q000188:drug therapy / Q000382:microbiology* / Q000473:pathology; D005260:Female; D024841:Fluoroquinolones / Q000627:therapeutic use*; D005838:Genotype; D005938:Glucocorticoids / Q000627:therapeutic use*; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D011379:Prognosis; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000302:isolation & purification / Q000472:pathogenicity*; D014792:Visual Acuity
D004269:DNA, Bacterial; D024841:Fluoroquinolones; D005938:Glucocorticoids