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Relationship of Virulence Factors and Clinical Features in Keratitis Caused by Pseudomonas Aeruginosa

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Relationship of Virulence Factors and Clinical Features in Keratitis Caused by Pseudomonas Aeruginosa Immunology and Microbiology Relationship of Virulence Factors and Clinical Features in Keratitis Caused by Pseudomonas aeruginosa Naoko Oka,1 Takashi Suzuki,1 Eri Ishikawa,1 Satoshi Yamaguchi,1,2 Naoki Hayashi,3 Naomasa Gotoh,3 and Yuichi Ohashi1 1Department of Ophthalmology, Ehime University Graduate School of Medicine, Toon, Ehime, Japan 2ROHTO Pharmaceutical Co., Ltd., Osaka, Japan 3Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, Yamashina, Kyoto, Japan Correspondence: Takashi Suzuki, PURPOSE. To examine bacterial virulence factors in Pseudomonas aeruginosa isolates from Department of Ophthalmology, contact lens (CL) wearers and non–CL wearers with P. aeruginosa keratitis, and to investigate Ehime University Graduate School of relationships between virulence factors and clinical features of keratitis. Medicine, Shitsukawa, Toon, Ehime 791-0295, Japan; METHODS. The study involved 25 subjects including 18 CL and 7 non–CL-related P. aeruginosa [email protected] keratitis patients. Slit-lamp photographs of all subjects were captured, and the focus Submitted: June 24, 2015 occupancy ratio (FOR) was defined as the total focus area/entire cornea area, using image Accepted: September 22, 2015 processing software. Twenty-five clinical P. aeruginosa isolates from keratitis were assessed for protease production, elastase production, biofilm formation, bacterial swimming and Citation: Oka N, Suzuki T, Ishikawa E, swarming motility, cell surface hydrophobicity, and genes encoding the type III secretion et al. Relationship of virulence factors and clinical features in keratitis caused system (TTSS) effectors (ExoU and ExoS). by Pseudomonas aeruginosa. Invest RESULTS. Ring abscess was found in 9 of 18 CL-related P. aeruginosa keratitis cases (CL[þ] Ophthalmol Vis Sci. 2015;56:6892– ring[þ] group) but not in another 9 cases (CL[þ] ring[À] group). Expression or prevalence of 6898. DOI:10.1167/iovs.15-17556 virulence factors in P. aeruginosa isolates from the CL(þ) ring(þ) group, CL(þ) ring(À) group, and CL(À) group were compared. The FOR for CL(þ) ring(þ) or CL(À) was higher than for CL(þ) ring(À)(P < 0.05 and P < 0.01, respectively). The rate of positive swimming motility for CL(þ) ring(þ) or CL(À) was higher than for CL(þ) ring(À)(P < 0.05), whereas the rate of positive swarming motility for CL(þ) ring(þ) was higher than for CL(þ) ring(À)or CL(À)(P < 0.05). Prevalence of an exoSþ/exoU-genotype for CL(þ) ring(þ) or CL(À) was higher than for CL(þ) ring(À)(P < 0.05). In the CL-related group, expression of elastase and swarming motility significantly correlated with FOR. CONCLUSIONS. Swimming motility, swarming motility, and TTSS ExoS could play a major role in the determination of clinical features of P. aeruginosa keratitis. Keywords: Pseudomonas aeruginosa, keratitis, virulence factors, protease, swarming motility eratitis caused by Pseudomonas aeruginosa can progress loproteases, inducing the destruction of corneal stroma.8 Along K rapidly with suppurative infiltration, and can lead to with these virulence factors, the Type III secretion system corneal perforation and melt, resulting in the loss of vision.1 (TTSS) is involved in the pathogenesis of keratitis.13–15 The Contact lens (CL) wearers are especially susceptible to TTSS transports toxins to host cells, and includes a needle-like development of P. aeruginosa keratitis. Ring abscess, which apparatus, effector proteins (ExoS and ExoU), and a pore- is a ring-shaped accumulation of polymorphonuclear leuko- forming protein. P. aeruginosa isolates contain two TTSS cytes surrounding a central corneal lesion, is a well-known genotypes that involve the exoS gene in invasive strains and the hallmark of P. aeruginosa keratitis.2,3 Along with ring abscess, exoU gene in cytotoxic strains.16 Moreover, P. aeruginosa– serrated or satellite lesions with keratitis are sometimes found associated cellular structures, such as the flagella,17,18 pili,19 in P. aeruginosa keratitis.4,5 Pseudomonas aeruginosa can and lipopolysaccharide,20 also have been studied. Flagella of P. show various clinical features, but little is known about factors aeruginosa assume a motility that is related to adhesion and that determine these clinical features. invasion in the corneal epithelium, and activation of the To understand the mechanism of pathogenesis in keratitis immune response.17,21 Specifically, the motility of flagella in caused by P. aeruginosa, the virulence factors as well as liquid media is known as swimming, and the motility of flagella extracellular products, including proteases,6–8 exotoxin A,9 and on semisolid surfaces is called swarming, which shows fractal- biofilms,10 have been investigated. Of these factors, proteases, like patterns of radiating tendril on 0.5% to 0.7% agar including metalloproteases such as alkaline protease, elastase A, plates.22–24 It is also thought that swarming motility is an and elastase B,11 are important in virulence. We recently important factor in the resistance to antibiotics and the survival reported that MucD protease inhibits neutrophil recruitment in of P. aeruginosa in tissues associated with biofilm formation.23 the cornea, and plays an important role in the pathogenesis of Few reports have focused on the associations between keratitis.12 Pseudomonas aeruginosa elastase activates metal- clinical features and virulence factors in human clinical cases. Copyright 2015 The Association for Research in Vision and Ophthalmology, Inc. iovs.arvojournals.org j ISSN: 1552-5783 6892 Downloaded from iovs.arvojournals.org on 09/28/2021 Virulence Factors in P. aeruginosa Keratitis IOVS j October 2015 j Vol. 56 j No. 11 j 6893 (http://imagej.nih.gov/ij/; provided in the public domain by the National Institutes of Health, Bethesda, MD, USA). The outlines of each focus and the entire cornea were manually traced, and the focus area and cornea area were measured using the application tool of the software. The focus occupancy ratio (FOR) of each keratitis case was defined as the total focus area/entire cornea area (Fig. 1).25 Informed consent was obtained from the patients after explanation of the nature and possible consequences of the study. This study was approved by the Ehime University Review Board and adhered to the tenets of the Declaration of Helsinki. Bacterial Strains Clinical isolates of P. aeruginosa obtained from keratitis cases were tested. Our institution has collected and stocked all organisms causing ocular infection, including keratitis and endophthalmitis, from 2003, and used the clinical isolates of P. aeruginosa from our collection. All strains were stored in Microbank (Pro-Lab Diagnostics, Ontario, Canada) at À808C. For investigation of virulence factors, strains were grown on brain heart infusion agar plates, and then cultured in 10 mL of Luria-Bertani (LB) broth and incubated at 378C for 18 hours, with shaking at 250 rpm. Cells were collected by centrifuga- tion and washed three times with PBS, and continuously used in each assay. Determination of Virulence Factors Proteolytic Activity. The modified azocasein assay to assess the proteolytic activity of P. aeruginosa was used as previously described.26 Overnight cultures (500 lL) were transferred to 1.5-mL tubes. The tubes were centrifuged at 7000g for 4 minutes, and the culture supernatants were collected, then 75 lL each supernatant and 125 lL 0.2% azocasein (Sigma-Aldrich Corp., St. Louis, MO, USA) were mixed in a 1.5-mL tube. After incubation in a 5% CO2 incubator at 378C for 30 minutes, 600 lL 10% trichloroacetic acid was added to the mixture, then incubated at room temperature for 30 minutes. The mixture was centrifuged at 10,000g for 10 FIGURE 1. Determination of the FOR. (A) Tracing the focus, (B) tracing the entire cornea; FOR was defined as A/B. minutes, and the supernatant was transferred to a new 1.5-mL tube. A solution of 10 M NaOH (375 lL) was added to each 1.5- mL tube, and 200 lL mixture was transferred to a 96-well The relationship between clinical features of P. aeruginosa microtiter plate (Costar, Corning, NY, USA). Absorption at 440 keratitis and virulence factors of keratitis isolates is therefore nm was measured in a microtiter plate reader (Immuno-Mini still not completely known. NJ-2300; Nalge Nunc International KK, Bunkyo-ku, Tokyo, In the present study, bacterial virulence factors in P. Japan). aeruginosa isolates from CL wearers or non–CL wearers with Elastase Activity. The elastase activity of P. aeruginosa P. a e r u g i n o s a keratitis were examined, to elucidate the culture fluids was quantitated by elastin Congo Red assays, as relationships between virulence factors and clinical features previously modified.27,28 Overnight cell cultures of 5-mL of keratitis. cultures in PTSB (5% peptone; Difco, Detroit, MI, USA) and 0.25% trypticase soy broth (Difco) were washed and resus- pended in 10 mL PTSB to an OD600 of 0.05. The cultures were MATERIALS AND METHODS incubated at 378C for 16 hours with rapid shaking, then the Patients and Clinical Features culture supernatants were filtered (0.45-lm filters; Millipore, Bedford, MA, USA). Elastin Congo Red (Sigma-Aldrich Corp.) The clinical records of P. aeruginosa keratitis cases seen at and 0.75 mL reaction buffer (0.05 M Tris, 0.5 mM CaCl2, pH Ehime University Hospital from 2003 to 2014 were retrospec- 7.5) was added to 0.25 mL culture filtrates, and the mixtures tively reviewed, and patients with culture-proven P. aerugino- were incubated at 378C for 24 hours with shaking. The sa keratitis were enrolled. The collected data included age, sex, reactions were centrifuged at 18,000g for 15 minutes, and the predisposing factors, and days visiting our hospital after absorbance of the supernatants was read at 495 nm using a complaining of symptoms. The size, shape, and location of microplate reader.
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