Gram-Negative Bacterial Keratitis: A 15-Year Review of Clinical Aspects

PURPOSE: In this study we investigated pathogenic organisms, antibiotic susceptibility, and clinical characteristics of patients with Gram-negative bacterial keratitis and elucidated risk factors for poor visual outcomes. METHODS: The authors performed a retrospective chart review of 161 eyes (169 isolates) with Gram-negative bacterial keratitis between January 1998 and December 2012 at Yeungnam University Hospital. The study was divided into 5 periods for analysis of the bacteriological profiles and in vitro antibiotic sensitivity. The epidemiological and clinical characteristics were compared according to 3 groups (Pseudomonas species, Enterobacter species, and Serratia marcescens). Additionally, logistic regression analysis was performed to determine the risk factors. RESULTS: The prevalence of Gram-negative organisms increased from 34.7 to 73.2% between the 1st and 5th periods (p < 0.001). Pseudomonas spp. was the most commonly isolated organism (55 eyes, 32.5%) over the total period, followed by Enterobacter spp. (41 eyes, 24.3%) and Serratia marcescens (33 eyes, 19.5%). The effective antibiotics against Gram-negative bacterial pathogens isolated from culture were cefepime (94.5%), levofloxacin (93.4%), ciprofloxacin (93.0%), and amikacin (92.3%). The incidence was higher in the elderly over 60 years of age and in early adulthood patients in their 20s and 30s. The frequent predisposing factors were contact lens wearing and corneal trauma. S. marcescens had the shortest corneal epithelium healing time (p = 0.012) and the most favorable visual outcome after treatment (p = 0.004) compared with the other species. Risk factors for poor visual outcomes included a best corrected visual acuity less than 0.1 at initial evaluation (p < 0.001) and central corneal lesion (p = 0.027). CONCLUSIONS: Gram-negative bacterial keratitis tended to increase and Pseudomonas spp. was the most common isolate. The clinical prognosis was most favorable in S. marcescens. Early diagnosis of Gram-negative bacterial keratitis and appropriate antibiotic selection including cefepime, quinolone, or amikacin are recommended.

Uptake of volatile n-alkanes by Pseudomonas PG-I.

Using a bacterial species Pseudomonas PG-1, evidence has been obtained which indicates that uptake of n-pentane to n-octane by microbial cells takes place primarily from the gas phase either directly or via the aqueous phase. Specific growth rate increased along with the increase in substrate concentration but above the alkane concentration of 0·3% by volume, specific growth rate decreased indicating substrate inhibition of growth. In the case of less volatile alkanes, n-nonane and n-decane, substrate transfer is predominantly through substrate solubilization system elaborated by the cells. EDTA, a strong inhibitor of hydrocarbon solubilization by the cells, inhibited growth on these two alkanes but had negligible effect on growth on n-pentane to n-octane.