The patterns of in vitro antimicrobial susceptibility and resistance of bacterial keratitis isolates in Glasgow, United Kingdom

Abstract

Trends in antibiotic sensitivity of pathogenic bacteria change with time and the emergence of resistance to commonly used antibiotics is not uncommon. The aim of this study is to identify the antibiotic susceptibility and resistance patterns in a tertiary referral centre that commonly manages corneal infections. This is a retrospective review of microbiology reports of corneal scrapes in a tertiary care hospital. There were 205 positive corneal scrapes (32 per cent) in 1995 to 1998 and 147 (28 per cent) in 2004 to 2007. There was increased incidence of Staphylococcus aureus (18 to 21 per cent) (p = 0.16), Moraxella catarrhalis (1.5 to 5 per cent) (p = 0.5), pseudomonas species (6 to 14.5 per cent) (p = 0.25) and non-lactose fermenting coliforms (1.5 to 7 per cent) (p = 0.5). In vitro resistance of gram-positive bacterial isolates to ciprofloxacin was increased from 5 to 7 per cent (p = 0.5). The in vitro susceptibility of gram-positive organisms to dual therapy with cefuroxime and gentamicin were 98 per cent in 1995 to 1998, and 94 per cent in 2004 to 2007 (p = 0.1). Pseudomonas species were 100 per cent susceptible to cefuroxime in the first period but developed 100 per cent resistance in the later period (p = 0.0002). However, the susceptibility of gram negative bacterial isolates to dual therapy with cefuroxime and gentamicin (p = 1) and monotherapy with ciprofloxacin (p = 1) was 100 per cent in both periods. The in vitro resistance to chloramphenicol to gram-positive organisms was reduced to 5 from 12 per cent (p = 0.19) but there was an increase in resistance of gram-negative organisms from 23 to 36 per cent (p = 0.3). Despite limitations, this study demonstrates that the fortified antibiotics such as 5% cefuroxime 1.5% gentamicin may be the appropriate choices for most episodes of bacterial keratitis, either as an initial therapy or after identification of in vitro susceptibility of bacterial isolates.