Antibiotic resistance profile in bacterial keratitis: a single-centre study

Given the change in resistance and susceptibility patterns with time, it is critical to closely examine the changes in the trends of antibiotic resistance in bacterial keratitis to tailor appropriate empirical therapy, reduce financial burden, and lessen ocular morbidity.1Ibrahim YW Boase DL Cree IA. Epidemiological characteristics, predisposing factors and microbiological profiles of infectious corneal ulcers: the Portsmouth corneal ulcer study.Br J Ophthalmol. 2009; 93: 1319-1324Crossref PubMed Scopus (92) Google Scholar This report aims to assess the patterns of antibiotic resistance and susceptibility within cultured bacterial corneal ulcers at a major tertiary care centre over a 13-year period. This was a retrospective study on bacterial keratitis cases from 2007 to 2019 at King Saud University, Riyadh, Saudi Arabia. Corneal scraping using Kimura spatulas was performed in all patients, and cultures were plated on blood, chocolate, Sabouraud dextrose agar, and thioglycolate broth. Plates were checked daily for a total of 7 days. An automated system Vitek 2 and Vitek AST 580 Card (BioMerieux Inc, Durham, NC) was used to determine susceptibilities and resistance. Patients with negative cultures were excluded from the study. Interpretation of the results was done according to the National Committee for Clinical Laboratory Standards. Antibiotic resistance data were thoroughly reviewed from 2007 to 2019. Of the 162 patients included, 69 (42.6%) were male, and 93 (57.4%) were female. Table 1 describes the susceptibility rates for different gram-positive organisms during the study period.Table 1Antibiotic sensitivities of gram-positive organisms.OrganismAmoxicillin–clavulanic acidAmpicillinCeftriaxoneErythromycinVancomycinStaphylococcus aureus23/23 (100.0%)4/0 (100.0%)4/6 (66.7%)12/19 (63.2%)19/20 (95.0%)CoNS37/39 (94.9%)2/9 (22.7%)2/4 (50.0%)8/9 (88.9%)27/29 (93.1%)Streptococcus pneumonia31/31 (100.0%)11/14 (78.6%)21/21 (100.0%)12/16 (75.0%)19/19 (100.0%)Other streptococci12/12 (100.0%)1/2 (50.0%)7/7 (100.0%)1/2 (50.0%)5/6 (83.3%)CiprofloxacinLevofloxacinTMP-SMXOfloxacinStaphylococcus aureus—23/23 (100.0%)23/23 (100.0%)5/7 (71.4%)CoNS3/4 (75.0%)37/39 (94.9%)37/39 (94.9%)11/12 (91.7%)Streptococcus pneumonia5/5 (100.0%)31/31 (100.0%)31/31 (100.0%)2/2 (100.0%)Other streptococci2/2 (100.0%)12/12 (100.0%)12/12 (100.0%)2/2 (100.0%)CoNS, coagulase-negative staphylococci; TMP-SMX, trimethoprim-sulfamethoxazole Open table in a new tab CoNS, coagulase-negative staphylococci; TMP-SMX, trimethoprim-sulfamethoxazole The most common organisms were coagulase-negative staphylococci (CoNS; n = 39), Pseudomonas (n = 33), and Streptococcus pneumoniae (n = 31). In diabetic patients, the most common organisms were CoNS (19 of 64), S. pneumoniae (17 of 64), and Moraxella (8 of 64). In contrast, Pseudomonas (27 of 40), CoNS (5 of 40), and Staphylococcus aureus (4 of 40) were the most common in contact lens wearers. Of the 23 S. aureus isolates, 5 were found to be methicillin resistant S. aureus (MRSA; 21.7%). CoNS demonstrated high sensitivity to vancomycin (93.1%) and amoxicillin–clavulanic acid (94.9%) and variable sensitivity to fluoroquinolones (75.0%–94.9%). Fluoroquinolones provided excellent coverage against other tested streptococci (100%). Table 2 demonstrates gram-negative bacteria susceptibilities to different antibiotics. Pseudomonas (n = 33) was the most common isolated gram-negative organism. Pseudomonas had excellent susceptibility to levofloxacin and ciprofloxacin (100%) but lower susceptibility to ofloxacin (62.5%). Moraxella exhibited 100% susceptibility to tested fluoroquinolones and cephalosporins.Table 2Antibiotic sensitivities of gram-negative organisms.OrganismClindamycinLevofloxacinGentamicinTetracyclineTMP-SMXPseudomonas—33/33 (100.0%)30/32 (93.8%)33/33 (100.0%)33/33 (100.0%)Moraxella3/3 (100.0%)15/15 (100.0%)6/6 (100.0%)15/15 (100.0%)15/15 (100.0%)Other gram-negatives1/1 (100.0%)7/7 (100.0%)5/7 (71.4%)7/7 (100.0%)7/7 (100.0%)AmpicillinCeftriaxoneCeftazidimeCiprofloxacinOfloxacinPseudomonas0/3 (0.0%)12/15 (80.0%)24/31 (77.4%)18/18 (100.0%)5/8 (62.5%)Moraxella4/5 (80.0%)7/7 (100.0%)9/9 (100.0%)6/6 (100.0%)2/2 (100.0%)Other gram-negatives2/3 (66.7%)2/5 (40.0%)4/4 (100.0%)3/3 (100.0%)0/3 (0.0%)TMP-SMX, trimethoprim-sulfamethoxazole Open table in a new tab TMP-SMX, trimethoprim-sulfamethoxazole This study showed an excellent susceptibility profile of both gram-positive and gram-negative bacteria to fluoroquinolones and trimethoprim-sulfamethoxazole. The overall susceptibility pattern was higher in gram-negative than gram-positive organisms. Fluoroquinolones, except ofloxacin, were generally effective agents against gram-positive cocci and gram-negative bacilli. Gram-positive bacteria susceptibility to cephalosporins in our sample was not as high as other studies.2Zhang Z Cao K Liu J Wei Z Xu X Liang Q. Pathogens and antibiotic susceptibilities of global bacterial keratitis: a meta-analysis.Antibiotics (Basel). 2022; 11: 238Crossref Scopus (5) Google Scholar The data also demonstrated the presence of resistant isolates to various antibiotics, notably vancomycin. Gram-negative organisms, namely Pseudomonas and Moraxella, were found to be pan-sensitive to fluoroquinolones (ciprofloxacin and levofloxacin), tetracycline, and trimethoprim-sulfamethoxazole. Similarly, Pseudomonas displayed excellent sensitivity to moxifloxacin and ciprofloxacin in San Francisco.3Peng MY Cevallos V McLeod SD Lietman TM Rose-Nussbaumer J. Bacterial keratitis: isolated organisms and antibiotic resistance patterns in San Francisco.Cornea. 2018; 37: 84-87Crossref PubMed Scopus (67) Google Scholar Pseudomonas also had 100% sensitivity to ciprofloxacin and norfloxacin in Mexico during 2007–2011.4Hernandez-Camarena JC Graue-Hernandez EO Ortiz-Casas M et al.Trends in microbiological and antibiotic sensitivity patterns in infectious keratitis: 10-year experience in Mexico City.Cornea. 2015; 34: 778-785Crossref PubMed Scopus (66) Google Scholar We also found Pseudomonas to have some resistance to commonly used agents such as ceftazidime, ofloxacin, and gentamycin in variable degrees. In other local studies, it was shown that Pseudomonas had a lower resistance to ceftazidime—7.6% and 5.6% as reported by Almizel et al. and Al-Dhaheri et al, respectively.5Almizel A Alsuhaibani FA Alkaff AM Alsaleh AS SM Al-Mansouri Bacterial profile and antibiotic susceptibility pattern of bacterial keratitis at a tertiary hospital in Riyadh.Clin Ophthalmol. 2019; 13: 2547-2552Crossref PubMed Scopus (5) Google Scholar,6Al-Dhaheri H Al-Tamimi M Khandekar R Khan M Stones D Ocular pathogens and antibiotic sensitivity in bacterial keratitis isolates at King Khaled Eye Specialist Hospital, 2011 to 2014.Cornea. 2016; 35: 789-794Crossref PubMed Scopus (25) Google Scholar This study provides a retrospective review of antibiotic susceptibility among bacterial keratitis cases. Remarkable sensitive rates were shown with levofloxacin and trimethoprim-sulfamethoxazole among gram-positive and gram-negative organisms. A low ofloxacin susceptibility rate was observed with S. aureus and Pseudomonas isolates. In contrast to other local studies, vancomycin resistance in bacterial keratitis also was demonstrated. Topical antibiotic treatment and prophylaxis strategies should be guided by local antibiotic resistance patterns. The authors have no proprietary or commercial interest in any materials discussed in this letter.