Bacterial isolates in microbial keratitis: Three-year trend analysis from North India.

Sir,

We read with great interest the article titled “Types of organisms and in-vitro susceptibility of bacterial isolates from patients with microbial keratitis: A trend analysis of 8 years” by Das et al.[1] As a tertiary eye care provider and one of the biggest cornea departments in north India, we congratulate the authors for their brilliant work, would like to use this opportunity to reflect upon, and compare the microbial profile and antibiotic sensitivity seen in our practice. We agree with the authors that local epidemiological studies are required to provide evidence-based management of microbial keratitis,[1] and hence, wanted to add our data from north India to their study, to give a pan India perspective to our readers. What Das et al.[1] have demonstrated beautifully is that a good microbiological evaluation of infective keratitis is invaluable for correct diagnosis and appropriate therapy. This may also improve the chances of a successful clinical outcome. As a protocol, treatment should be initiated from smears, without waiting for the results of culture and sensitivity. Initial empirical therapy for bacterial keratitis should involve frequent instillation of broad-spectrum antibiotic drops. Appropriately, targeted antimicrobial therapy backed by microbiological investigations should be the first step, and if resistance to primary therapy is noted, microbiology results need to be reviewed and changed to appropriate antimicrobials.

At our institute, a retrospective audit was done to review collective microbiological profile and sensitivity pattern of all ocular bacterial infections of 3 years, from January 2015 to December 2017. A total of 1,169 cultures in this period grew bacteria. Gram-positive bacteria represented 76.6% (n = 895) of all isolates, whereas 274 (23.4%) cultures isolated gram-negative bacteria. The most common gram-positive bacteria isolated were coagulase-negative Staphylococcus (56.2%), whereas Pseudomonas spp. (64.2%) was the most commonly isolated gram-negative bacteria. Coagulase-negative staphylococcus in our study depicted variable sensitivity to cephalosporins (70.8%) and fluoroquinolones (92.6%). Consistent with the authors' findings,[1]100% of our Staphylococcus aureus cases were sensitive to vancomycin, with relatively poor sensitivity to ciprofloxacin (68.6%). Authors found that cephalosporins worked best for Streptococcus, however, in our group, maximum sensitivity was seen for moxifloxacin (92.9%). Third generation cephalosporins, vancomycin, and moxifloxacin had good sensitivity for all gram-positive bacteria. The various bacteria and their sensitivity patterns are depicted in Tables 1 and 2.

Table 1

Antibiotic Sensitivity Pattern for Isolated Gram-positive Bacteria

Organism	Number	Amikacin	Moxifloxacin	Ciprofloxacin	Gentamycin	Tobramycin
Pseudomonas	176	107 (60.8%)	93 (52.8%)	100 (56.8%)	105 (59.7%)	92 (52.3%)
Moraxella	9	9 (100%)	8 (88.9%)	8 (88.9%)	9 (100%)	9 (100%)
Other Enterics	45	44 (97.8%)	33 (73.3%)	44 (97.8%)	37 (82.2%)	38 (84.4%)
Gram-Negative Rods	30	30 (100%)	30 (100%)	28 (93.3%)	30 (100%)	24 (80%)

Table 2

Antibiotic Sensitivity Pattern for Isolated Gram-negative Bacteria

Organism	Number of microorganisms	Ceftazidime	Vancomycin	Moxifloxacin	Ciprofloxacin	Gatifloxacin	Gentamycin
Staphylococcusaureus	64	58 (90.6%)	64 (100%)	58 (90.6%)	44 (68.6%)	34 (53.1%)	57 (87.1%)
Coagulase-Negative Staphylococcus	503	356 (70.8%)	467 (92.8%)	466 (92.6%)	334 (66.4%)	275 (54.7%)	444 (88.3%)
Streptococcus	169	152 (89.9%)	153 (90.5%)	157 (92.9%)	131 (77.5%)	116 (68.6%)	155 (91.7%)
Diphtheroids	91	82 (90.1%)	84 (92.3%)	80 (81.9%)	64 (70.3%)	57 (62.6%)	83 (91.2%)

Sensitivity pattern for Pseudomonas spp., the most common isolated gram-negative bacteria, was less than 60% for all the five antibiotics tested in our analysis and is thus alarming. Our findings were not consistent with the authors' findings,[1] where they found more than 80% sensitivity for aminoglycosides and more than 85% sensitivity for fluoroquinolones in the Pseudomonas group. Worrying trends of multi-drug resistant Psuedomonas spp. are already showing around the world,[23] a reflection of which, we are also beginning to see in our clinics. Other gram-negative bacteria such as Moraxella, other enterics, and gram-negative rods displayed good susceptibility to fluoroquinolones and various aminoglycosides.

Our results are consistent with the authors' study, demonstrating predominance of gram-positive bacteria among ocular infections. Similar microbiological profile has been reported in studies from other geographical regions in India[4] and the west.[5]

Finally, we would like to echo authors' recommendations about the importance of cultures for identifying organism and their sensitivity pattern. Integrating microbiological work-up and avoiding “cocktail therapy” for microbial keratitis is the only way forward in this era of ever increasing drug resistance.

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Conflicts of interest

There are no conflicts of interest.