Dr. Nikhil Govindwar, G17113, Dr.Seema Ramakrishnan
Purpose : To assess the in vitro antibiotic susceptibility of Pseudomonas spp . isolated from bacterial keratitis over a 5 year period with special emphasis on fluoroquinolone susceptibilities.
Methods : All corneal scraping cultures positive for Pseudomonas spp. (n=147) isolated from patients with bacterial keratitis at the Aravind Eye Hospital, Pondicherry from March 2013 – March 2017 were evaluated. Cultures were performed in liquid and solid media and susceptibility testing was done against amikacin, gentamicin, tobramycin, moxifloxacin, gatifloxacin, levofloxacin, cefotaxime, ciprofloxacin, ofloxacin, polymyxin B, piperacillin/tazobactum by Kirby-Bauer disc diffusion method.
Results: Among the fluoroquinolones, maximum susceptibility was found to be for gatifloxacin (96%) and least for moxifloxacin (74%). Among the aminoglycosides, amikacin showed the maximum susceptibility (93%).
Conclusions : The fluoroquinolones remain a good choice in the treatment of ocular
infections, with high susceptibility of Pseudomonas spp. but resistance to moxifloxacin is increasing in the recent past.
Among the aminoglycosides, amikacin was found to be highly effective against Pseudomonas corneal ulcers as compared to gentamycin and tobramycin. The results show a need for continuous monitoring of bacterial resistance trends.
Bacterial keratitis is a significant cause of ocular morbidity that can result in severe visual impairment .[1] For medical management of bacterial eye infections, treatment with broad spectrum antibiotics may be instituted before pathogen identification and antibiotic susceptibility tests are available.[2] Antibiotics are generally effective for treatment of most cases of bacterial ocular infections. However, holes in therapy emerge because of the frequent indiscriminate use of antibiotics, which has led to the development of resistance to many commonly used antimicrobials. [3],[4],[5],[6] Patients with serious keratitis like large corneal ulcers or with a clinical picture suggestive of any unusual organisms, however should be cultured to identify the causative agent.[7] In such cases, in order to start specific therapy, it is necessary to perform meticulous laboratory investigations followed by sensitivity testing. Studies related to in vitro antibiotic sensitivity provide important information to health care providers who often have to select a first line antibiotic treatment without the benefit of having the microbiologic testing results.
Analysis of the bacterial trends of keratitis reveals that Pseudomonas spp. is an important cause of bacterial keratitis in India.[8] In vitro studies of antibacterial susceptibility tests by various authors have shown an increased resistance of various bacteria to commonly used antimicrobials.[9] Fluoroquinolones were used as an effective monotherapy for many patients with microbial keratitis as they provide a good coverage for most of the gram positive and gram negative bacteria.[1] However, reports on emergence of resistance to fluoroquinolones have recently been published with special emphasis to Pseudomonas spp.[5]
The purpose of the present study is to assess the in vitro antibiotic susceptibility of
Pseudomonas isolates of keratitis patients during five years period to the commonly used antimicrobials and to look specifically for susceptibility to fluoroquinolones.
Materials and Methods :
All consecutive patients with suspected Pseudomonas keratitis, who underwent a diagnostic corneal culture at Aravind Eye Hospital Pondicherry from March 2013 to March 2017 were included in the study. The data reviewed in this study was retrospectively obtained from the microbiology laboratory records. Ulceration was defined as a loss of corneal epithelium with underlying stromal infiltration and suppuration associated with signs of inflammation with or without hypopyon. All patients had thoroughly undergone detailed slit lamp biomicroscopic examination by an ophthalmologist. Corneal scrapings were taken under aseptic conditions using a sterile kimura’s spatula after application of local anesthetic eye drops. The material scraped from the leading edge and the base of the ulcer was directly inoculated onto solid media (5% sheep blood agar, chocolate agar, potato dextrose agar) and incubated at 37 ºC. Potato dextrose agar was incubated at 25 ºC for 7 days. All the isolates were identified by routine biochemical tests. In vitro susceptibility testing was done by Kirby-Bauer disk diffusion method for all the Pseudomonas isolates.
Results :
Susceptibility testing was done against amikacin, gentamycin, tobramycin, moxifloxacin, gatifloxacin, levofloxacin, ciprofloxacin, ofloxacin ,ceftazidime, cefotaxim, polymyxin, chloramphenicol, piperacillin on culture positive pseudomonas spp.
| Sr.no | Antibiotic | Susceptibility |
| 1 | Levofloxacin | 91.03 % |
| 2 | Moxifloxacin | 74.14 % |
| 3 | Gatifloxacin | 95.89 % |
| 4 | Ciprofloxacin | 90.47 % |
| 5 | Ofloxacin | 90.47 % |
| 6 | Tobramycin | 91.78 % |
| 7 | Gentamycin | 89.79 % |
| 8 | Amikacin | 93.19 % |
| 9 | Chloramphenicol | 34.18 % |
| 10 | Polymyxin | 98.63 % |
| 11 | Piperacillin | 79.10 % |
| 12 | Cefotaxim | 27.97 % |
| 13 | Ceftazidime | 48.59 % |
From the above table it can be noted that amongst the fluoroquinolones, susceptibility is minimum for moxifloxacin. Results from present study shows that Pseudomonas is most susceptible to polymyxin ,gatifloxacin and amikacin. Fluoroquinolones are concentration dependent antibiotics and when bacteria are exposed to sub lethal concentration, resistance can be induced.[7] It has been said that following routine systemic use, clinically significant resistance to moxifloxacin may develop among isolates of P.aeruginosa. This increasing resistance in systemic isolates suggests that increasing resistance to this drug can be expected in ocular infections. Recent studies have also shown an increased in vitro resistance of ocular isolates to fluoroquinolones. [3],[4],[5].
In conclusion, this study analysed one of the common causes of corneal ulcer in our population and susceptibility of the organism towards the commonly used antibiotics. It can be concluded that the fluoroquinolones remain a good choice in the treatment of gram negative ocular infections but resistance to moxifloxacin is increasing in the recent past. Gatifloxacin can be the initial drug to start with but should be used judiciously to avoid bacterial resistance to it and to ensure their future potency.
References :
1) Alexandrakis G, Alfonso EC, Miller D. Shifting trends in bacterial keratitis in South Florida and emerging resistance to fluoroquinolones. Ophthalmology 2000; 107 :1497- 502.
2 ) Maria Regina Chalita, Ana Luisa Hofling-Lima, Augusto Paranhos, Pulo Schor, Rubens Belfort. Shifting Trends in Invitro Antibiotic Susceptibilities for common ocular isolates during a period of 15 years. Am J Ophthalmol. 2004; 137 :43-51.
3) Kunimoto DY, Sharma S, Garg P, Rao GN. Invitro susceptibility of bacterial keratitis pathogens to ciprofloxacin. Emerging Resistance. Ophthalmology 1999; 106 :80-5.
4) Goldstein MH, Kowalski RP, Gordon YJ. Emerging fluoroquinolone resistance in bacterial keratitis. Ophthalmology 1999; 106 :1313-8.
5) Garg P, Sharma S, Rao GN. Ciprofloxacin resistant Pseudomonas Keratitis. Ophthalmology 1999; 106 :1319-423.
6) Jensen HG, Felix C. Invitro susceptibilities of ocular isolates in North and South America. Cornea 1998; 17 :79-87.
7) Regis P.Kowalski, Lisa M.Karenchak, Eric G.Romanowski. Infectious disease: changing antibiotic susceptibility. Ophthalmol Clin N Am 2003;16 :1-9.
8) Srinivasan M, Gonzales CA, Celine George, Vicky Cevallos, Mascarenhas JM, Asokan B, et al. Epideomology and aetiological diagnosis of corneal ulceration in Madurai, South India. British Journal of Ophthalmology 1997; 81 :965-71.
9) Srikanth K, Kalavathy CM, Thomas PA, Jesudasan CAN. Susceptibility of common ocular bacterial pathogens to antibacterial agents. Journal of TNOA 1998; 39 :49-50.
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