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Table of Contents
ORIGINAL ARTICLE
Year : 2022  |  Volume : 4  |  Issue : 1  |  Page : 16

Bacterial profile and antimicrobial resistance in a Tertiary Hospital in Mexico


1 Department of Cornea and Refractive Surgery, Association to Prevent Blindness in Mexico, Hospital Dr. Luis Sánchez Bulnes, Mexico City, Mexico
2 Department of Clinical Sciences, Division of Health Sciences, University of Monterrey, San Pedro Garza García, Nuevo León, Mexico
3 Wilmer Eye Institute, Baltimore, Maryland, USA

Date of Submission21-Dec-2021
Date of Acceptance20-Jan-2022
Date of Web Publication23-Mar-2022

Correspondence Address:
Dr. Francisco Beltran
Department of Cornea and Refractive Surgery, Association to Prevent Blindness in Mexico, Hospital Dr. Luis Sánchez Bulnes, Mexico City
Mexico
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/pajo.pajo_132_21

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  Abstract 


Objective: The objective of this study was to report the characteristics and the bacterial microbiological frequency of the etiological agents and the antibiotic sensitivity of the isolated pathogens in infectious keratitis in Mexico between 2012 and 2016.
Methods: This was a retrospective, cross-sectional, and observational study; medical records of all patients who presented in the cornea department in Mexico with infectious keratitis from 2012 to 2016 were reviewed. Demographic data, Gram stain, and microorganisms obtained in the culture and antibiotic sensitivities were evaluated by disc diffusion test.
Results: In the studied period, a total of 639 (40.67%) cases that had a positive culture were included; 54.5% were male with an average age of 48.50 ± 20.43. Gram-positive agents were the most frequent with 80.66% of cases. The most frequent causative agent was Staphylococcus epidermidis (36.61%). The most frequent Gram-negative agent was Pseudomonas aeruginosa (7.55%). The antibiotic with the highest sensitivity was netilmicin (90.3%), followed by moxifloxacin (82.3%) and gatifloxacin (81.3%). Among fortified antibiotics, ceftazidime had a sensitivity of 78% while vancomycin 43.8% (for Gram positive).
Conclusion: Bacteria are the most common cause of infectious keratitis, Staphylococcus and Pseudomonas as the most common isolates. There was low resistance to netilmicin and fourth-generation fluoroquinolones for these isolates.

Keywords: Antibiotic, bacterial keratitis, culture, resistance, sensitivity


How to cite this article:
Beltran F, Vazquez Romo KA, Oyervides Alvarado JA, Gonzalez Dibildox LA, Betancourt NR, León MG, Quintela EH. Bacterial profile and antimicrobial resistance in a Tertiary Hospital in Mexico. Pan Am J Ophthalmol 2022;4:16

How to cite this URL:
Beltran F, Vazquez Romo KA, Oyervides Alvarado JA, Gonzalez Dibildox LA, Betancourt NR, León MG, Quintela EH. Bacterial profile and antimicrobial resistance in a Tertiary Hospital in Mexico. Pan Am J Ophthalmol [serial online] 2022 [cited 2022 May 25];4:16. Available from: https://www.thepajo.org/text.asp?2022/4/1/16/340606




  Introduction Top


Microbial keratitis is an ophthalmological emergency, which threatens the integrity of the eyeball; this can result in a poor visual prognosis; therefore, it needs timely detection, as well as punctual treatment.[1] The most frequent etiological agent is bacterial, and less frequently, it can be caused by fungi or viruses.[2],[3]

The most common risk factors associated with microbial keratitis are eye trauma, use of contact lenses, use of topical steroids, history of eye surgery, and autoimmune diseases.[2],[3],[4],[5],[6],[7],[8],[9]

The ideal management begins with the collection of samples for culture and staining; after this, generally, empirical treatment is indicated, which can be based on broad-spectrum topical agents or combinations of topical fortified medications.[4],[10]

The objective of this study is to report the characteristics and microbiological frequency of the isolated pathogens in bacterial infectious keratitis in Mexico between 2012 and 2016 as well as to report the patterns of resistance and sensitivity to the antibiotics most commonly used in this pathology.


  Methods Top


A retrospective, cross-sectional, and observational study was conducted to review the records of patients with a retrospective diagnosis by reviewing the records of patients with a presumptive diagnosis of infectious keratitis diagnosed between January 2012 and December 2016 of the cornea department at an academic tertiary referral center in Mexico. Before the start of the study, the ethics committee of our institution approved the research protocol.

Demographic data, Gram stain, and microorganisms were obtained in the culture, and the antibiogram was analyzed.

Corneal scraping and cultures are routinely obtained when a patient is diagnosed with infectious keratitis. Two samples are taken from the conjunctiva and three from the corneal infiltrate. They were performed routinely, using a calcium alginate swab, after instilling a topical anesthetic (Tetracaine, Ponti Ofteno, Laboratories Sophia, Zapopan, Jalisco, Mexico). The samples are placed in different culture media: blood agar, chocolate agar, mannitol salt agar, liquid nutrient medium, BiGGY medium, and Sabouraud-Emmons. Gram and Giemsa staining are analyzed on all samples taken.

We included patients with a diagnosis of infectious keratitis who had positive cultures, and attended the hospital at leaste two times in order to confirm the diagnosis. We excluded patients with other causes of keratitis or patients with negative cultures or with cultures in whom the microorganisms could not be identified.

Antibiotic sensitivity is determined using the Kirby–Bauer disk diffusion susceptibility test. The interpretation was done using guidelines from the Clinical and Laboratory Standards Institute for antimicrobial susceptibility testing..[11] Bacterial sensitivity was classified as susceptible and resistant. To perform the analysis, we divided the bacteria according to the gram stain (gram negative and gram positive), later to distinguish between different types of Staphylococcus they were classified as coagulase positive and coagulase negative.

Descriptive statistics were carried out to analyze the variables, reporting in percentages for categorical variables and average with their standard deviation for continuous variables. The programs (IBM, version 21 for Mac) and GraphPad Prism 8 software (version 8.01; GraphPad Software Inc., La Jolla, CA) were used for statistical analysis and graph creation.


  Results Top


In the period studied, 1571 records were obtained with the diagnosis of infectious keratitis, of which 685 (43.60%) cases had a positive culture. In 46 (6.71%) cases, a fungi was recovered and in 639 (93.3%) cases, culture was positive for bacteria. We only include bacterial-positive culture, of them, 54.5% were male sex and the average age was 48.50 ± 20.43 (range 1–93), 36.77% (235) of the patients had more than one positive culture, for which a total of 874 positive cultures were obtained. In [Table 1], we can see the distribution by year of the total of positive cultures. Gram-positive agents were the most frequent with 80.66% of cases. The most frequent causative agent was Staphylococcus epidermidis, which was cultivated in 36.61% of cases. The most frequent causal agent within the Gram negatives was Pseudomonas aeruginosa, which was present in 7.55% of the cases. The annual distribution of positive cultures according to the Gram is shown in [Table 2].
Table 1: Distribution by year of the total of positive cultures

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Table 2: Cultures divided by year of Gram positive and Gram negative

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Regarding antibiotic sensitivity, the antibiotic with the highest general sensitivity was netilmicin with 90.3% of the cultures, followed by moxifloxacin with a sensitivity of 82.3% and gatifloxacin with 81.3%. Among the fortified antibiotics, ceftazidime had a sensitivity of 78%, and for Gram positive, vancomycin had a sensitivity of 43.8%%. In [Table 3], we can see the sensitivity of all antibiotics according to the causative agent.
Table 3: Sensitivity of all antibiotics according to the causative agent

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  Discussion Top


In our study, it was found that 40.67% of the cultures were positive. This is slightly higher than that reported by Hernández-Camarena et al.[12] who studied a similar population (third-level hospital) between 2002 and 2011, and found a culture positivity of 38%, and also what was reported by Shalchi et al.[13] and Ting et al.[14] in England, who studied 476 and 133s patients and reported a positivity of 34.2% and 37.7%, respectively. However, other authors have reported a higher recovery rate, such as Lichtinger et al.,[15] who reported a recovery rate of 57.4% in a 16-year study conducted at a university hospital in Toronto and evaluating 2330 samples from patients with bacterial keratitis as well as Alexandrakis who reported a 50% positivity in a study of bacterial keratitis in a tertiary hospital in Florida.[16] This may be influenced by several factors, among the most important is that we studied patients with infectious keratitis of any aetiology, while in the studies by Lichtinger et al. and Alexandrakis et al.[15],[16] exclusively studied patients with bacterial keratitis, and some studies have shown greater recovery of bacterial causative agents than fungi and Acanthamoeba.[5],[6] Another well-recognized factor is the use of antibiotics before treatment. sampling,[13] which was widely used in our patients since our hospital is a reference center, an example is the use of anesthetics with preservatives, as well as the type of anesthetic since tetracaine produces inhibition of bacterial growth.[17]

The most common causal agent we found in our results was S. epidermidis, a member of the normal flora of the skin and mucosa,[18] which is similar to that reported by Hernández-Camarena et al. with 25%.[19]

As for Streptococcus pneumoniae, in our results, we found an increase of almost double the isolated strains with 5.7% to that reported by Hernández-Camarena et al., who presented 2%.[20]

Regarding sensitivity, the antibiotic with the highest sensitivity was netilmicin. this coincides with what was reported by Vanzzini and Col who found 90% to netilmicin for the most frequent causal agent in our study S. epidermidis.[21] However, it is important to note that the sensitivity of netilmicin, as well as fourth-generation fluoroquinolones, was decreased compared to the study by Vanzzini et al.[21] who reported a 100% sensitivity of netilmicne for coagulase-negative Staphylococcus, the majority being S. epidermidis. This could be because this study was carried out 2 years after netilmicin was introduced to the Mexican market in 2009, so its indiscriminate use will produce this decrease in the sensitivity.[22] Another possible reason is that the study by Vanzinni et al included samples from other infectious diseases such as conjunctivitis, endophthalmitis, while in our study all the samples were from the cornea. With respect to fluoroquinolones, the same pattern is observed, Vanzzini et al.[21] reported a sensitivity of 97.53% for moxifloxacin and gatifloxacin, while in our study we reported a sensitivity of 82.3% and 81.3%, respectively, so they had a greater decrease than that found for netilmicin. This pattern of decrease in sensitivity of the fourth generation has already been reported in other studies.[13]

The most common Gram-negative bacterial agent in our study was P. aeruginosa with 39% of cases. In our study, there is a slight trend to increase year by year; this has been previously reported in different studies.[7],[13],[23]

The antibiotic with the highest sensitivity to Gram-negative bacteria was netilmicin with a sensitivity of 89.93%. This is because netilmicin belongs to the aminoglycoside family, a modified synthetic derivative (N-ethyl) of sisomicin extracted from Micromonospora inyoesis.[24]

Previous studies reported a high sensitivity of Gram-negative bacteria to fourth-generation fluoroquinolones such as moxifloxacin and gatifloxacin. In our study, we found that the sensitivity was 75.83% for both moxifloxacin and gatifloxacin, which is higher than that reported by 53.3% and 60%, respectively.[25] This could be due to the number of years of introduction of the drug in that country, which is related to drug sensitivity. There are current studies that have found bacterial resistance to these agents.[26]

In our study, we found greater effectiveness in Gram positive versus Gram negative, with 83% and 75%, respectively.

This study has some limitations: the first is that the population studied is from a third-level hospital, so it does not necessarily reflect the causative agents and sensitivity of infections in the general population. Furthermore, since clinical evolution is not included, it is not possible to ensure that in vitro results translate into a clinical response.


  Conclusion Top


Bacteria are the most common cause of infectious keratitis, Staphylococcus and Pseudomonas as the most common bacterial isolates. There was low resistance to netilmicin and fourth-generation fluoroquinolones for these isolates.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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    Tables

  [Table 1], [Table 2], [Table 3]



 

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