Comparison of Antimicrobial Resistance in Pseudomonas Isolated from Raw Spinach Grown with and Without Chemical Fertilizers
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Abstract
Background: Antimicrobial resistance is an increasing public health concern that extends into agricultural and food-production environments. Fresh leafy vegetables such as spinach may serve as reservoirs for resistant bacteria, particularly when consumed raw or minimally processed. Objective: This study aimed to compare the antimicrobial resistance patterns of Pseudomonas spp. isolated from raw spinach cultivated with chemical fertilizers and spinach cultivated without chemical fertilizers. Methods: An observational cross-sectional laboratory-based comparative study was conducted on 60 raw spinach samples, including 30 samples from chemically fertilized fields and 30 from non-fertilized fields. Samples were collected using the zigzag sampling technique and transported under cold-chain conditions. Presumptive Pseudomonas spp. were isolated using standard culture methods and identified through colony characteristics, Gram staining, oxidase testing, motility, and non-lactose-fermenting behavior. Antimicrobial susceptibility testing was performed using the Kirby-Bauer disk diffusion method on Mueller-Hinton agar, and results were interpreted according to Clinical and Laboratory Standards Institute criteria. Data were analyzed using frequencies, percentages, chi-square test, and Fisher’s exact test where applicable. Results: Pseudomonas spp. were isolated from 24 of 60 samples (40.0%). Isolation was higher in fertilized spinach than in non-fertilized spinach, but the difference was not statistically significant (14/30, 46.7% vs. 10/30, 33.3%; p = 0.292). All isolates were susceptible to imipenem and meropenem. Cefotaxime resistance was significantly higher in fertilized isolates than non-fertilized isolates (10/14, 71.4% vs. 2/10, 20.0%; p = 0.036), as was ceftazidime resistance (6/14, 42.9% vs. 0/10, 0.0%; p = 0.024). Moxifloxacin resistance was detected only in fertilized isolates, but the difference was not statistically significant. Conclusion: Raw spinach cultivated with chemical fertilizers showed significantly higher cephalosporin resistance among Pseudomonas spp. isolates, while carbapenem susceptibility remained preserved. These findings support the need for antimicrobial resistance surveillance in fresh produce and improved monitoring of agricultural practices
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