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Updated: Sep 28, 2026
Epithelial Cell Infection Analyses with Shigella
Published on: February 9, 2024
Shifting serotypes, plasmid profile analysis and antimicrobial resistance pattern of shigellae strains isolated from
1National Institute of Cholera and Enteric Diseases, Kolkata, India.
Insights
Shigella strains in Kolkata show changing species prevalence and increasing antibiotic resistance, particularly to tetracycline, co-trimoxazole, and nalidixic acid. This highlights reduced efficacy of common treatments for shigellosis in the region.
Area of Science:
- Microbiology
- Infectious Diseases
- Epidemiology
Background:
- Shigellosis remains a significant public health concern, especially in developing countries.
- Understanding the evolving epidemiology of Shigella, including serotype distribution and antimicrobial resistance, is crucial for effective treatment and control.
Purpose of the Study:
- To investigate the serotype prevalence, antimicrobial resistance patterns, and plasmid profiles of Shigella strains isolated from pediatric patients in Kolkata, India.
- To identify epidemiological shifts in Shigella species and their resistance trends over a six-year period.
Main Methods:
- Serotyping of 166 Shigella strains isolated from stool samples.
- Antimicrobial susceptibility testing against 12 agents, including determination of minimum inhibitory concentrations (MICs).
- Plasmid profile analysis using gel electrophoresis.
Main Results:
- Shigella flexneri (58%) was the predominant species, a shift from previous trends where Sh. dysenteriae 1 was common.
- High resistance rates were observed for tetracycline (>90%), co-trimoxazole (>90%), and ampicillin (67%).
- A statistically significant increase in resistance to tetracycline, nalidixic acid, and furazolidone was noted over the study period, indicating decreased drug efficacy.
Conclusions:
- The study reveals a changing epidemiological landscape of Shigella in Kolkata, with a rise in Sh. flexneri and increasing multidrug resistance.
- Decreased susceptibility to furazolidone, co-trimoxazole, and nalidixic acid necessitates re-evaluation of empirical treatment guidelines for shigellosis in this region.
- Plasmid analysis provided insights into the genetic basis of resistance and serotype distribution.
Abstract:
One hundred and sixty-six shigellae strains, isolated from stool samples of paediatric patients (< 5 years old) at a Childrens' Hospital in Kolkata, India during the period of 1995-2000 were examined for serotyping, drug resistance pattern and plasmid profiles. Sh. flexneri (58 %) was found to be commonest isolate of total shigellae, followed by Sh. sonnei (28 %), Sh. boydii (9%) and Sh. dysenteriae (5%). This profile of species was in sharp contrast to the picture obtained before 1995, when Sh. dysenteriae 1 predominated over Sh. flexneri. In Sh. flexneri strains, Sh. flexneri 2a (35%) was the most prevalent serotype, following Sh. flexneri 3a (31%), Sh. flexneri 6 (14%), Sh. flexneri 2b (11%) and Sh. flexneri 4 (9%). Resistance patterns of the strains to 12 commonly used antimicrobial agents and minimum inhibitory concentrations (MICs) of the antibiotics were also tested. All strains were found uniformly susceptible to norfloxacin, but more than 90% strains were resistant to tetracycline, co-trimoxazole and 67% strains were resistant to ampicillin. Resistance to amoxicillin, chloramphenicol and nalidixic acid was found in 55% (range 45-74%), 46% (range 40-60%) and 29% (range 15-40%) strains respectively. Overall, shigellae strains showed statistically significant increase in resistance against tetracycline, nalidixic acid and furazolidone (P < 0.05) over the years of this study. This indicates decreased efficacy of furazolidone, cotrimoxazole and nalidixic acid for the empirical treatment of shigellosis in Kolkata. Although a few strains showed intermediate susceptibility to ciprofloxacin (4%) and cefotaxime (10%) by disk diffusion test, but the MICs of those antibiotics were within the normal limits. Almost 57% of the strains were resistant to four or more drugs with high MICs of the antibiotics. Plasmid profile analysis revealed presence of large plasmid of 220 kb in majority of the strains except in Sh. sonnei and a correlation between presence of smaller plasmids and shigellae serotypes. Hence this study reports epidemiological change of shigellae species in Kolkata, India with regard to serotypes and antibiotic resistance patterns.
