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Updated: Apr 30, 2026
Author Spotlight: Advancements in Understanding and Combatting Shigella Infections
Published on: February 9, 2024
Genetic characterization of Shigella spp. isolated from diarrhoeal and asymptomatic children
Santanu Ghosh1, Gururaja P Pazhani1, Swapan Kumar Niyogi1
1Division of Bacteriology, National Institute of Cholera and Enteric Diseases, Kolkata, India.
Insights
Asymptomatic children carry multidrug-resistant Shigella, increasing transmission risks in endemic areas. This study highlights their role in spreading Shigella spp. with virulence genes.
Area of Science:
- Microbiology
- Infectious Diseases
- Genetics
Background:
- Shigella spp. are a major cause of bacterial dysentery worldwide, particularly in children.
- Antimicrobial resistance and virulence factors in Shigella contribute to disease severity and transmission.
- Understanding the characteristics of Shigella in both symptomatic and asymptomatic individuals is crucial for controlling outbreaks.
Purpose of the Study:
- To analyze the phenotypic and genetic traits of Shigella spp. from diarrheal (case) and asymptomatic (control) children.
- To investigate antimicrobial resistance, integron carriage, plasmid-mediated quinolone resistance (PMQR), virulence genes, and Shigella pathogenicity island (SH-PAI).
- To determine the role of asymptomatic carriers in the transmission of multidrug-resistant Shigella.
Main Methods:
- Isolation and identification of Shigella spp. from 91 diarrheal and 17 asymptomatic children.
- Antimicrobial resistance profiling, detection of integrons, PMQR genes (aac(6')-Ib-cr, qnrS1), and virulence-associated genes (ipaH, virF, sat, setA, setB, sen, ial).
- Analysis of the Shigella pathogenicity island (SH-PAI) in all isolates.
Main Results:
- High rates of fluoroquinolone resistance were observed in both cases (68.1%) and controls (82.3%).
- Integron carriage was significantly higher in cases (76.9%) than controls (35.5%), with atypical class 1 integrons found exclusively in cases.
- Integrons, PMQR genes, and various virulence genes were more prevalent in Shigella isolates from diarrheal cases compared to asymptomatic controls.
Conclusions:
- Asymptomatic children harbor multidrug-resistant Shigella spp. possessing significant virulence genes.
- These findings suggest that asymptomatic carriers play a critical role in the transmission dynamics of Shigella in endemic regions.
- Interventions targeting asymptomatic carriers may be essential for controlling Shigella infections in communities.
Abstract:
Phenotypic and genetic characteristics of Shigella spp. isolated from diarrhoeal and asymptomatic children aged up to 5 years were analysed in this study. In total, 91 and 17 isolates were identified from diarrhoeal (case) and asymptomatic (control) children, respectively. All the isolates were tested for antimicrobial resistance, the presence of integrons, plasmid-mediated quinolone resistance (PMQR), virulence-associated genes and Shigella pathogenicity island (SH-PAI). The majority of the Shigella spp. from cases (68.1%) and controls (82.3%) were found to be resistant to fluoroquinolones. Integron carriage was detected more in cases (76.9%) than in controls (35.5%). Atypical class 1 integron was detected exclusively in Shigella flexneri from cases but not from the controls. PMQR genes such as aac(6')-Ib-cr and qnrS1 were detected in 82.4 and 14.3% of the isolates from cases and in 53 and 17.6% in controls, respectively. Shigella isolates from cases as well as from controls were positive for the invasive plasmid antigen H-encoding gene ipaH. The other virulence genes such as virF, sat, setA, setB, sen and ial were detected in Shigella isolates in 80.2, 49.4, 27.4, 27.4, 80.2 and 79.1% of cases and in 64.7, 52.9, 17.6, 17.6, 64.7 and 64.7% of controls, respectively. The entire SH-PAI was detected in S. flexneri serotype 2a from cases and controls. In an isolate from a control child, the SH-PAI was truncated. Integrons, PMQR and virulence-encoding genes were detected more frequently in cases than in controls. In diarrhoea endemic areas, asymptomatic carriers may play a crucial role in the transmission of multidrug-resistant Shigella spp. with all the putative virulence genes.
