Changing Trends in the Prevalence of Shigella Species: Emergence of Multi-Drug Resistant Shigella sonnei Biotype g in Bangladesh

Abstract

Shigellosis, caused by Shigella species, is a major public health problem in Bangladesh. To determine the prevalence and distribution of different Shigella species, we analyzed 10,827 Shigella isolates from patients between 2001 and 2011. S. flexneri was the predominant species isolated throughout the period. However, the prevalence of S. flexneri decreased from 65.7% in 2001 to 47% in 2011, whereas the prevalence of S. sonnei increased from 7.2% in 2001 to 25% in 2011. S. boydii and S. dysenteriae accounted for 17.3% and 7.7% of the isolates respectively throughout the period. Of 200 randomly selected S. sonnei isolates for extensive characterization, biotype g strains were predominant (95%) followed by biotype a (5%). Resistance to commonly used antibiotics including trimethoprim-sulfamethoxazole, nalidixic acid, ciprofloxacin, mecillinam and ampicillin was 89.5%, 86.5%, 17%, 10.5%, and 9.5%, respectively. All isolates were susceptible to ceftriaxone, cefotaxime, ceftazidime and imipenem. Ninety-eight percent of the strains had integrons belonging to class 1, 2 or both. The class 1 integron contained only dfrA5 gene, whereas among class 2 integron, 16% contained dhfrAI-sat1-aadA1-orfX gene cassettes and 84% harbored dhfrA1-sat2 gene cassettes. Plasmids of ∼5, ∼1.8 and ∼1.4 MDa in size were found in 92% of the strains, whereas only 33% of the strains carried the 120 MDa plasmid. PFGE analysis showed that strains having different integron patterns belonged to different clusters. These results show a changing trend in the prevalence of Shigella species with the emergence of multidrug resistant S. sonnei. Although S. flexneri continues to be the predominant species albeit with reduced prevalence, S. sonnei has emerged as the second most prevalent species replacing the earlier dominance by S. boydii and S. dysenteriae in Bangladesh.

Molecular and phenotypic characterization of strains of Shigella sonnei isolated over 31 years suggests the circulation of two prevalent subtypes in São Paulo State, Brazil

“…Authors in Taiwan, Bangladesh, Bhutan, Iran and Argentina observed similarities above 70 % among strains of S. sonnei using PFGE (Lee et al, 2003;Ud-Din et al, 2013;Ruekit et al, 2014;Farshad et al, 2015). These data corroborate those of the present study because the strains of the PFGE-A and PFGE-B groups had a similarity above 70.8 % between each other (Fig.…”

Risk factors and outcome of Shigella encephalopathy in Bangladeshi children

“…In Bangladesh the resistance of Shigella sonnei to ciprofloxacin is increasing dramatically. It has been shown that in 2007, 10% of the strains were resistant to ciprofloxacin, and by 2011, the resistant strains peaked to 70% [1]. We also observed the similar trend i.e.…”

Recent Outbreaks of Shigellosis in California Caused by Two Distinct Populations of Shigella sonnei with either Increased Virulence or Fluoroquinolone Resistance

“…Unlike some of the other U.S. isolates deposited as a part of GenomeTrakr project, CA isolates did not cluster with European FQ-resistant isolates and likely represent a direct introduction event. As S. sonnei is becoming more common in developing countries (13, 14), as in many of the countries in South and Southeast Asia, it could further increase the risk of clonal expansion and global dissemination of FQ-resistant strains of S. sonnei .…”

“…Infections caused by S. boydii are relatively uncommon worldwide (12). There is an emerging global trend of S. sonnei replacing S. flexneri in areas of developing countries undergoing economic growth and improvement in sanitation, such as Vietnam (13), and Bangladesh (14). …”