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Multilocus sequence typing of multidrug-resistant Salmonella strains circulating in poultry farms of Bangladesh


Salmonella is one of the most important foodborne zoonotic pathogens, and becoming multidrug-resistant (MDR), which represents a serious public health concern worldwide. This study aimed to identify the circulating MDR strains of Salmonella through cutting edge molecular techniques including gene specific PCR, RAPD-PCR, ribosomal gene sequencing, and multilocus sequence types (MLST) in the poultry industry of Bangladesh. Two hundred Salmonella isolates were retrieved from 154 samples comprising droppings (n = 60), cloacal swabs (n = 60), feeds (n = 14), feeding water (n = 14), and handler’s swab (n = 6) from 14 commercial layer farms of Bangladesh. The isolates were confirmed as Salmonella through invA gene specific PCR, and further genotyping was done by RAPD-PCR, and 16S rRNA sequencing. The isolates were distributed into 18 different genotypes according to RAPD typing. The phylogenetic analysis identified three diverging phylogroups such as S. enterica Litchfield, S. enterica Enteritidis and S. enterica Kentucky with 11, 8, and 6 strains, respectively. The in vitro antibiogram profiling the Salmonella isolates through disc diffusion method using 13 commercially available antibiotics revealed highest resistance against doxycycline (91.5%) followed by tetracycline and ampicillin (86.0%, in each), and 72.0% isolates as MDR, being resistant to ≥ 5 antibiotics. The MLST typing was carried out based on the PCR amplification of seven housekeeping genes (aroC, hisD, hemD, purE, secA, thrA, and dnaN). MLST typing also revealed three sequence types (STs) such as ST11, ST198, and ST214 in these isolates, and eBURST analysis showed ST11 as the founder genotype. The three STs were highly resistant to tetracyclines and quinolone group of antibiotics, and all of the isolates harboring S. enterica Litchfield showed the highest resistance. Circulating common MLSTs with MDR properties in different farms confirmed the possibility of a common route of intra-farm transmission. We report for the first time of the association serovar Litchfield (ST11) in avian salmonellosis with MDR properties which is an urgent public health concern in Bangladesh.

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The authors would like to acknowledge Bangladesh Academy of Science–United States Department of Agriculture (BAS–USDA) (Grant no: BAS -USDA PALS DU LSc-34) for supporting the project and a PhD student. We would like to further acknowledge University Grants Commission (UGC), Ministry of Science and Technology, Bangladesh, for supporting reagents and equipment.

Author information




KFS and OS carried out the studies (sampling, sequencing, molecular, and data analysis) and participated in drafting the manuscript. MNH visualized figures, interpreted data and results, critically reviewed and edited the manuscript. MS and MAH developed the hypothesis, supervised the whole work, and helped to prepare and critically revise the manuscript. All authors read and approved the final manuscript.

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Correspondence to Munawar Sultana or M. Anwar Hossain.

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Ethical approval was granted from the Ethics Committee of the Faculty of Biological Sciences, University of Dhaka, Bangladesh who has approved the procedure under the Reference 71/Biol.Scs./2018-2019.

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The authors declare that they have no competing interests.

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Sultana, K.F., Saha, O., Hoque, M.N. et al. Multilocus sequence typing of multidrug-resistant Salmonella strains circulating in poultry farms of Bangladesh. Braz J Microbiol (2021).

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  • Salmonella
  • MLST
  • MDR
  • Poultry farms
  • Bangladesh
  • Khandokar Fahmida Sultana
  • OtunSaha
  • And M. Nazmul Hoque contributed equally