Multidrug-resistant (MDR) isolates of S. enterica subsp. enterica serovar Typhi (S. typhi), the causative agent of typhoid fever, prevalent in parts of Asia and Africa are often associated with the dominant H58 haplotype, which harbors an IncHI1 plasmid with multiple resistance genes to first-line drugs, including ^blaTEM-1 (ampicillin), catA1 (chloramphenicol), dfrA7, sul1, sul2 (sulfamethoxazole/trimethoprim) and strAB (streptomycin) resistance genes.¹

The recent emergence of a novel, extensively drug-resistant (XDR) S. typhi H58 clone with additional resistance to fluoroquinolones and third-generation cephalosporins has been reported in Sindh, Pakistan.^1,2 This XDR clone encodes a chromosomally located resistance region and harbors the antibiotic resistance-associated IncY plasmid p60006, specific to XDR isolates in this phylogenetic branch.¹ This plasmid encodes additional elements, including the extended-spectrum beta-lactamase (^blaCTX-M-15) and fluoroquinolone (qnrS) resistance genes, and exhibited high sequence identity to plasmids found in other enteric bacteria, particularly Escherichia coli, isolated from widely distributed geographic locations.¹

Five strains of this XDR S. typhi clone from the Pakistan outbreak have been recently added to the BEI Resources catalog, expanding our collection of bacteria with unique resistance profiles to support antimicrobial resistance research:

References:

1. Klemm, E. J., et al. “Emergence of an Extensively Drug-Resistant Salmonella enterica Serovar Typhi Clone Harboring a Promiscuous Plasmid Encoding Resistance to Fluoroquinolones and Third-Generation Cephalosporins.” MBio 9 (2018): e00105-18. PubMed: 29463654.
2. Chatham-Stephens, K., et al. “Emergence of Extensively Drug-Resistant Salmonella Typhi Infections Among Travelers to or from Pakistan - United States, 2016-2018.” MMWR Morb. Mortal. Wkly. Rep. 68 (2019): 11- 13. PubMed: 30629573.

Image:  Computer-generated image of Salmonella serotype Typhi bacteria (CDC/Medical Illustrator)