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REPJP01, an emerging multidrug-resistant strain of Salmonella Typhi, was first identified in Pakistan (2016) and subsequently reported in US cases (2018). Notably, 90% of clinical isolates demonstrate resistance to five first-line antimicrobials: ampicillin, ceftriaxone, chloramphenicol, ciprofloxacin, and trimethoprim-sulfamethoxazole. Marchello et al. collectively analyzed 55,459 isolates (from 198 studies) and revealed that in Asia (2015–2018), 32.6% of isolates were multidrug-resistant (MDR; resistant to chloramphenicol, ampicillin, and trimethoprim-sulfamethoxazole in their study), with 5.7% resistant to third-generation cephalosporins and 8.3% to azithromycin. Interestingly, Pakistan reported extensively drug-resistant (XDR) strains (2.6% of isolates; MDR plus fluoroquinolone and cephalosporin resistance). In Africa, MDR prevalence rose steadily each decade (1990–2018), though XDR emergence remains unreported.  The H58 haplotype which is MDR has emerged as the dominant Salmonella Typhi lineage, driving widespread epidemics across Asia and Africa. This lineage demonstrates a competitive advantage over other serovar Typhi lineages, particularly with exposure to antimicrobials. While fluoroquinolones remain a frontline treatment, their efficacy is increasingly threatened by resistance mechanisms—notably mutations in gyrA (encoding DNA gyrase subunit A), a key drug target.

Recent studies reveal that the Rab GTPase Rab32 and its guanine nucleotide exchange factor BLOC-3 form a conserved pathway that both restricts Salmonella Typhi to human hosts and mediates its killing in macrophages of non-susceptible species. These proteins, previously recognized for their role in intracellular membrane trafficking—particularly in melanin synthesis through enzyme transport to melanosomes—are now identified as central players in innate immunity against typhoidal Salmonella.

Animal reservoir: Salmonella Typhi is a human-restricted serovar.

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