Molecular detection of antimicrobial resistance genes and virulence-associated protein expression profiling in multidrug-resistant Salmonella enterica serovar typhi clinical isolates.

BACKGROUND

Salmonella enterica serovar Typhi is a major bacterial pathogen responsible for typhoid fever, and the emergence of multidrug-resistant strains represents a serious public health concern. This study aimed to characterize clinical S. Typhi isolates from Baghdad, Iraq, by evaluating antimicrobial resistance patterns, resistance and virulence-associated genes, and protein expression profiles.

METHODS

One hundred blood samples were collected from patients clinically diagnosed with typhoid fever. Suspected isolates were cultured on Salmonella-Shigella agar and identified using the VITEK 2 Compact system. Antimicrobial susceptibility testing was performed, and PCR was used to detect antimicrobial resistance and virulence-associated genes. Protein expression patterns under different environmental conditions were analyzed using SDS-PAGE.

RESULTS

Among the 100 suspected cases, S. enterica serovar Typhi was confirmed in 40 patients (40%). The study population included 58 males and 42 females, with ages ranging from 10 to 65 years. Among the collected samples, S. Typhi isolates demonstrated considerable resistance to several antibiotic classes, including β-lactams, aminoglycosides, and cephalosporins, while carbapenems, piperacillin/tazobactam, and trimethoprim/sulfamethoxazole remained effective. Molecular analysis revealed the presence of major resistance determinants, including blaCTX-M-28, blaTEM-9, qnrA, qnrB, dfr genes, and class 1 integrons. SDS-PAGE analysis showed variations in the expression of virulence-associated proteins, including SipA-D, FliC, and FliD, under different pH conditions.

CONCLUSIONS

The findings indicate the emergence of multidrug-resistant S. Typhi strains in Baghdad and highlight the importance of continuous molecular surveillance, rational antibiotic use, and strengthened antimicrobial stewardship programs to control the spread of resistant pathogens and improve typhoid fever management.