Antimicrobial Susceptibility Pattern of Salmonella spp. Isolated from Enteric Fever Patients in Nepal
Anu Maharjan1, Binod Dhungel1, Anup Bastola2
1Central Department of Microbiology, Tribhuvan University, Kirtipur, Kathmandu 44618, Nepal.
Introduction:
Enteric fever, a systemic infection caused by Salmonella enterica Typhi and S. enterica Paratyphi is one of the most common infections in developing countries such as Nepal. Aside from irrational practices of antibiotic use, mutations in chromosomal genes encoding DNA gyrase and Topoisomerase IV and by plasmid mediated quinolone resistant (PMQR) genes are suggested mechanisms for the development of resistance to nalidixic acid and reduced susceptibility to ciprofloxacin. Regardless of high endemicity of enteric fever in Nepal, there is paucity of studies on prevalence and drug-resistance of the pathogen. Therefore, this study aimed to assess the antibiotic susceptibility pattern of Salmonella isolates and determine the minimum inhibitory concentration of ciprofloxacin.
Methods:
A total of 1298 blood samples were obtained from patients with suspected enteric fever, attending Sukraraj Tropical and Infectious Disease Hospital (STIDH) during March-August, 2019. Blood samples were inoculated immediately into BACTEC culture bottles and further processed for isolation and identification of Salmonella Typhi and S. Paratyphi. Axenic cultures of the isolates were further subjected to antimicrobial susceptibility testing (AST) by using the modified Kirby-Bauer disc diffusion method based on the guidelines by CLSI. The minimum inhibitory concentration (MIC) of ciprofloxacin was determined by agar-dilution method.
Results:
Out of 1298 blood cultures, 40 (3.1%) were positive for Salmonella spp. among which 29 (72.5%) isolates were S. Typhi and 11 (27.5%) isolates were S. Paratyphi A. In AST, 12.5% (5/40), 15% (6/40) and 20% (8/40) of the Salmonella isolates were susceptible to nalidixic acid, ofloxacin and levofloxacin, respectively, whereas none of the isolates were susceptible to ciprofloxacin. The MIC value for ciprofloxacin ranged from 0.06-16 µg/mL in which, respectively, 5% (2/40) and 52.5% (21/40) of the isolates were susceptible and resistant to ciprofloxacin. None of the isolates showed multidrug-resistance (MDR) in this study.
Conclusion:
This study showed high prevalence of quinolone-resistant Salmonella spp., while there was marked re-emergence of susceptibilities to traditional first option drugs. Hence, conventional first-line-drugs and third-generation cephalosporins may find potential usage as the empirical drugs for enteric fever. Although our reporting was free of MDR strains, extensive surveillance, augmentation of diagnostic facilities and treatment protocol aided by AST report are recommended for addressing the escalating drug-resistance in the country.
Insights
Enteric fever in Nepal shows high quinolone resistance in Salmonella. However, susceptibility to older drugs like nalidixic acid is re-emerging, suggesting potential for their use alongside improved diagnostics.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Enteric fever, caused by Salmonella Typhi and Paratyphi, is prevalent in Nepal.
- Antibiotic resistance is a growing concern, linked to gene mutations and plasmid-mediated quinolone resistance (PMQR) genes.
- Limited studies exist on Salmonella drug resistance in Nepal, necessitating local surveillance.
Purpose of the Study:
- To determine the antibiotic susceptibility patterns of Salmonella isolates from suspected enteric fever cases in Nepal.
- To establish the minimum inhibitory concentration (MIC) of ciprofloxacin for these isolates.
Main Methods:
- Blood samples from 1298 patients with suspected enteric fever were collected over six months.
- Salmonella Typhi and Paratyphi were isolated and identified using standard microbiological techniques.
- Antimicrobial susceptibility testing (AST) and ciprofloxacin MIC determination were performed according to CLSI guidelines.
Main Results:
- Out of 1298 samples, 40 (3.1%) yielded Salmonella, with 29 Typhi and 11 Paratyphi A.
- None of the isolates were susceptible to ciprofloxacin; 52.5% were resistant.
- Susceptibility to nalidixic acid, ofloxacin, and levofloxacin was low (12.5%, 15%, and 20% respectively).
- No multidrug-resistant (MDR) strains were identified.
Conclusions:
- A high prevalence of quinolone-resistant Salmonella was observed.
- A resurgence in susceptibility to older drugs like nalidixic acid was noted.
- Conventional first-line drugs and third-generation cephalosporins may be considered for empirical treatment.
- Enhanced surveillance and diagnostics are crucial for managing escalating drug resistance.
