Multiple antibiotic resistance index (MARI) of human-isolated Salmonella species: a practical bacterial antibiotic surveillance tool

Objectives: Drug-resistant Salmonella plays a significant role in disease morbidity and mortality worldwide. The present study aimed to determine the multiple antibiotic resistance index (MARI) of Salmonella isolated from children hospitalized for gastroenteritis in Hong Kong. Methods: Salmonella isolates from stool samples of children aged from 30 days to <5 years were confirmed by using MALDI-TOF MS and subjected to serotyping methods according to the White–Kauffmann–Le Minor scheme. Antimicrobial susceptibility was determined by agar disc diffusion. Results: A total of 101 Salmonella isolates were serogrouped into Group B (n= 46, 45.5%), Group C (n = 9, 9.0%) or Group D (n = 46, 45.5%), and successfully classified into S. Enteritidis (n = 15) and S. Typhimurium (n= 7). Overall Salmonella susceptibilities demonstrated the highest level of resistance to ampicillin (76.2%), ciprofloxacin (54.0%) and tetracycline (61.2%) whereas MDR strains had high resistance toward ampicillin (100%), tetracycline (100%), cotrimoxazole (84.6%), chloramphenicol (83.3%) and ciprofloxacin (83.3%). MARI revealed that 80.2% of Salmonella including all MDR strains (n= 13) had indexes greater than 0.2. Conclusions: The MARI captures a snapshot of a high rate of antibiotic use and resistance in the isolated Salmonella, indicating the urgent need for continuous antimicrobial susceptibility surveillance and control of antibiotic prescription in selecting effective treatments for human diseases.