Azithromycin minimum inhibitory concentration (MIC) creep and clinical-microbiological profile of typhoidal and nontyphoidal Salmonella isolates from blood specimens at a tertiary care hospital in Pune, India

Abstract

The Salmonella strains causing bloodstream infection show wide genetic diversity together with different antibiotic resistance profiles worldwide. The response of typhoidal Salmonella to standard antimicrobial treatments has become increasingly concerning during the past few decades. This study was conducted to evaluate the occurrence rate, antibiotic susceptibility patterns, and clinical characteristics of patients with Salmonella bacteraemia in a tertiary care hospital in Pune, Maharashtra, India. A cross-sectional study was conducted from March 2024 to March 2025, analysing blood culture-confirmed cases of enteric fever. All patients with Salmonella -positive cultures were included, and data were gathered from clinical and microbiology records. Out of 6,862 blood cultures processed, 42 (0.6%) tested positive for Salmonella species. Of these, 50% were Salmonella Typhi , 36% were Salmonella Paratyphi A , and the remaining 14% included S. Cholerasuis, S. Typhimurium , and S. Gallinarum . All S. Typhi and S. Paratyphi A isolates were fully susceptible to first-line antibiotics, including chloramphenicol, amoxicillin, and co-trimoxazole, as well as to ceftriaxone and cefixime. However, 78.5% of isolates showed reduced susceptibility to ciprofloxacin. Initial disc diffusion testing suggested potential azithromycin resistance in 11 isolates, but confirmatory E-strip testing found none to be resistant based on MIC values. One S. Paratyphi A isolate exhibited a notably high MIC of 24 µg/mL, which is not classified as resistant according to U.S. NARMS guidelines.. The increasing azithromycin MIC values among typhoidal Salmonella indicate potential resistance development, so additional research should assess azithromycin susceptibility patterns in detail.