Evolving Antimicrobial Susceptibility Patterns in Salmonella spp. Isolated from Blood Specimens, Over 10 Years: A Retrospective Observational Analysis

Introduction: Species of Salmonella, particularly Salmonella Typhi and Salmonella Paratyphi, remain a significant cause of Bloodstream Infections (BSIs) in developing countries, complicated further by rising antimicrobial resistance. These infections contribute substantially to morbidity, mortality and the public health burden, especially in regions with poor sanitation and limited access to healthcare. The emergence of MultidrugResistant (MDR) Salmonella strains has rendered many first-line antibiotics less effective, complicating treatment strategies. Aim: To assess the prevalence of Salmonella spp. and the antimicrobial patterns of Salmonella isolates over a ten-year period (2014–2024) at a tertiary care hospital in Tamil Nadu, India. Materials and Methods: This was a retrospective observational study conducted at Chettinad Hospital and Research Institute, Kelambakkam, Tamil Nadu, India. Blood culture records from January 2014 to December 2024 were reviewed. All patients with confirmed Salmonella-positive blood cultures were included. Blood samples were processed using standard microbiological protocols, including conventional and automated (BACTEC) methods and antibiotic susceptibility was tested using the Kirby-Bauer disc diffusion method as per Clinical and Laboratory Standards Institute (CLSI) guidelines. Demographic details such as age and gender were documented. Data were compiled using Microsoft Excel and analysed using Statistical Package for the Social Sciences (SPSS) version 20.0; categorical data were expressed in percentages. Results: Among the 304 isolates, S. Typhi was the most frequently identified species (225, 74%), followed by Salmonella Paratyphi A (66 isolates, 21.7%), Salmonella Paratyphi B (7 isolates, 2.3%) and Salmonella Typhimurium (6 isolates, 2%). A male predominance (213, 70.1%) was observed and the greatest occurrence (162, 53.3%) was recorded in the 21-60 years of age group. Antibiotic sensitivity analysis revealed sustained susceptibility of all serotypes to ceftriaxone, tetracycline, chloramphenicol and cotrimoxazole. However, a predominant level of ciprofloxacin resistance was reported in S. Typhi and S. Paratyphi A isolates. Year-wise data showed fluctuating resistance patterns, with a notable dip in ceftriaxone sensitivity in 2020 and variable trends in ampicillin and chloramphenicol resistance. Conclusion: Over the past decade, S. Typhi remained the predominant pathogen isolated from BSIs, particularly affecting adults. Although conventional antibiotics continue to be effective, alarming fluoroquinolone resistance trends underscore the need for routine antimicrobial surveillance and judicious antibiotic use. The findings reinforce the importance of empirical therapy guided by local susceptibility patterns and highlight the ongoing challenge of managing drug-resistant Salmonella infections in endemic regions.