Microbiological Spectrum and Antimicrobial Susceptibility Patterns in Cellulitis: A Retrospective Observational Study at a Tertiary Care Hospital

Introduction: Cellulitis is the most common skin and soft-tissue infection affecting lower limbs, especially in individuals with comorbidities associated with relative immunosuppression, poor peripheral circulation and impaired wound healing. It poses diagnostic and therapeutic challenges due to changing trends in causative organisms and the rise in Antimicrobial Resistance (AMR). Aim: To investigate the clinico-demographic and microbiological profile of patients with cellulitis. Materials and Methods: A retrospective observational study was conducted in the Department of Microbiology at Kempegowda Institute of Medical Sciences, Bangalore, Karnataka, India, from January 2022 to December 2023. A total of 100 clinically diagnosed, culture-positive cases of cellulitis were included. Samples were processed using standard microbiological techniques on Blood agar, MacConkey agar, and Chocolate agar, followed by organism identification and antimicrobial susceptibility testing using the VITEK-2 automated system. Demographic parameters, including age and gender, were obtained from patient records. The Chi-square goodnessof-fit test and Fisher’s exact test (with correction) were used for statistical analysis. A p-value <0.05 was considered statistically significant. Results: A total of 100 culture-positive cellulitis cases were analysed. The lower limb was the most commonly affected site 84 (84%), patients aged 61-70 years constituted the largest age group 38 (38%), and males predominated 69 (69%). Among 117 isolates, 83 (71%) were recovered from monomicrobial infections, while 34 (29%) were isolated from 17 polymicrobial infections. Staphylococcus aureus was the predominant isolate 21 (18%), followed by Acinetobacter spp. 21 (18%), Pseudomonas aeruginosa 20 (17%) and Escherichia coli 19 (16%). A high prevalence of Methicillin-Resistant S. aureus (MRSA) 15/21 (71.4%) was observed. S. aureus showed high susceptibility to linezolid and rifampicin 18/21 (85.7% each), while E. coli demonstrated high susceptibility to amikacin and gentamicin 13/19 (68.4%). Acinetobacter baumannii exhibited poor susceptibility to most tested antimicrobials. Conclusion: Cellulitis was predominantly associated with gram-negative bacilli and non-fermenting organisms, with S. aureus, Acinetobacter spp., P. aeruginosa, and E. coli as the major pathogens. A high burden of MRSA was observed. Non-fermenters showed comparatively better susceptibility to carbapenems, although resistance remains a concern. The findings highlight the importance of early culture-guided therapy and rational antibiotic use in the management of cellulitis.