Clinical and Microbiological Profile of Serratia spp. Isolates and an Exploratory Comparison of Antimicrobial Resistance by Acquisition Setting: A Two-Year Retrospective Study

Abstract

Purpose To describe the clinical and microbiological profile of Serratia spp. isolates recovered at a tertiary-care hospital and to explore whether resistance differed by the acquisition category recorded in the source data. Patients and Methods We retrospectively reviewed 157 consecutive clinical isolates from 146 patients recovered from September 27, 2019, through September 27, 2021. The primary between-group analysis retained one first-listed isolate per patient (n=146); Fisher’s exact tests, odds ratios with 95% confidence intervals, and Holm adjustment across 12 antimicrobials were used. A generalized estimating equation analysis of all 157 isolates, clustered by patient, was performed as a sensitivity analysis. Results Serratia marcescens accounted for 128/157 isolates (81.5%), and sputum or tracheal aspirate accounted for 86/157 (54.8%). Resistance was lowest for trimethoprim/sulfamethoxazole (2/157, 1.3%), gentamicin (6/157, 3.8%), amikacin (7/157, 4.5%), and meropenem (7/157, 4.5%), and highest for imipenem (27/157, 17.2%). In the patient-level analysis, 90 isolates were community-classified and 56 were hospital-classified. Ertapenem resistance was 6/90 (6.7%) versus 11/56 (19.6%; odds ratio 3.42, 95% CI 1.19–9.86), but the comparison did not remain significant after Holm adjustment (nominal p=0.031; adjusted p=0.342). No antimicrobial showed a multiplicity-adjusted between-group difference. The clustered all-isolate analysis yielded the same overall interpretation. Conclusion This study provides a historical local description of Serratia isolates collected in 2019–2021. The acquisition-category comparisons were exploratory and did not identify a robust resistance difference after accounting for repeated isolates and multiple comparisons. These data should not be used alone to guide current empirical therapy.