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.