Molecular Detection of Virulence-Associated, Regulatory, and Antimicrobial-Resistance Genes in Serratia marcescens Isolated from Urinary Tract Infections

Abstract

Objective: Serratia marcescens is an opportunistic, gram-negative bacterium related to healthcare-associated and other clinically important infections. The aim of this work was to evaluate some virulence, regulatory and antimicrobial resistance genes of S. marcescens strains obtained from UTI patients in Mosul city, Iraq. Methods: During February – June 2024, 150 samples were taken from Midstream urine of UTI patients. Conventional culture and biochemical testing were used to characterize presumptive isolates and VITEK-2 Compact system was used for identification; and 16S rRNA gene sequencing used for additional molecular identification. The obtained isolates were screened for flhD, pigP, shlA, phlA, aac(6′)-Ib-cr, blaIMP and blaOXA-48 by conventional PCR. Results: S. marcescens was isolated from 150 urine samples with 8 isolates recovered (5.3%). 100% of all isolates were positive for the virulence associated genes shlA, phlA, flhD and pigP, as well as the regulatory genes. The resistance-associated gene aac(6′)-Ib-cr was found in 100% of the eight isolates. Both of the carbapenemase associated genes, blaIMP and blaOXA-48, were present in 7 of 8 isolates (87.5%). The results revealed high prevalence of the examined virulence- and resistance-associated genetic determinants, and they were often found in the same organisms. The results are the molecular detection of the targeted genes and not necessarily the expression of these genes or the corresponding phenotypic characteristics. Conclusion: This small number of urinary S. marcescens isolates contained multiple virulence-associated/regulatory and antimicrobial resistance determinants. These observations are at the molecular level and should not be interpreted as population level resistance or functional virulence or phenotypic antimicrobial resistance, as only eight isolates were examined and no such testing was performed. Additional studies with larger numbers of patients incorporating phenotypic susceptibility testing and functional assays with more sophisticated molecular typing will be necessary to determine the clinical and epidemiological importance of the results.