Vol. 7, Issue 1, Part A (2025)

Serratia marcescens demonstrate significant antibiotic resistance with widespread dissemination leading to infections associated with high morbidity and mortality rates worldwide. The development of antibacterial resistance occurs by numerous mechanisms. So, the aim of this study was to detect phenotypically some of these mechanisms in multidrug-resistant S. marcescens. 
Methods: Nine isolates of S. marcescens were isolated from various clinical specimens and tested phenotypically for antibiotic susceptibility using the disc diffusion method. Biofilm formation using microtiter plate method, efflux pump activity through the ethidium bromide cartwheel technique, ESBL by double disc synergy test, and Carbapenemase enzyme production by Modified Hodge test (MHT), Boronic acid test , and Imipenem EDTA -synergy test.
Results: All nine S. marcescens isolates were Multidrug-resistance (MDR). Phenotypic analysis revealed that all isolates (100%) demonstrated efflux pump activity, (5)55.5% produced ESBL, Carbapenemase producers were 5(55.5%) found out by MHT metod . Among the carbapenemase producer 4\5 (44.4%) isolates were class A KPC and class B MBL producers. Additionally, all isolates (100%) were capable of biofilm formation. 
Conclusions: These data indicate that S. marcescens strains isolated from various clinical human cases possess active efflux pump, Beta-Lactamase enzymes activity and biofilm forming capabilities, which interplay in antibiotic resistance and highlights the importance of prudent antibiotic use in hospitals to prevent the spread of multidrug- resistant S. marcescens.