Abstract
Objectives: Genetic elements such as plasmids play a role in spreading multi-antibiotic resistance, a global threat. Therefore, the purpose of this study was to investigate the antibiotic susceptibility and plasmid profiles of multidrug-resistant (MDR) uropathogenic Serratia marcescens.
Methods: Fifty Serratia marcescens isolates were obtained from urine samples of patients presenting with urinary tract infection (UTI) in Southeastern Nigeria. Bacteria samples were identified via their characteristic red pigmentation and other biochemical tests. The disc diffusion method was used for antibiotic susceptibility testing. Plasmids were extracted using the alkaline lysis method, and electrophoresis was done on a 1% agarose gel. Extracted DNA plasmids were visualized using the ultraviolet light illuminator and a photo documentation system. Plasmid curing was carried out using acridine orange.
Results: Antibiotic susceptibility testing of isolates revealed 41 (82%) were resistant to one or more antibiotics tested, and 8 (16%) isolates exhibited resistance to three or more antibiotics (MDR). Of the eight MDR isolates, five (63%) had plasmids with molecular weights ranging from 33 kb to 58 kb. One isolate (S9) was cured and became sensitive to ceftriaxone, but not cefuroxime or ceftazidime. Notably, one isolate (S23), initially sensitive to ciprofloxacin, became resistant post-plasmid curing.
Conclusion: The findings show that most resistant bacteria containing plasmids were immune to curing as they remained resistant to antibiotics after curing. This result confirms a concern about the growing presence of MDR plasmids of S. marcescens in healthcare facilities in Southeastern Nigeria. J Microbiol Infect Dis 2022; 12(1):12-18.

Key words: Antibiotic resistance, Serratia marcescens, Plasmid profiling, Urinary tract infection