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Serratia marcescens is an important nosocomial pathogen that causes a variety of infections, especially urinary tract and bloodstream infections. The emergence and spread of multidrug-resistant Serratia marcescens producing extended-spectrum beta-lactamases is a threat to public health worldwide at present. Extended-spectrum β-lactamases (ESβLs) including TEM, SHV, and CTX-M are the predominant types that confer resistance to beta-lactam group of antibiotics. Many reports have been investigated ESBL-producing isolates of Enterobacteriaceae in Iraq. However, there are few studies concerned about ESβL-producing Serratia marcescens particularly, detection of ESBLs encoding genes. Therefore this study aimed to identify ESβLs encoding genes in Serratia marcescens isolates from a neonatal intensive care unit. Fifty isolates were identified phenotypically using the VITEK® 2 compact system. For confirming the identification of bacterial strains, molecular detection of housekeeping LuxS gene was done using species-specific designed primers. Antibiogram was performed using the VITEK® 2 compact system. A phenotypic confirmatory test for ESβLs producers was performed using a combination disc method. The ESβLs encoding genes, including blaTEM, blaSHV, and blaCTX-M, were amplified using a PCR-based technique; the amplified products of some selected isolates were sequenced. Molecular detection of isolates using PCR-based amplification of the LuxS gene showed that all isolates possessed this gene. The patterns of antimicrobial resistance for isolates under study showed very high resistance to cephalosporins, while they were susceptible to carbapenem drugs and tigecycline. Findings based on the PCR technique showed that the prevalence of ESβLs encoding genes of isolates was 13 (26%), 31 (62%), and 46 (92%) for blaTEM, blaSHV, and blaCTX-M respectively. In the present study, it was concluded that blaCTX-M gene was the most prevalent ESβLs-encoding gene among ESβLs producing Serratia marcescens isolates.
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