Molecular Identification, Enzymatic Activity and Antibiotic Resistance Profiles of Bacteria Isolated from Merlangius merlangus

The present study intended to examine the cultivable bacterial microbiota of Merlangius merlangus, an ecologically valuable fish species from the Black Sea. Serial dilution and pre-enrichment steps were undertaken before isolation. Ten different isolates were isolated from muscle, gill, and intestinal tissues of fresh specimens. Molecular identification by 16S rRNA gene sequence showed all isolates to be members of Enterobacteriaceae, comprised of the genera Morganella, Providencia, Proteus, Klebsiella, and Escherichia. As one of the isolates (S09) was found to exhibit the highest similarity with a validly published species within the genus Morganella, with a relatively low value of 99.11%, it could be a new taxon. Extracellular enzyme tests showed variable presence of lipase and urease activities among isolates but no detectable amylase, caseinase, lecithinase, or DNase activities. Antimicrobial susceptibility testing was consistent with high rates of multidrug resistance, with eight isolates being resistant to three or more antibiotic groups. Resistance was greatest against amoxicillin/clavulanic acid, tetracycline, and sulfamethoxazole/trimethoprim, with all isolates showing susceptibility to imipenem. The observations point to the occurrence of metabolically active, environmentally adapted, and resilient bacterial forms in M. merlangus, with food safety implications and concern for antimicrobial resistance dissemination in aquatic ecosystems. Further, the uniqueness of the phylogenetic status of isolate S09 suggests an additional polyphasic taxonomic study. Future research involving metagenomes will be required to characterize host-associated bacterioplankton communities comprehensively, including their ecological functions.