Study of pathogenic activity and antibiotic resistance of cultured heterotrophic bacteria isolated from water and bottom sediments of the deep zone of the western part of the North Caspian sea

Abstract

Commercial development of aquatic biological resources (ABR) of the Caspian Sea necessitates constant monitoring of the ABR habitat. Microbiota studies are of particular relevance, since bacterial communities largely determine the quality of the FBR habitat. The purpose of this work is to identify opportunistic and sanitary-indicative bacteria that have pathogenicity factors and antibiotic resistance and pose a danger for aquatic biological resources. The paper presents data on the taxonomic composition of saprotrophic bacterioplankton and bacteriobenthos in the waters of the Northern Caspian Sea in the period from 2013 to 2018. Water samples were taken annually in summer and autumn. The work used generally accepted methods for identifying bacteria by morphological and physiological-biochemical characteristics, as well as methods for determining antibiotic resistance and pathogenic activity. During the research period (2013–2018), more than 2000 isolates of saprotrophic bacteria belonging to 28 taxa were isolated from water samples and bottom sediments of the northern part of the Caspian Sea. The taxonomic composition of saprotrophic bacterioplankton and bacteriobenthos did not differ significantly in the number of taxa identified, but differed somewhat in the proportion of species, especially at the level of larger taxonomic groups. The study of bacterial virulence showed that the occurrence of various pathogenic properties in bacteria did not have a common direction in a number of years. Microorganisms isolated from water and soil of the northern part of the Caspian Sea had multiple antibiotic resistance to various groups of drugs. During the study period, high resistance of isolated bacteria (62–92% of isolated isolates) to benzylpenicillin and ampicillin was noted. In general, the presence of bacteria in the water and bottom sediments of the Northern Caspian Sea that have pathogenicity factors and multiple antibiotic resistance indirectly indicated the stress of the bacteriocenosis in the research area.