Phenotypic and genetic investigation of virulence and antibioresistance hallmarks in Escherichia coli strains isolated from Black Sea water on Romanian coast

The aim of this study was to investigate by phenotypic and molecular tools the antibiotic resistance profile and the virulence markers of 100 environmental Escherichia coli strains isolated from marine water in Constanta, Romania. The antibiosusceptibility testings were performed by disk diffusion method (CLSI, 201, including the phenotypic screening of beta-lactamases. The presence of different antibiotic resistance markers was correlated with the plasmidial pattern of the analyzed strains. Eleven (11) virulence factors were tested by using specific culture media. PCR was performed for the following antibiotic resistance and virulence genes: sul 1, 2, 3, aggR, EAST-1, AAFI/II. The tested strains exhibited high susceptibility to imipenem, ceftriaxone, cefoxitin and nitrofurantoin (99%), tobramycin (98%), cephtazidime (97%), gentamycin and amikacin (96%), ciprofloxacin (93%), nalidixic acid and chloramphenicole (92%) sulphametoxazole (89%) and high resistance levels to ampicillin (94%). The tested strains exhibited between 1 and 8 antibioresistance markers, the most frequent associations being: MP+SXT (10%), AMP+C (9%), AMP+CIP (8%) and AMP+NA (7%). Morevoer, the tested strains exhibited tolerance to heavy metals, i.e. to Zn (72%), Mn (98%), Cu (98%), Co (95%), and Ni (99%). 43,6% strains exhibiting resistance to beta-lactam antibiotics proved to be positive for the presence of beta-lactamases when tested by nitrocephine rapid test. The synergy test was negative for all tested strains. 25% of the tested strains exhibited at least one plasmid with variable molecular weights. Concerning the virulence hallmarks harboured by the sea water strains, 44% exhibited capacity of adherence to the cellular substrate (adherence indexes of 30% with localized, aggregative and diffuse patterns) and inert substrata (60%). Unexpectedely, an important number of strains (70.37%) also exhibited invasion ability of HeLa cells demonstrating the potential of these strains to colonize the animal and human tissues and to initiate an infectious process.The tested strains produced mucinase (100%), lysin-decarboxilase (93%), aesculin hydrolysis (67%) and β-hemolysins (6%).