Abstract
Live feeds are utilized in marine fish hatcheries to feed and promote the health of finfish larvae due to their nutritional advantages. The presence of detrimental bacteria in rotifer culture can cause disease outbreaks in larval rearing. Nevertheless, the use of UV application to disinfect seawater is not very effective to eliminate and inactivate all pathogenic agents presented in the raw surface water. To investigate new methods of disinfection, two experiments were conducted at the University of Miami Experimental Hatchery (UMEH) to quantify and test for antibiotic susceptibility for Vibrio spp. and the total coliforms by using plate counting method and treating with two water-soluble antibiotics, Tobramycin and Minocycline, at concentrations of 30 μg/mL, 100 μg/mL and 200 μg/mL. In the first experiment, water samples from Virginia Key Bear Cut, Florida were collected from five locations beginning from surface water, settling tank, sand filter, after a 120 watts UV instrument and after a 80 watts UV instrument respectively. No fecal coliform colonies were observed by plate counting method after UV disinfections, implying a complete inactivation by UV irradiation, but V. vulnificus, V. parahaemolyticus and V. alginolyticus were observed in all samples. In the second experiment, the isolation of several pure strains of bacteria was performed to test the susceptibility to these antibiotics on Mueller Hinton Agar (MHA). After measuring the zone of inhibition, all bacteria strains isolated after the 80 watts UV instrument were highly sensitive to the antibiotics, but when antibiotics were applied to bacteria in UV treated water, resistance to all dosages of antibiotics was observed indicating the presence of multi- antibiotic resistance (MAR) bacteria in the water. The transmission of multi-antibiotic resistance bacteria through the food chain may cause serious problems to consumers and different treatments and technologies are needed, such as ozone and ultrasound, to completely disinfect incoming and discharge water to generate pathogen free water.