Comparison of Antibiotic Resistance in Aeromonas
Isolated
from Fish Collected from Heavy Metal Contaminated and
Uncontaminated Streams: Effect of Fish Trophic Status
INTRODUCTION
Antibiotic resistance is a significant public health problem. Increasing prevalence of antibiotic resistance has caused alarm for more than a decade (Cohen 1992; Neu 1992). Once confined to specialty units in hospitals, antibiotic resistant pathogens are now worldwide which demands worldwide evaluation and management (Levy 1997, 1998). An understanding of the mechanisms and factors that affect the acquisition and dissemination of antibiotic resistance traits is crucial if we expect to abate this trend. We have previously shown that antibiotic resistance in stream sediment bacteria increases along heavy metal contamination gradients (McArthur and Tuckfield 2000). This research suggests that exposure to heavy metals at concentrations above background may influence the frequency, abundance, and types of antibiotic resistance genes available in the environment. These genes could be subsequently transmitted to water-borne human pathogens.
Some water-associated bacteria can cause disease in normal hosts. Aeromonas spp. cause bacterial septicemia on fish and can be readily isolated from most fish with or without lesions. Recreational and subsistence fishing are important components of rural life especially in the southern United States. A recent study on factors affecting exposure of people to heavy metal and radioactively contaminated fish near the U.S. Department of Energy Savannah River Site (SRS) found that there are significant ethnic and socioeconomic differences in fishing and fish consumption along the Savannah River (Burger et al. 1999). Some groups consume more than 3 times the average consumption for recreational fishing. Aeromonas hydrophila infects many fish on the SRS and has been found to occur more frequently on fish collected from disturbed lentic and lotic environments (Esch and Hazen 1979, 1980, Hazen and Fliermans 1979, Fletcher person. com.) than fish collected from more pristine habitats.
Aeromonas hydrophila is capable of producing gastroenteritis, wound infection, and bacteremia in humans (Janda 1988; Haburchak 1996). Aminoglycosides, fluorinated quinolones, tetracyclines, and extended spectrum beta-lactam antibiotics are variably important in the therapy of specific aerobic Gram-negative infections. Unfortunately antibiotic resistance to all agents is increasing. Anecdotal evidence suggests that handling of Aeromonas infected fish can transmit multiple antibiotic resistant (MAR) Aeromonas to humans (Haburchak 1996)
Based on our previous studies that have shown an increase in antibiotic resistant bacteria along heavy metal contamination gradients we hypothesized that Aeromonas isolated from fish collected in a heavy metal contaminated stream would have higher incidences of antibiotic resistant (AR and MAR) Aeromonas than fish collected from a more pristine stream.
