Persistence of sucrose fermenting and nonfermenting vibrios in tissues of Manila clam species, Ruditapes philippinarum, depurated in seawater at two different temperatures

The High Risk of Bivalve Farming in Coastal Areas With Heavy Metal Pollution and Antibiotic-Resistant Bacteria: A Chilean Perspective

Anthropogenic pollution has a huge impact on the water quality of marine ecosystems. Heavy metals and antibiotics are anthropogenic stressors that have a major effect on the health of the marine organisms. Although heavy metals are also associate with volcanic eruptions, wind erosion or evaporation, most of them come from industrial and urban waste. Such contamination, coupled to the use and subsequent misuse of antimicrobials in aquatic environments, is an important stress factor capable of affecting the marine communities in the ecosystem. Bivalves are important ecological components of the oceanic environments and can bioaccumulate pollutants during their feeding through water filtration, acting as environmental sentinels. However, heavy metals and antibiotics pollution can affect several of their physiologic and immunological processes, including their microbiome. In fact, heavy metals and antibiotics have the potential to select resistance genes in bacteria, including those that are part of the microbiota of bivalves, such as Vibrio spp. Worryingly, antibiotic-resistant phenotypes have been shown to be more tolerant to heavy metals, and vice versa, which probably occurs through co- and cross-resistance pathways. In this regard, a crucial role of heavy metal resistance genes in the spread of mobile element-mediated antibiotic resistance has been suggested. Thus, it might be expected that antibiotic resistance of Vibrio spp. associated with bivalves would be higher in contaminated environments. In this review, we focused on co-occurrence of heavy metal and antibiotic resistance in Vibrio spp. In addition, we explore the Chilean situation with respect to the contaminants described above, focusing on the main bivalves-producing region for human consumption, considering bivalves as potential vehicles of antibiotic resistance genes to humans through the ingestion of contaminated seafood.

Temperature effects on the growth and survival of tdh positive Vibrio parahaemolyticus in tissues of postharvest Manila clam (Ruditapes philippinarum)

Bivalve storage at inadequate temperatures contains greater densities of Vibrio parahaemolyticus. The objective of the present study was to determine if there were any differences in growth and survival of potentially pathogenic V. parahaemolyticus (tdh positive) in relation to nonpathogenic V. parahaemolyticus (tdh-trh negative) levels in Manila clams (Ruditapes philippinarum) when exposed to different postharvest temperatures. Clams were depurated then exposed to known doses of both potential pathogenic and nonpathogenic V. parahaemolyticus for 24 h. Clams were then kept at the following temperatures corresponding to the Mediterranean summer (28 °C), winter (15 °C) and refrigeration (4 °C) for 96 h. Vibrio parahaemolyticus densities were determined at 0, 24, 48, 72 and 96 h of postharvest storage. Both isolates of V. parahaemolyticus multiplied rapidly in live clams held at 28 °C, (increase of 3 logs CFU/g at 72 h). Nonpathogenic V. parahaemolyticus in clams stored at 4 °C and 15 °C showed 1 log CFU/g and 2 log CFU/g decrease at 96 h, respectively, while no significant differences were detected for pathogenic V. parahaemolyticus at these temperatures after 96 h.

Impact of milk fish farming in the tropics on potentially pathogenic vibrios

Ratios of sucrose-negative to sucrose-positive vibrios on TCBS agar (suc-/suc+) indicate the abundance of potential human pathogenic non-cholera vibrios in coastal mariculture environments of the Lingayen Gulf (Philippines. In guts of adult maricultured milkfish (Chanos chanos) of suc- vibrios reached extreme peak values ranging between 2 and 545 million per g wet weight. Suc- vibrios outnumbered suc+ vibrios in anoxic sediments, too, and were rarely predominant in coastal waters or in oxidized sediments. Suc-/suc+ ratios in sediments increased toward the mariculture areas with distance from the open sea at decreasing redox potentials. There is circumstantial evidence that suc- vibrios can be dispersed from mariculture areas to adjacent environments including coral reefs. An immediate human health risk by pathogenic Vibrio species is discounted, since milkfish guts contained mainly members of the Enterovibrio group. A representative isolate of these contained proteolytic and other virulence factors, but no genes encoding toxins characteristic of clinical Vibrio species.

Uptake and retention of Vibrio parahaemolyticus in a cohabitating population of Ruditapes decussatus and Ruditapes philippinarum under experimental conditions

The presence of Vibrio parahaemolyticus in bivalve mollusc is an important cause of foodborne illnesses, and their levels are influenced by environmental changes, such as temperature and salinity. Clams are common species in estuaries and are used in environmental monitoring programmes. Present study compared the uptake and retention of nonpathogenic V. parahaemolyticus by two species of clam (Ruditapes decussatus and R. philippinarum), cohabitating in a closed system. Results showed no significant differences were found between both species of clams. Bacterial levels are following a similar trend with values between 3.48 and 3.70 log CFU/g for R. decussatus and between 3.15 and 3.49 log CFU/g for R. philippinarum. So, in the absence of water renewal, high and stable levels of V. parahaemolyticus were observed in cultured clams after exposure. Changes in physical parameters should be taken into account to design surveillance programmes in bivalves, and sampling should focus on species that have faster filtration rates at that water temperature since they potentially represent the worst-case scenario.