Bacteria are known to be abundant in seawater around coral zones, in coral tissues, and within their surface microlayer (Lampert et al., 2006; Rosenberg et al., 2007), and each of these habitats supports the existence of different bacterial species (Koren & Rosenberg, 2006; Littman et al., 2009). Several studies documented that the bacterial population associated with corals are specific and any anthropogenic pressure and environmental effects could affect the health of the corals (Chimetto et al., 2009; Nithyanand & Pandian, 2009; Ceh et al., 2011). Intensive use of antimicrobial agents in aquaculture develops drug-resistant bacteria and transmits the resistance genes to other bacteria in the aquatic environment. Due to this practice, resistance genes may get disseminated among native bacterial flora of humans and aquatic animals by horizontal gene transfer (Kruse & Sorum, 1994; Akinbowale et al., 2006).
Integrating conjugative elements (ICEs) are mobile genetic elements that are increasingly recognized as important mediators of horizontal gene transfer among prokaryotes (Burrus et al., 2006). In the past decade, an increasing number of ICEs have been described in several bacterial groups. These ICEs play an important role in the dissemination of antimicrobial resistance genes in several pathogens and in commensal bacteria. Most of the studies on SXT/ICEs are carried out in clinical isolates of Vibrio cholerae. However, the presence of SXT/ICEs in other bacterial species from several ecosystems is less understood. One of such unexplored ecosystems is the marine environment where the presence of SXT/ICEs has been reported in Photobacterium damselae ssp. piscicida (Osorio et al., 2008) and other bacterial strains taxonomically related to Vibrio scophthalmi, Vibrio splendidus, Vibrio alginolyticus, Shewanella haliotis, and Enterovibrio nigricans (Rodríguez-Blanco et al., 2012). The increasing number of reports of antimicrobial resistance conferring the SXT-related ICEs in diverse pathogens and other environmental isolates presumably reflects the overuse of drugs that reaches several ecosystems supporting the selection of resistance gene transfer. Through screening and cataloging the SXT-related ICEs, we can detect diversity and accessory functions of ICEs and understand their roles in facilitating the rapid adaptation of prokaryotes to changing environments. The SXT/ICE was first reported from V. cholerae O139 conferring the resistance to four antimicrobials, namely trimethoprim, streptomycin, sulfamethoxazole, and chloramphenicol (Waldor et al., 1996). Later, Hochhut et al. (2001) described that SXT is genetically and functionally related to the IncJ element R391/ICE from Providencia rettgeri resistance to kanamycin and mercury. However, it is very likely that more comprehensive studies would detect SXT-related elements in many pathogenic and nonpathogenic bacterial species.
Coral mucus is a rich substrate for microorganisms (Lampert et al., 2006). To date, very few systematic studies have been undertaken on abundance and diversity of microorganisms associated with the corals from Andaman Sea. In this study, we present our results on the identification of 18 heterotrophic culturable bacteria from the mucus of the coral Fungia echinata from Andaman Sea and Nicobar Islands, India, and detection of SXT/R391 ICEs targeting the integrase gene.