Carbapenem resistance bacteria (CRB) are not only restricted to clinical settings, where they cause serious infection, but can also spread within natural ecosystem. Studies on the presence of carbapenem resistance in the environment have been mostly conducted on freshwater habitats, such as rivers and lakes, and nothing known for marine ecosystem. Here, we investigated carbapenem resistance in coastal seawater along the eastern coast of Sydney. To identify potential sources for resistance, we also analysed wastewater, storm water, and terrestrial run-off water. CRBs were isolated on a range of media and identified by 16S rRNA gene sequencing. The community profile of CRBs in the different samples type were compared using qualitative unweighted UniFrac (UW) distance analysis.

A wide range of CRBs were found in the seawater samples, which differed between the locations we sampled. We found many CRBs bacteria that belonged to genera that have not been previously described to contain carbapenem resistance, including Brevundimonas, Rheinheimera, Frondibacter, and Alteromonas.  CRBs profile in stormwater and run-off water were not different to the ones in seawater (UW sig = 0.172), indicating that they are potential sources for the CRBs found in seawater. This is also consistent with the fact that a storm event during our study had a significant impact on the CRBs profile in seawater. A genomic library for the CRBs on the genus Rheinheimera in E. coli, identified several clones that contained a gene for a novel protein related to subclass B3 metallo-beta-lactamases. As this novel gene was able to be expressed in E. coli and was phylogenetically related to a sequence found in Enterobacter cloacae, it has possibly been subject to horizontal gene transfer between Enterbacteriacaea and environmentally derived Rheinheimera (family Chromatiaceae).

Our study revealed that CRBs with a wide taxonomic diversity exist in marine environment, that some of them are derived from land run-off and that their carbapenem resistance genes might potentially be shared with enteric bacteria.