As filterfeeders, freshwater sponges encounter bacteria in streams, rivers and lakes including those from faecal sources like enterococci and coliforms, which can exhibit antibiotic resistance with potential clinical impacts through e.g. infection of humans from recreational use of these environments. Filterfeeding trials verified the potential of Irish freshwater sponges Ephydatia fluviatilis and Spongilla lacustris, which occupy wide ranges in the northern hemisphere, to reduce the abundance of Escherichia coli in ambient water. Plate counts of bacterial abundance were more reliable than monitoring methods involving turbidity or fluorescence measurements. Laboratory and field studies tested the application of the sponges for biomonitoring of microbial water quality. In the laboratory both sponge species retained Enterococcus faecalis in lower abundances than E. coli. Although gradual changes of abundance of enterococci and coliforms in sponge samples were also observed along a longitudinal river reach transect, the between river differences in retention of enterococci and coliforms were greater than within a single river. The sponges’ potential for facilitating conjugal antibiotic resistance transfer was explored in microcosms with E. faecalis strains resistant to either vancomycin or rifampicin. Lack of a significant difference between transconjugant numbers on double selection plates from microcosms with live or dead sponges suggested that filtration activity had no decisive role in conjugal transfer of monitored resistance traits. Sponge gemmule surfaces were found to be associated with bacteria resistant to ampicillin, erythromycin, rifampicin, tetracycline, trimethoprim and vancomycin. Methanol extracts from freshwater sponges inhibited the growth of some nosocomial bacteria, with adult sponge extracts having a higher inhibitory effect than extracts from gemmule-grown sponges, indicating the contribution of the sponge microbiome. The antimicrobial properties of sponge samples varied with collection site, and the combination of sponge extracts from several sites caused the better inhibitor to become diluted and less effective as an antimicrobial agent.
- Freshwater sponges
- Antimicrobial properties