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If not properly treated, hospital wastewaters become a route for dissemination of antibiotic-resistant bacteria to the environment. Even with disinfection, many hospital bacteria survive classical methods such as chlorination or UV irradiation. A novel, effective and economically feasible methods for removal of such bacteria from wastewaters would be desirable. One of the prominent hospital pathogens is bacterium Acinetobacter baumannii. Due to its extraordinary resistance to many classes of antibiotics, especially to carbapenems that were for long time the “last resort” drug, it has become common to detect multiple -, extensive- and even pan-drug resistant isolates of A. baumannii worldwide, both in hospital settings but also in natural environments. Over the last few years, it has been shown without a doubt that in Croatia, A. baumannii along with other Gram-negative pathogens readily disseminates to surface waters via hospital wastewaters, and that it readily passes wastewater treatment plant. Therefore, we tested natural mineral zeolite, enriched with silver by ion-exchange (AgNZ) as a substrate for disinfection of wastewater. The antibacterial efficacy of AgNZ was tested in flow system (biofilter) with pure bacterial cultures, but also with real effluent wastewater from Zagreb wastewater treatment plant. In experiments with real wastewater, we measured the numbers of all carbapenem-resistant bacteria, not just A. baumannii. The biofilter filled with AgNZ and constantly fed with bacterial suspension at 30 ml h-1 flow rate eliminated all of the A. baumannii cells (100 % removal) during 4 days of the experiment and remained effective by removing up to 3 Log values for 14 days. In experiments with real wastewater, the biofilter was effective in removing 90-100 % of carbapenem-resistant bacteria during 4 days. By using X-Ray microtomography it was also shown that particle size of biofilter filling is important from technological point of view, as small sized particles caused biofilter breakthrough by causing preferential flow-paths to emerge. However, after regeneration the biofilter became active again suggesting possile long-time use of AgNZ as biofilter filling. Here presented study is a contribution to “One Health” approach as it proposes a sustainable step forward in reduction of antibiotic resistance dissemination from hospitals to the environment and vice-versa. |
