Abstract
Rhizobiales are environmental bacteria often multidrug resistant (MDR) as other members of the rhizosphera. Some sub-populations of Rhizobiales are known as human-associated (in Rhizobium pusense and Ochrobactrum anthropi for instance). We aimed to evaluate the impact of runoff water from the hospital of Montpellier (2700 beds) on the presence of MDR and/or human-associated Rhizobiales. We therefore studied waters, sediments, epilithic and epiphytic biofilms upstream and downstream the hospital in an urban river running nearby during 5 weeks. A cultivation-based approach on a selective medium containing antibiotics was combined with a cultivation-independent method, i.e., Rhizobiales-specific 16S rRNA gene PCR and Temporal Temperature Gel Electrophoresis (TTGE), in order to describe the MDR cultivable community. A higher frequency of TTGE signals was observed in samples downstream than upstream the hospital (92% and 47%, respectively). The 10 detected OTUs belonged to the genera Ochrobactrum/Brucella, Pseudochrobactrum, Agrobacterium and Rhizobium. The groups « O. anthropi/Brucella » and « Pseudochrobactrum lubricantis » were the major OTUs, each representing 32% of the TTGE bands and they were mostly present downstream. Sediment community profiles seemed more stable over time than water communities. P. lubricantis group was mainly epiphytic while O. anthropi group was more often in epilithic biofilms. Among major OTUs, twenty-one O. anthropi strains were isolated and studied by MultiLocus Sequence Typing and compared to a collection of strains including 70 strains isolated in patients of the Montpellier hospital. The river strains were divided into 14 sequence types (ST), some of them being undescribed, confirming the high genetic diversity of this species. Six STs included both river and clinical strains (mainly from cystic fibrosis patients). Finally, 4 river strains (1 upstream and 3 downstream the hospital) belonged to the human-specific clonal complex CC4, which had never been previously isolated outside of clinical settings. These results suggested the dissemination of MDR and/or human-asociated Rhizobiales, mainly downstream the hospital. This result worths to be confirmed in order to propose the follow-up of autochthonous particular populations of Rhizobiales as markers of anthropisation.