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International audience; ObjectiveCarbapenemase-producing Enterobacteriaceae (CRE) and Enterococcus faecium resistant to vancomycin (VRE) constitute major threats to public health worldwide. The Pacific area is concerned and has implemented strategies to control antimicrobial resistance (AMR). However, accurate epidemiological data are rarely reported. Our study aimed to present the strategies applied to prevent and control the spread of highly resistant bacteria in the Pacific territory of New Caledonia.Patients and methodsCohort prospective study of all cases of highly resistant bacteria (HRB) isolated in New Caledonia from September 2004 to December 2020. Evaluation of the impact of the infection control measures implemented in healthcare settings: screening strategy, cohorting unit, IT tools and control of antibiotic prescriptions.ResultsA total of 346 patients with HRB were identified. Most of them (63.0%) were infected or colonized by VRE (n = 218) and 128 by CRE. While the number of CREs significantly increased from 2013 to 2020 (P < 0.0001), control procedures have limited their dissemination. Most patients were colonized by IMP-4-CRE (n = 124/128). The incidence density of VRE significantly decreased from 38.52 for 100,000 hospitalisation-days in 2015 to 4.19 for 100,000 hospitalisation-days in 2019 due to systematic screening of patients before sanitary repatriation from Australia and cohorting implementation. The risk of VRE diffusion is now well under control.ConclusionsOur study confirms that it is possible to control the spread of AMR in a circumscribed territory by means of a global control strategy involving screening, cohorting unit, IT tools and antibiotic prescription controls.

The ecological restoration of nickel mining-degraded areas in New Caledonia is strongly limited by low availability of soil mineral nutrients, metal toxicity, and slow growth rates of native plant species. In order to improve plant growth for restoration programs, special attention was paid to interactions between plant and soil microorganisms. In this study, we evaluated the influence of inoculation with Curtobacterium citreum BE isolated from a New Caledonian ultramafic soil on arbuscular mycorrhizal symbiosis and growth of Tetraria comosa, an endemic sedge used in restoration programs. A greenhouse experiment on ultramafic substrate was conducted with an inoculum comprising two arbuscular mycorrhizal fungi (AMF) species isolated from New Caledonian ultramafic soils: Rhizophagus neocaledonicus and Claroideoglomus etunicatum. The effects on plant growth of the AMF and C. citreum BE inoculated separately were not significant, but their co-inoculation significantly enhanced the dry weight of T. comosa compared with the non-inoculated control. These differences were positively correlated with mycorrhizal colonization which was improved by C. citreum BE. Compared with the control, co-inoculated plants were characterized by better mineral nutrition, a higher Ca/Mg ratio, and lower metal translocation. However, for Ca/Mg ratio and metal translocation, there were no significant differences between the effects of AMF inoculation and co-inoculation.

In New Caledonia, one third of the main island is covered by ultramafic soils characterized by high levels of metals and low levels of plant nutrients. In these soils, metal tolerant bacteria may play a role in plant adaptation to the edaphic constraints. Recently, two new bacteria species belonging to the genus Burkholderia sensu lato were isolated from rhizospheric roots of pioneer plant growing in New Caledonian ultramafic soils and were able to tolerate high metal concentrations. The purpose of this study was to determine the major mechanisms by which these two bacteria were able to tolerate metals and if they were able to reduce metal absorption by plants from which they were isolated. Bioaccumulation, adsorption on cell surface, ability to form biofilm and production of exopolysaccharides were assessed. A focus was carried out on Ni, generally the most toxic metal in New Caledonian ultramafic soils. All experiments were performed in comparison with a reference strain isolated from a non-ultramafic habitat, Paraburkholderia caribensis MWAP64T. The two ultramafic bacterial species showed a high tolerance to Ni with a Ni–IC50 of 5 mM for Caballeronia novacaledonica STM10272T and 30 mM for Paraburkholderia ultramafica STM10279T, values significantly higher than those of P. caribensis MWAP64T (2 mM). The major mechanism involved in the bacterial Ni tolerance was related to biofilm formation for C. novacaledonica STM10272T and to acidic exopolysaccharide production for P. ultramafica STM10279T. Both species alleviated metal contents in roots of Tetraria comosa, an endemic pioneer herbaceous species growing on New Caledonian ultramafic soils.

The present study focused on the characterization of 10 Curtobacterium citreum strains isolated from the rhizosphere of pioneer plants growing on ultramafic soils from New Caledonia. Taxonomic status was investigated using a polyphasic approach. Three strains (BE, BB, and AM) were selected in terms of multiple-metal resistance and plant-growth-promoting traits. They were tested on sorghum growing on ultramafic soil and compared with the reference strain C. citreum DSM20528T. To better understand the bacterial mechanisms involved, biosorption, bioaccumulation, and biofilm formation were investigated for the representative strain of the ultramafic cluster (strain BE) versus C. citreum DSM20528T. The polyphasic approach confirmed that all native isolates belong to the same cluster and are C. citreum. The inoculation of sorghum with strains BE and BB significantly reduced Ni content in shoots compared with inoculation with C. citreum DSM20528T and control values. This result was related to the higher Ni tolerance of the ultramafic strains compared with C. citreum DSM20528T. Ni biosorption and bioaccumulation showed that BE exhibited a lower Ni content, which is explained by the ability of this strain to produce exopolysaccharides involved in Ni chelation. We suggested that ultramafic C. citreum strains are more adapted to this substrate than is C. citreum DSM20528T, and their features allow them to enhance plant metal tolerance.