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Dialysis waters: should we look for Mycobacteria?

A Cannas(1) P Dal Monte(2) F Messina(1) F Bisognin(2) O Butera(1) S Zannoli(3) G Dirani(3) G Gatti(3) E Girardi(1) C Fontana(1) V Sambri(3,4)

1:National Institute for Infectious Diseases "L. Spallanzani" IRCCS, Rome, Italy; 2:Microbiology Unit, IRCCS Azienda Ospedaliero Universitaria di Bologna, Bologna, Italy; 3:Unit of Microbiology, The Greater Romagna Area Hub Laboratory, Cesena, Italy; 4:Department Medical and Surgical Sciences (DIMEC)-Alma Mater Studiorum, University of Bologna, Bologna, Italy

Nontuberculous mycobacteria (NTM) are common environmental contaminants and, as opportunistic pathogens, they could colonize or infect immunocompromised patients.

Consecutive ultrapure dialysis fluid samples were collected during one year in the Emilia Romagna region, and processed by Microbiology Units at IRCCS University Hospital of Bologna and at The Great Romagna Hub Laboratory, Pievesestina.

Concentrated samples were cultured for 42 days. Mycobacterium saskatchewanense was identified in positive cultures by MALDI-TOF technique and isolates were sent to the National Institute for Infectious Diseases “L. Spallanzani” (INMI) for epidemiological investigation by Whole Genome Sequencing (WGS) using Illumina system. Sequences were analysed with SeqSphere+ RIDOM software, by core genome Multi-Locus-Sequence-Typing (cgMLST of 5090 alleles), upon alignment to the reference genome (ID Genbank NZ_AP022573.1).

Thirty-five strains of M. saskatchawanense were isolated from 722 dialysis samples. The WGS analysis allowed the creation of a phylogenetic tree [Minimum Spanning Tree (MST)]. Genetic distances between the strains were below 15 alleles. Raw sequence reads are available under the BioProject accession number PRJNA1055936.

This explorative analysis showed the presence of M. saskatchawanense genetically close strains in fluid samples from dialysis systems, raising the question whether this and other mycobacteria should be routinely searched for in sanitary waters. Furthermore, alternative disinfection methods of the devices should be explored, in order to efficaciously eliminate potential sources of human infection. A potential explanation for the role of NTMs in medical devices could be their ability to form biofilms, thus further investigation in this area is warranted.

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