Letter to the Editor Characterization of Mycobacterium chimaera in a heater-cooler unit in Latvia Janis Kimsis MSc 1 , Ilva Pole MSc 2 , Inga Norvaisa MD 2 , Uga Dumpis MD, PhD 3 and Renate Ranka PhD 1 1 Latvian Biomedical Research and Study Centre, Riga, Latvia, 2 Riga East University Hospital, Riga, Latvia and 3 Pauls Stradins Clinical University Hospital, Riga, Latvia To the Editor—Mycobacterium chimaera (M. chimaera) is an opportunistic environmental mycobacterium belonging to the M. avium–M. intracellulare complex. Transmission of M. chimaera from contaminated heater-cooler unit (HCU) water tanks to patients is a risk during open-heart surgery. 1 Specifically, investigations have revealed that the contaminated HCU devices (Stockert 3T) came from one particular manufacturing facility, LivaNova in Munich, Germany, and were a likely source for cardiothoracic surgery–related severe M. chimaera infections that occurred in Switzerland, Germany, The Netherlands, and the United Kingdom. 2 The importance of HCUs lies in their ability to regulate the body temperature of a patient during cardiac surgery. However, evidence suggests that the airborne transmis- sion of aerosolized bacteria from the water tanks was responsible for these infections. 2 Currently, the extent of global outbreaks is unknown, but the burden of invasive M. chimaera was estimated to be 156–282 cases per year in 10 countries where most cardiac-valve replacements are performed. 3 We investigated the possible presence of M. chimaera in HCUs in the Cardiothoracic Department, Latvian Centre of Cardiology of Pauls Stradins Clinical University Hospital, Latvia. The water of HCUs was sampled before they underwent the routine disinfection procedure in May, 2017. Samples were cultured on Bactec MGIT 960 system (Becton Dickinson, Heidelberg, Germany). The growth of myco- bacteria was observed in 2 samples. DNA was isolated and the M. chimaera was identified using a GenoType NTM-DR version 1.0 kit (Hain Lifescience, Nehren, Germany). Both isolates, designated LV-2017-1-HCU and LV-2017-2-HCU, were subjected to whole-genome sequencing with 150× coverage on an Ion Proton System (Thermo Fisher Scientific, Waltham, MA). For the bioin- formatics analysis, reads in samples produced in this study were aligned to the M. chimaera reference genome JCM_14737 (ENA accession no. PRJNA324238) using the bwa MEM algorithm. Variants were called and marked based on the published criteria 4 using BCFtools. Sequences of both isolates were compared to strains ZUERICH-1 (DSM 101591) and ZUERICH-2 (DSM 101592), representatives of the major M. chimaera groups 1 and 2. 5 For the phylogenetic analysis, raw sequencing reads of the iso- lates LV-2017-1-HCU and LV-2017-2-HCU were mapped against the M. chimaera type strain FI-01069 (DSM 44623) 6 and compared with strain ZUERICH-1 and 127 other publicly available data sets of M. chimaera isolates belonging to subgroup 1.1 and previously collected in Denmark, Germany, The Netherlands, the United Kindgom, Ireland, the United States, Australia, and New Zealand (available in the European Nucleotide Archive; http:// www.ebi.ac.uk/ena). 4,5,7 The analysis was performed using CSI Phylogeny 1.4 software, Center of Genomic Epidemio- logy (https://cge.cbs.dtu.dk/services/CSIPhylogeny/), with default settings but including the reference in the final tree. 8 Molecular phylogenetic analysis was performed using the maximum likeli- hood method. The phylogenetic tree was built from 176 SNP posi- tions of 130 M. chimaera isolates and was visualized in MEGA6. Results In total, 2,555,838 and 1,544,268 sequencing reads were generated for samples LV-2017-1-HCU and LV-2017-2-HCU, respectively. The sequencing reads were deposited in the European Nucleotide Archive (ENA) under study numbers ERS3734298 and ERS37 34299. Molecular phylogenetic analysis revealed that both Latvian HCU‘s samples were closely related to the strain ZUERICH-1 (Fig. 1A). Specific SNP signatures 5 for subgroup 1.1. (substitutions of guanine (G) by adenine (A) at positions 113,518 and 209,278 of the DSM 44623T genome—GenBank accession no. LQOO00 000000) were found in both Latvian isolates. This result suggested that they belong to the subgroup 1.1 which contains most M. chimaera isolates from water systems or exhaust air of LivaNova HCUs in clinical use, isolates from HCUs sampled at the LivaNova production site, and isolates from related patients in different countries. 5 During the phylogenetic analysis of the isolates LV-2017-1- HCU and LV-2017-2-HCU, the sequencing coverage was 92.3% and 78% of the reference genome, respectively. The percentage of the reference genome covered by all isolates was 43.8%. As expected, the isolates within the subgroup 1.1 showed little diversity, with a median pairwise distance of 2 SNPs (range, 0–40). 5 A median pairwise distance for the Latvian LV-2017-1- HCU and LV-2017-2-HCU isolates were 32 (range, 31–40) and 4 (range, 3–12) SNPs, respectively. The results showed that M. chimaera sequences from HCU in Latvia genetically clustered with the isolates from HCUs in The Netherlands, the United States, and Germany (samples 110, 128, 180, 187, 2015-22-15-01), as well as isolates from patients in The Netherlands (sample 198) and USA (samples 2015-22-63, 2015-22-79, 2015-22-80) (Fig. 1B). Author for correspondence: Renate Ranka, E-mail: renate_r@biomed.lu.lv Cite this article: Kimsis J, et al. (2020). Characterization of Mycobacterium chimaera in a heater-cooler unit in Latvia. Infection Control & Hospital Epidemiology, https://doi.org/ 10.1017/ice.2020.1226 © The Author(s), 2020. Published by Cambridge University Press on behalf of The Society for Healthcare Epidemiology of America Infection Control & Hospital Epidemiology (2020), 1–3 doi:10.1017/ice.2020.1226 Downloaded from https://www.cambridge.org/core. 08 Jul 2021 at 06:05:09, subject to the Cambridge Core terms of use.