Identification and characterisation of a novel multidrug-resistant streptococcus, Streptococcus toyakuensis sp. nov., from a blood sample

Objectives: In 2018, we isolated multidrug-resistant alpha-haemolytic streptococci TP1632 from the blood of a 34-year-old patient with bacteraemia. This study aimed to characterise a-haemolytic streptococci TP1632 and elucidate its multidrug resistance mechanisms. Methods: TP1632 was characterised by whole genome sequencing and biochemical testing. Based on the genome sequence, digital DNA-DNA hybridization (dDDH) and average nucleotide identity based on BLAST (ANIb) values were calculated. In addition, antimicrobial-resistance mechanisms were evaluated by ResFinder and transformation assay using Streptococcus mitis. Results: TP1632 showed resistance to ss-lactams, macrolides, and quinolones. Genomic analysis revealed that dDDH and ANIb values between TP1632 and S. mitis were 56.3% and 93.63%, respectively, indicating TP1632 as the novel species. TP1632 exhibited macrolide resistance genes such as mef(A), msr(D), and erm(B) and tetracycline resistance gene tet(M). In addition, amino acids at position 81 in GyrA and 79 in ParC were tyrosine and isoleucine, respectively. When penicillin-binding proteins of TP1632 were introduced into S. mitis, recombinants showed ss-lactam resistance. Thus, acquired resistance genes and low affinities towards antimicrobial agents contribute to multidrug resistance. Conclusion: Our findings indicated that multidrug-resistant TP1632 is a novel species in the genus Streptococcus. Furthermore, antimicrobial resistance of this strain could transfer horizontally among ahaemolytic streptococci. These data indicated the risk of emergence of multidrug-resistant streptococci not only as a pathogen but also a reservoir of antimicrobial resistance. This isolate was proposed as a novel species, Streptococcus toyakuensis sp. nov. The type strain is TP1632(T) (= JCM 34623(T) = CCUG 75492(T)). (c) 2022 The Author(s). Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)