Functional genomic insights into aac(6')-I-associated kanamycin resistance in Leuconostoc citreum DMLC16.

Authors

Sumin Lee, Sojeong Heo, Yura Moon, Minkyeong Kim, Do-Won Jeong

Published in

Food microbiology. Volume 142. Pages 105299. Epub Sep 02, 2026.

Abstract

Leuconostoc (L.) citreum strain DMLC16 was initially selected as a candidate starter culture for fermented foods. However, it exhibited a minimum inhibitory concentration (MIC) of 256 mg/L against kanamycin, exceeding the European Food Safety Authority threshold for resistance. To determine whether this resistance was intrinsic or acquired, comparative genomic analysis was performed with four additional L. citreum strains. Only DMLC16 was found to harbor the aminoglycoside 6'-N-acetyltransferase (aac(6')-I) gene. An adjacent IS30 family transposase and a putative recognition sequence (5'-TGTTGAGTACAGGTTG-3') were also identified, and the surrounding chromosomal region contained a replication initiation protein typically associated with plasmids, strongly suggesting that aac(6')-I represents an acquired trait. Functional validation confirmed its role in resistance: cloning of aac(6')-I conferred increased kanamycin MICs in Gram-positive hosts, rising from 4 to 64 mg/L in Staphylococcus aureus RN4220 and from 2 to 32 mg/L in Lactococcuscremoris MG1363. These findings indicate that L. citreum DMLC16 carries an acquired genetic determinant conferring kanamycin resistance. In contrast, species-level comparative genomic analysis suggested that conserved sequence variations in the 16S rRNA gene and gidB may contribute to the intrinsic kanamycin resistance phenotype of L. citreum. These observations highlight the need for strain-level genomic screening to identify acquired resistance determinants, together with further investigation of species-wide kanamycin susceptibility patterns and the genetic basis of intrinsic resistance. Importantly, L. citreum strains harboring aac(6')-I should not be considered suitable candidates for industrial starter cultures.

PMID:
42901652
Bibliographic data and abstract were imported from PubMed on 21 Oct 2026.

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