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Abstract
Leuconostoc spp. are environmental microorganisms commonly associated with fermented foods. Absence of antibiotic resistance (AR) in bacteria is a critical issue for global food safety. Herein, we updated the occurrence of AR genes in the Leuconostoc genus through in silico analyses of the genomes of 17 type strains. A total of 131 putative AR traits associated with the main clinically relevant antibiotics were detected. We found, for the first time, the lsaA gene in L. fallax ATCC 700006T and L. pseudomesenteroides NCDO 768T. Their amino acid sequences displayed high similarities (59.07% and 52.21%) with LsaA of Enterococcus faecalis V583, involved in clindamycin (CLI) and quinupristin-dalfopristin (QUD) resistance. This trait has different distribution patterns in Leuconostoc nontype strains—i.e., L. pseudomesenteroides, L. lactis and L. falkenbergense isolates from fermented vegetables, cheeses, and starters. To better explore the role of lsaA, MIC for CLI and QUD were assessed in ATCC 700006T and NCDO 768T; both strains were resistant towards CLI, potentially linking lsaA to their resistant phenotype. Contrarily, NCDO 768T was sensitive towards QUD; however, expression of lsaA increased in presence of this antibiotic, indicating an active involvement of this trait and thus suggesting a revision of the QUD thresholds for this species.
Highlights
Leuconostoc spp. belong to the functional group of Lactic Acid Bacteria (LAB) and are generally found on green vegetation and roots; from this natural habitat, they disseminate to various plant niches, such as lychee fruits (L. litchi [1]), palm wine (L. palmae [2]) cabbage and rutabaga (L. rapi [3]), cucumbers, carrots, olives, silage, soybeans (L. mesenteroides strains [4,5]) coffee beans (L. holzapfelii [6]) and quinoa samples (L. lactis and L. mesenteroides isolates, [7]) where they can actively participate in the fermentation process
The annotated sequences of the 17 type strains of the Leuconostoc genus were downloaded from NCBI database and aligned against the protein sequences in CARD to retrieve all putative antibiotic resistance (AR) genes carried by these strains
Further phenotypic analysis should include gene cloning, knock-out vector development and minimum inhibitory concentrations (MICs) determination in strains with the disrupted gene as it was performed both by Singh and colleagues in 2002 to characterize lsaA in almost 500 strains of Enterococcus strains [29] and by Shi and coauthors in 2020 to characterize lsaD in Lactococcus garvieae strains [66]
Summary
Leuconostoc spp. belong to the functional group of Lactic Acid Bacteria (LAB) and are generally found on green vegetation and roots; from this natural habitat, they disseminate to various plant niches, such as lychee fruits (L. litchi [1]), palm wine (L. palmae [2]) cabbage and rutabaga (L. rapi [3]), cucumbers, carrots, olives, silage, soybeans (L. mesenteroides strains [4,5]) coffee beans (L. holzapfelii [6]) and quinoa samples (L. lactis and L. mesenteroides isolates, [7]) where they can actively participate in the fermentation process. Leuconostoc spp. have been associated with foods of animal origin including dairy (L. citreum, L. lactis, L. mesenteroides, L. falkebergense [13,14]), fish (i.e., L. mesenteroides in molluscs, [5]) and both in fresh and fermented meat products (L. carnosum, L. citreum, L. mesenteroides and L. gelidum; [15,16,17]) Their impact on dairy technology is mainly related to their ability to produce CO2 , which is responsible for the eye formation in some cheeses, and other aroma compounds, such as diacetyl and acetoin, significantly contributing to the flavor of the final product [18]. Leuconostoc spp. have been frequently found in infections caused by multiple microorganisms in patients following vancomycin treatment, towards which they are intrinsically resistant due to the presence of pentadepsipeptide with D-Lactate at the C-terminal in the peptidoglycan instead of a D-Alanine [18]
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