Phenotypic and Genome-based Approaches for Antibiotic Resistance Assessment in Lactic Acid Bacteria: a Focus on the Genera Leuconostoc and Lactobacillus

The emergence of antibiotic resistance (AR) among bacteria in foodstuff has become a huge issue to public healthcare systems in recent decades. Indeed, resistant foodborne bacteria can cause serious health effects directly or via the transmission of the AR genes to pathogens, causing illnesses that are difficult to treat. Lactic acid bacteria (LAB) represent a chief component within the composite microbiota of fermented foods. Recently, the crucial role of LAB as reservoir of potentially transmissible AR genes has been increasingly recognized, highlighting the need for expanding the current knowledge on LAB mobile resistome and providing further insight into the evolution and spread of AR in the food chain. In the present study, the antimicrobial susceptibility profiles and the genetic basis of the resistance were investigated for two relevant genera of LAB, i.e. Leuconostoc and Lactobacillus, through the application of standard methods, such as phenotypic testing, conjugation experiments and PCR assay, and whole-genome sequencing (WGS)-based approaches. In the first part of the dissection, the contribution of these two approaches in the characterization of AR features for the genus Leuconostoc was investigated, revealing that genome-based analysis was more informative than conventional molecular techniques. Indeed, WGS-based analysis revealed the presence of genes coding for aminoglycoside resistance, such as aad6, sat4 and aphA-3, for streptogramin A resistance, as vatE, and for tetracycline, such as tet(S), in the genome sequence of the multidrug resistant L. mesenteroides subsp. mesenteroides LbE16 strain. In addition, this approach highlighted for the first time the presence of a erm(B)-bearing Tn917 transposon in the genome of L. mesenteroides subsp. dextranicum LbE15. Antibiotic susceptibility testing and conjugation experiments allowed to confirm the resistance phenotype for those Leuconostoc strains and provided the first evidence of the erythromycin resistance transfer between L. mesenteroides and E. faecalis, supplying novel proof that AR LAB can act as a reservoir of acquired AR genes. Therefore, standard methods should be combined with the WGS-based approaches to validate the hypothesis emerged from the in silico prediction of AR features. In the last part of the dissection, the combination of phenotypic susceptibility testing and genome-based analysis was performed for the whole genus Lactobacillus. This analysis revealed a positive correlation between phenotype and genotype for the 67% of the cases examined, where the genes aac(3), lsa and cml(A) involved in the resistance towards aminoglycoside, clindamycin and chloramphenicol, respectively, were found for the first time in Lactobacillus strains. In addition, acquired determinants coding for tetracycline and erythromycin resistance were simultaneously detected in L. amylophilus DSM 20533T and L. amylotrophicus DSM 20534T. Whereas, L. ingluviei DSM 15946T harboured the Tn916-like transposon carrying the genes tet(M) and tet(L), highlighting the potential of these AR genes to be horizontally transferred to other microorganisms. The results reported in this study may be utilized as a starting point for the generation of new and more focused scientific protocols and regulatory procedures based on WGS approaches for the safety assessment of Leuconostoc and Lactobacillus strains employed as starter cultures, food preservatives or probiotic by food and probiotic stakeholders

Exploring Antibiotic Resistance Diversity in Leuconostoc spp. by a Genome-Based Approach: Focus on the {lsaA} Gene

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 Enterococcusfaecalis 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

Draft genome sequence of three antibiotic-resistant Leuconostoc mesenteroides strains of dairy origin

Leuconostoc mesenteroides is a lactic acid bacterium (LAB) commonly associated with fermented foods. Here, we report the genome sequence of three selected dairy strains, showing atypical antibiotic resistances (AR). Genome analysis provided a better understanding of the genetic bases of AR in Leuconostoc and its potential transferability among foodborne bacteria.Peer Reviewe

Whole genome analysis as a tool for the safety assessment of antibiotic resistance in food-processing bacteria

Trabajo presentado en la 2nd EFSA Scientific Conference, celebrado en Milán, Italia, del 14 al 16 de octubre de 2015Acquisition of antibiotic resistances (AR) by pathogens leads ultimately to a failure of antibiotic therapy. The food chain is considered a key player in the transmission of AR determinants to pathogens from reservoirs in commensal and beneficial bacteria. Therefore, the absence of transmissible AR genes in bacteria used as starter and adjunct cultures for food and feed processing is considered to be critical (EFSA, 2012; EFSA Journal, 10:2740). Genome sequencing allows the inspection of the whole genetic makeup of bacteria in the search for the basis of desirable and undesirable traits, including that of AR. Thus, in silico sequence analysis and comparison against databases can be used as a tool for the safety assessment of microorganisms intended to be used in food systems. This communication reports on the genome analysis of three Leuconostoc mesenteroides strains of dairy origin showing atypical resistances to tetracycline (LbT16), erythromycin and clindamycin (LbE15), and kanamycin, streptomycin, tetracycline and virginiamycin (LbE16). Genes encoding for erythromycin [erm(B)] and tetracycline [tet(S)] resistance had already been detected by PCR. Genome analysis confirmed the presence of these genes and identified others which encode uncommon AR in lactic acid bacteria. Analysis of the genes and their flanking regions revealed a potential of some to be horizontally transferred to other bacteria. This study demonstrates the effectiveness of combining genome sequencing and bioinformatics analysis as an affordable tool for the safety assessment of food bacteria. This innovative approach could become a novel paradigm in the selection programs of starters for the food industry.Peer Reviewe

Whole-metagenome-sequencing-based community profiles of Vitis vinifera L. cv. Corvina berries withered in two post-harvest conditions

Vitis vinifera L. cv. Corvina grape forms the basis for the production of unique wines, such as Amarone, whose distinctive sensory features are strongly linked to the post-harvest grape withering process. Indeed, this process increases sugar concentration and changes must characteristics. While microorganisms involved in must fermentation have been widely investigated, few data are available on the microbiota of withered grapes. Thus, in this paper, a whole metagenome sequencing (WMS) approach was used to analyse the microbial consortium associated with Corvina berries at the end of the withering process performed in two different conditions (“traditional withering,” TW or “accelerated withering,” AW), and to unveil whether changes of drying parameters could have an impact on microbial diversity. Samples of healthy undamaged berries were collected and washed, to recover microorganisms from the surface and avoid contamination with grapevine genetic material. Isolated DNA was sequenced and the data obtained were analyzed with several bioinformatics methods. The eukaryotic community was mainly composed by members of the phylum Ascomycota, including Eurotiomycetes, Sordariomycetes, and Dothideomycetes. Moreover, the distribution of the genera Aspergillus and Penicillium (class Eurotiomycetes) varied between the withered berry samples. Instead, Botryotinia, Saccharomyces, and other wine technologically useful microorganisms were relatively scarce in both samples. For prokaryotes, 25 phyla were identified, nine of which were common to both conditions. Environmental bacteria belonging to the class Gammaproteobacteria were dominant and, in particular, the TW sample was characterized by members of the family Pseudomonadaceae, while members of the family Enterobacteriaceae dominated the AW sample, in addition to Sphyngobacteria and Clostridia. Finally, the binning procedure discovered 15 putative genomes which dominated the microbial community of the two samples, and included representatives of genera Erwinia, Pantoea, Pseudomonas, Clostridium, Paenibacillus, and of orders Lactobacillales and Actinomycetales. These results provide insights into the microbial consortium of Corvina withered berries and reveal relevant variations attributable to post-harvest withering conditions, underling how WMS could open novel perspectives in the knowledge and management of the withering process of Corvina, with an impact on the winemaking of important Italian wines

Draft Genome Sequence of the Probiotic Yeast Kluyveromyces marxianus fragilis B0399

Here, we report the draft genome sequence of Kluyveromyces marxianus fragilis B0399, the first yeast approved as a probiotic for human consumption not belonging to the genus Saccharomyces The genome is composed of 8 chromosomes, with a total size of 11.44\ua0Mb, including mitochondrial DNA

Draft Genome Sequence of Three Antibiotic-Resistant Leuconostoc mesenteroides Strains of Dairy Origin

Leuconostoc mesenteroides is a lactic acid bacterium (LAB) commonly associated with fermented foods. Here, we report the genome sequence of three selected dairy strains, showing atypical antibiotic resistances (AR). Genome analysis provided a better understanding of the genetic bases of AR in Leuconostoc and its potential transferability among foodborne bacteria

Antibiotic susceptibility profiles of dairy Leuconostoc, analysis of the genetic basis of atypical resistances and transfer of genes in vitro and in a food matrix

In spite of a global concern on the transfer of antibiotic resistances (AR) via the food chain, limited information exists on this issue in species of Leuconostoc and Weissella, adjunct cultures used as aroma producers in fermented foods. In this work, the minimum inhibitory concentration was determined for 16 antibiotics in 34 strains of dairy origin, belonging to Leuconostoc mesenteroides (18), Leuconostoc citreum (11), Leuconostoc lactis (2), Weissella hellenica (2), and Leuconostoc carnosum (1). Atypical resistances were found for kanamycin (17 strains), tetracycline and chloramphenicol (two strains each), and erythromycin, clindamycin, virginiamycin, ciprofloxacin, and rifampicin (one strain each). Surprisingly, L. mesenteroides subsp. mesenteroides LbE16, showed resistance to four antibiotics, kanamycin, streptomycin, tetracycline and virginiamycin. PCR analysis identified tet(S) as responsible for tetracycline resistance in LbE16, but no gene was detected in a second tetracycline-resistant strain, L. mesenteroides subsp. cremoris LbT16. In Leuconostoc mesenteroides subsp. dextranicum LbE15, erythromycin and clindamycin resistant, an erm(B) gene was amplified. Hybridization experiments proved erm(B) and tet(S) to be associated to a plasmid of ≈35 kbp and to the chromosome of LbE15 and LbE16, respectively. The complete genome sequence of LbE15 and LbE16 was used to get further insights on the makeup and genetic organization of AR genes. Genome analysis confirmed the presence and location of erm(B) and tet(S), but genes providing tetracycline resistance in LbT16 were again not identified. In the genome of the multi-resistant strain LbE16, genes that might be involved in aminoglycoside (aadE, aphA-3, sat4) and virginiamycin [vat(E)] resistance were further found. The erm(B) gene but not tet(S) was transferred from Leuconostoc to Enterococcus faecalis both under laboratory conditions and in cheese. This study contributes to the characterization of AR in the Leuconostoc-Weissella group, provides evidence of the genetic basis of atypical resistances, and demonstrates the inter-species transfer of erythromycin resistance

Effective identification of Lactobacillus casei group species: Genome-based selection of the gene mutL as the target of a novel multiplex PCR assay

Lactobacillus casei, Lactobacillus paracasei and Lactobacillus rhamnosus form a closely related taxonomic group (the L. casei group) within the facultatively heterofermentative lactobacilli. Strains of these species have been used for a long time as probiotics in a wide range of products, and they represent the dominant species of nonstarter lactic acid bacteria in ripened cheeses, where they contribute to flavour development. The close genetic relationship among those species, as well as the similarity of biochemical properties of the strains, hinders the development of an adequate selective method to identify these bacteria. Despite this being a hot topic, as demonstrated by the large amount of literature about it, the results of different proposed identification methods are often ambiguous and unsatisfactory. The aim of this study was to develop a more robust species-specific identification assay for differentiating the species of the L. casei group. A taxonomy-driven comparative genomic analysis was carried out to select the potential target genes whose similarity could better reflect genome-wide diversity. The gene mutL appeared to be the most promising one and, therefore, a novel species-specific multiplex PCR assay was developed to rapidly and effectively distinguish L. casei, L. paracasei and L. rhamnosus strains. The analysis of a collection of 76 wild dairy isolates, previously identified as members of the L. casei group combining the results of multiple approaches, revealed that the novel designed primers, especially in combination with already existing ones, were able to improve the discrimination power at the species level and reveal previously undiscovered intraspecific biodiversity

Whole genome analysis as a tool for the safety assessment of antibiotic resistance in food-processing bacteria

Acquisition of antibiotic resistances (AR) by pathogens leads ultimately to a failure of antibiotic therapy. The food chain is considered a key player in the transmission of AR determinants to pathogens from reservoirs in commensal and beneficial bacteria. Therefore, the absence of transmissible AR genes in bacteria used as starter and adjunct cultures for food and feed processing is considered to be critical (EFSA, 2012; EFSA Journal, 10:2740). Genome sequencing allows the inspection of the whole genetic makeup of bacteria in the search for the basis of desirable and undesirable traits, including that of AR. Thus, in silico sequence analysis and comparison against databases can be used as a tool for the safety assessment of microorganisms intended to be used in food systems. This communication reports on the genome analysis of three Leuconostoc mesenteroides strains of dairy origin showing atypical resistances to tetracycline (LbT16), erythromycin and clindamycin (LbE15), and kanamycin, streptomycin, tetracycline and virginiamycin (LbE16). Genes encoding for erythromycin [erm(B)] and tetracycline [tet(S)] resistance had already been detected by PCR. Genome analysis confirmed the presence of these genes and identified others which encode uncommon AR in lactic acid bacteria. Analysis of the genes and their flanking regions revealed a potential of some to be horizontally transferred to other bacteria. This study demonstrates the effectiveness of combining genome sequencing and bioinformatics analysis as an affordable tool for the safety assessment of food bacteria. This innovative approach could become a novel paradigm in the selection programs of starters for the food industry