Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2021 Dec 18;10(12):3145.
doi: 10.3390/foods10123145.

Antimicrobial Susceptibility of Lactobacillus delbrueckii subsp. lactis from Milk Products and Other Habitats

Noam Shani  1 , Simone Oberhaensli  2 , Hélène Berthoud  1 , Remo S Schmidt  3 , Hans-Peter Bachmann  3
Affiliations

Antimicrobial Susceptibility of Lactobacillus delbrueckii subsp. lactis from Milk Products and Other Habitats

Noam Shani et al. Foods. .

Abstract

As components of many cheese starter cultures, strains of Lactobacillus delbrueckii subsp. lactis (LDL) must be tested for their antimicrobial susceptibility to avoid the potential horizontal transfer of antibiotic resistance (ABR) determinants in the human body or in the environment. To this end, a phenotypic test, as well as a screening for antibiotic resistance genes (ARGs) in genome sequences, is commonly performed. Historically, microbiological cutoffs (MCs), which are used to classify strains as either 'sensitive' or 'resistant' based on the minimal inhibitory concentrations (MICs) of a range of clinically-relevant antibiotics, have been defined for the whole group of the obligate homofermentative lactobacilli, which includes LDL among many other species. This often leads to inaccuracies in the appreciation of the ABR status of tested LDL strains and to false positive results. To define more accurate MCs for LDL, we analyzed the MIC profiles of strains originating from various habitats by using the broth microdilution method. These strains' genomes were sequenced and used to complement our analysis involving a search for ARGs, as well as to assess the phylogenetic proximity between strains. Of LDL strains, 52.1% displayed MICs that were higher than the defined MCs for kanamycin, 9.9% for chloramphenicol, and 5.6% for tetracycline, but no ARG was conclusively detected. On the other hand, all strains displayed MICs below the defined MCs for ampicillin, gentamycin, erythromycin, and clindamycin. Considering our results, we propose the adaptation of the MCs for six of the tested clinically-relevant antibiotics to improve the accuracy of phenotypic antibiotic testing.

Keywords: Lactobacillus delbrueckii; SNP-based phylogeny; antimicrobial susceptibility; broth microdilution; genome sequencing; kanamycin.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in designing this study; in the collection, analyses, or interpretation of data; in manuscript writing; or in the decision to publish the results.

Figures

Figure 1
Figure 1
SNP-based phylogenetic tree of Lactobacillus delbrueckii subsp. bulgaricus strains assessed in this study. The scale shows the rate of single nucleotide polymorphisms.
Figure 2
Figure 2
SNP-based phylogenetic tree of the Lactobacillus delbrueckii subsp. lactis strains assessed in this study. Country and biological origin, as well as the defined minimal inhibitory concentration of kanamycin (MICs, pink bars, along with their numerical values expressed in mg/L) are displayed. For strains that did not grow in the test medium or that have not been tested, MIC of kanamycin is indicated with ‘0′. The scale shows the rate of single nucleotide polymorphisms.
Figure 3
Figure 3
Combined minimal inhibitory concentration (MIC) distributions for Lactobacillus delbrueckii subsp. lactis and L. delbrueckii subsp. bulgaricus. The dashed lines indicate the current microbiological cutoffs (MCs) as defined by the European Food Safety Authority, and the dotted lines represent the calculated MCs based on the MICs measured in this study.
Figure 4
Figure 4
Minimal inhibitory concentration (MIC) distributions for Lactobacillus delbrueckii subsp. lactis only. The dashed lines indicate the current microbiological cutoffs (MCs) as defined by the European Food Safety Authority, and the dotted lines represent the calculated MCs based on the MICs measured in this study.
See this image and copyright information in PMC

References

    1. Bourdichon F., Alper I., Bibiloni R., Dubois A., Laulund S., Miks M., Morelli L., Yao S. Inventory of Microbial Food Cultures with Safety Demonstration in Fermented Food Products. Volume 495. Bulletin of the International Dairy Federation; Brussels, Belgium: 2018. pp. 1–74. Update of the Bulletin of the IDF 455–2012.
    1. El Kafsi H., Binesse J., Loux V., Buratti J., Boudebbouze S., Dervyn R., Kennedy S., Galleron N., Quinquis B., Batto J.-M., et al. Lactobacillus delbrueckii ssp. lactis and ssp. bulgaricus: A chronicle of evolution in action. BMC Genom. 2014;15:1–12. doi: 10.1186/1471-2164-15-407. - DOI - PMC - PubMed
    1. Sieuwerts S., de Bok F.A.M., Hugenholtz J., van Hylckama Vlieg J.E.T. Unraveling Microbial Interactions in Food Fermentations: From Classical to Genomics Approaches. Appl. Environ. Microbiol. 2008;74:4997–5007. doi: 10.1128/AEM.00113-08. - DOI - PMC - PubMed
    1. Somerville V., Berthoud H., Schmidt R.S., Bachmann H.-P., Meng Y.H., Fuchsmann P., von Ah U., Engel P. Functional strain redundancy and persistent phage infection in Swiss hard cheese starter cultures. ISME J. 2021:1–12. doi: 10.1038/s41396-021-01071-0. - DOI - PMC - PubMed
    1. Schmid M., Muri J., Melidis D., Varadarajan A.R., Somerville V., Wicki A., Moser A., Bourqui M., Wenzel C., Eugster-Meier E., et al. Comparative Genomics of Completely Sequenced Lactobacillus helveticus Genomes Provides Insights into Strain-Specific Genes and Resolves Metagenomics Data Down to the Strain Level. Front. Microbiol. 2018;9:63. doi: 10.3389/fmicb.2018.00063. - DOI - PMC - PubMed

LinkOut - more resources