ORCID

https://orcid.org/0000-0003-4119-4318

ResearcherID/Other

Scopus Author ID: 7004091733

Document Type

Article

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

Disciplines

Bacteriology | Biochemistry | Biochemistry, Biophysics, and Structural Biology | Microbial Physiology | Microbiology | Pathogenic Microbiology

CIT Disciplines

Microbiology; Biochemical research methods

Publication Details

Bioengineered

Abstract

A total of 220 lactic acid bacteria isolates were screened for antifungal activity using Aspergillus fumigatus and Aspergillus niger as the target strains. Four Lactobacillus strains exhibited strong inhibitory activity on agar surfaces. All four were also identified as having strong inhibitory activity against the human pathogenic fungi Microsporum canis, Microsporum gypseum and Epidermophyton floccosum. One of the four lactobacilli, namely Lb. reuteri ee1p exhibited the most inhibition against dermatophytes. Cell-free culture supernatants of Lb. reuteri ee1p and of the non-antifungal Lb. reuteri M13 were freeze-dried and used to access and compare antifungal activity in agar plate assays and microtiter plate assays. Addition of the Lb. reuteri ee1p freeze-dried cell-free supernatant powder into the agar medium at concentrations greater than 2% inhibited all fungal colony growth. Addition of the powder at 5% to liquid cultures caused complete inhibition of fungal growth on the basis of turbidity. Freeze-dried supernatant of the non-antifungal Lb. reuteri M13 at the same concentrations had a much lesser effect. As Lb. reuteri M13 is very similar to the antifungal strain ee1p in terms of growth rate and final pH in liquid culture, and as it has little antifungal activity, it is clear that other antifungal compounds must be specifically produced (or produced at higher levels) by the anti-dermatophyte strain Lb. reuteri ee1p. Reuterin was undetectable in all four antifungal strains. The cell free supernatant of Lb. reuteri ee1p was analyzed by LC-FTMS using an Accela LC coupled to an LTQ Orbitrap XL mass spectrometer. The high mass accuracy spectrum produced by compounds in the Lb. reuteri ee1p strain was compared with both a multianalyte chromatogram and individual spectra of standard anti-fungal compounds, which are known to be produced by lactic acid bacteria. Ten antifungal metabolites were detected.

Guo_ et_al_T1-10.4161_bbug.19624.csv (1 kB)
Table 1. Summary of antifungal activity of isolated lactic acid bacteria against selected Aspergillus species (incubation was performed at 37°C or 30°C)

Guo_et_al_T2-10.4161_bbug.19624.csv (1 kB)
Table 2. Zone sizes (mm) around bacterial streaks indicating antifungal activity of lactic acid bacteria against the dermatophytes Microsporum canis, Microsporum gypseum and Epidermophyton floccosum. The table includes the most inhibitory antifungal LAB strain and a negative control strain for each, indicated by an asterisk. Negative control strains have the same growth rates and exhibit the same final culture pH as their respective antifungal partner

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