Detection of antibiotic resistance in probiotics of dietary supplements

Abstract

Background: Probiotics are live microorganisms that confer nutrition- and health-promoting benefits if consumed in adequate amounts. Concomitant with the demand for natural approaches to maintaining health is an increase in inclusion of probiotics in food and health products. Since probiotic bacteria act as reservoir for antibiotic resistant determinants, the transfer of these genes to pathogens sharing the same intestinal habitat is thus conceivable considering the fact that dietary supplements contain high amounts of often heterogeneous populations of probiotics. Such events can confer pathogens protection against commonly-used drugs. Despite numerous reports of antibiotic resistant probiotics in food and biological sources, the antibiogram of probiotics from dietary supplements remained elusive.

Findings: Here, we screened five commercially available dietary supplements for resistance towards antibiotics of different classes. Probiotics of all batches of products were resistant towards vancomycin while batch-dependent resistance towards streptomycin, aztreonam, gentamycin and/or ciprofloxacin antibiotics was detected for probiotics of brands Bi and Bn, Bg, and L. Isolates of brand Cn was also resistant towards gentamycin, streptomycin and ciprofloxacin antibiotics. Additionally, we also report a discrepancy between the enumerated viable bacteria amounts and the claims of the manufacturers.

Conclusions: This short report has highlighted the present of antibiotic resistance in probiotic bacteria from dietary supplements and therefore serves as a platform for further screenings and for in-depth characterization of the resistant determinants and the molecular machinery that confers the resistance.

Fig. 1

The recovery and enumeration of probiotic bacteria from dietary supplements. (a) Representative MRS agar plates of probiotics bacteria recovered from Bi, Bg, L, Bn and Cn dietary supplements showing different colony morphologies and densities. (b) Comparison of the enumerated probiotics bacteria to that claimed by the manufacturers of the respective products (Table 1). Error bars represent standard error of the mean (n = 2)

Fig. 2

The antibiotic susceptibility profile of probiotic bacteria in the dietary supplements. (a) Representative MRS agar plates of bacteria lawn of Bi, Bn, Bg, Cn and L dietary supplements layered with antibiotic discs showing susceptibility towards multiple antibiotics as characterized by the presence of ‘clear’ inhibition zones. (b) Mean inhibition zones measured from the bacteria lawn of Bi, Bn, Bg, Cn and L dietary supplements layered with the respective antibiotic discs. Error bars represent standard error of the mean (n ≥ 2) and (*) represents inhibition zone present in only certain batches of bacteria in the respective dietary supplement