Rapid Identification and Quantification of Lactobacillus rhamnosus by Real-Time PCR Using a TaqMan Probe

Bacteraemia Caused by Probiotic Strains of Lacticaseibacillus rhamnosus—Case Studies Highlighting the Need for Careful Thought before Using Microbes for Health Benefits

Lactic acid bacteria belonging to Lactobacillus spp. and Lacticaseibacillus spp. are a natural part of fermented milk and other food products, probiotic supplements and human microbiota. They mainly belong to mucosal microflora, especially oral, vaginal and intestinal. Lacticaseibacillus spp. strains included in probiotics are generally characterised as safe microorganisms, and the species are concerned bacteria with very low pathogenic potential. However, infections caused by Lactobacillus spp. and Lacticaseibacillus spp., including bacteraemia and endocarditis, occur occasionally. The aim of the study was to present two cases of bacteraemia due to Lacticaseibacillus rhamnosus associated with the use of a probiotic product. It afflicted patients in intensive care units. The investigation was preliminarily based on clinical and microbiological recognition of the cases. The initial observation was laboratory confirmed with the application of pulsed-field gel electrophoresis (PFGE) results. Identical PFGE patterns were obtained for the evaluated strains and the strains derived from a commercially available probiotic that was administered to those patients. The increasing number of studies describing opportunistic infections due to probiotic strains of Lacticaseibacillus spp. should result in verifying the safety of probiotic formulations used in immunocompromised patients and forming detailed guidelines for the use of probiotics among patients from several risk groups.

N, O-codoped hierarchical porous graphitic carbon for electrochemical immunosensing of Lactobacillus rhamnosus GG

An ultrasensitive label-free electrochemical immunosensor was fabricated for quantitative detection of Lactobacillus rhamnosus GG (LGG). The N/O co-doped three-dimensional hierarchical porous graphitic (THPG) carbon was synthesized by a one-step synthesis of polyaniline hydrogel, and followed by simple carbonization and chemical activation procedures. Because of the unique structure design, the obtained THPG carbon networks possess an ultra-large specific surface area of 4859 m² g^-1 along with a class of highly graphitic carbons. The results offer an enormous surface area and excellent electrical conductivity for label-free electrochemical immunosensing of probiotic L. rhamnosus strain. Under optimal conditions, the immunosensor showed a good linear relationship between peak current and concentration of LGG (R² = 0.9976), with a detection limit of 2 CFU mL^-1. Furthermore, this label-free immunosensor also shows good specificity, long-term stability, and reliability, and could be applied to detect probiotic LGG in dairy products and drinks with satisfactory results. The present protocol was shown to be quite promising for practical screening and functional evaluation of probiotic products containing LGG. A ultrasensitive label-free electrochemical immunosensor based on THPG carbon was fabricated for detection of Lactobacillus rhamnosus GG.

Quantification of Major Bacteria and Yeast Species in Kefir Consortia by Multiplex TaqMan qPCR

Kefir grains are complex microbial systems of several groups of microorganisms. The identification and quantification of the microbial composition of milk kefirs was described in several studies, which provided an insight into the microbial consortia in this complex ecosystem. Nevertheless, the current methods for identification and quantification are not appropriate for deeper studies on kefir consortia, e.g., population dynamics and microbial interactions in kefir grains. This requires another sensitive and reliable quantitative method. Therefore, this study aims to develop multiplexed qPCR assays to specifically detect and quantify, as an example, several microorganisms of the milk kefir microbial community. Primer-probe sets, which target species-specific genes in six bacteria and five yeasts, were designed, and their sensitivity and specificity to the target species was analyzed in simplex as well as four multiplex qPCR assays. The self-designed multiplex assays were applied for the detection of target bacteria and yeast species in milk kefirs, in both, grain and beverage fractions. Detection of all target microorganisms in simplex and multiplex qPCR was achieved by good linearity, efficiency, repeatability and reproducibility in all assays. When the designed assays were applied on six kefirs, all target microorganisms were detected in different samples, but not all in one kefir sample. The two ubiquitous lactobacilli Lactobacillus kefiranofaciens and Lb. kefiri were present in all six kefirs studied, but were associated with different other yeasts and bacteria. Especially on the yeast community a significant diversity was observed. In general, multiplex TaqMan qPCR as developed here was proven to have high potential for specific identification of target microorganisms in kefir samples and for the first time, eleven target bacteria and yeasts of kefir microbiota were rapidly detected and quantified. This study, thus, provides a fast and reliable protocol for future studies on kefir and other similar microbial ecosystems.