Aerobic spores pose serious problems for both food product manufacturers and consumers. Milk is particularly at risk and thus an important issue of preventive consumer protection and quality assurance. The spore-former Bacillus cereus is a food poisoning Gram-positive pathogen which mainly produces two different types of toxins, the diarrhea inducing and the emetic toxins. Reliable and rapid analytical assays for the detection of B. cereus spores are required, which could be achieved by combining in vitro generated aptamers with highly specific molecular biological techniques. For the development of routine bioanalytical approaches, already existing aptamers with high affinity to B. cereus spores have been characterized by surface plasmon resonance (SPR) spectroscopy and fluorescence microscopy in terms of their dissociation constants and selectivity. Dissociation constants in the low nanomolar range (from 5.2 to 52.4 nM) were determined. Subsequently, the characterized aptamers were utilized for the establishment and validation of an aptamer-based trapping technique in both milk simulating buffer and milk with fat contents between 0.3 and 3.5%. Thereby, enrichment factors of up to 6-fold could be achieved. It could be observed that trapping protocol and characterized aptamers were fully adaptable to the application in milk. Due to the fact that aptamer selectivity is limited, a highly specific real time PCR assay was utilized following trapping to gain a higher degree of selectivity.

A GM1-liposome aptamer sandwich LFA was developed and compared with AuNP-based competitive aptamer and aptamer-antibody sandwich LFAs for cholera toxin detection.

No abstract

SummaryThis study compared the secretomes (proteins exported out of the cell) of Propionibacterium freudenreichii of different origin to identify plausible adaptation factors. Phylosecretomics indicated strain‐specific variation in secretion of adhesins/invasins (SlpA, InlA), cell‐wall hydrolysing (NlpC60 peptidase, transglycosylase), protective (RpfB) and moonlighting (DnaK, GroEL, GaPDH, IDH, ENO, ClpB) enzymes and/or proteins. Detailed secretome comparison suggested that one of the cereal strains (JS14) released a tip fimbrillin (FimB) in to the extracellular milieu, which was in line with the electron microscopy and genomic analyses, indicating the lack of surface‐associated fimbrial‐like structures, predicting a mutated type‐2 fimbrial gene cluster (fimB‐fimA‐srtC2) and production of anchorless FimB. Instead, the cereal strain produced high amounts of SlpB that tentatively mediated adherent growth on hydrophilic surface and adherence to hydrophobic material. One of the dairy strains (JS22), producing non‐covalently bound surface‐proteins (LspA, ClpB, AraI) and releasing SlpA and InlA into the culture medium, was found to form clumps under physiological conditions. The JS22 strain lacked SlpB and displayed a non‐clumping and biofilm‐forming phenotype only under conditions of increased ionic strength (300 mM NaCl). However, this strain cultured under the same conditions was not adherent to hydrophobic support, which supports the contributory role of SlpB in mediating hydrophobic interactions. Thus, this study reports significant secretome variation in P. freudenreichii and suggests that strain‐specific differences in protein export, modification and protein–protein interactions have been the driving forces behind the adaptation of this bacterial species.