Evaluation of Petrifilm Lactic Acid Bacteria Plates for Counting Lactic Acid Bacteria in Food

Versatile gold-silver-PB nanojujubes for multi-modal detection and photo-responsive elimination against bacteria

Bacterial infections have become a serious threat to global public health. Nanomaterials have shown promise in the development of bacterial biosensing and antibiotic-free antibacterial modalities, but single-component materials are often less functional and difficult to achieve dual bacterial detection and killing. Herein, we report a novel strategy based on the effective integration of multi-modal bacterial detection and elimination, by constructing the versatile gold-silver-Prussian blue nanojujubes (GSP NJs) via a facile template etching method. Such incorporation of multi-components involves the utilization of cores of gold nanobipyramids with strong surface-enhanced Raman scattering (SERS) activity, the shells of Prussian blue as both an efficient bio-silent SERS label and an active peroxidase-mimic, and functionalization of polyvinyl pyrrolidone and vancomycin, respectively endowing them with good colloidal dispersibility and specificity against S. aureus. The GSP NJs show operational convenience in the SERS detection and excellent peroxidase-like activity for the sensitive colorimetric detection. Meanwhile, they exhibit robust near-infrared photothermal/photodynamic effects, and the photo-promoted Ag⁺ ions release, ultimately achieving a high antibacterial efficiency over 99.9% in 5 min. The NJs can also effectively eliminate complex biofilms. The work provides new insights into the design of multifunctional core-shell nanostructures for the integrated bacterial detection and therapy.

Effect of UV Filters during the Application of Pulsed Light to Reduce Lactobacillus brevis Contamination and 3-Methylbut-2-ene-1-thiol Formation While Preserving the Physicochemical Attributes of Blonde Ale and Centennial Red Ale Beers

Pulsed light (PL) is a novel, non-thermal technology being used to control the microbial spoilage of foods and beverages. Adverse sensory changes, commonly characterized as "lightstruck", can occur in beers when exposed to the UV portion of PL due to the formation of 3-methylbut-2-ene-1-thiol (3-MBT) upon the photodegradation of iso-α-acids. This study is the first to investigate the effect of different portions of the PL spectrum on UV-sensitive beers (light-colored blonde ale and dark-colored centennial red ale) using clear and bronze-tinted UV filters. PL treatments with its entire spectrum, including the ultraviolet portion of the spectrum, resulted in up to 4.2 and 2.4 log reductions of L. brevis in the blonde ale and centennial red ale beers, respectively, but also resulted in the formation of 3-MBT and small but significant changes in physicochemical properties including color, bitterness, pH, and total soluble solids. The application of UV filters effectively maintained 3-MBT below the limit of quantification but significantly reduced microbial deactivation to 1.2 and 1.0 log reductions of L. brevis at 8.9 J/cm² fluence with a clear filter. Further optimization of the filter wavelengths is considered necessary to fully apply PL for beer processing and possibly other light-sensitive foods and beverages.

Bacteriocin production and inhibition of Bacillus subtilis by Lactobacillus paracasei HD1.7 in an indirect coculture system

A broad-spectrum antimicrobial peptide named Paracin 1.7 was produced by Lactobacillus paracasei HD1.7, which was isolated from Chinese sauerkraut juice. In this study, the influence of cocultivation on the communication mechanism of L. paracasei HD1.7 and Bacillus subtilis was investigated. The two bacterial strains were grown in monoculture and indirect coculture, and the growth of both bacteria and bacteriocin production as well as the transcriptional level of luxS in L. paracasei HD1.7 and spo0A in B. subtilis were monitored. Bacteriocin production and cell numbers were increased significantly when L. paracasei HD1.7 cells were indirectly cocultured with B. subtilis, and bacteriocin-producing L. paracasei HD1.7 can prevent the growth and sporulation of B. subtilis. After indirect coculture with B. subtilis, the expression of luxS in L. paracasei HD1.7 increased in the exponential growth phase and decreased in the stationary phase compared to monoculture. The expression of spo0A in B. subtilis dropped in the indirect coculture compared to the monoculture. It indicate that the upregulation of luxS is due to a response to a secreted compound produced by B. subtilis. The results show L. paracasei HD1.7 has an amensalism on B. subtilis, while B. subtilis has a commensalism on L. paracasei HD1.7.

3M Petrifilm Lactic Acid Bacteria Count Plate Is a Reliable Tool for Enumerating Lactic Acid Bacteria in Bacon

ABSTRACT

This study aimed to evaluate the behavior of Petrifilm Lactic Acid Bacteria Count Plates (PLAB) as an alternative methodology to enumerate lactic acid bacteria (LAB) in bacon. Bacon samples (n = 40) were obtained from retail sale, 10-fold diluted with buffered peptone water (BPW, 0.2% [w/v]) and Letheen broth, and subjected to LAB enumeration according to four protocols: (i) de Man Rogosa Sharpe (MRS) agar, pH 5.7, 30°C; (ii) MRS, pH 5.7, 30°C, anaerobiosis; (iii) all-purpose Tween agar (APT), 25°C; and (iv) PLAB, 30°C. Colonies were enumerated at 24, 48, and 72 h, and the results expressed as log CFU per gram for comparison by analysis of variance and regression (P < 0.05). Furthermore, colonies were randomly selected and characterized as LAB (Gram staining and catalase). Mean LAB counts from MRS and PLAB did not present significant differences independently of incubation time or diluent (P > 0.05), whereas counts in APT with BPW after 24 h were significantly lower (P < 0.05). PLAB counts with BPW (24, 48, and 72 h) presented significant correlation with MRS (r ranging from 0.87 to 0.89; in anaerobiosis, r ranging from 0.94 to 0.95) and APT (r ranging from 0.84 to 0.86). With Letheen broth, PLAB (24, 48, and 72 h) presented significant correlation with MRS (r ranging from 0.92 to 0.94; in anaerobiosis, r ranging from 0.93 to 0.96) and APT (r ranging from 0.77 to 0.79). In total, 1,032 colonies (97%) from 1,063 colonies were characterized as LAB. Thus, PLAB can be considered as an alternative tool for enumerating LAB in bacon, with reliable results even after 24 h of incubation.

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