Effect of Magnesium Acetate on the Antimold Activity of Lactobacillus

ABSTRACT The antimold activity of lactic acid bacteria (LAB) is used in food biopreservation. The aim of this study was to evaluate the effect of magnesium acetate added to de Man Rogosa Sharpe (MRS) medium on the antimold activity of three LAB strains (Lactobacillus plantarum, Lactobacillus brevis, and Lactobacillus fermentum) against molds contaminating food (Aspergillus oryzae, Aspergillus niger, Penicillium chrysogenum, Fusarium avenaceum, and Rhizopus arrhizus) and their ability to produce organic acids (acetic acid, lactic acid, and phenyllactic acid). The antimold activity of LAB strains was evaluated using the overlay method, and the concentration of the organic acids was determined with the gas chromatography technique. Changes in viable cell counts and the pH of LAB culture also were monitored over a 48-h period. The results show that the growth inhibition of all the molds (except R. arrhizus) was higher in LAB strain cultures on MRS with magnesium acetate agar than on MRS agar, and inhibition increased over the 48 h. Magnesium acetate added to MRS broth stimulated the production of acetic acid by all LAB strains in the first 8 h and slightly stimulated the production of lactic acid by L. plantarum during the first 24 h. No adverse effect of magnesium acetate on growth of LAB strains was noted. The results confirm that magnesium acetate enhances the antimold activity of LAB strains.

Novel multiplex-PCR for rapid detection of Bacillus anthracis spores present in soils of Sirajganj district in Bangladesh

Bacillus anthracis spores were isolated and detected from soil samples (n=72) using multiplex-PCR method. The bacteria were isolated and primarily identified as Bacillus anthracis using selective Polymyxin B - Lysozyme - EDTA - Thallous acetate agar. A multiplex-PCR method targeting three genes; rpoB of genome, pag of pX01 and cap of pX02 was done to confirm the isolated bacteria. Among 72 soil samples, the viable B. anthracis spores could be extracted from 14 (19.44%) samples. However, both pX01 and pX02 plasmids were harbored in 5 (6.94%) isolates. On the other hand, pX01 and pX02 was present in 8 (57.14%) and 11 (78.57%) isolates, respectively. This two-step-method was found to be easy, accurate and rapid in identification of B. anthracis spores from soil samples and to identify the toxigenic plasmids present in this bacterium. Progressive Agriculture 26:67-70, 2015

Enumeration of Hydrogen Sulfide-Producing Bacteria from Anaerobically Packaged Pork

The influence of medium composition, pH, incubation time and gaseous atmosphere during incubation on enumeration of H2S-producing bacteria from anaerobically packaged pork was determined. Samples of anaerobically packaged pork were plated and H2S-producing bacteria isolated. Stock cultures of these isolates were prepared, diluted and pour-plated with Lead Acetate Agar (LAA) containing various concentrations of cysteine (0.001 to 0.005%) at different pH values (5.0 to 8.0). The inoculated plates were incubated at 21°C for various periods (3 to 6 d) under different gaseous atmospheres (N2, CO2 or mixtures of both). The conditions resulting in optimized recovery and enumeration of H2S-producing bacteria from anaerobically packaged pork consisted of pour-plating the isolates with LAA to which 0.003 to 0.005% cysteine was added and pH adjusted to 7.5–8.0 plus incubation in an atmosphere of 5%CO2–95%N2 for 5 to 6 d at 21°C.

Convenient microscopic tests for yeast viability and sporogenic capability

Drops of cell suspension are seeded on nutrient medium containing 5% purified agar and spread between the agar surface and a cover glass. The liquid phase is absorbed by the concentrated agar, so that the cells are held in situ between glass and agar. After incubation nongerminated cells and micro-colonies are counted microscopically. Sporogenic capability is assessed by seeding very dense cell suspensions on acetate agar and covering with Teflon F.E.P. membrane which is permeable to oxygen.

Lactobacilli in milk used for commercial cheesemaking

SummaryThe numbers of lactobacilli, including pediococci and some leuconostocs, in raw and heat treated milks at twenty-six cheese factories in different parts of the country were determined over a period of 12 months, by plating on acetate agar. Counts in the raw milks varied from < 1 to > 100000/ml, but were usually within the range 100 to 10000/ml. Widely different times and temperatures of heat treatment were in use at the different creameries, some of which destroyed most of the lactobacilli present, whilst others had less effect. Post heat treatment re-infection of the milk in the vat with lactobacilli usually occurred.

731. Lactobacilli in cheese starter cultures

For a survey of the numbers of lactobacilli present in milk used for cheese-making in creameries, counts were made on an acetate-agar medium (1) selective for lactobacilli. It was observed that the numbers of lactobacilli in the milk in the cheese vat sometimes greatly increased after the addition of the starter to the milk. When these starters were plated on acetate agar growth of lactobacilli, sometimes in large numbers, suggested contamination of the starters with these organisms. The starters in use at sixteen different creameries were then examined on acetate agar, and seven were found to contain lactobacilli. Representative colonies of these organisms were picked from each starter and these strains identified physiologically using the methods of Briggs(2) and Wheater(3,4), and serologically using the group sera of Sharpe(5) and Sharpe & Wheater(6). Table 1 shows the numbers and species of lactobacilli present in the starters. Each starter was sampled several times, usually at monthly intervals.

699. Lactobacilli in Cheddar cheese: 1. The use of selective media for isolation and of serological typing for identification

A comparison of three different media, yeast dextrose agar, tomato dextrose agar and acetate agar (which is selective for lactobacilli) showed that the acetate medium was satisfactory for the isolation and counting of lactobacilli from Cheddar cheese during ripening. Lactobacilli were isolated on this medium in the early stages of ripening when the large numbers of starter streptococci growing on the other media were completely suppressed. Lactobacilli isolated were identified biochemically and serologically. Serological typing was found to be a useful method of identifying large numbers of isolates and of assessing the incidence and distribution of particular types in the cheese.We wish to thank Dr A. T. R. Mattick for his interest and helpful advice in this work; Dr L. A. Mabbitt for preparation of the cheese samples; Miss H. R. Chapman for making the experimental cheese; and Mrs P. Jarrett for technical assistance.