H. W. Walker

Inhibition of Aspergillus flavus and selected gram-positive bacteria by chelation of essential metal cations by polyphosphates

A simple well-plate technique was utilized to determine the effect of various metals on the growth of microorganisms in media containing different polyphosphates. Aspergillus flavus and four gram-positive bacteria were completely inhibited by media containing 1% of various alkaline polyphosphates, whereas four gram-negative bacteria were not. Significant differences were observed between the type of polyphosphate added, the type of metal added, and the species of gram-positive bacterium inhibited. The addition of Mg2+ stimulated growth of A. flavus and Bacillus cereus in the presence of tetrasodium pyrophosphate, whereas Mn2+ permitted growth of A. flavus and Staphylococcus aureus in the presence of sodium hexametaphosphate. Iron supplementation allowed the growth of S. aureus and Listeria monocytogenes on media containing 1 % tetrasodium pyrophosphate. A method for determining the amount of calcium and magnesium in water was modified to detect free Mg2+ by replacing EDTA with phosphate. The addition of free Mg2+, but not Mg2+ chelated by tetrasodium pyrophosphate, permitted the growth of B. cereus on a medium containing tetrasodium pyrophosphate. It is speculated that polyphosphates specifically inhibited A. flavus and gram-positive bacteria by removing essential metals from cation-binding sites located within their cell walls.

Food borne illness from clostridium perfringens

Large numbers of Clostridium perfringens in food are frequently the cause of a mild form of food illness. The organism if widespread in the environment and occurs normally in soil and in the intestinal tract of animals. Sperulation of large numbers of cells in the intestinal tract of animals results in the release of an enterotoxin that produces abdominal cramps and diarrhea. Animals and serological techniques are used to assay for the enterotoxin. Several selective media and confirmatory tests have been developed for quantitative and qualitative recovery of the organism from foods. Proper sanitation and temperature control can limit occurrence and growth in foods.

Inhibition of Mold Growth and Mycotoxin Production in High-Moisture Corn Treated with Phosphates

Mold growth and mycotoxin production were studied in high-moisture (20%) corn treated with tetrasodium pyrophosphate (TSPP); acid and alkaline sodium polyphosphate, glassy (SPG), also known as sodium hexametaphosphate; sodium tripolyphosphate (STPP); and tricalcium phosphate. Six mold cultures belonging to the genera Aspergillus , Fusarium , and Penicillium were tested in corn varieties highly resistant or highly susceptible to mold infection in the field, and in a mixture of five other varieties of corn. The acidic SPG, as well as TSPP and STPP totally prevented or reduced mold growth when added in powder form to corn at 1.0% or 2.0% (w/w), regardless of corn variety and high moisture content. Phosphates afforded protection in whole and damaged kernels. Similar results were obtained with 2.0% acidic SPG and TSPP when added in spray form. Whenever mold growth occurred, treatment of corn with 1.0% or 2.0% (w/w) TSPP and acidic or alkaline SPG inhibited (P<0.01) aflatoxin production by aspergilli.

Inhibition of Growth and Aflatoxin Production of Aspergilli in Medium Containing Phosphates

Mycelial growth and mycotoxin production of Aspergillus flavus and A. parasiticus were studied in Sabouraud dextrose agar containing pure or blended pyro-, poly- or meta-phosphates during 9 d of incubation at 30°C. Pure tetrasodium pyrophosphate (TSPP) and sodium polyphosphate, glassy (SPG, formerly hexametaphosphate), as well as a commercial phosphate blend and three combinations all containing various proportions of sodium acid pyrophosphate (SAPP), TSPP and SPG were tested. Inhibition of growth of aspergilli was observed in media containing 2.0% TSPP and 1.0 and 2.0% SPG and 2.0% of the commercial phosphate blend. Lower concentrations of single or blended phosphates allowed only limited, atypical mycelial growth. Sporulation was totally inhibited by 2.0% concentrations of single or blended phosphates, and so was production of aflatoxins B1 and G1. TSPP or SPG at 1.0% reduced (P<0.05) aflatoxin production from parts per million (controls) to parts per billion.

Resistance of Spores of Bacillus subtilis var. niger Produced From Subcultures of Spores Surviving Hydrogen Peroxide Exposure

The purpose of this work was to determine if the resistance of bacterial spores could be increased by subculturing spores that had survived exposure to hydrogen peroxide. Spores surviving exposure to 5% hydrogen peroxide held at 50 C were subcultured, allowed to sporulate and subsequently exposed to hydrogen peroxide as before. After 10 generations of subculturing, the resistance of the spores had not increased. It is concluded that, in food processes in which high concentrations of hydrogen peroxide are used to sterilize food processing equipment and food packaging materials, the development of a resistant spore population is unlikely.

Influence of pH, Temperature, Curing Agents, and Water Activity on Germination of PA 3679 Spores1

The influence of pH, temperature, water activity, and curing agents on germination of spores of Clostridium sporogenes (PA 3679) was examined. The most influential factor was pH; least germination occurred at pH 5.5, and most at pH 7.0, the highest pH tested. Germination occurred over a temperature range of 4 to 55 C, with maximal germination at 35 and 45 C. NaCl was more inhibitory than NaNO2 and NaNO3 at pH 7.0 at the levels used. At pH 5.5 and 6.0, NaNO2 stimulated germination.