The survival of two microbial contaminants,
Enterobacter cloacae and
Pseudomonas paucimobilis, in yoghurts manufactured from cow's milk and soymilk was investigated during storage for 45 days at 4 ...and 12 °C. Sensory panel tests performed before microbiological investigation, showed that the flavor of soy-yoghurts made with cocoa powder or malt added did not have the beany taste of soy beans.
Both contaminants were significantly resistant to low pH values during storage for 32 days at 4 °C. The survival at 4 °C was remarkable in both plain and flavored yoghurts and a population close to 10
2 C.F.U./ml was observed after 38 days of storage. Experiments performed with soymilk yoghurts showed an enhanced survival of
P. paucimobilis at 4 °C compared to the storage in cow's milk yoghurts; microbial values were close to 7-8 × 10
6 C.F.U./ml after 16 days. Soymilk exhibited a protective effect on
L. delbrueckii subsp.
bulgaricus and
S. thermophilus at 12 °C and, compared to the survival in cow's milk yoghurts, a larger number of viable cells of both probiotic microorganisms (10
6 and 10
8 C.F.U./ml, respectively) were observed after 36 days of storage.
Many and different pharmaceutical products with probiotic value are presently commercialised on the italian market. On this regard, a microbiological investigation was carried out to screen the ...microorganisms incorporated into these products, commonly used in animal feeding.
After determination of the cell number and viability of bacteria, different experiments were performed
in vitro in order to characterise the microorganisms and to evaluate their probiotic value.
Among all the strains identified, best results were obtained with
Enterococcus faecium SF 68 whereas
Bacillus subtilis, Bacillus toyoi and
Lactobacillus strains appeared less effective as far as concerned our investigation. Moreover, the identification profiles of microorganisms confirmed the presence of
Lactobacillus species with a poor probiotic value and in disagreement with the claimed composition of the product.
In defined mixed cultures experiments, the antagonism of
E. feacium versus an
Enterobacter strain was demonstrated and was attributed to acid and/or antimicrobials production. On the other hand, a strain of
L. leichmannii was not able to inhibit the same fecal isolate in similar experiments even at a high inoculum level (ca. 8.0 x 10
7c.f.u./ml).
The susceptibility of five Aeromonas hydrophila strains and one Escherichia coli strain to chlorine was studied under carefully controlled laboratory conditions. Of the Aer. hydrophila strains, two ...were from untreated water, two from tap water (immediately downstream of a water treatment plant) and one from the DSM collection. The study included disinfectant concentration (0·1, 0·2 and 0·5 mg l−1), pH (6, 7 and 8) and temperature (4, 21 and 32 °C) as controlled variables. The results indicated that the untreated water strains, the DSM strain and the E. coli strain were inactivated within 1 min of chlorine treatment. The strains from chlorinated water (TW11 and TW27) showed a different susceptibility to chlorine disinfection, the rate of inactivation being greater at pH 6 than at pH 8 for both strains. Under the standard conditions of temperature 21 °C, pH 7 and chlorine concentration 0·2 mg l−1, an increase or decrease of approximately 1 log unit in the number of bacteria did not affect the kill rate of the strains TW11 and TW27.
The bacterium Aeromonas hydrophila may be an agent of waterborne infection and is frequently found in chlorinated water supplies. The present study tested the sensitivity of different strains of ...Aeromonas to various concentrations of hypochlorite under controlled laboratory conditions. Experimental variables were disinfection concentrations of 0.1, 0.2, and 0.5 mg per litre, pH 6, 7 and 8 and operating temperatures of 4, 21 and 32C. A strain of Escherichia coli was used as a negative control. The Aeromonas strain isolated from untreated water, that from the DSM culture collection and the negative control were inactivated within 1 minute of chlorine treatment. The 2 strains isolated from chlorinated water demonstrated different susceptibilities. Both strains were less resistant to chlorine disinfection at pH 6 compared with pH 8. Only one of the strains was more susceptible at higher temperatures. Chlorine-resistant strains of Aeromonas may survive and multiply in public water supplies, especially where there is a lower chlorine concentration, higher pH and lower temperature. More research should focus on water nutrient concentrations and pathogen residence time in the water supply.
The effect of glucose oxidase (GOX)-catalase (CAT) in different GOX/glucose combinations on the growth of gram-positive bacteria such as Staphylococcus aureus and Bacillus cereus was evaluated. ...Growth of S aureus and B. cereus was clearly suppressed by 2.0 and 4.0 mg/ml glucose, resp., when combined with 0.5 U/ml and 2.0 U/ml of GOX concentration. Higher GOX and glucose concentrations rapidly decreased the pH. The combination of both GOX and CAT enzymes caused more decrease of pH compared with the use of GOX alone, suggesting that the antibacterial effect of GOX/glucose system was mainly due to a pH decrease by gluconic acid production in the system. However, different GOX/CAT glucose concen-trations had no effect on growth of B. cereus, a spore-forming bacterium.
Many and different probiotic pharmaceutical products are presently commercialised in the world. On this regard, a microbiological investigation was carried out to screen the microorganisms ...incorporated into these products, commonly used for human health. After determination of the cell number and viability of bacteria, several experiments were performed in vitro in order to characterise the microorganisms and to evaluate their probiotic value. Among all the strains identified, best results were obtained with Lactobacillus rhamnosus, Enterococcus faecium and Saccharomyces cerevisiae as far as regards growth rates, pH and bile salts tolerance. Moreover, the identification profiles of microorganisms showed a better reliability for the products containing a single species whereas the ones composed of different strains were usually not satisfactory. In some cases, the presence of Lactobacillus and Saccharomyces species was in disagreement with the claimed composition of the product and some species of lactobacilli, bifidobacteria and streptococci were found not viable. In defined mixed cultures experiments, the antagonism of Lactobacillus acidophilus and Enterococcus faecium versus Yersinia enterocolitica was demonstrated and explained as acid and/or antimicrobials production.
Der probiotische Wert einiger pharmazeutischer Produkte des italienischen Marktes werden bewertet. Nach Bestimmung der Zellzahl und Lebensfaehigkeit der Bakterien werden in vitro-Experimente zur ...Charakterisierung der Mikroorganismen und der Bewertung ihres probiotischen Wertes durchgefuehrt. Unter den identifizierten Bakterienstaemmen wurden die besten Resultate mit Enterococcus faecum SF 68 erhalten, waehrend Bacillus subtilis, Bacillus toyoi und Lactobacillus-Staemme weniger wirksam waren.
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