Safety-related properties of staphylococci isolated from food and food environments.

AIMS: To test some safety-related properties within 321 staphylococci strains isolated from food and food environments. METHODS AND RESULTS: The isolates were identified as Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus saprophyticus, Staphylococcus pasteuri, Staphylococcus sciuri, Staphylococcus warneri and Staphylococcus xylosus. Decarboxylase activity was quite common for the various Staphylococcus spp., and tyrosine was the most frequently decarboxylated amino acid. The frequency of antibiotic resistance was highest in Staph. pasteuri and Staph. xylosus. Several of the isolates were tolerant to QAC compounds, and in some cases, QAC tolerance was present in antibiotic-resistant strains. Most of the strains displayed moderate to high adhesion rates to stainless steel and Teflon(®). The strains that readily formed biofilms belonged to the species Staph. aureus, Staph. epidermidis and Staph. pasteuri. CONCLUSIONS: An high incidence of some safety hazards was found within the staphylococcal strains of food origin tested in this study. In particular, amino acid decarboxylase activity and biofilm-forming ability were common within strains, and antibiotic resistance and tolerance to QAC-based compounds occurred frequently as well. These characteristics are an important safety concern for food industry. SIGNIFICANCE AND IMPACT OF THE STUDY: This work gives a first picture of safety hazards within staphylococcal species isolated from food environments. The presence of disinfectant-resistant staphylococci is a concern because resistance can be genetically transferred between the various Staphylococcus species. This could lead an increase and spread of resistant enterotoxic staphylococci and/or pathogenic staphylococci.

Evaluation of amino acid-decarboxylative microbiota throughout the ripening of an Italian PDO cheese produced using different manufacturing practices.

AIM: To investigate the presence of biogenic amines (BAs) in Montasio cheese produced by using different cheese manufacturing practices. METHODS AND RESULTS: Three batches of Montasio cheese were made in the following way: batch A using raw milk and natural milk culture, batch B with thermized milk and natural milk culture and batch C with thermized milk and natural milk culture added of a commercial starter culture. During 120 days of ripening analyses were performed for microbial counts and BA content; indeed, the potential to produce BAs was screened in lactic acid bacteria and Enterobacteriaceae isolates. At the end of ripening, the total BA contents of cheeses from batches A, B and C were 166.3, 207.3 and 29.8 mg kg(-1), respectively. Amino acid decarboxylase activity was widespread among isolates. CONCLUSIONS: The BA content of Montasio cheese from the three batches was below the threshold proposed as potentially toxic. The highest BA content was found in cheese produced using thermized milk and natural milk culture; therefore, the thermal treatment of milk was not enough by itself to reduce the counts of decarboxylase-positive bacteria in cheese. The use of selected starters guaranteed a low BA content in Montasio cheese. SIGNIFICANCE AND IMPACT OF THE STUDY: The study of the effects of some technological processes on the incidence of decarboxylative microbiota in 'protected denomination of origin' cheeses could provide useful information on the hygienic risk related to their production.

The capacity of Enterobacteriaceae species to produce biogenic amines in cheese.

The amino acid decarboxylating activity and production of biogenic amines by 104 cheese-associated Enterobacteriaceae species (58 Enterobacter, 18 Serratia, eight Escherichia, seven Hafnia, six Arizona, four Citrobacter and three Klebsiella) were investigated. All strains could decarboxylate at least two amino acids in Möller's broth and in Niven's medium, and the decarboxylase activity was strain specific. In a laboratory medium containing all free amino acids, all strains could produce more than 100 ppm cadaverine, putrescine was produced by 96% of strains. Tyramine and histamine were produced in the lowest concentrations. A positive correlation existed between cadaverine concentration and Enterobacteriaceae counts in cheese, that may have caused the increase in decarboxylase content. This study suggests that it is possible to limit the presence of cadaverine in cheese, thereby controlling the Enterobacteriaceae counts, a sign of contamination during cheese making and/or storage.

Mitochondrial DNA restriction enzyme analysis and evaluation of the enological characteristics of Saccharomyces cerevisiae strains isolated from grapes of the wine-producing area of Collio (Italy).

A total of 70 strains of Saccharomyces cerevisiae were isolated from different grapes from the Collio Region. Chemical parameters and mitochondrial DNA (mtDNA) restriction patterns were determined. Higher alcohols were the main parameter useful for differentiating between strains, whereas the mtDNA analysis demonstrated a high genetic variability between strains. A weak correlation was observed when the dendrograms obtained from the chemical and genetic results were compared.

Glycerol and other fermentation products of apiculate wine yeasts.

Ninety-six strains of apiculate wine yeasts were studied for their ability to produce glycerol, acetaldehyde, ethyl acetate, sulphur dioxide and hydrogen sulphide in synthetic medium. Hanseniaspora guilliermondii produced smaller quantities of glycerol, acetaldehyde and hydrogen sulphide than Kloeckera apiculata, whereas the production of ethyl acetate and sulphur dioxide was found to be similar. Strains characterized by different capacities and properties were found for both species. The existence of apiculate strains differing in secondary compound production is of technological interest, as these yeasts constitute potential flavour producers. Selected strains of apiculate yeasts might favour an enhanced flavour formation and yield desirable characteristics to the final product.

Microbiological quality of artisanal ice cream.

In the course of the years 1990 and 1991, 396 samples of artisanal ice-cream had been collected from different ice-cream shops in Udine and province and analysed. All tested flavours contained aerobic germs, coliforms, Enterococci and yeasts in different quantities. In the analysed samples neither Salmonellae spp., nor Listeria monocytogenes nor Staphylococcus aureus were detected. Numerous species of coliforms and yeasts were randomly isolated and identified. The statistical analysis, used to compare the variables (flavour, month, year), showed significant differences among the samples analysed in the two years. In September, the means of the total aerobic count were significantly different from the ones of July and of August. No significant differences were noted in the means of coliforms, total aerobic counts and yeasts in the different flavours. The techniques for recovery of freeze-stressed coliforms in artificially contaminated samples of ice-cream showed that the three techniques, which use both selective and non-selective mediums, are better than those ones, which use only selective mediums. Lastly, with regard at the coliform values, the ice-creams tested have small-medium quality. In fact 26% of the ice-creams cannot be sealed, according to the Italian Ministry Ordinance (October 11, 1978).