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  • Author: Jacek Osek x
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Abstract

The aim of the study was to investigate if the enterotoxigenic strains of S. aureus isolated from raw milk are able to produce staphylococcal enterotoxins (SEs) A - E. A total of 168 of S. aureus isolates from raw milk collected in the south - east region of Poland (Lubelskie Province) were tested for SE production by the ELFA, while multiplex PCR was applied for detection of enterotoxin genes (sea, seb, sec, sed, see). It was found that 20 (11.9%) out of 168 strains were positive for one or more classical SE markers and 19 of them produced a detectable level of enterotoxins. The results obtained by mPCR and ELFA were in agreement, when the presence of A, B, and D toxin types was tested; whereas SEC was not found by the ELFA although the S. aureus was positive for the respective gene. The results of the two methods showed that mPCR identified one more strain potentially producing enterotoxin than the ELFA, which may suggest that the enterotoxigenic S. aureus are not always able to express the toxin protein.

Abstract

In the present study, 25 Escherichia coli strains isolated from beef, pork, and poultry meat, and producing extendedspectrum β-lactamases (ESBL) (18 strains) or AmpC- cephalosporinases (7 strains) were tested for antimicrobial resistance using the minimum inhibitory concentration method with 16 antimicrobial agents. All examined strains were resistant to ampicillin and the first-generation cephalosporins. Variable resistance to the third-generation cephalosporins (40%-100% among ESBLproducing strains and 0-72% among AmpC-producing strains) was noted. Less than 30% of examined strains were resistant to ciprofloxacin. All isolates were susceptible to the fourth-generation cephalosporins, cephalosporins connected with inhibitors of β-lactamases, carbapenems, and gentamycin

Abstract

The aim of this paper is to give an overview of the presence of biogenic amines, particularly histamine, in various food products, discuss the most important factors influencing their accumulation, and address potential toxicity and safe limits in food. Biogenic amines are natural components of animal and plant raw materials, where they are present at concentrations appearing non-harmful to human health. Their increased content in foods results from the activity of endogenous enzymes or from the microbial decarboxylation of amino acids during controlled or spontaneous fermentation, processing, storage, and distribution. General knowledge of biogenic amines, factors favouring their formation and their safe limits in food are useful in preventing exposure to their toxic effects on the human body. Based on this information, appropriate prophylaxis can be applied, which will consist primarily of maintenance of good hygiene standards of raw materials and products, employment of appropriate processing procedures and upkeep of sanitary food storage conditions.

Abstract

Introduction

In recent years, there has been a great interest in biogenic amines such histamine, as they are associated with the quality and safety of some kinds of fermented foods. The aim of this study was to evaluate the effect of temperature and storage time on the content of histamine in cheeses.

Material and Methods

Samples of mould and hard cheeses were examined with RP-HPLC with an organic-aqueous mobile phase containing acidic buffer and chaotropic salt. The samples were stored either at 22 ± 2°C for 42 days (mould and hard cheeses) or at 4 ± 2°C for 112 days (mould cheeses) and 133 days (hard cheeses).

Results

The mean total histamine content in cheeses stored at 22°C was higher than the content in those stored at 4°C, with the highest concentrations found in Gorgonzola Piccante cheese (730.47 mg/kg). Histamine concentration in some types of cheeses exceeded the toxic threshold dose, indicating that after long or inadequately cool storage they may not be safe for consumers.

Conclusion

To protect cheeses from contamination with histamine-producing bacteria and to safeguard consumers from poisoning, factors conducive to this amine’s formation should be minimised during cheese processing. Suitable temperature and time during storage of cheeses are recommended to avoid the intoxication. Monitoring of this toxin in food is necessary to ensure safety of consumers.

Abstract

Introduction: The study objective was to develop and evaluate a new TaqMan multiplex real-time PCR method for Salmonella, L. monocytogenes, and verotoxigenic Escherichia coli (VTEC) detection in slaughtered animal carcasses.

Material and Methods: The procedure included an enrichment step, DNA extraction, and two multiplex real-time PCRs. The first PCR detected the invA and hly genes of Salmonella and L. monocytogenes respectively, the second the vtx1, vtx2, and eae genes of VTEC.

Results: The validation of this method resulted in 100% relative sensitivity, specificity, and accuracy as compared to the reference ISO methods. The limit of detection per swab sample was established at 1 cfu for Salmonella and L. monocytogenes and 2 cfu for VTEC. The authors analysed 265 slaughterhouse-collected swabs from cattle, pig, and poultry carcasses. Among 125 from cattle, 51 were positive for VTEC, 29 for Salmonella, and 1 for L. monocytogenes. Among swabs from pig carcasses (n = 95), three, two, and one sample were positive for these pathogens respectively. None of the microorganisms tested for was identified in 45 samples of poultry origin.

Conclusion: The obtained results showed that the method developed can rapidly identify the main bacterial pathogens that may contaminate carcasses of food-producing animals.

Abstract

This study describes preparation of test samples composed of freeze-dried strain of S. aureus and powdered milk as a matrix. In the first part of the study, the number of S. aureus cells freeze-dried in skim milk or horse serum were compared at two levels of contamination (104 and 105 cfu g-1). The analysis of the samples was performed three times within a week. The preliminary results showed that the samples composed of S. aureus freeze-dried in horse serum were more stable and homogeneous than those prepared with skim milk. These results were further confirmed after analysing a higher number of such samples. Therefore, this procedure was then chosen for preparation of the samples for proficiency tests (PTs). Homogeneity and stability of these samples were checked according to ISO 13528. The results obtained showed that the samples met the criteria of stability and homogeneity required for PTs and were used in PT for enumeration of S. aureus in powdered milk.

Abstract

The study was carried out on live bivalve molluscs available on Polish market. Microbiological tests were performed for the presence of Salmonella sp., Vibrio parahaemolyticus, spore-forming anaerobe bacteria, and coagulase-positive Staphylococcus sp., and for the enumeration of Escherichia coli. ELISA was used for the determination of marine biotoxins, paralytic shellfish poisoning (PSP), amnesic shellfish poisoning (ASP), and diarrhoeic shellfish poisoning (DSP). Microbiological examinations were performed according to ISO and Polish Standards. Salmonella sp. was not detected in any sample tested. Coagulase-positive staphylococci were identified in 9.0% of the samples. V. parahaemolyticus was isolated from 17.0% of mussels. Shellfish were highly contaminated by anaerobes, which were isolated from 68.0% of the samples. The number of E. coli ranged from <2.0 x 101 up to >1.8 x 104 MPN/100 g. The majority of mussels were free from the marine biotoxins tested or contained them bellow the permitted level. The analysis of microbiological and toxicological status of raw bivalve molluscs available on Polish market indicates that they are generally safe for the consumers.

Abstract

A total of 135 L. monocytogenes strains isolated from slaughtered cattle and beef meat were tested by the pulsed field gel electrophoresis (PFGE). The AscI restriction analysis revealed a genetic heterogeneity among investigated isolates since 31, 9, and 35 profiles were distinguished among hide, carcass, and meat strains, respectively. The PFGE profiles of the isolates were also analysed in relation to serotypes, virulence genes, and antimicrobial resistance. It was shown that strains displaying the same PFGE type were of the same serotype while correlation between pulsotype and antimicrobial resistance was poor. The obtained results suggest that a cross-contamination between bovine hides and carcasses may occur during the slaughter process. Moreover, identification of identical PFGE types among L. monocytogenes found during a study period may suggest a common source of contamination or presence of persistent strains able to survive for a long time. These results emphasise the importance of molecular subtyping methods, including PFGE, in monitoring and tracking pathogen contamination along food chain.

Abstract

The aim of the study was to identify the potential sources of contamination of traditionally made cheeses during their production with Staphylococcus aureus . The samples were collected at nine dairy farms at different points of manufacturing the cheeses. Isolation and enumeration of coagulase positive staphylococci (CPS) on Baird- Parker RPF agar was conducted, and detection of staphylococcal enterotoxins (SEs) was performed using ELISA and ELFA. The genes encoding SEs were identified by PCR. CPS were isolated from 51 samples with the highest level of contamination in mature cheese up to 107 CFU g-1. No SEs were detected in tested samples; however, enterotoxic CPS strains were found.

Abstract

The high performance liquid chromatography with diode array detection was used for the study. The histamine was detected in 14.6% and 17.8% of the samples of fresh and smoked fish respectively. The highest concentrations of the compound were found in smoked herring and smoked sprat (17.7 mg/kg and 24.1 mg/kg respectively). Histamine concentration in fresh and smoked fish did not exceed the allowable limit, indicating that they are safe for consumers.