Isabel García-Jalón

Characterization of Listeria monocytogenes and Listeria innocua from a vegetable processing plant by RAPD and REA

The incidence of Listeria monocytogenes in a vegetable processing plant was investigated over a 23-month period. Frozen ready-to-eat vegetable samples, well as the plant environment, were sampled. The molecular subtyping techniques, Random Amplified Polymorphic DNA (RAPD) and Restriction Endonuclease Analyses (REA), were performed to help investigate the origin and routes of Listeria dissemination. The low and sporadic incidence of L. monocytogenes made it impossible to establish an epidemiological sequence in the processing plant, though a case of cross-contamination between tomato and ratatouille was detected. Listeria innocua subtyping, however, allowed us to determine the prevalence of several strains in vegetables, and their presence on machinery samples suggested the possibility of cross-contamination during processing. The low incidence of L. monocytogenes indicated that the risk of listeriosis transmission by vegetable consumption is low. On the other hand, the isolation of the same strain of L. innocua in several surveys pointed out the risk of colonisation on surfaces and machinery. The persistence of Listeria spp. is a cause for concern as can lead to future contamination of vegetables processed in the plant and to a possible increased risk for health. Therefore, periodic controls for the presence of Listeria spp. and a further review of the cleaning and disinfection procedures used in frozen vegetable plants are recommended.

Partial replacement of sodium chloride with potassium chloride in dry fermented sausages: Influence on carbohydrate fermentation and the nitrosation process

Two types of dry fermented sausages were manufactured: type A with traditional formulation and type B with reduced sodium content. pH and a(w) values and the counts of aerobic mesophiles, Enterobacteriaceae and lactobacilli micro-organisms during the ripening of both fermented sausages were similar. Final lactic acid contents were also similar, but carbohydrate content was significantly lower in type B sausage. Content of acetic, propionic and butyric acids were significantly higher in type B, suggesting a higher heterofermentative activity. Also type B sausage showed lower nitrate level and higher chemical conversion percentage, suggesting a higher nitrosation intensity.

Relationship between consumer food safety knowledge and reported behavior among students from health sciences in one region of Spain.

A survey was conducted to investigate the relationship between knowledge about food safety and actual food handling practices among Spanish university students (mainly from the health sciences disciplines) who usually prepare meals at home. Based on level of education in food safety topics, students were divided in three groups: high, which included students from Food Science and Nutrition; medium, which included students from other health sciences; and low, which included students from non-health-related studies. More than two thirds of the 562 people selected had an accurate knowledge of the eight foodborne pathogens included in the survey, but only 5.2% were able to identify Staphylococcus aureus as a foodborne pathogen. Significant differences in responses were found depending on educational level concerning the food safety topic. For food handling, up to 60% of the responses reflected accurate knowledge of proper storage of prepared meals and washing of hands and materials to avoid cross-contamination. However, with the exception of questions related to storage temperature, there was considerable difference between knowledge and reported behavior. Although 98.6% of the participants recognized the importance of hand washing before and during food preparation, only one quarter (24.4%) affirmed that they washed their hands with soap and water. On questions concerning food practices, more accurate answers were given by the older students. Women answered questions regarding cross-contamination more accurately, whereas men were more accurate in response to questions concerning temperature and food preservation. In general, students with more knowledge of food hygiene had better reported practices, but even these students reported some high-risk behaviors. These results confirm the need to improve educational programs, ensuring that the acquired knowledge actually modifies consumer behavior.

Prevalence of extended-spectrum β-lactamase-producing Enterobacteriaceae in meat products sold in Navarra, Spain.

Patterns of resistance in β-lactamase-producing Enterobacteriaceae family were investigated in isolates from 141 meat products (beef, poultry and pork) purchased in Spain. The strains that grow in ChromID ESBL agar plates were confirmed using the paired disk diffusion method. Resistance to amoxicillin/clavulanic acid, ceftazidime, ceftriaxone, aztreonam, cefpodoxime, gentamicin, doxycycline, cotrimoxazol, norfloxacin, piperacillin/tazobactam, fosfomycin and cefoxitin were tested following CLSI recommendations. Minimum inhibitory concentrations were determined by the MicroScan® NM37 panel and β-lactamase genes were detected using multiplex PCR and sequencing. Results show poultry as the meat product having the highest prevalence (84%), with Escherichia coli being the predominant bacteria (71.3%). Predominant β-lactamase types were CTX-M (37.8%), followed by CTX-M+TEM combination (20.7%), TEM (17%), SHV (12.2%), TEM+SHV combination (10.9%) and OXA (1.2%). 93.9% of the strains were resistant to one or more β-lactam antibiotics. Results indicate a widespread distribution of ESBL-producing Enterobacteriaceae in meat products, with a high rate of β-lactam resistance and a low rate of AmpC cephalosporinase-producing strains.

Listeria monocytogenes and ready-to-eat seafood in Spain: study of prevalence and temperatures at retail.

The aim of this study was to obtain data from refrigerated ready-to-eat seafood products at retail in Spain (young eels, crabstick and smoked salmon), regarding prevalence and levels of Listeria monocytogenes, storage temperatures and the impact of transport conditions (type of bag) on the temperature of the product. The one-year surveillance period was carried out according to the EC Regulation No. 2073/2005, taking 5 units/batch and analyzing 250 samples following ISO 11290-1/A1 and ISO 11290-2/A methodologies. Low prevalence of L. monocytogenes was observed in surimi products, while 4.8% of smoked salmon samples were positive for Listeria with low levels (<10 cfu/g) and uneven pathogen distribution. A single company was responsible for 80% of the positive lots. All purchased products showed values higher than 4 °C at retail and an average increase of 2.5 °C or up to 6.2 °C was recorded when isothermal or plastic shopping bags were used for transport, respectively. To avoid noncompliance of the Food Safety Objective for L. monocytogenes in seafood RTE products more efforts from all stakeholders are needed, with special attention so as to improve control and maintenance of refrigerators at retail and to enhance consumer education regarding food safety practices.

High dissemination of extended-spectrum β-lactamase-producing Enterobacteriaceae in effluents from wastewater treatment plants

Water environments play an important role in the dissemination of antibiotic-resistant bacteria among humans, animals and agricultural sources. In order to assess the spread of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae, we analyzed 279 effluent samples from 21 wastewater treatment plants in Navarra (northern Spain). A total of 185 cefpodoxime-resistant bacteria were isolated on ChromID ESBL agar plates, with high predominance of Escherichia coli among isolated species (73%). ESBL production was determined by different methods, concluding its presence in 86.5% of the isolates by the combination disk test, 75.7% by double-disk synergy test and 73.5% by MicroScan(®) NM37 automated system. PCR and sequencing analysis showed that the predominant β-lactamases (bla) genes were blaCTx-M (67.4%) followed by blaTEM (47%), blaSHV (17.4%) and blaOxA (8.3%); furthermore, two or more β-lactamases genes were found in 34.9% of the isolates. The results demonstrate the high prevalence of ESBL-producing Enterobacteriaceae in effluent water from wastewater treatment plants and confirm the need to optimize current disinfection procedures and to improve management of wastewater in an effort to minimize reservoirs of resistant bacteria. Further studies are needed for examining the presence of these bacteria in other environments and for determining the potential dissemination routes of these resistances as well as their impact on human health.

Antimicrobial susceptibility of Listeria monocytogenes isolated from food and clinical cases in Navarra, Spain.

The susceptibility of 440 Listeria monocytogenes strains isolated from food (n=401) and clinical cases (n=39) between 1995 and 2005 was determined by standard agar dilution and E-test methods. Antimicrobial drugs currently used in veterinary and human therapy were tested, and they included penicillin G, ampicillin, cephalothin, gentamicin, chloramphenicol, tetracycline, doxycycline, trimethoprim, erythromycin, and clindamycin. The sensitivity of strains was established using Clinical and Laboratory Standards Institute (formerly NCCLS) breakpoints and MIC50 (the MIC for 50% of the strains) to MIC90 values. In general, isolates were susceptible to the majority of the antimicrobials tested, including beta-lactamics and aminoglycosides, which are normally used in the treatment of listeriosis. Resistance to tetracycline and doxycycline was found in five strains isolated from fresh trout belonging to the same fish farm. Molecular analysis by restriction endonuclease analysis showed a similar profile, suggesting the persistence of a strain well adapted to the presence of tetracycline in the environment of a fish farm, which is frequently used in aquaculture in order to prevent infections of fish.