No abstract

Listeria monocytogenes is a main etiological factor of listeriosis, spread mainly by food products. In recent years, an increasing number of patients with listeriosis and an augmentation in L. monocytogenes antibiotic resistance, e.g. to penicillin and ampicillin, has been reported. The aim of the study was to characterise the L. monocytogenes strains isolated from fish-processed food products. Species identification, based on the multiplex-PCR reaction, was performed, and the genetic similarity of the isolates was analysed with the RAPD technique. The strains, in the form of planktonic cells and a biofilm, were subjected to drugsusceptibility analysis, and the effect of disinfectants on the bacillus cells was evaluated. All of the analysed strains were of the Listeria monocytogenes species. Three genetically distant strains were detected, i.e. Lm I, Lm II and Lm III. Approximately 66.6% penicillin-resistant and 66.6% cotrimoxazole-resistant strains were found. No erythromycin-resistant strain was detected. The Lm II strain was simultaneously resistant to four antibiotics, i.e. penicillin, ampicillin, meropenem and cotrimoxazole. The strongest biofilm was formed on aluminium foil and the weakest on rubber. The tested disinfectant antibiofilm effectiveness was related to the type of surface. The most effective agent was paracetic acid and hydrogen peroxide (elimination rate 5.10-6.62 log CFU × cm −2 and 5.70-7.39 log CFU × cm −2 after 1-and 5-min exposure, respectively) and the least-sodium hydroxide (elimination rate 0.52-1.20 log CFU × cm −2 and 0.98-1.81 log CFU × cm −2 after 1-and 5-min exposure, respectively). Further studies on a greater number of L. monocytogenes strains are recommended.

The aim of the study was to evaluate the effect of propylene film coated with solution of chitosan (CH), ethanolic extracts of propolis (EEP), and bee pollen (EEBP) and its combination on L. monocytogenes number in wrapped salmon, salami, and cheese. Sterile fragments of propylene film were coated with solution containing CH, CH+EEP, CH+EEBP, and CH+EEP+EEBP. The coated film was applied directly after preparation (AP) after 10 days of storage from preparation (AS). L. monocytogenes strains isolated from cheese, salmon, and salami were transferred on adequate food type. ATCC 19111 reference strain was placed on all examined slices. Contaminated slices were wrapped in the coated film. The film adhered strictly to the slices surface and was left for 0, 1, 6, 12, and 24 hours. Antilisterial activity of AP film was additionally assessed during 15-day storage of products wrapped in the coated film. In conclusion, the chitosan-coated film exhibited antibacterial activity. Incorporation of EPP and EEBP enhanced this activity. The antilisterial activity depended on the type and concentration of solutions, the types of food, and the origin of strains. This study proved that the time that passed since the use of coated film for packing food was of great importance.

The aim of research was to evaluate an effect of weather conditions in the years of study considering the air temperature and precipitation as well as granulometric distribution of soil, taking into account the temperature and moisture content, on asymptomatic infection caused by Clavibacter michiganensis subsp. sepedonicus (Cms) in leaves and tubers. The level of infection of leaves and tubers with Cms was differentiated by the thermal and humidity conditions occurring in the years of research. The granulometric distribution of soil (soil profile) had a significant effect on the level of leaf infection. In the year 2014, with moderate temperature and humidity, the highest intensity of leaves and tubers infection was observed on soil of the highest moisture content -sandy loam. In the years with extreme weather conditions, i.e. the drought in 2015 or the abundant rainfall in 2016, the most intensive infection was observed in leaves and tubers grown on soil of low humidity -slightly loamy sand and loamy sand. The degree of infection was found to decrease with increasing air temperature and precipitation level as well as with the increase of soil moisture. On the other hand, increasing soil temperature favoured infection in tubers. ResumenEl objetivo de esta investigación fue evaluar el efecto de las condiciones meteorológicas en los años de estudio, considerando la temperatura del aire y la precipitación, así como la distribución granulométrica del suelo, tomando en cuenta la temperatura y el contenido de humedad, en la infección asintomática causada por Clavivacter michiganensis subesp. Sepedonicus (Cms) en hojas y tubérculos. El nivel de infección de las hojas y los tubérculos con Cms se diferenció por las condiciones térmicas y de humedad que se presentaron en los años de la investigación. La distribución granulométrica del suelo (perfil del suelo) tuvo un efecto significativo en el nivel de infección foliar. En el año 2014, con moderada temperatura y humedad, la más alta intensidad de infección de hojas y tubérculo se observó en suelo con el contenido de humedad más alto, franco arenoso. En los años con las condiciones meteorológicas extremas, i. e., la sequía en 2015, o la lluvia abundante en 2016, la infección más intensiva se observó en hojas y tubérculos cultivados en suelo de baja humedad, ligeramente areno-arcilloso y areno-arcilloso. El grado de infección se encontró que disminuía con el aumento de la temperatura del aire y el nivel de precipitación, así como con el incremento de humedad del suelo. Por otro lado, al aumentar la temperatura del suelo se favorecía la infección en los tubérculos.

There are a lot of research on the effect of radiation on the number of bacteria in food products. However, there is almost no information about the effect of strain properties, such as drug susceptibility, virulence, etc., on their resistance to ionizing radiation. An increasing number of drug resistant bacterial strains isolated from food, encourages to take up this research subject.