Changes in the behavior of Staphylococcus aureus strains in the presence of oxacillin under the effect of gamma radiation

Staphylococcus aureus (S. aureus) as a major pathogen is implicated in a wide range of foodborne and hospital-acquired infections, its methicillin resistant variants contribute to the spread of β-lactam antibiotic resistance. It is essentially important to destroy these pathogens, their resistance genes and the antibiotics in wastewaters. For this purpose reactions of reactive radicals (advanced oxidation processes), first of all hydroxyl radicals (•OH), are suggested. Here the radiolysis of water supplied these radicals. In the experiments B.01755 oxacillin sensitive and B.02174 resistant S. aureus strains were used to study their behaviorr in suspensions under the effect of irradiation in presence and absence of oxacillin. Oxacillin inactivation depended on concentration of the antibiotic used (0.042 and 1 g dm-3), higher concentration required a higher dose. When 106-109 CFU cm-3 S. aureus suspensions were irradiated with γ-radiation the bacteria were inactivated at low absorbed doses: 4 orders of magnitude decrease ocurred in the number of culturable cells at ∼0.6 kGy dose. Both cell membrane and DNA suffered considerable damages during irradiation. Due to the membrane damage the cells could not be stained, and the DNA content of cells in several days period was released into the solution. In DNA damage the oxacillin resistance mecA gene was also modified, it did not multiply in PCR test. These findings are important from the point of view of applying irradiation technology to stop the spread of antibiotic resistance.

Inhibition of Foodborne Pathogenic Bacteria by Excreted Metabolites of Serratia marcescens Strains Isolated from a Dairy-Producing Environment

Serratia marcescens strains from a dairy-producing environment were tested for their inhibitory effect on Listeria monocytogenes, Salmonella Hartford, Yersinia enterocolitica and Escherichia coli. Inhibition of foodborne pathogens was observed in the case of a non-pigmented Serratia strain, while the pigment-producing isolate was able to inhibit only Y. enterocolitica. The co-culturing study in tryptone soya broth (TSB) and milk showed that the growth of Salmonella was inhibited in the first 24 h, but later the pathogen could grow in the presence of the Serratia strain even if its cell concentration was 1000 times higher than that of Salmonella. However, we found that (1) concentrated cell-free supernatants had stronger inhibitory activity, which confirms the extracellular nature of the antagonistic compound(s). We proved that (2) protease and chitinase enzymes can take part in this mechanism, but they are not the main inhibitory compounds. The presence of prodigiosin was observed only in the case of the pigmented strain; thus, (3) we hypothesized that prodigiosin does not take part in the inhibition of the pathogens. However, (4) the combined effect of different extracellular metabolites might be attributed to the inhibitory property. Application of concentrated S. marcescens cell-free supernatant can be an effective antibacterial strategy in the food industry, mainly in the form of a bio-disinfectant on surfaces of food-processing areas.

Characterisation of Pseudomonas lundensis CP-P-5 as a potential antagonist of foodborne pathogenic bacteria

Previously isolated Pseudomonas lundensis CP-P-5 had antagonistic activity against Salmonella Hartford, Yersinia enterocolitica, and Escherichia coli. In this study, determination of its antagonistic mechanism and potential field of application in food industry was aimed. Using cellophane-test and microcultures of the test strain's cell-free supernatant mixed with the pathogens, our results showed that cells of P. lundensis CP-P-5 and its concentrated cell-free supernatants were effective against the foodborne bacteria, and the supernatants contained more than one compound responsible for inhibitory activity. Searching for the antagonistic compound, NaOH, protease, and heat treatments were done to the supernatants, and proteolytic activity and siderophore production were also tested using the antagonistic strain. Our results support the potential applicability of P. lundensis CP-P-5 as a bioprotective agent against foodborne pathogens in food processing environments.

Searching for Antagonistic Activity of Bacterial Isolates Derived from Food Processing Environments on Some Food-Borne Pathogenic Bacteria

Bacterial strains with inhibitory effect on Salmonella Hartford, Listeria monocytogenes, Yersinia enterocolitica, and Escherichia coli, respectively, were isolated. Out of the 64 bacteria originated from food processing environments, 20 could inhibit at least one of the tested pathogens, and it was proved that growth decline of the pathogenic bacteria was more remarkable by co-culturing than by using cell-free supernatants of the isolates. Seven different genera (Pseudomonas, Bacillus, Paenibacillus, Macrococcus, Staphylococcus, Serratia, and Rothia) reduced the pathogens’ growth during the time period of analysis, and the strongest inhibitory effect was observed after 24 h between 15 and 30 °C. Sensitivity of the tested human pathogenic bacteria against the inhibitory strains was distinct, as Y. enterocolitica could be inhibited by numerous isolates, while S. Hartford proved to be the most resistant. Our results reveal that the isolated bacteria or their excreted metabolites could hinder pathogen growth when used in sufficient quantities.

Antagonistic Effect of Pseudomonas sp. CMI-1 on Foodborne Pathogenic Listeria monocytogenes

Bacterial isolates derived from food or raw food materials of animal origin were screened for potential antagonistic activity against foodborne pathogenic Listeria monocytogenes. Using the agar spot method, ten out of the 94 tested bacteria showed antilisterial activity. All of the antagonistic isolates identified by sequence analysis as strains of the genus Pseudomonas were able to inhibit the growth of all the examined Listeria species including the ruminal pathogenic L. ivanovii and the opportunistic human pathogenic L. innocua. Pseudomonas sp. CMI-1 had the highest inhibitory effect on the growth of different Listeria strains. Co-culturing studies revealed that the inhibition of L. monocytogenes could not be achieved efficiently. Although the population of the Pseudomonas sp. CMI-1 strain increased by up to 10 orders of magnitude during 2 days of culturing period at 20 °C in the presence of L. monocytogenes, the cell count of the pathogen also increased by approx. 6 orders of magnitude. At the same time, appropriate inhibition of cell-free supernatants generated from 6-day-old cultures of Pseudomonas sp. CMI-1 was observed. The inhibitory compound of this antagonistic strain is presumably a chromopeptide siderophore, whose activity and production can be affected by iron supplementation, and which had an absorption maximum typical of siderophores of fluorescent Pseudomonas species. Production of the antilisterial substance was influenced by the oxygen concentration, as in static cultures the concentration of the siderophore was higher than in shake flask cultures.

[Phytochemical and antimicrobial investigation of Epilobium angustifolium L]

Phytochemical studies of Epilobium angustifolii herba aimed the determination of the active ingredients; antimicrobial activity of the aqueous and ethanolic extracts against human pathogenic bacteria and fungi was also examined. Six flavonoid and 4 phytosterol fractions were identified by thin layer chromatography, while tannins were present in low concentration. It has been shown that not only the ethanolic but also the aqueous extracts had inhibitory effect on certain pathogenic microorganisms, therefore E. angustifolium could be used for the development of external phytotherapic or disinfectant preparations.