GC-MS/FID analysis, antibacterial activity and modes of action of essential oils from three Aframomum species found in Cameroon against foodborne pathogenic bacteria

Background: The current study examined the chemical profile and in vitro antibacterial activity of essential oils (EOs) extracted from Aframomum danielli (leaves and seeds), Aframomum chlamydentum (leaves), and Aframomum melegueta (leaves) against foodborne pathogenic bacteria. Methods: The hydro-distillation technique using a Clevenger-type apparatus was used to extract EOs, whereas the Gas Chromatography-Mass Spectrometry (GC-MS) and GC coupled to Flame Ionization Detector (GC-FID) allowed the chemical characterization of oil constituents. The broth micro-dilution method was applied for the determination of the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Besides, some modes of action were studied on the cell membrane integrity and biofilm formation of Salmonella typhi. Results: The major compounds identified from EOs of A. danielli seeds were eucalyptol (48.707%), limonene (11.368%), beta pinene (10.342-10.335%), and alpha terpineol (8.785-9.049%), whereas EOs from A. danielli leaves were dominated by sabinene (42.87%), beta pinene, (11.22%), caryophyllene (7.84%), terpinen-4-ol (5.68%), linalool (3.48%) and gamma terpinene (2.02%). Major volatile markers from EOs of A. chlamydentum leaves comprised beta pinene (49.72%), caryophyllene (10.62%), alpha pinene (6.21%) and linalool (2.96%), while those of EOs from A. melegueta included beta pinene (37.15%), caryophyllene (17.64%), caryophyllene oxide (8.72%) and alpha pinene (8.26%). This study is the first to report on the chemical constituents of EOs from A. chlamydentum. Test oils displayed significant antibacterial activity with the MIC ranging from 0.0625 to 0.5% (v/v). EOs from A. melegueta (leaves) appeared to be the most active, acting against all tested bacteria. All EOs identified displayed bactericidal effects against Citrobacter freundii, a bacterium known to cause a broad range of infections associated with a higher rate of in-hospital mortality. The EOs from A. melegueta may act through perturbation of cell membrane integrity and permeability as well as the inhibition of bacterial biofilm formation. Conclusion: Our findings suggest the possible application of essential oils in agricultural food products for the control of bacterial diseases.

Molecular characterization of foodborne pathogenic bacteria recovered from fermented meat products

Foodborne pathogenic bacteria are causing diseases with a significant effect on human health and the economy. The four most common bacterial foodborne pathogens were isolated from different fermented meat products and characterized molecularly in the current study. A total of 20 random samples of fermented meat products, including Hotdog, pepperoni, salami, sausage, and luncheon (4 from each), were collected from different markets to be examined bacteriologically for detection of foodborne pathogenic bacteria. The samples were tested by culture for the presence of bacteria. PCR was used as a diagnostic tool for the proper identification of foodborne pathogenic bacteria. So, the pure isolates were identified and confirmed by PCR- based method using specific primers for each genus. The isolated pathogenic bacteria were identified as Escherichia coli 0157:H7, Listeria monocytogenes, Salmonella sp. and Staphylococcus aureus. Out of 20 samples, only one sample contains E. coli 0157:H7. Listeria monocytogenes and Salmonella spp. were isolated from two samples. At the same time, S. aureus was found in 6 samples, one of which was mecA positive. The results revealed the presence of foodborne pathogenic bacteria in fermented meat samples. So, to decrease the human hazard risk and a major public health threat associated with foodborne pathogenic bacteria and their toxins, a greater emphasis should be applied in control and prevention of contamination during processing and manipulation.

Antimicrobial Efficacy and Spectrum of Phosphorous-Fluorine Co-Doped TiO2 Nanoparticles on the Foodborne Pathogenic Bacteria Campylobacter jejuni, Salmonella Typhimurium, Enterohaemorrhagic E. coli, Yersinia enterocolitica, Shewanella putrefaciens, Listeria monocytogenes and Staphylococcus aureus

Contamination of meats and meat products with foodborne pathogenic bacteria raises serious safety issues in the food industry. The antibacterial activities of phosphorous-fluorine co-doped TiO2 nanoparticles (PF-TiO2) were investigated against seven foodborne pathogenic bacteria: Campylobacter jejuni, Salmonella Typhimurium, Enterohaemorrhagic E. coli, Yersinia enterocolitica, Shewanella putrefaciens, Listeria monocytogenes and Staphylococcus aureus. PF-TiO2 NPs were synthesized hydrothermally at 250 °C for 1, 3, 6 or 12 h, and then tested at three different concentrations (500 μg/mL, 100 μg/mL, 20 μg/mL) for the inactivation of foodborne bacteria under UVA irradiation, daylight exposure or dark conditions. The antibacterial efficacies were compared after 30 min of exposure to light. Distinct differences in the antibacterial activities of the PF-TiO2 NPs, and the susceptibilities of tested foodborne pathogenic bacterium species were found. PF-TiO2/3 h and PF-TiO2/6 h showed the highest antibacterial activity by decreasing the living bacterial cell number from ~106 by ~5 log (L. monocytogenes), ~4 log (EHEC), ~3 log (Y. enterolcolitca, S. putrefaciens) and ~2.5 log (S. aureus), along with complete eradication of C. jejuni and S. Typhimurium. Efficacy of PF-TiO2/1 h and PF-TiO2/12 h NPs was lower, typically causing a ~2–4 log decrease in colony forming units depending on the tested bacterium while the effect of PF-TiO2/0 h was comparable to P25 TiO2, a commercial TiO2 with high photocatalytic activity. Our results show that PF-co-doping of TiO2 NPs enhanced the antibacterial action against foodborne pathogenic bacteria and are potential candidates for use in the food industry as active surface components, potentially contributing to the production of meats that are safe for consumption.

Research on the Biofilm Formation of Staphylococcus aureus after Cold Stress

Staphylococcus aureus is a common food pathogen and has a strong tolerance to environmental stress. Here, the biofilm formation of S. aureus strains after cold stress for 24 weeks were investigated. It was found that the biofilm formation of S. aureus CICC 21600, CICC 22942, W1, W3, and C1 cells was enhanced after cold stress for 20 weeks. What is more, the mRNA levels of the clfA, icaA, icaB, icaC or icaD genes in these strains were increased for >2-fold. The increased gene transcription levels were consistent with the increase in the polysaccharide content in the biofilm matrix of these S. aureus strains after cold stress. Meanwhile, hydrophobicity and the adhesion proteins also played a role in the formation of biofilms. The biofilm of S. aureus cells can be effectively degraded by snailase and proteinase K (125 µg/mL + 20 µg/mL) mixture. In summary, S. aureus frozen at −20 °C for 12 to 20 weeks is still a potential hazard. Food factory equipment should be cleaned in a timely manner to avoid outbreaks of foodborne pathogenic bacteria due to contamination.

Genomic Analysis of Lytic Phage V09 that Targets Pathogenic Vibrio Parahaemolyticus

Phage therapy is a promising approach to control foodborne pathogenic bacteria. In this study, a lytic phage against Vibrio parahaemolyticus, designated Vibrio phage V09, was isolated from surface water in Shanghai, China and its genomic DNA was sequenced. The data demonstrated that phage V09 is a double-stranded DNA phage. Its genome consists of 243,881 base pairs (42.6% guanine-cytosine content) encoding 377 open reading frames and with 27 tRNAs detected. According to phylogenetic analysis, phage V09 can be considered a member of the subfamily Tevenvirinae and family Myoviridae.