Activity of Binary Combinations of Natural Phenolics and Synthetic Food Preservatives against Food Spoilage Yeasts

Natural compounds are a suitable alternative to synthetic food preservatives due to their natural origin and health-promoting properties. In the current study, phenolic–phenolic and phenolic–synthetic combinations were tested for their antibiofilm formation, anti-planktonic growth, and anti-adhesion properties against Debaryomyces hansenii, Wickerhamomyces anomalus (formerly Pichia anomala), Schizosaccharomyces pombe, and Saccharomyces cerevisiae. The phenolics were vanillin and cinnamic acid, while the synthetic preservatives were sodium benzoate, potassium sorbate, and sodium diacetate. The vanillin–cinnamic acid combination had synergistic effect in all the tested yeasts for the biofilm inhibition with a fractional inhibitory concentration index (FICI) of ≤0.19 for W. anomalus, 0.25 for S. pombe, 0.31 for S. cerevisiae, and 0.5 for D. hansenii. Most of the phenolic–synthetic combinations had indifferent interaction regarding biofilm formation. The vanillin–cinnamic acid combination also had higher activity against spoilage yeasts adhesion on the abiotic surface and planktonic growth compared to the phenolic–synthetic combinations. For the phenolic–synthetic anti-planktonic activity, synergistic interaction was present in all the vanillin–synthetic combinations in S. pombe, vanillin–sodium benzoate and vanillin–potassium sorbate in S. cerevisiae, vanillin–sodium benzoate in W. anomalus, and cinnamic acid–sodium diacetate in S. pombe. These results suggest a novel antimicrobial strategy that may broaden the antimicrobial spectrum and reduce compound toxicity against food spoilage yeasts

Culture media supplemented with inorganic salts improve the growth and viability of several bacterial strains

In order to improve growth and storage conditions for bacterial cultures, commonly used basic culture media, Luria-Bertani broth (LB) and glucose-yeast extract (GY) were tested along with their supplemented versions (LBS and GYS) containing a complex set of inorganic salts required for common physiological processes. The growth kinetics and viability of 15 representative strains were compared on LB/LBS or GY/GYS. Growth kinetics were examined during a 24 h period. Five out of 15 strains showed enhanced growth on LBS and GYS. Three strains showed very low viability (3 months or lower) both on the basic and salt-supplemented media. Six strains could be equally recovered after 6 or 12 months both from LB/LBS and from GY/GYS. Six of the tested 15 bacterial strains showed significantly better recovery rate on the inorganic-supplemented media LBS or GYS than on basic LB or GY. These results show that inorganic supplement of basic media may significantly improve the growth and viability of several bacterial strains

Essential-oil component combinations: possibilities against respiratory tract pathogens

Nowadays, the excessive use of antimicrobials leads to the growing appearance of resistant pathogens in the case of respiratory tract infections (RTIs). Therefore, the discovery of new alternatives, which could support their therapy is an important challenge. Combination of the effective substances is one of the possible solutions. Based on this possibility, several studies focused on the interaction between essential oils (EOs) and their volatiles in the last decade.                Therefore, the aim of the present study was to evaluate the most effective EO components of cinnamon bark, thyme, clove, peppermint, and citronella oils. Direct bioautography (DB) was used in the detection of interaction profiles of trans-cinnamaldehyde, eugenol, thymol, menthol, geraniol, citronellal, and citral against methicillin-resistant Staphylococcus aureus (MRSA, 4262), resistant Pseudomonas aeruginosa (RPA, 34205), and P. aeruginosa (ATCC 27853). First, the minimal detectable dose (MDD) of individual components was determined. According to the MDD values, the combined, as well as the individual compounds, were applied to the TLC plates. The diameters of the inhibition zones were measured with the Motic Images Plus 2.0 program. The statistical analysis was performed with the Mann-Whitney-Wilcoxon test of the R Studio 1.1.383 program.                In the case of P. aeruginosa, a combination of thymol and menthol was active; against RPA, trans-cinnamaldehyde combined with thymol was found to be effective. Against MRSA, menthol combined with trans-cinnamaldehyde, and eugenol also showed enhanced activity.                According to our knowledge, we applied for the first time the DB for the detection of antimicrobially effective combinations of EO compounds. It could be regarded as a cost-effective and quick screening method. In the future, we would like to focus on the combinations of EOs and their main components with antibiotics as well