Quantitative assessment of tolerance response to stress after exposure to oregano and rosemary essential oils, carvacrol and 1,8-cineole in Salmonella Enteritidis 86 and its isogenic deletion mutants ∆dps, ∆rpoS and ∆ompR

The Fate of 1,8-cineole as a Chemical Penetrant: A Review

The stratum corneum continues to pose the biggest obstacle to transdermal drug delivery. Chemical penetrant, the first generation of transdermal drug delivery system, offers a lot of potential. In order to fully examine the permeation mechanism of 1,8-cineole, a natural monoterpene, this review summarizes the effects of permeation-enhancing medications on drugs that are lipophilic and hydrophilic as well as the toxicity of this substance on the skin and other tissues. For lower lipophilic drugs, 1,8-cineole appears to have a stronger osmotic-enhancing impact. An efficient and secure tactic would be to combine enhancers and dose forms. 1,8-cineole is anticipated to be further developed in the transdermal drug delivery system and even become a candidate drug for brain transport due to its permeability and low toxicity.

Phytochemicals: potential alternative strategy to fight Salmonella enterica serovar Typhimurium

The rise of multidrug resistant (MDR) microorganisms is a great hazard worldwide and has made it difficult to treat many infectious diseases adequately. One of the most prevalent causes of outbreaks of foodborne illness worldwide is Salmonella. The ability of this and other harmful bacteria to withstand antibiotics has recently proven crucial to their effective control. Since the beginning of time, herbal medicines and phytochemicals have been employed for their potent antibacterial action and there is a growing trend toward the production of plant based natural products for the prevention and treatment of pathogenic infections. Numerous phytochemicals have been proven effective against the molecular determinants responsible for attaining drug resistance in pathogens like efflux pumps, membrane proteins, bacterial cell communications and biofilms. The medicinal plants having antibacterial activity and antibiotics combination with phytochemicals have shown synergetic activity against Salmonella enterica serovar Typhimurium. The inhibitory effects of tannins on rumen proteolytic bacteria can be exploited in ruminant nutrition. Improved control of the rumen ecology and practical use of this feed additive technology in livestock production will be made possible by a better knowledge of the modulatory effects of phytochemicals on the rumen microbial populations in combination with fermentation. This review focuses on the development of antibacterial resistance in Salmonella, the mechanism of action of phytochemicals and the use of phytochemicals against S. enterica serovar Typhimurium. The advances and potential future applications of phytochemicals in the fight against resistant are also discussed.

Sigma factor RpoS positively affects the spoilage activity of Shewanella baltica and negatively regulates its adhesion effect

Shewanella baltica is the dominant bacterium that causes spoilage of seafood. RpoS is an alternative sigma factor regulating stress adaptation in many bacteria. However, the detailed regulatory mechanism of RpoS in S. baltica remains unclear. This study aims to investigate the regulatory function of RpoS on spoilage activity and adhesion ability in S. baltica. Results revealed that RpoS had no effect on the growth of S. baltica, but positively regulated the spoilage potential of S. baltica accompanied by a slower decline of total volatile basic nitrogen, lightness, and the sensory score of fish fillets inoculated with rpoS mutant. RpoS negatively regulated the adhesion ability, which was manifested in that the bacterial number of rpoS mutant adhered to stainless steel coupon was higher than that of the S. baltica in the early stage, and the biofilm formed on glass slide by rpoS mutant was thicker and tighter compared with S. baltica. Transcriptomic analysis showed that a total of 397 differentially expressed genes were regulated by RpoS. These genes were mainly enrichment in flagellar assembly, fatty acid metabolism/degradation, and RNA degradation pathways, which were associated with motility, biofilm formation and cold adaptation. This study demonstrated that RpoS is a primary regulator involved in flagellar assembly mediated biofilm formation and cold adaptation-related spoilage activity of S. baltica. Our research will provide significant insights into the control of microbiological spoilage in seafood.

Microbial resistance to sanitizers in the food industry: review

Hygiene programs which comprise the cleaning and sanitization steps are part of the Good Hygiene Practices (GHP) and are considered essential to ensure food safety and quality. Inadequate hygiene practices may contribute to the occurrence of foodborne diseases, development of microbial resistance to sanitizers, and economic losses. In general, the sanitizer resistance is classified as intrinsic or acquired. The former is an inherent characteristic, naturally present in some microorganisms, whereas the latter is linked to genetic modifications that can occur at random or after continuous exposure to a nonnormal condition. The resistance mechanisms can involve changes in membrane permeability or in the efflux pump, and enzymatic activity. The efflux pump mechanism is the most elucidated in relation to the resistance caused by the use of different types of sanitizers. In addition, microbial resistance to sanitizers can also be favored in the presence of biofilms due to the protection given by the glycocalyx matrix and genetic changes. Therefore, this review aimed to show the main microbial resistance mechanisms to sanitizers, including genetic modifications, biofilm formation, and permeability barrier.

Polyphenolic phytochemicals as natural feed additives to control bacterial pathogens in the chicken gut

Poultry provides an important protein source consumed globally by human population, and simultaneously, acts as a substantial reservoir of antibiotic resistant bacterial species such as Escherichia coli, Salmonella, Campylobacter, Clostridium perfringens. These bacterial species can include commensal strains with beneficial roles on poultry health and productivity, and pathogenic strains not only to poultry but zoonotically to man. This review paper evaluates the role of phytochemicals as possible alternatives to antibiotics and natural anti-bacterial agents to control antibiotic resistance in poultry. The focus of this paper is on the polyphenolic phytochemicals as they constitute the major group; carvacrol oil (the active ingredient of oregano), thymol oil (the main ingredient of oregano), oregano oil, and tannins oil as feed additives and their mechanism of actions that might enhance avian gut health by controlling antibiotic-resistant bacterial strains spread in poultry.

Evaluation of Structural Changes and Molecular Mechanism Induced by High Hydrostatic Pressure in Enterobacter sakazakii

The contamination of infant milk and powder with Enterobacter sakazakii poses a risk to human health and frequently caused recalls of affected products. This study aims to explore the inactivation mechanism of E. sakazakii induced by high hydrostatic pressure (HHP), which, unlike conventional heat treatment, is a nonthermal technique for pasteurization and sterilization of dairy food without deleterious effects. The mortality of E. sakazakii under minimum reaction conditions (50 MPa) was 1.42%, which was increased to 33.12% under significant reaction conditions (400 MPa). Scanning electron microscopy (SEM) and fluorescent staining results showed that 400 MPa led to a loss of physical integrity of cell membranes as manifested by more intracellular leakage of nucleic acid, intracellular protein and K⁺. Real-time quantitative PCR (RT-qPCR) analysis presents a downregulation of three functional genes (glpK, pbpC, and ompR), which were involved in cell membrane formation, indicating a lower level of glycerol utilization, outer membrane protein assembly, and environmental tolerance. In addition, the exposure of E. sakazakii to HHP modified oxidative stress, as reflected by the high activity of catalase and super oxide dismutase. The HHP treatment lowered down the gene expression of flagellar proteins (fliC, flgI, fliH, and flgK) and inhibited biofilm formation. These results determined the association of genotype to phenotype in E. sakazakii induced by HHP, which was used for the control of food-borne pathogens.

Review on Stress Tolerance in Campylobacter jejuni

Campylobacter spp. are the leading global cause of bacterial colon infections in humans. Enteropathogens are subjected to several stress conditions in the host colon, food complexes, and the environment. Species of the genus Campylobacter, in collective interactions with certain enteropathogens, can manage and survive such stress conditions. The stress-adaptation mechanisms of Campylobacter spp. diverge from other enteropathogenic bacteria, such as Escherichia coli, Salmonella enterica serovar Typhi, S. enterica ser. Paratyphi, S. enterica ser. Typhimurium, and species of the genera Klebsiella and Shigella. This review summarizes the different mechanisms of various stress-adaptive factors on the basis of species diversity in Campylobacter, including their response to various stress conditions that enhance their ability to survive on different types of food and in adverse environmental conditions. Understanding how these stress adaptation mechanisms in Campylobacter, and other enteric bacteria, are used to overcome various challenging environments facilitates the fight against resistance mechanisms in Campylobacter spp., and aids the development of novel therapeutics to control Campylobacter in both veterinary and human populations.

Physiological alterations involved in inactivation of autochthonous spoilage bacteria in orange juice caused by Citrus essential oils and mild heat

This study investigated physiological alterations involved in the inactivation of Levilactobacillus (L.) brevis and Leuconostoc (Lc.) mesenteroides in orange juice caused by Citrus lemon essential oil (CLEO) and C. reticulata essential oil (CREO) alone and combined with mild heat treatment (MHT). Damage in DNA, membrane integrity, membrane potential, metabolic and efflux activity of bacterial cells were measured after exposure (6 and 12 min) to CLEO or CREO (0.5 μL/mL) and/or MHT (54 °C) using flow cytometry. Limonene was the major constituent in CLEO (66.4%) and CREO (89.4%). The size of the damaged cell subpopulations increased (p < 0.05) after longer exposure time and varied with the tested essential oil and/or bacterial isolate. After exposure to CLEO and CREO alone, the cell subpopulations with damage in measured physiological functions were in a range of 19.6-66.8% and 23.8-75.9%, respectively. Exposure to CREO resulted in larger Lc. mesenteroides cell subpopulations (35.4-68.7%) with damaged DNA, permeabilized and depolarized membrane and compromised metabolic or efflux activity compared to L. brevis (23.8-58.0%). In contrast, exposure to CLEO led to higher damaged L. brevis cell subpopulations (35.1-77%) compared to Lc. mesenteroides (25.3-36.6%). Exposure to combined treatments (CLEO or CREO and MHT) affected the measured physiological functions in almost the entire L. brevis and Lc. mesenteroides cell population (up to 99%), although the damage extension on each isolate varied with tested essential oil. Results show that inactivation of L. brevis and Lc. mesenteroides cells caused by CLEO and CREO alone and combined with MHT in orange juice involves a multi-target action, which causes DNA damage, altered permeability and depolarization of membrane and compromised metabolic and efflux activities.

Successive exposure to Mentha piperita L. essential oil affects the culturability and induces membrane repair in a persister epidemic Salmonella Typhimurium PT4

This study had as aims to evaluate the effects of successive exposures to Mentha piperita L. essential oil (MPEO) on culturability and physiological functions of Salmonella Typhimurium PT4. S. Typhimurium PT4 cells (10⁸ log CFU/mL) were exposed to the same (1.25 μL/mL) or increasing MPEO concentrations (1.25-80 μL/mL) during 252 h. At each 36-h interval, the viable cell counts, and distinct cell functions were assessed using plate counting and flow cytometry, respectively. As the exposure time to the same MPEO concentration increased, the population of S. Typhimurium PT4 cells with damaged, permeabilized and depolarized membrane, and compromised efflux activity decreased. Otherwise, S. Typhimurium PT4 cells with damaged membrane physiological functions increased over the exposure to increasing concentrations of MPEO. Genomic analyses showed that the strain carries 17 genes associated with stress responses and the persistence of the tested strain among sources associated with poultry spanning more than 16 years and its virulence for humans. Therefore, successive exposure to a sublethal concentration of MPEO induced S. Typhimurium PT4 cells capable of maintaining the membrane integrity and its functions despite their non-culturable state.

Exploitation of plant extracts and phytochemicals against resistant Salmonella spp. in biofilms

Salmonella is one of the most frequent causes of foodborne outbreaks throughout the world. In the last years, the resistance of this and other pathogenic bacteria to antimicrobials has become a prime concern towards their successful control. In addition, the tolerance and virulence of pathogenic bacteria, such as Salmonella, are commonly related to their ability to form biofilms, which are sessile structures encountered on various surfaces and whose development is considered as a universal stress response mechanism. Indeed, the ability of Salmonella to form a biofilm seems to significantly contribute to its persistence in food production areas and clinical settings. Plant extracts and phytochemicals appear as promising sources of novel antimicrobials due to their cost-effectiveness, eco-friendliness, great structural diversity, and lower possibility of antimicrobial resistance development in comparison to synthetic chemicals. Research on these agents mainly attributes their antimicrobial activity to a diverse array of secondary metabolites. Bacterial cells are usually killed by the rupture of their cell envelope and in parallel the disruption of their energy metabolism when treated with such molecules, while their use at sub-inhibitory concentrations may also disrupt intracellular communication. The purpose of this article is to review the current available knowledge related to antimicrobial resistance of Salmonella in biofilms, together with the antibiofilm properties of plant extracts and phytochemicals against these detrimental bacteria towards their future application to control these in food production and clinical environments.

Efficacy of oregano and rosemary essential oils to affect morphology and membrane functions of noncultivable sessile cells of Salmonella Enteritidis 86 in biofilms formed on stainless steel

AIMS

This study evaluated the efficacy of essential oil from Origanum vulgare L. (oregano; OVEO) and Rosmarinus officinalis L. (rosemary; ROEO) to inactivate sessile cells of Salmonella enterica serovar Enteritidis 86 (SE86) in young and mature biofilms formed on stainless steel.

METHODS AND RESULTS

Ultrastructural alterations and damage in different physiological functions caused by OVEO and ROEO in noncultivable sessile cells of SE86 were investigated using scanning electron microscopy and flow cytometry. OVEO (2·5 μl ml^-1 ) and ROEO (40 μl ml^-1 ) were effective to eradicate young and mature biofilms formed by SE86 sessile cells on stainless steel surfaces; however, the efficacy varied with exposure time. OVEO and ROEO caused alterations in morphology of SE86 sessile cells, inducing the occurrence of bubbles or spots on cell surface. OVEO and ROEO compromised membrane polarization, permeability and efflux activity in noncultivable SE86 sessile cells. These findings show that OVEO and ROEO act by a multitarget mechanism on SE86 membrane functions.

CONCLUSIONS

ROEO and OVEO showed efficacy to eradicate SE86 sessile cells in preformed biofilms on stainless steel, displaying a time-dependent effect and multitarget action mode on bacterial cell membrane.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study provides for the first time the effects of OVEO and ROEO on morphology and physiological functions of noncultivable sessile cells of S. Enteritidis biofilms preformed on stainless steel surfaces.