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The emergence of antibiotic resistance in pathogenic bacteria has led to renewed interest in exploring the potential of plant-derived antimicrobials (PDAs) as an alternative therapeutic strategy to combat microbial infections. Historically, plant extracts have been used as a safe, effective, and natural remedy for ailments and diseases in traditional medicine. Extensive research in the last two decades has identified a plethora of PDAs with a wide spectrum of activity against a variety of fungal and bacterial pathogens causing infections in humans and animals. Active components of many plant extracts have been characterized and are commercially available; however, research delineating the mechanistic basis of their antimicrobial action is scanty. This review highlights the potential of various plant-derived compounds to control pathogenic bacteria, especially the diverse effects exerted by plant compounds on various virulence factors that are critical for pathogenicity inside the host. In addition, the potential effect of PDAs on gut microbiota is discussed.

The efficacy of electrolyzed oxidizing water for inactivatingEscherichia coli O157:H7, Salmonella enteritidis, and Listeria monocytogenes was evaluated. A five-strain mixture of E. coli O157:H7,S. enteritidis, or L. monocytogenes of approximately 108 CFU/ml was inoculated in 9 ml of electrolyzed oxidizing water (treatment) or 9 ml of sterile, deionized water (control) and incubated at 4 or 23°C for 0, 5, 10, and 15 min; at 35°C for 0, 2, 4, and 6 min; or at 45°C for 0, 1, 3, and 5 min. The surviving population of each pathogen at each sampling time was determined on tryptic soy agar. At 4 or 23°C, an exposure time of 5 min reduced the populations of all three pathogens in the treatment samples by approximately 7 log CFU/ml, with complete inactivation by 10 min of exposure. A reduction of ≥7 log CFU/ml in the levels of the three pathogens occurred in the treatment samples incubated for 1 min at 45°C or for 2 min at 35°C. The bacterial counts of all three pathogens in control samples remained the same throughout the incubation at all four temperatures. Results indicate that electrolyzed oxidizing water may be a useful disinfectant, but appropriate applications need to be validated.

Bovine mastitis is the most significant economic drain on the worldwide dairy industry. Concerns regarding poor cure rates, emergence of bacterial resistance, and residues in milk necessitate development of alternative therapeutic approaches to antibiotics for treatment of mastitis. A variety of free fatty acids and their monoglycerides have been reported to exert antimicrobial activity against a wide range of microorganisms. The objective of our study was to examine the efficacy of caprylic acid, a short-chain fatty acid, and its monoglyceride, monocaprylin, to inactivate common mastitis pathogens, including Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus uberis, Staphylococcus aureus, and Escherichia coli. Milk samples containing 50 mM or 100 mM caprylic acid, and 25 mM or 50 mM monocaprylin were inoculated separately with a 3-isolate mixture of each of the 5 pathogens, and incubated at 39 degrees C. Populations of surviving bacteria were determined at 0 min, 1 min, 6 h, 12 h, and 24 h of incubation. Both caprylic acid and monocaprylin reduced all 5 pathogens by >5.0 log cfu/mL after 6 h of incubation. Among the bacterial species tested, Strep. agalactiae, Strep. dysgalactiae, and Strep. uberis were most sensitive, and E. coli was most tolerant to caprylic acid and monocaprylin. Results of this study indicate that caprylic acid and monocaprylin should be evaluated as alternatives or adjuncts to antibiotics as intra-mammary infusion to treat bovine mastitis.

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ABSTRACTThe efficacies oftrans-cinnamaldehyde (TC) and eugenol (EG) for reducingSalmonella entericaserovar Enteritidis colonization in broiler chickens were investigated. In three experiments for each compound, 1-day-old chicks (n= 75/experiment) were randomly assigned to five treatment groups (n= 15/treatment group): negative control (-veS. Enteritidis, -ve TC, or EG), compound control (-veS. Enteritidis, +ve 0.75% [vol/wt] TC or 1% [vol/wt] EG), positive control (+veS. Enteritidis, -ve TC, or EG), low-dose treatment (+veS. Enteritidis, +ve 0.5% TC, or 0.75% EG), and high-dose treatment (+veS. Enteritidis, +ve 0.75% TC, or 1% EG). On day 0, birds were tested for the presence of any inherentSalmonella(n= 5/experiment). On day 8, birds were inoculated with ∼8.0 log10CFUS. Enteritidis, and cecal colonization byS. Enteritidis was ascertained (n= 10 chicks/experiment) after 24 h (day 9). Six birds from each treatment group were euthanized on days 7 and 10 after inoculation, and cecalS. Enteritidis numbers were determined. TC at 0.5 or 0.75% and EG at 0.75 or 1% consistently reduced (P< 0.05)S. Enteritidis in the cecum (≥3 log10CFU/g) after 10 days of infection in all experiments. Feed intake and body weight were not different for TC treatments (P> 0.05); however, EG supplementation led to significantly lower (P< 0.05) body weights. Follow-upin vitroexperiments revealed that the subinhibitory concentrations (SICs, the concentrations that did not inhibitSalmonellagrowth) of TC and EG reduced the motility and invasive abilities ofS. Enteritidis and downregulated expression of the motility genesflhCandmotAand invasion geneshilA,hilD, andinvF. The results suggest that supplementation with TC and EG through feed can reduceS. Enteritidis colonization in chickens.

One milliliter of culture containing a five-strain mixture of Escherichia coli O157:H7 (approximately 10(10) CFU) was inoculated on a 100-cm2 area marked on unscarred cutting boards. Following inoculation, the boards were air-dried under a laminar flow hood for 1 h, immersed in 2 liters of electrolyzed oxidizing water or sterile deionized water at 23 degrees C or 35 degrees C for 10 or 20 min; 45 degrees C for 5 or 10 min; or 55 degrees C for 5 min. After each temperature-time combination, the surviving population of the pathogen on cutting boards and in soaking water was determined. Soaking of inoculated cutting boards in electrolyzed oxidizing water reduced E. coli O157:H7 populations by > or = 5.0 log CFU/100 cm2 on cutting boards. However, immersion of cutting boards in deionized water decreased the pathogen count only by 1.0 to 1.5 log CFU/100 cm2. Treatment of cutting boards inoculated with Listeria monocytogenes in electrolyzed oxidizing water at selected temperature-time combinations (23 degrees C for 20 min, 35 degrees C for 10 min, and 45 degrees C for 10 min) substantially reduced the populations of L. monocytogenes in comparison to the counts recovered from the boards immersed in deionized water. E. coli O157:H7 and L. monocytogenes were not detected in electrolyzed oxidizing water after soaking treatment, whereas the pathogens survived in the deionized water used for soaking the cutting boards. This study revealed that immersion of kitchen cutting boards in electrolyzed oxidizing water could be used as an effective method for inactivating foodborne pathogens on smooth, plastic cutting boards.

Salmonella enterica is one of the most ubiquitous enteropathogenic bacterial species on earth, and comprises more than 2500 serovars. Widely known for causing non-typhoidal foodborne infections (95%), and enteric (typhoid) fever in humans, Salmonella colonizes almost all warm- and cold-blooded animals, in addition to its extra-animal environmental strongholds. The last few decades have witnessed the emergence of highly virulent and antibiotic-resistant Salmonella, causing greater morbidity and mortality in humans. The emergence of several Salmonella serotypes resistant to multiple antibiotics in food animals underscores a significant food safety hazard. In this review, we discuss the various antibiotic-resistant Salmonella serotypes in food animals and the food supply, factors that contributed to their emergence, their antibiotic resistance mechanisms, the public health implications of their spread through the food supply, and the potential antibiotic alternatives for controlling them.