Acinetobacter baumannii is a multidrug resistant pathogen capable of causing a wide spectrum of clinical conditions in humans. Acinetobacter spp. is ubiquitously found in different water sources. Chlorine being the most commonly used disinfectant in water, the study investigated the effect of chlorine on the survival of A. baumannii in water and transcription of genes conferring antibiotic resistance. Eight clinical isolates of A. baumannii, including a fatal meningitis isolate (ATCC 17978) (~108 CFU/mL) were separately exposed to free chlorine concentrations (0.2, 1, 2, 3 and 4 ppm) with a contact time of 30, 60, 90 and 120 second. The surviving pathogen counts at each specified contact time were determined using broth dilution assay. In addition, real-time quantitative PCR (RT-qPCR) analysis of the antibiotic resistance genes (efflux pump genes and those encoding resistance to specific antibiotics) of three selected A. baumannii strains following exposure to chlorine was performed. Results revealed that all eight A. baumannii isolates survived the tested chlorine levels during all exposure times (p > 0.05). Additionally, there was an up-regulation of all or some of the antibiotic resistance genes in A. baumannii, indicating a chlorine-associated induction of antibiotic resistance in the pathogen.

Many pathogenic bacteria and fungi produce potentially lethal toxins that cause cytotoxicity or impaired cellular function either at the site of colonization or other locations in the body through receptor-mediated interactions. Various factors, including biotic and abiotic environments, competing microbes, and chemical cues affect toxin expression in these pathogens. Recent work suggests that several natural compounds can modulate toxin production in pathogenic microbes. However, studies explaining the mechanistic basis for their effect are scanty. This review discusses the potential of various plant-derived compounds for reducing toxin production in foodborne and other microbes. In addition, studies highlighting their anti-toxigenic mechanism(s) are discussed.

Aflatoxins (AF) are toxic metabolites primarily produced by molds, Aspergillus flavus and Aspergillus parasiticus. Contamination of poultry feed with AF is a major concern to the poultry industry due to severe economic losses stemming from poor performance, reduced egg production, and diminished egg hatchability. This study investigated the inhibitory effect of 2 generally regarded as safe (GRAS), natural plant compounds, namely carvacrol (CR) and trans-cinnamaldehyde (TC), on A. flavus and A. parasiticus growth and AF production in potato dextrose broth (PDB) and in poultry feed. In broth culture, PDB supplemented with CR (0%, 0.02%, 0.04% and 0.08%) or TC (0%, 0.005%, 0.01% and 0.02%) was inoculated with A. flavus or A. parasiticus (6 log CFU/mL), and mold counts and AF production were determined on days 0, 1, 3, and 5. Similarly, 200 g portions of poultry feed supplemented with CR or TC (0%, 0.4%, 0.8%, and 1.0%) were inoculated with each mold, and their counts and AF concentrations in the feed were determined at 0, 1, 2, 3, 4, 8, and 12 weeks of storage. Moreover, the effect of CR and TC on the expression of AF synthesis genes in A. flavus and A. parasiticus (aflC, nor1, norA, and ver1) was determined using real-time quantitative PCR (RT-qPCR). All experiments had duplicate samples and were replicated 3 times. Results indicated that CR and TC reduced A. flavus and A. parasiticus growth and AF production in broth culture and chicken feed (P<0.05). All tested concentrations of CR and TC decreased AF production in broth culture and chicken feed by at least 60% when compared to controls (P<0.05). In addition, CR and TC down-regulated the expression of major genes associated with AF synthesis in the molds (P<0.05). Results suggest the potential use of CR and TC as feed additives to control AF contamination in poultry feed.

c Salmonella enterica serovar Enteritidis is a major foodborne pathogen in the United States, causing gastroenteritis in humans, primarily through consumption of contaminated eggs. Chickens are the reservoir host of S. Enteritidis. In layer hens, S. Enteritidis colonizes the intestine and migrates to various organs, including the oviduct, leading to egg contamination. This study investigated the efficacy of in-feed supplementation with trans-cinnamaldehyde (TC), a generally recognized as safe (GRAS) plant compound obtained from cinnamon, in reducing S. Enteritidis cecal colonization and systemic spread in layers. Additionally, the effect of TC on S. Enteritidis virulence factors critical for macrophage survival and oviduct colonization was investigated in vitro. The consumer acceptability of eggs was also determined by a triangle test. Supplementation of TC in feed for 66 days at 1 or 1.5% (vol/wt) for 40-or 25-week-old layer chickens decreased the amounts of S. Enteritidis on eggshell and in yolk (P < 0.001). Additionally, S. Enteritidis persistence in the cecum, liver, and oviduct in TC-supplemented birds was decreased compared to that in controls (P < 0.001). No significant differences in feed intake, body weight, or egg production in birds or in consumer acceptability of eggs were observed (P > 0.05). In vitro cell culture assays revealed that TC reduced S. Enteritidis adhesion to and invasion of primary chicken oviduct epithelial cells and reduced S. Enteritidis survival in chicken macrophages (P < 0.001). Follow-up gene expression analysis using real-time quantitative PCR (qPCR) showed that TC downregulated the expression of S. Enteritidis virulence genes critical for chicken oviduct colonization (P < 0.001). The results suggest that TC may potentially be used as a feed additive to reduce egg-borne transmission of S. Enteritidis. Salmonella enterica serovar Enteritidis is one of the major foodborne pathogens in the United States responsible for causing enteric illnesses in humans (1). Eggs are the primary source of S. Enteritidis infection of humans (1, 2). Approximately 90 billion eggs are produced and 67.5 billion shell eggs consumed annually in the United States (3). Thus, the microbiological safety of eggs is a major concern to the government, the poultry industry, and consumers due to the potential impacts on public health and the economy. Chickens act as asymptomatic carriers of S. Enteritidis, resulting in its environmental dissemination and potential infection of humans. Humans contract S. Enteritidis infection via consumption of contaminated, raw, or undercooked eggs, and several epidemiological studies have confirmed this association between human salmonellosis and egg consumption (4, 5).Despite the implementation of various pre-and postharvest control measures, S. Enteritidis remains a major cause of eggborne disease outbreaks in the United States (1). Recently, the U.S. Centers for Disease Control and Prevention (CDC) reported that the incidence of foodborne salmonellosis did not decrease signi...

Salmonella enteritidis (SE) is a major foodborne pathogen that causes human infections largely by consumption of contaminated eggs. The external surface of eggs becomes contaminated with SE from multiple sources, highlighting the need for effective egg surface disinfection methods. This study investigated the efficacy of three GRAS-status, phytochemicals, namely carvacrol (CR), eugenol (EG), and β-resorcylic acid (BR) applied as pectin or gum arabic based coating for reducing SE on shell eggs. White-shelled eggs, spot inoculated with a 5-strain mixture of nalidixic acid (NA) resistant SE (8.0 log CFU/mL) were coated with pectin or gum arabic solution containing each phytochemical (0.0, 0.25, 0.5, or 0.75%), and stored at 4°C for 7 days. SE on eggs was enumerated on days 0, 1, 3, and 7 of storage. Approximately 4.0 log CFU/egg of SE was recovered from inoculated and pectin or gum arabic coated eggs on day 0. All coating treatments containing CR and EG, and BR at 0.75% reduced SE to undetectable levels on day 3 (P < 0.05). Results suggest that the aforementioned phytochemicals could effectively be used as a coating to reduce SE on shell eggs, but detailed studies on the sensory and quality attributes of coated eggs need to be conducted before recommending their use.

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Escherichia coli O157: H7 (EHEC) is a major foodborne pathogen largely transmitted to humans through the consumption of undercooked ground beef. This study investigated the efficacy of two food-grade, plant-derived antimicrobials, namely rutin (RT), and resveratrol (RV) with or without chitosan (CH) in enhancing EHEC inactivation in undercooked hamburger patties. Further, the effect of aforementioned treatments on beef color and lipid oxidation was analyzed. Additionally, the deleterious effects of these antimicrobial treatments on EHEC was determined using scanning electron microscopy (SEM). Ground beef was inoculated with a five-strain mixture of EHEC (7.0 log CFU/g), followed by the addition of RT (0.05%, 0.1% w/w) or RV (0.1, 0.2% w/w) with or without CH (0.01% w/w). The meat was formed into patties (25 g) and stored at 4°C for 5 days. On days 1, 3, and 5, the patties were cooked (65°C, medium rare) and surviving EHEC was enumerated. The effect of these treatments on meat color and lipid oxidation during storage was also determined as per American Meat Science Association guidelines. The study was repeated three times with duplicate samples of each treatment. Both RT and RV enhanced the thermal destruction of EHEC, and reduced the pathogen load by at least 3 log CFU/g compared to control (P < 0.05). The combination of RT or RV with CH was found to be more effective, and reduced EHEC by 5 log CFU/g (P < 0.05). EHEC counts in uncooked patties did not decline during storage for 5 days (P > 0.05). Moreover, patties treated with RV plus CH were more color stable with higher a∗ values (P < 0.05). SEM results revealed that heat treatment with antimicrobials (CH + RV 0.2%) resulted in complete destruction of EHEC cells and extrusion of intracellular contents. Results suggest that the aforementioned antimicrobials could be used for enhancing the thermal inactivation of EHEC in undercooked patties; however, detailed sensory studies are warranted.

Irrigation water, particularly if applied overhead, could be an important source of bacterial contamination to fresh produce. The colonization, survival, and proliferation of exogenous bacterial pathogens can be strongly influenced by the produce microbiota. In this study, spinach grown in an organic field was irrigated with ground water and potential alternative irrigation water including reclaimed wastewater, and urban runoff water, over a period of 2 weeks. Water and spinach samples were collected before and after irrigation for bacterial plate count, qPCR, and community profiling using 16S rDNA high-throughput sequencing analyses. The average bacterial population densities on spinach (6.50 ± 0.04 log CFU/g, 7.40 ± 0.10 log 16S copies/g) were significantly higher than those in irrigation water (3.61 ± 0.12 log CFU/ml, 4.94 ± 0.13 log 16S copies/ml). The composition and relative abundance of spinach microbiomes varied with different types of irrigation waters; however, the most abundant microbial taxa on spinach were not significantly affected by the irrigation with different types of water. Shigella, Salmonella, Listeria, Campylobacter spp., and pathogenic Escherichia coli were not detected in this study. This study provides information on the microbial ecology of diverse bacterial communities on spinach surface after irrigation by different types of water, which can benefit future studies on the interaction of microbes on produce, and the prevention of foodborne pathogens and plant disease.