Salmonella Enteritidis and Campylobacter jejuni are the two major foodborne pathogens transmitted through poultry products. Since chickens are the reservoir hosts of these pathogens, with their intestinal colonization being the most significant factor causing contamination of meat and eggs, with oviduct infection also a contributing factor, finding an effective pre-processing strategy for reducing colonization of chickens with these pathogens is critical. An antimicrobial treatment that can be applied via feed would be the most practical and economically viable approach for use by poultry producers. A natural, safe, non-toxic antimicrobial would be the most acceptable by producers and consumers. The use of the plant-derived, GRAS-status molecules, caprylic acid, trans-cinnamaldehyde, eugenol, carvacrol and thymol as feed supplements for reducing cecal and/or oviduct populations of S. Enteritidis and C. jejuni in chickens will be addressed.
Caprylic acid (CA) (octanoic acid) is a natural, eight-carbon medium chain fatty acid (MCFA) present in coconut oil, palm kernel oil, caprine milk, and bovine milk, and is a food-grade chemical approved by the FDA as generally regarded as safe (GRAS). One of our first reports examined the anti-Salmonella potential of CA on rapid reduction of SE (>5.0 log CFU) in chicken cecal contents in vitro. On a positive note, CA was minimally inhibitory (P<0.05) towards endogenous cecal population of anaerobic bacteria. Based on these data we designed a study to determine the prophylactic potential of CA in controlling the SE in commercial broiler chicks. Birds fed with either 0.7 or 1% CA supplemented via feed for 18 days resulted in consistently decreased SE populations recovered from the treated birds on days 7 and 10 after challenge in cecum, cloaca, liver, spleen, intestine and crop (P<0.05). Feed intake and body weight did not differ between the treated and control groups. Histological examination revealed no pathological changes in the cecum and liver of CA supplemented birds. Additionally, CA supplementation did not significantly affect the cecal pH or the cecal endogenous bacteria. These result suggest that prophylactic CA supplementation via feed could reduce SE colonization in chickens without adverse effects.
The therapeutic efficacy of CA in reducing SE in chickens was studied next. CA was supplemented in the feed at 0.7 or 1% for the last 5 days before slaughter at either 3 or 6 weeks of age. As observed with the prophylactic supplementation, CA at 0.7 or 1% significantly decreased SE populations in the cecum, small intestine, cloaca, liver, and spleen in both 3- and 6-week experiments (P<0.05). Additionally, feed intake and body weight did not differ between the groups (P≥0.05). These results confirmed our hypothesis that CA could be used as a potential antibacterial feed additive to reduce S. Enteritidis colonization in broiler chickens. The therapeutic efficacy of CA for reducing C. jejuni was also investigated and it was found that 0.7% and 1.4% CA reduced cecal C. jejuni counts by 3 to 5 log10 CFU/g.
Plant derived antimicrobials
Plant-derived essential oils are a group of natural molecules that have been traditionally used as dietary constituents, especially to preserve foods and enhance food flavor. The antimicrobial properties of several plant-derived essential oils have been demonstrated, and a variety of active components in these oils have been identified. Based on the in vitro screening of antibacterial activity of several plant-derived antimicrobials (PDAs) on Salmonella and Campylobacter, we found four molecules with potential to inactivate these pathogens in poultry: trans- cinnamaldehyde (TC), eugenol, carvacrol and thymol. Trans-cinnamaldehyde is a major component of the bark extract of cinnamon. It is a GRAS compound approved for use in foods by the FDA. Data from our laboratory indicated that the TC at 0.5% and 1.5% did not produce any cytotoxic effect on human epithelial cell lines and urinary tract cells in vitro, respectively. TC possesses antimicrobial activity towards a wide range of foodborne pathogens, including Gram-positive and Gram-negative bacteria. Eugenol is an active ingredient in the oil from cloves (Eugenia caryophillis) and the antibacterial activity of clove oil and eugenol has been well documented.
Carvacrol and thymol are major ingredients in oregano oil obtained from Origanum glandulosum. The oil has been found effective against bacterial and fungal infections of the gastrointestinal and genitourinary tract.
TC significantly reduced SE and C. jejuni populations in cecal contents without affecting the total cecal endogenous populations. At 0.2 and 0.35% TC inactivated SE by 9 log10 CFU/ml, compared to the controls after incubation for 24 h. Although exhibiting slightly lower antibacterial potential compared to TC, eugenol, carvacrol and thymol at 0.75 and 1% also resulted in significant reductions in pathogen populations after 24 h of incubation. It was also observed that C. jejuni was more sensitive to all the PDAs. For example, all PDAs at ~0.1% significantly reduced the pathogen after 24 h of incubation. In a drinking water study we found that TC at 0.06% inactivated SE completely after 24h in water with 1% feces at 12.5 and 25 °C. Our results indicate that TC is effective in killing SE in chicken’s drinking water, and could be used as an additive to control water-borne SE colonization in chickens. The efficacy of these PDAs in reducing the intestinal colonization of SE and C. jejuni in chickens was also studied. Day old broiler chicks were supplemented with either 0.5 or 0.75% TC, and 0.75 or 1% eugenol via feed for 20 days. TC at 0.5 and 0.75% and eugenol at 1% reduced (P<0.05) S. Enteritidis in the cecum (~3 log10 CFU/g) and cloaca (~2 log10 CFU/g), respectively after 10 days of infection. Neither compound altered the p, or endogenous cecal microflora counts (P>0.05). Feed intake and body weight were unaffected by TC, however, eugenol-treated groups had significantly lower (P<0.05) body weights compared to controls. In market age broilers the PDAs reduced cecal colonization of SE by ~1.5 log10 CFU/g (P<0.05) and in the cloacal contents, TC and eugenol decreased SE populations by ~1.5 and 2 log10 CFU/g, respectively (P<0.05).
Although all parts of chicken reproductive tract are prone to SE colonization, the isthmus is likely a critical site in terms of persistent reproductive tract colonization and egg membrane contamination by the pathogen. Since no established chicken oviduct epithelial cell (COEC) lines are available commercially, we isolated primary COEC from the isthmus of chicken oviducts. All four PDAs significantly reduced SE adhesion and invasion of COEC (P<0.05). In general, the PDAs decreased SE adhesion and invasion of COEC by 40% and 50%, respectively.
References are available on request.