ISSUE FOCUS 32 FEED & ADDITIVE MAGAZINE August 2023 Salmonella belongs to the group of gram-negative bacteria and is part of the natural flora of many animal species. Of the serotypes isolated from birds, only two can cause disease with high mortality in poultry: S. gallinarum and S. pullorum (typhoid group), unique to poultry species. All other serotypes (non-typhoid group) however are largely carried asymptomatically by poultry and can be carried over to humans by contaminated poultry products. Indeed, today, salmonellosis is still one of the most reported zoonotic diseases in humans worldwide, and poultry products such as meat and eggs are considered major vehicles. To effectively reduce salmonellosis in humans, the transmission of this pathogen from poultry should be minimized as much as possible. The epidemiology of non-typhoid Salmonella, however, is very complex as the bacteria are widespread in the environment and can enter a poultry house in many ways: either horizontal (via contaminated feed or drinking water, farm personnel, equipment, and animals) or vertical (from the parent stock through the hatchery) transmission. In addition, several serotypes can be present in a poultry flock at the same time and within-flock prevalence differences may occur, making the use of vaccines not always effective. Although several intervention strategies are implemented today in poultry rearing—driven by regional regulations and national control plans—Salmonella is still omnipresent. Medium-chain fatty acids (MCFAs) are saturated unbranched monocarboxylic acids (from C6 to C12) with strong antibacterial effects against a broad range of pathogens, including Salmonella. MCFAs can approach the phospholipid bilayer of bacterial cell membranes only when undissociated, which happens more pronouncedly at an environmental pH below their pKa value. MCFAs work by disrupting the bacterial cell membrane, leading to cell leakage (Figure 1.1), followed by entering the bacteria (1.2) where the dissociation process (driven by the neutral intracellular pH) leads to cell acidification (1.3) and DNA intercalation by dissociated MCFAs molecules (1.4), ultimately blocking bacterial replication. The more MCFA molecules are undissociated, the more pronounced the above effects will be. Indeed, the minimal inhibitory concentration (MIC) value of MCFAs against Salmonella decreases about 4- to 8-fold for every unit the pH drops. This implies that the gizzard of poultry (where pH is very low) is the primary site of action for MCFAs, forming a strong barrier that limits Salmonella passage to the hindgut. MEDIUM-CHAIN FATTY ACIDS AS A NATURAL CONTROL STRATEGY TO REDUCE SALMONELLA COLONIZATION IN POULTRY David Hermans Poultry Product Developer Agrimprove
RkJQdWJsaXNoZXIy MTUxNjkxNQ==