Approaches to prevent and control Campylobacter spp. colonization in broiler chickens: a review

In vitro studies have demonstrated antibacterial activity of essential oils (EOs) against Listeria monocytogenes, Salmonella typhimurium, Escherichia coli O157:H7, Shigella dysenteria, Bacillus cereus and Staphylococcus aureus at levels between 0.2 and 10 microl ml(-1). Gram-negative organisms are slightly less susceptible than gram-positive bacteria. A number of EO components has been identified as effective antibacterials, e.g. carvacrol, thymol, eugenol, perillaldehyde, cinnamaldehyde and cinnamic acid, having minimum inhibitory concentrations (MICs) of 0.05-5 microl ml(-1) in vitro. A higher concentration is needed to achieve the same effect in foods. Studies with fresh meat, meat products, fish, milk, dairy products, vegetables, fruit and cooked rice have shown that the concentration needed to achieve a significant antibacterial effect is around 0.5-20 microl g(-1) in foods and about 0.1-10 microl ml(-1) in solutions for washing fruit and vegetables. EOs comprise a large number of components and it is likely that their mode of action involves several targets in the bacterial cell. The hydrophobicity of EOs enables them to partition in the lipids of the cell membrane and mitochondria, rendering them permeable and leading to leakage of cell contents. Physical conditions that improve the action of EOs are low pH, low temperature and low oxygen levels. Synergism has been observed between carvacrol and its precursor p-cymene and between cinnamaldehyde and eugenol. Synergy between EO components and mild preservation methods has also been observed. Some EO components are legally registered flavourings in the EU and the USA. Undesirable organoleptic effects can be limited by careful selection of EOs according to the type of food.

Success in nature depends upon an ability to perceive and adapt to the surrounding environment. Bacteria are not an exception; they recognize and constantly adjust to changing situations by sensing environmental and self-produced signals, altering gene expression accordingly. Autoinducer-2 (AI-2) is a signal molecule produced by LuxS, an enzyme found in many bacterial species and thus proposed to enable interspecies communication. Two classes of AI-2 receptors and many layers and interactions involved in downstream signalling have been identified so far. Although AI-2 has been implicated in the regulation of numerous niche-specific behaviours across the bacterial kingdom, interpretation of these results is complicated by the dual role of LuxS in signalling and the activated methyl cycle, a crucial central metabolic pathway. In this article, we present a comprehensive review of the discovery and early characterization of AI-2, current developments in signal detection, transduction and regulation, and the major studies investigating the phenotypes regulated by this molecule. The development of novel tools should help to resolve many of the remaining questions in the field; we highlight how these advances might be exploited in AI-2 quorum quenching, treatment of diseases, and the manipulation of beneficial behaviours caused by polyspecies communities. © 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

Antimicrobial peptides and proteins (AMPs) are a diverse class of naturally occurring molecules that are produced as a first line of defense by all multicellular organisms. These proteins can have broad activity to directly kill bacteria, yeasts, fungi, viruses and even cancer cells. Insects and plants primarily deploy AMPs as an antibiotic to protect against potential pathogenic microbes, but microbes also produce AMPs to defend their environmental niche. In higher eukaryotic organisms, AMPs can also be referred to as 'host defense peptides', emphasizing their additional immunomodulatory activities. These activities are diverse, specific to the type of AMP, and include a variety of cytokine and growth factor-like effects that are relevant to normal immune homeostasis. In some instances, the inappropriate expression of AMPs can also induce autoimmune diseases, thus further highlighting the importance of understanding these molecules and their complex activities. This Primer will provide an update of our current understanding of AMPs.