China
Africa
Explore chapters and articles related to this topic
Host Defense and Parasite Evasion
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2015
Eric S. Loker, Bruce V. Hofkin
Another example of a collaborative, mutualistic arrangement to achieve infection of an invertebrate host is provided by entomopathogenic nema-todes such as Steinernema and Heterorhabditis (see also Box 7.2). Infective Steinernema larvae actively search for, find, and infect insect hosts. Once in the insect, they release from special areas of their intestine mutualistic bacteria (Xenorhabdus) that then proliferate rapidly in the host insect’s hemocoel, producing a number of factors that damage the host’s hemocytes. The bacteria also inhibit expression of host-produced antimicrobial peptides, such as cecropin, and inhibit prophenoloxidase and thus melanization. Furthermore, the bacteria produce antimicrobial factors that prevent the growth of opportunistic bacteria and release enzymes that degrade molecules produced by the host insect, providing a nutrient soup that favors growth of their associated nematodes. Consequently, both Xenorhabdus and Steinernema proliferate in the host, which is soon killed. Eventually thousands of larval nematodes leave the host insect, each carrying an inoculum of these specialized bacteria to facilitate infection of a hapless new host. Because of their efficiency in killing insects, entomopathogenic nematodes have been used widely as biological control agents.
Spread and Control of Microbes
Published in Jim Lynch, What Is Life and How Might It Be Sustained?, 2023
Biocontrol bacteria have not been exploited greatly by the agrochemical industry. A notable exception, however, is the insect parasitic nematodes, which release Xenorhabdus bacteria when they absorb them through orifices. This process was developed at HRI Littlehampton and now produced in the town by the agrochemical company BASF in 20 fermentation vessels generating 40 trillion nematodes. Extensive studies at HRI over many years also showed the capacity of the bacterium Bacillus thuringiensis to control insect pests biologically by producing a crystal toxin. The toxin production can be genetically modified, and the gene has been inserted into plants, such as cotton to control boll weevil larvae and which is exploited commercially, even though there have been some concerns in India particularly that some beneficial insects could be affected. One strain of the bacterium could even kill mosquitos, although it has generally been considered that malaria control by this means would be uneconomic. Baculoviruses have been deployed with due consideration to environmental factors which govern their survival, especially in forests. Diseases have also been controlled successfully. The classic early successes were the control of crown gall of fruit trees and roses using the bacterium Agrobacterium tumefaciens, and the control of root rot of pine by the fungus Peniophora gigantea. These control processes, along with many other potential applications for a range of crops and trees, are reviewed in the book I edited with John Hobbie in Microorganisms in Action. Such approaches seemed to be a great way of producing healthy crops without loading the environment with chemicals described in Chapter 3. However, my comments made in 1988 were made with some caution because it was clear that the agrochemical industry felt threatened by this alternative to chemicals. Despite the extensive efforts on the International Organisation of Biological Control, the position today is that biocontrol practices have not been universally accepted or optimally utilised. The limitations to uptake have included risk-averse and unwieldy regulatory processes, increasingly bureaucratic barriers to access biocontrol agents, insufficient communication of the economic, and environmental benefits with the public and stakeholders which include growers and politicians. The biocontrol disciplines have also been fragmented. This is disappointing but could be remedied, and this will be considered again in the final chapter.
The relevance of studying insect–nematode interactions for human disease
Published in Pathogens and Global Health, 2022
Zorada Swart, Tuan A. Duong, Brenda D. Wingfield, Alisa Postma, Bernard Slippers
Knowledge on interspecies interactions gained from studying EPN systems is not limited to the field of nematode infections. The symbiotic bacteria of EPN represent as important models to study bacteria-host interactions, as nematode–host interactions [17]. Bacteria from the genera Photorhabdus and Xenorhabdus (the symbionts of Heterorhabditis and Steinernema, respectively) form part of the Enterobacteriaceae [75]. Other members of this family include the common human pathogens, Escherichia coli, Salmonella spp., Yersinia spp. and Proteus spp. In fact, Proteus mirabilis – one of the most common causative agents of urinary tract and hospital-acquired infections [76,77–78] – is the closest phylogenetic relative to Photorhabdus and Xenorhabdus. Therefore, an understanding of pathogenicity in the entomopathogenic bacteria can contribute to a search for similarities in human pathogens. The discovery of such orthologous virulence pathways could reveal strategies for the prevention and treatment of P. mirabilis infection in humans.