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Evolutionary Biology of Parasitism
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2023
Eric S. Loker, Bruce V. Hofkin
Among the myriads of organisms living in close association with other organisms, there are several organisms that straddle the boundaries with parasitism. Many organisms are harmless commensals unless and until the host becomes debilitated in some way, after which they assume the status of facultative parasites. This phenomenon is particularly true of ciliate protists living on the surface of fishes. For example, Brooklynella hostilis normally glides over the surface of the gills of fish feeding harmlessly on sloughing gill epithelium. If the fish becomes stressed, as in captivity, the ciliate can attack the gills and denude them of cells, killing the fish in the process. A transition for such an organism to obligatory parasitism is easy to envision. Mites in particular provide many examples of species that are trending toward parasitic lifestyles, and multiple origins of parasitism in mites from predatory ancestors are likely. The mite Kennethiella trisetosa is phoretic on a wasp parasitoid (Ancistrocerus antilope) that lays its eggs on caterpillars (Figure 7.30). At the time of the wasp’s oviposition, the mite disembarks and not only feeds from the caterpillar but also extracts hemolymph from the larvae of the wasp developing in the caterpillar. Examples like this demonstrate that the paths to parasitism are many and often potentially devious in their course.
Host-Parasite Relationships
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
The microbes that live on the body′s surfaces and in the hollow organs are usually considered to be commensals benefiting from the association. Commensals gain food and shelter for themselves and do little or no harm to their hosts. In some cases these microbes can be shown to benefit their hosts, and the relationship is thus mutualistic. The microbial inhabitants of the lower bowel of humans, for example, benefit their hosts. If they are eliminated by antibiotic treatment, the microbes that then may colonize the region may cause severe diarrhea. The microbes living in the rumen of cattle are clearly mutualistic since they digest cellulose for the host animals.
Ayurveda and COVID-19
Published in Srijan Goswami, Chiranjeeb Dey, COVID-19 and SARS-CoV-2, 2022
The beauty of the immune system is that it is intelligent; it does not indiscriminately destroy all bacteria that enter the system. There are many bacteria that are happily living within us. They are known as commensals. These bacteria do not harm the system. In fact, some of them¸ such as lactobacilli, have a symbiotic relationship with the individual. They live and thrive in the intestine and, in turn, create and provide the much-needed vitamin B to the individual. Other commensals live in the body and do the job of protecting us from pathogenic bacteria and fungi by not allowing them to take root or grow in their space. The immune system recognizes these friendly bacteria and does not harm them. The immune system is also equipped to identify and eliminate any aberrant cells in the body, such as cancer cells. It is only when the immune system gets weak that some cancer cells escape and start growing. We have to understand the immune system, and find out how it works, learns, develops, and becomes efficient. There are two types of immune system in the human being, namely, inherent and adaptive.
Modeling spatial interaction networks of the gut microbiota
Published in Gut Microbes, 2022
Xiaocang Cao, Ang Dong, Guangbo Kang, Xiaoli Wang, Liyun Duan, Huixing Hou, Tianming Zhao, Shuang Wu, Xinjuan Liu, He Huang, Rongling Wu
Third, the networks reconstructed by qdODE can omnidirectionally capture ecological interactions that occur among microbes. It can cover all possible types of microbial interactions, including mutualism (two microbes promote each other by producing factors that are beneficial for both interacting parties), antagonism (two microbes inhibit each other), commensalism (one microbe promotes its partner whereas the latter does not affect the former), amensalism (one microbe inhibits the other and the other is neutral), and parasitism (one microbe inhibits the other but the latter promotes the former). The opposite to parasitism is altruism (one microbe promotes the other but the latter inhibits the former).25,49,52 A microbe may actively manipulate other microbes (by promoting or inhibiting the latter) and, meanwhile, it may be passively manipulated by other microbes. In an idopNetwork, one can identify the numbers of such active links and passive links for each microbe. If a microbe has more active links than passive links, it is regarded as a leader microbe. If a microbe’s active links are more than the average of all microbes (i.e., connectivity), then this microbe is a mighty hub or keystone microbe that is believed to play a pivotal role in maintaining microbial communities. If a microbe has less links, including active and passive, than the average, it is a solitary microbe. The ecological interpretation of these strategies will stimulate researchers to explore the mass, energetic, or signal basis of microbial interactions.53
Prevotella species as oral residents and infectious agents with potential impact on systemic conditions
Published in Journal of Oral Microbiology, 2022
Eija Könönen, Dareen Fteita, Ulvi K. Gursoy, Mervi Gursoy
Research into the genus Prevotella has increased considerably over the past years. Prevotella has a wide intra-genus variation, which leads to a variety of properties between Prevotella species. Interest is focused on their involvement as commensals and potentially pathogenic organisms at different locations of the human body. In the oral cavity, Prevotella are important members of bacterial communities on various mucosal surfaces and in saliva as well as in dental biofilms above and below the gumline. However, knowledge of individual Prevotella species other than P. intermedia and P. nigrescens and their role in keeping homeostasis or interfering in dysbiotic biofilms is still limited. As regards P. melaninogenica, on the one hand, it belongs to the core oral bacteriome in individuals with healthy oral tissues but, on the other hand, it seems to be involved in many pathogenic conditions inside and outside the mouth. Is it a bystander or an active player in these cases? Also, the influence of behavioral and lifestyle factors on oral Prevotella is not clear. For example, an interesting question whether diet could have an impact on oral Prevotella species remains to be answered. Furthermore, increasingly attractive is the potential link of oral Prevotella organisms to systemic conditions not usually connected to microbes.
Novel avenues for identification of new antifungal drugs and current challenges
Published in Expert Opinion on Drug Discovery, 2022
Fungi are simple eukaryotic organisms that are able to colonize various environments around the planet. It is estimated that there are approx. 2 million different species. They are ubiquitous in nature and are vital for the recycling of nutrients contained in organic matter (most species of fungi are saprophytes). They coexist with other organisms on the basis of mutualism, commensalism, and, unfortunately, parasitism [1,2]. Higher fungi have been used by people in the kitchen, brewing, viticulture, and folk medicine for thousands of years. Microscopic as well as higher fungi are used in biotechnology for the production or biotransformation of various substances and, in recent years, also popular for the green synthesis of nanoparticles. Biologically active secondary metabolites of higher fungi and microscopic fungi have become the inspiration for the design of drug structures [3–5].