Pathogenicity and Virulence
Julius P. Kreier in Infection, Resistance, and Immunity, 2022
Any microorganism that is able to infect a host and produce disease is a pathogen. IVllcroorganisms vary in their ability to produce disease; some organisms such as Vibrio cholerae, the agent of cholera, or Yersinia pestis, the cause of plague, are able to produce disease in normal healthy hosts. These bacteria are thus overt pathogens and must be distinguished from those organisms which function as opportunists and produce disease only when a break in the host′s normal defense mechanisms enables them to become established. Included in this latter group of opportunists are members of the normal flora such as Escherichia coli, Staphylococcus aureus, and certain fungi such Candida albicans, as well as some free-living bacteria such as Pseudomonas aeruginosa and Legionella pneumophila.
Bacterial Infections of the Oral Cavity
K. Balamurugan, U. Prithika in Pocket Guide to Bacterial Infections, 2019
Bacterial infections contribute to a major deal in the dental, oral, and general health of the individual. Dental caries and periodontal disease are the most common diseases of the oral cavity. The disease-causing microorganisms seem to exhibit a definite site specific pathogenicity. Streptococcus mutans—a caries-producing microorganism causes lesion only when on the tooth structure. Lactobacillus acidophilus is commonly seen in deep carious lesions. Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis, which are associated with periodontal infections when present on enamel structure, was not found to be cariogenic. But species particular to caries or periodontal disease are not isolated, although associations were present (Aas et al., 2005). The complexity of the oral environment demands the study of pathogens to be carried out as a consortium of microorganisms. Culture-independent molecular techniques, site, and subject specificity of the microorganisms seem to play a major role in isolating the etiology and understanding the behavior of the bacterial infections (Loesche et al., 1992). Periodontal disease is not a universal phenomenon. It is surprising that severe forms of this disease affect a group of population who are abnormally susceptible (Genco and Borgnakke, 2013).
Pathobiology of Amebiasis
Roberto R. Kretschmer in Amebiasis: Infection and Disease by Entamoeba histolytica, 2020
Both for working on the pathogenesis of amebiasis, as well as for writing this chapter, our group has found it convenient to distinguish between the concepts of pathogenicity and virulence, which in the literature are often used interconvertibly. By pathogenicity we understand the capacity to cause disease of a given strain of amebas, so on the basis of this property we consider only two types of amebas: pathogenic and nonpathogenic. On the other hand, by virulence we refer to the degree to which pathogenicity is expressed, usually graded as low, intermediate and high, on the basis of arbitrary and subjective criteria. It follows that there can be no pathogenic amebas without virulence, or nonpathogenic amebas with some degree of virulence. We believe that this separation of the concepts of pathogenicity and virulence should be preserved as long as the mechanisms of both features are not completely and clearly delineated. Of course, we are fully aware that pathogenicity and virulence are not absolute properties of the parasite, but rather expressions of the specific host-parasite model under consideration, which also includes many important environmental conditions. Nevertheless, there are some indications that in human and in some experimental forms of amebiasis, pathogenicity, and virulence may depend more on the parasite than on the host.
Oral prosthetic microbiology: aspects related to the oral microbiome, surface properties, and strategies for controlling biofilms
Published in Biofouling, 2021
Douglas Roberto Monteiro, Victor Eduardo de Souza Batista, Anne Caroline Morais Caldeirão, Rogério de Castilho Jacinto, Juliano Pelim Pessan
Regarding the prevalence of Candida species in CD wearers, cultures from palatal mucosa and internal denture surface have identified several species, which are listed in descending order of prevalence: Candida albicans, Candida glabrata, Candida tropicalis, Candida dubliniensis, Candida parapsilosis, Candida krusei, Candida guilliermondii, and Candida lipolytica (Zomorodian et al.2011). Isolates of Saccharomyces cerevisiae, Trichosporon capitatum, and Trichosporon beigelii have also been found, but at lower prevalence (Zomorodian et al.2011). Denture biofilm exhibits higher Candida colonization compared with dental biofilm, probably due to the greater adhesion capacity of this species to acrylic surfaces (Kang et al.2013). Other factors associated with Candida colonization include low salivary pH and sugar intake (Martori et al.2017). However, it should be noted that the adhesion of Candida species depends on the coaggregation to the pre-formed biofilm via interactions with different microorganisms. These interactions may be synergistic, potentiating the growth of some species and invasion of the mucosa by Candida spp. (Diaz et al.2012), with significant impacts on the pathogenicity of the microorganisms involved.
A case report: septic shock due to (tropical) pyomyositis and multiple metastatic embolisms caused by Panton Valentine Leukocidin-positive methicillin-sensitive staphylococcus aureus in a 12-year-old boy
Published in Acta Clinica Belgica, 2022
Valérie Vanbiervliet, Ignace Demeyer, Filip Claus, Kristien Van Vaerenbergh
Staphylococcus aureus (S. aureus) is an important human pathogen and it causes various types of infections, both in nosocomial and community setting. Based on methicillin susceptibility, it is divided into two major groups: methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). Numerous virulence factors enable the organism to be a successful pathogen through different mechanisms of action. An important virulence factor is Panton-Valentine Leukocidin toxin (PVL). PVL is a membrane pore-forming protein responsible for cell leakage and cell death. PVL producing S. aureus causes more severe infections. Although commonly associated with community-acquired methicillin-resistant S. aureus (CA-MRSA), several outbreaks due to methicillin-susceptible S. aureus have been reported [1].
Stromal Keratitis with Endophthalmitis Caused by Vittaforma Corneae in an Immunocompetent Patient: A Case Report
Published in Ocular Immunology and Inflammation, 2019
Lalida Pariyakanok, Vannarut Satitpitakul, Prasart Laksanaphuk, Kitiya Ratanawongphaibul, Chaturong Putaporntip, Somchai Jongwutiwes
To date, it remains unknown whether different clinical presentations in human microsporidiosis are influenced by the route of infections or different tissue tropisms of each species. However, an in vitro study has shown that spores of Vittaforma corneae could be internalized into various cell types comparable to those belonging to the genus Encephalitozoon; thereby, favoring the importance of infection route.6 On the other hand, severe ocular microsporidiosis has been diagnosed in both immunocompromised and immunocompetent hosts as reported herein.3 It is therefore likely that the interplay between host immunity and yet unknown pathogen virulence factors could determine disease severity. Undoubtedly, further studies are mandatory to resolve this issue.
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