EMERGING PATHOGENS IN VERTEBRATES: BIOLOGY, GENOMICS AND INFECTIVITY OF BACTERIA ASCRIBED TO THE MIDICHLORIACEAE FAMILY
Tesi di Dottorato
Data di Pubblicazione:
2017
Citazione:
EMERGING PATHOGENS IN VERTEBRATES: BIOLOGY, GENOMICS AND INFECTIVITY OF BACTERIA ASCRIBED TO THE MIDICHLORIACEAE FAMILY / A. Cafiso ; tutor: C. Bazzocchi; coordinatore: F. Gandolfi. DIPARTIMENTO DI MEDICINA VETERINARIA, 2017 Apr 04. 29. ciclo, Anno Accademico 2016. [10.13130/cafiso-alessandra_phd2017-04-04].
Abstract:
This PhD thesis is the outcome of a wider project focused on studying the biology, genomics and infectivity of bacteria ascribed to the Midichloriaceae family. Midichloriaceae are a group of bacteria extremely diversified in terms of the ecological and taxonomic diversity of their hosts. Members of the family Midichloriaceae can be considered as a wide bacterial group, still to be investigated under several aspects. In particular, the association of members of the family Midichloriaceae with parasites (such as ticks, fleas and parasitic amoebae) suggests that these bacteria could be potentially infectious to vertebrates (including humans) and even responsible for medical and veterinarian diseases. The researchers conducted in this PhD project have been focused on three main topics: i) possible involvement of a midichloriacea in a disease (red mark syndrome; RMS) affecting rainbow trout; ii) in-depth analysis of different aspects concerning the hard tick Ixodes ricinus and its intramitochondrial symbiont Midichloria mitochondrii (i.e. antibiotic treatment of the arthropod, salivary glands vs. ovaric tissue comparative proteomics, transmission of the symbiont to the vertebrate host); iii) presence of M. mitochondrii-related bacteria in different tick species.
A brief description of each topic of the work done is here reported:
i) RMS is a chronic skin disease of unknown etiology affecting farmed rainbow trout Oncorhynchus mykiss in Europe. It consists of single or multiple skin lesions usually localized on the trunk of fish approaching market size. Many authors suppose that a bacterial infection could be the cause of the disease. Some studies have reported a possible correlation between the presence of a Rickettsia-like organism (subsequently ascribed to the family Midichloriaceae) and RMS skin lesions. Our work concerning the possible involvement of a midichloriacea in RMS in rainbow trout resulted in the detection of bacteria of this family, besides in skin lesions, in various internal organs and in the bloodstream. No bacteria were found in unaffected fish and in healthy skin samples from affected individuals. Bacteria were detected also in fish ponds water were RMS-affected fish are farmed. These results give support to the hypothesis of the involvement of these bacteria in developing RMS. It is possible that some free-living eukaryotes could host or be the vector of this midichloriacea.
ii) M. mitochondrii is the most prevalent symbiont of the hard tick I. ricinus, present in 100% of eggs and adult females of wild I. ricinus populations. This bacterium is intracellular and is the only known symbiont able to invade the mitochondria of the host cells. However, the role that M. mitochondrii plays in the host metabolism has yet to be elucidated. In addition, multiple lines of evidence indicate the possibility of the transmission of this bacterium to the vertebrate host during the tick blood meal.
In order to investigate the role of M. mitochondrii in the biology of the tick host, we performed an antibiotic treatment on I. ricinus individuals, with the aim of reducing/eliminating the symbiont, and to potentially observe the dynamic of bacterial infection in the tick host. We microinjected engorged adult females of I. ricinus with tetracycline, and we allowed the resulting larvae to feed on gerbils treated with the same antibiotic. The amount of M. mitochondrii was evaluated at different stages of the experiment using molecular techniques. In addition we evaluated the presence/absence of the symbiont DNA in the blood of gerbils used for the larval feeding. The performed treatments did not allow to eliminate the symbiont population from the host tick, however it allowed to reduce the multiplication that occurs after the larval blo
Tipologia IRIS:
Tesi di dottorato
Keywords:
midichloria spp.; midichloria mitochondrii; symbiosis; tick; ixodes ricinus; transmission; red mark syndrome; oncorhynchus mykiss; midichloriaceae
Elenco autori:
A. Cafiso
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