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      Inactivation of rickettsiae

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          A reliable and complete inactivation is an indispensable premise for any concentration of rickettsiae or for the development of diagnostic strategies based on their antigens. This study deals with the testing of methods to inactivate rickettsiae.

          Rickettsia honei was used as a model organism. The inactivating potency of formalin, Qiagen® antiviral lysozyme (AVL) buffer, heating to 56 °C, and β-propiolactone was analyzed in cell culture.

          The inactivation limits for rickettsiae were 0.1% formalin about 10 min, Qiagen AVL buffer about 5 min, 56 °C about 5 min, 0.125% β-propiolactone about 1 h, and 0.0125% β-propiolactone overnight. The interpretation was limited by cytotoxic effects of the inactivation procedures and by the culturally achievable rickettsial density in the cell culture supernatants that were used for the inactivation experiments.

          Reliable modes of inactivation were identified, allowing for the secure handling of rickettsial antigens for diagnostic purposes.

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          Most cited references 12

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          Rickettsioses as paradigms of new or emerging infectious diseases.

           D Raoult,  V Roux (1997)
          Rickettsioses are caused by species of Rickettsia, a genus comprising organisms characterized by their strictly intracellular location and their association with arthropods. Rickettsia species are difficult to cultivate in vitro and exhibit strong serological cross-reactions with each other. These technical difficulties long prohibited a detailed study of the rickettsiae, and it is only following the recent introduction of novel laboratory methods that progress in this field has been possible. In this review, we discuss the impact that these practical innovations have had on the study of rickettsiae. Prior to 1986, only eight rickettsioses were clinically recognized; however, in the last 10 years, an additional six have been discovered. We describe the different steps that resulted in the description of each new rickettsiosis and discuss the influence of factors as diverse as physicians' curiosity and the adoption of molecular biology-based identification in helping to recognize these new infections. We also assess the pathogenic potential of rickettsial strains that to date have been associated only with arthropods, and we discuss diseases of unknown etiology that may be rickettsioses.
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            Rickettsia felis from cat fleas: isolation and culture in a tick-derived cell line.

            Rickettsia felis, the etiologic agent of spotted fever, is maintained in cat fleas by vertical transmission and resembles other tick-borne spotted fever group rickettsiae. In the present study, we utilized an Ixodes scapularis-derived tick cell line, ISE6, to achieve isolation and propagation of R. felis. A cytopathic effect of increased vacuolization was commonly observed in R. felis-infected cells, while lysis of host cells was not evident despite large numbers of rickettsiae. Electron microscopy identified rickettsia-like organisms in ISE6 cells, and sequence analyses of portions of the citrate synthase (gltA), 16S rRNA, Rickettsia genus-specific 17-kDa antigen, and spotted fever group-specific outer membrane protein A (ompA) genes and, notably, R. felis conjugative plasmids indicate that this cultivatable strain (LSU) was R. felis. Establishment of R. felis (LSU) in a tick-derived cell line provides an alternative and promising system for the expansion of studies investigating the interactions between R. felis and arthropod hosts.
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              Serological differentiation of murine typhus and epidemic typhus using cross-adsorption and Western blotting.

              Differentiation of murine typhus due to Rickettsia typhi and epidemic typhus due to Rickettsia prowazekii is critical epidemiologically but difficult serologically. Using serological, epidemiological, and clinical criteria, we selected sera from 264 patients with epidemic typhus and from 44 patients with murine typhus among the 29,188 tested sera in our bank. These sera cross-reacted extensively in indirect fluorescent antibody assays (IFAs) against R. typhi and R. prowazekii, as 42% of the sera from patients with epidemic typhus and 34% of the sera from patients with murine typhus exhibited immunoglobulin M (IgM) and/or IgG titers against the homologous antigen (R. prowazekii and R. typhi, respectively) that were more than one dilution higher than those against the heterologous antigen. Serum cross-adsorption studies and Western blotting were performed on sera from 12 selected patients, 5 with murine typhus, 5 with epidemic typhus, and 2 suffering from typhus of undetermined etiology. Differences in IFA titers against R. typhi and R. prowazekii allowed the identification of the etiological agent in 8 of 12 patients. Western blot studies enabled the identification of the etiological agent in six patients. When the results of IFA and Western blot studies were considered in combination, identification of the etiological agent was possible for 10 of 12 patients. Serum cross-adsorption studies enabled the differentiation of the etiological agent in all patients. Our study indicates that when used together, Western blotting and IFA are useful serological tools to differentiate between R. prowazekii and R. typhi exposures. While a cross-adsorption study is the definitive technique to differentiate between infections with these agents, it was necessary in only 2 of 12 cases (16.7%), and the high costs of such a study limit its use.

                Author and article information

                European Journal of Microbiology and Immunology
                Akadémiai Kiadó, co-published with Springer Science+Business Media B.V., Formerly Kluwer Academic Publishers B.V.
                1 September 2013
                : 3
                : 3
                : 188-193
                [ 1 ] Department of Tropical Medicine at the Bernhard Nocht Institute, German Armed Forces Hospital of Hamburg, Bernhard Nocht street 74, D-20359, Hamburg, Germany
                [ 2 ] Institute for Microbiology, Virology and Hygiene, University Hospital Rostock, Rostock, Germany
                [ 3 ] Institute for Microbiology of the German Armed Forces, Munich, Germany
                Author notes
                [* ] 0049-40-6947-28743, 0049-40-6947-28709, Frickmann@
                Original Article


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