Contemporary diagnostics for medically relevant fastidious microorganisms belonging to the genera Anaplasma,Bartonella,Coxiella,OrientiaandRickettsia

Abstract

Many of the human infectious pathogens - especially the zoonotic or vector-borne bacteria - are fastidious organisms which are difficult to cultivate because of their strong adaption to the infected host culminating in their near complete physiological dependence on this environment. These bacterial species exhibit reduced multiplication rates once they are removed from their optimal ecological niche. This fact complicates the laboratory diagnosis of the disease and hinders the detection and further characterization of the underlying organisms, e.g. at the level of their resistance to antibiotics due to their slow growth. Here, we describe the current state of microbiological diagnostics for five genera of human pathogens with a fastidious laboratory lifestyle. For Anaplasma spp., Bartonella spp., Coxiella burnetii, Orientia spp., and Rickettsia spp. we will summarize the existing diagnostic protocols, the specific limitations for implementation of novel diagnostic approaches, and the need for further optimization or expansion of the diagnostic armamentarium. We will reflect upon the diagnostic opportunities provided by new technologies including mass spectrometry and next-generation nucleic acid sequencing. Finally, we will review the (im)possibilities of rapidly developing new in vitro diagnostic tools for diseases of which the causative agents are fastidiously growing and therefore hard to detect.

Cat Scratch Disease in Children

“…Patients with unilateral lymphadenopathy and a history of cat exposure need a diagnostic evaluation of CSD (29,30). Laboratory findings of CSD are variable, high levels of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), leukocytosis and anemia have been described most (14,40). Microbiological analyses involve classical culture methods, and serological and molecular testing.…”

“…Cultivation of bacteria is always the gold standard for detection of live pathogens in human samples. Since Bartonella species are fastidious, biochemically inert and slow growing bacteria, classical culture techniques on solid agars are not sensitive enough and should be supplemented with serological and molecular methods (40). Novel approaches combine liquid Bartonella-Alphaproteobacteria growth medium for pre-enrichment growth of bacteria sampled in human specimens, such as blood or tissue biopsy, followed by molecular polymerase chain reaction (PCR) testing.…”

“…Although molecular testing is most sensitive analysis for most intracellular pathogens. A direct PCR test from the blood of CSD patients is of limited value for patients with a very low bacteremia level, while in the case of tissue specimens, the sample collection requires invasive medical procedures that are often avoided by doctors (40,41). The most common and readily available method for diagnosis of SCD is serological testing of B. henselae in blood samples of infected patients (41).…”

“…On the other hand, the sensitivity and specificity of IFA testing are higher than ELISA, but the production of B. henselae IFA antigen is complicated. The production of antigen by liquid medium for ELISA testing is easier and faster (40). A titer of immunoglobulin G (IgG) greater than 1:256 strongly suggests an active or recent infection.…”

“…A positive immunoglobulin M (IgM) test suggests acute disease, but IgM production time is very short and transitory. Given all the shortcomings of serological assays, negative serology does not rule out CSD in a patient with typical epidemiological and clinical features (40)(41)(42)(43). Radiological imaging diagnostic methods are important for patients with suspected atypical CSD with bone or visceral involvement (32).…”