Development of fluorogenic probe-based and high-resolution melting-based polymerase chain reaction assays for the detection and differentiation of Bartonella quintana and Bartonella henselae

Duplex real-time PCR assay with high-resolution melt analysis for the detection and quantification of Listeria species and Listeria monocytogenes in meat products

Listeria contamination in foods of animal origin is one of the most concerning food safety issues. A duplex, SYBR green-based, real-time PCR assay was developed with high-resolution melting analysis-based differentiation of the genus Listeria and Listeria monocytogenes. The primers were designed and tested against other related foodborne pathogens. The assay was optimized for standard parameters in a non-orthogonal fashion and validated following international standards. The LODabs and LOQ of the assay were calculated to be 0.78 and 1.56 ng of the target DNA. The LODrel of the assay was found to be 1% Listeria DNA in background DNA. The assay was evaluated for applicability in artificially spiked samples, providing a 120 CFU/ml detection. The assay was validated with proficiency test samples and also with samples collected for surveillance analysis. This well-established and validated assay can be utilized as a qualitative and quantitative tool for addressing the Listeria contamination in the food safety contexts.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05695-2.

Cat scratch disease: What to do with the cat?

Purpose

Cat scratch disease (CSD) frequently has ophthalmologic manifestations. The ophthalmologist's approach to treating neuroretinitis is familiar, but few eye care providers are comfortable answering the next question of “what do I do with my cat?” Published guidelines are often vague in answering the complexities of real-life conundrums that can lead patients and their doctors to believe that risk mitigation should involve removal of the animal. Here, we present demonstrative scenarios informed by clinical practice and provide updated recommendations.

Observations

A 10-year-old boy presented with reduced vision in the right eye. Funduscopic examination identified optic nerve head edema with subretinal fluid, and a macular star developed one week later, consistent with the diagnosis of neuroretinitis. Serology confirmed Bartonella henselae antibodies and a diagnosis of CSD. The father disclosed that the family has recently adopted three kittens, who have scratched the boy and the patient's younger sister. The physician and patient's family find themselves at a loss regarding best practices for what should be done with the kittens.

Conclusions and Importance

B. henselae has been detected in a variety of mammals and can be transmitted via vectors such as fleas. Even well-appearing animals can transmit the bacteria, months to years after their initial infection. Symptoms, clinical and laboratory findings will depend on bacterial load and strain virulence, as well as the physiological/immunological status of the host, with people at the extremes of age and the immunocompromised being at greater disease risk. Flea control is crucial to minimize transmission risk. Our veterinary expert (EBB) recommends testing (with serology and PCR) and treating infected animals (with doxycycline and a quinolone). Patients should be counseled to speak with their pets’ veterinarian. When addressing the concerns of our CSD patients in clinical practice, ophthalmologists should be aware of the strategies for minimizing Bartonella transmission risk, and cognizant of the One Health approach for managing zoonoses.

Unbiased screen for pathogens in human paraffin-embedded tissue samples by whole genome sequencing and metagenomics

Identification of bacterial pathogens in formalin fixed, paraffin embedded (FFPE) tissue samples is limited to targeted and resource-intensive methods such as sequential PCR analyses. To enable unbiased screening for pathogens in FFPE tissue samples, we established a whole genome sequencing (WGS) method that combines shotgun sequencing and metagenomics for taxonomic identification of bacterial pathogens after subtraction of human genomic reads. To validate the assay, we analyzed more than 100 samples of known composition as well as FFPE lung autopsy tissues with and without histological signs of infections. Metagenomics analysis confirmed the pathogenic species that were previously identified by species-specific PCR in 62% of samples, showing that metagenomics is less sensitive than species-specific PCR. On the other hand, metagenomics analysis identified pathogens in samples, which had been tested negative for multiple common microorganisms and showed histological signs of infection. This highlights the ability of this assay to screen for unknown pathogens and detect multi-microbial infections which is not possible by histomorphology and species-specific PCR alone.

Molecular Detection of Bartonella spp. in China and St. Kitts

Bartonella are vector-borne hemotropic bacteria that infect a wide variety of hosts, including people. While there are PCR assays that can identify individual or groups of Bartonella, there is no reliable molecular method to simultaneously detect all species while maintaining genus specificity and sensitivity. By comparing highly conserved 16S rRNA sequences of the better-recognized Bartonella spp. on GenBank, we selected primers and probes for a genus-specific pan-Bartonella FRET-qPCR. Then, a gltA-based Bartonella PCR was established by selecting primers for a highly variable region of gltA, of which the sequenced amplicons could identify individual Bartonella spp. The pan-Bartonella FRET-qPCR did not detect negative controls (Brucella spp., Anaplasma spp., Rickettsia spp., Coxiella burnetii, and Wolbachia) but reliably detected as few as two copies of the positive control (Bartonella henselae) per reaction. There was complete agreement between the pan-Bartonella FRET-qPCR and the gltA-based Bartonella PCR in detecting Bartonella in convenience test samples from China and St. Kitts: cats (26%; 81/310), Ctenocephalides felis (20%; 12/60), cattle (24%; 23/98), and donkeys (4%; 1/20). Sequencing of the gltA-based Bartonella PCR products revealed B. henselae (70%; 57/81) and B. clarridgeiae (30%; 24/81) in cats and C. felis (67%; 8/12, and 33%; 4/12, respectively) and B. bovis in cattle (23.5%; 23/98) and donkeys (4.0%; 1/24). The pan-Bartonella FRET-qPCR and gltA-based Bartonella PCR we developed are highly sensitive and specific in detecting recognized Bartonella spp. in a single reaction. The pan-Bartonella FRET-qPCR is convenient requiring no gel electrophoresis and providing copy numbers, while the gltA-based Bartonella PCR reliably differentiates individual Bartonella species. The use of these PCRs should greatly facilitate large-scale surveillance studies and the diagnosis of infections in clinical samples.