Bacteriological culture and direct PCR for detecting the Mycobacterium tuberculosis complex in the Italian eradication campaign: a decade of experience at the National Reference Laboratory

Abstract

Aims: Our study evaluates the capacity of direct real-time PCR for detecting Mycobacterium tuberculosis complex (MTBC), with a focus on diagnostic performances and the feasibility of implementing this protocol in an eradication campaign. Specifically, we compare the effectiveness of the direct PCR method to various culture systems used by the Italian National Reference Laboratory over the last decade to detect MTBC.

Methods and results: Bovine tissue samples were routinely tested and analyzed for bovine tuberculosis (bTB) confirmation using microbiological culture (solid and liquid media), histopathological analysis, and a direct PCR assay targeting IS6110, an insertion sequence specific to the MTBC that is widely used for tuberculosis diagnosis. The direct real-time PCR demonstrated a high concordance (K = 0.871) with microbiological culture, as well as good sensitivity (91.84%) and specificity (95.24%). In contrast, histopathology demonstrated lower concordance (K = 0.746) and performance levels (sensitivity 91.41%, specificity 82.88%). Liquid media promoted faster and more efficient growth of MTBC than solid media. M. bovis and M. caprae had the comparable ability to respond to the direct real-time PCR test and grow on the microbiological medium.

Conclusions: This study confirms that direct real-time PCR can detect MTBC with high diagnostic accuracy within a few days. This study found no significant differences in performance between culture media and direct PCR for M. bovis and M. caprae.

Keywords: Mycobacterium bovis; Mycobacterium caprae; bovine tuberculosis; microbiological culture; real-time PCR.