Laboratory diagnosis of Mycobacterium xenopi and its clinical relevance

Abstract number: P1414

Davidson S., Abed Yassin A., Gruper M., Braun E., Sprecher H.

Background: Accurate laboratory detection of mycobacterial infection is of utmost importance. Unfortunately, very little is currently known about the performance of automated systems widely used in clinical laboratories.

Methods: Over a period of 3 years (2006–2008), 37 MGIT tubes were scored as negative by the BACTEC™ MGIT 960™ system (Becton-Dickinson). At the end of 6 weeks of incubation they were visually inspected, as recommended by the manufacturer. If positive, an acid-fast stain was performed. Acid fast isolates were then specified using an Hsp65-based PCR assay. 35 of these isolates were identified as Mycobacterium Xenopi. These isolates were assessed using Pulse field Gel Electrophoresis (PFGE) and the epidemiological and clinical characteristics of patients with M. Xenopi positive cultures were retrospectively analyzed.

Results: The yearly false-negative detection rate of the automated system studied was 1% as opposed to the <0.5% false negative detection rate mentioned by the manufacturer. During the study period, 35 samples were erroneously diagnosed as negative by the automated system and were finally identified as M. Xenopi positive cultures. Eight cultures out of 17, 7 out 13 and 0 out 10 were isolated from patients hospitalised in one internal medicine department during 2006, 2007 and 2008 respectively. During 2006–7, this department was temporarily re-located due to local refurbishment work, and transferred back to its permanent location in 2008, suggesting that M. Xenopi isolation in this department was dependent upon collection site location. M. Xenopi-positive cultures were mostly of respiratory origin (86%). Patient disease course and clinical features were not consistent with atypical mycobacterial infection in most of the cases.

Conclusions: The false-negative detection rate of the BACTEC MGIT 960 system is higher than previously reported and is mainly accounted for by M. Xenopi cases. The pathogenic relevance of M. Xenopi isolation is questionable.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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