Nontuberculous mycobacteria isolated from specimens of pulmonary tuberculosis suspects, Northern Tunisia: 2002\u20132016

Reem Gharbi,Besma Mhenni,Helmi Mardassi,Saloua Ben Fraj

doi:10.1186/s12879-019-4441-1

Abstract

BackgroundReports on the worldwide ascending trend of pulmonary nontuberculous mycobacteria (NTM) isolation rates and their effective role in respiratory tract infections are compelling. However, as yet, there are no such data relating to Tunisia.MethodsHere we carried out a retrospective review of mycobacterial cultures originating from Northern Tunisia, which have been processed in the laboratory of mycobacteria of the Institut Pasteur de Tunis, during the time period 2002–2016. All pulmonary NTM (PNTM) isolates available for culture were characterized phenotypically and their taxonomic status was further established based on polymorphisms in rpoB, 16S rRNA, hsp65, and sodA DNA gene sequences.ResultsOf the 10,466 specimens collected from HIV-negative Tunisian patients with presumptive clinical pulmonary TB, 60 (0.6%) yielded PNTM isolates. An overall annual PNTM isolation prevalence of 0.2/100,000 was estimated. As far as could be ascertained, this isolation rate accounts amongst the lowest reported hitherto throughout the world. Among the 30 NTM isolates that were available for culture, 27 (90.0%) have been identified to the species level. The most commonly encountered species was Mycobacterium kansasii (23.3%) subtype 1. Strikingly, all M. kansasii cases were male patients originating from Bizerte, an industrialized region particularly known for iron industry. The remaining NTM species were M. fortuitum (16.6%), M. novocastrense (16.6%), M. chelonae (10.0%), M. gordonae (6.6%), M. gadium (6.6%), M. peregrinum (3.3%), M. porcinum (3.3%), and M. flavescens (3.3%). There were no bacteria of the M. avium complex, the most frequently isolated NTM globally, and the main driver of the rise of NTM-lung diseases.ConclusionsThis study uncovered an exceptional low prevalence of PNTM isolation among HIV-negative TB suspects in Northern Tunisia, suggesting a very low burden of NTM pulmonary disease. However, the frequent isolation of M. kansasii subtype 1, the most pathogenic subtype, particularly from the industrialized region of Bizerte, strongly suggests its effective involvement in a typical pulmonary disease.

Highlights

Reports on the worldwide ascending trend of pulmonary nontuberculous mycobacteria (NTM) isolation rates and their effective role in respiratory tract infections are compelling
Mycobacterium tuberculosis complex (MTBC) and M. leprae, the vast majority of mycobacteria are environmental organisms that usually act as opportunistic pathogens, causing localized or disseminated infections [1, 2]
Pulmonary samples We carried out a retrospective review of mycobacterial cultures originating from Northern Tunisia (Tunis, Bizerte, and Zaghouan), which have been processed in the laboratory of mycobacteria of the Institut Pasteur de Tunis, Tunisia

Summary

Introduction

Reports on the worldwide ascending trend of pulmonary nontuberculous mycobacteria (NTM) isolation rates and their effective role in respiratory tract infections are compelling. Mycobacteria encompass a large taxonomic group distributed in various aquatic and terrestrial environments These are acid-fast bacilli (AFB) belonging to the genus Mycobacterium. Mycobacterium tuberculosis complex (MTBC) and M. leprae, the vast majority of mycobacteria are environmental organisms that usually act as opportunistic pathogens, causing localized (skin and soft tissues, lymph nodes, bones, lungs) or disseminated infections [1, 2]. These opportunistic species are often collectively termed nontuberculous mycobacteria (NTM), but are known as atypical mycobacteria, pathogenic environmental mycobacteria, or mycobacteria other than tuberculosis. Like MTBC members, pathogenicity in NTM is predominantly correlated with slow growth [4]

Methods

Results

Discussion

Conclusion