Isolation, biochemical and molecular identification of Nocardia species among TB suspects in northeastern, Tanzania; a forgotten or neglected threat?

Background: Pulmonary nocardiosis mimic pulmonary tuberculosis in most clinical and radiological manifestations. In Tanzania, where tuberculosis is one of the major public health threat clinical impact of nocardiosis as the cause of the human disease remains unknown. The objective of the present study was to isolate and identify Nocardia isolates recovered from TB suspects in Northeastern, Tanzania by using biochemical and molecular methods.

Methods: The study involved 744 sputum samples collected from 372 TB suspects from four periphery diagnostic centers in Northeastern, Tanzania. Twenty patients were diagnosed as having presumptively Nocardia infections based on microscopic, cultural characteristics and biomèrieux ID 32C Yeast Identification system and confirmed using 16S rRNA and hsp65 gene specific primers for Nocardia species and sequencing.

Results: Biochemically, the majority of the isolates were N. asteroides (n = 8/20, 40%), N. brasiliensis (n = 4/20, 20%), N. farcinica (n = 3/20, 15%), N. nova (n = 1/20, 5%). Other aerobic actinomycetales included Streptomyces cyanescens (n = 2/20, 10%), Streptomyces griseus, Actinomadura madurae each (n = 1/20, 5%). Results of 16S rRNA and hsp65 sequencing were concordant in 15/17 (88. 2%) isolates and discordant in 2/17 (11.8%) isolates. Majority of the isolates belonged to N. cyriacigeorgica and N. farcinica, four (23.5%) each.

Conclusions: Our findings suggest that Nocardia species may be an important cause of pulmonary nocardiosis that is underdiagnosed or ignored. This underscores needs to consider pulmonary nocardiosis as a differential diagnosis when there is a failure of anti-TB therapy and as a possible cause of human infections.