[Rifampicin-resistant Mycobacterium bovis BCG strain isolated from an infant with NEMO mutation]

It is well known that disseminated Mycobacterium bovis BCG infection is developed after BCG vaccination in infants with congenital cellular immune deficiencies such as mutations in genes along the interleukin (IL)-12/interferon (IFN)-γ pathway and mutations in nuclear factor-kB essential modulator (NEMO). In this report, a rifampicin-resistant M.bovis BCG strain isolated from an infant with NEMO defect was presented. An 8-month-old male infant with NEMO defect admitted to the pediatric outpatient clinic of our hospital with fever, generalized lymphadenopathy and hepatosplenomegaly. Microscopic examination of the smears prepared from lymph node and liver biopsy specimens revealed abundant amount (3+) of acid-fast bacilli (AFB). Rifampicin-susceptible Mycobacterium tuberculosis complex (MTC) was detected by real-time PCR (GeneXpert MTB/RIF; Cepheid, USA) in the samples. The growth of mycobacteria was determined on the 20th day of culture performed in MGIT960 system (Becton Dickinson, USA). The isolate was identified as M.bovis BCG by GenoType MTBC kit (Hain Lifescience, Germany) and defined as M.bovis BCG [SIT 482 (BOV_1)] by spoligotyping. In the primary anti-tuberculosis drug susceptibility test performed by MGIT960 system, the isolate was found susceptible to rifampicin (RIF), isoniazid (INH), streptomycin (STM) and ethambutol (EMB). Then anti-tuberculosis treatment was started to the patient. However, the patient at the age of 2 years, re-admitted to the hospital with the complaint of hepatosplenomegaly. Smear of spontaneously draining abscess material obtained from subcutaneous nodules revealed intensive AFB positivity (3+) once again. In the present instance RIF-resistant MTC was detected with GeneXpert system in the specimen. The growth of mycobacteria was determined on the 13th day of culture and isolate was identified as M.bovis BCG. The present isolate was found susceptible to INH, STM and EMB but resistant to RIF. A mutation in the rpoB gene (codon 531, S531L) associated with RIF resistance was detected by using the partial sequencing of the rpoB gene. Patient died due to disseminated bovis BCG infection and multiple organ failure. To our knowledge, there are only six RIF-resistant M.bovis BCG strains isolated from patients in the literature. However, this is the first RIF-resistant M.bovis BCG strain isolated from a NEMO-deficient patient.