Comparative analysis of phenotypic and genotypic antibiotic susceptibility patterns in Mycobacterium avium complex

OBJECTIVE

Phenotypic (Sensititre Myco, pDST) and genotypic drug susceptibility testing (GenoType NTM DR, gDST) in M. avium complex (MAC) have become available as standardized assays, but comparable data is needed. This study aimed to investigate the phenotypic and genotypic drug susceptibility patterns in MAC clinical isolates.

METHODS

Overall, 98 isolates from 85 patients were included. pDST and gDST were performed on all isolates and results compared regarding specificity and sensitivity using pDST as a reference method. The impact of drug instability on pDST results was studied using a biological assay over 14 days. In addition, the evolution of antimicrobial resistance was investigated in sequential isolates of 13 patients.

RESULTS

Macrolide resistance was rare, 1.2% (95% CI 0.7-7.3) of isolates in the base cohort. No aminoglycoside resistances were found, but 14.1% of the studied isolates (95% CI 7.8-23.8) showed intermediate susceptibility. The GenoType NTM DR identified two out of four macrolide-resistant isolates. Antibiotic stability was demonstrated to be poor in rifampicin, rifabutin, and doxycycylin.

CONCLUSIONS

pDST results in NTM for unstable antibiotics must be interpreted with care. A combination of pDST and gDST will be useful for the guidance of antimicrobial therapy in MAC-disease.

Nontuberculous Mycobacterium infection complicated with Haemophagocytic syndrome: a case report and literature review

Background

Non-tuberculous mycobacterial (NTM) infection is usually observed in patients with immunosuppressive conditions. It may also cause unregulated immune responses. While there have been increasing numbers of reported tuberculosis-related HPS (haemophagocytic syndrome), HPS caused by NTM infection is still very rarely reported.

Case presentation

We report a previously healthy 21-year-old Chinese female with fever, night sweats and fatigue, in whom HPS was diagnosed according to the HLH-2004 criteria. Mycobacterium intracellulare was cultured from her peripheral blood. After treatment with corticosteroid, clarithromycin, rifampicin, ethambutol and amikacin, the patient finally recovered. We also reviewed relevant publications on NTM infection complicated with HPS and found 11 cases, including ours. Clinical presentations, diagnoses and prognoses were analysed and summarized to deepen our understanding of this rare condition.

Conclusions

Most reported NTM-related cases were caused by disseminated infection. The lack of localized symptoms might add to the difficulty involved in making the right diagnosis. While it usually takes time to obtain tissue or blood culture results, granuloma in a bone marrow biopsy might be an early indicator of possible mycobacterial infection. Although treatment varied, the overall prognosis of NTM-related HPS was promising.

The Italian registry of pulmonary non-tuberculous mycobacteria - IRENE: the study protocol

Background

A substantial increase in pulmonary and extra-pulmonary diseases due to non-tuberculous mycobacteria (NTM) has been documented worldwide, especially among subjects suffering from chronic respiratory diseases and immunocompromised patients. Many questions remain regarding the epidemiology of pulmonary disease due to NTM (NTM-PD) mainly because reporting of NTM-PD to health authorities is not mandated in several countries, including Italy. This manuscript describes the protocol of the first Italian registry of adult patients with respiratory infections caused by NTM (IRENE).

Methods

IRENE is an observational, multicenter, prospective, cohort study enrolling consecutive adult patients with either a NTM respiratory isolate or those with NTM-PD. A total of 41 centers, including mainly pulmonary and infectious disease departments, joined the registry so far. Adult patients with all of the following are included in the registry: 1) at least one positive culture for any NTM species from any respiratory sample; 2) at least one positive culture for NTM isolated in the year prior the enrolment and/or prescribed NTM treatment in the year prior the enrolment; 3) given consent to inclusion in the study. No exclusion criteria are applied to the study. Patients are managed according to standard operating procedures implemented in each IRENE clinical center. An online case report form has been developed to collect patients’ demographics, comorbidities, microbiological, laboratory, functional, radiological, clinical, treatment and outcome data at baseline and on an annual basis. An IRENE biobank has also been developed within the network and linked to the clinical data of the registry.

Conclusions

IRENE has been developed to inform the clinical and scientific community on the current management of adult patients with NTM respiratory infections in Italy and acts as a national network to increase the disease’s awareness.

Trial registration

Clinicaltrial.gov: NCT03339063.