**1. Introduction**

Cystic fibrosis (CF) is an inherited, autosomal, recessive genetic disorder caused by mutation in the cystic fibrosis transmembrane conductance receptor regulator (CFTR) gene [1]. It affects 1 in 2000–3000 newborns [2]. The CFTR gene is responsible for the regulation of the chloride channel, located at the apical surface of various epithelial cells [1,3]. CFTR mutation results in the dysregulation of the chloride ions flow, increased water absorption and secretion condensation. In the respiratory tract, the presence of thick mucus and impaired bronchial mucociliary clearance cause increased susceptibility to bacterial and

**Citation:** Wyrostkiewicz, D.; Opoka, L.; Filipczak, D.; Jankowska, E.; Skorupa, W.; Augustynowicz-Kope´c, E.; Szturmowicz, M. Nontuberculous Mycobacterial Lung Disease in the Patients with Cystic Fibrosis—A Challenging Diagnostic Problem. *Diagnostics* **2022**, *12*, 1514. https://doi.org/10.3390/ diagnostics12071514

 Academic Editor: Alessandro Russo

Received: 3 June 2022 Accepted: 19 June 2022 Published: 21 June 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

fungal colonization [1]. As the eradication of pathogens is disturbed, chronic colonization, with temporary exacerbations of inflammatory bronchitis is observed.

Recently, infections with nontuberculous mycobacteria (NTM) were identified as an emerging clinical problem in CF patients [4,5]. Positive respiratory cultures for NTM were obtained in CF patients 400 times more frequently compared to the general population [6]. The most frustrating scenario is the possibility of direct or indirect person-to-person transmission of NTM in CF centers, especially following *M. abscessus* colonization.

The recognition of lung disease caused by NTM (NTMLD) is based on clinical, radiological and microbiological criteria. Nevertheless, in CF patients NTMLD is very difficult to diagnose due to many similarities in clinical and radiological presentation between pulmonary exacerbations caused by bacterial pathogens and those caused by NTM.

## **2. Aim**

The aim of the present study was to assess the frequency of NTM isolations in CF patients hospitalized in the pulmonary department, serving as a hospital CF center, and to describe challenges concerning the recognition of NTMLD in those patients.

#### **3. Material and Methods**

Cystic fibrosis patients, who were hospitalized due to pulmonary exacerbations (PEX), in the 1st Department of Lung Diseases National Tuberculosis and Lung Diseases Research Institute, between 2010 and 2020, were retrospectively assessed for the presence of NTM in respiratory specimens.

CF was recognized based on clinical and radiological symptoms, high level of chloride in sweat tests and finally confirmed with the presence of CFTR mutations.

Clinical data registered in the hospital database at the time of NTM isolation were analyzed. Chest CT scans performed at the time of NTM isolation were reviewed by the two pulmonologists and one radiology specialist and compared to previous radiologic documentation of the patients.

The sputum or bronchial washings obtained during fiberoptic bronchoscopy were decontaminated with sodium hydrochloride and N-acetyl-L-cysteine. Smears for acid-fast bacilli (AFB) were stained with auramine fluorochrome. Fluorochrome-positive specimens were confirmed by the Ziehl–Neelsen method. Gene Xpert MTB/Ultra Cepheid test was performed in the case of AFB positivity. The strains were cultured on a solid medium (egg-based Lowenstein–Jensen) and in the automated system MGIT (Becton Dickinson, Franklin Lakes, NJ, USA).

Identification of NTM species was performed with the GenoType CM test (Hain Lifescience), versions 1.0 and 2.0. *M. chimera* was identified with the GenoType NTM-DR test, based on 23S rRNA gene polymorphism. The principles of the procedure were described previously [7].

The project was accepted by the Institutional Ethical Committee (No. 9/2015).
