Clinical and genomic features of Mycobacterium avium complex: a multi-national European study.

BACKGROUND: The Mycobacterium avium complex (MAC) comprises the most frequent non-tuberculous mycobacteria (NTM) in Central Europe and currently includes twelve species. M. avium (MAV), M. intracellulare subsp. intracellulare (MINT), and M. intracellulare subsp. chimaera (MCH) are clinically most relevant. However, the population structure and genomic landscape of MAC linked with potential pathobiological differences remain little investigated. METHODS: Whole genome sequencing (WGS) was performed on a multi-national set of MAC isolates from Germany, France, and Switzerland. Phylogenetic analysis was conducted, as well as plasmids, resistance, and virulence genes predicted from WGS data. Data was set into a global context with publicly available sequences. Finally, detailed clinical characteristics were associated with genomic data in a subset of the cohort. RESULTS: Overall, 610 isolates from 465 patients were included. The majority could be assigned to MAV (n = 386), MCH (n = 111), and MINT (n = 77). We demonstrate clustering with less than 12 SNPs distance of isolates obtained from different patients in all major MAC species and the identification of trans-European or even trans-continental clusters when set into relation with 1307 public sequences. However, none of our MCH isolates clustered closely with the heater-cooler unit outbreak strain Zuerich-1. Known plasmids were detected in MAV (325/1076, 30.2%), MINT (62/327, 19.0%), and almost all MCH-isolates (457/463, 98.7%). Predicted resistance to aminoglycosides or macrolides was rare. Overall, there was no direct link between phylogenomic grouping and clinical manifestations, but MCH and MINT were rarely found in patients with extra-pulmonary disease (OR 0.12 95% CI 0.04-0.28, p < 0.001 and OR 0.11 95% CI 0.02-0.4, p = 0.004, respectively) and MCH was negatively associated with fulfillment of the ATS criteria when isolated from respiratory samples (OR 0.28 95% CI 0.09-0.7, p = 0.011). With 14 out of 43 patients with available serial isolates, co-infections or co-colonizations with different strains or even species of the MAC were frequent (32.6%). CONCLUSIONS: This study demonstrates clustering and the presence of plasmids in a large proportion of MAC isolates in Europe and in a global context. Future studies need to urgently define potential ways of transmission of MAC isolates and the potential involvement of plasmids in virulence.

A Puerto Rican Variant of Lady Windermere Syndrome: Reanalyzing the Characteristics of Non-tuberculous Mycobacterial Infection.

Lady Windermere syndrome (LWS) is a disease caused by a non-tuberculous Mycobacterium (NTM) that is commonly found in thin women who voluntarily suppress their cough reflex. The NTM that causes this syndrome is Mycobacterium avium complex, an organism commonly present in chlorinated city water and soil. Patients with LWS are tall, lean, elderly white women. We report a case of an immunocompetent 81-year-old thin Puerto Rican female with a recurrent cough since childhood, who was misdiagnosed with tuberculosis (TB) and prophylactically treated. While the patient fitted the clinical picture of NTM pulmonary infection based on symptoms, imaging, and microbiologic findings, her demography and morphologic features were not completely consistent with published findings. The incidence and prevalence of NTM lung disease are rising worldwide due to the aging population, increased use of immunosuppressive medications, and prevalence of chronic pulmonary obstructive disease and bronchiectasis. The goal of this report is to increase awareness of LWS as one of the diagnoses that should be considered in patients presenting with clinical findings resembling TB and bring attention to the different clinical characteristics this patient with LWS possessed.

Single-cell transcriptomics by clinical course of Mycobacterium avium complex pulmonary disease.

Mycobacterium avium complex pulmonary disease (MAC-PD) has a heterogeneous clinical course. However, immune profiles associated with MAC-PD clinical course are limited. We performed single-cell RNA sequencing of peripheral blood mononuclear cells from 21 MAC-PD patients divided into three clinical courses: group A, spontaneous culture conversion; group B, stable disease without antibiotic treatment; and group C, progressive disease with antibiotic treatment. A lower proportion of NK cells and higher proportion of monocytes were noted in group C compared to combined groups A and B. The proportion of classical monocytes was higher in group C compared to groups A and B, while the proportion of non-classical monocytes decreased. EGR1, HSPA1A, HSPA1B, and CD83 were up-regulated in spontaneous culture conversion group A compared to progressive disease group C. Up-regulation of MYOM2 and LILRA4 and down-regulation of MT-ATP8, CD83, and CCL3L1 was found in progressive disease group C. PCBP1, FOS, RGCC, S100B, G0S2, AREG, and LYN were highly expressed in favorable treatment response compared to unfavorable response. Our findings may offer a comprehensive understanding of the host immune profiles that influence a particular MAC-PD clinical course and could suggest an immunological mechanism associated with the disease progression of MAC-PD.

Long-term Outcomes of Adjunctive Lung Resection for Nontuberculous Mycobacteria Pulmonary Disease.

Background: Adjunctive lung resection is recommended for select patients with nontuberculous mycobacteria (NTM) pulmonary disease (PD). However, data are limited on long-term recurrence rates in patients infected with major pathogens, including Mycobacterium avium complex (MAC) and Mycobacterium abscessus (MABC). Methods: In this prospective observational study, we retrospectively analyzed data from 125 patients with MAC-PD (n = 90) or MABC-PD (n = 35) who underwent adjunctive lung resection. We evaluated microbiological response, postoperative complications, recurrence, and all-cause mortality over a median 80-month follow-up. Results: Persistent culture positivity (64%) was the most common indication for surgery, followed by hemoptysis, recurrent pneumonia, or radiologic deterioration. Postoperative complications occurred in 18 (14%) patients, with no surgery-related deaths. Treatment outcomes did not significantly differ between the MAC- and MABC-PD groups. Cure with culture conversion was achieved in 112 (90%) patients. Recurrence occurred in 37 (33%) of 112 patients, of which 18 (49%) cases were attributed to reinfection by different NTM species or subspecies. The MAC group had higher recurrence rates than the MABC group (Kaplan-Meier curve, log-rank test, P = .043) and was significantly associated with recurrence in the multivariable analysis (adjusted hazard ratio, 2.71; 95% CI, 1.23-5.99). However, mortality was higher in the MABC-PD group than the MAC-PD group (7/35 vs 4/90, P = .006). Conclusions: Adjunctive lung resection with antibiotics helps to reduce bacterial burden and manage symptoms in patients with NTM-PD. However, it does not prevent recurrence, which is mostly caused by reinfection.

Protein-energy restriction-induced lipid metabolism disruption causes stable-to-progressive disease shift in Mycobacterium avium-infected female mice.

BACKGROUND: Disease susceptibility and progression of Mycobacterium avium complex pulmonary disease (MAC-PD) is associated with multiple factors, including low body mass index (BMI). However, the specific impact of low BMI on MAC-PD progression remains poorly understood. This study aims to examine the progression of MAC-PD in the context of low BMI, utilising a disease-resistant mouse model. METHODS: We employed a MAC infection-resistant female A/J mouse model to compare the progression of MAC-PD under two dietary conditions: one group was fed a standard protein diet, representing protein-energy unrestricted conditions, and the other was fed a low protein diet (LPD), representing protein-energy restriction. FINDINGS: Our results reveal that protein-energy restriction significantly exacerbates MAC-PD progression by disrupting lipid metabolism. Mice fed an LPD showed elevated fatty acid levels and related gene expressions in lung tissues, similar to findings of increased fatty acids in the serum of patients who exhibited the MAC-PD progression. These mice also exhibited increased CD36 expression and lipid accumulation in macrophages upon MAC infection. In vitro experiments emphasised the crucial role of CD36-mediated palmitic acid uptake in bacterial proliferation. Importantly, in vivo studies demonstrated that administering anti-CD36 antibody to LPD-fed A/J mice reduced macrophage lipid accumulation and impeded bacterial growth, resulting in remarkable slowing disease progression. INTERPRETATION: Our findings indicate that the metabolic status of host immune cells critically influences MAC-PD progression. This study highlights the potential of adequate nutrient intake in preventing MAC-PD progression, suggesting that targeting CD36-mediated pathways might be a host-directed therapeutic strategy to managing MAC infection. FUNDING: This research was funded by the National Research Foundation of Korea, the Korea Research Institute of Bioscience and Biotechnology, and the Korea National Institute of Health.

Mycobacterium gordonae: the canary in the coal mine?

Mycobacterium gordonae (M. gordonae) is a species of nontuberculous mycobacteria (NTM) that rarely causes infection. It has previously been labeled the most common NTM contaminant. Bronchiectasis is a disease characterized by abnormal airway dilation leading to chronic cough, sputum production and pulmonary infections. Patients with bronchiectasis are at higher risk of NTM-lung disease with more pathogenic NTM species including Mycobacterium avium complex (MAC) and Mycobacterium abscessus (M. abscessus). The relationship between bronchiectasis and less-pathogenic NTM species such as M. gordonae is less well understood. We performed a retrospective study on patients who had M. gordonae isolated from respiratory specimens at UConn Health between May 2nd, 2010 and October 18th, 2022. M. gordonae was isolated 74 times from 56 patients. It was isolated 35 (47.3%) times from 31 patients with bronchiectasis and 39 (52.7%) times from 26 patients without bronchiectasis. Data was available on all mycobacterial cultures sent from May 2nd 2018 to October 18th 2022. Mycobacterial cultures sent from patients with bronchiectasis were significantly more likely to grow M. gordonae than patients without bronchiectasis (4.3% vs. 1.6%, P=0.007). Furthermore, when considered at the patient level, there remained a significant increased rate of M. gordonae isolation among patients with bronchiectasis (7.1% vs. 2.2%, P<0.001). We then looked at past and future isolation of more pathogenic NTM species and found a non-statistically increased rate of isolation of more pathogenic NTM species including MAC and M. abscessus in patients with bronchiectasis (45.2% vs. 29%, P=0.09). Based on our results, isolation of M. gordonae should raise suspicion of chronic airway disease and defects in host immune response, such as those seen in bronchiectasis. Furthermore, isolation of M. gordonae may suggest increased risk of infection with more pathogenic NTM species such as MAC and M. abscessus.

Disinfection and monitoring of Mycobacterium avium complex in the environment: A novel approach to the management of hot tub lung.

A 45-year-old man visited our hospital with a chronic cough and breathing difficulties. Chest computed tomography revealed diffuse granular shadows. Mycobacterium avium (M. avium) was cultured from bronchoalveolar lavage fluid (BALF). Surgical lung biopsy revealed non-necrotizing granulomas, and M. avium-specific PCR was positive in the tissue. M. avium was also cultured in a sample from the inlet of the patient's bathtub. Mycobacterium avium tandem repeat variable-number tandem-repeat loci (MATR-VNTR) analysis confirmed that the M. avium cultured from BALF and the bathtub inlet had identical allele profiles. The patient's symptoms and oxygenation improved while the patient was in hospital, presumably because of lack of ongoing exposure to M. avium. He was diagnosed with hot tub lung. We advised the patient to avoid bathing to avoid re-exposure. However, the patient was unwilling to follow this advice. Therefore, his bathtub and pipework were disinfected by heating them to over 70 °C. We confirmed that the disinfection has been successful by repeated culture of environmental samples. Three months after resuming bathtub use, the patient's symptoms resolved, and the pulmonary shadows seen on the initial radiography did not recur. For the treatment of hot tub lung, disinfection of M. avium complex in the environment should be considered and the environment should be monitored to confirm eradication.

Opportunistic Infections and Malignancies in a Patient With HIV/AIDS and a Critically Low CD4 Count of 1 Cell/µL.

We present a 45-year-old African American male with a medical history of advanced-stage HIV/AIDS (CD4 count: 1 cell/µL) and poor adherence to highly active antiretroviral therapy (HAART), who presented with symptoms of diarrhea, weakness, and respiratory distress. Upon admission, duodenal and colonic biopsies revealed a diffuse histiocytic infiltrate consistent with Mycobacterium avium complex (MAC), and a cecal biopsy was positive for Kaposi sarcoma (KS). Further workup showed consolidation and a right pleural effusion on chest X-ray, suggesting a pneumonia infection. The patient's hypoglycemic state and lung consolidation raised concerns for sepsis, despite negative blood cultures for the first 24 hours. The patient was initiated on HAART and treated with azithromycin, rifabutin, and ethambutol for disseminated MAC. Despite the aggressive immunotherapy, the patient's condition did not improve, and he eventually expired. This case uniquely highlights the wide range of opportunistic infections and malignancies that can present in individuals with advanced-stage HIV/AIDS, underscoring the importance of early recognition and treatment. This susceptible demographic warrants further research due to the non-solidified prognosis of individuals with severe immunodeficiency.

Differential radiological features of patients infected or colonised with slow-growing non-tuberculous mycobacteria.

Non-tuberculous mycobacterial pulmonary disease (NTM-PD) is considered a growing health concern. The majority of NTM-PD cases in Europe are caused by slow-growing mycobacteria (SGM). However, distinct radiological features of different SGM remain largely uninvestigated. We applied a previously described radiological score to a patient cohort consisting of individuals with isolation of different SGM. Correlations between clinical data, species and computed tomography (CT) features were examined by logistic and linear regression analyses, as well as over the course of time. Overall, 135 pulmonary CT scans from 84 patients were included. The isolated NTM-species were mainly Mycobacterium avium complex (MAC, n = 49), as well as 35 patients with non-MAC-species. Patients with isolation of M. intracellulare had more extensive CT findings compared to all other SGM species (coefficient 3.53, 95% Cl - 0.37 to 7.52, p = 0.075) while patients meeting the ATS criteria and not undergoing therapy exhibited an increase in CT scores over time. This study provides insights into differential radiological features of slow-growing NTM. While M. intracellulare exhibited a tendency towards higher overall CT scores, the radiological features were similar across different SGM. The applied CT score might be a useful instrument for monitoring patients and could help to guide antimycobacterial therapy.

Lady Windermere Syndrome: A Rare Differential Diagnosis for Hemoptysis.

Mycobacterium avium complex (MAC) is often observed in immunocompromised individuals. However, when pulmonary MAC infection occurs in immunocompetent individuals, particularly elderly females, characteristically involving the middle lobe and lingula lobe of the lung, it is known as Lady Windermere syndrome (LWS). A 64-year-old female patient with no significant comorbidities presented with a history of low-grade intermittent fever and dry cough for one-month duration complicated with hemoptysis for two days. Her initial investigations and imaging were negative, except for the high-resolution CT (HRCT) finding of bronchiectasis involving the middle lobe and lingula lobe suggestive of MAC infection, which was further confirmed by positive sputum culture for MAC. LWS is a condition that is rarely encountered in clinical settings and seldom described in the literature. Especially in resource-limited settings, arriving at a diagnosis is further hindered by the scarce availability of advanced imaging such as HRCT. In clinical settings where pulmonary tuberculosis is endemic, the differentiation of the two conditions is of paramount importance as the treatment regimens for the two conditions are quite different.

Clinical Characteristics and Treatment Outcomes of Pulmonary Diseases Caused by Coinfections With Multiple Nontuberculous Mycobacterial Species.

BACKGROUND: Coinfections with multiple nontuberculous mycobacterial (NTM) species have not been widely studied. We aimed to evaluate the clinical characteristics and treatment outcomes in patients with NTM-pulmonary disease (PD) caused by coinfection with multiple NTM species. METHODS: We retrospectively reviewed patients with NTM-PD at a tertiary referral hospital in Korea between March 2012 and December 2018. Coinfection was defined as two or more species of NTM pathogens isolated from the same respiratory specimen or different specimens within three months. RESULTS: Among 1,009 patients with NTM-PD, 147 (14.6%) NTM coinfections were observed (average age 64.7 years, 69.4% women). NTM species were identified more frequently (median 6 vs. 3 times, P < 0.001) in the coinfection group than in the single species group, and follow-up duration was also longer in the coinfection group (median 44.9 vs. 27.1 months, P < 0.001). Mycobacterium avium complex (MAC) and M. abscessus and M. massiliense (MAB) were the dominant combinations (n = 71, 48.3%). For patients treated for over six months in the MAC plus MAB group (n = 31), sputum culture conversion and microbiological cure were achieved in 67.7% and 41.9% of patients, respectively. We divided the MAC plus MAB coinfection group into three subgroups according to the target mycobacteria; however, no statistical differences were found in the treatment outcomes. CONCLUSION: In NTM-PD cases, a significant number of multiple NTM species coinfections occurred. Proper identification of all cultured NTM species through follow-up is necessary to detect multispecies coinfections. Further research is needed to understand the nature of NTM-PD in such cases.

Disseminated mycobacterium avium complex spinal osteomyelitis in a patient with interferon gamma receptor deficiency: A case report.

Disseminated mycobacterium avium complex (MAC) infection is rare and is classically associated with immunodeficient states. Osteomyelitis is a rare manifestation of disseminated MAC infection. The overwhelming majority of MAC infections occur in patients with human immunodeficiency virus (HIV). Disseminated MAC infection has been described in interferon gamma receptor deficiency, an immunodeficiency mechanistically linked to mycobacterial infection. We present a case of disseminated MAC vertebral osteomyelitis in a patient with interferon gamma receptor deficiency.

Omadacycline drug susceptibility testing for non-tuberculous mycobacteria using oxyrase to overcome challenges with drug degradation.

BACKGROUND: Drug susceptibility testing (DST) protocol of omadacycline against non-tuberculous mycobacteria has not yet been established. We developed a method to accurately determine MIC omadacycline MIC against Mycobacterium abscessus (Mab), Mycobacterium avium-complex (MAC), and Mycobacterium kansasii (Mkn). METHODS: First, we identified the oxyrase concentration not affecting Mab, MAC, and Mkn growth followed by omadacycline MIC experiments with and without oxyrase using reference and clinical strains. RESULTS: Oxyrase 0.5 % (v/v) stabilized omadacycline in the culture medium. The median omadacycline MIC was 1 mg/L for Mab and 8 mg/L for Mkn. For MAC, the median omadacycline MIC was 2 mg/L for M. avium, 256 mg/L for M. intracellulare, and 4 mg/L for M. chimaera (p < 0.0001). Wilcoxon matched-pairs signed rank test revealed statistically lower MICs with oxyrase for all MAC subspecies (p < 0.0001), all Mab subspecies (p < 0.0001), and Mkn (p = 0.0002). The decrease in MICs with oxyrase was 17/18 of Mab, 14/19 of Mkn, 8/8 of M. avium, 4/5 M. chimera, but only 11/18 of M. intracellulare (p < 0.013). CONCLUSION: Use of 0.5 % oxyrase could be a potential solution to reliable and reproducible omadacycline MIC of Mab. However, oxyrase demonstrated a variable effect in reducing MICs against MAC and Mkn.

Prominent transcriptomic changes in Mycobacterium intracellulare under acidic and oxidative stress.

BACKGROUND: Mycobacterium avium complex (MAC), including Mycobacterium intracellulare is a member of slow-growing mycobacteria and contributes to a substantial proportion of nontuberculous mycobacterial lung disease in humans affecting immunocompromised and elderly populations. Adaptation of pathogens in hostile environments is crucial in establishing infection and persistence within the host. However, the sophisticated cellular and molecular mechanisms of stress response in M. intracellulare still need to be fully explored. We aimed to elucidate the transcriptional response of M. intracellulare under acidic and oxidative stress conditions. RESULTS: At the transcriptome level, 80 genes were shown [FC] ≥ 2.0 and p < 0.05 under oxidative stress with 10 mM hydrogen peroxide. Specifically, 77 genes were upregulated, while 3 genes were downregulated. In functional analysis, oxidative stress conditions activate DNA replication, nucleotide excision repair, mismatch repair, homologous recombination, and tuberculosis pathways. Additionally, our results demonstrate that DNA replication and repair system genes, such as dnaB, dinG, urvB, uvrD2, and recA, are indispensable for resistance to oxidative stress. On the contrary, 878 genes were shown [FC] ≥ 2.0 and p < 0.05 under acidic stress with pH 4.5. Among these genes, 339 were upregulated, while 539 were downregulated. Functional analysis highlighted nitrogen and sulfur metabolism pathways as the primary responses to acidic stress. Our findings provide evidence of the critical role played by nitrogen and sulfur metabolism genes in the response to acidic stress, including narGHIJ, nirBD, narU, narK3, cysND, cysC, cysH, ferredoxin 1 and 2, and formate dehydrogenase. CONCLUSION: Our results suggest the activation of several pathways potentially critical for the survival of M. intracellulare under a hostile microenvironment within the host. This study indicates the importance of stress responses in M. intracellulare infection and identifies promising therapeutic targets.

Amikacin Liposome Inhalation Suspension in the Real-World Management of Refractory Mycobacterium avium Complex Pulmonary Disease.

The increasing prevalence of Mycobacterium avium complex (MAC) pulmonary disease poses a significant therapeutic challenge, particularly due to the limited efficacy and systemic toxicity associated with conventional guideline-based therapy. Amikacin liposome inhalation suspension (ALIS) has been developed, yet its real-world application remains underreported. This retrospective analysis, conducted from March 2021 to February 2024, examined ALIS's clinical use in patients aged 20 years or older with refractory MAC pulmonary disease at our institution. The primary objective of this study is to describe the patient characteristics and clinical trajectories associated with the initiation of ALIS therapy in real-world settings for individuals diagnosed with MAC pulmonary disease. Of 11 patients initiated on ALIS, one was excluded due to financial constraints impacting continuation. The analysis proceeded with the remaining 10 subjects. The mean age of participants was 70.2 years, with a predominance of female patients (n = 7, 70%) and a higher incidence of M. avium infections (n = 6, 60%). Forty percent of the cohort (n = 4) had a history of ethambutol-induced optic neuritis leading to the cessation of the drug. The average interval from the initiation of guideline-based therapy to the start of ALIS was 8.5 ± 6.9 years (mean ± standard deviation). The majority (80%) presented with positive Gaffky scores at ALIS initiation, and a significant proportion exhibited resistance to clarithromycin and ethambutol. Comorbid conditions, including diabetes and previous cancer, were noted. The study also observed elevated anti-MAC antibody levels. Treatment duration varied, with fatigue leading to discontinuation in two cases. Treatment-emergent adverse events were documented in individual patients, each presenting with grade 1 severity: hemoptysis (n = 1, 10%), elevated creatinine levels (n = 1, 10%), and dysphonia (n = 2, 20%) were observed, respectively. Correlation analysis revealed a significant inverse relationship between body mass index (BMI) and ALIS discontinuation due to fatigue, and a positive correlation between Gaffky scores and C-reactive protein (CRP) levels. These results underscore the potential benefits and limitations of ALIS, suggesting that timely intervention and comprehensive healthcare support are crucial for optimal outcomes in the treatment of advanced MAC pulmonary disease.

Bedaquiline susceptibility testing of Mycobacterium abscessus complex and Mycobacterium avium complex: A meta-analysis study.

OBJECTIVE: This study aims to estimate the overall in vitro activity of bedaquiline (BDQ) against clinical isolates of Mycobacterium abscessus complex (MABS) and M. avium complex (MAC), considering BDQ as a repurposed drug for non-tuberculous mycobacteria (NTM) infections. METHODS: We conducted a systematic review of publications in PubMed/ MEDLINE, Web of Science, and Embase up to 15 April 2023. Studies were included if they followed the Clinical and Laboratory Standards Institute (CLSI) criteria for drug susceptibility testing (DST). Using a random effects model, we assessed the overall in vitro BDQ resistance rate in clinical isolates of MABS and MAC. Sources of heterogeneity were analysed using Cochran's Q and the I2 statistic. All analyses were performed using CMA V3.0. RESULTS: A total of 24 publications (19 reports for MABS and 11 for MAC) were included. Using 1 µg/mL and 2 µg/mL as the breakpoint for BDQ resistance, the pooled rates of in vitro BDQ resistance in clinical isolates of MABS were found to be 1.8% (95% confidence interval [CI], 0.7-4.6%) and 1.7% (95% CI, 0.6-4.4%), respectively. In the case of MAC, the pooled rates were 1.7% (95% CI, 0.4-6.9%) and 1.6% (95% CI, 0.4-6.8%) for 1 µg/mL and 2 µg/mL, respectively. CONCLUSION: This study reports the prevalence of BDQ resistance in clinical isolates of MABS and MAC. The findings suggest that BDQ holds potential as a repurposed drug for treating MABS and MAC infections.

Minimum inhibitory concentrations of azithromycin in clinical isolates of Mycobacterium avium complex in Japan.

The latest guidelines include azithromycin as a preferred regimen for treating Mycobacterium avium complex (MAC) pulmonary disease. However, serially collected susceptibility data on clinical MAC isolates are limited, and no breakpoints have been determined. We investigated the minimum inhibitory concentrations (MICs) of azithromycin and clarithromycin for all MAC strains isolated in 2021 from a single center in Japan, excluding duplicates. The MICs were determined using a panel based on the microbroth dilution method, according to the latest Clinical and Laboratory Standards Institute recommendations. The MICs were determined for 318 MAC strains. Although there was a significant positive correlation between the MICs of azithromycin and clarithromycin, the MICs of azithromycin tended to be higher than those of clarithromycin. Among the cases in which the strains were isolated, 18 patients initiated treatment, including azithromycin treatment, after sample collection. Some patients infected with stains with relatively high azithromycin MICs achieved a microbiological cure with azithromycin-containing regimens. This study revealed a higher MIC distribution for azithromycin than clarithromycin, raising questions about the current practice of estimating azithromycin susceptibility based on the clarithromycin susceptibility test result. However, this was a single-center study that included only a limited number of cases treated with azithromycin. Therefore, further multicenter studies that include a greater number of cases treated with azithromycin are warranted to verify the distribution of azithromycin MICs and examine the correlation between azithromycin MICs and treatment effectiveness.IMPORTANCEThe macrolides serve as key drugs in the treatment of pulmonary Mycobacterium avium complex infection, and the administration of macrolide should be guided by susceptibility test results. Azithromycin is recommended as a preferred choice among macrolides, surpassing clarithromycin; however, drug susceptibility testing is often not conducted, and clarithromycin susceptibility is used as a surrogate. This study represents the first investigation into the minimum inhibitory concentration of azithromycin on a scale of several hundred clinical isolates, revealing an overall tendency for higher minimum inhibitory concentrations compared with clarithromycin. The results raise questions about the appropriateness of using clarithromycin susceptibility test outcomes for determining the administration of azithromycin. This study highlights the need for future discussions on the clinical breakpoints of azithromycin, based on large-scale clinical research correlating azithromycin susceptibility with treatment outcomes.

Biofilm Development by Mycobacterium avium Complex Clinical Isolates: Effect of Clarithromycin in Ultrastructure.

BACKGROUND: The Mycobacterium avium complex includes the commonest non-tuberculous mycobacteria associated with human infections. These infections have been associated with the production of biofilms in many cases, but there are only a few studies about biofilms produced by the species included in this group. METHODS: Three collection strains (M. avium ATCC25291, M. intracellulare ATCC13950, and M. chimaera DSM756), three clinically significant strains (647, 657, and 655), and three clinically non-significant ones (717, 505, and 575) of each species were included. The clinical significance of the clinical isolates was established according to the internationally accepted criteria. The biofilm ultrastructure was studied by Confocal-Laser Scanning Microscopy by using BacLight Live-Dead and Nile Red stains. The viability, covered surface, height, and relative autofluorescence were measured in several images/strain. The effect of clarithromycin was studied by using the technique described by Muñoz-Egea et al. with modifications regarding incubation time. The study included clarithromycin in the culture medium at a concentration achievable in the lungs (11.3 mg/L), using one row of wells as the control without antibiotics. The bacterial viability inside the biofilm is expressed as a percentage of viable cells. The differences between the different parameters of the biofilm ultrastructure were analyzed by using the Kruskal-Wallis test. The correlation between bacterial viability in the biofilm and treatment time was evaluated by using Spearman's rank correlation coefficient (ρ). RESULTS: The strains showed differences between them with all the studied parameters, but neither a species-specific pattern nor a clinical-significance-specific pattern were detected. For the effect of clarithromycin, the viability of the bacteria contained in the biofilm was inversely proportional to the exposure time of the biofilm (ρ > -0.3; p-value < 0.05), excluding two M. chimaera strains (M. chimaera DSM756 and 575), which showed a weak positive correlation with treatment time (0.2 < ρ < 0.39; p-value < 0.05). Curiously, despite a clarithromycin treatment of 216 h, the percentage of the biofilm viability of the strains evaluated here was not less than 40% at best (M. avium 717). CONCLUSIONS: All the M. avium complex strains studied can form biofilm in vitro, but the ultrastructural characteristics between them suggest that these are strain-specific characteristics unrelated to the species or the clinical significance. The clarithromycin effect on MAC species is biofilm-age/time-of-treatment-dependent and appears to be strain-specific while being independent of the clinical significance of the strain.

Rare Case of Mycobacterium Avium Complex Peritonitis in a Patient with Multiple Myeloma Undergoing Peritoneal Dialysis.

Mycobacterium avium complex (MAC) infections can present as a variety of severe diseases. While it has a predilection for immunocompromised patients such as those with Human immunodeficiency virus (HIV), it can also affect immunocompetent patients as well. One of the rare yet severe diseases that MAC infections can present is MAC peritonitis. Often hard to distinguish from other causes of peritonitis, high clinical suspicion should be maintained for those who are susceptible. Here we present an 85-year-old female with a past medical history of end-stage renal disease on peritoneal dialysis who presented with nausea and vomiting. She was found to have tenderness around her peritoneal dialysis site and was noted to have mild ascites. Her labs were significant for several electrolyte abnormalities, leukocytosis, and ascitic fluid obtained during a previous admission, and serology was positive for acid-fast bacilli. It was further revealed that the species was Mycobacterium avium complex. Initially, she started on rifampin, isoniazid, pyrazinamide, and ethambutol (RIPE), subsequently antibiotics were changed to azithromycin, ethambutol, and rifampin after MAC identification in acid-fast bacilli culture. We aim to highlight this rare presentation of peritonitis secondary to MAC.

A health literacy analysis of online patient-directed educational materials about mycobacterium avium complex.

Introduction: Mycobacterium avium complex (MAC) is a complex lung infection requiring multi-disciplinary approach and management. Due to limited clinician-patient interactions, clinicians may refer patients to online resources to learn about the diagnosis, prognosis, and treatment of MAC. The American Medical Association (AMA) recommends educational materials be written at a sixth-grade reading level and the National Institutes of Health (NIH) recommends that patient education materials be written at an eighth-grade reading level; however, several evaluations found these materials inaccessible due to high literacy levels. To date, there has never been a health literacy assessment of MAC patient education materials. The study aims to assess the health literacy of online patient education materials about MAC. Methods: The patient education materials were evaluated for readability, actionability, understandability and clarity. Readability was assessed through the Flesch-Kincaid Grade Level Scale (FkGL), SMOG Index, Coleman Liau Index (CLI), Gunning Fog Index (GFI), and Automated Readability Index (ARI). Actionability and understandability was evaluated using the Patient Education Materials Assessment Tool (PEMAT). The Centers for Disease Control (CDC) Clear Communication Index (CCI) was used to assess clarity. Results: Ten patient education resources were evaluated: CDC, Cleveland Clinic, Mayo Clinic, JAMA, American Thoracic Society (ATS), National Jewish Health, UpToDate, CHEST, WebMD, and Medline. The mean readability scores were as follows: FkGL (9.76), SMOG index (9.82), CLI (13.54), GFI (11.66), ARI (9.15). Four patient education materials were written at a sixth-grade reading level and eight patient education materials were written at an eighth-grade reading level. The majority of the materials received a passing score for understandability but failed to achieve a passing score for actionability. Cleveland Clinic, JAMA, and ATS all received a passing clarity score, indicating that they are easy to read. No patient education materials were available on UpToDate. Conclusion: Most patient education materials scored poorly for actionability and clarity while scoring highly for readability and understandability. This study should serve as a guide for clinicians interested in offering online education materials to their patients. Increasing access to readable MAC educational materials should be a priority for those working at the intersection of public health, clinical care, and communications.