Recovery of Non-tuberculous Mycobacteria from Water is Influenced by Phenotypic Characteristics and Decontamination Methods

A New Culture Method for the Detection of Non-Tuberculous Mycobacteria in Water Samples from Heater-Cooler Units and Extracorporeal Membrane Oxygenation Machines

The isolation of non-tuberculous mycobacteria (NTM) from cultures is particularly laborious due to the potential overgrowth of coexisting non-acid fast bacilli. To reduce the overgrowth of these non-mycobacterial organisms, a decontamination step with NaOH or cetylpyridinium chloride is highly recommended before plating the samples on the culture medium. However, due to their toxicity, decontamination solutions tend to decrease NTM recovery from clinical and environmental samples. Here, we tested an alternative method for NTM recovery based on the use of NTM Elite agar, a selective medium that does not require a decontamination step. Using NTM Elite agar, we were able to detect non-tuberculous mycobacteria in 27.7% (30/108) of water samples analyzed. The average time to NTM detection was 18 days, but some strains required longer to grow, perhaps due to the stressful environmental conditions (periodical disinfection of devices). NTM Elite agar's effectiveness in inhibiting background flora was proven by the isolation of NTM from samples with and without background flora, showing no statistically significant differences in detection rates for different total viable counts of background flora (p = 0.4989). In conclusion, our findings indicate that effective NTM recovery from HCU- and ECMO-derived water samples can be achieved via filtration and direct culture of the filters on NTM Elite agar. This simple procedure can speed up laboratory work and provide an improved method, successfully resulting in low contamination and high detection rate, in addition to being less time-consuming. Its sensitivity and lack of a decontamination step make this protocol particularly useful for monitoring the effectiveness of device disinfection in hospital settings, even in the presence of low NTM loads. Reading timeframes should probably be extended to 7 weeks (i.e., well beyond the standard 4 weeks advised by the manufacturer), in order to isolate even the slow-growing mycobacteria. However, an extended incubation period is not necessary for exclusion of M. chimaera contamination of the devices, as M. chimaera isolation times do not generally exceed 3 weeks.

Mitigation of nontuberculous mycobacteria in hospital water: challenges for infection prevention

PURPOSE OF REVIEW

The purpose of this review is to summarize recent literature on nontuberculous mycobacteria in water of healthcare systems. Despite improvement in identification techniques and emergence of infection prevention and control programs, nontuberculous mycobacteria remain present in hospital water systems, causing outbreaks and pseudo-outbreaks in healthcare settings.

RECENT FINDINGS

Waterborne outbreaks and pseudo-outbreaks of nontuberculous mycobacteria continue to affect hospitals. Improvements in methods of identification and investigation, including MALDI-TOF and whole genome sequencing with evaluation of single nucleotide polymorphisms, have been used successfully in outbreak and pseudo-outbreak investigations. Recent studies have shown control of outbreaks in immunocompromised patients through the use of sterile water for consumption, as well as control of pseudo-outbreaks by using sterile water for procedures. Construction activities have been implicated in outbreaks and pseudo-outbreaks of nontuberculous mycobacteria. Water management programs are now required by the Joint Commission, which will likely improve water risk mitigation.

SUMMARY

Improvement in detection and identification of nontuberculous mycobacteria has led to increasing recognition of waterborne outbreaks and pseudo-outbreaks. Water management programs are of vital importance in infection prevention.

Recovery of Mycobacteria from Heavily Contaminated Environmental Matrices

For epidemiology studies, a decontamination method using a solution containing 4.0% NaOH and 0.5% tetradecyltrimethylammonium bromide (TDAB) represents a relatively simple and universal procedure for processing heavily microbially contaminated matrices together with increase of mycobacteria yield and elimination of gross contamination. A contamination rate only averaging 7.3% (2.4% in Cluster S; 6.9% in Cluster R and 12.6% in Cluster E) was found in 787 examined environmental samples. Mycobacteria were cultured from 28.5% of 274 soil and water sediments samples (Cluster S), 60.2% of 251 samples of raw and processed peat and other horticultural substrates (Cluster R), and 29.4% of 262 faecal samples along with other samples of animal origin (Cluster E). A total of 38 species of slow and rapidly growing mycobacteria were isolated. M. avium ssp. hominissuis, M. fortuitum and M. malmoense were the species most often isolated. The parameters for the quantitative detection of mycobacteria by PCR can be significantly refined by treating the sample suspension before DNA isolation with PMA (propidium monoazide) solution. This effectively eliminates DNA residue from both dead mycobacterial cells and potentially interfering DNA segments present from other microbial flora. In terms of human exposure risk assessment, the potential exposure to live non-tuberculous mycobacteria can be more accurately determined.

Validation of a Novel Diagnostic Approach Combining the VersaTREK™ System for Recovery and Real-Time PCR for the Identification of Mycobacterium chimaera in Water Samples

Mycobacterium chimaera is an emerging pathogen associated with endocarditis and vasculitis following cardiac surgery. Although it can take up to 6-8 weeks to culture on selective solid media, culture-based detection remains the gold standard for diagnosis, so more rapid methods are urgently needed. For the present study, we processed environmental M. chimaera infected simulates at volumes defined in international guidelines. Each preparation underwent real-time PCR; inoculates were placed in a VersaTREK™ automated microbial detection system and onto selective Middlebrook 7H11 agar plates. The validation tests showed that real-time PCR detected DNA up to a concentration of 10 ng/µL. A comparison of the isolation tests showed that the PCR method detected DNA in a dilution of ×10² CFU/mL in the bacterial suspensions, whereas the limit of detection in the VersaTREK™ was <10 CFU/mL. Within less than 3 days, the VersaTREK™ detected an initial bacterial load of 100 CFU. The detection limit did not seem to be influenced by NaOH decontamination or the initial water sample volume; analytical sensitivity was 1.5 × 10² CFU/mL; positivity was determined in under 15 days. VersaTREK™ can expedite mycobacterial growth in a culture. When combined with PCR, it can increase the overall recovery of mycobacteria in environmental samples, making it potentially applicable for microbial control in the hospital setting and also in environments with low levels of contamination by viable mycobacteria.

Improved detection of non-tuberculous mycobacteria in hospital water samples

Non-tuberculous mycobacteria (NTM) are opportunistic pathogens commonly colonizing hospital water systems, and may be responsible for healthcare-associated infections (HAI). Investigation of HAI and outbreaks caused by NTM necessitates water analyses. However, NTM are slow-growing bacteria within the mesophilic community present in water, and are difficult to detect. Prior to culture on specific media, their recovery usually requires decontamination and concentration steps. We assessed the effectiveness of filtration as regards the recovery of 7 NTM species in hospital water samples. We also compared the use of cetylpyridinium chloride (CPC) at different concentrations and Sodium Hydroxide (NaOH) 4% in decontamination of water samples with mesophilic bacteria. Our laboratory protocol showed that membrane filtration was suitable for concentration and recovery of NTM from water. Sample decontamination with CPC was more NTM-preservative than NaOH. A combination of CPC at 0.005% and filtration allowed detection of NTM at low concentrations, ranging from 3 to 98 CFU/100mL according to the NTM species.

Evaluation of a new culture medium for isolation of nontuberculous mycobacteria from environmental water samples

Nontuberculous mycobacteria (NTM) are waterborne pathogens commonly found in building water systems where they are a primary concern to vulnerable patient populations and can cause severe disease. The recovery of NTM from environmental samples can be a laborious undertaking and current pre-treatment methods and selective media lack sensitivity. We explored the use of the highly selective Rapidly Growing Mycobacteria (RGM) medium for culturing NTM from environmental water samples compared to existing methods. In total, 223 environmental water samples, including potable and non-potable water, were cultured for NTM using three culture media. In addition to direct culture on RGM medium, each sample was cultured on Middlebrook 7H10 medium and Mitchison 7H11 medium after pre-treatment with 0.2M KCl-HCl. Additionally, 33 distinct species of NTM were inoculated onto RGM medium and 7H10 medium in parallel to directly compare their growth. The use of RGM medium alone without pre-treatment provided a sensitivity (91%) comparable to that offered by culture on both 7H10 and 7H11 with acid pretreatment (combined sensitivity; 86%) with significantly less overgrowth and interference from other organisms on RGM medium. The average concentration of NTM observed on RGM medium alone was comparable to or greater than the NTM concentration on either medium alone or combined. Thirty-three species were examined in parallel and all tested strains of 27 of these species successfully grew on RGM medium, including 19 of 21 from the CDC’s healthcare-associated infections species list. RGM medium was successful at recovering environmental NTM without a pre-treatment, greatly reducing labor and materials required to process samples. Simplification of culture processing for environmental NTM will allow for a better assessment of their presence in building water systems and the potential for reduced exposure of susceptible populations.

Cost analysis of smear microscopy and the Xpert assay for tuberculosis diagnosis: average turnaround time

INTRODUCTION

Rapid and accurate tuberculosis detection is critical for improving patient diagnosis and decreasing tuberculosis transmission. Molecular assays can significantly increase laboratory costs; therefore, the average time and economic impact should be evaluated before implementing a new technology. The aim of this study was to evaluate the cost and average turnaround time of smear microscopy and Xpert assay at a university hospital.

METHODS

The turnaround time and cost of the laboratory diagnosis of tuberculosis were calculated based on the mean cost and activity based costing (ABC).

RESULTS

The average turnaround time for smear microscopy was 16.6 hours while that for Xpert was 24.1 hours. The Xpert had a mean cost of USD 17.37 with an ABC of USD 10.86, while smear microscopy had a mean cost of USD 13.31 with an ABC of USD 6.01. The sensitivity of smear microscopy was 42.9% and its specificity was 99.1%, while the Xpert assay had a sensitivity of 100% and a specificity of 96.7%.

CONCLUSIONS

The Xpert assay has high accuracy; however, the turnaround time and cost of smear microscopy were lower than those of Xpert.

Nontuberculous mycobacteria: A report of eighteen cases from a tertiary care center in India

Context

Nontuberculous mycobacteria (NTM) are ubiquitous mycobacteria present in environment and generally affect patients with either structural lung disease or immunosuppression and commonly involve lungs, lymph node, or skin.

Materials and Methods

Between July 2016 and February 2019, 18 cases of NTM were diagnosed and their relevant clinical, diagnostic, and treatment details were recorded after taking informed consent.

Results

We report 18 cases of NTM involving lungs (n = 11), skin and soft tissue (n = 3), joint (n = 2), genitourinary (n = 1), and central nervous system (n = 1). History of immunosuppression was present in two patients, whereas history of some form of intervention was seen in six patients. Mycobacterium fortuitum group (n = 5) was the most commonly isolated organism, followed by Mycobacterium avium complex (n = 4), Mycobacterium abscessus (n = 3), Mycobacterium kansasii (n = 2), and Mycobacterium chelonae (n = 1). In two patients, M. chelonae and M. abscessus were isolated in succession. Of these 18 patients, clinical response was present in 15 of the patients. Diagnosis and treatment of NTM in resource limited settings is extremely challenging.

Conclusion

Most of the patients with NTM are misdiagnosed and are treated as tuberculosis in India, sometimes with a multidrug resistance regimen, which results in significant morbidity and mortality. We present these cases to shed some light on the epidemiology of NTM in this part of India.