Rapid detection and determination of the aerodynamic size range of airborne mycobacteria associated with whirlpools

Biological Particles in the Indoor Environment

Airborne microorganisms are very difficult to assess accurately under field conditions owing to differences in the sample collection efficiency of the selected sampler and variations in DNA extraction efficiencies. Consequently, bioaerosol abundance and biodiversity can be underestimated, making it more difficult to link specific bioaerosol components to diseases and human health risk. Owing to the low biomass in air samples, it remains a challenge to obtain a representative microbiological sample to recover sufficient DNA for downstream analyses. Improved sampling methods are particularly crucial, especially for investigating viral communities, owing to the extremely low biomass of viral particles in the air compared with other environments. Without detailed information about sampling, characterization and enumeration techniques, interpretation of exposure level is very difficult. Despite this, bioaerosol research has been enhanced by molecular tools, especially next-generation sequencing approaches that have allowed faster and more detailed characterization of air samples.

Molecular approaches for the detection and monitoring of microbial communities in bioaerosols: A review

Bioaerosols significantly affect atmospheric processes while they undergo long-range vertical and horizontal transport and influence atmospheric chemistry and physics and climate change. Accumulating evidence suggests that exposure to bioaerosols may cause adverse health effects, including severe disease. Studies of bioaerosols have primarily focused on their chemical composition and largely neglected their biological composition and the negative effects of biological composition on ecosystems and human health. Here, current molecular methods for the identification, quantification, and distribution of bioaerosol agents are reviewed. Modern developments in environmental microbiology technology would be favorable in elucidation of microbial temporal and spatial distribution in the atmosphere at high resolution. In addition, these provide additional supports for growing evidence that microbial diversity or composition in the bioaerosol is an indispensable environmental aspect linking with public health.

Review of bioaerosols in indoor environment with special reference to sampling, analysis and control mechanisms

Several tiny organisms of various size ranges present in air are called airborne particles or bioaerosol which mainly includes live or dead fungi and bacteria, their secondary metabolites, viruses, pollens, etc. which have been related to health issues of human beings and other life stocks. Bio-terror attacks in 2001 as well as pandemic outbreak of flue due to influenza A H1N1 virus in 2009 have alarmed us about the importance of bioaerosol research. Hence characterization i.e. identification and quantification of different airborne microorganisms in various indoor environments is necessary to identify the associated risks and to establish exposure threshold. Along with the bioaerosol sampling and their analytical techniques, various literatures revealing the concentration levels of bioaerosol have been mentioned in this review thereby contributing to the knowledge of identification and quantification of bioaerosols and their different constituents in various indoor environments (both occupational and non-occupational sections). Apart from recognition of bioaerosol, developments of their control mechanisms also play an important role. Hence several control methods have also been briefly reviewed. However, several individual levels of efforts such as periodic cleaning operations, maintenance activities and proper ventilation system also serve in their best way to improve indoor air quality.

Release of free DNA by membrane-impaired bacterial aerosols due to aerosolization and air sampling

We report here that stress experienced by bacteria due to aerosolization and air sampling can result in severe membrane impairment, leading to the release of DNA as free molecules. Escherichia coli and Bacillus atrophaeus bacteria were aerosolized and then either collected directly into liquid or collected using other collection media and then transferred into liquid. The amount of DNA released was quantified as the cell membrane damage index (ID), i.e., the number of 16S rRNA gene copies in the supernatant liquid relative to the total number in the bioaerosol sample. During aerosolization by a Collison nebulizer, the ID of E. coli and B. atrophaeus in the nebulizer suspension gradually increased during 60 min of continuous aerosolization. We found that the ID of bacteria during aerosolization was statistically significantly affected by the material of the Collison jar (glass > polycarbonate; P < 0.001) and by the bacterial species (E. coli > B. atrophaeus; P < 0.001). When E. coli was collected for 5 min by filtration, impaction, and impingement, its ID values were within the following ranges: 0.051 to 0.085, 0.16 to 0.37, and 0.068 to 0.23, respectively; when it was collected by electrostatic precipitation, the ID values (0.011 to 0.034) were significantly lower (P < 0.05) than those with other sampling methods. Air samples collected inside an equine facility for 2 h by filtration and impingement exhibited ID values in the range of 0.30 to 0.54. The data indicate that the amount of cell damage during bioaerosol sampling and the resulting release of DNA can be substantial and that this should be taken into account when analyzing bioaerosol samples.

Cough aerosols of Mycobacterium tuberculosis predict new infection: a household contact study

RATIONALE

Airborne transmission of Mycobacterium tuberculosis results from incompletely characterized host, bacterial, and environmental factors. Sputum smear microscopy is associated with considerable variability in transmission.

OBJECTIVES

To evaluate the use of cough-generated aerosols of M. tuberculosis to predict recent transmission.

METHODS

Patients with pulmonary tuberculosis (TB) underwent a standard evaluation and collection of cough aerosol cultures of M. tuberculosis. We assessed household contacts for new M. tuberculosis infection. We used multivariable logistic regression analysis with cluster adjustment to analyze predictors of new infection.

MEASUREMENTS AND MAIN RESULTS

From May 2009 to January 2011, we enrolled 96 sputum culture-positive index TB cases and their 442 contacts. Only 43 (45%) patients with TB yielded M. tuberculosis in aerosols. Contacts of patients with TB who produced high aerosols (≥10 CFU) were more likely to have a new infection compared with contacts from low-aerosol (1-9 CFU) and aerosol-negative cases (69%, 25%, and 30%, respectively; P = 0.009). A high-aerosol patient with TB was the only predictor of new M. tuberculosis infection in unadjusted (odds ratio, 5.18; 95% confidence interval, 1.52-17.61) and adjusted analyses (odds ratio, 4.81; 95% confidence interval, 1.20-19.23). Contacts of patients with TB with no aerosols versus low and high aerosols had differential tuberculin skin test and interferon-γ release assay responses.

CONCLUSIONS

Cough aerosols of M. tuberculosis are produced by a minority of patients with TB but predict transmission better than sputum smear microscopy or culture. Cough aerosols may help identify the most infectious patients with TB and thus improve the cost-effectiveness of TB control programs.

Microbial structure and chemical components of aerosols caused by rotating brushes in a wastewater treatment plant

PURPOSE

Bacterial community structure and the chemical components in aerosols caused by rotating brushes in an Orbal oxidation ditch were assessed in a Beijing municipal wastewater treatment plant.

METHODS

Air samples were collected at different distances from the aerosol-generating rotating brushes. Molecular culture-independent methods were used to characterize the community structure of the airborne bacteria in each sample regardless of cell culturability. A clone library of 16S rDNA directly amplified from air DNA of each sample was constructed and sequenced to analyze the community composition and diversity. Insoluble particles and water-soluble ions emitted with microorganisms in aerosols were analysis by a scanning electron microscope together with energy dispersive X-ray spectroscopy and ion chromatogram analyzer.

RESULTS

In total, most of the identified bacteria were Proteobacteria. The majority of sequences near the rotating brushes (the main source of the bioaerosols) were Proteobacteria (62.97 %) with β-(18.52 %) and γ-(44.45 %) subgroups and Bacteroidetes (29.63 %). Complex patterns were observed for each sampling location, suggesting a highly diverse community structure, comparable to that found in water in the Orbal oxidation ditch. Accompany with microorganisms, 46.36 μg/m(3) of SO (4) (2-) , 29.35 μg/m(3) of Cl(-), 21.51 μg/m(3) of NO (3) (-) , 19.76 μg/m(3) of NH (4) (+) , 11.42 μg/m(3) of PO (4) (3-) , 6.18 μg/m(3) of NO (2) (-) , and elements of Mg, Cl, K, Na, Fe, S, and P were detected from the air near the aerosols source.

CONCLUSIONS

Differences in the structure of the bacterial communities and chemical components in the aerosols observed between sampling sites indicated important site-related variability. The composition of microorganisms in water was one of the most important sources of bacterial communities in bioaerosols. Chemical components in bioaerosols may provide a media for airborne microorganism attachment, as well as a suitable microenvironment for their growth and survival in the air. This study will be benefit for the formulation of pollution standards, especially for aerosols, that take into account plant workers' health.

Real-time PCR detection of environmental mycobacteria in house dust

Analysing the number and species of microbes in indoor dust is needed for assessment of human exposure to microbes in dwellings. Environmental mycobacteria are common heterotrophic bacteria in both natural and man-made environments and potential inducers of human immune system. Culture of mycobacteria from samples rich with other microbes is difficult due to the slow growth rate of mycobacteria and this has hampered the studies on their role in indoor human exposure. A quantitative, real-time 5'-nuclease (TaqMan) PCR assay was developed to detect environmental mycobacteria in indoor dust samples. The specificity of the primers and the probe targeting the 16S rDNA of mycobacteria, tested with 26 mycobacterial and 10 non-mycobacterial but related species, proved to be high. When tested on 20 indoor dust samples collected from five homes, the assay gave counts varying between 4.8 x 10(4) and 7.2 x 10(6)cell/g, being on average 1.1 x 10(3) times higher than culture. Seasonal variation in the dust counts of mycobacteria was observed by both culture and qPCR. Total of 140 isolates considered as mycobacteria by Ziehl-Neelsen staining and GLC-analyses were subjected to PCR analysis with the mycobacterial primers, and 39 isolates to partial 16S rDNA sequencing. All proved to be mycobacteria and revealed high diversity of mycobacterial species in the dust samples. Majority of the sequences were related to M. terrae and M. avium complexes.

Identification of mycobacteria in peat moss processing plants: application of molecular biology approaches

Peat moss processing plant workers are exposed to high concentrations of bioaerosols. Although mycobacteria have been cultured from peat moss, no study has examined the workers' exposure to mycobacterial bioaerosols. We evaluated the presence of mycobacteria in air samples from peat moss processing plants using molecular biology approaches (cloning-sequencing and polymerase chain reaction (PCR)) and the workers exposure using immunoglobulin G (IgG) complexes to mycobacteria. In addition, species detected in air samples and in peat moss were compared. Two peat moss processing plants were chosen among 14 previously studied. A total of 49 clones were sequenced. Real-time PCR was also performed on the same air samples to evaluate the airborne concentration of mycobacteria and estimate exposure levels. Several Mycobacterium species were present in the air samples (M. malmoense, M. smegmatis, M. graceum, M. bohemicum, and M. interjectum). Mycobacterium avium was recovered by culture in peat moss but not in the air using the molecular approach. Total airborne Mycobacterium concentration was estimated at 8.2 x 10(8)/m3. Workers had IgG against the mycobacterial mix and M. avium, suggesting significant exposure. The findings from air samples, supported by IgG measurements, demonstrate that peat moss processing plant workers are exposed to mycobacteria in addition to other biological agents.

Role of ventilation in airborne transmission of infectious agents in the built environment - a multidisciplinary systematic review

There have been few recent studies demonstrating a definitive association between the transmission of airborne infections and the ventilation of buildings. The severe acute respiratory syndrome (SARS) epidemic in 2003 and current concerns about the risk of an avian influenza (H5N1) pandemic, have made a review of this area timely. We searched the major literature databases between 1960 and 2005, and then screened titles and abstracts, and finally selected 40 original studies based on a set of criteria. We established a review panel comprising medical and engineering experts in the fields of microbiology, medicine, epidemiology, indoor air quality, building ventilation, etc. Most panel members had experience with research into the 2003 SARS epidemic. The panel systematically assessed 40 original studies through both individual assessment and a 2-day face-to-face consensus meeting. Ten of 40 studies reviewed were considered to be conclusive with regard to the association between building ventilation and the transmission of airborne infection. There is strong and sufficient evidence to demonstrate the association between ventilation, air movements in buildings and the transmission/spread of infectious diseases such as measles, tuberculosis, chickenpox, influenza, smallpox and SARS. There is insufficient data to specify and quantify the minimum ventilation requirements in hospitals, schools, offices, homes and isolation rooms in relation to spread of infectious diseases via the airborne route. PRACTICAL IMPLICATION: The strong and sufficient evidence of the association between ventilation, the control of airflow direction in buildings, and the transmission and spread of infectious diseases supports the use of negatively pressurized isolation rooms for patients with these diseases in hospitals, in addition to the use of other engineering control methods. However, the lack of sufficient data on the specification and quantification of the minimum ventilation requirements in hospitals, schools and offices in relation to the spread of airborne infectious diseases, suggest the existence of a knowledge gap. Our study reveals a strong need for a multidisciplinary study in investigating disease outbreaks, and the impact of indoor air environments on the spread of airborne infectious diseases.

Incorporating polymerase chain reaction-based identification, population characterization, and quantification of microorganisms into aerosol science: A review

The quantity, identity, and distribution of biomass in indoor and outdoor aerosols are poorly described. This is not consistent with the current understanding of atmospheric chemistry or the microbiological characterization of aquatic and terrestrial environments. This knowledge gap is due to both difficulties in applying contemporary microbiological techniques to the low biomass concentrations present in aerosols, and the traditional reliance of aerosol researchers on culture-based techniques-the quantitative limitations and ecological biases of which have been well-documented and are now avoided in other environmental matrices. This article reviews the emergence of the polymerase chain reaction (PCR) as a nonculture-based method to determine the identity, distribution, and abundance of airborne microorganisms. To encourage the use of PCR-based techniques by a broad spectrum of aerosol researchers, emphasis is given to the critical, aerosol specific method issues of sample processing, DNA extraction, and PCR inhibition removal. These methods are synthesized into a generalized procedure for the PCR-based study of microbial aerosols-equally applicable to both indoor and outdoor aerosol environments.

16S rRNA targeted sandwich hybridization method for direct quantification of mycobacteria in soils

Boreal soils have been suspected reservoirs of infectious environmental mycobacteria. Detection of these bacteria in the environment is hampered by their slow growth. We applied a quantitative sandwich hybridization approach for direct detection of mycobacterial 16S rRNA in soil without a nucleic acid amplification step. The numbers of mycobacterial 16S rRNA molecules found in the soil indicated the presence of up to 10(7) to 10(8) mycobacterial cells per gram of soil. These numbers exceed by factor of 10 to 100 x the previous estimates of mycobacteria in soil based on culture methods. When real-time PCR with mycobacteria targeting primers was used to estimate the number of 16S rDNA copies in soil, one copy of 16S rDNA was detected per 10(4) copies of 16S rRNA. This is close to the number of 16S rRNA molecules detected per cell by the same method in laboratory pure cultures of M. chlorophenolicum. Therefore a major part of the mycobacterial DNA in the studied soils may thus have represented metabolically active cells. The 16S rRNA sandwich hybridization method described in this paper offers a culture independent solution for tracking environmental reservoirs of viable and potentially infectious mycobacteria.

Bioaerosol mass spectrometry for rapid detection of individual airborne Mycobacterium tuberculosis H37Ra particles

Single-particle laser desorption/ionization time-of-flight mass spectrometry, in the form of bioaerosol mass spectrometry (BAMS), was evaluated as a rapid detector for individual airborne, micron-sized, Mycobacterium tuberculosis H37Ra particles, comprised of a single cell or a small number of clumped cells. The BAMS mass spectral signatures for aerosolized M. tuberculosis H37Ra particles were found to be distinct from M. smegmatis, Bacillus atrophaeus, and B. cereus particles, using a distinct biomarker. This is the first time a potentially unique biomarker was measured in M. tuberculosis H37Ra on a single-cell level. In addition, M. tuberculosis H37Ra and M. smegmatis were aerosolized into a bioaerosol chamber and were sampled and analyzed using BAMS, an aerodynamic particle sizer, a viable Anderson six-stage sampler, and filter cassette samplers that permitted direct counts of cells. In a background-free environment, BAMS was able to sample and detect M. tuberculosis H37Ra at airborne concentrations of >1 M. tuberculosis H37Ra-containing particles/liter of air in 20 min as determined by direct counts of filter cassette-sampled particles, and concentrations of >40 M. tuberculosis H37Ra CFU/liter of air in 1 min as determined by using viable Andersen six-stage samplers. This is a first step toward the development of a rapid, stand-alone airborne M. tuberculosis particle detector for the direct detection of M. tuberculosis bioaerosols generated by an infectious patient. Additional instrumental development is currently under way to make BAMS useful in realistic environmental and respiratory particle backgrounds expected in tuberculosis diagnostic scenarios.

Mycobacteria in drinking water distribution systems: ecology and significance for human health

In contrast to the notorious pathogens Mycobacterium tuberculosis and M. leprae, the majority of the mycobacterial species described to date are generally not considered as obligate human pathogens. The natural reservoirs of these non-primary pathogenic mycobacteria include aquatic and terrestrial environments. Under certain circumstances, e.g., skin lesions, pulmonary or immune dysfunctions and chronic diseases, these environmental mycobacteria (EM) may cause disease. EM such as M. avium, M. kansasii, and M. xenopi have frequently been isolated from drinking water and hospital water distribution systems. Biofilm formation, amoeba-associated lifestyle, and resistance to chlorine have been recognized as important factors that contribute to the survival, colonization and persistence of EM in water distribution systems. Although the presence of EM in tap water has been linked to nosocomial infections and pseudo-infections, it remains unclear if these EM provide a health risk for immunocompromised people, in particular AIDS patients. In this regard, control strategies based on maintenance of an effective disinfectant residual and low concentration of nutrients have been proposed to keep EM numbers to a minimum in water distribution systems.

The genetics of nontuberculous mycobacterial infection

The molecular aetiology of familial susceptibility to disseminated mycobacterial disease, usually involving weakly pathogenic strains of mycobacteria, has now been elucidated in more than 30 families. Mutations have been identified in five genes in the interleukin-12-dependent interferon-gamma pathway, highlighting the importance of this pathway in human mycobacterial immunity. Knowledge derived from the study of these rare patients contributes to our understanding of the immune response to common mycobacterial pathogens such as Mycobacterium tuberculosis and Mycobacterium leprae, which remain major public health problems globally. This knowledge can be applied to the rational development of novel therapies and vaccines for these important mycobacterial diseases.