Quantitative Microbial Population Characterization   to Reveal Sources of Bacteria in Indoor Air D Hospodsky 1, J Qian 1, ...
Humans may affect the indoor microbiome• Issue — To what extent and in what ways do occupants  influence airborne bacteria...
Study site: University classroom   Volume = 90 m3; Room AER = 6 per hour                                                  ...
Methods• Sampling: 2 × 2 (indoor, outdoor × occupied, unoccupied)    -   Sampled 4 d occupied (104 person-h); 4 d unoccupi...
Occupancy strongly influences particle levels                    Unoccupied (19 Sep 09)          Occupied (3 Nov 09)Ref.: ...
Resuspension from carpet is a strong contributor                                   Each 1 person case                     ...
Indoor PM mass strongly enhanced w/ occupancy                   The “occupied” to “vacant” PM10 mass concentration ratio i...
Bacterial genomes even more strongly enhanced!         The “occupied” to “vacant” PM10 bacterial genome concentration rati...
Floor dust is especially enriched in bacterial DNARef.: D Hospodsky et al., PLoS One 7(4), e34867, 2012; Bacterial mass es...
Emission rates quantified by material balance                       Peak > 9 µm                                          P...
Significant contributor: Human microbiome                              Prominent bacterial taxa in the human microbiome (C...
Indoor air differs from HVAC filter cake                                Prominent bacterial taxa in the human microbiome (...
Summary and conclusions for this study site• Human occupancy contributes strongly to the concentration of indoor  airborne...
Ongoing work: Additional classroom sites                                           14
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Quantitative microbial population characterization to reveal sources of bacteria in indoor air

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Presentation in Sloan-Foundation Sponsored Workshop on the Indoor Microbiome delivered at Healthy Buildings 2012 Conference, Brisbane, Australia, 9 July 2012

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Quantitative microbial population characterization to reveal sources of bacteria in indoor air

  1. 1. Quantitative Microbial Population Characterization to Reveal Sources of Bacteria in Indoor Air D Hospodsky 1, J Qian 1, N Yamamoto 1,2, W NAZAROFF 3, J Peccia 1 1 Yale University, New Haven, CT USA; 2 Japan Society for the Promotion of Sciences, Tokyo, Japan; 3 University of California, Berkeley, CA USA [Funding: Alfred P. Sloan Foundation] Healthy Buildings 2012 Brisbane, Australia 9 July 2012 Denina Hospodsky Jing Qian Naomichi Yamamoto WW Nazaroff Jordan Peccia 1
  2. 2. Humans may affect the indoor microbiome• Issue — To what extent and in what ways do occupants influence airborne bacteria in indoor environments?• Approach — Study the indoor microbiome in a university classroom. 2
  3. 3. Study site: University classroom Volume = 90 m3; Room AER = 6 per hour Outside air: 25-100% HVAC intake MERV 8 filters (upstream) Filters (downstream) Coils 3
  4. 4. Methods• Sampling: 2 × 2 (indoor, outdoor × occupied, unoccupied) - Sampled 4 d occupied (104 person-h); 4 d unoccupied - Continuous size-resolved particles (OPC, 0.3-10 µm) - Time-integrated filter samples (cascade impactor, PM10, PM2.5) - Floor dust (sieved, resuspended, and sampled as PM37 & PM10) - Carbon dioxide (air-exchange rate determination)• Analytical methods - Gravimetric (PM mass) - DNA quantification: real-time PCR with universal bacterial primers targeting 16S rRNA encoding genes - DNA sequencing: pyrosequencing on a GS-FLX 454 platform - Analysis via QIIME (“quantitiative insights into microbial ecology”) 4
  5. 5. Occupancy strongly influences particle levels Unoccupied (19 Sep 09) Occupied (3 Nov 09)Ref.: J Qian et al., Indoor Air (in press, 2012). 5
  6. 6. Resuspension from carpet is a strong contributor Each 1 person case involved walking; the 30 persons were seated One person walking on carpet contributes more than 30 people sitting on plastic.Ref.: D Hospodsky et al., PLoS One 7(4), e34867, 2012 6
  7. 7. Indoor PM mass strongly enhanced w/ occupancy The “occupied” to “vacant” PM10 mass concentration ratio indoors was 15 to 1.Refs.: J Qian et al., Indoor Air (in press, 2012); D Hospodsky et al., PLoS One 7(4), e34867, 2012 7
  8. 8. Bacterial genomes even more strongly enhanced! The “occupied” to “vacant” PM10 bacterial genome concentration ratio indoors was 66 to 1.Refs.: J Qian et al., Indoor Air (in press, 2012); D Hospodsky et al., PLoS One 7(4), e34867, 2012 8
  9. 9. Floor dust is especially enriched in bacterial DNARef.: D Hospodsky et al., PLoS One 7(4), e34867, 2012; Bacterial mass estimated as 655 fgper bacterium with an average of four 16S rDNA gene copies per bacterium. 9
  10. 10. Emission rates quantified by material balance Peak > 9 µm Peak ~ 3-5 µm C = indoor concentration; f = indoor proportion of outdoor level; Cout = outdoor concentration; N = number of occupants; E = per person emission rate; Q = ventilationRef.: J Qian et al., Indoor Air (in press, 2012). rate; k = deposition rate constant; V = volume 10
  11. 11. Significant contributor: Human microbiome Prominent bacterial taxa in the human microbiome (Costello et al., 2009) Samples show clear representation from the dominant bacteria of the human microbiome. Five taxa — Propionibacterineae, Staphyloccus, Streptococcus, Enterobacteriaceae, and Corynebacterineae — comprise 17% and 20% of all bacteria in indoor air and in floor dust, respectively.Refs.: D Hospodsky et al., PLoS One 7(4), e34867, 2012; EK Costello et al., Science 326, 1694, 2009. In all, 16 samples wereanalyzed by 454 pyrosequencing. The effort yielded 10.7k partial 16S rDNA gene sequences with average length of 500 bp. 11
  12. 12. Indoor air differs from HVAC filter cake Prominent bacterial taxa in the human microbiome (Costello et al., 2009) Bacterial communities in indoor air during human occupancy were significantly different from the communities associated with the HVAC filter dust (p < 0.001).Refs.: D Hospodsky et al., PLoS One 7(4), e34867, 2012; EK Costello et al., Science 326, 1694, 2009. 12
  13. 13. Summary and conclusions for this study site• Human occupancy contributes strongly to the concentration of indoor airborne bacterial genomes.• DNA sequences point to important contributions of human microflora, either by direct shedding, or resuspension from surfaces (e.g., carpet).• Current or previous occupants of a room can contribute substantially to human inhalation exposure to bacterial DNA. We live in this microbial soup, and a big ingredient is our own microorganisms. Mostly, people are resuspending what’s been deposited before. The floor dust turns out to be the major source of the bacteria we breathe. 13
  14. 14. Ongoing work: Additional classroom sites 14

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