Introduction The degree to which bacteria in the human respiratory tract are aerosolised by individuals is not established. Building on our experience sampling bacteria exhaled by individuals with pulmonary tuberculosis using face masks, we hypothesised that patients with conditions frequently treated with antimicrobials, such as chronic obstructive pulmonary disease (COPD), might exhale significant numbers of bacteria carrying antimicrobial resistance (AMR) genes and that this may constitute a previously undefined risk for the transmission of AMR.
Methods Fifteen-minute mask samples were taken from 13 patients with COPD (five paired with contemporaneous sputum samples) and 10 healthy controls. DNA was extracted from cell pellets derived from gelatine filters mounted within the mask. Quantitative PCR analyses directed to the AMR encoding genes: blaTEM (β-lactamase), ErmB (target methylation), mefA (macrolide efflux pump) and tetM (tetracycline ribosomal protection protein) and six additional targets were investigated. Positive signals above control samples were obtained for all the listed genes; however, background signals from the gelatine precluded analysis of the additional targets.
Results 9 patients with COPD (69%), aerosolised cells containing, in order of prevalence, mefA, tetM, ErmB and blaTEM, while three healthy controls (30%) gave weak positive signals including all targets except blaTEM. Maximum estimated copy numbers of AMR genes aerosolised per minute were mefA: 3010, tetM: 486, ErmB: 92 and blaTEM: 24. The profile of positive signals found in sputum was not concordant with that in aerosol in multiple instances.
Discussion We identified aerosolised AMR genes in patients repeatedly exposed to antimicrobials and in healthy volunteers at lower frequencies and levels. The discrepancies between paired samples add weight to the view that sputum content does not define aerosol content. Mask sampling is a simple approach yielding samples from all subjects and information distinct from sputum analysis. Our results raise the possibility that patient-generated aerosols may be a significant means of AMR dissemination that should be assessed further and that consideration be given to related control measures.
- antimicrobial resistance
- aerosol sampling
- airborne dissemination
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Contributors MK: study conceptualisation, data collection, laboratory processing of COPD and volunteer samples, data interpretation, statistical analysis and drafting of manuscript. MYR, CMLW and JA: assistance with laboratory processing of samples. MA: collection of volunteer samples and extraction of DNA. KH: assistance with laboratory processing of samples and manuscript review. CEB: project supervision. MRB: study conceptualisation and manuscript drafting and review.
Funding This work was supported by a grant from the Dowager Countess Eleanor Peel Trust and the UK MRC (MR/P023061/1).
Competing interests None declared.
Patient consent Obtained.
Ethics approval Ethical approval was obtained from the East Midlands Research Ethics Committee (REC) approval 08/H0406/189. Additionally, aerosol DNA extracts were available from 10 healthy volunteers previously recruited at the University of Leicester between September and October 2015 (departmental ethics committee approval: 2369-ma680-3i).
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement All data collected as part of this study and used to reach the above conclusions are included within this article and in the online supplementary material. Data displayed within this article are available upon request from MK.
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