Airborne MRSA and Total Staphylococcus aureus as Associated With Particles of Different Sizes on Pig Farms

Abstract

Airborne methicillin-resistant Staphylococcus aureus (MRSA) have previously been found on pig farms, which may lead to nasal deposition of MRSA in humans via inhalation. The anterior nares are the main niche for S. aureus, and S. aureus can cause, e.g. wound infection and pneumonia. The aim of this study was to acquire knowledge about the potential deposition of airborne MRSA, specifically, and of total S. aureus (including both methicillin-sensitive S. aureus and MRSA, in the following called S. aureus) in the different parts of the airways during occupancy on pig farms. Measurements of airborne MRSA and S. aureus were performed on four pig farms using a six and a three-stage sampler during different work tasks, such as high-pressure cleaning and everyday inspection. MRSA were quantified using MRSA-selective agar, and S. aureus were quantified using Staphylococcus selective agar. The identity of the bacteria were confirmed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The geometric mean (GM) concentrations of MRSA and S. aureus were 447 cfu/m3 air and 1.8 × 103 cfu/m3 air, respectively. The highest concentrations of MRSA and S. aureus were found among pigs in a weaner stable and during high-pressure cleaning of an empty stable, respectively. The lowest concentrations of MRSA and S. aureus were found in a stable with sick pigs and in feed-storages, respectively. Most MRSA and S. aureus were associated with particles between 7 and 12 µm. On average, the particle size fractions potentially depositing in the upper airways constituted 70%, in the primary and secondary bronchi 22%, and in the terminal bronchi and alveoli 8% of the inhalable MRSA and S. aureus concentration. Across the sampled areas, the geometric mean diameter (Dg) of particles with MRSA and S. aureus were 7.2 and 6.4 µm, respectively, and no significant difference was found between these Dgs. The Dg of the airborne particles with the studied bacterium was significantly associated with the different locations on the farms. The largest Dgs were found in the air samples from the aisles and on the fence to the pens, while the smallest Dgs were found in samples from the pens among the pigs and in samples taken at greater distances from the pigs: in the hallway, feed-storage, and entry room. In conclusion, airborne MRSA and S. aureus were found in sample fractions potentially depositing in all six parts of the airways. However, the majority was found to potentially deposit in the upper airways. The concentration of airborne MRSA and S. aureus and MRSA, as well as the fraction potentially depositing in the different parts of the airways, depended on the specific work task being performed and the location on the farm.

Measurement of dust‐borneMRSAin pig farms using different approaches

“…In a study using a DGI‐1570 sampling at 50 l min −1 on to a filter, on a pig farm, no MRSA was found though MRSA was found using the ASCI (Madsen et al . ). In a study using Impingers and IOM samplers, higher exposures to MRSA were measured using IOM samplers (Friese et al .…”

“…The GSP, IOM and Triplex cyclone can be used for brief durations such as 10 min and up to 8–10 h. The Andersen six‐stage cascade impactor (ASCI) has been used for decades and has previously been used to sample airborne MRSA in pig farms (Madsen et al . ). The ASCI can only be used as a stationary sampler, and it samples directly on agar using a flow rate of 28·3 l min −1 .…”

“…; Madsen et al . ), and exposure to MRSA is a potential occupational health problem affecting people working on the farms (van Cleef et al . ; Geenen et al .…”

“…), the ASCI for 4–20 min (Madsen et al . ) and the Respicon for 3 h (Madsen et al . ) on animal farms and in a pig slaughterhouse.…”

“…) and the Respicon for 3 h (Madsen et al . ) on animal farms and in a pig slaughterhouse. The samples are treated differently after sampling.…”