Hungarian researchers who drilled down into stable dust to reveal the types of bacteria present found that most were common soil-dwelling varieties.
Air quality in stables has been the subject of several studies over the years, with elevated levels of dust linked to asthma-related problems in horses.
There is some indication, too, that allergens in the dust, among them endotoxins, may also cause inflammation in human airways and may exceed safe levels in stables.
Monitoring studies have concentrated mainly on determining the concentration of breathable particles and identifying culturable fungi and their toxins.
“However, these particles do not only directly affect the respiratory system, but might act as a carrier conveying toxic contaminants and biological agents such as bacteria,” Nora Kovats and her colleagues noted in the International Journal of Occupational Medicine and Environmental Health.
The nine-strong study team collected and analysed resuspended dust from air samples collected from what they described as a typical 20-horse Hungarian stable.
They tested the samples at a genetic level to learn more about the microbial community inhabiting these particles, and whether they conveyed hazardous pathogenic bacteria.
In total, 1491 different taxa were identified. Of them, 384 were identified to species level and 961 to genus level.
They were dominated by common soil and organic material-dwelling bacteria, with 59.4% of them found to be gram-negative organisms and 40.2% gram-positive. The most common soil-dwelling bacteria detectd were pedobacter and rhizobium species.
Pathogens, they reported, occurred at low abundance, and were almost exclusively restricted to human pathogens recognised for their adaptability.
There was, they said, a prevalence of Staphylococcus species.
“Staphylococcus cells can be maintained for relatively long periods of time on various surfaces and can survive in aerosols for extended periods,” they noted.
Amongst rare bacteria detected in the genetic testing by only one read in the analysis were Bacillus anthracis, which causes anthrax, Legionella sp. (identified only to genus level) and Aerococcus viridans, which has rarely been reported to cause endocarditis or septic arthritis.
“The overall objective of this study was to obtain a snapshot of the culturable microbiota of respirable fraction of stable resuspended dust,” they said in their conclusion.
Analysis that revealed that most of the bacteria found were naturally present on soil particles and on organic material such as hay or straw.
“Somewhat against our starting hypothesis, these particles have not conveyed pathogens posing hazard to horses’ health; however, some human pathogens have been identified.”
Kováts was joined in the research by Eszter Horváth, Beatrix Jancsek-Turóczi, András Hoffer, András Gelencsér, Péter Urbán, Írisz E. Kiss, Zoltán Bihari and Csaba Fekete. They were variously affiliated with the University of Pannonia, the Hungarian Academy of Science, the University of Pécs, and Bay Zoltán Nonprofit Ltd.
Microbiological characterization of stable resuspended dust
Nora Kováts, Eszter Horváth, Beatrix Jancsek-Turóczi, András Hoffer, András Gelencsér, Péter Urbán, Írisz E. Kiss, Zoltán Bihari, Csaba Fekete.
Int J Occup Med Environ Health 2016;29(3):375–380