Preservation efficiency and storage effects for viable and culturable Staphylococcus aureus

Abstract

Airborne Staphylococcus aureus is associated with human infections, thereby requiring exposure monitoring for risk assessment. To secure data accuracy, changes in biological properties of S. aureus during sampling and sample storage should be minimized. This study assessed preservation efficiency (PE) of bioaerosol sampling methods by spiking S. aureus in deionized water (DW), phosphate-buffered saline (PBS) or Tween mixture (TM) and loading cell suspensions in AGI-30 or BioSampler, followed by sampling with HEPA-filtered air. S. aureus bioaerosols were also sampled and stored up to 3 and 29 days to assess changes in culturable and viable cell counts, respectively. Cell viability was determined based on membrane integrity. Results show BioSampler preserved S. aureus better than AGI-30 (P < 0.05), particular with TM in which 96–97% and 68–72% of cells remained culturable and viable, respectively, after sampling for 30–60 min. The highest PE for AGI-30 was observed in DW, i.e., 86–93% and 39–62%, respectively, for culturable and viable cells. PBS presented the least efficiency among fluids to preserve viable cells in both samplers (P < 0.05). Samples stored at 5 °C showed less changes in viable and culturable cell counts over time than those at 25 °C. Moreover, storage at 5 °C impacted differently on cell culturability and viability, evident by slightly decreased culturable counts but significantly increased viable counts in both TM and DW (P < 0.05). This suggests S. aureus at 5 °C kept culturability while restored membrane integrity. Overall, S. aureus is preferable to be collected in TM by BioSampler and stored at 5 °C.