A Comparison of Passive and Active Dust Sampling Methods for Measuring Airborne MRSA in Pig Farms

Study Abstract:

Authors: Anne Rittscher, Abel A. Vlasblom, Birgitta Duim, Peter Scherpenisse, Isabella van Schothorst, Inge M. Wouters, Liese Van Gompel, Lidwien A.M. Smit

     Methicillin resistant strains of Staphylococcus aureus (MRSA) are resistant to most b-lactam antibiotics. Pigs are an important reservoir of livestock associated MRSA (LA-MRSA), which is genetically distinct from both hospital and community acquired MRSA. Occupational exposure to pigs on farms can lead to LA-MRSA carriage by workers. There is a growing body of research on MRSA found in the farm environment, the airborne route of transmission, and its implication on human health. This study aims to compare two sampling methods used to measure airborne MRSA in the farm environment; passive dust sampling with electrostatic dust fall collectors (EDCs), and active inhalable dust sampling using stationary air pumps with Teflon filters.

Paired dust samples using  EDCs and GSP samplers, totaling 87 samples, were taken from seven Dutch pig farms, in multiple compartments housing pigs of varying ages. Total nucleic acids of both types of dust samples were extracted and targets indicating MRSA (femA, nuc, mecA) and total bacterial count (16S rRNA) were quantified using quantitative Real Time PCRs.

MRSA could be measured in all stationary pump samples and in 94% of the EDCs, additionally MRSA was present on every farm sampled. There was a strong positive relationship between the paired MRSA levels found in EDCs and those measured on filters (Normalized by 16S rRNA; Pearson’s correlation coefficient r=0.94, Not Normalized; Pearson’s correlation coefficient r=0.84).

This study suggests that EDCs can be used as an affordable and easily standardized method for quantifying airborne MRSA levels in the pig farm setting.