JA:2021-20. Source Attribution of MRSA Exposure and Carriage among Dairy Workers

Abstract

ABSTRACT Purpose: Dairy farmers experience a heavy burden of bioaerosol-related respiratory ailments. Bioaerosols are known to contain inflammagens (specifically endotoxin), and a diverse bacterial community that is associated with upper respiratory inflammation and pulmonary decrement among workers. However, identifying casual agents (beyond endotoxin) is still an area that warrants further research. Industrialization and modernization of the dairy industry has led to dramatic changes in production, work organization, and tasks. Consequently, exposure patterns have been altered. Recently, we demonstrated that the mass of dairy bioaerosols is predominantly present in particle size ranges that span 10–100 μm in aerodynamic diameter; these are known to deposit in the upper respiratory system (i.e., the nasopharyngeal region). The nose contains complex bacterial communities, and this microbiome may play a role in the inflammatory response to bioaerosols. Recently, the nasal microbiome in dairy farmers was shown to contain over two times the bacterial diversity (and abundance) as compared to non-farmers. It is believed that this diversity is protective against the colonization of methicillin-resistant Staphylococcus aureus (MRSA). In contrast, persistent nasal carriage of MRSA, specifically livestock-associated strain, has been demonstrated in swine production workers. Recent evidence shows an increase in soft tissue infections caused by livestock associated (LA)-MRSA among at risk populations. The objective of this research was to characterize the presence and carriage of Staphylococcus spp. with a focus on LA-MRSA in the nose of dairy workers. Methods: We collected nasal lavage samples before and after each shift across 5 consecutive days. The presence of MRSA in each sample was evaluated using culture-based methods, specifically tryptic soy agar, mannitol salt agar, Chromagar Staph Aureus, and Chromagar MRSA II. Antibiotic sensitivity was conducted using Kirby Disc Diffusion method using tetracycline, vancomycin, and cefoxitin. Further genetic MRSA confirmation is to be accomplished using PCR and MALDI-TOF. Results/Findings: To date, up to 4% of participants were identified to be carriers of MRSA, and up to 16% of participants were identified to be carriers of Staphylococcus aureus. Based on the results from selective media, the MRSA is attributed to mixed sources, including livestock. Confirmation of these isolates will be conducted using matrix-assisted laser desorption/ionization time-of-flight and polymerase chain reaction methods. Practical application: Based on previous pilot studies and initial results, further investigation into LA-MRSA prevalence among dairy workers is needed to help inform control strategies.