Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) is a dynamic and tenacious pathogenic bacterium which is prevalent in livestock farming environments. This study investigated the possibility of MRSA spread via bioaerosol transmission from an indoor chicken farm environment to outdoors downwind (up to 50 m). The concentration of total airborne bacteria colony formation units (CFUs) was decreased with increasing sampling distance ranging from 9.18 × 101 to 3.67 × 103 per air volume (m3). Among the 21 MRSA isolates, 15 were isolated from indoor chicken sheds and exposure square areas, whereas 6 were isolated from downwind bioaerosol samples. Molecular characterization revealed that all of them carried the staphylococcal cassette chromosome mec (SCCmec) VIII, and they were remarkably linked with the hospital-associated MRSA group. Spa typing analysis determined that all MRSA isolates belonged to spa type t002. Virulence analysis showed that 100% of total isolates possessed exfoliative toxin A (eta), whereas 38.09% and 23.80% strains carried exfoliative toxin B (etb) and enterotoxin A (entA). Additionally, all of these MRSA isolates carried multidrug resistance properties and showed their resistance against chloramphenicol, ciprofloxacin, clindamycin, tetracycline, and erythromycin. In addition, chi-squared statistical analysis displayed a significant distributional relationship of gene phenotypes between MRSA isolates from chicken farm indoor and downwind bioaerosol samples. The results of this study revealed that chicken farm indoor air might act as a hotspot of MRSA local community-level outbreak, wherein the short-distance dispersal of MRSA could be supported by bioaerosols.
Highlights
Previous studies related to pathogenic microbes highlighted that diverse Grampositive and Gram-negative bacteria such as S. aureus, Escherichia coli, Streptococcus suis, and Actinobacillus pleuropneumoniae are most prevalent in livestock farming bioaerosol samples [23,24]
Gibbs et al [25] reported a similar trend in decreased airborne bacteria colony formation units (CFUs) in downwind sampling zones up to 150 m distance from the swine barn area, which is consistent with our results
It could be suggested that the bioaerosol samples in the present study had adequate potential to carry and transmit the Methicillin-resistant Staphylococcus aureus (MRSA) strains from the chicken shed indoor air to the surrounding downwind ambient environment
Summary
Antibiotic-resistant strains of Gram-positive pathogens, especially S. aureus, have been isolated from diverse environments such as hospitals, long-term care facilities, rivers, sediments, lakes, soil, and even the deep ocean [1,2]. Bioaerosol-associated risk related to S. aureus remains to be fully understood. The dispersion of microorganisms comprising the pathogenic bacteria associated with bioaerosols can spread in different environments due to their highly aerodynamic properties, such as small diameter and lightweight [3]. Several occupational units (food processing, livestock, waste dumping station, agricultural farmland) and human activities (coughing, sneezing, washroom, and floor cleaning) are important sources of bioaerosol formation in the air [4,5]. Kabelitz et al [6]
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