Ecological distribution of Staphylococcus in integrated farms within Washington DC–Maryland

Abstract

Mixed crop livestock farming (MCLF) is a growing practice in organic farming where livestock and crops are grown near each other to promote environmental sustainability through recycling. However, MCLF livestock are reservoirs of many zoonotic pathogens, such as Staphylococcus spp., and can serve as sources of cross-contamination for plant food products. A surveillance study was conducted to determine the prevalence and antibiotic-resistance patterns of various Staphylococcus spp. species isolated from the environment of multiple MCLFs and produced from pre-harvest and post-harvest levels within the DC–Maryland metropolitan area. A total of 3038 environmental and pre-harvest produce and 836 post-harvest produce samples were collected from eight farms and two retail supermarkets. In addition, 36 skin swabs from farmworkers and university students were also collected. PCR was used to confirm the presence of Staphylococcus spp. in all samples. Major species were identified using a species-specific multiplex PCR. An antibiogram assay was performed to determine antibiotic resistance profiles. The overall prevalence of Staphylococcus spp. was 12.18% pre-harvest and 7.54% post-harvest. The most identified species was Staphylococcus epidermidis (19.86%), while most isolates remained unknown (73.90%). Approximately 83.33% of skin swabs were positive for Staphylococcus spp., with Staphylococcus xylosus being the predominant species (16.7%). The highest percentage of isolates were resistant to aminoglycosides and macrolides, with 24.11% of tested samples being multidrug-resistant. S. epidermidis had the most resistance compared to the other species. This study suggests that antibiotic-resistant Staphylococcus spp. is present in mixed farm environments, and proper steps need to be taken to control the transmission between livestock, crops, and humans.