We analyzed highly vancomycin-resistant Gram-positive bacteria isolated from the saliva of migratory songbirds captured, sampled, and released from a birdbanding station in western Kansas. Individual bacterial isolates were identified by partial 16S rRNA sequencing. Most of the bacteria in this study were shown to be Staphylococcus succinus with the majority being isolated from the American Robin. Some of these bacteria were shown to carry vanA, vanB, and vanC vancomycin-resistance genes and have the ability to form biofilms. One of the van gene-carrying isolates is also coagulase positive, which is normally considered a virulence factor. Other organisms isolated included Staphylococcus saprophyticus as well as Enterococcus gallinarum. Given the wide range of the American Robin and ease of horizontal gene transfer between Gram-positive cocci, we postulate that these organisms could serve as a reservoir of vancomycin-resistance genes capable of transferring to human pathogens.

The antibiotic vancomycin was developed by Eli Lilly in the 1950s in response to the growing number of Staphylococcus aureus infections that were resistant to penicillin. Vancomycin was not widely used at the time because of its high toxicity. However, use of vancomycin in the United States has increased dramatically since the 1980s because of the emergence of methicillin resistant Staphylococcus aureus (MRSA) and Enterococcus species. There are three known mechanisms for vancomycin resistance: 1) target site modification by van genes, 2) biofilm formation, and 3) bacterial cell wall thickening. Of these mechanisms, target site modification is the most common. In this study, we analyzed cultivable highly vancomycin-resistant Gram-positive bacteria from the saliva of migratory songbirds, which were captured at the bird banding station at Fort Hays State University in previous work. Individual bacterial isolates were identified by partial 16S rRNA sequencing. The majority of the identified bacteria were Staphylococcus succinus, with the majority being isolated from American Robin, which is commonly found in all of North America. Some of these bacteria carry vanA, vanB, and vanC genes and also have the ability to form biofilms. One of the van gene-carrying isolates is also coagulase-positive which is also considered a strong virulence factor. Given the wide range of the American Robin and ease of gene transfer between Gram-positive cocci, we postulate that these organisms could serve as a source of vancomycin resistance genes in human pathogens.