LAUSR

β-Hemolytic Streptococcus (BHS) species are important pathogens with both human and veterinary significance. In human medicine, BHS are considered universally susceptible to β-lactams while BHS of veterinary origin have been reported with up to 8% β-lactam resistance. Recently, veterinary diagnostic laboratories were made aware of significant variability of test method performance for BHS among laboratories. This article explores potential sources of error in antimicrobial susceptibility test performance and result interpretation that may have contributed to the unusual rates of resistance to β-lactams observed in this bacterial species. In addition, potential impacts to research, clinical practice, surveillance, and public health will be discussed.