A side by side image of a bacterial growth media with white antibiotic disks and zones around them. On the left a zone with a sharp edge, onthe right a zone with a hazy, fuzzy edge

#MicroRounds (Day 977): "day at the beach" For a lab to conclusively detect beta-lactamase in Staphylococcus spp. this is the zone-edge test (aka "sandy beach test"). Around a penicillin disk a sharp ("cliff"): beta-lac(+). A fuzzy edge ("beach"): (-) #ASMClinMicro #IDTwitter

A black bacterial culture media with a lot of bacterial colonies. Caption reads, Bordetella holmesii Respiratory culture – other flora present Regan-Lowe agar: charcoal based – horse blood; charcoal neutralizes fatty acids, peroxides; AmpB, cephalexin Silvery, pearly colonies PCR: carries insertion sequence IS481 (like B. pertussis, but fewer copies than B. pertussis)

#MicroRounds (Day 976): "Home sweet holmesii" A respiratory culture on charcoal Regan-Lowe medium (supports Bordetella growth, neutralizes toxic compounds): Bordetella holmesii. Silvery colonies. In PCR, B. holmesii carries IS481 (like B. pertussis) #ASMClinMicro #IDTwitter