The cefazolin inoculum effect in methicillin-susceptible Staphylococcus aureus blood isolates: their association with dysfunctional accessory gene regulator (agr)

Abstract

We evaluated the clinical significance of the cefazolin inoculum effect (CIE) in methicillin-susceptible Staphylococcus aureus (MSSA) isolates. In total, 146 isolateswere recovered frompatientswithMSSA bacteremia at 9 hospitals in Korea. The CIE was observed in 16MSSA isolates, andwhile type Awas the only detected β-lactamase in MSSA isolates exhibiting the CIE, no strains expressing type B, C, or D β-lactamases exhibited this effect. The CIE was only observed in agr group III and I isolates andwas significantly more common in isolateswith agr dysfunction than in thosewith functional agr (P b 0.001). Even among isolates producing type A β-lactamase, the CIEwas also prevalent in isolateswith dysfunctional agr than in isolates with functional agr (P=0.025). This study demonstrates an association between the CIE of MSSA isolates and agr dysfunction, in addition to those between the CIE and type A β-lactamase.