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The cefazolin inoculum effect in methicillin-susceptible Staphylococcus aureus blood isolates: their association with
Yu Mi Wi1, Young Kyoung Park2, Chisook Moon3
1Division of Infectious Diseases, Samsung Changwon Hospital, Sungkyunkwan University School of Medicine, Changwon, Republic of Korea; Department of Medicine, The Graduate School of Yonsei University, Seoul, Republic of Korea.
Abstract:
We evaluated the clinical significance of the cefazolin inoculum effect (CIE) in methicillin-susceptible Staphylococcus aureus (MSSA) isolates. In total, 146 isolates were recovered from patients with MSSA bacteremia at 9 hospitals in Korea. The CIE was observed in 16 MSSA isolates, and while type A was 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 and was significantly more common in isolates with agr dysfunction than in those with functional agr (P<0.001). Even among isolates producing type A β-lactamase, the CIE was also prevalent in isolates with 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.
Insights
The cefazolin inoculum effect (CIE) in methicillin-susceptible Staphylococcus aureus (MSSA) is linked to specific beta-lactamase types and importantly, to Agr dysfunction. This finding aids in understanding MSSA resistance mechanisms.
Area of Science:
- Microbiology
- Infectious Diseases
- Clinical Pharmacy
Background:
- The cefazolin inoculum effect (CIE) is a phenomenon observed in Staphylococcus aureus, potentially impacting treatment efficacy.
- Methicillin-susceptible Staphylococcus aureus (MSSA) remains a significant pathogen, and understanding resistance mechanisms is crucial for effective therapy.
Purpose of the Study:
- To investigate the clinical significance and associated factors of the cefazolin inoculum effect (CIE) in methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia isolates.
- To determine the relationship between CIE, beta-lactamase production, and accessory gene regulator (agr) group/function in MSSA.
Main Methods:
- Analysis of 146 MSSA isolates from patients with bacteremia across nine Korean hospitals.
- Detection of beta-lactamase types (A, B, C, D) and assessment of agr group (I-IV) and functionality (dysfunction vs. functional).
- Evaluation of the cefazolin inoculum effect (CIE) prevalence and its correlation with beta-lactamase production and agr status.
Main Results:
- The CIE was observed in 16 out of 146 MSSA isolates.
- Type A beta-lactamase was the only type detected in MSSA isolates exhibiting CIE; types B, C, and D were not associated with CIE.
- CIE was significantly more prevalent in MSSA isolates with agr dysfunction (P<0.001) and was observed in agr groups III and I.
- Even among isolates producing type A beta-lactamase, CIE was more common in those with dysfunctional agr (P=0.025).
Conclusions:
- The cefazolin inoculum effect (CIE) in MSSA is significantly associated with agr dysfunction.
- Type A beta-lactamase production is linked to the CIE in MSSA.
- Understanding these associations can inform therapeutic strategies for MSSA infections.
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