Cefazolin inoculum effect in methicillin-susceptible Staphylococcus aureus clinical isolates

Area of Science:

• Microbiology
• Infectious Diseases
• Clinical Pharmacy

Background:

• The Cefazolin inoculum effect (CInE) is a phenomenon where bacterial susceptibility to cefazolin decreases with higher bacterial concentrations.
• Methicillin-susceptible Staphylococcus aureus (MSSA) is a common cause of bacterial infections.
• Understanding CInE prevalence is crucial for guiding appropriate antibiotic therapy.

Purpose of the Study:

• To determine the prevalence and characteristics of Cefazolin inoculum effect (CInE) in clinical Methicillin-susceptible Staphylococcus aureus (MSSA) isolates in Japan.
• To assess the correlation between the presence of the blaZ gene and the occurrence of CInE.

Main Methods:

• Collection and identification of clinical MSSA isolates from a Japanese setting.
• Phenotypic testing for Cefazolin inoculum effect (CInE) using standard microbiological methods.
• Molecular detection of the blaZ gene in the collected isolates.

Main Results:

• A total of 35.5% (39 out of 110) of the clinical MSSA isolates harbored the blaZ gene.
• None of the tested MSSA isolates exhibited the phenotypic criteria for Cefazolin inoculum effect (CInE).
• The presence of the blaZ gene did not correlate with the occurrence of CInE in this cohort.

Conclusions:

• The prevalence of Cefazolin inoculum effect (CInE) among clinical MSSA isolates in Japan appears to be very low.
• The blaZ gene, while present in a significant proportion of isolates, was not associated with CInE in this study.
• Further research may be needed to elucidate the mechanisms and clinical implications of CInE in MSSA.