Investigation of the cefazolin inoculum effect in blood culture-isolated methicillin-susceptible Staphylococcus aureus strains: A Japanese multicenter study

IF 1.8 4区医学 Q3 INFECTIOUS DISEASES

Diagnostic microbiology and infectious disease Pub Date : 2026-07-01 Epub Date: 2026-02-28 DOI:10.1016/j.diagmicrobio.2026.117345

Shinnosuke Fukushima , Shuma Tsuji , Kazuyoshi Gotoh , Koji Iio , Sakura Ogawa , Norihito Koyanagi , Yuji Ito , Hiroshi Koganemaru , Atsushi Yoshida , Hideharu Hagiya

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Abstract

Background

Cefazolin inoculum effect (CInE) is a microbiological phenomenon where the MIC of cefazolin against methicillin-susceptible Staphylococcus aureus (MSSA) strains increases with higher bacterial volumes.

Method

We retrospectively investigated the prevalence and characteristics of the CInE among MSSA strains isolated from blood cultures at three Japanese hospitals. The collected isolates were screened for blaZ using PCR, and the cefazolin minimum inhibitory concentration (MIC) for the blaZ-positive MSSA isolates was measured at standard and high inoculum volumes. CInE-positive MSSA strains were defined as those with a cefazolin MIC ≥16 μg/mL at 10⁷ CFU/mL and ≤8 μg/mL at 10⁵ CFU/mL. In these blaZ-positive strains, we performed blaZ typing and tested a modified nitrocefin-based rapid examination to detect the CInE.

Results

We collected 329 MSSA strains isolated from blood cultures. Of these, 96 (29.2%) were positive for the blaZ gene, with the following genotypes: type A (15, 15.6%), type B (3, 3.1%), type C (77, 80.2%), type D (0, 0.0%), and non-type (1, 1.0%). Among 96 blaZ-positive MSSA isolates, 11 exhibited the CInE, all of which harbored blaZ type A. The rapid nitrocefin test detected CInE positivity with high sensitivity (100%), specificity (94.1%), and diagnostic accuracy (94.8%).

Conclusion

This study highlighted the low prevalence of CInE-presenting MSSA isolates in Japan. When the cefazolin MIC is ≥1 μg/mL or the penicillin G MIC is ≥0.25 μg/mL, the rapid nitrocefin test may be useful for considering the CInE in patients with high bacterial volume MSSA infections.

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头孢唑林对血培养分离的甲氧西林敏感金黄色葡萄球菌接种效果的研究：一项日本多中心研究。

背景：头孢唑林接种效应（CInE）是一种微生物学现象，头孢唑林对甲氧西林敏感金黄色葡萄球菌（MSSA）的MIC随着细菌体积的增加而增加。方法：回顾性调查日本三家医院血培养分离的MSSA菌株中CInE的流行情况和特征。采用PCR方法对收集到的菌株进行blaZ筛选，并在标准和高接种量下测定头孢唑林对blaZ阳性MSSA菌株的最低抑菌浓度（MIC）。cfazolin MIC≥16 μg/mL （107 CFU/mL）和≤8 μg/mL （105 CFU/mL）的MSSA菌株为cine阳性。在这些blaze阳性菌株中，我们进行了blaZ分型，并测试了一种改进的基于硝基萘的快速检测方法来检测CInE。结果：从血培养中分离到329株MSSA。其中blaZ基因阳性96例（29.2%），基因型分别为A型（15.6%）、B型（3.3.1%）、C型（77.80.2%）、D型（0.0%）和非型（1.0%）。在96株blaZ阳性的MSSA分离株中，11株为CInE，均为blaZ a型。快速硝基芬试验检测出CInE阳性，灵敏度（100%）、特异性（94.1%）和诊断准确率（94.8%）较高。结论：本研究强调了日本呈现cine的MSSA分离株的低流行率。当头孢唑林MIC≥1 μg/mL或青霉素G MIC≥0.25 μg/mL时，快速硝基芬试验可用于考虑高菌量MSSA感染患者的CInE。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Diagnostic microbiology and infectious disease 医学-传染病学

CiteScore

5.30

自引率

3.40%

发文量

149

审稿时长

56 days

期刊介绍： Diagnostic Microbiology and Infectious Disease keeps you informed of the latest developments in clinical microbiology and the diagnosis and treatment of infectious diseases. Packed with rigorously peer-reviewed articles and studies in bacteriology, immunology, immunoserology, infectious diseases, mycology, parasitology, and virology, the journal examines new procedures, unusual cases, controversial issues, and important new literature. Diagnostic Microbiology and Infectious Disease distinguished independent editorial board, consisting of experts from many medical specialties, ensures you extensive and authoritative coverage.