Wang Yanyan, Wen Juan, Guo Binxin, Zheng Wenqi, Wang Junrui
Department of Laboratory Medicine, Affiliated Hospital of Inner Mongolian Medical University, 010050, Hohhot, People's Republic of China; Inner Mongolia Key Laboratory of Clinical Pathogenic Microorganism, The Affiliated Hospital of Inner Mongolian Medical University, 010050, Hohhot, People's Republic of China.
Department of Laboratory Medicine, Affiliated Hospital of Inner Mongolian Medical University, 010050, Hohhot, People's Republic of China.
Anaerobe. 2025 Feb;91:102924. doi: 10.1016/j.anaerobe.2024.102924. Epub 2024 Dec 4.
Strains of carbapenem-resistant Bacteroides fragilis have frequently emerged in recent years. In China, data on the genotypic and phenotypic characteristics of these antimicrobial-resistant anaerobic bacteria are scarce. Thus, the aim of this study was to characterize clinical isolates of carbapenem-resistant B. fragilis collected from a tertiary hospital in China using whole genome sequencing (WGS), phenotypic susceptibility tests, and a biofilm formation assay.
We analyzed 49 B. fragilis strains with different antimicrobial resistance profiles. Antimicrobial susceptibility was determined using the agar dilution method and biofilm formation using a crystal violet assay. Genomic characteristics were analyzed using WGS, and the transcription level of cfiA, which is responsible for carbapenem resistance, was determined using quantitative reverse transcription polymerase chain reaction (PCR). Carbapenem-sensitive isolates were used as controls.
All 49 B. fragilis isolates were biofilm producers and the percentage of carbapenem-resistant isolates was 42.86 % (21/49). The percentage of carbapenem-resistant isolates with medium-to-strong biofilm production ability was significantly lower than that of carbapenem-sensitive isolates (19.1 % vs. 88.9 %, p < 0.01). None of the carbapenem-resistant B. fragilis isolates carried bft. In contrast, 53.6 % (15/28) of the carbapenem-sensitive isolates carried bft, and all of them were fpn(+). All carbapenem-resistant isolates (21/21, 100 %) harbored cfiA and its upstream insertion sequence (IS) element. Three isolates (BF058, BF059, and BF060) carried the IS613 element, which was not immediately adjacent upstream to cfiA but was separated by a 1000-kb sequence encoding vatD. The quantitative PCR assay results revealed the elevated expression of cfiA mRNA among carbapenem-resistant isolates, although the relative expression levels varied greatly among isolates. However, a significant correlation between the relative expression level of cfiA mRNA and phenotypic carbapenem resistance was observed.
Carbapenem-resistant B. fragilis isolates carried a low frequency of virulence-related genes and showed weaker biofilm formation ability compared with carbapenem-sensitive B. fragilis isolates. CfiA was the dominant mediator of carbapenem resistance in B. fragilis. This study was the first to identify the structural plasticity of the cfiA-IS element, emphasizing the diverse and complex evolution of carbapenem resistance in B. fragilis, which warrants further investigation.
近年来，耐碳青霉烯类脆弱拟杆菌菌株频繁出现。在中国，关于这些耐药厌氧菌的基因型和表型特征的数据很少。因此，本研究的目的是使用全基因组测序（WGS）、表型药敏试验和生物膜形成试验，对从中国一家三级医院收集的耐碳青霉烯类脆弱拟杆菌临床分离株进行特征分析。
我们分析了49株具有不同耐药谱的脆弱拟杆菌菌株。采用琼脂稀释法测定药敏性，采用结晶紫法测定生物膜形成。使用WGS分析基因组特征，并使用定量逆转录聚合酶链反应（PCR）测定负责碳青霉烯耐药性的cfiA的转录水平。以碳青霉烯敏感分离株作为对照。
49株脆弱拟杆菌分离株均为生物膜产生菌，耐碳青霉烯类分离株的比例为42.86%（21/49）。耐碳青霉烯类且具有中度至强生物膜产生能力的分离株比例显著低于碳青霉烯敏感分离株（19.1%对88.9%，p<0.01）。耐碳青霉烯类脆弱拟杆菌分离株均未携带bft。相比之下，53.6%（15/28）的碳青霉烯敏感分离株携带bft，且均为fpn(+)。所有耐碳青霉烯类分离株（21/21，100%）均含有cfiA及其上游插入序列（IS）元件。三株分离株（BF058、BF059和BF060）携带IS613元件，其并非紧邻cfiA上游，而是被一个编码vatD的1000 kb序列隔开。定量PCR检测结果显示，耐碳青霉烯类分离株中cfiA mRNA表达升高，尽管各分离株的相对表达水平差异很大。然而，观察到cfiA mRNA的相对表达水平与表型碳青霉烯耐药性之间存在显著相关性。
与碳青霉烯敏感脆弱拟杆菌分离株相比，耐碳青霉烯类脆弱拟杆菌分离株携带毒力相关基因的频率较低，生物膜形成能力较弱。CfiA是脆弱拟杆菌中碳青霉烯耐药性的主要介导因子。本研究首次确定了cfiA-IS元件的结构可塑性，强调了脆弱拟杆菌中碳青霉烯耐药性的多样和复杂进化，这值得进一步研究。
