High prevalence of cfiA positive Bacteroides fragilis isolates collected at a teaching hospital in Hohhot, China

In China and several other countries, systematic surveillance data on drug resistance in anaerobes is limited due to challenges in routine anaerobic bacteriology in laboratories, particularly detection of phenotypic resistance [1]. However, according to some reports [2,3], the severity of drug resistance in anaerobes has been underestimated in China. Thus, there is a need to clarify this issue, especially for common anaerobic bacteria such as Bacteroides fragilis.

B. fragilis is a strictly anaerobic bacterium and is the most frequently isolated gram-negative anaerobic bacterium in multiple invasive infections [4,5]. Carbapenems are an effective agent for treating B. fragilis infections, but the emergence of carbapenem resistance in this species create a difficult situation for clinicians. The carbapenem resistance of B. fragilis isolates is mainly due to the presence of cfiA, which encodes metallo-β-lactamase (MBL). cfiA-positive strains usually exhibit an extensive range of resistance to almost all anti-anaerobic β-lactams [6]. In B. fragilis, cfiA is usually located close to its upstream IS element, which acts as a promoter to drive the transcription of cfiA gene [7]. Although few studies have reported a potential non-cfiA mediated carbapenem resistance mechanism in B. fragilis [2,8], the involvement of cfiA is still the dominant mechanism. Cordovana et al. [9] proved that cifA-positive B. fragilis isolates consistently showed carbapenemase activity regardless of their minimum inhibitory concentration (MIC) for carbapenems, which emphasizes the importance of cfiA in mediating carbapenem resistance in B. fragilis.

Early and rapid detection of B. fragilis infection and its antibiotic resistance phenotype is crucial for selecting appropriate antibiotic treatment that directly affects the disease outcome. In the field of clinical microbiology, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI–TOF MS) is an efficient tool in identification of anaerobic bacteria including B. fragilis and detection of its most important antibiotic resistance [9]. This technique is commonly used for accurately classifying B. fragilis strains as division I (cfiA-negative) and II (cfiA-positive) based on their characteristic mass spectra [10,11]. Some characteristic peak shifts (4711 → 4688 Da, 4817 → 4826 Da, 5017 → 5002 Da, 5204 → 5189 Da, and 5268 → 5282 Da) from division I to II strains were reported [10], but it remains unclear whether the characteristic spectra and peak shifts varied among isolates from various sources. Meanwhile, little is known about the specific mass spectra of B. fragilis isolates collected from China.

In this study, we investigated the prevalence of cfiA among B. fragilis clinical isolates collected from a 3000-bed tertiary hospital in China and explored the molecular mechanism underlying their carbapenem resistance. We also analyzed the performance of characteristic mass spectra in discriminating cfiA-positive B. fragilis isolates.

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