Antimicrobial susceptibility of Bacteroides fragilis group organisms in Hong Kong, 2020-2021

Comparison of disc diffusion and Sensititre® Broth Microdilution methods for antimicrobial susceptibility testing of Bacteroides fragilis group clinical isolates following the French guidelines

OBJECTIVES

This study aims to evaluate the concordance between the disc diffusion test (DDT) and custom-designed Sensititre® Broth Microdilution plates and to estimate their respective sensitivity and specificity for antimicrobial susceptibility testing (AST) of Bacteroides fragilis group (BFG) clinical isolates.

METHODS

AST was performed on 126 BFG isolates using both DDT and Sensititre® methods according to the 2024 CA-SFM guidelines. Cohen's kappa coefficients were used to assess concordance, while a Bayesian approach estimated sensitivity and specificity with 95 % confidence intervals (95 % CIs) for amoxicillin-clavulanate (AMC), piperacillin-tazobactam (PTZ), imipenem (IPM), clindamycin (CLI), metronidazole (MTR), and moxifloxacin (MXF).

RESULTS

Cohen's kappa coefficients with 95 % CIs for AMC, PTZ, IPM, CLI, MTR, and MXF were 0.92 (0.85-1.00), 0.70 (0.56-0.83), 0.96 (0.92-1.00), 0.98 (0.94-1.00), 0.96 (0.89-1.00), and 0.70 (0.58-0.82), respectively. DDT demonstrated sensitivity > 0.8 for all antibiotics, and specificity > 0.8 except for PTZ (0.51; 0.37-0.65) and CLI (0.71; 0.58-0.82). Sensititre® exhibited sensitivity > 0.9 for all antibiotics except for PTZ (0.86; 0.70-0.99), and specificity > 0.9 except for MXF (0.88; 0.75-0.99).

CONCLUSIONS

DDT and Sensititre® Broth Microdilution demonstrated strong concordance for most antibiotics. Predictive values estimated using Bayesian model showed that Sensititre® offered the highest overall sensitivity and specificity.

Clinical Outcomes and Molecular Characteristics of Bacteroides fragilis Infections

Bacteroides fragilis is the most common opportunistic anaerobic pathogen. In the absence of appropriate antimicrobial therapy, mortality rates associated with B. fragilis group infections can reach as high as 50%. Therefore, we aimed to elucidate the clinical characteristics and outcomes of B. fragilis infections and the molecular genetic characteristics of B. fragilis isolates. Forty B. fragilis clinical isolates were collected at Hanyang University Hospital between January 2022 and December 2023. Antimicrobial susceptibility was tested using the agar dilution method. Whole-genome sequencing was conducted using the Illumina platform (Illumina, San Diego, CA, USA). Various multilocus sequence types of B. fragilis were identified, including ST149 (N=4), ST11 (N=4), ST1 (N=3), ST21 (N=2), and ST157 (N=1). The insertion sequence (IS) IS1187, located upstream of cfiA, was associated with high-level carbapenem resistance in the ST157 isolate. B. fragilis toxin genes (bft ) were identified in 30% of isolates. The most common comorbidities were diabetes mellitus (26.5%) and non-metastatic cancer (23.5%). Five patients (14.7%) died within 30 days, and two (5.9%) deaths were directly attributable to B. fragilis infection. The emergence of high-level MIC carbapenem-resistant B. fragilis ST157 has led to caution in the presence of B. fragilis infections.

Recent development and fighting strategies for lincosamide antibiotic resistance

SUMMARYLincosamides constitute an important class of antibiotics used against a wide range of pathogens, including methicillin-resistant Staphylococcus aureus. However, due to the misuse of lincosamide and co-selection pressure, the resistance to lincosamide has become a serious concern. It is urgently needed to carefully understand the phenomenon and mechanism of lincosamide resistance to effectively prevent and control lincosamide resistance. To date, six mobile lincosamide resistance classes, including lnu, cfr, erm, vga, lsa, and sal, have been identified. These lincosamide resistance genes are frequently found on mobile genetic elements (MGEs), such as plasmids, transposons, integrative and conjugative elements, genomic islands, and prophages. Additionally, MGEs harbor the genes that confer resistance not only to antimicrobial agents of other classes but also to metals and biocides. The ultimate purpose of discovering and summarizing bacterial resistance is to prevent, control, and combat resistance effectively. This review highlights four promising strategies, including chemical modification of antibiotics, the development of antimicrobial peptides, the initiation of bacterial self-destruct program, and antimicrobial stewardship, to fight against resistance and safeguard global health.