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

OBJECTIVES: This retrospective study analyzed the susceptibility levels of Bacteroides fragilis group (BFG) in a hospital-based laboratory where disk diffusion test (DDT) was routinely performed. Isolates non-susceptible to imipenem and metronidazole by DDT were further investigated using a gradient method. METHODS: The DDT and MIC susceptibility data of clindamycin, metronidazole, moxifloxacin and imipenem obtained on Brucella blood agar for 1264 non-duplicated isolates during 2020-2021 were analyzed. Species identification was obtained by matrix-assisted laser desorption ionization time-of-flight mass spectrometry and 16S rRNA sequencing. Interpretative agreement of DDT results using the 2015 EUCAST tentative and 2021 CA-SFM breakpoints was compared against MIC as the reference. RESULTS: The dataset included 604 B. fragilis (483 division I, 121 division II isolates), 415 non-fragilis Bacteroides, 177 Phocaeicola and 68 Parabacteroides. Susceptibility rates for clindamycin (22.1-62.1%) and moxifloxacin (59.9-80.9%) were low and many had no inhibition zones. At the EUCAST and CA-SFM breakpoints, 83.0 and 89.4% were imipenem-susceptible, and 89.6% and 97.4 were metronidazole-susceptible. MIC testing confirmed 11.4% and 2.8% isolates as imipenem-non-susceptible and metronidazole-resistant, respectively. Significant numbers of false-susceptibility and/or false-resistance results were observed at the CA-SFM breakpoint but not the EUCAST breakpoint. Higher rates of imipenem and/or metronidazole resistance were detected in B. fragilis division II, B. caccae, B. ovatus, B. salyersiae, B. stercoris and Parabacteroides. Co-resistance to imipenem and metronidazole was detected in 3 B. fragilis division II isolates. CONCLUSIONS: The data demonstrated emerging BFG resistance to several important anti-anaerobic antibiotics and highlights the importance of anaerobic susceptibility testing in clinical laboratories to guide therapy.

Evaluation of a Lateral Flow Immunoassay for Rapid Detection of CTX-M Producers from Blood Cultures.

Bacteremia caused by extended-spectrum ß-lactamases-producing Enterobacterales has increased rapidly and is mainly attributed to CTX-M enzymes. This study aimed to evaluate the NG-Test® CTX-M MULTI lateral flow assay (CTX-M LFA) for rapid detection of CTX-M producers in blood cultures (BCs) positive for Gram-negative bacilli in spiked and clinical BCs. Retrospective testing was performed on BC bottles spiked with a collection of well-characterized Enterobacterales isolates producing CTX-M (n = 15) and CTX-M-like (n = 27) ß-lactamases. Prospective testing of clinical, non-duplicate BCs (n = 350) was performed in two hospital microbiology laboratories from April 2021 to March 2022 following detection of Gram-negative bacilli by microscopic examination. Results were compared against molecular testing as the reference. In the spiked BCs, the CTX-M LFA correctly detected all CTX-M producers including 5 isolates with hybrid CTX-M variants. However, false-positive results were observed for several CTX-M-like ß-lactamases, including OXY-1-3, OXY-2-8, OXY-5-3, FONA-8, -9, -10, 11, 13 and SFO-1. In clinical BCs, the CTX-M LFA showed 100% (95% CI, 96.0-100%) sensitivity and 99.6% (97.9-100%) specificity. In conclusion, this study showed that rapid detection of CTX-M producers in BC broths can be reliably achieved using the CTX-M LFA, thus providing an opportunity for early optimization of antibiotics.

The influence of cell morphology on microfluidic single cell analysis.

Microfluidics has been widely used in single cell analysis. Current protocols allow either spread or round cells to be analyzed. However, the contribution of cell morphology to single cell analysis has not been noted. In this study, four proteins (EGFR, PTEN, pAKT, and pS6) in the EGFR signaling pathway are measured simultaneously using microfluidic image cytometry (MIC) in glioblastoma cells U87. The results show that the MIC technology can reveal different subsets of cells corresponding to the four protein expression levels no matter whether they are round or spread at the time of the measurements. However, sharper distinction is obtained from round cells, which implies that cellular heterogeneity can be better resolved with round cells during in situ protein quantification by imaging cytometry. This study calls attention to the role of cell morphology in single cell analysis. Future studies should examine whether differences in data interpretation resulting from cell morphology could reveal altered biological meanings.