Heekang Choi, Daewon Kim, Mijung Kwon, Jung-Hyun Byun, Bonghwan Jin, Ki-Ho Hong, Hyukmin Lee, Dongeun Yong
Ann Clin Microbiol 2022 December, 25(4):109-118. Published on 20 December 2022.
Background: Rapid antimicrobial susceptibility testing (RAST) is important for the appropriate treatment of bloodstream infections. The QMAC-dRAST system (QuantaMatrix Inc., Korea) can directly perform RAST using positive blood culture samples with microscopic imaging. This study aimed to evaluate the performance of the QMAC-dRAST system for AmpCβ-lactamase-producing Enterobacterales.
Methods: Eighty isolates (20 Morganella morganii, 20 Serratia marcescens, 10 Klebsiella aerogenes, 10 Enterobacter cloacae, and 20 Citrobacter freundii) and 14 antimicrobial agents were included in the antimicrobial susceptibility testing (AST). The performance of the QMAC-dRAST system was evaluated by simulating the clinical blood culturing process. We conducted a comparative evaluation of the QMAC-dRAST and Vitek 2 systems (bioMérieux Inc., France). Broth microdilution tests were performed as the reference method to resolve any discrepancies in the AST results between the two systems.
Results: For 20 M. morganii and 20 S. marcescens, the categorical agreement (CA) between the QMAC-dRAST and Vitek 2 systems increased from 55.4% to 83.8% after AST algorithm optimization. Moreover, the discrepancy rates decreased as follows: from 19.1% to 5.4% very major errors (VME), from 38.3% to 4.3% major errors (ME), and from 14.6% to 12.1% minor errors (mE) for the QMAC-dRAST system compared to the Vitek 2 system. For all 80 tested isolates, the QMAC-dRAST system showed 93.0% CA, 1.7% VME, 2.3% ME, and 4.9% mE.
Conclusion: The QMAC-dRAST system was comparable to the Vitek 2 system after AST algorithm optimization for AmpC β-lactamase-producers, which are major pathogens and require time to express the enzyme. However, further modifications of the AST algorithm are still warranted.
Hyunsoo Kim, Young Ah Kim, Young Hee Seo, Hyukmin Lee, Kyungwon Lee
Ann Clin Microbiol 2022 December, 25(4):119-124. Published on 20 December 2022.
Background: The application of genotypic antimicrobial sensitivity tests (ASTs) is dependent on the reliability of the predictions of phenotypic resistance. In this study, routine AST results and the presence of corresponding antimicrobial resistance genes were compared.
Methods: Eighty-four extended-spectrum-β-lactamase-producing Escherichia coli isolates from poultry-related samples were included in the study. The disk diffusion method was used to test for susceptibility to antimicrobial compounds, except colistin susceptibility, which was tested using the agar dilution method. Whole-genome sequencing (WGS) was performed using a NextSeq 550 instrument (Illumina, USA). Antimicrobial resistance genes were detected using ResFinder 4.1.
Results: Concordance rates between the genotype and phenotype ranged from 35.7% (ciprofloxacin) to 96.4% (tetracycline). The presence of tet was a good predictor of phenotypic resistance.
Conclusion: The genotype was a good predictor of tetracycline phenotypic resistance, but there was a gap in the prediction of phenotypic ASTs for trimethoprim-sulfamethoxazole, chloramphenicol, gentamicin, and ciprofloxacin. We concluded that WGS-based genotypic ASTs are inadequate to replace routine phenotypic ASTs.
Choon-Mee Kim, Young-Jin Ko, Ji Ae Choi, Seong-Ho Kang, Geon Park, Sook-Jin Jang
Ann Clin Microbiol 2022 December, 25(4):125-136. Published on 20 December 2022.
Background: To solve the difficulty in determining the appropriate treatment regimen for patients infected with extensively drug-resistant Acinetobacter baumannii (XDRAB), it is necessary to develop various strategies to increase the therapeutic effect of antimicrobial agents. The purpose of this study was to select the treatment combination showing the greatest antimicrobial effect among seven candidate antimicrobial substances.
Methods: Seven strains of XDRAB were used in this study. The composition of the treatment consisted of colistin as the base and one of the seven antimicrobial substances, doripenem, minocycline, tigecycline, linezolid, fusidic acid, vancomycin, or alyteserin E4K peptide. The interaction between the drugs in each combination was evaluated by measuring the synergy rates using time-kill analysis.
Results: The synergy rates of the seven combinations tested in the time-kill assay in this study were as follows, in descending order from the combination with the highest synergy rate: colistin + minocycline (57.1%), colistin + alyteserin E4K (50.0%), colistin + tigecycline (42.9%), colistin + vancomycin (28.6%), colistin + doripenem (14.3%), colistin + fusidic acid (14.3%), and colistin + linzolid (0%). None of the combinations showed antagonism. The three combinations showing bactericidal activity and the rates of their bactericidal activity were colistin + alyteserin E4K combination (33.3%), colistin + minocycline (14.3%), and colistin + vancomycin (14.3%).
Conclusion: The colistin + minocycline and colistin + alyteserin E4K treatment combinations, which showed high synergy rates, can be considered as promising candidates for future in vivo experiments evaluating combination therapies.
[in Korean]
Young Ah Kim, Seok Hoon Jeong, Jong Hee Shin, Kyeong Seob Shin, Jeong Hwan Shin, Young Ree Kim, Hyun Soo Kim, Young Uh, Nam Hee Ryoo
Ann Clin Microbiol 2022 December, 25(4):137-145. Published on 20 December 2022.
Background: We compared the antimicrobial resistance rates (AMRs) of major glucose non-fermenting gram-negative bacilli, Acinetobacter baumannii and Pseudomonas aeruginosa, under different clinical conditions. The purpose of the study was to provide useful background data to set up infection control strategies for infection-vulnerable patients.
Methods: The AMRs of blood isolates were compared in various clinical conditions, using data from the Antimicrobial Resistance Surveillance System in Korea.
Results: A. baumannii blood isolates from patients with healthcare-associated infections, inpatients, or intensive care unit (ICU)-admitted patients consistently exhibited higher AMRs to most antimicrobials, except minocycline, tigecycline, and colistin, compared with those from patients with community-acquired infections, outpatients, or non-ICU-admitted patients, respectively. P. aeruginosa blood isolates from patients with healthcare-associated infections showed higher AMRs to most antimicrobials, except ceftazidime and aztreonam, compared with those from patients with community-acquired infections, but not compared to those from inpatients or ICU-admitted patients.
Conclusion: Higher AMRs were associated with A. baumannii bloodstream infections under various clinical conditions, such as healthcare-associated infections and infections in inpatients and ICU-admitted patients. Considering the high AMRs and the limited number of treatment options of A. baumannii, vigorous efforts should be used to prevent the spreading of A. baumannii infections in patients with vulnerable conditions.
Wee Gyo Lee, Joon Kim, Seung Soo Shin, Ji Won Park
Ann Clin Microbiol 2022 December, 25(4):147-154. Published on 20 December 2022.
Background: Rapid detection of the causative agents is essential for determining the appropriate treatment for patients with lower respiratory tract infections. We evaluated the performance of the Biofire FilmArray pneumonia panel (FA-PE; BioFire Diagnostics, USA) in the identification of bacterial pathogens and antibiotic resistance genes in endotracheal aspirate specimens.
Methods: A total of 43 non-duplicated endotracheal aspirates were included in this study. The performance of the FA-PE was assessed using the routine culture method as the reference standard.
Results: The FA-PE demonstrated 92.9% sensitivity and 79.3% specificity for the identification of 15 bacterial targets compared to routine bacterial culture. Four antimicrobial resistance genes in 43 specimens were detected by the FA-PE. The most frequently detected resistance genes were mecA/C and SCCmec in three specimens, followed by CTX-M in one specimen.
Conclusion: The FA-PE offers a rapid diagnostic method for lower respiratory tract infections. It may be useful at the early stage of pneumonia, before routine culture and antimicrobial susceptibility results are available.
[in Korean]
Hyun Jin Kim, Sungmin Kym, Qute Choi
Ann Clin Microbiol 2022 December, 25(4):155-160. Published on 20 December 2022.
Gemella sanguinis is a gram-positive, facultatively anaerobic coccus bacterium that has rarely been reported as a cause of infective endocarditis. A 41-year-old male patient with mitral valve prolapse visited the outpatient clinic presenting with fever. Transthoracic echocardiography and transesophageal echocardiography revealed myxomatous change and vegetation of the mitral valve. We isolated G. sanguinis from the patient’s blood, cultured it in both aerobic and anaerobic blood culture bottles, and identified it using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS; bioMérieux, France) and 16s rRNA sequencing. The isolated G. sanguinis was highly susceptible to penicillin and vancomycin and intermediately susceptible to erythromycin, clindamycin, and levofloxacin. Following the American Heart Association recommendations, this highly penicillin-sensitive isolate was eradicated with ceftriaxone and gentamicin, and the patient recovered and was discharged. To the best of our knowledge, this is the first reported case in Korea where G. sanguinis, the causative agent of endocarditis, was identified using MALDI-TOF MS and 16s rRNA sequencing and was treated with only antibiotics and without surgical valve replacement.
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