投稿分類 微生物

主委發表種類: 壁報

投稿標題(中): 從外部能力試驗的結果暗示VITEK®2系統中piperacillin-tazobactam藥物敏感性測試結果可能存在的系統性錯誤

投稿標題(英): A System Error of Antimicrobial Susceptibility Testing In VITEK®2 System Was Found During an External Proficiency Testing Survey of College of American Pathologists

投稿摘要: Objective: Participation of proficiency testings (PT) are essential for College of American Pathologists (CAP) or Taiwan Accreditation Foundation (TAF) -accredited laboratories, according to the requests of all common checklist (COM.01000) of CAP and 5.6.3 interlaboratory comparisons of ISO 15189, respectively. During the bacteriology survey (D-B 2018), the D-08 specimen came from a 42-year-old multiple sclerosis patient with infected bed sores over hip wound. The submitted bacteria identification result of this specimen was Alcaligenes faecalis, reported by VITEK®2 system in our routine works. The consensus for correct identification of this organism was the same as our submitted result. The grade result of this Alcaligenes faecalis susceptibility was code 26, an educational challenge. The required actions of this educational challenge code were: Review participant summary report for comparative results and document performance accordingly; evaluation criteria are not established for educational challenges; laboratories should determine their own evaluation criteria approved by their laboratory director for self-evaluation.
During review the susceptibility results report, all results (ceftazidime, gentamicin, amikacin, trimethoprim/sulfamethoxazole, meropenem, cefepime, levofloxacin and colistin) except one (piperacillin-tazobactam) were agree with the results of more than a half participants. The further survey of the inconsistent (piperacillin-tazobactam) result was requested as a nonconformity.

Materials and Methods: The bacteria strain of Alcaligenes faecalis from CAP PT program was re-isolated from stock (GermBank,CMP) in the -70oC refrigerator. The identification of this bacteria strain were repeated again by VITEK®2 system, BD Phoenix™ automated identification and susceptibility testing system and BD™ Bruker MALDI Biotyper™. The antimicrobial susceptibility testing of this bacteria strain were repeated again by VITEK®2 system, BD Phoenix™ automated identification and susceptibility testing system, disk diffusion test (without CLSI/FDA breakpoints) and microdilution test (by Microscan Panels) (MicroScan NM45 ,BECKMAN COULTER).
Results: The results of re-identification of VITEK®2 system, BD Phoenix™ automated identification and susceptibility testing system and BD™ Bruker MALDI Biotyper™ were all Alcaligenes faecalis, the same as each other. However the susceptibility test results of piperacillin-tazobactam MIC were still resistant in VITEK®2 system (MIC ≧128 ) but susceptible in others (MIC ≦4, in BD Phoenix™ automated identification and Microscan microdilution Panels, respectively). Although without CLSI breakpoints, disk diffusion showed significant inhibition zones (29 mm) and could be interpreted as susceptible by the zone diameter breakpoints of Pseudomonas aeruginosa.

Conclusions: According to the performance characteristics of VITEK®2 systems Product Information (p. 10-6, Table 127, 2013), the category agreement of piperacillin-tazobactam for Gr (-) antimicrobial susceptibility testing were 93.2% (with 0.9 very major error). There was no essential agreement data due to test contains less than five discrete concentrations. Besides, in the insert pages of VITEK®2 gram negative antimicrobial susceptibility testing (AST) cards (AST-N276 9304719 696), there was limitations for the piperacillin-tazobactam susceptibility result of Pseudomonas aeruginosa and perform an alternative method of testing prior to reporting results when a resistant result is obtained. During the review of external PT, we found there might be piperacillin-tazobactam susceptibility testing problems for Alcaligenes faecalis in VITEK®2 system. Further investigation of piperacillin-tazobactam susceptibility testing performance for other clinical Alcaligenes faecalis isolates (even other non-Enterobacteriaceae Gram negative bacteria) in VITEK®2 system might be necessary to clarify this problem.

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