Evaluation of the inoculation procedure using a 0.25 McFarland standard for the BD Phoenix automated microbiology system.

نویسندگان

  • J-L Donay
  • P Fernandes
  • P H Lagrange
  • J-L Herrmann
چکیده

Rapid bacterial identification (ID) and antimicrobial susceptibility tests (AST) can have a significant impact on the management of infections, especially those caused by antibiotic-resistant bacteria (1, 2, 5). However, these rapid automated methods do not overcome the need for the preparation of a suspension of the organism at a fixed density (0.5 to 0.6 McFarland standard [MF]; 1.5 10 CFU/ml). Subculturing the isolate to obtain the required number of colonies is the usual solution to insufficient numbers of colonies available on primary isolation agar plates, but this equates to a further 24-h delay in completing the test and, in turn, in providing results to the clinician. In these cases, the rapid automated methods offer no time advantage compared to manual methods. In order to overcome this problem, BD, for its Phoenix automated microbiology system, has recently developed new software and a database for ID using a lower inoculation density, a 0.25 MF (7.5 10 CFU/ml) instead of the previously used 0.5 MF, for the inoculation of panels. The new capability to determine ID involves the use of separate ID substrate databases for substrate reactions for each method. The AST inoculation density, 5 10 CFU/ml, is maintained following the procedure with the 0.25 MF by transfer of twice as much ID suspension (50 l instead of 25 l) to the AST broth. We conducted a prospective study over a 1-month period to evaluate and validate the possibility of using the 0.25 MF in our facility. This study compared inoculation with the currently used 0.5 MF, used for 6 years in our laboratory (3), to inoculation with a 0.25 MF for the exact same isolates (Table 1). Accurate ID at the species level was achieved for 95.5% of the isolates by use of the 0.25 MF and for 95.5% of the isolates by use of the 0.5 MF. Ten of 132 clinical isolates (7.3%) had discordant ID results by the two methods (Table 1). No discordant identification results were observed for Staphylococcus aureus and Pseudomonas aeruginosa isolates. Differences between the two ID approaches were not statistically significant. Errors were less than 1.4% among 2,654 performed AST. No very major errors (the method with the 0.25 MF indicating sensitivity and that with the 0.5 MF indicating resistance) were found. Totals of 32 (1.2%) major errors (ME; the method with the 0.25 MF indicating resistance and that with the 0.5 MF indicating sensitivity) and 37 (1.4%) minor errors (mE; the method with the 0.25 MF indicating an intermediate result and that with the 0.5 MF indicating sensitivity or resistance) were obtained (not shown). There were 7 ME and 7 mE for Enterobacteriaceae, 5 ME and 1 mE for staphylococci, 18 ME and 18 mE for Pseudomonaceae (mainly P. aeruginosa), and 2 ME and 11 mE for enterococci. Although we used the inoculation method with a 0.5 MF as the comparative method (which is not truly a reference method), we have 6 years of experience with this system and have confidence in its accuracy for most organism-antibiotic combinations. In addition, we developed several confirmatory tests for some combinations with which the system’s accuracy is weaker (3). The performance of the low-inoculum-density method based on presented results has allowed us to start to use this approach routinely in our laboratory. (Part of this work was presented at the 107th General Meeting of the American Society for Microbiology, Toronto, Ontario, Canada, 21 to 25 May 2007 [4].)

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Performance evaluation of the BD phoenix automated microbiology system in meropenem susceptibility testing of clinical Pseudomonas aeruginosa isolates.

I the management of pseudomonal infections, carbapenems are among the most potent and the last-line of antibiotics. Therefore, reliable in vitro susceptibility testing of the clinical isolates of Pseudomonas aeruginosa (P. aeruginosa) against carbapenems is of paramount importance for the healthcare outcome.1 However, in the post-market evaluations, it has been demonstrated that not all the tes...

متن کامل

Evaluation of the automated phoenix system for potential routine use in the clinical microbiology laboratory.

A comparative study was designed to evaluate the identification (ID) and antimicrobial susceptibility testing (AST) performances of the BD Phoenix Automated Microbiology System (Becton Dickinson Diagnostic Systems [BD], Pont de Claix, France). A total of 305 single clinical isolates were collected, and comparisons were made with routine manual methods in use in our microbiology laboratories. Th...

متن کامل

Evaluation of the BD Phoenix automated microbiology system for identification and antimicrobial susceptibility testing of Enterobacteriaceae.

We evaluated the accuracy of the BD Phoenix system for the identification (ID) and antimicrobial susceptibility testing (AST) of 251 isolates of the family Enterobacteriaceae representing 31 species. Organisms were inoculated onto the Phoenix panel according to the manufacturer's instructions. The results from conventional biochemical tests were used for the reference method for ID. Agar diluti...

متن کامل

Two-center collaborative evaluation of the performance of the BD Phoenix automated microbiology system for identification and antimicrobial susceptibility testing of Enterococcus spp. and Staphylococcus spp.

The performance of the BD Phoenix Automated Microbiology System (BD Diagnostic Systems, Sparks, Md.) was assessed for identification (ID) and antimicrobial susceptibility testing (AST) for the majority of clinically encountered bacterial isolates in a European collaborative two-center trial. A total of 469 bacterial isolates of the genera Staphylococcus (275 isolates), Enterococcus (179 isolate...

متن کامل

KPC screening by updated BD Phoenix and Vitek 2 automated systems.

Current BD Phoenix and Vitek 2 methodologies were assessed as screens for KPC β-lactamases. Using carbapenem MICs or expert system interpretations as screens, both systems exhibited high (97%) sensitivity in tests with 103 well-characterized Gram-negative isolates, 77 of which were KPC producers.

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:
  • Journal of clinical microbiology

دوره 45 12  شماره 

صفحات  -

تاریخ انتشار 2007