As presented at the 10th European Congress of Clinical Microbiology and Infectious Diseases (ECCMID), May 2000.
Determining Beta-Lactam Resistance among Gram-Negative Isolates in the Phoenix™ Automated Microbiology System. T. WILES, J. HEJNA, M. GOSNELL, C. YU AND V. KENNEDY BD Biosciences • 7 Loveton Circle • Sparks, MD, USA 21152
ABSTRACT
OBJECTIVES: To determine beta-lactam resistance among gram-negative isolates using the Phoenix™ Automated Microbiology System that is currently under development.
METHODS: Phoenix™ susceptibility test results of 210 gram-negative strains that included a challenge set of 110 isolates with known resistance mechanisms and 100 recently acquired clinical isolates were compared to results obtained with a NCCLS recommended Standard Broth Microdilution (SBM) method. Doubling concentrations of ampicillin, amoxicillin, ticarcillin, piperacillin, imipenem and meropenem were tested in both Phoenix™ and SBM.
RESULTS: The overall essential agreement ranged from 91 to 98%. Categorical agreement was from 95 to 100%. OBJECTIVES One very major error was observed with ticarcillin (1%) The beta-lactams are the most utilized and diverse class of all antimicrobial agents. The action of beta-lactams is to inhibit and one with piperacillin (1.3%). No other very major D-alanyl-D-alanine transpeptidase activity by forming stable errors were observed. The major error rates were as follows: esters with the opened lactam ring attached to the –OH group of the enzyme target site. Resistance to beta-lactams in gram- ampicillin (2.1%), amoxicillin (2.5%), ticarcillin (4.0%), negative organisms is often mediated by reduced outer piperacillin (3.1%), imipenem (0.6%) and meropenem (0%). membrane permeability or the production of beta-lactamases. The emergence of antimicrobial resistance among gram-negative CONCLUSIONS: The observations in this study indicate an bacteria, especially high-level resistance to more extended acceptable level of performance in the detection of gram- spectrum beta-lactams, has been reported. The reliable and rapid detection of gram-negative bacterial resistance to beta-lactams is negative resistance to the beta-lactam antibiotics. paramount to a successful therapeutic outcome. The Phoenix™ Automated Microbiology System (BD Biosciences, Sparks, MD, USA) (product currently under Very Major Major development) is intended for the rapid and automated Antibiotic Name n EA % CA % % (n) % (n) identification and susceptibility testing of clinically relevant Aminopenicillins Ampicillin 159 98 97 0 (0) 2.1 (1) bacteria. The emergence of antimicrobial resistance among Amoxicillin 170 95 97 0 (0) 2.5 (1) gram-negative bacteria, especially in species that are frequently Carboxypenicillin isolated from clinical specimens, has placed the emphasis on the Ticarcillin 181 91 95 1.0 (1) 4.0 (3) speed and reliability of automated systems. In the past two Acylureidopenicillin decades, laboratory automation in identification and Piperacillin 184 95 96 1.3 (1) 3.1 (3) susceptibility testing has become more acceptable and allows Carbapenems clinical laboratories to report results with a high degree Imipenem 192 92 99 0 (0) 0.6 (1) of consistency. Meropenem 190 98 100 0 (0) 0 (0) This evaluation investigated the performance of the Phoenix™ System in detecting recognized beta-lactam resistance mechanisms in gram-negative bacteria. The overall performance was based on the accuracy of susceptibility test results generated by the Phoenix™ System as compared to results using the NCCLS recommended test procedures. METHODS