Accuracy of identification and susceptibility results by direct inoculation of Vitek 2 cards from positive BACTEC cultures

Abstract

Rapid identification of bacteria and prompt acquisition of susceptibility results are valuable for patient care. The objective of the present study was to determine the accuracy of direct inoculation of Vitek 2 cards from positive BACTEC cultures compared to inoculation of the cards from subculture plates. Positive BACTEC cultures sampled between March 2001 and June 2002 were included. The results of direct inoculation were compared with the results of inoculation of Vitek 2 cards from subcultures. Of 161 gram-negative bacilli, 129 (80%) were correctly identified by direct inoculation compared to 145 of 161 (90%) by subculture. Susceptibility testing was performed on 2,862 antibiotic-isolate combinations. The essential agreement was 98.7%. The number of very major, major, and minor errors was 1 (0.2% of resistant strains), 1 (0.04% of susceptible strains), and 68, respectively. Direct identification of Staphylococcus spp. was not performed, but antimicrobial susceptibility was tested using 6,042 antibiotic-isolate combinations. The essential agreement was 95.2%. The number of very major, major, and minor errors was 73 (4.5% of resistant strains), 32 (0.8% of susceptible strains), and 106, respectively. Eighty-four percent of the very major errors occurred with trimethoprim-sulfamethoxazole. The results show that direct inoculation of Vitek cards is valuable as a rapid routine method for identification and susceptibility testing of gram-negative bacilli. For Staphylococcus spp., the susceptibility results obtained after direct inoculation of Vitek 2 cards are also acceptable except for those obtained with trimethoprim-sulfamethoxazole. Susceptibility results for this antibiotic, if obtained using direct inoculation, should not be reported to the clinician.

Evaluation of direct inoculation of the BD PHOENIX system from positive BACTEC blood cultures for both Gram-positive cocci and Gram-negative rods

“…These errors thus would not have clinical consequences. Funke et al [18] also described a categorical agreement of 99.0%, which is comparable with or higher than results from studies on other direct methods of AST [7,13-16,26]. Therefore, we conclude that also for GNR, results of the direct Phoenix method for AST can be used to guide antibiotic therapy in bloodstream infections.…”

“…Other studies that presented results of direct methods for AST of GPC showed variable results [13-16,25,26], which makes comparison difficult. But our results were comparable to those of the routine Phoenix method.…”

“…Lupetti et al showed a lower agreement of 94% for erythromycin as well, but observed no very major errors for trimethoprim-sulfamethoxazole. Some other studies on direct methods for AST showed some very major errors for trimethoprim-sulfamethoxazole [15,16,18], but only Kerremans et al [13] found a very high percentages of very major errors for this antibiotic in GPC, but not in GNR. Therefore, we conclude that the direct Phoenix method using SSTs can be used to reliably report results of AST for GPC, except for trimethoprim-sulfamethoxazole and erythromycin.…”

“…Although this method has been successfully tested for many automated systems [13-17], direct inoculation was reported only twice for the BD Phoenix Automated Microbiology System (BD), once for Gram-negative rods (GNR) [18] and once for Gram-positive cocci (GPC) [19]. Both studies compared their results of the direct method with results of the Vitek system.…”

Evaluación de la susceptibilidad directa desde hemocultivos positivos utilizando el sistema Vitek 2: comparación de dos protocolos rápidos

“…Se eliminó el sobrenadante y se removió el sedimento en la Laboratorio Clínico, Clínica Alemana de Santiago. superficie de gel con una tórula, para resuspenderlo en 2 ml de solución salina 0,45% y ajustarlo a McFarland 0,5-0,63 3 . Las suspensiones obtenidas mediante ambos protocolos fueron cargadas en las tarjetas Vitek 2 AST 249, según instrucciones del fabricante.…”