Improving detection of extended-spectrum beta-lactamase-producing bacteria in a deployed setting.

Introduction: Organisms that produce extended-spectrum beta-lactamase (ESBL) are significant causes of infection among deployed service members. These specific organisms have increased resistance to several antibiotics, limiting the choice of therapy for the provider. Currently, the deployed microbiology lab uses, by default, the Siemens NBPC30 panel to identify and measure antibiotic susceptibility of gram-negative organisms. However, when an ESBL is suspected, additional confirmatory testing is performed, during which time the health care provider is forced to use broad spectrum antibiotics to protect the patient from infection. In this study, we evaluated the NBPC30 and NBC41 panels for their ability to rapidly and accurately detect ESBL-producing organisms.

Methods: Identification and antimicrobial susceptibility testing of 79 strains of Enterobacteriaceae isolated from patients treated at Ibn Sina tertiary hospital (Baghdad) were performed using the NBPC30 and NBC41 panels. These results were confirmed using a Kirby-Bauer disk diffusion reference method described by the Clinical Laboratory Standards Institute. Sensitivities and specificities of the panels were determined in relation to this reference method.

Results: Sensitivity and specificity of the NBC41 were 96.7% and 89%, while they were 86.7% and 72% for the NBPC30 panel. False positive and false negative rates were higher for the NBPC30 panel.

Conclusion: Our data shows that the NBC41 panel is superior to the NBPC30 panel in rapidly identifying ESBL-producing organisms. Use of the NBPC41 panel decreases the turnaround time by 24 hours, allowing the provider to more accurately apply appropriate antibiotic therapy. Additionally, the NBPC41 panel provides more useful antibiotic susceptibility results compared to the NBPC30. We recommend use of this panel as a primary identification and susceptibility panel for gram-negative organisms.