Evaluation of the NDP Test, a Novel Chromogenic Test for Rapid Detection of Extended Spectrum β-Lactamase Producing Enterobacteriaceae

Background: The early detection of extended spectrum β-lactamase (ESBL) producers in clinical microbiology is now of great importance to optimize appropriate therapeutic schemes and to improve the patient outcome. The ESBL NDP (Nordmann/Dortet/Poirel) test has been recently developed for the early detection of ESBL producing organisms. It is based on the biochemical detection of the hydrolysis of the β-lactam ring of cefotaxime (a broad spectrum cephalosporin).

Aims: This study was done to evaluate the performance of NDP test in detection of ESBL producing organism directly from urine samples and blood cultures.

Place and Duration of Study: This is a Seven-months Cross sectional study conducted in Internal Medicine and Medical Microbiology & Immunology departments, Benha University, Egypt.

Methodology: A total of one hundred Gram negative bacterial isolates (60 urine isolates and 40 blood isolates) were tested for ESBL production by ESBL NDP test. All isolates were screened phenotypically for ESBL production with disc diffusion method then confirmed using the double disc synergy test (DDST).Characterization of ESBL encoding genes were done by multiplex PCR.

Results: In total, 39% were confirmed as ESBL positive using the DDST and PCR. The genetic analysis revealed that CTX-M was the most prevalent gene type (71.8%) followed by SHV genes (35.9%) then TEM genes (20.5%).For the detection of ESBL producers directly from urine samples, NDP test had a sensitivity of 90.5%, specificity of 100%, positive predictive value of 100% and negative predictive value of 95%. NDP test had an excellent performance when performed directly on blood culture, it had sensitivity, specificity, positive predictive value and negative predictive value, all of 100 %.

Conclusion: The NDP test is a rapid, sensitive, and specific test that could be introduced in clinical practice.