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Novel test speeds diagnosis of multi-resistant hospital pathogens

A team of researchers at the University of Cologne's faculty of medicine and the German Centre for Infection Research (DZIF) has achieved a scientific breakthrough in the accelerated diagnosis of multi-resistant hospital pathogens. Using a novel immuno-chromatographic method, the researchers detected bacteria that are resistant to the antibiotic group carbapenemes within 20 to 45 minutes from blood cultures with 100% certainty. Current test procedures still take up to 72 hours.

Patients with bloodstream infections caused by gram-negative pathogens such as Escherichia coli (E. coli) have a high mortality rate. However, the infection has so far usually been treatable with antibiotics. But due to the increased antibiotic resistance of bacteria, also against the group of carbapenems, therapy has become increasingly difficult. Infections with multi-resistant pathogens that are also resistant to such 'reserve antibiotics' often lead to ineffective antibiotic therapy and thus to higher mortality.

In order to detect pathogens such as E. coli in the bloodstream, methods are currently being used that take 16 to 72 hours to detect antibiotic resistance. Accelerated diagnostics is therefore an essential step in treating patients with infections caused by carbapenem-resistant bacteria faster and more specifically, and in curbing the spread of the pathogens. The resistance of gram-negative bacteria is usually caused by enzymes that can destroy antibiotics, including carbapenem antibiotics.

They are known as carbapenemases. The most common carbapenemases worldwide are Klebsiella pneumoniae carbapenemase (KPC), New Delhi metallo-betalactamase (NDM) and OXA-48. The present study examined blood samples mixed with carbapenemase-producing bacteria.

Three of the four most common carbapenemases – OXA-48, KPC and NDM – were discovered directly from positive blood cultures using a single test procedure without the need for time-consuming further cultivation on agar plates. The new method is fast, easy to use, inexpensive (approximately €10 per test) and can be performed in any clinical microbiology laboratory.

“With this procedure, we have come a giant step closer to our goal of being able to help patients infected with multi-resistant pathogens as quickly as possible”, said the lead author of the study, Professor Axel Hamprecht from the German Centre for Infection Research and the Institute for Medical Microbiology, Immunology and Hygiene at Cologne University Hospital. “In the case of the aggressive pathogens we are confronted with, every minute counts in order to start a targeted therapy. We now have to conduct follow-up studies in order to transfer our findings into clinical practice as quickly as possible.”

The proof-of-principle study, which is funded by the University of Cologne's faculty of medicine, proves the safety and efficacy of the new method. However, before the new method can replace conventional diagnostics and be introduced into clinical practice, further studies will be necessary.

Bloodstream infections caused by carbapenemase-producing Enterobacteriaceae (CPE) are associated with treatment failure and increased mortality. Detection of CPE from blood cultures (BC) by standard methods takes 16–72 hours, which can delay the initiation of appropriate antimicrobial therapy and compromise patient outcome. In the present study, we developed and evaluated a new method for the rapid detection of carbapenemases directly from positive BC using a new multiplex immunochromatographic test (ICT). The new ICT was assessed using 170 molecularly characterized Enterobacteriaceae clinical isolates including 126 CPE (OXA-48-like (N = 79), KPC (N = 18) and NDM (N = 29)). After spiking with bacteria and incubation in a BC system, blood from positive BC bottles was hemolyzed, bacteria concentrated by centrifugation and lysed. The lysate was transferred to the RESIST-3 O.K.N. ICT (Coris BioConcept, Gembloux, Belgium), which detects OXA-48-like, KPC and NDM carbapenemases. The final results of the ICT were read when they became positive, at the latest after 15 min. All CPE isolates (126/126) were correctly detected with the new protocol (100% sensitivity, 100% specificity). There was perfect concordance between ICT results and molecular characterization. Total time to result was 20–45 min.
Conclusions: This proof-of-principle study demonstrates that with the newly developed method, OXA-48-like, KPC and NDM carbapenemases can be reliably detected directly from positive BC bottles. The new method is more rapid than other currently available assays and can be performed in any routine microbiology laboratory. This can help to rapidly identify patients with CPE BSI and optimize the management of patients with these difficult-to-treat infections. Further studies are needed to assess the performance of the ICT in routine diagnostics.

Axel Hamprecht, Jörg Janne Vehreschild, Harald Seifert, Ahmad Saleh

[link url=""]University of Cologne material[/link]
[link url=""]PLOS One abstract[/link]

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