The species accuracy of the Most Probable Number (MPN) European Union reference method for enumeration of Escherichia coli in marine bivalves

- The European Union method for detection of Escherichia coli in bivalves had a species accuracy of 90%
- 10% were either Klebsiella pneumoniae, K. oxytoca, Citrobacter braakii, Enterobacter cloacae or Acinetobacter baumannii
- Identification by API 20E and MALDI-TOF MS gave similar results for 97% of isolates

Continuous European Union programmes with specified methods for enumeration of Escherichia coli in bivalves for human consumption are currently running. The objective of this research was to examine the species accuracy of the five times three tube Most Probable Number (MPN) EU reference method used for detection of E. coli in marine bivalves. Among 549 samples of bivalves harvested from Norwegian localities during 2014 and 2015, a total number of 200 bacterial isolates were prepared from randomly selected culture-positive bivalves. These presumptive E. coli isolates were characterized biochemically by the Analytical Profile Index (API) 20E, as well as by Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS). The majority of isolates (90%) were identified as E. coli, by both API 20E and MALDI-TOF MS. Ten isolates (5%) were identified as Klebsiella pneumoniae, while one isolate was identified as K. oxytoca by both methods, whereas three isolates were identified as Acinetobacter baumannii, Citrobacter braakii, and Enterobacter cloacae, respectively. The identification of the remaining six isolates were not in compliance between the two methods.