Urinary tract infection caused by a small colony variant form of capnophilic Escherichia coli leading to misidentification and non-reactions in antimicrobial susceptibility tests

Abstract

Background: Small colony and capnophilic variant cases have been separately reported, but there has been no reports of their simultaneous presence in one isolate. We report a case of Escherichia coli with coexpressed small colony and capnophilic phenotypes causing misidentification in automated biochemical kits and non-reactions in antimicrobial susceptibility test cards.

Case presentation: An 86-year-old woman developed urinary tract infection from a strain of Escherichia coli with SCV and capnophilic phenotypes in co-existence. This strain did not grow without the presence of CO2, and therefore proper identification from automated system was not possible. 16 s rRNA sequencing and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was able to identify the bacteria.

Conclusion: As these strains do not grow on culture parameters defined by CLSI or on automated systems, proper identification using alternative methods are necessary.