Investigation of relationship between serotype/biotype of Yersinia enterocolitica and colony morphology on selective agar

Abstract

Yersinia enterocolitica is a non-lactose-fermenting bacterium that forms colorless transparent colonies on Salmonella–Shigella (SS) agar. In 2016, lactose-fermenting Y. enterocolitica obtained from the stools of a patient with ileocecal inflammation and isolated on SS agar was confirmed by mass spectrometry. On the basis of the findings of a previous study, the bacterial species of small colonies that ferment lactose on SS agar were identified by fecal culture tests of patients presenting with clinical symptoms; as a result, five strains of Y. enterocolitica were detected. Five strains that fermented lactose on SS agar were identified as serotype O3, biotype 3, and Voges-Proskauer (VP)-reaction-negative, including three strains that were sucrose-fermenting-positive and two strains that were sucrose-fermenting-negative. VP-reaction-negative strains are difficult to extract and they form lactose-fermenting colonies on SS agar. Yersinia-selective medium should be added in routine methods when finding VP-reaction-negative strain.