Rapid urea broth as an intermediate step in the identification of possible Yersinia spp. isolated from faecal specimens submitted for bacterial culture

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ABSTRACT

Objectives: To investigate the use of a Rapid Urease broth as an intermediate step between isolation and identification of possible Yersinia spp. organisms from faecal bacterial cultures on Yersinia Isolation Agar (YIA).

Methods: Colonies on YIA which were dark red coloured with a transparent border (?bulls-eye') were inoculated into a Rapid Urea Broth and incubated at 35 ± 2°C for 4-24 hours. Organisms which were urease positive following 4 hours of incubation were identified by Biomeriuex Analytical Profile Index (API) testing, organisms which were urease negative following 4 hours of incubation were re-incubated overnight. Organisms which were urease positive following overnight incubation were identified using a RapID ONE.

Results: 105 possible Yersinia spp. isolates from patient specimens were tested, 93 were urea negative (identified as 1 Acinetobacter spp. , 78 Citrobacter spp., three Enterobacter spp., five Escherichia spp., four Pantoea spp., and two Serratia spp.), nine were urea positive following four hours incubation (identified as five Providencia spp., three Yersinia enterocolitica and one Yersinia pseudotuberculosis) and a further three were urease positive following overnight incubation (identified as two Klebsiella spp. and one Serratia spp.).

Conclusions: This study shows that the use of a Rapid Urea Broth for detection of urease activity is a time and cost saving intermediate step in the identification of possible Yersinia spp. isolates from faecal specimens. The urease result is available within four hours enabling identification testing to be performed on the same day; therefore turnaround-times are not affected by introducing this extra step. The projected savings in reagents and staff time led to the implementation of this method at Aotea Pathology Limited, Wellington, in September 2014.

Key words: Yersinia, faeces, rapid urease broth

NZJ Med Lab Sci 2015; 69: 50-52

INTRODUCTION

Yersinia enterocolitica (YE), and to a lesser extent Y. pseudotuberculosis, are the most common causative agents of Yersiniosis, a self-limiting gastrointestinal disease which is transmitted via the faecal oral-route (1-3). Investigation for Yersinia is part of routine investigation for faecal bacterial pathogens at Aotea Pathology Limited, Wellington, New Zealand. Yersinia spp. bacteria are gram-negative, non-spore forming bacilli, smaller than most others in the Enterobacteriaceae family and relatively slower growing (4).

To investigate patient faecal specimens for Yersinia spp. Aotea Pathology utilises Fort Richard Laboratories (NZ) Yersinia...