Rapid test for Campylobacter species

Oxoid has introduced a rapid colorimetric test for the differentiation of Campylobacter, Helicobacter and Arcobacter species from other bacteria growing on solid culture media. OBIS campy is a simple two-test procedure that determines both Gram status and the presence or absence of L-alanyl aminopeptidase (L-ALA) activity within 2 mins.

Campylobacter species are often difficult to differentiate from other bacteria, even when grown on selective media and in micro-aerobic conditions. They can often present polymorphic colonial characteristics and other micro-organisms with similar morphology may also be present - these can often be mistakenly identified as presumptive Campylobacter species. OBIS campy was developed to overcome these difficulties by screening for Gram status and L-ALA activity. Unlike other Gram-negative micro-organisms, Campylobacteraceae do not possess L-ALA.

OBIS campy is quick and easy to perform. Gram status is quickly determined by performing a Gram-lysis test on a glass slide with sodium hydroxide. Suspect colonies are then subjected to the L-ALA test by spreading across a reaction zone on the OBIS campy card. Each reaction zone of the card is impregnated with L-ALA substrate. If L-ALA activity is present, this substrate is hydrolysed and a strong purple reaction is produced on addition of a colour developer. This indicates that the test is negative for Campylobacter, Helicobacter or Arcobacter species. No colour reaction indicates the absence of L-ALA activity and the test can be considered as presumptive positive.

In trials, OBIS campy has proven to be accurate and reliable in the differentiation of Campylobacteraceae from other microorganisms, demonstrating a sensitivity of 100% and a specificity of 99.6%.