Vibrio spp. are naturally occurring marine bacteria that cause vibriosis, often through raw or undercooked seafood consumption. Current methods to isolate food and environmental Vibrio spp. focus on Vibrio parahaemolyticus (Vp) and V. vulnificus (Vv), however, the recent increase in prevalence of vibriosis caused by V. cholerae (Vc), V. alginolyticus (Va), V. fluvialis (Vf), and V. mimicus (Vm) highlights the need to better understand their ecology and prevalence.
This study evaluated the use of commercially available chromogenic agars to isolate and differentiate Vp, Vv, Vc, Va, Vf, and Vm. Up to 50 isolates of each species from both clinical and environmental origin were streaked to CHROMagarTM Vibrio, HardyCHROMTM Vibrio, and Vibrio ChromoSelect Agar. They were also streaked to TCBS, the current standard for vibrio isolation. The phenotypes of well-isolated colonies were observed, and the percentage of isolates with a typical phenotype for each species determined (Table 1).
On TCBS, Vp, Vv, and Vm colonies appeared green; Va appeared large yellow; Vc appeared yellow; and Vf was partially-fully inhibited, but grew yellow-green when present. On CHROMagarTM, Vp colonies appeared mauve; Vv, Vc, and Vm appeared green-blue; Va grew creamy; and Vf colonies ranged from white to light purple. On ChromoSelect, Vp grew blueish-green; Vv, Vc, and Vm grew purple, although Vv was partially-fully inhibited; Va appeared large, blueish-green, and spread; and Vf varied to include both blueish-green and purple pigments. On HardyCHROMTM, Vp grew teal; Vv, Vc, and Vm grew magenta to purple, but the agar around Vv fluoresced under UV light; Va ranged from clear, to clear with teal centers, to completely teal; and Vf grew variably, ranging from white, to colonies with both teal and/or purple pigment.
Vibrio spp. in this study grew a broader range of phenotypes on the chromogenic agars compared to TCBS, which may allow researchers to better differentiate and target species of interest in environmental samples. Preliminary results indicate that the chromogenic agars are also less inhibitory than TCBS (data not shown), and work is currently underway to compare recovery rates among them.