Direct plating on VVA and CPC+ followed by colony hybridization
was utilized to enumerate V. vulnificus from56 oyster samples collected
from May to December, 2007. Estimates obtained using either media
demonstrated similar regional and seasonal trends of total V. vulnificus
levels (Fig. 1). Highest mean levels each season were found in oysters
harvested from the Gulf Coast: 3.05 and 3.15 log CFU/g from May
to Jun, 3.64 and 3.61 log CFU/g from Jul to Sep, and 2.09 and
1.71 log CFU/g fromOct to Dec using VVA and CPC+media, respectively.
Mean levels in Atlantic Coast oysters were 2.73 and 2.23 log CFU/g
from May to Jun, 1.95 and 1.87 log CFU/g from Jul to Sep, and 1.75 and
1.40 log CFU/g fromOct to Dec using VVA and CPC+media, respectively.
Pacific Coast oysters hadmean levels of 1.96 and 0.80 log CFU/g from
May to Jun, 1.37 and 1.42 log CFU/g from Jul to Sep, and 1.60 and
1.60 log CFU/g from Oct to Dec samples from VVA and CPC+ media,
respectively.
Overall, the two plating media (VVA and CPC+) were equivalent
(P = 0.702) for enumeration of total V. vulnificus using DNA colony hybridization.
However, the average total colony count on CPC+ was
3.76 log CFU/g versus 4.35 log CFU/g on VVA, which was a statistically
significant difference (P b 0.001). Additionally, the difference inmedian
ratio of confirmed V. vulnificus to typical colonies on CPC+(75%) versus
VVA (23%) was statistically significant (P b 0.001).
Of the 14 V. vulnificus isolates recovered from direct plating on VVA,
64% were rrnA/vcgE, 14% were rrnB/vcgC, and 21% were vcgE and
untypeable by rrn (Table 1). In comparison, of the 16 isolates recovered
from CPC+, 75% were rrnA/vcgE, 6.3% were rrnB/vcgC, and 18% were