The different biochemical tests are listed in Table 3: Beta galactosidase, arginine hydrolase, lysine decarboxylase
, ornithine decarboxylase test were all negative for all strains.
test: Test tubes with lysine broth were inoculated with pure overnight isolate followed by incubation at 37[degrees]C for 4 days.
The stool sample was inoculated on MacConkey agar (Oxoid, UK) and xylose lysine decarboxylase
agar (XLD) (Oxoid, UK).
The isolates showed positive results for arginine dihydrolase, lysine decarboxylase
, ornithine decarboxylase, citrate utilization and HoS production.
Other tests included the glucuronidase, nitrate reduction, lysine decarboxylase
, orinithine decarboxylase, phenylalanine deamination, arabinose, oxidase and citrate utilization tests.
The biochemical tests showed positive results for O-nitrophenyl- b-D-galactopyranoside, arginine dehydrolyase, lysine decarboxylase
, citrate utilization, indole production, gelatinase and Voges Proskauer.
The strain was unusual because it was negative for the production of lysine decarboxylase
and b-galactosidase (ortho-nitrophenol test) and positive only for stx1.
Organisms are oxidase and ONPG positive, and lysine decarboxylase
The activity of the lysine decarboxylase
enzyme produced by bacteria results in breakdown of lysine and the formation of cadaverine with liberation of C[O.sub.2].
Because some strains of lysine negative Escherichia hermanii will cross react with 0157 sera; we employed the lysine decarboxylase
test on candidate sorbitol nonfermenters and lactose fermenters (8): 13 x 100 mm serology tubes (VWR Scientific, San Francisco, Calif.) of lysine decarboxylase
broth (test group) and decarboxylase base broth (control group) (Difco Laboratories, Detroit, Mich.) were prepared.
In Escherichia coli and some other coliforms, lysine decarboxylase
is encoded by cadA which participates in the decarboxylation of lysine and synthesis of cadaverine .
It was positive for ornithine decarboxylase, gelatinase, reduction of nitrates to nitrites, tolerance to 6% NaCl, and assimilation of caprate and malate, but negative for citrate utilization, arginine dihydrolase, lysine decarboxylase
, urease, indole production, assimilation of mannose, glucose, arabinose, mannitol, maltose, adipate, and acidification of glucose.