Question

Both blood and urine cultures are positive for an oxidase-negative, gram negative rod that is colorless on MacConkey's agar. Bichemical reactions include the following:

H2S: negative

Indole: Negative

Citrate: Positive

Phenylalanine deaminase: Negative

DNase: positive

Arabinose: alkaline

Rhamnose: alkaline

Lysine decarboxylase: Positive

Ornithine decarboxylase: Positive

What is the identity of this microbe?

Answer 1

From the biochemical reactions stated, the microbe identified as all the members belonging to the family Enterobacteriaceae. They are most commonly encountered organisms isolated from clinical specimens. These microbes are Gram-negative bacilli or coccobacilli/Rods, Lactose (Sugar) fermenters, capable of reducing nitrate to nitrite, grow on MAC (MacConkey's agar) plates, motile by peritrichous flagella, catalase positive and oxidase negative. Many are normal flora of the intestinal tract of humans and animals while others infect the intestinal tract. Some of the more common clinically important genera of the family Enterobacteriaceae includes Salmonella, Citobacter, Morganella, Enterobacter, Shigella, Proteus, Escherichia, Proteus, Klebsiella, Serratia.