This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Microbiology
All are true about listeria except 
Select and explain. 
A. Gram positive, B. PALCAM agar is used for isolation, C. Characteristic tumbling motility at 37degC, D. Umbrella shaped growth
C: Characteristic tumbling motility at 37degC
Answer: C: Characteristic tumbling motility at 37degC 
Explanation: L. monocytogenes is a gram-positive&; coccobacillus&;(coccoid rod) with a tendency to occur in chains. Peritrichous flagella are produced by the bacillus optimally at 20-30degC but only scantily or not at all at 37degC Culture media used for isolation are blood agar, chocolate agar, and PALCAM agar. It grows on ordinary media within a temperature range of 1deg to 45degC. Most cases of human disease are caused by serotypes 1/2a, 1/2b and 4b. The organism can be found as a pa of the gastrointestinal flora in healthy individuals. Human disease due to L. monocytogenes generally occurs in the setting of pregnancy or immunosuppression REF : ananthanarayana 10th ed