A laboratory assistant that works with mice recently noticed that their lymph nodes were swollen and that they had a lesion on their hand that was not there a few weeks ago. The lymph node tis-sue is sent to the laboratory for culture. The laboratory technologist noticed on the stained sample that there was an organism present that resembled a spiral, gram negative with flagella. The cultures

Question

grew no organisms. What is the most likely cause for the discrepancy?

a. The laboratory technologist misidentified the stain artifact as an organism.
b. The laboratory technologist did not culture the sample to media.
c. The organism is not able to grow on media and requires another method for iden-tification.
d. The organism was not allowed to incubate long enough.

Answer 1

C
S. minus causes rat-bite fever in humans and is referred to as sodoku. Specimens commonly submitted for diagnosis of sodoku include blood, exudate, or lymph node tissues. S. minus cannot be grown on synthetic media and appears as a thick, spiral, gram-negative organism with two or three coils and polytrichous polar flagella. Direct visualization of characteristic spirochetes in clinical specimens can be seen using Giemsa or Wright's stains. Diagnosis is definitively made by injection of lesion material or blood into experimental white mice or guinea pigs and subse-quent recovery 1 to 3 weeks after inoculation.