Unknown # 10 Essay

Unknown #10 produced no identifiable macroscopic characteristics as a broth, so the first step was to Gram stain a loopful to determine the microscopic characteristics. Gram staining not only helped identify Unknown #10’s microscopic morphology but it also helped ensure the specimen was a pure culture—no other bacteria were visible when Unknown #10 was Gram stained and observed under the microscope. Unknown #10’s key microscopic morphology was that it was a very small, Gram negative bacillus. Though bacilli can possibly form endospores, no empty white centers were visible which suggested that Unknown #10 was not an endospore forming bacteria. No quick endospore stain was performed to validate this assumption since only one assigned organism was endospore forming and unlike Unknown #10, that organism was Gram positive. By Gram staining alone, it was safe to eliminate the three Gram positive bacteria that could have been assigned: S. epidermidis, M. luteus, and B. megaterium. The second step was to streak plate Unknown #10 to observe its macroscopic

Starch amylase testing was equally unsubstantial since the only amylase producing bacteria was ruled out after Gram staining. Unknown #10’s negative citrate test result was also unhelpful because E. coli is citrate negative and P. vulgaris is a variable citrate producer that can also be citrate negative. H2S production in the Kligler’s Iron Agar test ultimately proved that Unknown #10 was Proteus vulgaris. P. vulgaris is the only assigned bacteria that produces H2S, so when a black precipitate obscured the yellow butt of the Kligler’s Iron Agar slant, E. coli was ruled out. Not only did the H2S product confirmed that Unknown #10 was P. vulgaris, it confirmed P. vulgaris’ motility. Only a motile bacteria could travel that far from the center of inoculation. Furthermore, it confirmed that P. vulgaris is a facultative