# 4. You streak an unknown bacterium on an EMB agar and incubate at room tempera
ID: 198716 • Letter: #
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# 4. You streak an unknown bacterium on an EMB agar and incubate at room temperature. After 48 hours of incubation, you observe NO growth on the plate. Is this unknown bacterium a lactose fermenter? Explain your answer. Add in as much detail as possible.
(8 pts) You are working in a microbial genetics laboratory studying lactose transport proteins. The bacterial strain you are working with, Escherichia coli strain SOS, has a mutated lactose transporter that does not transport lactose into the cell. You streak the bacterium onto an EMB plate and incubate at 37C for 48 hours. Describe what would be seen on the plate, and interpret these results. (2 pts) 1.) 2.) You inoculate strain SOS into a Fluid Thioglycollate Media tube and a semisolid agar tube. Afte doing some research on the strain, you discover that SOS is an obligate anaerobe that is non- motile. In the space below, draw the expected growth of strain SOS in these two media types. (1 pt) [staple this sheet to the front of your typed post lab] FTM Semisolid: 3.) You are working in a microbiology laboratory that is developing a media type to isolate certain types of bacteria. The types of bacteria you are trying to isolate are Gram-positive, motile, halophilic, mannitol fermenters that grow in the presence and absence of oxygen. What form of media would you use (tube or plate)? What components would you include in the media that would favor the growth of these types of organisms? List all components below and what purpose each component serves (selective, differential, indicator, etc.): (3 pts) 4.) You streak an unknown bacterium on an EMB agar and incubate at room temperature. After 48 hours of incubation, you observe NO growth on the plate. Is this unknown bacterium a lactose fermenter? Explain your answer. (2 pts)Explanation / Answer
4 Eosin methylene blue agar is a selective media for gram negative bacteria. It contains two stains Eosin red and methylene blue that are toxic to gram positive bacteria hence inhibits their growth. It also provides a color distinction between lactose fermenters and non fermenters. lactose fermentation by lactose fermenter bacteria will produce acids that will lower th pH resulting in production of purple-black colonies.
whereas lactose non-fermenter will not produce acid end products and will give colorless colonies. Therefore lactose fermenting bacteria will give dark nucleated colonies and lactose non fermenting bacteria will give colorless colonies when plated on EMB agar.
since the unknown bacteria showed no growth on EMB plate therefore it can be a gram positive bacteria as EMB media inhibits growth of gram positive bacteria. It cannot be a lactose fermenter as lactose fermenters grow and give dark colored colonies when plated on EMB agar. also the plate was incubated at room temperature and not at 370C this shows that the bacteria is non culturable at room temperature.
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