Taylor Edwards Partner
Partner: Tyler VoisinBIOL 2011-Sec 007
November 11, 2018
My partner and I were given an unknown bacterium to identify using a series of lab tests. We concluded that our bacterium was Enterobacter aerogenes. E. aerogenes is a gram negative bacteria, meaning its cell wall is composed of a thin layer of peptidoglycan. It is bacillus shaped and non-spore forming and therefore does not produce endospores. E. aerogenes is a facultative anaerobic bacterium- meaning it is able to grow under aerobic and anaerobic conditions both. E. aerogenes doesn’t contain mycolic acid which makes it a non-acid fast bacterium. It is also motile by means of its peritrichous flagella, meaning that the flagella projects in all directions.
The methyl-red and voges-proskauer tests, two of the experiments we performed near the beginning of our unknown bacteria expirement, allowed us to begin narrowing down which bacteria we were trying to identify. For example, E. aerogenes was negative for the methyl-red test, showing no color change. This lack of a color change indicates that E. aerogenes uses the butylene glycol pathway to metabolize the pyruvic acid to neutral end products. With this negative test result, we were able to eliminate half of the unknown bacterium as they would have generated a positive result. The voges-proskauer test yielded positive results for only a few bacterium and was even more helpful in identifying our unknown. A positive reaction for this test results in the bacterium turning a light red color, which E. aerogenes did. We then performed the Lactose Fermentation test. These results allowed us to narrow things down to two bacterial possibilities, and then helped correctly identify our unknown. Some of the experiments we did were not quite as helpful, such as the catalase and motility tests and the nitrate reduction. These tests did not exclude many bacterium, as the majority of the results were the same for most of the unknown gram-negative bacterial samples. My partner and I did not encounter any false positive or negative test results, as our bacteria reacted in the way you would expect it to. False positives or negatives can be caused by either contamination or following experimental procedures incorrectly. An example of this would be the lactose fermentation test. If you aren’t paying close attention, you could easily overlook the gas bubble produced as it is very small. This inattention to detail could result in a false negative for gas production. By performing multiple tests and through the process of elimination, we were left with only one possibility. Since our given sample matches all the characteristics of Enterobacter aerogenes and did not generate any false positives or negatives, we are confident that we correctly identified our unknown bacterium.
Enterobacter aerogenes’ normal habitat is fairly broad. According to microbewiki.edu the research found that it is found in soil, water, dairy products, and the intestines and gastrointestinal tract of both animals and humans. The bacteria found in soil and water is most likely there as a result of animal excretion, as it is present in their intestines. Bacteria found in the gastrointestinal tract are studied at clinical sites via stool samples. (“Enterobacter Aerogenes”, 2011) Enterobacter aerogenes is a nosocomial, meaning found in hospital and health care settings, and pathogenic bacterium and is the cause of opportunistic infections.
Microbewiki.edu research also found the following:
“…E. aerogenes are opportunistic and only infect those who already have suppressed host immunity defenses. Infants, the elderly, and those who are in the terminal stages of other disease or are immunosuppressed are prime candidates for such infections.” (“Enterobacter Aerogenes”, 2011)
E. aerogenes can be the cause of various diseases and infections, including urinary tract infections, gastrointestinal infections, skin and soft tissue infections, and even adult meningitis. It may also cause septic shock in patients in hospital settings, which leads to a higher mortality rate. E. aerogenes was originally named Aerobacter aerogenes until it was included in the Enterobacter genus in the 1960’s (Davlin-Regli & Pages, 2015). E. aerogenes is often confused with Klebsiella aerogenes, despite there being major differences between the two. For example, E. aerogenes is motile, while k. aerogenes is immotile. (Davlin-Regli & Pages, 2015)
Davin-Regli, A., & Pagès, J. M. (2015). Enterobacter aerogenes and Enterobacter cloacae; versatile bacterial pathogens confronting antibiotic treatment. Frontiers in microbiology, 6, 392. doi:10.3389/fmicb.2015.00392
Enterobacter aerogenes. (2011, April). Retrieved from https://microbewiki.kenyon.edu/index.php/Enterobacter_aerogenes