Identification of unknown organisms is useful in a wide variety of settings; from clinical diagnostics to environmental monitoring (1). Species of bacteria can differ fundamentally in aspects ranging from morphology to metabolism. Exploiting these differences can allow for identification of unknown organisms. Gross morphological characterizations are crude, and better replaced by more accurate and specific tests. At a fundamental level, tests such as the Gram stain divide bacteria in to two broad categories based on the characteristics of their cell wall (2). In this lab, the tests performed to elicit species identity can be put into three overlapping categories: selective, differential, and biochemical. Often, the primary basis of these three
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A given test or media may fall into multiple categories. Selective and differential tests are generally less effective at species identification, and consequently, are normally only capable of presumptive identification (3). This lab uses different types of media that are both selective and differential. Mannitol Salt agar (MSA), which contains high levels of sodium chloride kills most bacteria that are not members of the halotolerant Staphylococcus genus. MSA also contains mannitol, which allows differential identification because an indicator detects acid produced by the fermentation of mannitol (4). MacConkey agar, which is media containing crystal violet and bile salts inhibits Gram positive bacteria (5). The media is also differential since the fermentation of lactose is detectable on MacConkey agar by pH indicators. Eosin Methylene Blue agar (EMB) contains chemicals that inhibit Gram positive growth and can identify lactose and sucrose fermentation through the previously described pH detection (3,5). Sometimes, media is developed to identify specific organisms. An example of this is Chromogenic …show more content…
The properties of selective and differential media suggest that differences between the bacterial species could be used in this lab to identify these six species but their effectiveness is unknown. The efficacy of identifying a completely unidentified bacterium in a cost-sensitive manner using these test also has yet to be determined. We hypothesized that applying a combination of selective and differential media with biochemical tests would provide a presumptive identification of the first group of six unknown bacteria. We also hypothesized the identification an unknown member of the Enterobacteriaceae family referred to as unknown #53 could be definitively identified using the API 20E and other tests. To test the first hypothesis, samples of four of the six unknown bacteria were streaked onto plates of Mannitol Salt agar, MacConkey agar, and Eosin Methylene Blue agar to examine their growth on the media. Two other unknowns were streaked on Chromogenic agar to determine coliform status and look for the presence of E. coli. All six species were streaked on nutrient agar as a control. The additional unknown #53 was isolated on a MacConkey agar plate, gram stained, and subjected to the IMViC series of tests. A more rigorous set of tests, known as the API 20E test
A given test or media may fall into multiple categories. Selective and differential tests are generally less effective at species identification, and consequently, are normally only capable of presumptive identification (3). This lab uses different types of media that are both selective and differential. Mannitol Salt agar (MSA), which contains high levels of sodium chloride kills most bacteria that are not members of the halotolerant Staphylococcus genus. MSA also contains mannitol, which allows differential identification because an indicator detects acid produced by the fermentation of mannitol (4). MacConkey agar, which is media containing crystal violet and bile salts inhibits Gram positive bacteria (5). The media is also differential since the fermentation of lactose is detectable on MacConkey agar by pH indicators. Eosin Methylene Blue agar (EMB) contains chemicals that inhibit Gram positive growth and can identify lactose and sucrose fermentation through the previously described pH detection (3,5). Sometimes, media is developed to identify specific organisms. An example of this is Chromogenic …show more content…
The properties of selective and differential media suggest that differences between the bacterial species could be used in this lab to identify these six species but their effectiveness is unknown. The efficacy of identifying a completely unidentified bacterium in a cost-sensitive manner using these test also has yet to be determined. We hypothesized that applying a combination of selective and differential media with biochemical tests would provide a presumptive identification of the first group of six unknown bacteria. We also hypothesized the identification an unknown member of the Enterobacteriaceae family referred to as unknown #53 could be definitively identified using the API 20E and other tests. To test the first hypothesis, samples of four of the six unknown bacteria were streaked onto plates of Mannitol Salt agar, MacConkey agar, and Eosin Methylene Blue agar to examine their growth on the media. Two other unknowns were streaked on Chromogenic agar to determine coliform status and look for the presence of E. coli. All six species were streaked on nutrient agar as a control. The additional unknown #53 was isolated on a MacConkey agar plate, gram stained, and subjected to the IMViC series of tests. A more rigorous set of tests, known as the API 20E test