Serratia marcescens bacillus cereus report


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The purpose of this study is always to differentiate and identify two unknown organisms provided by the instructor in a chemical broth. It is only known the two creatures are via vomit; the first is gram-positive as well as the other is definitely gram-negative. You ought to first independent the two microorganisms by inoculating a chemical agar platter using the streak-plate method. Your initial streak-plate process was performed and placed in the incubator at 37¦C for 24-48 hours. After observing the expansion on this dish, it is reasonably obvious that a person of the creatures is Serratia marcescens.

However , it is necessary to perform the requisite tests to become certain that this can be accurate. The growth on this streak plate is bright white and red. With the color contrast, the separation of organisms is for certain and natural cultures may be grown. Every organism utilized to inoculate a water nutrient broth which was in that case incubated in 37¦C to get 18-24 several hours. The red growth is usually labeled #1 and the white colored growth #2.

Subsequent tests and procedures will be described in other places in this survey.


Gram Stain: The organisms must first always be identified as gram-negative or gram-positive. This is decided using a Gram Stain procedure. (Cappuccino & Sherman, 2008, p. 73) Using the fresh pure ethnicities grown in nutrient broth, a sample is placed on a slip and permitted to dry completely before warmth setting. The staining procedure is accomplished using initially Crystal Purple, rinsing, in that case Gram’s Iodine for a entrain, rinsing with alcohol, after that water, and lastly staining with Safranin and rinsing with water. Following blotting carefully, the glide is placed on a microscope and focused on the organism on the lowest zoom, progressing towards the highestmagnification with oil concentration. Using this process, the results were inconclusive for specimen #1, but #2 is definitely gram-positive rods. Example of beauty #1 primarily appeared to be gram-positive diplococci. Additional testing is required. Phenylethyl liquor agar (PEA): PEA is a selective method which is used to recognize gram-positive bacteria. Both organisms were inoculated onto opposing sides in the PEA menu and incubated at 37¦C for 18-24 hours. Declaration shows that pertaining to #1, there is absolutely no growth with no change in seen the channel, while #2 does have development, but with not any change in the appearance of the medium. This is further more indication that #2 is gram-positive, when #1 is most probably gram-negative.

MacConkey agar: MacConkey agar can be both a differential and selective moderate used to choose for gram-negative bacteria. Additionally, it differentiates lactose-fermenting bacteria coming from non-lactose-fermenting bacteria. Only #1 was used to inoculate this kind of medium. Following inoculation, home plate was incubated at 37¦C for 18-24 hours. Remark shows there exists a bright red growth although no difference in the appearance of the medium. This indicates no lactose fermentation, however since there may be growth, this means the bacterium in gram-negative. Mannitol sodium agar: This kind of medium was inoculated with specimens and incubated for 37¦C pertaining to 18-24 hours. There being simply no growth and no change in physical appearance of the moderate for either organism, this suggests there was simply no mannitol fermentation and they will not tolerate sodium.

Methyl Red/Voges-Proskauer tests: The Methyl Red-Voges Proskauer moderate was used to perform two testing. The methyl red check is used to recognize enteric bacteria based on sugar metabolism. The Voges-Proskauer check is used to determine if an enteric bacterium creates acidic or neutral end products. First, the method was inoculated with isolate #1, and incubated at 37¦C intended for 48 several hours. After incubation, 2 . a few ml in the medium was transferred to one more tube being used for the Voges-Proskauer evaluation. For the methyl reddish test, five drops of pH sign methyl reddish is added to one of the pontoons of medium. After getting gently combined by moving the conduit between the palms of the hands, the results are observed. The MR-VP broth has changed to a yellow-orange color. This is an adverse reaction and indicates that pyruvic chemical p was digested to natural end products. For the Voges-Proskauer test, 10 drops of Barritt’s reagent A is included with the second tube of channel.

The lifestyle was shaken, then right away 10 drops of Barritt’s reagent M was added andit was shaken once again. For the next a quarter-hour, the culture was shaken every three to four minutes. Observations were made in 15 minutes. There is no change in the moderate which indicates a negative reaction and in addition indicates that #1 would not ferment glucose. This is an additional contradiction of expected outcomes and is contradicted in the next test. Triple Sugar-Iron (TSI) agar agar test: This kind of test was used for the two isolates, #1 and #2, and is made to differentiate depending on differences in carbohydrate fermentation habits and hydrogen sulfide production. The medium used is actually a TSI slant. Each separate was inoculated into a TSI slant with a sterile needle with a stab-and-streak technique. Following inoculation, the slant pipes were incubated at 37¦C for 18-24 hours. Declaration showed #1 was crimson on the slant but yellowish in the butt of the conduit. In addition , the stab pathway revealed a few motility of the organism. This indicates the affected person is a motile, anaerobe that ferments sugar with no gas. Upon noticing #2, the entire medium was yellow having a small amount of liquefied at the bottom in the slant, and slight motility in the rute pathway. This indicates the affected person is a lactose/ sucrose/glucose fermenter, an anerobe and offers motility. Catalase test: This kind of test is to determine if the isolates can produce catalase in order to degrade poisonous hydrogen peroxide. To do this, some drops of 3% hydrogen peroxide had been placed on a smear of each of the dampens. As expected, isolate #1 bubbled nicely, suggesting the presence of catalase and allowing for the conclusion that #1 can be described as facultative anaerobe instead of a stringent anaerobe. Separate #2 acquired no reaction so the effect is, that produce catalase.

Oxidase test: This check is designed to distinguish among groups of bacteria based on cytochrome oxidase activity. Oxidase enzymes play an important function in electron transport during aerobic breathing. Both isolates were analyzed for oxidase by adding p-aminodi-methlyaniline oxalate to colonies produced on a moderate, and not had a effect, indicating that they cannot produce cytochrome oxidase.

Delicious chocolate agar: This kind of medium was used to grow colonies of isolate #2 to be used in the oxidase test. Following inoculation, the plate was incubated at 37¦C for 18-24 hours, prior to test. There were heavy gray growth about this enriched channel.

Blood agar: Blood agar agar can be used to develop fastidious creatures and also shows the hemolytic properties of some bacterias. Bacterium #2 was inoculated onto a blood agar agar plate utilizing a sterile loop. The menu was incubated at 37¦C for 24 hours. It had been then observed that there is heavy expansion on the dish with a clear ring about the colonies. This indicates lysis of red blood cells took place, which is beta-hemolysis. Starch hydrolysis test: Starch agar can be used to determine in the event that bacteria generate the chemical amylase which will breaks down starch, causing hydrolysis. The starch agar plate was inoculated with dampens #1 and #2 by using a sterile trap. After inoculation, the plate was incubated at 37¦C all day and night. The plate was then overloaded with Gram’s iodine which in turn reacts with starch to turn purple-blue. The two bacteria experienced growth for the starch, however , only isolate #2 had a ring surrounding the colonies. This suggests that the bacteria is confident for starch hydrolysis and the presence about amylase. #1 was unfavorable for starch hydrolysis, certainly not producing amylase. The following tables show the physiological and biochemical tests performed for this research, as well as the student’s observations and interpretations.

Table 1: Physical & Biochemical Test Effects ” #1 Serratia marcescens Test

Reagent or Media





Gram Discolor

Ravenscroft violet, iodine, alcohol, safranin


Reddish-purple tiny rods

Gram unfavorable

Slightly inconclusive. Appears like coccobacilli.

Selective multimedia

Phenylethyl alcohol agar


Zero growth

No change in medium

Gram adverse

Like a selective medium, PEA identifies this as a gram-negative bacteria. Differential/ Picky media

MacConkey agar


Red expansion

No change in medium

Gram negative

Indicates this can be a gram-negative bacterium

No lactose fermentation

Mannitol salt agar agar


Not any growth

No difference in medium

Zero mannitol fermentation

Does not tolerate sodium

Methyl Red

MR-VP broth

Methyl red indicator


Yellow-orange color in broth


Indicates that pyruvic acid was metabolized to neutral end products Voges- Proskauer

Barritt’s reactants A & B


Simply no change in method

Negative-should be positive

Does not ferment glucose

(contradicted below)

Double Sugar-Iron agar agar

TSI slant


Red color upon slant, yellowish in bottom, movement far from stab site Motile


Glucose fermentation, no gas


3% hydrogen peroxide


Bubbles present

Great for catalase

Shows presence of catalase; possible anaerobe


p-amino-dimethylaniline oxalate


No enhancements made on medium



Does not create cytochrome oxidase

Starch hydrolysis

Starch agar

Gram’s iodine



No enhancements made on medium


Will not produce amylase

Table 2: Physiological & Biochemical Check Results ” #2 Bacillus cereus Check

Reagent or Mass media





Gram Stain

Crystal purple, iodine, liquor, safranin


Magenta rods

Gram positive

Definitely gram positive rods

Selective media

Phenylethyl alcohol agar



No change in medium

Gram great

PEA selects to get gram positive organisms

Differential/ Picky media

Mannitol salt agar


Simply no growth

No change in medium


Simply no mannitol fermentation

Would not tolerate sodium

Enriched agar

Chocolate agar


Heavy gray progress

Grows very well on this method

Blood agar agar


Progress with very clear area around colonies

Confident for beta-hemolysis

An expected consequence for N. cereus

Triple Sugar-Iron agar

TSI slant


Moderate turned yellowish, small amount of liquid, motile

Positive for lactose/sucrose/ glucose fermentation

Fermentation happened creating an acidic pH in the moderate


3% hydrogen peroxide


Not any reaction

Negative intended for catalase

No catalase is present; anaerobic


p-amino-dimethylaniline oxalate


No change in channel

Oxidase negative

Does not generate cytochrome oxidase

Starch hydrolysis

Starch agar agar

Gram’s iodine


Growth with ring about colonies

Positive pertaining to starch hydrolysis

Shows the presence of amylase


The recognition of bacteria #1 was very easy as there are few organisms that have a red growth, and Serratia marcescens is the only one that is in our unknowns list. When the Gram spot was inconclusive for this bacterium, it was reasonable to use other tests to positively determine it. By inoculating PEA and MacConkey agar, it absolutely was possible to conclusively recognize #1 like a gram-negative affected person. Observation of the bacterium with oil concentration, seemed to show a diplococcus, however after completing the aforementioned physiological and biochemical tests, it should be concluded that separate #1 is probably a short pole. Once it can be determined to become a gram-negative pole, the oxidase test becoming negative contributes to doing a methyl red test out. This test out is also bad. The MacConkey agar signifies there is no lactose fermentation, bringing about the final bottom line that this patient is Serratia marcescens. Patient #2 must have been a gram-positive fishing rod from the earliest Gram spot. A spore stain had not been done, nevertheless positive effect for the starch hydrolysis test causes the final bottom line that this unknown is Bacillus cereus. Several other tests had been done, just like for detection of hemolysis and glucose fermentation. Every single result was consistent with expected results pertaining to B. cereus.


The patient presenting with vomiting very likely has foodstuff poisoning because of the contamination of your starchy dish such as pasta salad or rice. Bacillus cereus can be characterized by nausea and vomiting within ” six hours following ingesting the contaminated food. Other symptoms may include abs pain and headache. There’s also a diarrheal form of food poisoning due to B. cereus, in this illustration the illness reveals only with vomiting. The 2nd organism, Serratia marcescens, could be present in the vomit due to the same polluted food; nevertheless it could also have been around in the intestines of the patient, without creating a problem. (General Background, 2009) B. cereus food poisoning is usually self limiting and never very extreme. It has a extremely quick onset and generally resolves within several hours. Because of this, the illness often goes unreported. This emetic food poisoning is common year-round and can have an effect on everyone. Holiday providers unaware that uncooked rice is potentially a dangerous food seeing that B. cereuscan be present and actually survive food preparation. Prevention comes with refrigerating grain products immediately instead of cooling down before putting in the refrigerator. Good cleanliness is always important, but know that Bacillus cereus can be in uncooked grain, dried beans, cereals and spices, and this bacterium is definitely resistant to warmth.


(n. g. ). Recovered May 15, 2009, via Wikipedia: The Free Encyclopedia: http://en.wikipedia.org/ Alexander, S., & Strete, M. (2001). Microbiology: A Photo taking Atlas intended for the Laboratory. San Francisco, ainsi que al: Daryl Fox. Dark-colored, J., & Black, T. (2008). Microbiology: Principles and Explorations (7th ed. ). Jefferson City: John Wiley & Sons, Inc. Breed, R. H. (1957). Bergey’s Manual of Determinative Bacteriology (Seventh impotence. ). Baltimore: The Williams & Wikins Company. Cappuccino, J. G., & Sherman, N. (2008). Microbiology: A Laboratory Manual (Eighth male impotence. ). Bay area, CA: Pearson Benjamin Cummings. General Qualifications. (2009). (T. W. Company, Producer) Gathered May 12, 2009, by Serratia- Marcescens. org: http://www.serratia-marcescens.org/index.cfm Katelijne Dierick, e. a. (2005, Aug). Journal of General Microbiology. Retrieved May possibly 10, 2009, from Bar Med Central: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1233987 Nourishment, C. farreneheit. (2009, 04 9). Negative Bug Book: Foodborne Pathogenic Microorganisms. Gathered May twelve, 2009, from United States Fda: http://www.foodsafety.gov/~mow/chap12.html


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