SB2242 Microbiology Proof Reading and Paper Editing Services

SB2242 Microbiology Assignments solution

SB2242 Microbiology Proof Reading and Paper Editing Services


In microbiology isolation and identification of microorganism is exceptionally important. This is critical in understanding particular disease etiology and the best antibiotic to be used for the diseases treatment and the abilities of the bacteria to produce substances that might help it evade treatment such as having antibiotic resistance capabilities. The main aim of this laboratory experiment was to identify unknown bacteria B using morphological and biochemical tests. Different tests were used to identify the unknown bacteria including gram staining, microscopy to check for cellular morphology, spore formation, motility, Indole test, fermentation ability, amylase, catalase, and gelatinase production.

Materials and Methods:-

The unknown bacteria B morphological characteristics including colony, size, and appearance were physical development. After the physical examination of the colony characteristics on nutrient agar plate it was then necessary to carried out gram staining. In gram staining a single colony of unknown bacteria was picked using sterile wire loop and spread on glass slide. The crystal violet was used as the primary stain, 95% ethyl alcohol was used to decolorize the primary stain, while Gram’s iodine was used as a mordant, and safranin used as counter stain. The Gram positive bacteria contains peptidoglycan in their cell walls, hence, they retain the primary color which is dark purple (Pogmore et al., 2018). The unknown bacteria B stained deed purple red when observed under microscope, hence, positively identified as Gram positive with rod shape. The gram staining procedure was done by following instructions in the microbiology laboratory manual that was provided.

Motility test was carried out to determine if the unknown bacteria (B) was motile or non-motile. The motility of the bacteria B was established by stab inoculation of the single colony of the bacteria B into the motility media tubes provided, positive control and negative control were done together with unknown bacteria. A positive test presented diffuse growth away from the stab line of inoculation, demonstrated by turbidity extending sideways across the motility test medium (Luna et al., 2005). A negative motility was defined by growth confined to the stab line. The laboratory manual provided was used reference to perform the motility test.

Unknown bacterial B was further identified using multiple biochemical tests. Bacteria B was tested further to identify its ability to form spores and the type of spore produced if any. Based on the result interpretation from the manual there was no spore formation. Indole test was conducted to establish the ability of the unknown bacteria B to produce enzyme tryptophanase that breaks down tryptophan and reacts with Kovac’s reagent. According to Abbott (2011), Indole positive result is indicated by red surface layer while negative result doesn’t have the red surface layer.

Catalase test was also performed. Catalase test is important in differentiating catalase producing bacteria from non-catalase producing bacteria. In this test catalase acts by catalyzing the breakdown of hydrogen peroxide to oxygen and water. The bubbles of oxygen are produced in the presence of catalase producing bacteria while catalase negative bacteria don’t produce bubbles in presence of hydrogen peroxide (Cheesbrough, 2006).

Starch hydrolysis test was carried out on unknown bacteria B to check its ability to produce amylase that can hydrolyze starch. This test involved the use of a differential media which was starch agar plate. The media was inoculated by Unknown bacteria B. The starch agar plate with colonies of bacteria B was then flooded with Gram’s iodine. Clearing of light yellow/gold zone around bacterial colonies indicated presence of amylase while no clearing around the colonies indicated a negative amylase results (Xia et al., 2015). From the result there was clearing of light yellow zone indicating presence of amylase.

The ability of unknown bacteria B to produce gelatinase which liquefy gelatin was tested by performing gelatin hydrolysis test. The hydrolysis process by the gelatinase enzyme takes place in two sequential reaction. In the first reaction, the enzyme gelatinase breakdown the gelatin to polypeptide. Polypeptide is then further degraded to amino acid (Cheesbrough, 2006). A positive result was indicated by a partial liquefaction of the inoculated tube even after being subjected ice water.

Oxygen utilization test was performed to determine whether the unknown bacteria B was aerobic or anaerobic bacteria. Thioglycollate broth which is an enrichment media was used, the media contain numerous nutrient factors such as casein, yeast, beef extract, and oxidation-reduction indictor (resazurin). It supports growth of anaerobes, aerobes, microaerophilic, and fastidious microorganisms. The growth in the upper part of the media where the oxygen concentration was high is indicative of aerobic bacteria while anaerobic bacteria grows to the bottom of the media (Cowan, 2005)

The ability of the bacteria B to ferment lactose and glucose was tested. Phenol Red Lactose Broth, Phenol Red Glucose Broth were used. Sugar fermenting bacteria produces acid during fermentation that lowers the PH of the broth, hence, the phenol red indicator which is red in colour will change its colour to yellow due to acid production. At the same time, the gas produced is collected inside Durham’s tube. Therefore, a positive sugar fermentation is indicated by change in the colour of the broth from red to yellow (Cowan, 2005).


TABLE 1: Bacteria Tests and Results for Unknown bacteria B






Gram Stain

Determine bacteria B gram stain reaction

Crystal violet, Iodine, Alcohol, Safranin

Purple rods were observed

Gram positive

Motility test

Determine if the unknown bacteria B was motile or non-motile

Motility media

The colonies presented with diffuse turbid growth away from the stab line of inoculation


Indole test

Determine the ability of bacteria B to produce tryptophanase

Sterile tryptone water, Kovac’s reagent

No red surface ring was formed

Indole negative


Determine ability of bacteria B to produce catalase

Hydrogen peroxide

Active bubbling was seen

Catalase positive

Starch hydrolysis test

Determine the ability of bacteria B to produce amylase

Starch agar plate, grams iodine

Clearing of light yellow/gold zone around bacterial colonies

Amylase production

Gelatinase test

Determine ability of unknown bacteria B to produce gelatinase

Gelatin tubes, ice water

Partial liquefaction of the inoculated tube even after being subjected ice water

Gelatinase positive

Sugar fermentation

Determine the ability of unknown bacteria B to ferment lactose and glucose with gas production

Phenol Red Lactose Broth, Phenol Red Glucose Broth

The colour of Phenol Red Glucose Broth changed from red to yellow with no gas in the Durham’s tube. The color of Phenol Red Lactose Broth didn’t change and no gas produced in Durham’s tube.

Glucose fermenter but non-lactose fermenter.

Oxygen requirement

Determine whether unknown bacteria B was aerobic or anaerobic

Thioglycollate broth

There was growth at the uppermost part of the Thioglycollate broth.


Colony morphology

Determine the morphological characteristics of the unknown bacteria B

Nutrient Agar

From the physical observations made the bacteria B was rod shaped, with colonies having chain arrangement under microscopic examination

1mm in size, White in appearance, irregular edge shape.


The unknown bacteria B was identified as gram positive rode shaped. Following close observation and different Biochemical tests the unknown bacteria B was finally identified as Bacillus subtilis. Through gram staining it was possible to eliminate gram negative Enterobacteriaceae including Escherichia coliandKlebsiella pneumonia.According to Amin et al. (2015), Bacillus subtilis are known to be present in wide range of environment including soil and human  resource gastrointestinal tract, they are gram positive, rod-shaped, form endospores in unfavorable conditions. Furthermore, they are motile having a well-developed peritrichous flagella, they are aerobic, indole negative, and catalase positive, and they are non-lactose fermenters (Khan, 2018; Ayala et al., 2017). The other possible gram positive catalase positive bacteria was Staphylococcus aureus.Therefore, Gelatinase and amylase test were performed on the unknown bacteria B, the result revealed that the bacteria B was gelatinase and amylase positive this further excluding Staphylococcus aureuswhich is negative for both tests. Amylase test was used to eliminate Micrococcus luteus which was amylase negative while the Bacillus subtilis was amylase positive (Fangio et al., 2012). The only possible remaining bacteria were Bacillus polymyxa and Bacillus subtilis.Through sugar fermentation the two bacteria were differentiated, Bacillus polymyxahas the ability to ferment lactose and glucose with gas production while the unknown bacteria B was not lactose fermenter and gas production. Therefore, this confirmed the unknown bacteria B to be Bacillus subtilis.


In conclusion the unknown bacteria B was confirmed to be Bacillus subtilis based on the obtained results. Bacillus subtilis has been extensively studied around the world. This can be attributed to the probiotic characteristics it has and very high rate of genetic manipulability. Therefore, researchers use Bacillus subtilis in order to promote genetic research and due to its highly genetic manipulability levels. Bacillus subtilis has medical importance including its ability to produce toxic metabolites with antibiotic characteristics this substances include difficidin, oxydifficidin, bacilli, bacillomyin B, and Bacitracin


1.Abbott, S. L. (2011). Klebsiella, Enterobacter, Citrobacter, Serratia, Plesiomonas, and other Enterobacteriaceae. In Manual of Clinical Microbiology, 10th Edition (pp. 639-657). American Society of Microbiology.
2.Amin, M., Rakhisi, Z., & Ahmady, A. Z. (2015). Isolation and identification of Bacillus species from soil and evaluation  planningof their antibacterial properties. Avicenna Journal of Clinical Microbiology and Infection, 2(1).
3.Ayala, F. R., Bauman, C., Cogliati, S., Leñini, C., Bartolini, M., & Grau, R. (2017). Microbial flora, probiotics, Bacillus subtilis and the search for a long and healthy human longevity. Microbial Cell, 4(4), 133.
4.Cheesbrough, M. (2006). District laboratory practice in tropical countries. Cambridge university press.
5.Cowan, S. T. (2004). Cowan and Steel's manual for the identification of medical bacteria. Cambridge university press.
6.Fangio, M. F., Roura, S. I., & Fritz, R. (2010). Isolation and identification of Bacillus spp. and related genera from different starchy foods. Journal of food science, 75(4), M218-M221.
7.Khan, K. (2018). Isolation of bacteria from dairy-based popular sweetmeat named swandesh following the molecular identification of Bacillus species (Doctoral dissertation, BRAC Univeristy).
8.Luna, V. A., Peak, K. K., Veguilla, W. O., Reeves, F., Heberlein-Larson, L., Cannons, A. C. Cattani, J. (2005). Use of Two Selective Media and a Broth Motility Test Can Aid in Identification or Exclusion of Bacillus anthracis. Journal of Clinical Microbiology, 43(9), 4336–4341.
9.Pogmore, A. R., Seistrup, K. H., & Strahl, H. (2018). The Gram-positive model organism Bacillus subtilis does not form microscopically detectable cardiolipin-specific lipid domains. bioRxiv, 190306.
10.Xia, Y., Kong, Y., Seviour, R., Yang, H. E., Forster, R., Vasanthan, T., & McAllister, T. (2015). In situ identification and quantification of starch-hydrolyzing bacteria attached to barley and corn grain in the rumen of cows fed barley-based diets. FEMS microbiology ecology, 91(8).