Pathogenic Strains of Microorganisms – Lab Report Example

Introduction Pathogenic strains of microorganisms are the causes of many infectious diseases including ailments such as typhoid, tuberculosis, gonorrhea, syphilis among many others. Bacterial infections may either be caused by Gram-negative or Gram-positive bacteria. In a hospital setting, it is necessary to identify the causative microorganism for an accurate diagnosis of a patient’s disease. Such identification may be based on the morphological characteristics of the bacterial colonies as well as the biochemical traits of the pathogens (Vasanthakumari, 2009). Thereafter, the healthcare provider prescribes the most suitable antibiotic depending on the identity of the pathogen.
Recently, it has been shown that certain strains of bacteria have developed resistance to particular antibiotics. Therefore, antibiotic sensitivity tests help in determining the most effective antibiotic against a certain strain of microbe. As a result, the patient can get the most effective therapy.
This lab aims at establishing the biochemical characteristics of two bacteria namely Salmonella and E. coli using Microbact and IMViC test kits. It also aims at testing the efficacy of five antibiotics against these bacteria.
Methods
Microbact Biochemical Identification Kit (12A) was used to evaluate the bacterial utilization of 12 substrates. Sample inocula were prepared by diluting one to two colonies the provided pure cultures of Salmonella and E. coli in 2.5 ml of normal saline. Each well of the two test kits were inoculated with four drops of the inoculums and incubated for 18 to 24 hours at 35 oC. Thereafter, the color changes in the 12 substrates observed and interpreted to depict the utilization of the substrates by the microbes.
The IMViC test kit was used to carry out the indole, methyl red, Voges-Proskauer and citrate tests. D BBL™ Sensi-Disc™ Antimicrobial Susceptibility Test Discs were used to determine the antibiotic sensitivity of five antibiotics namely penicillin G, polymyxin B, streptomycin, tetracycline and vancomycin the two bacteria.
Results
Table 1: Microbact Kit results for Salmonella
4
+
Lysine
2
-
Ornithine
1
+
H2S
4
-
Glucose
2
-
Mannitol
1
-
Xylose
4
+
ONPG
2
+
Indole
1
+
Urease
4
-
V-P
2
+
Citrate
1
+
TDA
Table 2: Microbact Kit results for E. coli
4
+
Lysine
2
-
Ornithine
1
-
H2S
4
-
Glucose
2
-
Mannitol
1
-
Xylose
4
+
ONPG
2
+
Indole
1
+
Urease
4
-
V-P
2
+
Citrate
1
-
TDA
Table 3: IMViC Result
E. coli
Salmonella
Indole
+
-
Methyl Red
+
+
Voges Proskauer
-
-
Citrate
+
+
Table 4: Antibiotics results for E. coli, Staphylococcus and Salmonella
Clearing number (mm)
E. coli
Salmonella
Staphylococcus
Control
0
0
0
Penicillin G
11
10
11
Polymyxin B
18
15
16
Streptomycin
16
14
14.5
Tetracycline
34
29
24
Vancomycin
0
0
0
E. coli
PB=204 colonies
P=53 colonies
Salmonella
PB=1 colonies
S10=7 colonies
P=3 colonies
Discussion
E. coli was positive for indole, methyl red, and citrate tests implying that it contained tryptophanase enzyme and was able to ferment glucose into a blend of acids. E. coli was also capable of utilizing citrate as a carbon source as indicated by the positive citrate test. The Voges-Proskauer test was negative showing that E. coli could not generate acetoin from the degradation of glucose via a 2,3 butanediol fermentation. Salmonella, conversely, was positive for methyl red and citrate and negative for indole and Voges-Proskauer. These findings implied that Salmonella could ferment glucose into acids and utilize citrate. However, it did not contain tryptophanase and could not generate acetoin from glucose.
Salmonella could not utilize glucose, mannitol and xylose and did not contain ornithine decarboxylase enzyme. Salmonella did not contain tryptophan deaminase enzyme. The Bactrim and IMViC test results were consistent with the methyl red and Voges-Proskauer tests for both strains. However, there was a discrepancy between the indole test for Salmonella between the two kits. Both strains were capable of hydrolyzing urea.
The antibiotic resistance tests showed that all the three bacteria were resistant to Vancomycin as shown by zero zones of inhibition just like in the negative controls. The three strains were also resistant to penicillin G. The three strains were susceptible to polymyxin B and tetracycline. E. coli was highly susceptible to polymyxin B as it had the largest inhibition zone of the three strains. Salmonella and Staphylococcus showed intermediate susceptibility to streptomycin while E. coli showed susceptibility to streptomycin. However, the antibiotic that had the largest inhibition zones in the three strains was tetracycline. Therefore, it was concluded that tetracycline was the strongest antibiotic against E. coli, Salmonella and Staphylococcus.
Reference
 Vasanthakumari, R. (2009). Practical microbiology. New Delhi: BI Publications Pvt.