Lab Report : Control of Micro-organisms

Materials and Methods

Equipment Reagents
  • Style culture tubes
  • 1 tube of LB broth
  • 1 ml transfer pipettes
  • Bent glass rod
  • Beaker of ice
  • Ruler/ caliper
  • Maker pen
  • Alcohol
  • Water bath at 420 C
  • Agar plates
  • Eosin Methylene
  • TSA plate
  • Antibiotic disks


  • Strain #1200
  • Strain # BA-14


The first activity was designed to test air as a source of contamination. The student was expected to note the number and appearance of colonies, on TSA plates exposed on three surfaces, the laboratory bench, biological safety cabinet and the laminar flow cabinet. The students were to observe whether there were any differences from the front and the rear of the laminar as well as the biological safety cabinet.

The second test was designed to assess the contamination of surfaces. The students were to note any appearance on Eosin methyl blue agar and Mannitol Salt agar plate on the control and sample plate. The students were then later to compare the appearance of the growth on the sample and control and note whether there were any similarities in number and appearance of the growth. In addition, the student was to detect and observe the location and frequency of contamination.

The third laboratory activity was access the effectiveness of hand washing in eliminating microorganisms. Students were to note the appearance and the number of growth in the TSA plates inoculated from their fingers before and after hand washing. The fourth and the last student activity was to do an antimicrobial susceptibility testing. Plate preparation was done according to the manufacturer’s instructions. Sufficient molten agar was placed on a sterile Petri dish to a depth of four mm. Excess moisture was removed by drying the surface of agar using a drying agent. Precautions were taken, however, not to over dry the agar as that could affect the quality of the results.

Prior using, the plates were stored under 8-100 storage. Before selecting the sample organism, a control antimicrobial susceptibility testing was confirmed. This control was to act as a standard and to monitor test performance and resistance strains on the samples used. The control strains have been stored at -700 according to the guidance provided for European Consensus (EUCAST) (Wootton 13). Student subculture samples severally for non-selective media (TSA) to test for purity before carrying out antimicrobial susceptibility test.

Inoculation preparation and culturing was done according to the provided laboratory protocol direct colony suspension method was utilized in the inoculation procedure. Production of an even suspension was important for this particular test. A swab was used in to collect the sample and make a cross at the center of microbial susceptibility plate. Another stile dry swab was used to spread the sample even across the plate. Incubation was then done as per the instruction and standard operating procedure of the laboratory.

After incubation, the growth colonies were measured using a ruler and a caliper to the nearest millimeters. Colonies growing on the zone of inhibition were measured and subcultured for later identification. Antibiotic used for the process-included cefoxitin, Penclinin G, Gentamycin, Tetracycline, linezolid, and Chloramphenicol.

Results and discussion

While there are several methods important in the control of microorganisms, accessing the source of contamination is equally vital in the selection of the type and the method of disinfection. In the first test of assessing the source of air contamination, a growth of colonies was noted in the lab bench while both biological safety cabinet and the laminar flow cabinet did not express any kind of growth. While there were no differences in the number and appearances of the colonies at the biological safety cabinet and the laminar flow cabinet’ rear and the front sides, there were similarities for colonies observed on the laboratory benches among all classmates. Biological safety cabinet and the laminar flow cabinet are highly sterile and prevent any growth or pathogen entry. According to Meyers (8), the use of biological safety cabinet, especially around the institution, is vital in averting the spread of microbial infectious agents. The use of biosafety cabinets is suitable for preventing the spread of infectious microbial agents. As it is evident on the manifestation or the formation of colonies on the lab benches, it is important for a laboratory scientist to disinfect the working station through besides using a biosafety or laminar flow cabinet.

In the second activity of the assessing the contamination of surfaces, no growth on either plate was noted. It was not possible to assess whether the samples resembled that of E. coli or any other microbial agent. Therefore, the surface inoculated did not have any indication of fecal contamination. Although there were no growths on the plates, the absence does not indicate an absolute sterile surface. A non-selective agar was used for this procedure.

Hand washing is perhaps the best and most efficient protection against microbial infections (Burton et al 20). Apart from being recognized globally and internationally, the World Health Organization promotes and highly recommends hand hygiene and hand washing. The third activity assessed whether hand washing alone is sufficient in eliminating microbial agents. There was more growth on the plates inoculated form fingers before hand wash compared to the number of colonies after the hand wash. it was therefore concluded that hand wash alone could not alone protect the spread of infections. According to Burton and others (20), it is imperative to wear sterile groves beside thoroughly hand washing. Although alcohol-based hand wash is not sufficient method for preventing the spread of microbial infections.

Antimicrobial resistance test was the final laboratory activity. Based on the results, strain #1200 was susceptible to all the 6 antimicrobial drugs. Stain BAA-14 however, showed significant microbial resistance to Cefoxitin, Penicillin G, Gentamycin, and Tetracycline but strong susceptibility for the both Chloramphenicol and Linezolid. Antimicrobial resistance is a highly emerging issue. Apart from influencing the outcome of an infection, antimicrobial resistance increases treatment failure and threaten the effective treatment and management of a wide range of infectious agents including bacteria virus and parasites (Harbarth 1). There is an increasing need for an action plan, awareness and collaboration between governments, research institutes, agencies and other health sector is countering the problems of antimicrobial resistance.

Work Cited

Burton, Maxine, et al. "The effect of handwashing with water or soap on bacterial contamination of hands." International journal of environmental research and public health 8.1 (2011): 97-104.

Harbarth, S., et al. "Is reduced susceptibility to disinfectants and antiseptics a risk in healthcare settings? A point/counterpoint review." Journal of Hospital Infection 87.4 (2014): 194-202.

Mayers, Douglas. Antimicrobial Drug Resistance Handbook: Volume 2. Totowa, N.J: Humana, 2008. Internet resource.

Wootton, Mandy. "Version 12 May 2013."

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