Enterobacter Lab Report Sample Essay


The study of microbiology does not only require the aspect of academic understanding of the microscopic world but requires a practical understanding of lab protocols and procedures that are used in the identification, control and subsequent manipulation of microorganisms. This understanding plays a vital role in the clinical, industrial and the fields of pharmaceuticals. This lab report was therefore performed to ensure that the students got a clear understanding of the microorganisms. Due to this reason, the first experiment was to explore bacterial motility. This exploration involved the use of dynamic imaging through the lens.


Motility has been considered as one of the most dynamic features of the microbial world, this ability of the microorganisms to swim and crawl has been able to determine and influence their interactions both in their physical and chemical environments. In laboratory Motility testing using the semi-solid medium is commonly used for the identification of gram-negative bacteria of the Enterobacteriaceae family.  Motility testing is done in conjunction with other biochemical testing using special biochemical media. The procedure had initially involved making a wet mount by adding one drop of water to the slide and subsequently adding a small number of bacteria using the inoculation needle. A coverslip was then placed on top of the same and observed with a phase-contrast microscope. This test was aimed at detecting cell movement and behavior with due consideration to the different types of motility that include Brownian, streaming and true motility.

In this experiment, true motility was observed where the bacteria moved and consequently changed direction

Culture method

A microbial culture refers to a method of multiplying microorganisms by allowing them to freely reproduce in a predetermined culture under controlled laboratory conditions. It is important to note that microbial culture has helped determine the type of organisms and their abundance as well. In such experiments, microbiological cultures can be grown in Petri dishes that have a thin layer of agar-based growth medium. The growth medium is then inoculated with the desired bacteria coupled with a subsequent. There are however various additives that are poured into the plates and allowed to solidify, however, our experiment had used the stab cultures, a solid agar was formed in attest tube, bacteria was then introduced via inoculation needle into the center of the agar. 2/3 of the bacteria sample was inserted by stabbing into the solid agar by an inoculation needle.

The subsequent results had indicated motile growth at the stab line that looked fuzzy as well as cloudiness of the agar indicating motility. This experiment had indicated the possibility of occurrence of the following unknown organisms; staphylococcus epidermidis, Alcaligenes faecalis, Proteus mirabilis, Enterobacter cloacae, Micrococcus roseus, Bacillus subtilis among others.

The gram stain

Gram stain has been a common technique used to differentiate two large groups of bacteria based on the different composition of their cell walls. Due to this reason, the gram stain process helps in distinguishing between gram-positive and gram-negative by coloring these cells red or violet. Gram-positive bacteria stain violet due to the presence of a thick layer of peptidoglycan in their cell walls, which retains the crystal violet these cells are stained with.

Alternatively, Gram-negative bacteria stain red, which is attributed to a thinner peptidoglycan wall, which does not retain the crystal violet during the decoloring process. (Center 2015)

Our experiment, for the identification of whether the cell wall of the bacteria was gram-positive or negative; we had required a smear preparation of preheated bacteria subsequently stained with reagents; crystal violet for 30 seconds, the mordant-grams negative for 1 minute, decolorizer ethyl alcohol for 5-15 seconds. Distilled water was then utilized between stains to briefly wash off each stain. This experiment had indicated that gram-positive were stained violet while the gram-negative was stained pink.



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