Bacteria are the complex group of living things. Bacteria consist of only one cell. There are thousands of species of bacteria, but all of them are basically one of three different shapes. Some are rod or stick shaped; others are shaped like little balls. Some bacteria can live in temperatures above the boiling point and in cold below the freezing point. Bacteria may be helical or spiral in shape. Some bacteria cells exist as individuals while others cluster together to form pairs, chains, squares or other groupings.

Microorganisms have a significant impact on human life by their beneficial and harmful activities.  Since time immemorial, the pathogenic microbes have been a cause of concern for the society.  Deadly infectious diseases like AIDS, Leprosy, Meningitis, etc. cause large scale morbidity and mortality.  Besides, microorganisms also cause a number of plant diseases leading to massive economic setbacks. However, the useful activities of microbes far outnumber their harmful ones.  Besides, with the latest advances in biological sciences and technology, it is now possible to manipulate microbes for the benefit of mankind.

Bacteria have been used for decades for generation of specific products with industrial and medical applications.  Products like organic acids, solvents, enzymes, amino acids, etc. have immense economic value.  They can be used as food supplements, additives and in pharmaceuticals.  Besides, medical compounds like hormones, antibiotics, transformed steroids etc. will go a long way in alleviating human suffering. Bacteria and Viruses also have a significant role in environment management. They are important components of biogeochemical cycles with a major role in biodegradation.

Bacterial characterization testing motility of the bacteria

Hanging drop method

Many bacteria show no motion and are termed non-motile. However, in an aqueous environment, these same bacteria appear to be moving erratically. This erratic movement is due to Brownian movement. Brownian movement results from the random motion of the water molecules bombarding the bacteria and causing them to move.

True motility (self-propulsion) has been recognized in other bacteria and involves several different mechanisms. Bacteria that possess flagella exhibit flagella motion. Helical-shaped spirochetes have axial fibrils (modified flagella that wrap around the bacterium) that form axial filaments. These spirochetes move in a corkscrew- and bending-type motion. Other bacteria simply slide over moist surfaces in a form of gliding motion.

The above types of motility or non-motility can be observed over a long period in a hanging drop slide. Hanging drop slides are also useful in observing the general shape of living bacteria and the arrangement of bacterial cells when they associate together. A ring of Vaseline around the edge of the cover slip keeps the slide from drying out.

Wet mount Method

This is the simplest method for detection of motility and it can be used when no other method is available.

U Tube method

In this method for detection of bacterial motility, a ‘U’ shaped glass tube is used. The tube is filled with semi-solid agar. The bacteria are inoculated at one end of the tube. The motile bacteria will come on to the other end of the tube while the non-motile bacteria will remain at the site of inoculation.

Craige’s tube method

Cragie’s tube is the normal tube filled with semi solid agar containing a capillary inside it. The bacterial culture is inoculated into the capillary. Motile bacteria will come outside the capillary from the bottom and grow in the agar inside the outer tube whereas the non-motile bacteria will remain inside the capillary.

Bacterial characterization using microbiological examination

  • Direct Examination and Techniques: Direct examination of specimens is done for revealing their pathology. Microscopy can be identifying microorganisms. Immunoassays like immunofluorescence, immuno-peroxidase staining may detect specific microbial antigens. Genetic probes identify genus- or species.
  • Culture: Isolation of infectious agents usually requires specific media. Non selective media permit the growth of many microorganisms. Selective media contain inhibitory substances that permit the isolation of specific microorganisms.
  • Microbial Identification: Colony and cellular morphology can be permit preliminary identification. Growth characteristics under various conditions, utilization of sugars, enzymatic activity, immunoassays, and genetic probes are also used for determination.
  • Serodiagnosis: High titer of specific IgG antibodies or the presence of specific IgM antibodies may suggest or confirm a diagnosis.
  • Antimicrobial Susceptibility: Microorganisms, mainly bacteria, are tested in vitro to determine their susceptibility to antimicrobial agents.