Absence or Presence of Coliform Bacteria in Water

Who are Coliforms?

They are heterogeneous group of bacterial species composed of following genera,

• Escherichia

• Enterobacter

• Klebsiella

• Citrobacter

• Aeromonas

 

This group of organisms comes under the Family Enterobacteriaceae. Enterobacteriaceae can be divided into two categories termed as non coliforms and coliforms. Examples for non coliforms are Salmonella, Shigella, and Vibrio etc. Coliforms again can be subdivided into two categories such as total coliforms and fecal coliforms.

Escherichia coli is exclusively fecal in origin hence E.coli is comes under fecal Coliform group. Fecal coliforms are able to tolerate 44.50 C. And all other coliforms, Enterobacter, Klebsiella, Citrobacter and Aeromonas come under total coliforms because they are widely distributed in soils, vegetations and industrial waste.

Standard Plate Count Method

This is also known as the heterotrophic plate count. Standard plate count is a procedure for estimating the no of live heterotrophic bacteria in water. The test can provide useful information about water quality and supporting data on the significance of Coliform test results.

Water being prepared for a standard plate count is usually diluted with sterile water. Standard plate count is determined by multiplying the number of colonies on a plate by dilution of the sample. Measured quantities are mixed with a nutrient medium in a Petri dish and after incubation the above determination is done.

High concentrations of the general bacterial population may hinder the recovery of coliforms. Since strict anaerobes, autotrophies, and some other species will not grow in the conditions provided in this test, thus this is not a true count.

Counting Chamber Method - Estimation Bacteria Count

In counting chamber method not only bacteria but any unicellular organism can be counted. Counting chamber is a slide, 2-3 mm thick with an area in the center called the platform and surrounded on either side by a ditch. The platform has a known depth (0.1mm) and is lower than the remainder of the slide, so that when a coverslip is placed over it then depth is uniform and known.

On the platform an area is accurately divided into small squares, by lines ruled in the glass, to form a grid. In this 1mm2 is divided into 400 equal squares. Thus each small square has a volume of 1/400.1/10 mm3 (Area x Depth).

Microscopy of Living Cells

1.Negative Staining

Microorganism will not stain in this particular method but the medium/environment will stain. Staining will kill the microbe hence negative staining provides us the facility to observe the live cells. This method will be discussed more under the topic practicals.

2. Hanging drop procedure 

In this technique, a drop of medium containing cells is allowed to hang in the cavity slide. This method is used to study the motility of microorganism. There are two movements that can be observed, true movement and Brownian movement.

Microorganism changes its position in true movement where as in Brownian movement the organism oscillates at its place and does not change the position in the field. Brownian movement can be explained on the basis of the bombardment of small particles suspended in the fluid; with the cell.This method will be discussed more under the topic practicals.

Corynebacterium Diphtheria - Bacterial Infection

Corynebacterium diphtheria is Gram positive bacteria. And causative agent of diphtheria. Irregular rod shaped bacteria.

They enter the body via the respiratory route through throat and tonsils.Apseudomembrane is formed which may block the entrance of air and cause death due to the blockage and also because of the toxin they produced. Effective vaccines are available –DTP ( D-Diphtheria , T-Tetanus, P- pertusis). Penicillin ,erythromycin effective in diphtheria therapy.

Mycobacterium Tuberculosis - Bacterial Infection

This causes tuberculosis. There are two kinds of human tuberculosis infections: Primary infection, postprimary infection. Primary infection usually occurs from inhalation of droplets containing viable bacteria derived from an individual with an active pulmonary infection. After the entrance to the human body bacterium settles and grows in lungs. Aggregates of activated macrophages called tubercles then formed. This may sometimes lead to the extensive destruction of lung tissues, and spreads bacteria to the other body parts and causes death. Postprimary type of tuberculosis infection can occur in tuberculin positive individuals. Postprimary infections are chronic infections.

Tuberculin test

In most cases of tuberculosis acute infections does not occur. Although the person has exposed to the bacterium the infection remains localized and is normally inapparent, but this initial infection hyper sensitizes the individual to the bacteria or their products. And also alters the response of the individual to subsequent infections. The diagnostic test which is used to measure this hypersensitivity is called the tuberculin test.

A protein fraction –tuberculin extracted from M.tuberculosis is injected intradermally into a hypersensitive person.

It elicits a localized immune reaction at the site of injection which characterizes an induration and an edema at the site after 1-3 days from the injection.

Tuberculin positive – Individuals who exhibit such an infection. This does not indicate active disease but that the individual has been exposed to the bacterium at some time.

Bordetella Pertussis - Bacterial Infection

Causes an acute disease called pertussis –whooping cough which is a highly infectious respiratory disease. This is usually observed in children under one year of age. Small, gram negative, strictly aerobic cocobacillus bacterium.

Bacterium attaches to the cells of upper respiratory tract by secreting a specific adherence substance called filamentous hemagglutinin antigen.After the attachment the bacterium grows and secretes pertussis exotoxin. The particular exotoxin induces the synthesis of cyclic adenosine monophosphate. This will eventually damage host cells. B.pertussis may also produce an endotoxin too.

Symptoms are violent cough that usually lasts for six weeks. The whooping sound when the patient inhaling in deep breaths to get sufficient air.

 DTP vaccine is used. Due to the undesirable side effects of pertussis vaccine now second generation pertussis vaccine is now in use.(Side effects includes local swelling, redness, fever).