1.5. Lecture No. 33

So, here if we look at the standards that people use for analysis of microorganisms, for example CPCB standards for microorganisms will be like say 5 per 100 ml or 5 microorganisms for 100 ml. So, the microorganisms we are talking about are predominantly pathogens. Many of the pathogens are bacteria, there are a few viruses and all that but mainly bacteria and for water quality, people count the number of bacteria in it.

This chunk introduces the concept of microorganism standards, particularly regarding water quality. The CPCB (Central Pollution Control Board) standards specify that acceptable levels of microorganisms in water should be limited to 5 per 100 ml. It's important to note that the microorganisms discussed here are primarily pathogenic bacteria, which can pose health risks when present in water sources.

Think of it like checking the cleanliness of a drinking glass. If there are a few specks of dirt (representing the bacteria), it's generally acceptable, but if there are too many, it becomes unsafe to drink from. The same idea applies to ensuring our water is safe—keeping bacteria levels within certain limits is crucial for health.

How do you count say 5 per 100 ml? This bacteria size is around 1 to 10 microns, it means if I take 100 ml sample, I have to see it, it is difficult to count, so you need a microscope. So how do you do this? You take 100 ml of sample you filter it put it on a filter paper and observe the filter paper if somewhere in the filter paper there are 5-micron spots. Filter papers are big 2.5 centimeters in size, you have to search for 5 microns somewhere, so, it is not very easy.

Counting microorganisms like bacteria can be quite challenging due to their small size (1 to 10 microns). To count them effectively in a 100 ml water sample, a common method involves filtering the sample through filter paper, then examining the filter for indications of bacteria. However, this is not straightforward due to the tiny size of the microorganisms, making it difficult to accurately count them visually without advanced equipment.

Imagine looking for tiny grains of sand scattered on a large towel. Just like it's hard to find specific grains without a close look, counting microscopic bacteria requires careful filtering and searching to ensure accuracy.

One of the old standard methods is that people use what is called as a culturing method. A lot of people work on these various ways of doing it, but one of the simplest methods is to take a water sample and you culture the bacteria on a nutrient medium.

The culturing method is a classic way to quantify bacteria. This technique involves placing a water sample onto a nutrient-rich medium that supports bacterial growth. After allowing the sample to incubate for about 24 hours, the bacteria multiply and form visible colonies. Each colony can be counted to estimate the number of bacteria in the original sample, with each colony representing a colony-forming unit (CFU). This is a simple yet effective technique for microbial analysis.

Think of growing plants from seeds. Just as you plant seeds in soil, provide water, and wait for them to grow into plants (visible groupings), we take microbes and place them in a growth medium to see how they multiply into visible colonies.

If you have 100, you have no problem because there are other methods of doing it. But if you do culturing when you have very high concentrations, you already have a lot of dots and this at the end of one day, you may get a big jumble, a big mass and you cannot differentiate how many originally were there.

When the concentration of bacteria is very high, simply culturing a sample may lead to overcrowding, making it hard to distinguish between individual colonies. Therefore, it’s common practice to dilute the sample before culturing. For instance, if a sample is diluted tenfold, each dilution provides clarity and allows for accurate counting of colonies that develop, facilitating better data interpretation.

It’s like trying to count how many marbles are in a big jar when they’re all piled together. If you dilute them into smaller cups, you can more easily count each marble in those smaller groups!

Microbes are treated like particles, so you can also look at it like a particle and look at it in a microscope and there are a lot of instruments now available, which use microscopy in order to count bacterial cells.

In addition to culturing, there are advanced techniques like flow cytometry that analyze samples as they pass through a laser beam. These methods treat bacteria like particles, counting them as they flow through channels. This approach allows for real-time assessment but remains non-standard due to concerns about how representative the sample may be.

Consider how traffic cameras capture vehicles passing on the road. Just as the camera counts how many cars pass by, flow cytometry counts bacteria in a liquid as they flow through a detector, counting them one by one.

People use other ways of detecting bacteria also which includes putting a dye, something called staining. They put a dye, this dye will go and absorb on different organisms in order to distinguish between which bacteria which fungus it is.

Staining is a technique that enhances the visibility of microorganisms under a microscope by applying dyes that stick to specific bacteria or fungi. This allows scientists to distinguish between different types of microorganisms based on their color and morphological characteristics, providing more detailed information when analyzing samples.

Think of staining like adding food coloring to white icing on a cake. The colors help distinguish the decoration patterns—similarly, staining helps make different bacteria identifiable under the microscope, providing clear visual cues about their types.

In general, if the concentration of microorganisms is very high, it will show up as turbidity. So water is not clear, which means it could be because of bacteria a lot of bacteria is there so it is a suspended particulate matter and that’s why there is turbidity.

High concentrations of microorganisms often lead to water turbidity, or cloudiness, indicating an increased presence of suspended particles, including bacteria. However, turbidity alone doesn’t confirm the specific presence of pathogens, making direct culturing necessary to ascertain their viability and potential harmfulness.

It’s like seeing a muddy river; the murkiness signals something is amiss. Just as you'd need to test the water to find out what caused the muddiness, scientists must culture water samples to understand and manage the bacteria present.

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