Hello friends and welcome back. so today we are going to discuss colony morphology or colony characteristics. The very first thing you do or perform when you are given culture, you note down colony characteristics and then you proceed for identification. so for example, if you are given a soil sample and you perform serial dilutions and you plate out dilutions like 10^4 or 10^5, sometimes you get a crowed plate means lots of bacterial colonies are present on your Nutrient agar plate So what did you observe? You observe different kinds of bacteria which grow. Not just bacteria there are maybe say fungi or yeast cells growing on your plate. so how do you identify? Some colonies are very big enough some are very small some are pigmented, and some appear different like they are elevated or they have a different margin. So that's how you differentiate each and every colony from one another. So that is what we are going to study today. So first what is a colony? what does that mean or what is colony formation? We use a microscope to view a single bacterial cell as we cannot observe a cell with our naked eyes But we observe colonies on our media plate. What is the difference? As we provide all the required nutrients, all the environmental conditions for optimal growth of bacteria and what happens? when bacteria has everything required for growth it starts growing and multiplying and it multiplies a lot That it forms or produces millions of cells (which get pilled up) a colony. And that is what we observe on our media plate. Now all the cells in a colony have the same characteristics. Starting from a single bacterial cell, when everything required is present like nutrients, optimum, pH, temperature, and water; it starts growing. Bacterial cells keep on multiplying and eventually will form a big colony. One which we observe on our plate. That is what is a colony and colony formation. And now we are going to study about the morphology of the colony. A colony is defined as a visible mass of microorganisms all originating from a single mother cell. Definition of a colony. so you may get this in your viva questions in practicals or spotting. Some key features of these bacterial colonies which serve as important criteria for their identification and differentiation are listed below: These are 9 characteristics that are used for noting down colony characteristics of a colony First is the size of a colony, then shape, then margin, elevation, consistency or texture Then opacity, color, Gram staining, motility and some institutes include another characteristic known as surface Means how your colony appears? Is it shiny, is it glisters or dry, or just soft smooth? that is what the surface means. But generally, these are the 9 characters that are used for noting colony morphology/characteristic here this picture has different types of colonies 7 types of bacillus culture The center colony is of WILD TYPE Bacillus mycoides and other types are mutants. You can see the colony morphology changes. That is why we need to observe/ study colony morphology. Depending on the nutrients or environmental conditions provided it may happen that a colony for a particular culture may show slight changes. That is the reason you can't ignore colony morphology. The first colony characteristic is SIZE: The size of the colony can be a useful characteristic for identification. The diameter of a representative colony may be measured in millimeters or described in relative terms such as pinpoint, small, medium, to large. Pinpoint is punctiform then small, medium, and large Generally, you find bacterial colonies growing between small and medium, even are pinpoint (punctiform) But fungal (molds) colonies you will find them growing between medium to large Bacterial colonies we write size in diameter. Colonies larger than about 5 mm are likely to be motile organisms. So how to note down the size? You turn your media plate (back side of the plate where you label everything) So you observe your colonies, mark a well-isolated colony, and by using your scale you measure it So, for example, here it is shown that this particular colony is of 4mm So in this slide with examples, you can see differences in sizes. By observing the plate an isolated colony that is fully grown is selected You can not select a colony which is growing here because this one is small and not isolated and not grown fully. So go for any of these two, or there are also a few isolated colonies so you can select that selection of fully grown isolated colony is a must when it comes to determining size. Next is form: or shape of your colony So, it has 4 types; like it can be circular, irregular, filamentous or rhizoid. It refers to the shape of the colony . These forms represent the most common colony shapes you are likely to encounter. e.g; circular, irregular, there is no defined shape then there are filamentous and rhizoid. Then there is MARGIN THIRD CHARACTERISTIC. That can be entire, here you can see in this picture. Then there is undulate that is slightly lobated or irregular , filiform (filamentous) the actual colony and margin you can see is filamentous, curled (picture shown in my 2nd slide), lobate The margin simply means the edge of a colony. Common examples are entire (smooth), irregular, undulate (wavy), lobate (long lobes), curled, filiform The fourth characteristic is ELEVATION. There are different kinds of elevations which you observe in bacterial or yeast colonies So this describes the '' side -view'' of a colony. These are the most common elevation types. which you observe e.g. flat, raised, umbonate (having a knobby protuberance), Crateriform, convex, pulvinate (cushion-shaped) So these are different types and to observe elevation you take your plate to the level of your eyesight and observe by side view of the colony to know the type of elevation So you can observe the umbonate type of colony elevation from the top also as it is easy to identify Then this is- raised margin; only the margin of the colony is raised and the inner colony part is flat. The fifth characteristic is CONSISTENCY: Several terms that may be appropriate for describing the texture or consistency of bacterial growth are: dry, moist, viscid (sticks to loop, hard to get off), brittle/friable (dry, breaks apart easily), mucoid (sticky, mucus-like) the mucoid colonies are like this slimy and the exopolysaccharide that is secreted by the organisms, it sticks to the loop it is very sticky and you can see a thread-like structure coming out. that is how you identify the consistency. This is for the butyrous or butter-like consistency. That is shown by some bacteria and yeast cultures. Candida albicans (yeast) it looks dull and has butter-like consistency. Butyrous, slimy and dry There is one more characteristic -The appearance of the colony surface. Bacterial colonies are frequently shiny and smooth in appearance. Other surface descriptions might be: dull (opposite of glistening), in case of yeast like Candida albicans the surface is dull veined, rough, wrinkled (or shriveled), glistening means shiny. Actually, the colony shines bright !! That is about the surface Then next is colour/ pigment production: So some bacterial cultures are known for their pigment production they have that particular property. Sometimes it (pigment production) depends on the nutrient medium provided. so, for example on cetrimide agar Pseudomonas aeruginosa shows green pigment. and that is how you can easily identify that yes this particular culture is of Pseudomonas. Then the next is about Serratia marcescens, where you get red-orange colour colonies depending on that you can identify Serratia culture. When lipids/ fats are given in a Nutrient medium then the pigment production is high. Then in case of general identification also pigments are useful Because in case of Staphylococcus aureus and Staphylococcus epidermidis Staphylococcus aureus shows yellow pigmentation whereas Staphylococcus epidermidis shows white or dull so that is how colony characteristics are useful for identification. Then next is about opacity You need to observe whether the colony is transparent (clear) when light is passed through it. Opaque means not transparent ( cannot see through and through) so this one is opaque Translucent is almost clear but distorted vision like looking through frosted glass TRANSLUCENT IS THIS ONE. Where you cannot see everything clear Then there is iridescent which means changing color in reflected light. Generally, marine bacteria show such type of opacity Then comes Gram staining and motility. So this depends on your culture. In the case of fungi, you don't proceed for Gram staining motility. Lactophenol staining is done. Thus it depends on your culture After studying everything how will you note down your observations? So you make a table and note all the characters in one column and start writing your results. We will assume this colony morphology report is for Bacillus culture So the size is 8mm The shape is circular Margin is entire Elevation is Raised Consistency is Butyrous (cream like) Opacity is OPAQUE Colour is white Gram staining is Gram-positive rods Motility is Non-motile Generally for Bacillus, you get this kind of colony characteristics. but depending on the species characteristics may differ.