Bacteria and how they multiply

Bacteria – Microbiology issue 2…

Fuente: techni-K Consulting
In this second issue about microbiology, we’re going to focus on bacteria and how they multiply. We’ll first look at a bacteria cell and explain the various parts then the various shapes and multiplication process.  We’ll also explain about something you may have heard of – gram positive and gram negative…


A bacteria, when we’re talking about just one – is called a bacterium. A bacterium is made up of just one single cell.  Here is an example of what the single cell bacterium looks like:

On the outside of the cell are fimbriae.  The bacteria use these to attach themselves to other bacteria or surfaces.

As you can see in this example, this bacterium also has three long strands called flagella. The bacteria use these flagella to give them motion, to help them ‘swim along’ if you like.

The bacterium cell is contained by a cell wall.  The cell wall is protected by a capsule layer and inside the cell well there is a flexible membrane called the plasma membrane.

The inside of the cell is made up of cytoplasm, ribosomes and DNA.  These elements make up the ‘machine’ of the bacterium cell.  Allowing it to produce energy and also to multiply.

The different bacteria shapes…

There are many shapes of bacteria, as you can see from the picture below.



Bacteria are asexual.  This means that they are not like us, as they do not need a partner to multiply.  A bacterium can become two bacteria all by itself.  Then those two bacteria can each multiply again on their own and so, they become four bacteria.

The process that the bacteria use to multiply, is called binary fission.  Binary fission literally means, splitting in half. Let’s walk through the process, step-by-step.



The bacterium starts as just one cell.



In order to become 2 cells, the bacterium starts to replicate all of the internal parts of the cell – the mechanics of the cells that we talked about earlier, the cytoplasm, ribosomes and DNA.  As it does this the size of the cell gets bigger, so it also makes extra cell wall, capsule layer and more of the plasma membrane – you can see in this picture as the cell gets bigger it starts to separate as it starts to look more like 2 cells stuck together.



With all the internal parts of the cell complete, the internal parts of the cells divide completely.  The cell now just has to complete the production of the outer elements.



And when this is complete, the bacteria divide completely.  One has now become two.

So how long does this take?

The speed at which a bacterium can divide, is a really key point for us when we are trying to manage food safety. There are many factors which affect the speed at which a bacterium can divide.  And it is these factors, that we use to our advantage to stop them from dividing and growing to unsafe levels.

In the right conditions, a pathogenic (remember pathogens are the baddies) bacterium can divide every 10 to 20 minutes.  This means if you start off with 1 bacterium, even with a multiplication time of 20 minutes, after 4 hours you would have over 8,000 bacteria.


 All bacteria need is food and moisture to survive.  Time; we know is needed, to allow them to multiply.  The temperature has to be right for the specific type of bacteria, but most like temperatures within what we call the ‘danger zone’.
The danger zone is between 8°C and 63°C.  Colder than 8°C growth is slowed right down.  Hotter than 63°C growth also slows and bacteria start to die off.

Oxygen is an interesting one – because some bacteria need oxygen to grow and others like to grow where there is no oxygen.  Again, we’ll go into this in more detail when we look at preservation hurdles and product intrinsics.

Gram positive or gram negative?

You may have heard people talking about whether bacteria are gram positive or negative. Personally, I wouldn’t worry about this too much, it’s above and beyond what we need to know to manage food safety effectively.

But just in case someone is talking about it and you don’t want to feel like you don’t know what they’re on about – here are the basics.

There once was a man called Hans Christian Gram, who invented a staining technique – so he called it Gram staining after himself.

The staining technique will stain gram positive bacteria violet.  Gram negative bacteria do not pick up the stain, hence why they’re ‘negative’.

There are lots of reasons why the gram positive bacteria stain violet and gram negative bacteria don’t, but we don’t need to know that level of detail.  The most important thing that you need to remember is that you can get both gram negative pathogenic bacteria (e.g. Salmonella) and gram positive pathogenic bacteria (e.g. Listeria).

I hope you’ve found this useful.  If you’ve not read the previous post about microbiology you can read that here:

In the next post, we’ll take a look at how viruses work. As always, please add your comments and questions to the comments box below.

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