Everything You Need To Know About Chlamydia Bacteria 

Chlamydia is a bacterial infection that can be transmitted through contact with infected genital fluids.

It can be spread through various different types of sexual acts, and if a pregnant woman gets chlamydia they can pass it on to their baby.

Everything You Need To Know About Chlamydia Bacteria

As chlamydia is a bacterial infection, it can be treated with antibiotics.

If left untreated it can cause irreparable damage to the reproductive system. 

If you want to know more about the different types of chlamydia bacteria, the classification of those bacteria, their characteristics, and the microscopy, then keep reading.

We have put together this useful guide to tell you everything you need to know. 

What Is Chlamydia Bacteria? 

Chlamydia bacteria is an intracellular genus of bacteria that can cause infectious diseases in both humans and animals.

There are three species of chlamydia that are responsible for the infections that arise in humans, and those strains of bacteria are thriving all over the world in developed, developing and underdeveloped countries.

The most common chlamydia bacteria in the United States and Australia is chlamydia trachomatis, and it is actually the most common bacterial agent of all STDs in those areas. 

Chlamydia trachomatis, chlamydia psittaci and chlamydia pneumoniae are the three types of chlamydia bacteria that cause infections in humans.

There are also other species of chlamydia bacteria including chlamydia suis, chlamydia aviu, chlamydia abortus and chlamydia pecorum. 

During their lifespan, chlamydia bacteria can switch between two different forms that are morphologically distinct from each other.

They have an elementary body, which is how they present before they have invaded their host.

These bodies are infectious, and will find a host to invade. They cannot produce their own energy as they are metabolically inactive.

Once inside the host, the elementary body will become a reticulate body.

These bodies are not infected, and they are metabolically active. 

Chlamydia Classification 

All living organisms are biologically classed into a domain, a phylum, a class, an order, a family, a genus and a species.

The domain has the most number of organisms in it as it is the most general classification.

This decreases gradually until you reach the species which is very specific. 


Chlamydia is classified in the bacteria domain.

Chlamydia is a prokaryotic organism which means it is a single celled organism without internal membranes.

This means that chlamydia cells, like other prokaryotic bacteria, have a very simple structure without any organelles that are bound by a membrane.

Different types of bacteria can be found in all sorts of environments all over the world. 


Chlamydia is classified in the chlamydiae phylum which is made up of obligate intracellular types of bacteria with an oval shape.

These types of bacteria can infect humans and animals and they are very diverse. Some of them cause harm to the host organism and some of them don’t.

Some of them even live as symbiotes, which means that the biological link between the bacteria and the host is mutually beneficial to both organisms.


The Chlamydiae phylum is split into different orders, and chlamydia bacteria comes under chlamydiales.

Chlamydiales can not only infect humans and animals, they can also infect free living amoebae, vertebrates and invertebrates.

They can also be transmitted by ticks from one living organism to another. 


The chlamydiaceae is made up of gram negative chlamydia bacteria.

This means that these bacteria are resistant to crystal violet staining in the gram staining methodology of differentiating different types of bacteria. 


 All three types of chlamydia bacteria that cause human infection fall into the genus chlamydia, but they are separated into different species. 

What Are The Different Characteristics Of Chlamydia Bacteria? 

Chlamydia bacteria have different characteristics that separate it from other types of bacteria. Here are some of the characteristics you can expect to see from chlamydia bacteria.


Chlamydia bacteria are spread all over the world and are widely distributed.

Chlamydia trachomatis is the most common form of sexually transmistted bacteria, but the rate of infection varies depending on the region.

Areas that are in poverty tend to see a higher rate of infection for the blinding trachoma strain, such as certain areas of Asia, Africa and the Western Pacific. 

The chlamydia bacteria was thought to have originated around seven million years ago, but the first infection of chlamydia trachomatis that has been traced was in 27th Century BC.

The infection led to a spread of sexually transmitted disease and ocular disease. 

The number of new cases of sexually transmitted chlamydia is gradually decreasing every year, but it is still very prevalent- especially in young adults aged 18 to 26 years old.

Around half the world population of adults aged 20 and above show serological evidence of a previous chlamydia infection.

There are over 100 million cases of trachoma blinding every year, some of them irreversible and others that are treatable.

Around 15% of blindness across the worldwide population has been caused by Chlamydia trachoma. 

Cellular Biology 

As mentioned earlier, one of the characteristics of the chlamydia genus is that the bacteria is gram negative.

This means that they are resistant to crystal violet staining.

This is because of the thin peptidoglycan – the rigid cytoplasmic membrane that surrounds the cell.

Most bacteria have a thin peptidoglycan, but certain types of chlamydia have a barely detectable peptidoglycan. 

Chlamydia pneumoniae and chlamydia trachomatis encode proteins that are involved in the synthesis of the peptidoglycan, as well as a protein that lives on the outer membrane of chlamydia trachomatis and chlamydia psittaci.

The various proteins that are found on the membrane of the cells are used to help differentiate the various types of chlamydia bacteria. 

But why is the peptidoglycan different for certain forms of chlamydia bacteria compared to other bacteria?

Studies suggest that it is actually an evolutionary adaptation.

It benefits the bacteria to have a thinner or non-existent peptidoglycan as it allows the bacteria cells to enter the cells of their hosts more easily, and enables them to thrive there by absorbing more substances through their cell membrane to convert into energy. 

Chlamydia trachomatis have their own characteristics that sets them apart from other types of chlamydia bacteria.

Chlamydia trachomatis is not motile, which means that it does not have the necessary cell structure required for movement.

It travels through the genital fluid of the host as it is transmitted to another host.

Chlamydia trachomatis bacteria can be coccoid shaped or rod shaped.

They have reticulate bodies that range in size from 800 nanometers to 900 nanometers in diameter, and infectious bodies that range in size from 300 nanometers to 400 nanometers in diameters. 

Chlamydia Pnuemoniae differ from trachomatis in that they have an elongated coccoid shape.

They have pear-shaped elementary bodies which range in size from 200 nanometers to 400 nanometers in diameter. 

Life Cycle And Reproduction 

As noted previously, the three types of chlamydia bacteria that cause bacterial infections in humans are chlamydia trachmatis, chlamydia pneumoniae, and chlamydia psittaci.

Each type of bacteria has its own method for infecting their host. 

Chlamydia trachomatis is sexually transmitted.

This means that it is passed from one human to another via the genital fluids.

Chlamydia pisttaci infects birds as well as humans, and it can be passed between hosts from contacts with infected birds.

This is why the bacterial infection is sometimes called parrot fever.

One of the factors that increases the spread of these bacterial infections is that they can often be asymptomatic or take a long time to present symptoms.

This means that someone could be spreading the bacterial infection unknowingly for a long time before they realize that they are affected, by which time a lot of other people will also be infected.  

Each strain of chlamydia bacteria has a different incubation period.

Some strains of chlamydia trachomatis take only a few days to incubate within the host, whilst some strains of chlamydia pneumoniae will incubate for several years.

Other types of chlamydia bacteria have an incubation period of a few months. 

When the symptoms do begin to present themselves, the expression of the bacterial infection in humans will differ depending on which strain of chlamydia bacteria they have been infected with.

Chlamydia pneumoniae causes issues in both the upper and the lower respiratory tract whereas chlamydia psittaci can cause mild illnesses or pneumonia. 

Transmission Of Disease

There are two main modes of disease transmission used by chlamydia bacteria – direct contact transmission and respiratory transmission.

For example, conjunctivitis, trachoma, lymphogranuloma and other types of chlamydia trachomatis transmission take place via direct contact transmissions.

A contaminated hand could touch a hand towel in a shared bathroom. Someone else could then use that hand towel, then rub their eyes or their mouth.

Someone could also cause the bacterial infection to spread to a secondary site in their own body – a contaminated hand could be used to rub their own eyes which will spread the bacteria from the urogenital tract to the eyes.

In the case of pregnant women, the birth canal is already infected with bacteria.

As the baby passes through the birth canal their eyes and mouth will come into contact with contaminated genital fluid, passing on the disease. 

In contrast to chlamydia trachomatis, chlamydia psittaci and chlamydia pneumoniae are transmitted through the respiratory system.

Chlamydia pneumoniae is transmitted from human to human, whereas chlamydia psittaci is transmitted from bird to human. 

Everything You Need To Know About Chlamydia Bacteria

Elementary Bodies VS Reticulate Bodies 

If we are talking about the life cycle of chlamydia bacteria as one of its characteristics, then we need to take a closer look at what happens when the bacteria cell alternates from an elementary body to a reticulate body. 

As mentioned earlier, elementary bodies are metabolically inactive.

They are quite small and have a rigid membrane on the outside of the cell with proteins on the surface.

The membrane has a high content of the amino acid cysteine, that has been cross-linked with disulfide.

This membrane helps the bacteria to thrive even in difficult environments outside of a host. 

The cell membrane is also used to help the bacteria to invade their host.

They begin by attaching their cell membrane to the host using ligands (messenger molecules).

These ligands attach to the receptor cells of the host cell, which means that the bacteria can then release effectors into the host cell cytoplasm.

There are various proteins in the host cell that assist with this process, but the full details of the process have not yet been fully discovered and understood. 

Once the effectors have been injected into the host cell cytoplasm, a vacuole forms around them.

This is where the elementary bodies can then become reticulate bodies which takes around two hours.

If multiple elementary bodies are able to attach to the cell membrane of the host then multiple effectors will be injected into the host cell.

This could lead to one large vacuole made of up the various effectors infused into one. 

Reticulate bodies differ from elementary bodies in that they are metabolically active.

They do not have the same rigid membrane, but instead they have an inner and an outer membrane.

They also reside inside a vacuole which protects them from antibiotics and allows them to enter the host’s lysosomes.

Reticulate bodies are larger than elementary bodies and they are intercellular.

The cytoplasm of reticulate bodies is high in nucleic acid and it has a granular consistency. 

The reticulate bodies go through a process called binary fission, which is the asexual reproduction of the cells to increase the population.

Within a few hours, the number of bacteria cells within the host will have rapidly grown.

Within 48 hours to 72 hours after the initial elementary body enters the host cell, some of the reticulate bodies will revert back to elementary bodies and leave the host.

Alternatively, some of the new cells made through binary fission will become elementary bodies rather than reticulate bodies. 

When the elementary bodies are released into the extracellular environment they will look for a new hose in order to continue spreading.

In some cases, the act of leaving the host cell as an elementary body will destroy the host cell, but in other cases the cell will not be damaged.

Once the elementary body finds a new host cell the cycle will begin again. 

Elementary Bodies Exiting The Host Cell 

There are two ways that an elementary body can leave the host cell – lysis of the host cell or extrusion of the vacuole.

The bacteria can only exit the host cell once it has transformed from a reticulate body into an elementary body. 

What is lysis of the host cell? This is the exit method that causes the death of the host cell.

A process called cysteine proteases ruptures the membrane of the host cell (cysteine is an amino acid which is found in high concentration in cell membranes).

This allows the elementary body to be released, but it also causes the cell membrane to disintegrate (lysis). 

Extrusion of the vacuole occurs after the bacteria cell and the host cell have interacted.

The surface of the vacuole folds in on itself, then the plasma membrane of the host cell begins to furrow.

The cell is pinched, which forces the vacuole out of the host cell but tends to leave the host cell intact. 

Microscopy Of Chlamydia Bacteria

Microscopy is used to confirm the presence of chlamydia bacteria and to investigate infected cells by looking for vacuoles.

In order to use a microscope to look for chlamydia bacteria, the following method can be used. 

First you will need to collect a sample of chlamydia bacteria, which is usually done using cotton swabs with calcium alginate and dacron.

These are taken from the patient who is suspected to have a chlamydia infection.

You should not use a wooden implement to collect the sample, as the wood contains certain substances which can be toxic to the bacteria and could ultimately contaminate or destroy your specimen. 

The sample may be taken from the anal canal, the nasal canal, the genital tract or the ocular region depending on what kind of infection you are looking for.

If you are not preparing the sample for microscopy straight away then it needs to be stored in the correct conditions.

For example if a nasopharyngeal swab is taken from a patient and needs to be sent off to a lab for testing, the sample should be stored in a cell culture media until it reaches the lab and is ready to be processed. 

Equipment And Requirements

You will need: 

  • A sample of the suspected infected cells
  • A fluorescent microscope
  • A clean glass slide
  • Giemsa Stain (remember that chlamydia bacteria are resistant to crystal violet stain) 
  • Ethanol 95% 



Before you can look at your sample under the microscope you need to stain it. 

  • Step One –  Wipe the swab on a clean glass slide in order to transfer some of the sample onto the glass. Let this air dry before moving on to the next step. 
  • Step Two –  Use methanol to fix the sample to the glass slide. This will take around 5 minutes of methanol exposure. Let this air dry before moving onto the next step. 
  • Step Three –  The next step is to stain the specimen by covering it with Giemsa for around one hour. 
  • Step Four –  After an hour, rinse the slide in 95% ethanol to remove any excess dye before you observe the slide. 


Once the staining process is complete, you can observe your sample under the microscope.

The vacuoles are basophilic, which means that they will show up as a pink/blue color under the microscope.

If you notice the presence of vacuoles, then it is very likely that there is chlamydia bacteria in the sample.

This means that the patient the sample was taken from probably has a chlamydia bacterial infection. 


Chlamydia bacteria has characteristics that set it apart from other types of bacteria.

Included in the chlamydia bacteria genus are various forms of chlamydia bacteria with different features.

Some of them infect humans, others infect humans and animals. They have differing incubation periods and methods of transmission. 

You can use a microscope to confirm the presence of chlamydia bacteria in a sample specimen, but it needs to be dyed first. 

Jennifer Dawkins

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