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Different Types of Infections in the Mouth – Part 1 – Opportunistic Infections

May 20, 2019

Sorry to say this, the mouth is a dirty place. It is full of various types of organisms that create the environment of the mouth. It’s always changing.

Most of the time life moves on. The body’s immune systems keep these organisms under control. Remember we are changing the environment depending on what comes in and how our immune system handles it.

Let’s talk about some of these organisms.


  • Aerobic: these bacteria love oxygen and are the most common type of organism in the mouth. This is understandable as we breathe in air through the mouth.
  • Anaerobic: these bacteria hate oxygen and cannot survive in a high oxygen environment. In fact when there are a lot of aerobic bacteria in a site, the oxygen content in that site starts to drop in the lower layers allowing anaerobic bacteria to survive. They are nastier bacteria that can use compounds to prevent the immune system attacking them.
  • Facultative anaerobes: bacteria are amazing. These organisms can switch from being aerobes to anaerobes.
  • Fungi: these include yeasts, moulds & Candida Albicans. They are in competition with bacteria. Most of the fungus are oxygen loving. They are like micro plants. In fact these organisms are the basis of antibiotics as the fungi produce substances that kill bacteria.

Infections in the mouth are mainly opportunistic infections. These organisms co-exist with the body without problems.  However if there is an opportunity to find themselves in a situation that is away from competition or the body’s immune defences then they will go for it!

Most opportunistic infections are bacterial.

Through diet and poor cleaning habits certain bacteria are favoured and can cause decay, gum disease, and root canal infections. Physical situations such as impacted wisdom teeth allow bacteria to multiple hidden from being cleaned.

Pus draining through a root canal

Opportunistic fungal infections occur mainly when the environment is less conducive to bacteria; this occurs with antibiotics killing the bacteria but does not affect fungi.

Fungal infection on the tongue due to antibiotic therapy

Also, when the environment greatly favours fungi, such as under dentures which are continually worn or at the corners of the lips that have deep furrows (known as angular chelitis).

Inflamed palate from a fungal infection under horseshoe shaped denture

Next instalment in this series: Different Types of Infections in the Mouth – Part 2 – Viral & Parasites

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Welcome Dr Esther to the Seymour Dental Team