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Examples of diseases caused by opportunistic pathogens

Staphylococci cause infections when they attach and coat prosthetic devices, such as intravenous lines and prosthetic joints
Intestinal villi. Small finger-like projections that extend into the lumen of the small intestine
© University of East Anglia

In this article we will review examples of diseases caused by opportunistic pathogens and the areas they affect.


Staphylococci cause infections when they attach and coat prosthetic devices, such as intravenous lines and prosthetic joints. In immune-compromised patients line infections can cause severe sepsis.

The Respiratory Tract

The upper respiratory tract, including the nose and pharynx, has a normal flora that may include asymptomatic carriage of potential pathogens. Many of these are secondary pathogens can only after a viral infection has damaged the respiratory track epithelium.

Carried by >50% people Potential pathogens
Staphylococcus spp. e.g. Staphylococcus aureus
Staphylococcus epidermidis (up to 40% carriage)
α-haemolytic streptococci Streptococcus pyogenes (<10%)
Haemophilus spp. Haemophilus influenzae (>50%)
Neisseria spp. Neisseria meningitidis (<10%)
Diphtheroids Corynebacterium diphtheriae (<1%)

The Gastrointestinal Tract

The gut contains a multitude of microbes and the genus and species of microbe’s changes as you travel down the gut from the mouth towards the anus. Each defecation releases millions of microbes that are rapidly replaced to replenish the gut. Under normal circumstances, these microbes are harmless and essential to health. However, if the bowel wall becomes damaged then these bacteria can cause peritonitis, intra-abdominal abscesses and sepsis. To prevent this, peri-operative prophylactic antibiotics are given to prevent infection in high-risk abdominal surgery.

Following antibiotic treatment for different infections caused by pathogens, the normal gut microbiome is disrupted as our normal bowel flora, are destroyed by the drugs. This can cause diarrhoea. Clinically, the most severe manifestation of antibiotic-associated diarrhoea is Clostridium difficile associated disease (CDAD). In this condition, the loss of normal microbial flora cased by the antibiotics can allows the relatively resistant spores of C. difficile, either carried asymptomatically by the patient or acquired from the healthcare environment, to germinate into pathogenic bacterial cells. These bacteria release toxins that damage the bowel and cause severe diarrhea. In turn this leads to the release of C. difficile spores into the environment where they can remain for weeks waiting to infect the next person with a disturbed gut microbiome. In addition the use of antibiotics can result in the accumulation of antibiotic resistant microbes within the gut environment.

© University of East Anglia
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Using Infection Control to Combat Antimicrobial Resistance

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