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Understanding antibiotic resistance
Understanding antibiotic resistance

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1.2 Common bacterial pathogens of humans

Most bacteria found in or on the human body are harmless commensals living on the body without having any detrimental effect. However, a tiny proportion – about 500 species – are pathogenic, that is they are capable of causing disease. These bacteria may evade the body’s normal defences to colonise or invade body cells and tissues, or they may produce harmful toxins. Many bacteria are opportunistic pathogens. These take advantage of an unusually vulnerable host and adapt quickly to the changed conditions.

Activity 2 Common bacterial pathogens and infectious diseases

Timing: Allow about 10 minutes

You might recognise the names of some important pathogenic bacteria shown in Figure 2. Note how different species of bacteria have characteristic shapes: for example, the spherical (coccus)-shaped Streptococci and the rod-shaped Klebsiella.

Can you name the infectious diseases that they cause? Click on reveal to see the answer.

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Figure 2 High magnification images of common bacterial pathogens in humans taken using a scanning electron microscope.
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The figure shows scanning electron micrographs of common bacterial pathogens in humans. Part (a) is a scanning electron micrograph of Streptococcus pneumoniae which appear as chains of red oval shaped cells on a grey background. Part (b) is a scanning electron micrograph of Escherichia coli bacteria which appear as yellow rod shaped cell clustered on a grey background. Part (c) is a scanning electron micrograph of methicillin-resistant Staphylococcus aureus which appear as a chain of yellow spheres on a dark background. Part (d) is a scanning electron micrograph of Mycobacterium tuberculosis which appear as a large clump of red rod shaped bacteria on a dark background. Part (e) is a scanning electron micrograph of two Klebsiella pneumoniae bacteria which appear as two red, rod shaped cells wrapped in a long blue filament. Part (f) is a scanning electron micrograph of Neisseria gonorrhoeae which appear as individual purple kidney shaped cells on a dark background.

Figure 2 High magnification images of common bacterial pathogens in humans taken using a scanning electron microscope.
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Answer

  • a.S. pneumoniae is a common cause of pneumonia and ear infections.
  • b.Pathogenic strains of E. coli are a common cause of diarrhoeal disease, for example as a result of food poisoning, and of urinary infections.
  • c.MRSA is a particular threat in healthcare settings where it can cause sepsis and death if not treated quickly.
  • d. M. tuberculosis causes tuberculosis (TB).
  • e.K. pneumoniae is a common cause of many healthcare-associated infections including pneumonia, and bloodstream and wound infections.
  • f.N. gonorrhoeae causes the sexually transmitted infection gonorrhoea.

Until the mid-twentieth century, bacterial infections were notoriously difficult to treat and were a leading cause of human morbidity and mortality worldwide. Then, in the 1930s, antibiotics were introduced and the outcomes for bacterial infection improved dramatically.

The next section introduces these new wonder drugs of the twentieth century – antibiotics.