Atlant’s Column: Cliffhangers

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Welcome to the section on which explores, analyzes and explains fascinating microscopical structures.

Streptococcus bacteria

The picture shows one of the biggest killers of humanity: the pneumococci (Streptococcus pneumoniae). These bacteria possess a kind of armour made of long sugar molecules that make them inaccessible. Moreover, this armour has a negative charge, which prevents them from adhering to surfaces. Like rubber balls the bacteria bounce off and work their way through the airways deeper into the body until they end up in the middle ear or in the lungs. There they strike.

Text by science writer Atlant Bieri
Photography by Martin Oeggerli

Their mass propagation causes otitis media or pneumonia. If they get into the blood stream, they may even cause meningitis or death. Particularly weak immune systems such as those of young children or elderly people succumb to the pressure of the pneumococci and thus the body collapses. Worldwide, they are responsible for 11 percent of all child deaths.

In healthy adults, however, pneumococci rarely have a chance. Since they always arrive via the respiratory tract, they must inevitably pass through the nasal mucosa. It is the realm of the phagocytes, which prepare for the invaders a brutal reception. It means full stop for the pathogens.
But pneumococci are very flexible. They immediately change their strategy and put all their attack energy into the defence. For this, the formerly highly mobile bacteria now deliberately cling down to the nasal mucosa. Biologists call this form of existence “biofilm“.


Streptococcus bacteria growing on sterile surface

Armored with sugar molecules

This is the stage the bacteria in the picture have reached. They are just about to form a biofilm. First, they put down their armor of sugar molecules. As a consequence, they lose their negative charge and now stick tightly to any surface. The sugar molecules of all the bacteria flow into one single big lake, which protects them equally from the attacks of the immune system. They exude more sugars into the lake until it reaches a depth of 25 micrometres. Compared with a human this would amount to approximately forty metres.

To enhance their defence even more, they reduce the activity of some 50 genes. The energy saved is put into the production of stress proteins, which increase their resistance towards antibiotics a thousandfold.

All these measures protect the bacteria from the constant bombardment of the immune system for some weeks or even years. In this state, however, they can cause no more infections. Even if they managed to contaminate the bloodstream, they would not be a threat, as researchers discovered recently. What is still a mystery is the question, under what circumstances the pneumococci transform from their harmless biofilm stage back into potential killers.

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Continue reading Atlant’s Column: The Fungal Plague, August 2012, or go back to the archive