Microbiology and Immunology

Bacterial adaptation WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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virulence factors. For example, streptococci, staphylococci

and pneumococci produce hyaluronidase, an enzyme that

breaks down hyaluronic acid, a host tissue cement. They also

produce proteases, nucleases and lipases that depolymerize

host proteins, nucleic acids and fats. Clostridia that cause gas

gangrene produce collagenase, and κ-toxin, which breaks

down the collagen network supporting the tissues.

The ways in which pathogens bring about damage to the

host are diverse. Only rarely are symptoms of a disease due

simply to the presence of a large number of microorganisms,

although a large mass of bacterial cells can block vessels or

heart valves or clog the air passages of the lungs. In many

cases, pathogenic bacteria produce toxins that are responsible

for host damage. Toxins released extracellularly are called

exotoxins, and these may travel from the focus of infection to

distant parts of the body and cause damage in regions far

removed from the site of microbial growth. The first example

of an exotoxin to be discovered was the diphtheriatoxin pro-

duced by Corynebacterium diphtheriae.Some Gram negative

bacteria produce lipopolysaccharides as part of their cell

walls, which under some conditions can be toxic. These are

called endotoxins and have been studied primarily in the gen-

era Escherichia, Shigella,and Salmonella.

See alsoAnti-adhesion methods; Antibiotic resistance, tests

for; Immune system; Immunofluorescence; Immunology;

Infection and resistance; Infection control

BACTERIA, ECONOMIC USES AND BENE-

FITS•seeECONOMIC USES AND BENEFITS OF MICROORGAN-

ISMS

BBacterial adaptationACTERIAL ADAPTATION

Bacteriahave been designed to be adaptable. Their sur-

rounding layers and the genetic information for these and

other structures associated with a bacterium are capable of

alteration. Some alterations are reversible, disappearing

when the particular pressure is lifted. Other alterations are

maintained and can even be passed on to succeeding genera-

tions of bacteria.

The first antibiotic was discovered in 1929. Since then,

a myriad of naturally occurring and chemically synthesized

antibioticshave been used to control bacteria. Introduction of

an antibiotic is frequently followed by the development of

Scanning electron micrograph of Escherichia coli, the cause of a gastrointestinal infection that can lead to severe complications.

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