Host-microbe relationship

Relationships of organisms

Symbiosis - the coexistence of two or more different organisms.

• Endosymbiosis x ectosymbiosis
• Symbiont – any microorganism that shares at least part of its life with another organism
• Three forms of symbiosis:
  1. commensalism – benefits the commensal and does not harm the host (normal gut flora)
  2. mutualism – both partners benefit (Escherichia coli and production of vitamin B12 and K, making colonization by pathogens more difficult)
  3. parasitism – the organism harms the host - directly or just deprives it of nutrients - intracellular parasites, ectoparasites (lice), endoparasites (tapeworms)

Parasite and saprophyte

• A parasite is an organism that at least sometimes requires another living organism
• Saprophyte - a microbe does not need another organism, only non-living organic matter
  • Pathogenic saprophytes – Clostridium botulinum, Histoplasma capsulatum

Infection

__ Infekce

There are several definitions for the term infection or contagion:

1. The presence of a microorganism in a particular host.
2. The penetration of an infectious agent into an organism, multiplication inside and adverse effects on its surfaces (in contrast to this stands colonization - colonization by a non-pathogenic or pathogenic microbe without disease symptoms).
3. Conflict between a microbe and its host (even asymptomatic infection).

Process of infection

The process and severity of infection can be influenced by several factors:

On the part of the microbe

• pathogenicity;
• virulence;
• infectious dose.

From the macroorganism side

• degree of non-specific resistance - overall fitness, genetic factors (population resistance);
• specific immunity - primary, secondary reactions;
• age, nutrition, lifestyle.

Other circumstances

• Environmental influences (e.g. seasonal variations - respiratory infections in cold weather),
• gateway infection (e.g. tularemia).

Stages of infection

1. Incubation period;
2. period of prodromal symptoms - non-specific symptoms;
3. typical syndrome;
4. recovery - relapse may occur;
5. relapse - after recovery.

Forms of infection

According to manifestations

1. Inaparent.
2. Manifest.
   • Subclinical - non-characteristic symptoms.
   • Abortive - poorly expressed symptoms.
   • Clinical form of infection - all symptoms expressed.

According to the range

1. Local (possibly also focal).
2. Systemic (sometimes referred to as massive) - when it affects the whole system or a substantial part (e.g. influenza, pulmonary TB, meningitis, pyelonephritis...).
3. Generalized (regularly e.g. typhoid fever, spotted fever, most exanthematous viruses).

According to the course

1. Acute (days).
2. Subacute (months).
3. Fulminant (violent).
4. Chronic (years).
   • Asymptomatic chronic infections.
     • Mainly viruses, bacteria – Rickettsia prowazekii, Chlamydia trachomatis, Salmonella typhi, Mycobacterium tuberculosis.
     1. Persistent - agents present in an infectious detectable form.
     2. Latent - in the body in a non-infectious form.

References

Related articles

• Pathogenicity and virulence of bacteria

Sources

• JANSKÝ, Petr. Zpracované otázky z mikrobiologie [online]. [cit. 2012-02-01]. <https://www.yammer.com/wikiskripta.eu/uploaded_files/3804405>.

Kategorie:Mikrobiologie Kategorie:Biologie