Transcript pathogen
Pathogenicity and virulence MUDr. Lenka Černohorská, Ph.D. Symbiosis • Commensalism – 1 partner profits, 2nd is not damaged (bacteria of intestinal flora) • Mutualism – reciprocate profit, for ex. E. coli – vitamine K, protection of body surfaces (Staphylococcus epidermidis) • Parasitism – 1 partner profits, 2nd is damaged (direct or indirect effect – food competition) Relationships and their dynamics • between a microbe and a host – tendence to equilibrate the powers • the dynamic and duration of a disease is dependent on these relationships Mutualism Commensalism Parasitism Parasite Ecological “gangster” – steal and kill! In microbiology – Parasitology - parasitic protozoa or helmints (Toxoplasma gondii, Ascaris lumbricoides…) Parasite is a beeing, who needs for life another living organism // an opposite saprophyt – needs only organic substances from not living organisms Pathogenicity = Ability to damage and cause a disease 1. species characteristic – is related to whole microbial species 2. natural (Yersinia pestis - pest)/experimental (Treponema pallidum - syfilis in rabbit) 3. must be related to host species (species susceptibility) Microb able to damage and cause a disease pathogen Koch‘s postulates 1. 2. 3. 4. 5. The organism must be isolated from every patient with the disease The organism must be isolated and cultured outside the body in pure culture The pure organism must cause the disease in healthy, susceptible animals The organism must be recovered from the inoculated animal The antibody to the organism should be detected in the patient´s serum Pathogenicity • Obligate (primary) pathogen cause disease in healthy persons – typhus, syfilis etc. • Facultative (opurtune) – the disease is caused only in imunocompromited patients- for ex. E. coli – normal flora of large intestine, but also causative agens of 80 % urinary tract infections, wound infections... Virulence = quantitative measure of patogenicity and is related to a strain 1. 2. 3. 4. is an individual characteristic can be measured : the number of organism needed to kill half the host – 50% letal dose - LD50 and the number needed to cause infection in half the host – 50% infectious dose - ID50 genetic changes are possible as well as changes of virulence made by an environment – pasaging in suboptimal conditions ( virulence, preparation of BCG vaccine - TBC), or on susceptible host ( virulence, danger of laboratory infection!) Analogies: patogenicity/virulence - microbe species/individual susceptibility (resistance) - macroorganism Factors of pathogenicity 1. 2. 3. Contagiosity – transmissivity – high (respiratory viral infections), low (Clostridium tetani) Invasiveness – interfering with the host defence mechanism – entrance (adherence and penetration), division and dissemination Toxigenicity – ability to destroy – due to microbe himself or host reaction Thank you for your attention