1: What is a pathogen? Flashcards
What are gnotobiotic animals and what is different about them?
Gnotobiotic animals are germ free.
They need 30% more calories because microflora degrade and ferment indigestible plant material. They have less vascularisation and poor developed villi, and an underdeveloped mucosal immune response.
What is the function of gut microflora?
Gut microflora induces immune responses, including production of antimicrobial peptides. Gut anaerobes also release small simplified carbohydrates (butyric acid) which is taken up the bloodstream and used by the host.
What is an endogenous infection and how can it be caused?
Diseases by normal microflora, are caused by normal microflora at the wrong place or abnormalities in host defence.
What are the four examples of normal microflora at the wrong place?
Damage to the epithelium, new sites for normal microflora, foreign bodies and wrong host.
What does damage to the colon epithelium cause? Name an example.
Damage to the colon epithelium (spontaneous or after surgery) results in the infiltration of gut microflora in the peritoneum. Some pathogens are synergistic and can cause abscess formation by coinfection of for example E.coli and B.fragilis.
What is an example for infection by new site for normal microflora?
New sites for normal microflora like urinary tract infections (cystitis) can result in bladder and kidney infections. Urinary tract infections are mostly caused by E.coli. Cystitis is mainly in woman because of the close proximity of the urethra and anus.
What is infection by wrong host?
Different mammals have similar composition of gut flora, however, with strain-specific bacteria. Infection with these strain specific bacterial in another host can have serious effects.
Name 3 examples of infection by wrong host.
- Outbreak of E.coli 0157:H7 in the US, where Apple Juice was infected by deer droppings with E.coli.
- Salmonella poisoning after little girls kissed a frog.
- Cat/dog bites. Infection with C. canimorsus (normal oral floral of cats/dogs) leads to sepsis.
What are the four examples of infection by abnormalities in host defence?
Can be a genetic defect, suppression of the immune response, other infections or antibiotics.
What is an example of infection by genetic defects?
Herpesvirus is persistent and present in 50-100% of the population. It infects the endothelial cells and resides in the nerve cells, and on reactivation moves back to the endothelial cells, so it is not present in the CNS. But herpes simplex encephalitis (HSE) is a rare complication of HSV-1 infection in the brain. HSE susceptibility is genetic because it is caused by TLR3 pathway defects. TLR3 binds dsDNA and starts production of Type 1 interferon, which are effective against viral infection.
Why can endogenous infections be caused by antibiotics?
Antibiotics kill antibiotic-sensitive species and can lead to massive outgrowth of endemic species or colonisation by antibiotic resistant new species, like C. difficile and E. faecalis.
Why are bacteria of the normal microflora good pathogens?
Because they are always present, have factors for colonization which can also be used for virulence, are adapted to the metabolism in the host and some virulence factors are needed to withstand other organisms, such as grazing protozoa.
Why are vertebrates the ideal breeding ground for bacteria?
Because of the ambient temperature, a high numberof nutrients and good transport of metabolites and waste.
What do pathogens have to overcome for exogenous infection?
They have to colonizate mucosal surfaces, cross anatomical barriers, invade tissue, breach host defences and also disseminate.
What are the problems with M. tuberculosis virulence?
There is no clear factor (toxin) involved in the disease symtomps, and the question is even if tuberculosis causes a disease since 90% of the infected people never develop tuberculosis.
