Chapter 9 The Host-Parasite Relationship Flashcards
How does the distribution of microorganisms change throughout the body?
Populations of microorganisms vary in species and quantity depending on the location in the body
How did molecular biology/bioinformatics change microbiology?
molecular biology/Bioinformatics can be used to describe organisms that cannot be grown in culture
What kind of classification are Diphtheroids (taxonomic genus, species, or just a group?)
Describe the diphtheroids
Not a genus or species, just a group of irregular, clumped at variable and random angles, sometimes called “Chinese letters,” short, Gram-positive, aerobic bacilli. Diphtheroid bacteria are most often Proprionibacterium (P. acnes->acne) and Corynebacterium spp.
How does the microbiota inhibit potential pathogens?
- skin bacteria produce fatty acids, which discourage other species from invading
- gut bacteria release a number of factors with antibacterial activity (bacteriocins, colicins) as well as metabolic waste products that help prevent the establishment of other species
- vaginal lactobacilli maintain an acid environment, which suppresses growth of other organisms
- sheer number of bacteria in intestine microbiota outcompetes others for living space
- gut bacteria release organic acids, which may have some metabolic value to the host; they also produce B vitamins and vitamin K in amounts large enough to be valuable if diet is deficient
- antigenic stimulation provided by intestinal flora helps ensure normal development of immune system
What is an example of commensalism in the large intestine of man?
Host provides enviroment and Bacteriodes spp. ferment digested food
What is an example of mutualism in the rumen of cattle?
Host provides environment and Bacteriodes spp. metabolize host food to fatty acids and gases Host uses fatty acids as energy source
What is an example of parasitism in the large intestine of man?
Host provides environment. Entamoeba histolytica (protozoa) feed on mucosa causing ulcers and dysentery
How do DNA and RNA viruses invade and infect cells?
DNA viruses such as herpes viruses have their own DNA, and use only the host’scellular machinery to make more DNA and more virus protein and glycoprotein. These are then reassembled into new virus particles before they are released from the cell
How do RNA retroviruses replicate inside the cell?
RNA retroviruses (e.g. HIV) first make viral DNA, using their reverse transcriptase, insert this DNA into the host’s genetic material so that viral RNA can be transcribed, and then translate some of the RNA into virus protein. The viral protein and RNA are then reassembled into new particles and released.
Parasites evade the host by eliciting minimal response. Give an example and explain
Herpes simplex virus- survives in host cells for long periods in a latent stage- no pathology
Parasites evade the host by evading the effects of the response. Give an example and explain
Mycobacteria- survive unarmed in granulomas designed to localize and destroy infection
Parasites evade the host by depressing the host’s response. Give examples and explain
HIV- destroy T cells; malaria- depress immune responsiveness
Parasites evade the host by antigenic change. Give examples and explain
viruses, spirochetes, trypanosomes- all change target antigens so host response is ineffective
Parasites evade the host by rapid replication. Give examples and explain
viruses, bacteria, protozoa- produce acute infections before recovery and immunity
Parasites evade the host by surviving in weakly responsive individuals. Give an example and explain
Genetic heterogeneity in host population means some individuals respond weakly or not at all, allowing organism to reproduce freely; examples in all groups
