MMG 301 Introductory Microbiology, Dr. Frank DazzoAnimal-Microbe InteractionsPrevious pertinent topics already covered:1. Microbial pathogenesis:A. Animal diseases caused by eukaryotic microorganisms:• malaria (Plasmodium falciparum)• amoebic dysentery (Entamoeba histolytica),• trypanosomiasis (Trypanosoma),• amoebic meningocephelitis (Naegleria fowleri)• Pfiesteria "cell from hell" fish infectionsB. Fatal human diseases caused by bacteria:• pyogenic skin wounds (Staphylococcus aureus)• lyme disease (Borellia burgdorferi)• gonorrhea (Neisseria gonorrhoeae)• various exotoxicities:diphtheria – Corynebacterium diphtheriae,botulism – Clostridium botulinum,teatnus – C. tetani,cholera – Vibrio cholera• bacterial respiratory tract infections (Streptococcuspyogenes, Klebsiella pneumoniae)• bacterial meningitis (Neisseria meningitidis)• tuberculosis (Mycobacterium tuberculosis)• syphilis (Treponemia pallidum)• gastrointestinal infections/diarrhea: Escherichia coli,Salmonella, Shigella)• Legionaires disease: Legionella pneumophila• Anthrax (bioterrorist agent): Bacillus anthracisC. Significant human diseases caused by viruses(grouped according to their route of dissemination):• Respiratory infectious droplets: influenza, common cold,measles, mumps, chickenpox, smallpox, "severe acuterespiratory syndrome" = SARS• Direct contact with bodily fluids: AIDS, hepatitis B, herpes• Fecal contamination: gastroenteritis, hepatitis A, polio• Insect vectors: West Nile, equine encephalitis2. Normal human - microflora interactions:• commensalistic, mutualistic, or opportunistic in scope;• includes microflora on skin, oral cavity, gastrointestinaltract, genitourinary tract, respiratory tract.3. Mutualistic animal – microbial symbioses:• Bioluminescent Vibrio in cavity below eyes of marine fish• Bacterial endosymbionts in tube worm near deep seahydrothermal vents2 other majormicrobe-animalinteractions:termite hindgutand rumen haveanaerobicfermentationsthat providemajor sourcesof methane.• Sources of cellulases: 1) termites themselves, 2) anaerobiccellulolytic protozoans in hindgut of "lower" termites. Hindgut of"higher" termites contain no protozoans nor bacterial cellulases.• The termite and protozoan cellulases depolymerize celluloseto glucose, which then is fermented by various gut microbesinto acetate (absorbed & used by the termite), CO2 and H2.• The CO2 + H2 products have 2 major fates in the termite gut:(1) favored fate is microbial acetogenesis CO2 + H2 →→→→ CH3COOH(acetate) assimilated by the termite, and (2) the competing reactionis microbial methanogenesis CO2 + 4H2 →→→→ CH4 + 2H2O• Methanogenesis is mediated by free-living methanoarchaeaand other methanoarchaea endosymbionts of protozoa Phase contrast (A) and epifluorescence microscopy (B) of thetermite gut contents showing ingested wood particles (yellow)and protozoa (arrows) containing many endosymbioticmethanoarchaea that produce a green autofluorescent enzymecofactor (F420) required for methanogenesis.Microbiology of the Termite hindgut:Major food consumption: wood(high in cellulose, low in fixed N).Obligatory mutual symbiosis:termite completely dependent on itshindgut microflora to provide its C +N nutrition derived from anaerobicdegradation of the wood particles.Two types of spirochetes: someare free-living N2-fixers and othersare ectosymbionts attached to thesurface of flagellated protozoawhere they provide some motility.ABRumen ecosystem: warm-blooded herbivores, cow sheep goatsIngested plant feed travels from the esophagus to the reticulum andquickly to the large rumen vat where it is digested microbiologically,then passes to the acidic stomach (omasum, abomasum), then smalland large intestines.• A vast diversity of rumen microbes decompose the ingested plantmaterial into volatile fatty acids that are absorbed and utilized by theanimal, plus gas fermentation products that the animal expels.• Cellulolytic bacteria and protozoa extracellularly hydrolyze celluloseto cellobiose (disaccharide of glucose) + glucan oligosaccharides.• Many anaerobic bacteria ferment these glucose oligomers intovarious volatile fatty acids (acetate, propionate, butyrate) that areabsorbed and assimilated by the animal, plus CO2↑↑↑↑ + CH4↑↑↑↑.Fistula sample
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