Transcript PowerPoint
32 Microbial Interactions 1 Copyright © McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display. Microbial Interactions… • Symbiosis = an association of two or more different species of organisms • relationships can be intermittent and cyclic or permanent • Types of interactions include – mutualism, cooperation, predation, commensalism, parasitism, amensalism, and competition 2 Mutualism • Some reciprocal benefit to both partners • Relationship with some degree of obligation – partners cannot live separately • Mutualist and host are dependent on each other 3 4 Commensalism • One organism benefits and the other is neither harmed nor helped (neutral) • Commensal - organism that benefits • Often syntrophic - growth of one organism depends on or is improved by growth factors, nutrients, or substrates provided by another organism growing nearby • Can also involve modification of environment by one organism, making it more suited for another organism 5 Examples of Commensalism • Microbial succession during spoilage of milk – fermenting bacteria promote growth of acid tolerant species • Formation of biofilms – initial colonizer helps other microorganisms attach • Skin or surface microbes on plants or animals – host plant or animal releases volatile, soluble, and particulate organic compounds used by commensals 6 Cooperation • Like commensalism, a positive (not obligate) symbiosis which involves syntrophic (one organism lives off the byproducts of another) relationships • Benefits both organisms in relationship • Differs from mutualism because cooperative relationship is not obligatory 7 Predation • Among microbes involves a predator species that attacks, usually killing its prey • Bdellovibrio penetrates cell wall, grows outside plasma membrane • Benefits by providing nutrients for primary producers Parasitism • One organism gains (parasite) and the other is harmed (host) • Always some coexistence between host and parasite • Successful parasites have evolved to co-exist in equilibrium with their hosts – if balance upset, host or parasite may die 8 Ammensalism • Negative impact of one organism on another based on release of a specific compound • Some examples – antibiotic production by fungi and bacteria – use of antibiotic-producing streptomycin by ants to control fungal parasites – bacteriocin production by bacteria – production of antibacterial peptides by insects and mammals • e.g., cecropins, defensins, and athelicidins – production of organic acids during fermentation 9 Competition • Occurs when two organisms try to acquire or use the same resource • Two possible outcomes of competition – one organism dominates • competitive exclusion principal – two organisms overlap too much in their resource use, and one population is excluded – two organisms share the resource • both survive at lower population levels 10 Human-Microbe Interactions • The human body is a diverse environment – specific niches are present – dynamic relationships exist • Microbiome – all the genes of the host and the microbiota – goal is to determine the impact that microbial gene function has on human health • Pathogenicity – ability to produce pathological change or disease • Pathogen – any disease-producing microorganism 11 Normal Microbiota of the Human Body • Normal microbiota or microflora – microbes regularly found at an anatomical site • Relationship begins at birth – varies with environment and food source – Bifidobacteria • found in breast fed babies • protrophic – can synthesize all amino acids and growth factors from simple carbohydrates 12 The Relationship between Normal Microbiota and the Host • Usually mutually beneficial – normal microbiota often prevent colonization by pathogens – bacterial produces, e.g., vitamins B and K are beneficial to the host • Opportunistic pathogens – members of normal microbiota that produce disease under certain circumstances • Compromised host – debilitated host with lowered resistance to infection 13 14 Skin • Commensal microbes include both resident and transient microbiota • Mechanically strong barrier • Inhospitable environment – slightly acidic pH – high concentration of NaCl – many areas low in moisture – constant sloughing of skin cells • Inhibitory substances (e.g., lysozyme, cathelicidins) 15 Acne Vulgaris • Caused in part by activities of Propionibacterium acnes – sebum • fluid secreted by oil glands • accumulates, providing hospitable environment for P. acnes – comedo • plug of sebum and keratin in duct of oil gland • results from inflammatory response to sebum accumulation 16 Nose and Nasopharynx • Staphylococcus aureus and S. epidermidis – predominant bacteria present – found just inside nostrils • Nasopharynx may contain low numbers of potentially pathogenic microbes – e.g., Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae 17 Oropharynx • Division of the pharynx lying between the soft palate and the upper edge of the epiglottis – alpha-hemolytic streptococci – diphtheroids – Gram-negative cocci – anaerobes in tonsillar crypts 18 Respiratory Tract • No normal microbiota • Microbes moved by: – continuous stream of mucous generated by ciliated epithelial cells – phagocytic action of alveolar macrophages – lysozyme in mucus 19 Eye and External Ear • Eye – from birth throughout a human life, small numbers of bacterial commensals are found on the conjunctiva of the eye – the predominant bacterium is Staphylococcus epidermidis • External ear – similar to skin flora as well as fungi 20 Mouth • Contains organisms that survive mechanical removal by adhering to gums and teeth – contribute to formation of dental plaque, dental caries, gingivitis, and periodontal disease • Within hours of birth, the oral cavity is colonized by microorganisms from the surrounding environment 21 Stomach Small Intestine • Most microbes killed • Divided into three areas by acidic conditions – some survive if pass through stomach very quickly – duodenum – some can survive if ingested in food particles – jejunum • contains few organisms – ileum • flora present becoming similar to that in colon • pH becomes more alkaline 22 Large Intestine (Colon) • Largest microbial population of body – eliminated from body by peristalsis, desquamation, and movement of mucus – replaced rapidly because of their high reproductive rate – most of the microbes present are anaerobes – Bacteroides thetaiontaomicron • colonizes exfoliated host cells, food particles, and sloughed mucus 23 Genitourinary Tract • Kidneys, ureter, and bladder – normally free of microbes • Distal portions of urethra – few microbes found • Female genital tract – complex microbiota in a state of flux due to menstrual cycle – acid-tolerant lactobacilli predominate 24