Bacteria-Host Relations 2024 PDF

1 Department of Microbiology, Faculty of Medicine, Urmia University of Medical Sciences, Urmia, West Azerbaijan, Iran By; Dr. akbari 2024 2 Microorganism-Host relationships...

1 Department of Microbiology, Faculty of Medicine, Urmia University of Medical Sciences, Urmia, West Azerbaijan, Iran By; Dr. akbari 2024 2 Microorganism-Host relationships Bacteria  References for more study 3 Diagnostic Microbiology; Bailey & Scott's Textbook of bacteriology; Kenneth Todar Cellular microbiology; Brian Henderson Wiley  The nature of environment-microorganism-host 4 relationships Microorganism Host Environment 5 The nature of microorganism-host relationships Host Microorganism  6 Symbiosis  In biology, symbiosis is defined as "life together", i.e., that two organisms live in an association with one another.  Bacteria-host relationships in humans 7 Types of symbiotic associations; 1- Mutualism Both members of the association benefit. Example; lactic acid bacteria that live on the vaginal epithelium of a woman. 8 Mutualism  Nutrients  Stable environment  Protection  Transport  Stimulation and development of immune system  Nutrients Microorganism Host  9 2. Commensalism  There is apparent benefit to one member of the association.  Example. S. epidermidis on the skin of humans as long as it doesn’t cause illness.  Commensalism 10  Nutrients  Stable environment  Protection  Transport !? Microorganism Host  11 Commensalism  If a presumed commensal relationship is studied in detail, parasitic or mutualistic characteristics often emerge.  12 3. Parasitism  In biology, the term parasite refers to an organism that grows, feeds and is sheltered on the survival of its host.  The parasite is capable of causing damage to the host.  Parasitism 13  Induce harmful effects  No benefit  Nutrients  Stable environment  Protection  Transport Microorganism Host  Question 14 Parasitism ? ? Commensalism Normal Microbiota Nonindigenous Parasites ? Mutualism  15 Dysbiosis Disruption of the normal microflora can lead to disease by the elimination of needed organisms or allowing the growth of inappropriate bacteria. Example, following exposure to antibiotics and suppression of the intestinal normal flora, C. difficile is able to proliferate and express enterotoxins, leading to inflammation of the colon (antibiotic-associated colitis).  Normal Microbiota (Normal Flora) 16  Microbiome is a term that describes the genome of all the microorganisms, symbiotic and pathogenic, living in and on all vertebrates.  Microbiota are the range of microorganisms that may be commensal, or pathogenic found in and on all multicellular organisms.  Normal Microbiota (Normal Flora) 17  Normal Microbiota are absence in;  Internal tissues and fluids e.g. blood, brain, muscle, etc.  Normal Microbiota presence on;  The surface tissues, i.e., skin and mucous membranes.  The composition of the normal flora 18  The normal flora of humans consist of more than 200 species of bacteria.  The makeup of the normal flora on the individual may be influenced by various factors;  Genetics  Age  Sex  Stress  Nutrition and diet  Bacterial normal flora on human body 19  The normal flora of humans consists of a few eukaryotic fungi and protists, but bacteria are the most numerous. ++ = nearly 100 percent + = common (about 25 percent) +/- = rare (less than 5%)  Predominant bacteria at various anatomical locations in adults 20  Normal Microbiota (Normal Flora) 21  Colonization of normal flora  In first, at the moment of birth and passage through the birth canal.  Handling and feeding of the infant after birth; on the skin, oral cavity and intestinal tract in about 48 hours.  Adult human houses about 1012 bacteria on the skin, 1010 in the mouth, and 1014 in the gastrointestinal tract.  The composition of the normal flora 22  The composition of the normal flora can be changed by; 1- Weaning (intestinal tract) 2- The eruption of the teeth (oral cavity) 3- The onset and cessation of ovarian functions (vagina)  23  The effects of the normal flora are inferred by microbiologists between "germ-free" animals (which are not colonized by any microbes) and conventional animals (which are colonized with a typical normal flora).  24 Beneficial effects of the normal flora 1. The normal flora synthesize and excrete vitamins  In humans, enteric bacteria secrete Vitamin K and Vitamin B12, and lactic acid bacteria produce certain B-vitamins.  Germ-free animals may be deficient in Vitamin K to the extent that it is necessary to supplement their diets.  Beneficial effects of the normal flora 25 2. The normal flora prevent colonization by pathogens  By competing for attachment sites or for essential nutrients.  In some experiments, germ-free animals can be infected by 10 Salmonella bacteria, while the infectious dose for conventional animals is near 106 cells. 26  Beneficial effects of the normal flora 27 3. The normal flora may antagonize other bacteria  Through the production of substances which inhibit or kill nonindigenous species.  The intestinal bacteria produce nonspecific fatty acids and peroxides to highly specific bacteriocins, which inhibit or kill other bacteria.  Beneficial effects of the normal flora 28 4. The normal flora stimulate the development of certain tissues  The intestinal lymphatic tissues (Peyer's patches) of germ-free animals are poorly- developed compared to conventional animals.  29 Beneficial effects of the normal flora 5. The normal flora stimulate the production of natural antibodies  "Natural" antibodies; Antibodies produced against to normal flora. (antibody- mediated immune (AMI)).  Natural antibodies cross react with certain related pathogens, and thereby prevent their infection or invasion.  30 Germ-free animals characteristics: 1. Vitamin deficiencies. 2. Increased susceptibility to infectious disease 3. Poorly developed immune system, especially in the gastrointestinal tract 4. Lack of "natural antibody" or natural immunity to bacterial infection  Harmful effects of the normal flora 31 1. Bacterial synergism between a member of the normal flora and a potential pathogen. Cross-feeding; The normal flora supplying a vitamin or some other growth factor that a pathogen needs in order to grow.  Harmful effects of the normal flora 32 2. Competition for nutrients  Bacteria in the gastrointestinal tract must absorb some of the host's nutrients or transform them into other metabolisable compounds. For this, some nutrient(s) may be lost to the host.  Germ-free animals are known to grow more rapidly and efficiently than conventional animals.  Antibiotics added into the food of farm animal to grows faster and earlier marketing; Spread of bacterial antibiotic resistance within the farm animals, as well as humans.  Harmful effects of the normal flora 33 3. Induction of a low grade toxemia  Minute amounts of bacterial toxins (e.g. endotoxin) may be found in the circulation.  Harmful effects of the normal flora 34 4. The normal flora may be agents of disease  Endogenous disease if they reach a site or tissue  Most endogenous bacterial diseases are opportunistic infections.  Harmful effects of the normal flora 35 5. Transfer to susceptible hosts  Can be transferred to other individuals where they can produce disease.  N. meningitidis, S. pneumoniae, H. influenzae and S. aureus, in upper respiratory tract and E. coli, Salmonella or Clostridium in the gastrointestinal tract and produce disease in other individuals. 36 Tissue specificity  37  Tissue specificity is the bacterial preference for certain tissues for growth. Tissue specificity is usually due to properties of both the host and the bacterium.  Tissue specificity 38  Host properties for tissue tropism of bacteria include; o Nutrients and growth factors (Lactobacillus acidophilus; Vaginal glycogen) o Oxygen o pH o Temperature  39 Tissue specificity Bacterial properties for tissue tropism include; o Specific adherence o Biofilm formation  40 Specific adherence Specific adherence involves biochemical interactions between bacterial surface components (ligands or adhesins) and host cell molecular receptors.  The bacterial components are capsules, fimbriae, or cell walls.  The receptors on human cells are glycoprotein molecules located on the host cell or tissue surface.  Examples of bacterial specific adherence to host cells or tissue 41  42 Biofilm formation  Some of the indigenous bacteria are able to construct biofilms on a tissue surface, or they are able to colonize a biofilm built by another bacterial species.  Biofilm formation steps 43 1) Bacterial species attaches specifically or non specifically to a surface 2) Micro-colony formation 3) Secretion of carbohydrate slime (exopolymer) 4) Maturation and formation of the architecture of the biofilm 5) Detachment/Dispersion of the biofilm  Biofilm formation 44 Microbial cells attach to the surface through; Appendages like pilli and flagella. Physical forces like vander Waal's forces and electrostatic interactions etc. Hydrophobicity of the surface of microbes. Microorganisms attach more likely to the hydrophobic and non-polar surface like Teflon and other plastics, than to hydrophilic and polar surface like metals and glass.  Biofilm formation 45  In micro-colony formation, microbial cells get start to multiplication and division.  46  In maturation stage, microbial cells communicate with one another through auto-inducer signals and certain gene products are expressed, that are considered important for the formation of EPS.  EPS has a channels which are filled with water and act as a circulatory system, used to distribute important nutrients and remove waste products from the communities of micro- colonies in the biofilm.  Biofilm circulatory system developing with maturation.  47 Detachment/dispersion of biofilm  Microbial cells within the biofilm perform quick multiplication and dispersion in order to convert from sessile into motile form.  Microbial within the biofilm produce different saccharolytic enzymes that help to release the surface of the microbes into a new area for colonization. For instance; o E. coli produces N-acetyl-heparosan lyase o P. aeruginosa and P. fluorescens produce alginate lyase o Streptococcus equi produces hyaluronidase  In this phase, microbial cells upregulate the expression of proteins related to flagella formation, to let the bacteria move to a new site. 48 49  Biofilm formation 50  Dental plaque on the teeth are the classic biofilm.  Bacteria may reach a thickness of 300-500 cells on the surfaces of the teeth and produce a high concentrations of bacterial metabolites, which result in dental disease. 51