PowerPoint ® Lecture Presentations prepared by John Zamora Middle Tennessee State University C H A P T E R © 2015 Pearson Education, Inc. Microbial Interactions with Humans 23

© 2015 Pearson Education, Inc Beneficial Human–Microbial Interactions Most microorganisms are benign Few contribute to health, and fewer pose direct threats to health Normal microbial flora Microorganisms usually found associated with human body tissue Humans are colonized by microorganisms at birth

© 2015 Pearson Education, Inc Beneficial Human–Microbial Interactions Pathogens Microbial parasites Pathogenicity The ability of a parasite to inflict damage on the host Virulence Measure of pathogenicity Opportunistic pathogen Causes disease only in the absence of normal host resistance

© 2015 Pearson Education, Inc Beneficial Human–Microbial Interactions Infection Situation in which a microorganism is established and growing in a host, whether or not the host is harmed Disease Damage or injury to the host that impairs host function

© 2015 Pearson Education, Inc Beneficial Human–Microbial Interactions Animals provide a favorable environment for the growth of many microorganisms Infections frequently begin at sites in the animal's mucous membranes Figure 23.1

© 2015 Pearson Education, Inc Microflora of the Skin The skin surface varies greatly in chemical composition and moisture content Three microenvironments: Dry skin, Moist skin, Sebaceous skin Figure 23.2

© 2015 Pearson Education, Inc Microflora of the Oral Cavity Saliva contains antimicrobial enzymes High concentrations of nutrients near surfaces in the mouth promote localized microbial growth The tooth consists of a mineral matrix (enamel) surrounding living tissue (dentin and pulp) Figure 23.3

© 2015 Pearson Education, Inc Microflora of the Oral Cavity Bacteria colonize tooth surfaces by first attaching to acidic glycoproteins deposited there by saliva Most microorganisms are facultatively aerobic Some are obligately anaerobic Some are obligately aerobic Figure 23.4

© 2015 Pearson Education, Inc Microflora of the Gastrointestinal Tract The human gastrointestinal (GI) tract Consists of stomach, small intestine, and large intestine Responsible for digestion of food, absorption of nutrients, and production of nutrients by the indigenous microbial flora Contains to microbial cells

© 2015 Pearson Education, Inc. SCFAs Distal Gut Microbiota Metabolism of dietary fibre (10% of caloric intake) Colonization Resistance (barrier effect) Immunomodulation (innate immunity, inflammation) Production of essential molecules (vitamins) Bacteriocins (germ warfare) Gut-brain axis (nerves, neurotransmitters) Saccharolytic Fermentation FISH image: Justin Yamashita

© 2015 Pearson Education, Inc Microflora of Mucosal Tissues Examples: staphylococci, streptococci, diphtheroid bacilli, and gram-negative cocci The lower respiratory tract lacks microflora in healthy individuals Figure 23.7 A restricted group of organisms colonizes the upper respiratory tract

© 2015 Pearson Education, Inc Microflora of Mucosal Tissues Urogenital tract The bladder is typically sterile in both males and females Altered conditions (such as change in pH) can cause potential pathogens in the urethra (such as Escherichia coli and Proteus mirabilis) to multiply and become pathogenic E. coli and P. mirabilis frequently cause urinary tract infections in women

© 2015 Pearson Education, Inc Microflora of Mucosal Tissues The vagina of the adult female is weakly acidic and contains significant amounts of glycogen Lactobacillus acidophilus, a resident organism in the vagina, ferments the glycogen, producing lactic acid Lactic acid maintains a local acidic environment

© 2015 Pearson Education, Inc. Nature Reviews Microbiology 9, (January 2011) Microflora seeding

© 2015 Pearson Education, Inc Pathogenicity and Virulence Pathogens use various strategies to establish virulence Virulence is the relative ability of a pathogen to cause disease Figure 23.9

© 2015 Pearson Education, Inc Pathogenicity and Virulence Measuring virulence Virulence can be estimated from experimental studies of the LD 50 (lethal dose 50 ) The amount of an agent that kills 50% of the animals in a test group (Figure 23.10) Highly virulent pathogens show little difference in the number of cells required to kill 100% of the population as compared to 50% of the population

© 2015 Pearson Education, Inc. Figure Pathogenicity and Virulence

© 2015 Pearson Education, Inc Pathogenicity and Virulence Attenuation The decrease or loss of virulence Toxicity Organism causes disease by means of a toxin that inhibits host cell function or kills host cells Toxins can travel to sites within host not inhabited by pathogen

© 2015 Pearson Education, Inc Pathogenicity and Virulence Invasiveness Ability of a pathogen to grow in host tissue at densities that inhibit host function Can cause damage without producing a toxin Many pathogens use a combination of toxins, invasiveness, and other virulence factors to enhance pathogenicity

© 2015 Pearson Education, Inc Adherence Bacteria and viruses that initiate infection often adhere specifically to epithelial cells through interactions between molecules on the surfaces of the pathogen and the host cell Figure EPECVibrio cholerae capsule

© 2015 Pearson Education, Inc Adherence Bacterial adherence can be facilitated by Extracellular macromolecules that are not covalently attached to the bacterial cell surface: Slime layer, capsule (Figure 23.13) Fimbriae and pili bind glycoproteins (Figure 23.14) Figure 23.13Figure E.coliS. pneumoniae

© 2015 Pearson Education, Inc Invasion, Infection, and Virulence Factors The initial inoculum of a pathogen is insufficient to cause host damage The pathogen must multiply and colonize the tissue The availability of nutrients is most important in affecting pathogen growth Pathogens may grow locally at the site of invasion or may spread throughout the body

© 2015 Pearson Education, Inc Invasion, Infection, and Virulence Factors Bacteremia: the presence of bacteria in the bloodstream Septicemia: bloodborne systemic infection May lead to massive inflammation, septic shock, and death Infection: any situation in which a microorganism (not a member of the local flora) is established and growing in a host

© 2015 Pearson Education, Inc Innate Resistance to Infection Hosts have innate resistance to most pathogens Natural host resistance Tissue specificity Physical and chemical barriers Figure 23.25

© 2015 Pearson Education, Inc Risk Factors for Infection Compromised host One or more resistance mechanisms are inactive The probability of infection is increased Age is an important factor Very young and very old individuals are more susceptible Stress can predispose a healthy individual to disease Diet plays a role in host susceptibility to infection Certain genetic conditions can compromise a host