27 1 Overview of HumanMicrobial Interactions Most microorganisms

27. 1 Overview of 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 © 2012 Pearson Education, Inc.

27. 1 Overview of 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 © 2012 Pearson Education, Inc.

27. 1 Overview of 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 © 2012 Pearson Education, Inc.

27. 2 Normal Microflora of the Skin • The skin is generally a dry, acid environment that does not support the growth of most microorganisms (Figure 27. 2) • Moist areas (e. g. , sweat glands) are readily colonized by gram-positive bacteria and other normal flora of the skin – Composition is influenced by • Environmental factors (e. g. , weather) • Host factors (e. g. , age, personal hygiene) © 2012 Pearson Education, Inc.

27. 3 Normal Microflora of the Oral Cavity • The oral cavity is a complex, heterogeneous microbial habitat • Saliva contains antimicrobial enzymes – But 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 27. 4) © 2012 Pearson Education, Inc.

Figure 27. 4 Enamel Dentin Gingival crevice Crown Pulp Gingiva Alveolar bone Periodontal membrane

Figure 27. 5 © 2012 Pearson Education, Inc.

27. 3 Normal Microflora of the Oral Cavity • Extensive growth of oral microorganisms, especially streptococci, results in a thick bacterial layer (dental plaque) • As plaque continues to develop, anaerobic bacterial species begin to grow © 2012 Pearson Education, Inc.

Figure 27. 6 Day 1 1436 mm 2 Day 10 22, 522 mm 2

Figure 27. 7 © 2012 Pearson Education, Inc.

27. 3 Normal Microflora of the Oral Cavity • As dental plaque accumulates, the microorganisms produce high concentrations of acid that results in decalcification of the tooth enamel (dental caries) • The lactic acid bacteria Streptococcus sobrinus and Streptococcus mutans are common agents in dental caries (Figure 27. 8) © 2012 Pearson Education, Inc.

27. 4 Normal 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 1013 to 1014 microbial cells © 2012 Pearson Education, Inc.

Figure 27. 9 Major bacteria present Esophagus Organ Prevotella Streptococcus Veillonella Esophagus Helicobacter Proteobacteria Bacteroidetes Actinobacteria Fusobacteria Stomach Major physiological processes Secretion of acid (HCl) Digestion of macromolecules p. H 2 Duodenum Enterococci Lactobacilli Bacteroides Bifidobacterium Clostridium Enterobacteria Enterococcus Escherichia Eubacterium Klebsiella Lactobacillus Methanobrevibacter (Archaea) Peptococcus Peptostreptococcus Proteus Ruminococcus Staphylococcus Streptococcus © 2012 Pearson Education, Inc. Jejunum Small intestine Continued digestion Absorption of monosaccharides, amino acids, fatty acids, water p. H 4– 5 Ileum Colon Anus Large intestine Absorption of bile acids, vitamin B 12 p. H 7

27. 4 Normal Microflora of the Gastrointestinal Tract • Functions and Products of Intestinal Flora – Intestinal microorganisms carry out a variety of essential metabolic reactions that produce various compounds • The type and amount produced is influenced by the composition of the intestinal flora and the diet • Compounds produced include: – Vitamins – Gas, organic acids, and odor – Enzymes © 2012 Pearson Education, Inc.

27. 5 Normal Microflora of Other Body Regions • A restricted group of organisms colonizes the upper respiratory tract – Examples: staphylococci, streptococci, diphtheroid bacilli, and gram-negative cocci • The lower respiratory tract lacks microflora in healthy individuals © 2012 Pearson Education, Inc.

Figure 27. 11 Upper respiratory tract Sinuses Nasopharynx Pharynx Oral cavity Larynx Trachea Lower

27. 5 Normal Microflora of Other Body Regions • Urogenital Tract – The bladder is typically sterile in both males and females – Altered conditions (such as change in p. H) 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 © 2012 Pearson Education, Inc.

27. 5 Normal Microflora of Other Body Regions • 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 © 2012 Pearson Education, Inc.

27. 6 Measuring Virulence • Pathogens use various strategies to establish virulence (Figure 27.

27. 6 Measuring 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 – 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 © 2012 Pearson Education, Inc.

Figure 27. 14 Percentage of mice killed 100 Highly virulent organism (Streptococcus pneumoniae) Moderately virulent organism (Salmonella enterica serovar Typhimurium) 80 60 40 20 101 102 103 104 105 106 Number of cells injected per mouse © 2012 Pearson Education, Inc. 107

27. 6 Measuring 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 © 2012 Pearson Education, Inc.

Figure 27. 13 Further exposure at local sites COLONIZATION EXPOSURE to pathogens ADHERENCE to skin or mucosa INVASION through epithelium and GROWTH Production of virulence factors TOXICITY: toxin effects are local or systemic INVASIVENESS: further growth at original and distant sites Further exposure © 2012 Pearson Education, Inc. TISSUE DAMAGE, DISEASE

27. 7 Entry of the Pathogen into the Host – Adherence • Specific Adherence – A pathogen must usually gain access to host tissues and multiply before damage can be done – Bacteria and viruses that initiate infection often adhere specifically to epithelial cells through macromolecular interactions on the surfaces of the pathogen and the host cell (Figure 27. 15) © 2012 Pearson Education, Inc.

Figure 27. 15 © 2012 Pearson Education, Inc.

27. 7 Entry of the Pathogen into the Host – Adherence • Bacterial adherence can be facilitated by – Extracellular macromolecules that are not covalently attached to the bacterial cell surface • Examples: slime layer, capsule – Fimbriae and pili © 2012 Pearson Education, Inc.

Figure 27. 16 © 2012 Pearson Education, Inc.

Figure 27. 18 © 2012 Pearson Education, Inc.

27. 6 Measuring 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 © 2012 Pearson Education, Inc.

27. 7 Entry of the Pathogen into the Host – Adherence • Pathogen Invasion – Starts at the site of adherence – May spread throughout the host via the circulatory or lymphatic systems © 2012 Pearson Education, Inc.

27. 8 Colonization and Infection • 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 © 2012 Pearson Education, Inc.

27. 9 Invasion • Pathogens produce enzymes that – Enhance virulence by breaking down or altering host tissue to provide access to nutrients • Example: hyaluronidase – Protect the pathogen by interfering with normal host defense mechanisms • Example: coagulase © 2012 Pearson Education, Inc.

27. 10 Exotoxins • Exotoxins – Proteins released from the pathogen cell as it

27. 10 Exotoxins • Cytolytic toxins – Work by degrading cytoplasmic membrane integrity, causing cell lysis and death • Toxins that lyse red blood cells are called hemolysins (Figure 27. 19) • Staphylococcal a-toxin kills nucleated cells and lyses erythrocytes (Figure 27. 20) © 2012 Pearson Education, Inc.

Figure 27. 19 © 2012 Pearson Education, Inc.

Figure 27. 20 Cytoplasmic membrane Influx of extracellular components © 2012 Pearson Education, Inc.

27. 10 Exotoxins • AB toxins – Consist of two subunits, A and B – Work by binding to host cell receptor (B subunit) and transferring damaging agent (A subunit) across the cell membrane (Figure 27. 21) • Examples: diphtheria toxin, tetanus toxin, botulinum toxin Animation: Diphtheria and Cholera Toxins © 2012 Pearson Education, Inc.

Figure 27. 21 Cytoplasmic membrane Diphtheria toxin Amino acid Diphtheria toxin Out Receptor protein

27. 10 Exotoxins • Clostridium tetani and Clostridium botulinum produce potent AB exotoxins that affect nervous tissue • Botulinum toxin consists of several related AB toxins that are the most potent biological toxins known (Figure 27. 22); tetanus toxin is also an AB protein neurotoxin (Figure 27. 23) © 2012 Pearson Education, Inc.

Figure 27. 22 Excitation signals from the central nervous system Muscle Normal Acetylcholine (A) induces contraction of muscle fibers © 2012 Pearson Education, Inc. Botulism Botulinum toxin, , blocks release of A, inhibiting contraction

Figure 27. 23 Inhibitory interneuron Inhibition Excitation signals from the central nervous system Tetanus toxin Muscle Normal Glycine (G) release from inhibitory interneurons stops acetylcholine (A) release and allows relaxation of muscle © 2012 Pearson Education, Inc. Tetanus toxin binds to inhibitory interneurons, preventing release of glycine (G) and relaxation of muscle

27. 10 Exotoxins • Enterotoxins – Exotoxins whose activity affects the small intestine – Generally cause massive secretion of fluid into the intestinal lumen, resulting in vomiting and diarrhea • Example: cholera toxin (Figure 27. 24) © 2012 Pearson Education, Inc.

Figure 27. 24 Normal ion movement, Na from lumen to blood, no net Cl movement Blood Intestinal epithelial cells Lumen of small intestine GM 1 Colonization and toxin production by V. cholerae Cholera toxin AB form GM 1 Vibrio cholerae cell Activation of epithelial adenylate cyclase by cholera toxin A subunits Adenylate cyclase ATP Cyclic AMP Na movement blocked, net Cl movement to lumen Massive water movement to the lumen; cholera symptoms © 2012 Pearson Education, Inc. Cholera toxin B subunit

27. 11 Endotoxins • Endotoxin – The lipopolysaccharide portion of the cell envelope of certain gram-negative Bacteria, which is a toxin when solubilized – Generally less toxic than exotoxins – The presence of endotoxin can be detected by the Limulus amoebocyte lysate (LAL) assay (Figure 27. 25) © 2012 Pearson Education, Inc.