Topic 9: Some Microbial Diseases of the Digestive System PDF

Because learning changes everything.® Topic 9 Some Microbial diseases of the Digestive System © 2022 McGraw Hill, LLC. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior writ...

Because learning changes everything.® Topic 9 Some Microbial diseases of the Digestive System © 2022 McGraw Hill, LLC. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill, LLC.  Anatomy, Physiology, and Ecology 1 Function of digestive system is to convert foods into absorbable nutrients to use for energy and raw materials for growth Digestive tract: Hollow tube from mouth to anus Gastrointestinal tract refers to stomach and intestines Accessory organs include salivary glands, liver, pancreas Major boundary with environment Contents provides a plentiful source of carbon and energy for microbes Mucous membrane only one cell layer thick separates microbial population from underlying tissue Damage allows microbes to penetrate; ingested pathogens often have mechanisms to breach © McGraw Hill, LLC 2  Anatomy, Physiology, and Ecology – Figure 24.1 Access the text alternative for slide images. © McGraw Hill, LLC 3  Anatomy, Physiology, and Ecology – Figure 24.2 The upper digestive system Includes mouth, salivary glands, esophagus, stomach The mouth and salivary glands Chewing grinds food into smaller pieces; saliva moistens, while amylase begins breakdown of starches Teeth protected by a hard substance called enamel Proteinaceous material from saliva adheres, creates thin film (pellicle) Bacteria attach, create biofilm called dental plaque Mineral salts deposit over time, create dental calculus or tartar Access the text alternative for slide images. © McGraw Hill, LLC 4  Anatomy, Physiology, and Ecology 2 The upper digestive system The mouth and salivary glands Damage to enamel allows microorganisms to enter tooth, cause decay or dental caries Microbes can accumulate in gingival crevice Gums become inflamed in response: gingivitis May recede from tooth root, allow bacteria access About 1,500 milliliter saliva produced daily Largest glands are the parotids (glands the mump virus infects) Rich in protective secretory IgA, antibacterial lysozyme, lactoferrin Over 600 types of bacteria found in mouth; members of Streptococcus most common Obligate anaerobes associated with halitosis bad breath © McGraw Hill, LLC 5  Anatomy, Physiology, and Ecology 3 The upper digestive system The esophagus: muscular tube from mouth to stomach Peristalsis pushes food toward stomach Mucus and saliva containing secretory IgA bathes lining Microbial population relatively sparse The stomach Expandable, sac-like structure with muscular wall Breaks down and stores food Highly acidic gastric juices denature proteins, activate pepsinogen to form protein-digesting enzyme pepsin Cells lining stomach protected by alkaline mucus Most bacterial cells cannot survive, so normal empty stomach has few © McGraw Hill, LLC 6  Anatomy, Physiology, and Ecology 4 The lower digestive system Small and large intestines, pancreas, liver The small intestine As stomach contents enter, pancreas and liver add alkaline digestive fluids that neutralize acid Emulsifying agent bile, helps break down fat globules; help absorb oils, fats, fat-soluble vitamins Residents resistant to bactericidal effects Villi, microvilli increase surface area to about 250 meters squared Major role in nutrient and fluid absorption: approximately 9 liters/day Amino acids, monosaccharides taken up by active transport that brings in Na+ ions Fatty acids, vitamins, minerals absorbed Dendritic cells, M cells, and Peyer’s patches monitor bacterial population © McGraw Hill, LLC 7  Anatomy, Physiology, and Ecology 5 The lower digestive system The large intestine Absorbs water; vitamins produced by resident microbiota Bacteria make up about one-third of fecal weight Anaerobic bacteria make up approximately 99% of population; facultative anaerobes make up balance Degrade wide variety of foods including substances (for example, fibers) indigestible by stomach, small intestines Important to human health: synthesize vitamins (like niacin, thiamine, riboflavin, vitamin B12 folic acid, vitamin K) Prevent pathogens from colonizing; stimulate mucosal immunity; opportunistic pathogens, some species can produce toxins linked to cancer Antibiotic treatment causes dysbiosis (imbalance in normal microbiota), that may lead to antibiotic-associated diarrhea © McGraw Hill, LLC 8  Anatomy, Physiology, and Ecology 6 The lower digestive system The pancreas: located behind stomach Produces hormones, alkaline digestive enzymes The liver: upper right portion of abdomen Produces bile, which is concentrated and stored in gallbladder; released into upper intestine Severe liver disease or obstruction of bile ducts can cause jaundice, yellow color of skin and eyes from buildup of bile component bilirubin in blood Detoxifies substances in the bloodstream (for example, ammonia and medications © McGraw Hill, LLC 9  Bacterial Diseases of the Upper Digestive System 1 Dental caries (tooth decay) Most common chronic disease; in 60% of U.S. teens Often synonymous with cavities, though a cavity is a consequence of dental caries. Signs and Symptoms Usually advanced before symptoms develop Discoloration, roughness, defect; tooth may break Severe throbbing pain of toothache usually first sign Causative Agent Streptococcus mutans, related Gram-positive cocci are cariogenic (caries generating); live only on teeth Thrive in acidic conditions that result from their fermentative lactic acid production Acidogenic (produce acid) and aciduric (tolerate acid) © McGraw Hill, LLC 10  Bacterial Diseases of the Upper Digestive System 3 Helicobacter pylori gastritis Barry Marshall drank culture of Helicobacter pylori in 1980s, demonstrated association with stomach ulcers Signs and Symptoms Most infections asymptomatic Gastritis, typically asymptomatic, can result in belching, loss of appetite, nausea and sometimes vomiting may occur Chronic gastritis can lead to stomach cancer Peptic ulcers produce localized abdominal pain, tenderness, bleeding Causative Agent: Helicobacter pylori Short, curved, Gram-negative microaerophile with multiple sheathed polar flagella © McGraw Hill, LLC 11  Helicobacter pylori Gastritis 1 Pathogenesis H. pylori survives acidic environment of stomach Produces urease, which converts urea in gastric juices to ammonia, creating alkaline compound that neutralizes stomach acid in microenvironment Burrows within mucus layer that coats stomach lining Avoids recognition by immune system receptors VacA (vacuolating cytotoxin) has multiple effects on cells, including damaging mitochondria, inducing apoptosis in epithelial cells, interfering with T cells CagA (cytotoxin-associated gene) in strains with higher risk of cancer; alters host cytoskeleton, cell signaling Damage to epithelial cells and inflammatory response resulting in decreased mucus production, cell damage Infections persist for years, often for life; 90% of those with stomach cancer are infected © McGraw Hill, LLC 12  Viral Diseases of the Upper Digestive System – Figure 24.7 Oral herpes simplex (cold sores; fever blisters) Signs and Symptoms Fever, small blisters in mouth that break in a day or two; produce painful superficial ulcers (incubation 2 to 20 days) Lesions heal within approximately 14 days without treatment, but virus persists Recurrent cold sores usually less severe Tingling, itching, burning; blisters, ulcerations usually heal within 7 to 10 days Can be transmitted to infants Signs and symptoms vary depending on the location of the virus Skin, eyes and mouth (SEM) can develop blisters and ulcers if exposed Source: Centers for Disease Control and Prevention; (inset): ©Frederick C. Skvara, MD Access the text alternative for slide images. © McGraw Hill, LLC 13  Oral Herpes Simplex 1 Causative Agent: Herpes simplex viruses (HSVs) Enveloped viruses with double-stranded linear DNA Two types: HSV-1 (most oral infections) and HSV-2 (usually genital infections) Persist throughout life as latent viruses; can reactivate Pathogenesis Virus multiplies in epithelium, destroys cells Some cells fuse to produce multinucleated giant cells Cell nucleus contains deeply staining area called intranuclear inclusion body where viruses replicate Viral DNA persists in nerve cells in latent form Stresses can reactivate (menstruation, sunburn, fever) © McGraw Hill, LLC 14  Focus on Diarrheal Diseases 1 Gastroenteritis; “stomach flu” (not influenza) Hundred of thousands of children die around the world due to diarrheal illnesses. All ages can be affected, though most are infants. Signs and Symptoms: diarrhea, loss of appetite, nausea, vomiting, perhaps fever; incubation period 1 to 2 days Small intestine: abundant, watery diarrhea Large intestine: small amounts of diarrhea with mucus, pus, and sometimes blood Dysentery: blood and pus in feces © McGraw Hill, LLC 15  Bacterial Diseases of the Lower Digestive System 1 Cholera Causes diarrhea so severe that it can be fatal within hours Seven pandemics have occurred since early 1800s The last one began in 1961 and continues to this day In 2011 Haiti had the highest number of recorded cases in a country in a single year Due to the civil war disrupting sanitation, water treatment, and access to health care, that number was surpassed in Yemen. © McGraw Hill, LLC 16  Cholera 1 Signs and Symptoms Incubation period of 12 to 48 hours Classic example of severe watery diarrheal disease “Rice water stool” appearance; can amount to 20 liters/day; dehydration can lead to organ failure and death Vomiting often occurs at onset; severe muscle cramps result from loss of fluids and electrolytes Causative Agent: Vibrio cholerae Curved, Gram-negative rod Several serotypes grouped by O antigen O1 serotype is pandemic; O139 in Asia Halotolerant, can grow in alkaline conditions © McGraw Hill, LLC 17  Cholera 2 Pathogenesis Sensitive to acid, so large numbers must be ingested Adhere to epithelial cells of small intestine, establish infection, produce cholera toxin, an A-B toxin B portion attaches irreversibly to specific receptors of the microvilli of the epithelial cells facilitating entry of the A portion A portion enters cells, locks the G protein into the “on” position resulting in nonstop activity of adenylate cyclase which converts ATP to cAMP High levels of cAMP cause cells to secrete chloride and other electrolytes yielding outpouring of fluid and salts from cells Toxin does not affect large intestine, but volume of fluid is too much to be absorbed, causing diarrhea V. cholera also produces a large multifunctional pore-forming toxin belonging to a group called MARTX toxins, can interfere with the inflammatory response could prevent colonization © McGraw Hill, LLC 18 © McGraw Hill, LLC  Cholera 4 Treatment and Prevention Rapid replacement of fluids and electrolytes given before damage to vital organs can occur Intravenous or oral rehydration therapy can decrease mortality from over 30% to less than 1% Clean water and adequate sanitation are key control measures Travelers should cook food immediately before eating and avoid fruit and ice contaminated with local water Vaccines available in many parts of world In 2016 FDA approved live attenuated oral vaccine against serotype 01 intended for travelers to endemic areas © McGraw Hill, LLC 20  Bacterial Diseases of the Lower Digestive System 2 Shigellosis Found all over the world, most commonly in areas lacking sewage treatment Estimated 80 to 165 million cases occur resulting in about 600,000 deaths per year Signs and Symptoms Incubation period 1 to 3 days Usually dysentery (bloody, mucoid diarrhea), some species cause watery diarrhea Headache, vomiting, fever, stiff neck, convulsions, joint pain Often fatal for infants in developing countries Causative Agents Four species of Shigella, Gram-negative rods: S. dysenteriae, S. flexneri, S. boydii, and S. sonnei S. dysenteriae most virulent, S. sonnei least virulent S. dysenteriae and S. flexneri most common in developing countries S. sonnei causes over two-thirds of cases in U.S. © McGraw Hill, LLC 21  \Shigella dysenteriae – more severe - Mortality Rate = 20 % © McGraw Hill, LLC  Bacterial Diseases of the Lower Digestive System 3 Escherichia coli gastroenteritis Signs and Symptoms Depend on strain Some cause watery diarrhea, others dysentery One group causes hemolytic uremic syndrome (HUS) causes blood vessel damage, Causative Agent: Escherichia coli Gram-negative rod closely related to Shigella Unlike Shigella, most strains ferment lactose © McGraw Hill, LLC 23  Bacterial Diseases of the Lower Digestive System – Figure 24.12 Escherichia coli Gastroenteritis Pathogenesis Variety of mechanisms Strain dependent Strains grouped into six pathovars (pathogenic varieties) based on their virulence factors Access the text alternative for slide images. © McGraw Hill, LLC 24  Bacterial Diseases of the Lower Digestive System 4 Salmonella gastroenteritis About 1.2 million cases in U.S. each year Outbreaks due to foods contaminated by animal feces Signs and Symptoms: Diarrhea, abdominal cramps, nausea, vomiting, headache, fever Incubation period 6 hours to 3 days Often short-lived and mild depending on strain, dose Causative Agent: Salmonella enterica Gram-negative rod; Enterobacteriaceae More than 2,400 serotypes based on somatic (O), flagellar (H), and capsular (K) antigens Significant in terms of epidemiology and disease © McGraw Hill, LLC 25  Bacterial Diseases of the Lower Digestive System 5 Enteric Fever (Typhoid and paratyphoid fevers) Examples of enteric fevers: systemic diseases that originate in the intestine Signs and Symptoms Incubation period of 1 to 4 weeks Progressively increasing fever over several days, severe headache, constipation, abdominal pain In severe cases, intestinal rupture, bleeding, shock, death Causative Agents Salmonella serotypes Typhi and Paratyphi Cases confirmed by blood culture © McGraw Hill, LLC 26  Bacterial Diseases of the Lower Digestive System 6 Clostridium difficile infection (CDI) Antibiotic-associated diarrhea, increasing in incidence and severity since early 2000’s Signs and Symptoms Ranges widely in severity Mild cases characterized by diarrhea with fever, pain beginning less than a week after infection More serious cases progress to colitis, sometimes with pseudomembranes; known as pseudomembranous colitis Severe cases are life-threatening ©McGraw-Hill Education © McGraw Hill, LLC 27  Clostridium difficile Infection 1 Causative Agent: Clostridium difficile (“C. diff”) Gram-positive, obligate anaerobic rod Forms endospores highly resistant to disinfectants, environmental conditions, so control is difficult Ingested endospores develop into vegetative cells that sometimes colonize large intestine Many strains; differ in pathogenicity Strains causing CDI produce toxins; hypervirulent strains increasing in prevalence Resistant to fluoroquinolones CDC considers C. diff an urgent health threat © McGraw Hill, LLC 28  Viral Diseases of Lower Digestive System: Intestinal Tract – Figure 24.15 Rotavirus gastroenteritis Most viral gastroenteritis around the world in infants and children is caused by rotaviruses Signs and Symptoms: abrupt vomiting, slight fever, followed shortly by profuse watery diarrhea Incubation 24 to 48 hours; usually clears within a week, but fatal dehydration can occur if fluids are not replaced Causative Agents: Rotaviruses Non-enveloped with a triple layered capsid and double-stranded, 11 segment RNA genome Major subgroup of Reoviridae Source: Dr. Erskine Palmer & Byron Skinner/CDC © McGraw Hill, LLC 29  Viral Diseases of Lower Digestive System: Intestinal Tract – Figure 24.17 At least 5 unrelated viruses can cause hepatitis, an inflammation of the liver Three types (A, B, and C) account for most cases Jaundice (yellowing of skin and whites of eyes) is most noticeable sign Patients should avoid alcohol, acetaminophen, and other chemicals that damage the liver Access the text alternative for slide images. © McGraw Hill, LLC 30  Viral Diseases of the Lower Digestive System—Liver 1 Hepatitis A (formerly, infectious hepatitis) Signs and Symptoms Acute illness; no known chronic form or carrier state Older children and adults develop jaundice, fever, fatigue, clay- colored feces, and vomiting after approximately 1 month incubation Most young children (80% develop chronic infection; related to cirrhosis, liver cancer Causative Agent: Hepatitis C virus Enveloped, single-stranded RNA virus of Flaviviridae Much genetic variability; types differ in pathogenicity, response Pathogenesis Infection generally from exposure to contaminated blood Disease process starts and stops © McGraw Hill, LLC 34