Bread and Butter Lecture "It may be s$%t to you, but it's my bread and butter." Dr. Richard Finkelstein, pioneer of cholera toxin biology, to medical students at University of Texas Southwestern Medical School, ca. 1980.
I. INFECTION VS. PREFORMED TOXIN A. Do the bacteria enter the body to cause disease or do we ingest their products preformed in our food? B. If we ingest preformed toxin, many of the 7 steps of pathogenesis are irrelevant.
Pathogenesis Web Learning Tool http://www.snaption.net/med/index3.htm
A. ENCOUNTER 1. Where do the bacteria come from? a. human FECAL contamination of food and water (direct, water, soil) b. NATURALLY INFECTED ANIMAL FOODS - meats and dairy products (non-typhoid Salmonella, Campylobacter, Vibrio vulnificus) c. contamination of food (usually fruits and vegetables) with SOIL - ENVIRONMENTAL (Clostridium perfringens). d. Many enteric pathogens are HUMAN ONLY (Salmonella enterica serovar Typhi, Shigella)
2. Think about how infection can be prevented in terms of: food handling (personnel) food preparation other public health considerations.
B. ENTRY: All ORALC. SPREAD - three possibilities: 1. Do not spread past the intestinal mucosa 2. Invade laterally within the intestines 3. Invade deeper to the draining lymph nodes, lymphatics, blood, and all through the bodyD. MULTIPLY 1. lots of food, but little or no oxygen in LARGE INTESTINE 2. chemical barriers to growth and multiplication - acid, bile 3. competition from normal flora 4. intracellular pathogens have difficult hurdles
E. EVADE DEFENSES of the alimentary tract: 1. Origination of disease - MOUTH: no significant barriers 2. STOMACH chemical barrier of gastric acidity, bactericidal, practically sterile. 3. SMALL INTESTINE: low inoculum from stomach, digestion (especially bile) and peristalsis prevent colonization
4. LARGE INTESTINE: heavily colonized with obligate ANAEROBES and some facultative anaerobes; NORMAL FLORA primary biological defense. Adherence critical. 5. No constitutive IMMUNOLOGICAL defenses, but phagocytes during inflammation, induced/specific defenses - only sIgA (importance of nursing of newborns), probably antibacterial peptide (cryptdins, defensins)
6. Think about WHO is more susceptible when some of these defenses are compromised. 7. Think about how VACCINATION could prevent infection and disease.What forms of protective immunity are relevant? sIgA IgG CMI – Th1 CMI – CTL
F. DAMAGE 1. toxins 2. invasion of epithelium 3. attaching-effacing adherence 4. inflammation
5. GENERAL relationship of damage to symptoms (major method of classifying and discussing different diseases) a. vomiting - rapid onset - usually toxin b. diarrhea - large volume, usually without blood or pus - usually small intestinal effects (secretory bowel) - usually from toxin - bloody diarrhea does not equal dysentery c. dysentery - smaller volume, pus (white cells), can be bloody, fever, abdominal pain - usually from large intestine (inflammatory bowel) - usually invasive organisms
Considerations in Diagnosis • Symptoms • vomiting • diarrhea • dysentery • Time frame relative to consumption • History • epidemiology (other cases?) • type of foods eaten • drugs (antibiotics, etc.) • travel
III. FOOD INTOXICATION (FOOD POISONING) - NO INFECTION (no viable bacteria need to encounter the host) - toxin preformed in the food as a result of bacterial contamination (soil or human)
A medical student attended a picnic at the Santa Fe River. She did not consume the chicken salad, hamburger, or ice cream, but did eat lots of potato salad, hot dogs, and beer. Four hours after returning home the student experienced profuse, projectile vomiting for several hours, followed by two loose stools. Vomiting continued even though her stomach was empty. No fever, or blood or pus in stools were noted by the student, who assumed she "drank too much." The following morning, the student ate and drank nothing, and was fine by the afternoon.
A. Staphylococcal food poisoning - Staphylococcus aureus - rapid onset, profuse vomiting, possibly diarrhea 1. ENCOUNTER - contamination from INFECTED FOOD HANDLER (human reservoir) 2. DAMAGE - enterotoxins released into food a. heat stable b. superantigens
A 55 year old male in good health ate home-canned green beans which had been stored for several months. The next day he experienced double and blurred vision, which he attributed to sleeplessness and stress over his impending lay-off. However, the following day he experienced dryness in his mouth and difficulty swallowing, which progressed to weakness in his neck muscles. Again, he attributed these symptoms to stress. Finally, on the third day, he began to experience respiratory distress with shallow and frequent breathing. Examination upon admission to the hospital examination revealed fixed and dilated pupils, despite clear sensorium. The patient was afebrile. The flaccid paralysis of neck and upper body muscles was noted.
B. Botulism - Clostridium botulinum - gram-positive rod, obligate anaerobe, spore former 1. ENCOUNTER - spores from soil-contamination (i.e., vegetables) germinate in anaerobic but incompletely processed CANNED (autoclaved) food
2. botulinum toxin a. neurotoxin - causes flaccid paralysis by inhibiting release of acetylcholine (no stimulatory signal) b. A-B type; heat labile c. encoded on LYSOGENIC BACTERIOPHAGE 3. DAMAGE – SYMPTOMOLOGY: ocular -> pharyngeal -> respiratory paralysis -> death 4. TREATMENT - supportive therapy (respiratory), anti-toxin 5. other diseases – INFECTIONS - infant botulism and wound botulism
During spring break, three medical students volunteered to go to Peru to help out in the rural clinics. They helped vaccinate infants and children and care for the numerous cases of enteric diseases. Their break was rewarding and uneventful.
Upon returning from Peru, one of the students experienced a sensation of intestinal fullness and increased bowel sounds. This was followed within hours by massive watery diarrhea which progressed from a brown color to clear and containing flecks of, what looked like, mucus. Being an independent type, the student examined his stool by Gram stain in the teaching lab and noticed gram-negative comma-shaped organisms, but no RBCs or WBCs. This student had no fever, but lost five pounds before seeking medical attention. The second student from Peru experienced a disease process very similar to the Mexico tourists, and the third Peru student experienced no intestinal problems all. All of the Peru students ate and drank similarly from communal food sources.
Vibrio choleraeWeb Based Teaching http://www.mgm.ufl.edu/~gulig/mmid/pathogenesis/cholerae_files/cholerae.swf
A. Vibrio cholerae - cholera - severe - rice water stool, death by dehydration; many cases are asymptomatic-mild - gram-negative, comma shaped bacterium - Classification: -O antigen O:1(Inaba and Ogawa serotpyes) -Biotype: El Torand Classical
Vibrio cholerae http://www.textbookofbacteriology.net/vcfla.jpeg
1. ENCOUNTER - contaminated water, vegetables 2. ENTRY - adherence factors – pili 3. SPREAD - none; localized to epithelial surface
4. DAMAGE - TOXINS a. heat labile enterotoxins – cholera i. A-B type toxins ii. B portion binds to GM1 gangliosides of host cells iii. A portion ADP-ribosylates stimulatory G protein of adenylate cyclase locking it in ON form iv. increases intracellular cAMP v. secretion of water and salts into lumen of intestine vi. absorptive functions intact; no cellular damage
Cholera Toxin A Bx5 http://www.rctb.net/images%5CCholera_holotoxin_cartoon.jpg
5. EVADE DEFENSES - none in non-immune host6. VACCINEScholera - killed cells injected intramuscularly, but live, attenuated under development7. TREATMENT cholera - oral or i.v. fluid and electrolyte replacement + antibiotics
A four year old boy vacationing in the northwestern United States ate a rare hamburger at the Greasy Grill. Late the following night (about 36 hours later) he was awakened by severe abdominal cramps, primarily in the right lower quadrant of the abdomen. Later in the morning , watery diarrhea occurring every 15-30 min developed, initially with small amounts of visible blood. Later in the day, bright red stools with what seemed to be pure blood appeared. He was nauseated, but not vomiting. His parents took him to an emergency care center later in the day. He had no fever, and examination of the abdomen was unremarkable except for increased bowel sounds. Because of an elevated WBC count, the boy was hospitalized. Frankly bloody stools continued, and a barium enema was performed, revealing edema of the ascending and transverse colon with areas of spasm. He was treated with i.v. fluids, antibiotics were avoided (why?).
C. Enterohemorrhagic E. coli (EHEC) - bloody diarrhea, hemolytic-uremic syndrome - O157:H7 serotype - sorbitol-negative1. ENCOUNTER - contaminated food from animals, mainly beef, also apple cider (and swimming pools); major problem - bovine fecal contamination2. ENTRY - adherence through specialized mechanism a. resistant to stomach acid (low infectious dose) b. attaching-effacing lesion c. identical to EPEC (see below)
Attaching-Effacing Lesion http://cahfs.ucdavis.edu/graphics/em_scans/ecoli_5-72.jpg
3. DAMAGE - a. although bloody diarrhea appears like invasive dysentery (e.g., Shigella, see below), the bacteria do not invade the epithelium, therefore little fever or pus in stool b. secrete a Shiga-like toxin (SLT/Stx) (see Shiga toxin, below) c. causes severe tissue damage in the large intestine, distal ileum because of capillary thrombosis
d. SLT may be transported into the blood where damage occurs to endothelial cells of the vasculature or kidneys e. hemolytic uremic syndrome (HUS) - mainly in very young; renal endothelial damage; microangiopathic hemolytic anemia; thrombocytopenia; thrombosis of glomerular capillaries f. different type 3 secreted protein, stimulates ATP secretion, converted to adenosine in lumen, fluid secretion
4. Diagnosis a. MacConkey agar with sorbitol ● EHEC is sorbitol-negative (what color will they be?) b. test for Stx 5. Treatment a. Symptomatic and supportive b. Avoid antibiotics because they can stimulate Stx production and HUS
IV. INVASIVE INFECTIONS - invade cells and tissue - DYSENTERY or BLOODY DIARRHEA
A 22-month-old boy of a middle class family attended a day care center which had experienced several cases of diarrhea earlier in the week. He became febrile (39C), lost his appetite, and developed watery diarrhea. The next day there was less diarrhea, but his parents noted mucus and bloody tinge to his stool. The number of bloody stools increased, and the boy began to vomit. The boy's parents took him to the emergency room where his fever was noted, and he was found to be dehydrated and had lost two pounds over the past two days. Microscopic examination of the stool sample revealed WBCs and RBCs. The child was placed on i.v. rehydration therapy and antibiotics and gradually recovered without lasting problems.
A. INVASION RESTRICTED TO INTESTINAL MUCOSA - primarily dysentery 1. Shigella dysenteriae, S. flexnerii, S. sonnei - gram-negative rods, enterics - symptomology: early stage - diarrhea, progressing to dysentery (blood, pus in stool), abdominal pain, tenesmus, fever
a. ENCOUNTER - humans only i. S. sonnei most common in U.S. ii. S. flexneri next iii. S. dysenteriae not endemic in U.S.b. Entry i. highly acid resistant ii. small inoculum (10-100 cells) iii. infection in colon c. SPREAD: laterally in intestines
c. DAMAGE: i. plasmid-encoded cellular invasion of epithelial cells of the colon (type III secretion system for injection of proteins into host) ii. lyse vacuole and replicate in cytoplasm iii. use host actin polymerization to move directly from cell to cell iv. cause cell death (cytotoxicity) and ulceration, inflammation
v. Shigella dysenteriae(ONLY) - potent cytotoxin (Shiga toxin) - Shiga toxin is an A-B toxin - inactivates ribosomes (deglycosylates rRNA) halting protein synthesis and killing the host cell - associated with hemolytic uremic syndrome
d. EVASION OF DEFENSES - intracellular location sequesters organisms from phagocytes, apoptosis of macrophagese. VACCINES: none to date, working on attenuated Shigella
B. INVASION PAST THE INTESTINE - many types of symptoms/disease depending on degree of invasion
During the same spring break as for case 1, a second year medical student went to a picnic at some springs on the Santa Fe River. Two days after the picnic, she had a brief period of vomiting followed by severe abdominal cramps and large volume, watery diarrhea. The diarrhea has continued for three days. She had a temperature of 38C and a few leukocytes but no RBCs in her stool. She had abdominal tenderness and hyperactive bowel sounds. She ate chicken salad, rare hamburger, and homemade ice cream at the picnic. The student took over the counter anti-diarrheal agents, and the symptoms resolved on the second day of home-treatment, so she did not seek medical help.
Salmonella web learning page: http://www.mgm.ufl.edu/~gulig/mmid/pathogenesis/sal_files/sal.swf
1.Salmonella enterica: typhoid fever (enteric fever), gastroenteritis, septicemia (vascular endothelium), focal infections; carrier state also possible - Nomenclature: One species (Salmonella enterica) with thousands of serovars (Typhi, Typhimurium, Enteritidis, etc.). Most of us take a shortcut and use the genus and serovar names.