Bacterial Infections of the GIT PDF

Alkafeel University- Bacteriology and mycology-Dr Ahmed Alshammari –lecture THREE Bacterial infections of the GIT The causes of gastrointestinal illness can vary widely, but such diseases can be grouped into two categories:  Those caused by infection (the growth of a pa...

Alkafeel University- Bacteriology and mycology-Dr Ahmed Alshammari –lecture THREE Bacterial infections of the GIT The causes of gastrointestinal illness can vary widely, but such diseases can be grouped into two categories:  Those caused by infection (the growth of a pathogen in the GI tract)  Intoxication (the presence of a microbial toxin in the GI tract). The digestive system contains normal microbiota, including archaea, bacteria, fungi, protists, and even viruses. Because this microbiota is important for normal functioning of the digestive system, alterations to the microbiota by antibiotics or diet can be harmful. The constant movement of materials through the gastrointestinal canal, the protective layer of mucus, the normal microbiota, and the harsh chemical environment in the stomach and small intestine help to prevent colonization by pathogens. Staphylococcal Food Poisoning (s. aureus) Cell morphology (Refer to the lecture TWO) Laboratory environment (Refer to the lecture TWO) Clinical demonstration Staphylococcal food poisoning is one form of food intoxication. When Staphylococcus aureus grows in food, it may produce enterotoxins that, when ingested, can cause symptoms such as nausea, diarrhea, cramping, and vomiting within one to six hours. Signs and symptoms resolve within 24 to 48 hours. S. aureus is often associated with: 1. Variety of raw or undercooked and cooked foods including meat and dairy products. 2. Commonly found on hands and can be transmitted to prepared foods through poor hygiene, including poor hand washing. ‫ مثل‬،‫استخدام األسطح امللوثة إلعداد الطعام‬ 3. Use of contaminated food preparation surfaces, such as cutting boards..‫ألواح التقطيع‬ 4. The greatest risk is for food left at a temperature below 60 °C (140 °F), which allows the bacteria to grow. There are at least 21 Staphylococcal enterotoxins and Staphylococcal enterotoxin- like toxins that can cause food intoxication. The enterotoxins are proteins that are resistant to low pH, allowing them to pass through the stomach. They are heat stable and are not destroyed by boiling at 100 °C. Even though the bacterium itself may be killed, the enterotoxins alone can cause vomiting and diarrhea, the symptoms may be caused by the enterotoxin functioning as a superantigen and provoking a strong immune response by activating T cell proliferation. Enterotoxin Intoxication S.aurus Symptoms 24-48H Frome(Uncoocked food cutting 1 board and poorly wash) Alkafeel University- Bacteriology and mycology-Dr Ahmed Alshammari –lecture THREE Enterobacteriacae The family Enterobacteriaceae comprises a very large group of Gram-negative bacteria. They inhabit soil, water, and also a common occupant of large bowel of humans & animals. Transmitted through the fecal-oral route. The most commonly encountered members of the Enterobacteriaceae in dairy products belong to 27 genera and include 1. Escherichia, 2. Shigella 3. Salmonella, 4. Enterobacter 5. Yersinia, 6. Klebsiella Cell morphology Enterobacteriaceae are a family of Gram-negative, facultative anaerobic, non- spore-forming rods. They can produce endotoxin lipopolysaccharide (LPS) and exotoxins, which act on host cells by damaging membranes, inhibiting protein synthesis, or altering metabolic pathways. Laboratory environment 1. Sampling : urine , pus, blood, septum, CSF 2. Microscopically Gram-negative Rod-shaped (usually short bacilli; about 1 – 5 μm), Characteristic antigens are known as enterobacterial common antigens (ECA). The outer membrane (O), flagella (H), and capsule (K) are antigens in most the enterobacteria. 3. Macroscopically Specimens suspected of containing members of the Enterobacteriaceae and related organisms are usually inoculated onto two media, a blood agar plate and a selective differential medium such as MacConkey‟s agar or eosin-methylene blue (EMB) agar. They are facultative anaerobes. They classify according to the lactose fermenter (E.coli, Klebsiella, citrobacter, enterobacter) and non-fermenter (salmonella, Shigella, proteus, Yersinia, serratia). 4. Biochemically Catalase positive, oxidase negative, reduction of nitrate to nitrite, acid production from glucose fermentation and Motile. 2 Alkafeel University- Bacteriology and mycology-Dr Ahmed Alshammari –lecture THREE Clinical demonstration Enterobacteriaceae cause a variety of human infections that can be broadly classified as either enteric diseases or extra intestinal infections such as urinary tract infections, bacteremia, and meningitis. capsular flagellated Bloody vomiting or in stool E. coli Infections Cell morphology Gram negative, capsular, flagellated, non-spore forming rod Laboratory environment ‎ 1. Sampling: stool, urine specimens 2. Microscopically: gram-negative (-ve) rod-shaped bacteria, arranged singly or in pairs 3. Macroscopically: facultative anaerobe. The types of media used for routine cultures should be limited to blood agar and MacConkey‟s agar. 4. Biochemically: motility and catalase positive, citrate and coagulase negative Clinical demonstration The strains of E.coli that cause gastroenteritis (Diarrheagenic E. coli) are subdivided into six coli strains pathotypes as follows: Species Pathogenesis Diarrheagenic E.coli Enterotoxogenic (ETEC) Attachment to the intestinal mucosa mediated by fimbria protein called CFA (colonization factor antigen) and elaboration of heat- stable and heat-labile enterotoxins. Enteroaggregative (EAEC) autoagglutination in a “stacked-brick” arrangement over the epithelium of the small intestine Enteropathogenic (EPEC) adhesion to intestinal mucosa, mediated by plasmid coded bundle- forming pill, which form cup-like projections called pedestals Enterohaemorrhagic (EHEC) presence of Shiga toxin 1 (Stx1) or 2 (Stx2) Shiga toxin (STEC) Verocytotoxin (VCEC) Enteroinvasive (EIEC) Invasions (pInv genes) into the colonic epithelium then lyse the phagocytic vacuole and replicate in the cell cytoplasm. Diffusely adhering E. Adhere to HEp-2 cells in a diffuse pattern in which the bacteria coli (DAEC) uniformly cover the entire cell surface. 3 Alkafeel University- Bacteriology and mycology-Dr Ahmed Alshammari –lecture THREE Shigellosis  Serogroup A: Shigella dysenteriae (12 serotypes)  Serogroup B: Shigella flexneri (6 serotypes)  Serogroup C: Shigella boydii (23 serotypes)  Serogroup D: Shigella sonnei (1 serotype) Cell morphology: facultative short gram-negative, anaerobic bacillus, non- capsulated, non-spore forming, and has fimbriae Laboratory environment 1. Sampling: stool sample 2. Microscopically: gram-negative, facultative anaerobic, non–spore-forming bacillus 3. Macroscopically: on TSI slant shows an alkaline slant and acidic, but with no gas, or H2S production, non–lactose fermenting, grow well on MacConkey agar. 4. Biochemically: nonmotile, indole negative Clinical demonstration  Shigellosis is only a human disease  Shiga toxin (Stx) is one of the most potent bacterial toxins known. Stx is found in Shigella dysenteriae 1 and EHEC  S. dysenteriae type 1and EHEC is able to produce Shiga toxin, which enter to the epithelium via specific receptor and leads to enterocytes damage by inhibit the protein synthesis, then the toxin can reach to the small blood vessels and attach to them via specific receptor then leads to leakages of the blood vessels. The toxin can reach and target the kidney‟s glomerulus, thus resulting in hemolytic uremic syndrome (HUS). Severe cases may require antibiotics such as ciprofloxacin and azithromycin Salmonellosis ‫الدواجن‬ (S. enterica and S. bongori) Salmonella is part of poultry‟s microbiota, so exposure to raw eggs and raw poultry can increase the risk of infection. Cell morphology : facultative anaerobic, motile gram-negative rods Laboratory environment ‎ 1. Sampling: stool sample 2. Microscopically: gram negative slender, elongated rod with rounded ends 3. Macroscopically: on SS agar, not ferment lactose, but produce hydrogen sulfide (H2S) gas 4. Biochemically: : catalase-positive, oxidase-negative 4 Alkafeel University- Bacteriology and mycology-Dr Ahmed Alshammari –lecture THREE Clinical demonstration ‎ Once the bacteria are ingested, they multiply within the intestines and penetrate the epithelial mucosal cells via M cells where they continue to grow. They trigger inflammatory processes and the hypersecretion of fluids. Once inside the body, they can persist inside the phagosomes of macrophages. Salmonella can cross the epithelial cell membrane and enter the bloodstream and lymphatic system. Some strains of Salmonella also produce an enterotoxin that can cause intoxication. Infected individuals develop fever, nausea, abdominal cramps, vomiting, headache, and diarrhea. Typhoidal Salmonella (Typhoid and paratyphoid Fever) Salmonella enterica, primarily serotype Typhi (S. typhi) and S.paratyphi S. typhi restricted to the human while S.paratyphi consider as a zoonotic pathogen. Cell morphology and Laboratory environment ‎ 1. Sampling: feces, urine, blood, or bone marrow. 2. Microscopically:rod-shaped Gram-negative bacteria 3. Macroscopically: The commonly used lab media for the isolation of Salmonella species are Desoxycholate Citrate Agar or XLD agar, Salmonella – Shigella agar and MacConkey agar. 4. Biochemically: negative for motility, citrate, indole and urease Clinical demonstration ‎ Unlike other Salmonella serotypes that primarily cause localized intestinal inflammation and diarrhea, Salmonella typhi and paratyphoid A, B, and C characteristically enter the bloodstream from the gastrointestinal tract, survive, and proliferate in macrophages, transported through the body, most notably to the liver and gallbladder. S typhi and paratyphi are clinically indistinguishable from each other. Fever, body aches, headache, nausea, lethargy, and a possible rash. Enterobacter E. cloacae, E. aerogenes, E. gergoviae, and E. agglomerans Cell morphology and Laboratory environment 1. Sampling : stool, blood samples 2. Microscopically: gram-negative bacteria ,a little pink rod, motile, facultative anaerobes 3. Macroscopically: on blood agar, large, smooth, flat colonies with entire margin without beta hemolysis. 4. Biochemically: catalase and citrate positive, indole negative Clinical demonstration 5 Alkafeel University- Bacteriology and mycology-Dr Ahmed Alshammari –lecture THREE Pathogenic Enterobacter can cause any of a variety of conditions, including eye and skin infections, meningitis, bacteremia (bacterial blood infection), pneumonia, and urinary tract infections. Yersiniosis Foodborne illness (Yersinia enterocolitica Y. and pseudotuberculosis) Gram –negative, facultative anaerobic, isolated frequently from soil, water, animals, and foods. Y. enterocolitica and Y. pseudotuberculosis can cause gastroenteritis. Cell morphology and Laboratory environment ‎ 1. Sampling: food, stool sample 2. Microscopically: gram negative, coccoid shaped, non-spore-forming bacillus 3. Macroscopically: deep red center (“bull's eye”) with a transparent margin on Cefsulodin-Irgasan-Novobiocin agar (CIN agar) 4. Biochemically: oxidase negative, catalase and urease positive Clinical demonstration ‎ Y. enterocolitica causes human infections whose symptoms include diarrhea, terminal ileitis, mesenteric lymphadenitis, arthritis, and septicemia. Y. pseudotuberculosis causes mesenteric lymphadenitis, diarrhea, and septicemia in humans. Intoxication can also result because of the activity of its endotoxin and exotoxins (enterotoxin and cytotoxin necrotizing factor) Cholera and Other Vibrios Cell morphology Vibrio cholerae, a gram-negative, possesses a single polar flagellum , „comma- shaped' bacterium Laboratory environment ‎ 1. Sampling: stool sample 2. Microscopically: non-capsulated, comma-shaped, gram-negative 3. Macroscopically: translucent, flat, yellow colonies with elevated centers on thiosulfate citrate bile salts sucrose (TCBS) agar. 4. Biochemically: motility, indole and oxidase positive Clinical demonstration Because V. cholerae is killed by stomach acid, relatively large doses are needed for infection. The motile cells travel through the mucous layer of the intestines, where they attach to epithelial cells and release cholera enterotoxin. 6  Alkafeel University- Bacteriology and mycology-Dr Ahmed Alshammari –lecture THREE The toxin is an A-B toxin with activity through adenylate cyclase. Within the intestinal cell, cyclic AMP (cAMP) levels increase, this activates a chloride channel and results in the release of ions into the intestinal lumen. This increase in osmotic pressure in the lumen leads to water also entering the lumen. As the water and electrolytes leave the body, it causes rapid dehydration and electrolyte imbalance. Diarrhea is so profuse that it is often called “rice water stool”. Other vibrio 1. V. parahemolyticus is associated with gastrointestinal illness via consumption of contaminated seafood. The bacteria produce a heat-stable hemolysin, leading to dysentery. 2. Vibrio vulnificus is found in warm seawater, the bacteria can be found in raw seafood, and ingestion causes gastrointestinal illness. 3. Aeromonas hydrophila and Plesiomonas shigelloides, are also associated with marine environments and raw seafood; they can also cause gastroenteritis. ‫البيئات البحرية واملأكوالت البحرية النيئة؛‬ Campylobacter jejuni Gastroenteritis Cell morphology Gram-negative, spiral or curved bacteria. They may have one or two flagella. Laboratory environment ‎ 1. Sampling: blood , rectal swab ‫حلزونية الشكل‬ 2. Microscopically: helical-shaped, non-spore-forming, Gram-negative 3. Macroscopically: on Campylobacter Blood Agar (CVA) appear as small, grayish in coloration, flat with irregular edges, non-hemolytic, mucoid colonies at 24 and 48 hours. 4. Biochemically: oxidase and catalase positive. Clinical demonstration ‎ ‫الدواجن‬ The primary route of transmission is through poultry that becomes contaminated ‫الذبح‬during ‫اثناء‬ slaughter, unpasteurized milk or contaminated water. In most cases, the illness is self-limiting and includes fever, diarrhea, cramps, vomiting, and sometimes dysentery. More serious signs and symptoms, such as bacteremia, meningitis, pancreatitis, cholecystitis, and hepatitis, sometimes occur. Peptic Ulcers (Helicobacter pylori) Cell morphology ‫لولب‬ H. pylori gram-negative, shaped like a corkscrew, or helix Laboratory environment ‎ 1. Sampling: breath or stool 7 Alkafeel University- Bacteriology and mycology-Dr Ahmed Alshammari –lecture THREE 2. Microscopically: gram-negative, S-shaped bacterium with 1 to 3 turns, 0.5 ×5 μm in length, with a tuft of 5 to 7 polar sheathed flagella 3. Macroscopically: translucent to pale grayish colonies of 0.5 to 1 mm in size on blood agar 4. Biochemically: positive for motility , catalase and oxidase Clinical demonstration ‎ H. pylori colonizes epithelial cells in the stomach using pili for adhesion. These bacteria produce urease, which breaks urea down into ammonia and carbon dioxide, ammonia neutralizes stomach acids to provide a more hospitable microenvironment. The infection damages the cells of the stomach lining, including those that normally produce the protective mucus that serves as a barrier between the tissue and stomach acid. Signs and symptoms include nausea, lack of appetite, bloating, burping, and weight loss. Bleeding ulcers may produce dark stools. In rare cases the infection leads to gastric cancer. Clostridium perfringens Gastroenteritis ‫األمراض املنقولة عن طريق الغذاء‬ Clostridium perfringens gastroenteritis is a generally mild foodborne disease that is associated with undercooked meats and other foods. Cell morphology Gram-positive, rod-shaped, endospore-forming anaerobic bacterium that is tolerant of high and low temperatures. ‎Laboratory environment ‎ 1. Sampling: stool sample 2. Microscopically: gram-positive bacteria, long, irregular (drumstick or spindle-shaped) cells with a bulge at their terminal ends (forms sub terminal spores). 3. Macroscopically: on blood agar, double zone of beta hemolysis, inner zone is complete hemolysis and outer zone is partial hemolysis. 4. Biochemically: negative for motility, catalase and indole Clinical demonstration ‎  At high temperatures, the bacteria can form endospores that will germinate rapidly in foods or within the intestine. Food poisoning by type A strains is common, that causes the clinical symptoms of cramps and diarrhea.  Gas gangrene caused by C.perfringens, it usually occurs rarely in the intestine, but mostly at the site of trauma or a recent surgical wound. Gas gangrene causes very painful swelling. The skin turns pale to brownish-red. When the swollen area is pressed, gas can be felt as a crackly sensation 8 Alkafeel University- Bacteriology and mycology-Dr Ahmed Alshammari –lecture THREE (crepitus). The edges of the infected area grow so quickly that changes can be seen over minutes. The area may be completely destroyed.  The differences between gas gangrene and necrotizing fasciitis (lecture 2): necrotizing fasciitis destroys the fat under your skin and the connective tissues that support your body (fascia) while gas gangrene infects and destroys your blood cells, blood vessels and muscle tissue. Pseudomembranous colitis/ antibiotic-associated diarrhea (Clostridium difficille) Gram-positive, toxin-producing bacterium rod that can be a commensal bacterium as part of the normal microbiota of healthy individuals. Cell morphology and ‎Laboratory environment ‎ 1. Sampling: stool sample 2. Microscopically: gram positive, rod-shaped bacteria 3. Macroscopically: The colonies of C. difficile on blood agar are irregular in shape with an undulate edge without hemolysis. 4. Biochemically: positive motility, negative catalase and indole Clinical demonstration ‎ C.difficile is the cause of approximately 25% of all cases of antibiotic-associated diarrhea (pseudomembranous colitis). Bacterium produces two toxins, Clostridium difficile toxin A (TcdA) and Clostridium difficile toxin B (TcdB). Infections begin with focal necrosis, then ulceration with exudate, and can progress to pseudomembranous colitis, which involves inflammation of the colon and the development of a pseudomembrane of fibrin containing dead epithelial cells and leukocytes. Mushy or porridge-like diarrhea, dehydration, fever, loss of appetite, and abdominal pain can result. Perforation of the colon can occur, leading to septicemia, shock, and death. Antibiotics most commonly involved include:  Macrolides, such as clarithromycin  Cephalosporins, such as cefdinir and cefpodoxime  Fluoroquinolones, such as ciprofloxacin and levofloxacin  Penicillins, such as amoxicillin and ampicillin 9 Alkafeel University- Bacteriology and mycology-Dr Ahmed Alshammari –lecture THREE Bacillus cereus Foodborne illness Bacillus cereus, commonly found in soil, is a gram-positive endospore-forming bacterium that can cause foodborne illness. Cell morphology and Laboratory environment ‎ 1. Sampling: food, stool or vomit samples 2. Microscopically: slightly curved rods with square ends 3. Macroscopically: appears on blood agar as large, flat, granular to ground- glass, β-hemolytic colonies of variable shape (circular to irregular) 4. Biochemically: positive for motility and catalase, negative for indole Clinical demonstration ‎ B. cereus endospores can survive cooking and produce enterotoxins in food after it has been heated; illnesses often occur after eating rice and other prepared foods left at room temperature for too long. The signs and symptoms appear within a few hours of ingestion and include nausea, pain, and abdominal cramps. B. cereus produces two toxins: one causing diarrhea, and the other causing vomiting. 10