Laboratory Identification of E. coli PDF

Laboratory Identification of E. coli Escherichia coli (E. coli) is a bacterium commonly found in the intestines of humans and animals. While most strains are harmless, certain pathogenic strains can cause severe illnesses. by Heba Rashed Learning Outcomes (LOs) On completion of this lecture, t...

Laboratory Identification of E. coli Escherichia coli (E. coli) is a bacterium commonly found in the intestines of humans and animals. While most strains are harmless, certain pathogenic strains can cause severe illnesses. by Heba Rashed Learning Outcomes (LOs) On completion of this lecture, the student will be able to: To know the Enterobacteriaceae To know the lactose fermenter organisms Recognize of laboratory identification of E.coli & klebsiella The family Enterobactericeae includes the following genera 1. Escherichia coli , 2. Klebsiella, 3. Citrobacter 4. Salmonella 5. Shigella 6. Proteus 7. Serratia 8. Enterobacter 9. Morganella 10.Providencia 11.Yersinia Classification of Enterobacteriaceae The family Enterobacteriaceae is divided according to fermentation of lactose into A. Lactose fermenters that ferment lactose producing rose pink colonies on MacConkey’s medium such as E.coli , Klebsiella , Enterobacter, Citrobacter. B. Lactose non-fermenters that do not ferment lactose producing pale yellow colonies on MacConkey’s medium such as Salmonella , Shigella, Proteus. Uses of MacConkey Agar Medium MacConkey agar is selective and differential medium. MacConkey agar is commonly used for the isolation of Gram negative enteric bacteria. It differentiates between lactose-fermenting and non lactose fermenting gram-negative rods by the color of colonial growth. What is E. coli? Gram-Negative BacteriaRod-Shaped Escherichia coli, commonly E. coli is a facultative known as E. coli, is a type anaerobic bacterium that of bacterium found in the can thrive in both oxygen- intestines of humans and rich and oxygen-deprived animals. environments. Commensal Pathogenic Strains Most strains of E. coli are Certain strains of E. coli harmless and part of the have evolved virulence normal intestinal flora, factors that can cause aiding in digestion and illness, leading to food nutrient absorption. poisoning, urinary tract infections, and other  Importance of E. coli Identification Public Health Clinical Diagnosis E. coli identification plays a Accurate identification is crucial role in protecting essential for diagnosing E. public health, especially coli infections, allowing for when associated with appropriate treatment and foodborne outbreaks or preventing complications. water contamination. Epidemiology Identifying E. coli strains helps researchers track outbreaks, identify sources of contamination, and develop effective prevention strategies. E. coli Morphology and Characteristics Rod-shaped Flagella for Capsule for Pili for Adhesion Morphology Movement Protection Pili are thin, hair-like E. coli bacteria are E. coli possesses Some strains of E. coli structures that extend Gram-negative, rod- flagella, which are hair- have a capsule that from the cell surface and shaped, with a length like appendages that surrounds the cell wall, facilitate adherence to of 2-3 micrometers enable them to freely in providing protection host cells, promoting and a width of 0.5-1 liquid environments, such against host defenses and colonization. micrometer. They are as the intestinal tract. environmental stresses. commonly found in the intestines of animals, including humans. Natural host of E.coli is intestinal tract of humans and animals They grow on ordinary medium. It is one of the organism that cause fecal pollution of water Morphology: Gram negative bacilli , motile, non-spore forming Some strain are capsulated Culture characters E.coli are aerobic and facultative anaerobic E.coli isolated from extraintestinal sources Diseases caused by E.coli intestinal diseases ( Diarrhea ) There are 5 types of diarrheagenic E.coli 1-Enterotoxigenic E.coli 2-Enteropathogenic E.coli 3-Enteroinvasive E.coli 4- Enteroaggregative E.coli 5-Enterohaemorrhagic E.coli: A. It causes bloody diarrhea or hemorrhagic colitis. B. It produce verocytotoxigenic toxins C. Antigenically O157:H7 Specimen Collection and Handling Sample Selection Choose the appropriate specimen based on the suspected infection, such as stool, urine, or blood. Collection Procedures Follow aseptic techniques to avoid contamination and ensure accurate results. Transport Media Use transport media to preserve the viability and integrity of the E. coli bacteria during transport to the laboratory. Labeling and Documentation Label the specimen container with patient information and date/time of collection. Timely Delivery Transport the specimen to the laboratory promptly to minimize any potential bacterial growth or degradation.  Primary Isolation and Culture Media Selective Media Differential Media Selective media inhibit Differential media allow the growth of other for the differentiation of bacteria, allowing E. coli E. coli from other to flourish. MacConkey bacteria based on their agar, for example, metabolic selects for gram-negative characteristics. Eosin bacteria like E. coli. methylene blue (EMB) agar differentiates lactose fermenters from non-fermenters.  Biochemical Identification Tests 1. Indole Production 2. Methyl Red Test The indole test identifies This test determines the bacteria that produce indole ability of bacteria to from tryptophan, a crucial produce acid from glucose amino acid. fermentation, leading to a red color change. 3. Voges-Proskauer Test 4. Citrate Utilization This test identifies bacteria This test determines the that produce acetoin, a ability of bacteria to use neutral product of glucose citrate as a sole carbon fermentation, indicated by a source, leading to a change pink color change. in the medium's color. Interpretation of E. coli Test Results Positive Result Negative Result Indicates the presence of E. coli in the sample. Indicates the absence of E. coli in the sample. Further investigation needed to determine the specific May not rule out the possibility of other bacterial or strain and associated risks. viral infections. Laboratory diagnosis Specimen : diarrhoeal stool sample, urine pus, CSF and blood Samples are examines by 1. Direct smear stained with Gram stain 2. Culture on MacConkey’s medium 3. Lactose fermenting colonies are identified by morphology and biochemical reactions In case of diarrhea isolated E.coli is tested by serotyping using specific O antigen and for toxin production by latex agglutination or ELISA E. coli Pathogenic Strains Enterohemorrhagic Enterotoxigenic E. Enteroinvasive E. coli Enteropathogenic E. E. coli (EHEC) coli (ETEC) (EIEC) coli (EPEC) EHEC strains produce ETEC strains cause EIEC strains invade the EPEC strains attach to the Shiga toxins, causing traveler's diarrhea, intestinal lining, leading intestinal lining, causing bloody diarrhea and characterized by watery to bloody diarrhea and diarrhea, vomiting, and potentially life- diarrhea, abdominal dysentery-like symptoms. dehydration, particularly threatening cramps, and vomiting. in infants. complications, such as hemolytic uremic syndrome (HUS). E. coli-associated Diseases and Infections Gastroenteritis Urinary Tract Respiratory Bacteremia Infections (UTIs) Infections E. coli is a common cause E. coli can spread to the of diarrhea, abdominal E. coli can cause UTIs, In rare cases, E. coli can bloodstream, causing cramps, and fever. This leading to symptoms like cause pneumonia, which bacteremia, a serious infection is often self- pain during urination, is an infection of the condition that requires limiting, but can be frequent urination, and lungs. immediate medical severe in infants, blood in the urine. attention. children, and the elderly. Prevention and Control Measures Sanitation and Safe Food Handling Water Treatment Vaccination Hygiene Cooking meat and Public water systems are No vaccine is currently Proper handwashing poultry to the required to treat water available to protect with soap and water recommended internal to remove pathogens, against E. coli infection. after using the restroom temperature kills E. coli. including E. coli. However, some vaccines and before handling food Cross-contamination can Home water treatment for other diarrheal is essential. Thorough cleaning and be prevented by methods, such as diseases, like rotavirus, disinfection of surfaces, separating raw meat boiling, can be used to can reduce the risk of especially in food from other foods and further reduce the risk complications. preparation areas, help using separate cutting of contamination. reduce contamination. boards and utensils. Clinical Significance and Public Health Impact Human Health Food Safety E. coli infections can lead Contaminated food and to severe complications, water are major sources of especially in vulnerable E. coli outbreaks, populations. impacting food security. Economic Burden Public Health Strategies E. coli outbreaks can result in significant Prevention and control healthcare costs and measures, including economic losses. hygiene practices, are crucial for managing E. coli.