E coli (Escherichia coli), is a type of bacteria that normally lives in your intestines. It’s also found in the gut of some animals. Most types of E. coli are harmless and even help keep your digestive tract healthy. But some strains can cause diarrhea if you eat contaminated food or drink fouled water.
Specimen:
Specimen include urine, pus, faeces, cerebrospinal fluid (Infants), and blood for culture or depending upon site of infections.
Morphology:
E.coli is a gram negative usually motile rod. A minority of strains are capsulate.
Cultural Characteristics:
Escherichia coli is an aerobe and facultative anaerobe. Optimum Temperature for the growth of E.coli is 36 – 37 ºC with most strains growing over the range 18 – 44 ºC.
Blood Agar:
Colonies of E.coli on blood agar 1 – 4 mm diameter after overnight incubation. Colonies may also appear mucoid and some strains of E.coli is hemolytic.
MacConkey agar:
Escherichia coli ferment lactose. They produced smooth pink color colonies on MacConkey Agar. Some Strains of E.coli are late or non-lactose fermenting.
CLED Agar:
They produced yellow colonies on Cystine lactose electrolyte deficient (CLED) agar.
Sorbitol MacConkey Agar:
All strains of E.coli and other enterobacteria ferment sorbitol except E.coli (VTEC) 0157 in non-sorbitol fermenting. E.coli (VTEC) 0157 identified by latex reagent testing.
XLD Agar:
E.coli strains produced yellow color colonies on Xylose Lysine Deoxycholate agar (XLD agar).
KIA (Kligler Iron Agar):
E.coli produce and acid deep and an acid slope with gas production and no H2S blacking.
Biochemical Reactions:
Biochemical tests are commonly used to identify and characterize bacteria, including Escherichia coli (E. coli). E. coli is a gram-negative, facultative anaerobic bacterium that can be found in various environments, including the human gut. Here’s a table of some common biochemical tests used for the identification of E. coli:
| Test Name | Test Result for E. coli |
|---|---|
| Gram Staining | Gram-negative |
| Morphology | Bacillus (rod-shaped) |
| Motility | Motile |
| Growth on MacConkey Agar | Lactose-fermenting |
| Indole Production | Positive |
| Methyl Red Test (MR) | Positive |
| Voges-Proskauer Test (VP) | Negative |
| Citrate Utilization | Negative (E. coli typically doesn’t use citrate) |
| Urease Test | Negative (E. coli is urease-negative) |
| Oxidase Test | Negative |
| Catalase Test | Positive |
| Triple Sugar Iron (TSI) Agar | Acid and gas production in both slant and butt |
| Sulfur Indole Motility (SIM) Test | Sulfur reduction and indole production, motile |
| Methyl Red-Voges-Proskauer (MR-VP) | MR positive, VP negative |
Antimicrobial susceptibility:
E.coli strains are sensitive to:
- Sulphonamides
- Trimethoprim
- Cotrimoxazole
- Nalidixic acid
- Nitrofurantoin
- Tetracycline
- Ampicillin
- Amoxycillin
- Cephalosporins
- Aminoglycosides
Diseases caused by E. coli are:
Escherichia coli (E. coli) is a bacterium that can cause a range of diseases and infections in humans. The severity of the illness can vary from mild to severe, depending on the strain of E. coli and the individual’s health. Here are some diseases and conditions caused by E. coli:
- Urinary Tract Infections (UTIs): E. coli is one of the most common causes of UTIs, particularly in women. It can lead to symptoms such as frequent urination, painful urination, and lower abdominal pain.
- Gastroenteritis: E. coli can cause gastroenteritis, which is inflammation of the stomach and intestines. Symptoms include diarrhea, abdominal cramps, nausea, and vomiting. The most well-known strain of E. coli associated with gastroenteritis is Enterotoxigenic E. coli (ETEC), which is often associated with contaminated food and water.
- Hemorrhagic Colitis: Some strains of E. coli, such as Enterohemorrhagic E. coli (EHEC), produce toxins that can cause bloody diarrhea and severe abdominal cramps. This condition can lead to a complication called Hemolytic Uremic Syndrome (HUS), which can result in kidney failure and other serious health problems.
- Traveler’s Diarrhea: E. coli is a common cause of traveler’s diarrhea, which can occur when individuals consume contaminated food or water while traveling to regions with poor sanitation.
- Foodborne Illness: E. coli can be transmitted through contaminated food, leading to outbreaks of foodborne illnesses. Contaminated ground beef, raw produce, and unpasteurized dairy products are some common sources of E. coli infections.
- Neonatal Meningitis: In rare cases, certain strains of E. coli can cause meningitis in newborns. This is a serious and life-threatening infection that affects the membranes surrounding the brain and spinal cord.
- Septicemia: E. coli can enter the bloodstream and cause septicemia (bloodstream infection). This can occur as a complication of other infections, such as urinary tract infections.
