Escherichia coli is one of the most frequent causes of many common bacterial infections, including cholecystitis, bacteremia, cholangitis, urinary tract infection (UTI), and traveler's diarrhea, and other clinical infections such as neonatal meningitis and pneumonia.
The genus Escherichia is named after Theodor Escherich, who isolated the type species of the genus. Escherichia organisms are gram-negative bacilli that exist singly or in pairs. E coli is facultatively anaerobic with a type of metabolism that is both fermentative and respiratory. They are either nonmotile or motile by peritrichous flagella. E coli is a major facultative inhabitant of the large intestine.
Acute bacterial meningitis
The vast majority of neonatal meningitis cases are caused by E coli and group B streptococcal infections (28.5% and 34.1% overall, respectively). Pregnant women are at a higher risk of colonization with the K1 capsular antigen strain of E coli. This strain is also commonly observed in neonatal sepsis, which carries a mortality rate of 8%; most survivors have subsequent neurologic or developmental abnormalities. Low birth weight and a positive cerebrospinal fluid (CSF) culture result portend a poor outcome. In adults, E colimeningitis is rare but may occur following neurosurgical trauma or procedures or complicating Strongyloides stercoralis hyperinfection involving the CNS.
E coli respiratory tract infections are uncommon and are almost always associated with E coli UTI. No virulence factors have been implicated. E coli pneumonia may also result from microaspiration of upper airway secretions that have been previously colonized with this organism in severely ill patients; hence, it is a cause of nosocomial pneumonia. However, E coli pneumonia may also be community-acquired in patients who have underlying disease such as diabetes mellitus, alcoholism, chronic obstructive pulmonary disease, and E coli UTI. E coli pneumonia usually manifests as a bronchopneumonia of the lower lobes and may be complicated by empyema. E coli bacteremia precedes pneumonia and is usually due to another focus of E coli infection in the urinary or GI tract.
E coli intra-abdominal infections often result from a perforated viscus (eg, appendix, diverticulum) or may be associated with intra-abdominal abscess, cholecystitis, and ascending cholangitis. Patients with diabetes mellitus are also at high risk of developing pylephlebitis of the portal vein and liver abscesses. Escherichia coli liver abscess is seen in the image below.
Intra-abdominal abscesses are usually polymicrobial and can be caused by spontaneous or traumatic GI tract perforation or after anastomotic disruption with spillage of colon contents and subsequent peritonitis. They can be observed in the postoperative period after anastomotic disruption. Abscesses are often polymicrobial, and E coli is one of the more common gram-negative bacilli observed together with anaerobes.
Cholecystitis and cholangitis result from obstruction of the biliary system from biliary stone or sludge, leading to stagnation and bacterial growth from the papilla or portal circulation. When bile flow is obstructed, colonic organisms, including E coli, colonize the jejunum and duodenum. Interestingly, partial obstruction is more likely than complete obstruction to result in infection, bacteremia, bactibilia, and gallstones.
As a cause of enteric infections, 6 different mechanisms of action of 6 different varieties of E coli have been reported. Enterotoxigenic E coli (ETEC) is a cause of traveler's diarrhea. Enteropathogenic E coli (EPEC) is a cause of childhood diarrhea. Enteroinvasive E coli (EIEC) causes a Shigella -like dysentery. Enterohemorrhagic E coli (EHEC) causes hemorrhagic colitis or hemolytic-uremic syndrome (HUS). Enteroaggregative E coli (EAggEC) is primarily associated with persistent diarrhea in children in developing countries, and enteroadherent E coli (EAEC) is a cause of childhood diarrhea and traveler's diarrhea in Mexico and North Africa. ETEC, EPEC, EAggEC, and EAEC colonize the small bowel, and EIEC and EHEC preferentially colonize the large bowel prior to causing diarrhea.
Shiga toxin–producing E coli (STEC) is among the most common causes of foodborne diseases. This organism is responsible for several GI illnesses, including nonbloody and bloody diarrhea. Patients with these diseases, especially children, may be affected by neurologic and renal complications, including HUS. Strains of STEC serotype O157-H7 have caused numerous outbreaks and sporadic cases of bloody diarrhea and HUS.
Kappeli et al looked at 97 non-O157 STECstrains in patients with diarrhea and found that HUS developed in 40% of patients; serotype O26:H11/H was most often associated with this syndrome.  Although strains associated with HUS were more likely to harbor STX 2 and EAE compared with those associated with bloody diarrhea , only 5 of the 8 patients with HUS had the STX2 gene; among the 3 patients with EAE -negative, STX2 -negative strains, only STX1 or STX1 and EHXA caused the HUS.
Urinary tract infections
The urinary tract is the most common site of E coli infection, and more than 90% of all uncomplicated UTIs are caused by E coli infection. The recurrence rate after a first E coli infection is 44% over 12 months. E coli UTIs are caused by uropathogenic strains of E coli. E coli causes a wide range of UTIs, including uncomplicated urethritis/cystitis, symptomatic cystitis, pyelonephritis, acute prostatitis, prostatic abscess, and urosepsis. Uncomplicated cystitis occurs primarily in females who are sexually active and are colonized by a uropathogenic strain of E coli. Subsequently, the periurethral region is colonized from contamination of the colon, and the organism reaches the bladder during sexual intercourse.
Uropathogenic strains of E coli have an adherence factor called P fimbriae, or pili, which binds to the P blood group antigen. These P fimbriae mediate the attachment of E coli to uroepithelial cells. Thus, patients with intestinal carriage of E coli that contains P fimbriae are at greater risk of developing UTI than the general population. Complicated UTI and pyelonephritis are observed in elderly patients with structural abnormalities or obstruction such as prostatic hypertrophy or neurogenic bladders or in patients with urinary catheters. Escherichia coli right pyelonephritis is seen in the image below.
E coli bacteremia is usually associated with UTIs, especially in cases of urinary tract obstruction of any cause. The systemic reaction to endotoxin (cytokines) or lipopolysaccharides can lead to disseminated intravascular coagulation and death. E coli is a leading cause of nosocomial bacteremia from a GI or genitourinary source.
Other miscellaneous E coli infections include septic arthritis, endophthalmitis, suppurative thyroiditis, sinusitis, osteomyelitis, endocarditis, and skin and soft-tissue infections (especially in patients with diabetes).
E coli is the leading cause of both community-acquired and nosocomial UTI. Up to 50% of females eventually experience at least one episode of UTI. E coli causes 12-50% of nosocomial infections and 4% of cases of diarrheal disease.
In tropical countries, EPEC is an important cause of childhood diarrhea. ETEC causes 11-15% of cases of traveler's diarrhea in persons visiting developing countries and 30-45% of cases of traveler's diarrhea among those visiting Mexico. EAggEC causes 30% of cases of traveler's diarrhea.
E coli neonatal meningitis carries a mortality rate of 8%, and most survivors have neurological or developmental abnormalities.
The mortality and morbidity associated with E coli bacteremia is the same as that for other aerobic gram-negative bacilli.
E coli infections have no recognized racial predilection.
E coli UTI is more common in females than in males because of differences in anatomic structure and changes during sexual maturation, pregnancy, and childbirth.
Men older than 45 years with prostatic hypertrophy are at an increased risk of UTI due to related bladder stasis.
Among neonates, E coli UTI is more common in boys than in girls, but circumcision reduces the risk.
E coli is an important cause of meningitis in neonates. In adults, E coli meningitis is due only to open CNS trauma or neurosurgical procedures.
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