Escherichia coli

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ESCHERICHIA COLI (E. COLI)BYSYLVANUS AITKINS
ESCHERICHIA COLI (E.COLI) AND SALMONELLA BY SYLVAN
US AITKINS
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OVERVIEW

• CHARACTERISTICS
• VIRULENCE FACTORS
• PATHOGENESIS EPIDEMIOLOGY
• CLINICAL FINDINGS
• LABORATORY DIAGNOSIS
• TREATMENT

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CHARACTERISTICS

• E.Coli is the most common cause of urinary tract
  infection and gram-negative sepsis.
• It is a STRAIGHT GRAM NEGATIVE ROD, a
  FACULTATIVE
• ANAEROBE.
• Normal flora of the mouth and intestine
  protecting the
• intestinal tract from bacterial infections.
• Produces small amounts of vitamin B12 and vitamin
  K.
• Colonizes newborns GI tract within hours after
  birth and is
• one of two important etiologic agents of NEONATAL
• MENINGITIS and TRAVELERS DIARRHOEA.

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CHARACTERISTICS

• E. Coli FERMENTS GLUCOSE, a property that
  distinguishes it from the two major intestinal
  pathogens, SHIGELLA and SALMONELLA.
• There are more than 700 different serotypes of E.
  coli
• distinguished by different surface proteins and
  polysaccharides

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CHARACTERISTICS

• It has 3 ANTIGENS that are used to identify the
  organisms in epidemiologic investigations
• ?O or cell wall antigen
• ? H or flagellar antigen
• ? K or capsular antigen.

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STRAINS

• O antigen
• Somatic (on LPS)
• 171 antigens
• H antigen
• Flagella
• 56 antigens
• K antigen
• Capsule and
• or fimbrial
• antigen
• 90 antigens
• STRAIN NAME -O18acH7K1
• 
  

18th O-antigen
7th H-antigen
1st K-antigen
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VIRULENCE FACTORS

• E.Coli has sveral clearly identified components
  that contributes to its ability to cause disease
• A PILI
• A CAPSULE
• ENDOTOXIN and
  3 EXOTOXIN

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PATHOGENESIS

• The Reservoir of E. Coli includes both humans and
  animals.
• The source of E.Coli that causes URINARY TRACT
  INFECTION is the patients own colonic flora that
  colonizes the urogenital area.
• The source of E.Coli that causes NEONATAL
  MENINGITIS is the Mothers birth canal the
  infection is acquired during birth.

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PATHOGENESIS

• E.Coli that causes TRAVELERs DIARRHOEA is
  acquired by ingestion of food or water
  contaminated with human faeces.
• NOTE The main reservoir of ENTEROHEMORRHAGIC
  E.Coli (O157) is cattle and the organism is
  acquired in undercooked meat.

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INTESTINAL TRACT INFECTION

• ADHERENCE- The Organism uses PILI that protrude
  from the bacterial surface to adhere to the cells
  of the JEJUNUM and ILEUM.
• ENTEROTOXIGENIC STRAINS of the bacteria
  synthesize ENTEROTOXINS (cell specific) which act
  on the cells of the JEJUNUM and ILEUM ot cause
  Diarrhoea.

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INTESTINAL TRACT INFECTION

• ENTEROTOXIGENIC STRAINS of E.Coli can produce
  either or both of two enterotoxins
• ?HEAT LABILE TOXIN (LT)- It acts by
  stimulating adenylate cyclase (mechanism of
  action similar to cholera toxin).
• ?HEAT STABLE TOXIN-It acts by stimulating
  guanylate cyclase.

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INTESTINAL TRACT INFECTION

• However, certain strains of E.Coli are
  ENTEROPATHIC (ENTEROINVASIVE) and cause bloody
  diarrhoea by direct invasion of the epithelium of
  the large intestine accompanied by inflammatory
  cells (NEUTROPLILS) in the stool.

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INTESTINAL INFECTION.

• Certain enterohemorrhagic strains of E.Coli
  (those with O157H7)serotype also cause bloody
  diarrhoea by producing an exotoxin called SHIGA
  TOXIN or VEROTOXIN.
• The toxin invades intestinal epithelial cells,
  lyse the phagosomal vacuole, spread through the
  cytoplasm and infect adjacent cells.

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INTESTINAL INFECTION

• Severe gastrointestinal distress
• Hemorrhagic colitis
• Crampy abdominal pain
• Watery diarrhea
• Little or no fever
• Bloody diarrhea
• New serotype O157H7
• 1983
• Undercooked hamburgers
• Farmland visitations

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SYSTEMIC INFECTION

• The CAPSULE and ENDOTOXIN play an important role
  in the pathogenesis involved in systemic
  infection.
• The capsular polysaccharide interferes with
  phagocytosis thereby enhancing the organisms
  ability to cause infections in various organs.
• Eg. E.Coli strains that cause neonatal meningitis
  usually have a specific capsule type called K1
  antigen.

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URINARY TRACT INFECTION

• Certain O serotypes of E.Coli prefrentially cause
  urinary tract infections.
• These UROPATHIC strains are characterized by
  PILI with adhesion proteins that bind to
  specific receptors on the urinary tract
  epithelium.
• The motility of E.Coli may aid its ability to
  ascend the urethra into bladder and ascend the
  ureter into kidneys.

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URINARY TRACT INFECTION
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CLINICAL FINDINGS

• E.Coli cause a variety of diseases both within
  and outside the intestinal tract.
• E.Coli is the leading cause of COMMUNITY ACQUIRED
  (common in women) and NOSOCOMIAL (common in both
  men and women and is associated with indwelling
  urinary catheters) Urinary Tract Infections.

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CLINICAL FINDINGS-UTI

• Urinary Tract infections can be limited to the
  Bladder or extend up the collecting system to the
  kidney.
• If only the Bladder is involved the disease is
  called CYSTITIS characterized by PAIN and
  FREQUENT URINATION.
• Infection involving the kidney is called
  PYELONEPHRITIS and it is characterized by FEVER,
  CHILLS and FLANK PAIN.

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CLINICAL FINDINGS- Meningitis

• E.Coli is one of the major causative agent of
  MENIGITIS and SEPSIS in Neonates.
• Exposure of the newborn to E.Coli occur during
  birth as a result of colonization of the vagina
  by these organism in approximately 25 of
  pregnant women.

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CLINICAL FINDINGS- Travelers Diarrhoea.

• Diarrhoea caused by ENTEROTOXIGENIC E. COLI is
  usually watery, NONBLOODY , SELF-LIMITED .
• It is frequently associated with Travel.

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CLINICAL FINDINGS- EHEC

• The O157H7 strains of E.Coli also cause bloody
  diarrhoea which can be complicated by HEMOLYTIC
  UREMIC SYNDROME. This syndrome is characterized
  by
• ?KIDNEY FAILURE
• ?HEMOLYTIC ANAEMIA- caused by exotoxin induced
  capillary damage.
• ?THROMBOCYTOPENIA

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LABORATORY DIAGNOSIS

• SPECIMES TO BE COLLECTED INCLUDE
• ?CSF, STOOL, BLOOD, URINE.
• Specimens suspected of containing ENTERIC
  gram-negative rods such as E.coli are grown
  initially on a blood agar plate and on
  differential medium such as EMB agar or Mac
  Conkeys agar.

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TREATMENT and PREVENTION

• Treatment of E.Coli infections depends on the
  site of disease and the resistance pattern of the
  specific isolate.
• Eg.-Uncomplicated lower UTIs can be treated for
  just 1 to 3 days with oral TRIMETHOPRIM-SULFAMETHO
  XOLE or an oral PENICILLIN.
• E.Coli sepsis Cephalosporins such CEFOTAXIME
  with or without an aminoglycoside Eg.Gentamicin

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TREATMENT AND PREVENTION

• Neonatal Meningitis can be treated with a
  combination of AMPICILLIN and CEFTAXIME

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TREATMENT AND PREVENTION

• There is no specific prevention for E.Coli
  infection such as immunization, however the
  following measures can be taken
• ?The incidence of UTI can be lowered judicious
  use and prompt withdrawal of catheters.
• ?Some case of sepsis can be prevented by prompt
  removal of or switching the site of intravenous
  lines.

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TREATMENT AND PREVENTION

• Travelers Diarrhoea can sometimes be prevented
  by prophylactic use of DOXYCYCLINE,
  CIPROFLOXACIN.
• Ingestion of uncooked food and unpurified water
  should be avoided while traveling in certain
  countries

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QUESTION

• Which of the following organisms causes diarrhoea
  by producing an enterotoxin that activate
  adenylate cyclase?
• A.Escherichia Coli
• Bacteroides fragilis
• Staphylococcus aureus
• Enterococcus faecalis

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CASE

• Maruff an 80yr old retired Biologist has been
  having episodes of POLYURIA and SUB PUBIC PAIN
  after undergoing PROSTATECTOMY as a result of BPH
  and been catheterized a couple of days after d
  surgery. Urine analysis revealed 50WBC and 10RBCs
  per high power field. Urine culture showed a thin
  film of bacterial growth which upon gram staining
  showed a Gram negative Rod.

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• Which of the following is the most likely
  organism to cause the infection?
• A. Escherichia coli
• B. Malaria
• C. Streptococcus faecalis
• D. Vibrio cholerae

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• SALMONELLA

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OVERVIEW

• CHARACTERISTICS
• VIRULENCE FACTORS
• PATHOGENESIS EPIDEMIOLOGY
• CLINICAL FINDINGS
• LABORATORY DIAGNOSIS
• TREATMENT

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CHARACTERISTICS

• SALMONELLA species cause ENTEROCOLITIS, ENTERIC
  FEVER such as TYPHOID EVER and SEPTECEMIA.
• It is a GRAM NEGATIVE ROD that do not ferment
  Lactose but do produce H2S- features used in its
  laboratory identification.

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CHARACTERISTICS

• There are 3 methods of naming salmonella.
• EWING divides the genus into three species
• ?SALMONELLA TYPHI
• ?SALMONELLA ENTERITIDIS
• ?SALMONELLA CHOLERAESUIS
• In his scheme, there is one SEROTYPE in S.TYPHI
  and S.CHOLERAESUIS and 1500 in S.ENTERITIDS.

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CHARACTERISTICS

• Clinically, salmonella spp are often thought to
  have two distinct categories, namely, the
  TYPHODIAL SPECIE (sal. typhi and paratyphi) i.e.
  those that cause typhoid fever, and the
  NONTYPHODIAL SPECIE (Sal. Enterocolitis) i.e.
  those that cause diarrhoea and metastatic
  infections.

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VIRULENCE FACTORS

• SALMONELLA SPP produces 3 antigens
• ?CELL WALL ANTIGEN- ANTIGEN O
• ?FLAGELLAR ANTIGEN- ANTIGEN H
• ?CAPSULAR ANTIGEN-ANTIGEN Vi
• These three are important for TAXONOMIC and
  EPIDEMIOLOGIC purpose.

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VIRULENCE FACTORS

• The O Antigens which are the outer
  polysaccharides of the cell wall are used to
  subdivide salmonella into into groups A-I.
• There are two forms of the H Antigens, Phase 1
  and 2.
• The Vi Antigens are ANTIPHAGOCYTIC and are the
  most important virulence factor for Sal.typhi.

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PATHOGENESIS

• ENTEROCOLITIS
• It is characterised by invasion of the epithelial
  and subepithelial tissue of the small and large
  intestines.
• The organism penetrate through both the mucosal
  cells into the LAMINA PROPRIA with resulting
  inflammation and diarrhoea.
• PMN Leukocytes limit infection to Gut and
  adjacent lymph nodes.

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ENTERIC FEVERS

• Infection begins in the small intestine with very
  few GIT signs and then spread to phagocytes of
  liver, gall bladder, and spleen leading to
  BACTEREMIA associated with onset of fever and
  other symptoms.
• Survival of the organism with phagosomes is a
  striking feature of the disease and can result in
  establishment of a CARRIER STATE and excretion of
  bacteria in feaces.

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SEPTICEMIA

• Septicemia accounts for 5-10 of salmonella
  infections and it occurs in either of the
  following settings
• 1.A patient with an underlying disease eg.Sickle
  cell anaemia or Cancer.
• 2.A child with Enerocolitis.
• Bacteremia results in the seeding of many organs
  with OSTEOMYELITIS, PNEUMONIA and MENINGITIS as
  the most common seguelae.

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EPIDEMIOLOGY

• Epidemiology is related to ingestion of food and
  water contaminated by human and animal waste.
• Salmonella Typhi is transmitted only in humans
  but however, poulty products including egg, milk
  and inadequately cooked have been implicated as
  well.
• Disease occurs WORLWIDE but common in
  underdeveloped countries.

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CLINICAL FINDINGS

• After a 12-48hrs incucation period, enterocolitis
  begins with nausea and vomiting which progresses
  to abdominal pain and diarrhoea with or without
  blood.
• Usually this disease lasts a few days and is self
  limited- dose not require medical care except in
  very young and very old people and
  immunocompromised people.

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CLINICAL FINDINGS

• In enteric fevers, the onset of illness is slow
  with persistent fever and constipation rather
  than vomiting and diarrhoea.
• Delirium,Tender abdomen, splenomegaly and ROSE
  SPOTS (Rose coloured macules) are often but
  rarely seen on the abdomen.
• LEUKOPENIA, ANAEMIA and abnormal LIVER FUNCTION
  TESTS are often associated with typhoid.

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LABORATORY DIAGNOSIS

• In enterocolitis, the organism is isolated from
  stool sample whilst for enteric fever, a blood
  culture is most likely to reveal the organism.
• Bone marrow cultures and stool cultures may also
  be positive especially in chronic carriers in
  which the organism is secreted into bile.

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LABORATORY DIAGNOSIS

• Salmonella isolate can be identified and grouped
  by slide agglutination test into serogroups A, B
  ,C or E based on its O antigen.
• For epidemiological purpose, definitive
  serotyping of the O,H and Vi antigens is
  performed by public health laboratories.
• WIDAL TEST- In certain cases when the organism is
  difficult to isolate the diagnosis is made
  serologically by detecting a rise in antibody
  titre in the patients serum.

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TREATMENT AND PREVENTION

• ENTEROCOLITIS is self limited but however fluid
  and electrolytes replacement may be required.
• The treatment of choice for ENTERIC FEVER and
  SEPTICEMIA is CEFTRIAXONE or CIPROFLOXACIN.
• Salmonella infections are prevented mainly by
  public health and personal hygiene measures.
• Two vaccines are available but the confer limited
  protection.

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QUESTIONS

• What is salmonella?
• What is salmonellosis?
• How do people get salmonellosis?
• What are the symptoms of salmonellosis?

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• GRACIAS.