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Escherichia coli

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Title: Escherichia coli


1
ESCHERICHIA COLI (E. COLI)BYSYLVANUS AITKINS
ESCHERICHIA COLI (E.COLI) AND SALMONELLA BY SYLVAN
US AITKINS
2
OVERVIEW
  • CHARACTERISTICS
  • VIRULENCE FACTORS
  • PATHOGENESIS EPIDEMIOLOGY
  • CLINICAL FINDINGS
  • LABORATORY DIAGNOSIS
  • TREATMENT

3
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.

4
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

5
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.

6
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
7
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

8
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.

9
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.

10
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.

11
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.

12
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.

13
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14
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.

15
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16
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

17
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.

18
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.

19
URINARY TRACT INFECTION
20
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.

21
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.

22
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.

23
CLINICAL FINDINGS- Travelers Diarrhoea.
  • Diarrhoea caused by ENTEROTOXIGENIC E. COLI is
    usually watery, NONBLOODY , SELF-LIMITED .
  • It is frequently associated with Travel.

24
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

25
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26
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.

27
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

28
TREATMENT AND PREVENTION
  • Neonatal Meningitis can be treated with a
    combination of AMPICILLIN and CEFTAXIME

29
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.

30
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

31
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

32
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.

33
  • Which of the following is the most likely
    organism to cause the infection?
  • A. Escherichia coli
  • B. Malaria
  • C. Streptococcus faecalis
  • D. Vibrio cholerae

34
  • SALMONELLA

35
OVERVIEW
  • CHARACTERISTICS
  • VIRULENCE FACTORS
  • PATHOGENESIS EPIDEMIOLOGY
  • CLINICAL FINDINGS
  • LABORATORY DIAGNOSIS
  • TREATMENT

36
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.

37
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.

38
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.

39
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.

40
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.

41
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.

42
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.

43
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.

44
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.

45
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.

46
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.

47
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.

48
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.

49
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.

50
QUESTIONS
  • What is salmonella?
  • What is salmonellosis?
  • How do people get salmonellosis?
  • What are the symptoms of salmonellosis?

51
  • GRACIAS.
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