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Bacterial Sexually Transmitted Infections


Three distinct bacterial pathogens causing sexually transmitted infections ... The most common bacterial sexually transmitted infection, with 104,155 cases ... – PowerPoint PPT presentation

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Title: Bacterial Sexually Transmitted Infections

Bacterial Sexually Transmitted Infections
  • Patrick Kimmitt

Today we are going to look at
  • Three distinct bacterial pathogens causing
    sexually transmitted infections
  • Neisseria gonorrhoeae
  • Chlamydia trachomatis
  • Treponema pallidum

We are going to consider
  • The organism, structure and physiology
  • The pathology of disease
  • Epidemiology
  • Laboratory diagnosis and treatment
  • There are many contrasts when looking at these
    uniquely adapted pathogens
  • You should be able to discuss each of these

GonorrhoeaNeisseria gonorrhoeae
Clinical and epidemiological aspects
  • 2nd commonest bacterial STI
  • 2004 22,335 cases reported to HPA
  • Most common age groups males 20-24
    females 16-19
  • Males usually symptomatic
  • Females often asymptomatic
  • Complications untreated females PID,
    infertility, ectopic pregnancy

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Symptoms (if present)
  • Males urethral discharge, severe burning on
  • Females vaginal discharge, yellow or
    blood-stained, pain on urination
  • Rectal infection gives rise to pain and discharge
  • Pharyngeal infection, sore throat

  • Both sexes disseminated infection on rare
    occasions septic arthritis, pustular rash, even
    infective endocarditis
  • Infection during pregnancy ophthalmia
    neonatorum of baby (conjunctivitis)
  • Dual genital infection with Chlamydia trachomatis
    usual to treat for both at time of gonorrhoea

Microbiological aspects
  • The causative organism is Neisseria gonorrhoeae,
    a Gram-negative diplococcus i.e. often see cells
    as a pair. The genus Neisseria contains one
    other pathogenic species, N. meningitidis, which
    is the principle cause of bacterial meningitis.
    There are also many commensal species of
    Neisseria, often found in the pharynx

  • N. gonorrhoeae is phagocytosed by
    polymorphonuclear neutrophils (pus cells) but
    resists intracellular destruction, remaining
    intact within the pus cell.
  • Readily cultivable, although it is sensitive to
    desiccation and requires aerobic incubation with
    5 to 10 carbon dioxide for growth. It grows as a
    small colony, often requiring 48 hours
    incubation. The colonies are grey, shiny, often
    with an irregular edge and showing colonial
    variation. The organism is catalase positive and
    rapidly oxidase positive.
  • No protective antibody response to gonorrhoea
    recurrent infections are common in people who are
    at risk.

Diagnostic Tests for Gonorrhoea
  • For urethral, cervical and rectal infections,
    microscopy (Gram strain) is a very useful
  • Gram-negative diplococci, with a coffee bean
    shape, are looked for within poymorphonuclear
    neutrophils (PMN)
  • For pharyngeal infections, microscopy is of no
    value because of the presence of commensal
    Gram-negative diplococci in the throat

Intracellular, Gram-negative diplococci - N.
  • Culture is mandatory - for identification and
    antibiotic sensitivity tests
  • Selective medium containing antibiotics and
    growth supplements (look this up)
  • e.g. Thayer Martin or New York City
  • PCR tests have been developed for the detection
    of N. gonorrhoeae infection and a single swab may
    be used in a double test to detect N. gonorrhoeae
    and Chlamydia trachomatis.

Identification Tests
  • Once you have cultured your samples you need to
    perform tests on single colonies to check/confirm
  • Oxidase test - result?
  • Gram stain what are you looking for?
  • Phadebact GC uses monoclonal antibody
  • API NH utilizes carbohydrates plus enzymes
    activity, similar to API 20E

  • The recommended treatment of gonorrhoea is
    either ceftriaxone (injectable) or cefixime
    (oral). As yet, no resistance has been reported
    to these third generation cephalosporins. In
    either case, a single dose is all that is
    necessary for the treatment of non-disseminated

ChlamydiaChlamydia trachomatis
ChlamydiaClinical and epidemiological aspects
  • The most common bacterial sexually transmitted
    infection, with 104,155 cases reported to the
    Health Protection Agency in 2004
  • The causative organism is Chlamydia trachomatis
  • The number of cases has risen steadily since the
    mid 1990s

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  • The infection has a longer incubation period than
    gonorrhoea, of 1 to 3 weeks
  • Asymptomatic infection is common in both sexes
    at least 50 in males and 70 in females
  • The highest rates of infection occur in young
    people under the age of 24

Signs and symptoms
  • Females
  • unusual vaginal discharge
  • bleeding (intramenstrual)
  • pain on urination
  • lower abdominal pain
  • Males
  • urethral discharge
  • burning and itching in genital area
  • pain on urination
  • epididymitis
  • Reiters Syndrome

  • In some cases the symptoms subside after a few
  • In either sex, complications may ensue in the
    case of untreated infection
  • In males, untreated infection may lead to
    epididymitis and Reiters Syndrome (arthritis)
  • In females, the consequences of untreated
    infection are pelvic inflammatory disease (PID)
    in 10 to 40 of cases

  • In up to 20 of patients with PID, infertility
    develops and the risk of ectopic pregnancy
  • The risk of infertility also increases if there
    has been more than one episode of PID
  • Infection in pregnancy can lead to infection of
    the baby - trachoma inclusion conjunctivitis or

  • Two other species of Chlamydia are known to be
    pathogenic for humans
  • C. pneumoniae is a cause of pneumonia and one
    of the agents of atypical pneumonia
  • C. psittaci is a respiratory pathogen in
    psittacine birds, such as parrots. The infection
    (a zoonosis) is transmissible to man, and may
    cause a severe pneumonia

Life cycle 1
  • obligate intracellular bacterial pathogen
  • all chlamydiae undergo a similar life cycle
    within the cell they are infecting
  • Elementary Bodies
  • the infective form of Chlamydia is the Elementary
    Body (EB), a dense, circular body, about 0.3µm in
    diameter. EBs are fairly inert and can survive
    outside the cell

Life cycle 2
  • Attachment
  • EBs carry glycosaminoglycan molecules on their
    surfaces that bind to receptors on the surface of
    certain cells
  • after attachment, the EB is taken into the cell
    by endocytosis and remains inside the endocytotic
    vacuole for the next phase of the life cycle

Life cycle 3
  • Reticulate Body Formation
  • the EB develops into a Reticulate Body (RB) which
    is larger (0.5 to 1.0µm) and metabolically
    active, although it uses host cell ATP-generating
    systems (?)
  • inside the vacuole, the RB grows and replicates
    its DNA
  • during this phase, the contents of the vacuole
    are termed an Inclusion Body

Life cycle 4
  • Staining of the Inclusion Body with iodine
    todemonstrateinfection of cellcultures

Life cycle 5
  • EB Formation and Release
  • after 18 to 24 hours,the RB reorganisesinto
    many EBswhich are releasedon cell rupture(24
    to 48 hoursafter infection)

Chlamydia trachomatis
  • Many different serotypes and these can be grouped
    according to the type of disease that they cause
  • Serotypes A, B and C cause a serious eye
    infection that begins with conjunctivitis and may
    progress (particularly with repeated infection)
    to conjunctival scarring and blindness trachoma
  • Serotypes D to K cause a less severe form of
    conjunctivitis that does not usually result in

  • very common in tropical countries and when
    sufferers dont get treated for the initial
  • transmitted via handsetc. and via flies

C. trachomatis STIs
  • The more common type of infection associated with
    D to K is sexually transmitted
  • NGU (non-gonococcal urethritis) in males (also
    called NSU non-specific urethritis)
  • urethritis, cervicitis, salpingitis in females
  • can lead to PID (pelvic inflammatory disease) and
    resulting infertility due to scarring of
    Fallopian tubes
  • also increased risk of ectopic pregnancy

  • Azithromycin is usually first choice single
    dose is enough
  • Alternatively can use doxycycline (adults) or
    erythromycin (babies) - Treat for extended
    periods (1-3 weeks due to prolonged replication

Lymphogranuloma venereum
  • Serotypes L1, L2 and L3 cause LGV (lymhogranuloma
  • begins with a genital ulcer,next inguinal lymph
    nodesenlarge and break down,discharging pus
  • if untreated, can lead toenlargement
    granulomatoushypertrophy of glands

Diagnosis of Chlamydial Infection
  • Because of the absolute requirement for a host
    cell Chlamydia cannot be grown on agar based
    culture media other methods used
  • Direct immunofluorescence using monoclonal
  • Tissue Culture in cycloheximide-treated McCoy
    cells detection of inclusion bodies by iodine
    staining or IF
  • ELISA for chlamydial antigen detection
  • Nucleic acid amplification tests (NAAT)
  • polymerase chain reaction (PCR)
  • ligase chain reaction (LCR)
  • strand displacement amplification (SDA)
  • transcription mediated amplification (TMA)
  • For descriptions, please see

  • Syphilis
  • Treponema pallidum

Clinical aspects
  • Caused by the spirochaete bacterium, Treponema
    pallidum ssp pallidum
  • Highly infectious
  • Starts with the development of one or more ulcers
    at the point of entry of the organism CHANCRE
  • A chancre is the lesion of primary syphilis
  • Typically painless

Primary syphilis
  • Appears up to 3 weeks post exposure
  • Heals in 2 to 6 weeks
  • If untreated, 40 of patients go on to develop
    secondary syphilis
  • 2º syphilis develops 2-6 weeks after appearance
    of a chancre
  • Rash including palms/soles, lymphadenopathy,
    flu-like symptoms
  • If still untreated, 2º syphilis may be followed
    by tertiary syphilis

Secondary syphilis
  • Tertiary syphilis develops 4 or more years after
    untreated primary syphilis
  • Tertiary syphilis (late syphilis) may affect many
    parts of the body
  • Characterized by slow growing granulomatous
    lesions which affect the nervous system, leading
    to general paralysis of the insane and
    demyelination of the spinal cord resulting in
    pains, loss of feeling and difficulty walking.
    Changes in the joint - so-called Charcot's joints
    may develop owing to loss of nerve supply.
    Dementia may occur. Very rarely changes in the
    aorta may result in an aneurysm.

Tertiary syphilis
  • The other 60 of untreated cases will develop
    latent syphilis
  • Latent syphilis may reactivate at any time to
    give rise to symptoms of later stages of syphilis
  • If infection is acquired in pregnancy, usually
    miscarriage or still-birth ensues. However, if
    the foetus survives, it may show signs of
    congenital syphilis the Hutchinsons Triad
    Hutchinsons teeth (pointed), deafness keratitis

  • There is a statutory requirement to test all
    pregnant women for anti-treponemal antibodies, so
    as to reduce the likelihood of congenital
  • Syphilis is a potentially devastating disease
    that is easy to treat, but it is essential that
    it is caught in the early stages. Treatment of
    later stages of the disease will halt its
    progress but not reverse any damage that has
    already occurred.

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  • There are other treponemal diseases, known as
    non-venereal treponematoses, which have to be
    born in mind when interpreting diagnostic tests
    for antibody. These are yaws, bejel and pinta.
    They are not endemic in the UK, but yaws is a
    common infection of childhood in parts of Africa
    and the West Indies.

Treatment of syphilis
  • Benzathine penicillin, given by intramuscular
    injection, is the first line treatment for
    syphilis. A single dose is sufficient to cure
    primary syphilis, although longer treatments are
    required for later stages, including the
    treatment of late latent syphilis.
  • Alternative drugs for penicillin-hypersensitive
    patients are ceftriaxone (injection) or
    doxycycline (oral).

Epidemiology of syphilis
  • In 2004 there were 2,254 cases of syphilis
    diagnosed in sexual health clinics in the UK
  • 870 increase since 1996!
  • Most common in males aged 20-24 years, females
    aged 25-34 years
  • Syphilis was most prevalent during the late
    1940s, but a resurgence occurred around the
    beginning of this century

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Microbiological Aspects
  • Treponema pallidum ssp pallidum is a very long,
    slender bacterium, which is about 0.1µm in
    diameter and 22µm in length
  • Since the maximum resolution of a bright-field
    microscope is 0.2µm, the organism cannot be seen
    in a Gram-stained slide
  • Cannot be grown in artificial culture

Treponema pallidum ssp pallidum(electron

  • The non-venereal treponematosis yaws is caused
    by T. pallidum ssp pertenue, bejel by T. pallidum
    ssp endenicum (also termed endemic syphilis) and
    pinta by T. carateum

Diagnosis of syphilis
  • Since it cannot be grown in vitro, microscopy or
    serology are used
  • What are the disadvantages of these?
  • Dark ground microscopy of fluid taken from an
    abraded ulcer treponemes apparent by virtue of
  • The organisms show cork-screw motility
  • Clinical information is v important

Treponema pallidum ssp pallidum by dark ground
Serological Tests
  • Disadvantages
  • an antibody response does not appear until about
    one week after the appearance of a chancre
  • No one test is 100 reliable for 1 syphilis
  • there is no way of distinguishing serologically
    between syphilis and the non-venereal

  • The tests may be grouped into 2 types specific
    tests and non-specific tests, but both types have
    enormous value in diagnosis all positive tests
    require confirmation using another method
  • Non-specific tests
  • Rapid plasma reagin (RPR) test
  • Venereal Diseases Research Laboratory (VDRL)
    carbon test
  • Employ cardiolipin as antigen
  • Alcoholic extract of ox heart


  • Serum is mixed with antigen on a card
  • Rotation for 8 minutes
  • Examine for agglutination
  • Double dilutions of positive sera to obtain a
  • Monitors treatment and activity of disease
  • Becomes positive 1-2 weeks post chancre
    appearance, high titre in 2º syphilis
  • Becomes negative after treatment
  • Biological false positives rheumatoid disease,
    viral pneumonitis, post vaccination, pregnancy

Treponemal (specific) tests
  • Treponema pallidum Particle Agglutination (TPPA)
  • Enzyme-Linked Immunoassay (ELISA)
  • Fluorescent Treponemal Antibody (Absorbed)

  • Serum diluted in microtitre plate
  • Gelatin particles control particles
  • Gelatin particles coated with treponemal antigen
    test particles
  • Added to different wells
  • Incubate
  • Observe for agglutination


  • TPPA is positive in 60 of cases of primary
    syphilis, 100 of cases of secondary syphilis
  • Remains positive for many years despite treatment
  • Very specific for treponemal diseases
  • False positives glandular fever, leprosy,
    Systemic lupus erythematosus

  • If an ELISA is used which detects both IgM and
    IgG antibody classes, this is an excellent screen
    test (can be automated) and will be positive at
    all stages of disease
  • Becomes positive 1 week after chancre develops
  • Remains positive despite treatment - IgG
  • Requires confirmatory test (e.g. TPPA)

FTA (Abs)
  • Indirect immunofluorescence test
  • Spot slide coated with treponemes
  • Serum absorbed (to remove non-specific treponemal
  • Serum added to spot, incubated, washed, dried
  • Anti-human globulin plus fluorescein added
    binds to antibody coating treponemes
  • Incubate, wash, dry slide, observe by UV
    microscopy for fluorescence


  • Seen as the gold standard test but used only in
    specialist laboratories
  • Becomes positive 1 week after development of a
    chancre, remains positive for years but becomes
    weaker in time
  • Strongest reaction when RPR is positive, i.e.
    when disease is active
  • False positives can occur in herpetic infection
    and in rheumatoid disease

Example 1
  • VDRL negative
  • TPHA negative
  • ELISA negative
  • Either negative or very early disease
  • Repeat if at risk

Example 2
  • Positive VDRL
  • Negative TPHA
  • Negative ELISA IgG

Example 3
  • VDRL positive
  • TPHA positive
  • ELISA positive - IgM
  • Recent/Active syphilis infection

Example 4
  • ELISA positive- IgG
  • TPHA positive
  • VDRL negative
  • Treponemal infection at some time-either treated
    or untreated latent/tertiary
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