miscellaneous bacteria - legionella eikenella and cardiobacterium

1. Legionella, Eikenella,
Cardiobacterium
Reshma Soman
MSc Microbiology
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2. Legionella pneumophila
• Name Legionnaires’ disease was given to an apparently new
illness which broke out among members of the American
Legion who attended a convention in Philadelphia in 1976.
• Fever, cough and chest pain, leading to pneumonia often
ending fatally
• Causative agent – Legionella pneumophila
• Gram negative rods whose natural habitat is water
• More than 50 genetically defined species, of which much most
important is Legionella pneumophila
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3. Legionella pneumophila
• Species can be subdivided into 3 subspecies:
– L pneumophila ssp pneumophila and L pneumophila ssp fraseri, which
have been described in human disease
– L pneumophila ssp pascullei, which has so far been isolated only from
the environment.
• 18 Legionella species have been associated with human disease,
but most infections are caused by just one of the many serogroups
of L pneumophila: serogroup 1.
• Other serogroups and species, such as L micdadei, L bozemanii
and L longbeachae, account for a few cases; other species rarely
cause infection.
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4. Legionella pneumophila
• L longbeachae infections make up more than a quarter of
diagnosed infections in Australia and New Zealand and may
be increasing in Europe.
• Infection is usually acquired accidently and the disease is not
transmissible from person to person.
• Rarely associated with other infections such as prosthetic
valve endocarditis or wound infection, but these are usually
nosocomial infections.
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5. Legionella pneumophila
• Legionellae give rise to two main clinical syndromes:
– Legionnaires’ disease, a pneumonia that may progress rapidly
unless treated with appropriate antibiotics. In previously healthy
subjects the mortality rate is about 10% but in those with
nosocomial infections the rate may be much higher.
– Pontiac fever, a brief febrile influenza – like illness that may be
slow to resolve fully, but does not cause death.
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6. Description
• In biological material or in water deposits, legionellae are short
rods or coccobacilli, but in cultures they become longer and are
sometimes filamentous.
• Weakly Gram –ve
• 2 – 5 x 0.1 – 0.3 μm in size, motile with polar or sub polar flagella.
• Poorly stained with Gram’s stain
• Stained by silver impregnation method
• Specific fluorescent antibody stains are used diagnostically
• They have not been demonstrated in patients with Pontiac fever.
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7. Legionella pneumophila
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8. Description
• Exacting in their growth requirements and grow best on
BufferedCharcoal Yeast Extract Agar (BCYE), which contains
iron plus cysteine as an essential growth factor.
• Some legionellae grow better in the presence of 2.5 – 5% CO₂
at 35 – 36°C, pH 6.9, 90% humidity
• Colonies usually appear after incubation for 48h to 5 days,
but species other than L pneumophila may take upto 10 days.
• Colonies – “cut glass” appearance on examination under the
plate microscope.
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9. BYCE medium
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10. Description
• Colonies of some Legionella species show blue – white
autofluorescence on illumination with long wave ultraviolet
light.
• Species and serogroups within species are characterized by
specific heat – stable LPS ags
• Subtyping is usually by the use of Mabs in an
immunoflourescence test.
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11. Pathogenesis
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12. Legionnaires’ disease
• Infection is almost always due to L pneumophila serogroup 1.
• Illness characterized by
– An incubation period of 2 – 10 days
– High fever
– Respiratory distress
– Confusion, hallucinations and occasionally, focal neurological
signs.
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13. Legionnaires’ disease
• Once infection is established, the patient develops pneumonic
consolidation with an outpouring of proteinaceous fibrinous
exudate, containing macrophages and polymorphs, into the
alveoli.
• Despite the outpouring of cells, patients usually produce little
sputum.
• Infection may extend to involve two or more lobes of the lung
and renal impairment leading to renal failure may occur.
• The severity of the disease may range from a rapidly
progressing fatal pneumonia to a relatively mild pneumonic
illness. 13

14. Legionnaires’ disease
• Patients who are debilitated, for eg by immunosuppression or
surgery, are more prone to infections, and their infections are
usually more severe than those encountered as sporadic
community cases.
• Smoking is a predisposing factor.
• The deterioration in body defences associated with ageing is
also important.
• Mode of infection – inhalation of aerosol of fine water
droplets containing the organism
• Aspiration of water containing legionellae can also lead to
infection. 14

15. Legionnaires’ disease
• Guinea pigs infected by inhalation of an aerosol containing
legionellae develop a lobular pneumonia that rapidly becomes
confluent.
• Instillation of a protease produced by L pneumophila into the
lungs of guinea pigs produces pneumonia that appears to be
the same as that caused by inhalation of the intact bacteria.
• At cellular level, legionellae are engulfed by monocytes and
can survive theirin as intracellular parasites.
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16. Pontiac fever
• Pathogenesis of this non – pneumonic, non – fatal form of
Legionella infection is not understood.
• Fever, chills, myalgia, headache
• Outbreaks with high attack rates may occur
• Milder , “influenza like illness”
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17. Laboratory diagnosis
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18. Laboratory diagnosis
• Respiratory secretions as well as pleural fluid, lung biopsy or
autopsy material, should be examined by microscopy and
culture.
• Gram – stained films are of little value except to demonstrate
the presence of other pathogens and organisms that may
interfere with the isolation of legionallae.
• Blood culture is an unrewarding procedure.
• Cultures are made on BCYE medium with and without
antibiotics added to suppress other respiratory tract flora.
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19. Laboratory diagnosis
• Potentially contaminated material such as sputum or post –
mortem material may be heated at 50°C for 30min inorder to
diminish growth by less heat – stable respiratory tract
organisms that may inhibit growth of legionellae in culture.
• In heavy infections, growth on BCYE medium may appear
after incubation for 48hr at 36°C in air, preferably enriched
with 2.5% CO₂ .
• Some longer so incubated 10 – 14 days
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20. Laboratory diagnosis
• Colonies having a “cut glass” appearance by plate microscopy,
and those fluorescing blue – white under UV light, are Gram
stained, and subcultured on to BA or cysteine deficident
medium to show that they will not grow on these media.
• Cultures are identified by use of specific antisera in an
immunofluorescence test or by gene sequencing.
• PCR – detect and type legionellae in clinical material –
quicker than culture and sometimes allow typing of organism
when culture is unsuccessful.
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21. Laboratory diagnosis
Immunofluoresecent staining with monoclonal or polyclonal
antisera is specific
But legionellae are usually hard to find in the scanty sputum
produced by patients
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22. Antigen tests
• Examination of urine for legionella antigen by ELISA is a
rapid and specific method of identifying L pneumophila as
the likely cause of a pneumonia.
• Most legionellae infections are now diagnosed by urine
antigen tests, but failure to detect urinary antigen doesnot
exclude infection with legionellae other than L pneumophila
serogroup 1
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23. Serology
• Ab takes atleast 8 days to develop after the onset of infection
• Some patients may not reach hospital until this period has
elapsed
• So it is worthwhile examining serum for antibodies to L
pneumophila on admission to hospital
• Sera should be taken at intervals to show the development of
antibodies or a rise in antibody titre
• Ab usually develop after 8 – 10 days of illness and then
increase in titre
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24. Serology
• But some patients may not produce ab for some weeks or
rarely for several months.
• A 4 - fold or greater rise in ab titre in a typical clinical case
indicates infection with legionella.
• A single titre of 256 or more is presumptive of infection.
• Ab may persist for months or years and can be a source of
confusion, as may cross – reacting ab produced by some
patients with Campylobacter infection.
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25. Treatment
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26. Treatment
• Intravenous macrolide is the std theapy in legionella
pneumonia
• Severe – fluroquinolone, rifampicin
• Aminoglycosides and β – lactam anibiotics – not effective
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27. Epidemiology
• 1976 – Legionnaires’ disease
• Legionellapneumonia has been reccognized as the only acute
bacterial pneumonia that may occur in outbreakform
• This is due to dissemination of bacteria in aerosols, which may
travel as much as 1 – 2 km fromthe source.
• Infected aerosols are usually generated from warm water sources,
typically:
– The ponds in cooling towers of refrigeration plants in air conditioning
system
– Domestic hot water systems in hotels and hospitals
– Warm water in nebulizers and oxygen line humidifiers
– Whirlpool spa baths and showers 27

28. Epidemiology
• Legionellae are engulfed by and survive within free living
amoebae and the bacteria may be protected from drying and
disinfectants when present in ameobic cysts.
• Legionnaires’ disease prevalent – late summer and autumn
• May be due to an increase in bac num in water from natural
sources and in cooling towers
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29. Control
• No vaccine
• Infected aerosol should be eradicated
• Legionellae can be eradicated from water in several ways
– Heat
– Disinfection with chlorine or other biocides, including chlorine
dioxide
– Cu – Ag ionization
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30. Eikenella corrodens
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31. Eikenella corrodens
• Oxidase +
• Facultative anaerobe
• Capnophilic
• Gram negative bacillus
• Name “corrodens” – characteristic pitting or corroding of
blood agar by colonies of bacterium
• Present – mouth, upper respiratory tract, gastrointestinal
tract of humans
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32. Eikenella corrodens
• Commensal of mucosal surfaces
• Infections follows salivary or fecal contamination and usually
involves skin and subcutaneous tissues though rarely
osteomyelitis, pneumonia, endocarditis, and meningitis may
occur.
• Sensitive to penicillin and tetracycline
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33. Cardiobacterium hominis
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34. Cardiobacterium hominis
• Gram negative
• Pleomorphic bacillus
• Occurs commonly as a commensal in the human nose and
throat may be endocarditis, particularly in those with pre –
existing cardiovascular disease
• Grows on blood agar under 3 – 5% CO₂ high humidity
• Ferments wide range of sugars
• Forms indole
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35. Cardiobacterium hominis
• Oxidase positive
• Catalase –
• Nitrate –
• Sensitive to many antibiotics
• Penicillin and Streptomycin – recommended drugs
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