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Bacterial Infections II Gramnegatives

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Causes UTI, bloodstream infections & meningitis, diarrhoea ... curved bacilli with spiral, S-shaped & seagull-like forms. highly motile ... – PowerPoint PPT presentation

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Title: Bacterial Infections II Gramnegatives


1
Bacterial Infections IIGram-negatives
  • Mark Pallen

2
The Gram Stain
Gram's
Crystal
iodine
violet
Decolorise with
acetone
Gram-positives
appear purple
Counterstain with
e.g. methyl red
Gram-negatives
appear pink
3
Gram-positive rods
Gram-positive cocci
Gram-negative rods
Gram-negative cocci
4
Anaerobic
Anaerobic
Gram-positive rods
Gram-positive cocci
Gram-positive
cocci
Anaerobic
Anaerobic
Gram-negative rods
Gram-negative cocci
5
Enteric Gram-negative rods
  • Lactose-fermenters (LFs)
  • Escherichia coli
  • Klebsiella pneumoniae
  • Non-lactose fermenters (NLFs)
  • Salmonella enterica
  • Shigella spp.
  • Proteus mirabilis
  • Pseudomonas aeruginosa

Pink on Macconkey Agar
Pale on Macconkey Agar
6
Escherichia coli
  • Gut commensal
  • Model lab organism
  • E. coli K12 isolated in 1922 from stool of a
    convalescent diphtheria patient in California
  • Pathogen
  • Causes UTI, bloodstream infections meningitis,
    diarrhoea
  • E. coli O157 causes haemorrhagic colitis and
    haemolytic uraemic syndrome

7
E. coli in the News
8
E. coli in the News
9
Salmonella enterica
  • one species, 2000 serovars
  • non-standard nomenclature common
  • S. enterica serovar Typhimurium
  • or S. typhimurium
  • Appears as a non-lactose fermenter
  • on MacConkey agar or similar selective agar

10
Salmonella Antigenic Structure
  • Kauffmann-White antigenic scheme
  • agglutination reactions with specific antisera
    against Salmonella antigens
  • O antigens
  • characteristic sequence of repeating
    polysaccharide units in LPS.
  • H antigens
  • flagellar antigens (protein) and may occur in one
    of two phase variations.

flagellated
(motile)
H antigen
(flagellin)
can undergo phase variation
O antigen
lipopolysaccharide, part of cell wall
11
Salmonella Laboratory Diagnosis
  • Biochemical tests and serological tests must be
    done in parallel
  • Some other bacteria, e.g. Citrobacter, may have
    similar serological profiles
  • Commercial kits commonly used, e.g. API20

12
Shigellathe cause of bacillary dysentery
  • 4 species increasing severity of disease
  • Shigella sonnei
  • gt90 of cases in E W
  • Shigella boydii
  • 1 of cases in E W
  • Shigella flexneri
  • 6 of cases in E W
  • Shigella dysenteriae
  • lt1 of cases in E W
  • Shigella sonnei is commonly acquired in
    UK,whilst the others tend to be imported,
    especially by holidaymakers

13
Shigella
  • Non-lactose-fermenting Gram-negative rod
  • O but no H antigens
  • non-motile
  • Identification scheme similar to Salmonella
  • Biochemistry and serology done in parallel
  • Colicin typing possible

14
Proteus mirabilis
  • Non-lactose-fermenting Gram-negative rod
  • Causes
  • UTI
  • Bloodstream infection
  • Swarming motility
  • Urease-positive

15
Pseudomonas aeruginosa
  • Opportunistic pathogen
  • Causes UTI, blood-stream infections, infections
    of burns, pneumonia
  • Targets
  • immunocompromised patients
  • burns patients
  • cystic fibrosis patients
  • grows aerobically on most media
  • greenish pigment production

16
Fastidious Gram-negative rods
  • Bordetella pertussis
  • Haemophilus influenzae
  • Legionella pneumophila

17
Bordetella pertussis
  • causes whooping cough
  • diagnosis by pernasal swab
  • after 5 days colonies like mercury droplets on
    selective agar

18
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19
Legionella pneumophila
  • causes Legionnaires disease, an atypical
    pneumonia
  • associated with hot water systems and air
    conditioning
  • grows on selective agar after several days

20
Curved Gram-negative rods
  • Campylobacter jejuni
  • Helicobacter pylori
  • Vibrio cholerae

21
Campylobacter jejuni
  • curved bacilli with spiral, S-shaped
    seagull-like forms
  • highly motile
  • single polar or bipolar unsheathed flagella

22
Campylobacter jejuni
  • Microaerophilic
  • need high concentration CO2, low concentration O2
  • Thermophilic
  • optimal growth 42C
  • Fastidious
  • blood or serum normally required
  • needs antibiotic-containing selective medium
  • grows in colonies resembling water droplets

23
Helicobacter Pylori
  • spiral motile Gram-negative bacillus
  • causally linked to
  • gastritis (Kochs postulates proven by
    volunteer!)
  • peptic ulceration
  • gastric carcinoma
  • produces huge amount of the enzyme urease
  • diagnosis
  • Biopsy microscopy, culture, rapid urease test
  • Serological techniques
  • C-14 urea breath test

24
Vibrio choleraethe cause of cholera
  • Vibrio cholerae O1
  • Curved Gram-negative rod
  • Traditionally two biotypes
  • "classical" and "El Tor
  • now also "Bengal O137
  • Clinical features
  • Profuse watery diarrhoea
  • Diagnosis
  • culture on selective medium, TCBS

25
Anaerobic Gram-negatives
  • Bacteroides fragilis
  • Fusobacterium
  • spindle-shaped
  • cause polymicrobial abscesses
  • often mixed in with aerobes
  • F. necrophorum causes necrobacillosis

26
Gram-negative cocci
  • Neisseria meningitidis
  • The meningococcus
  • Neisseria gonorrhoeae
  • The gonococcus

False-colour EM
27
Oxidase positive Identified by sugar fermentation
reactions MeninGos do Maltose Glucose
28
Neisseria gonorrhoeae
  • fragile organism
  • cannot survive in environment
  • no animal reservoir
  • Gram-negative diplococcus
  • kidney bean shaped
  • often intracellular in clinical samples
  • Causes gonorrhoea

29
Unusual Gram-negatives
  • Chlamydias
  • obligate intracellular pathogens with complex
    life cycle
  • cause trachoma, pneumonia, STDs
  • Rickettsias
  • obligate intracelllar pathogens
  • cause typhus, Rocky Mountain spotted fever etc.
  • Coxiella burnetti
  • obligate intracelllar pathogen
  • causes Q fever

30
Unusual Gram-negatives
  • Spirochaetes
  • thin spiral bacteria with endoflagellum
  • visualised with silver staining or dark-ground
    microscopy
  • Treponema pallidum
  • causes syphilis
  • Leptospira icterohaemorrhagica
  • causes Weil's disease
  • Borrelia burgdorferi
  • causes Lyme arthritis

31
Summary
  • Enteric Gram-negative rods
  • LFs versus NLFs
  • E. coli, Salmonella, Shigella, Proteus,
    Pseudomonas
  • Curved Gram-negative rods
  • Campylobacter, Helicobacter, Vibrio
  • Fastidious Gram-negative rods
  • Bordetella, Haemophilus, Legionella
  • Anaerobic Gram-negative rods
  • Gram-negative cocci
  • Meningococcus
  • Gonococcus
  • Unusual Gram-negatives
  • Chlamydia, Rickettsia, Coxiella, Spirochaetes

32
Further Reading
  • http//medweb.bham.ac.uk/http/depts/inf/teach/BDS/
    bdslect.htm
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