Gram Negative Organisms

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Gram Negative Organisms
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2094
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2096
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Classification

• Gram negative cocci
• aerobic vs anaerobic
• Gram negative bacilli
• aerobic vs anaerobic

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Pathogenic mechanisms

• Capsule
• Cell wall
• Endotoxin - lipopolysaccharide
• Adherence mechanisms
• Flagella - motility
• Exotoxins

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Gram negative cocci

• Aerobic
• Neisseriaceae
• Neisseria spp.
• Moraxella spp
• Anaerobic
• Veillonellaceae
• Veillonella spp.

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Gram negative bacilli

• Aerobic
• Pseudomonaceae
• Legionellaceae
• Brucella spp., Bordetella spp
• Microaerophilic
• Spirillaceae
• Campylobacter spp., Helicobacter spp.
• Facultatively anaerobic
• Enterobacteriaceae
• Vibrionaceae e.g V. cholerae
• Anaerobic
• Bacteroides spp.

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Neisseriaceae

• Gram negative diplococci (kidney shaped pairs)
• Fastidious
• N. meningitidis
• N. gonorrhoea

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N. meningitidis

• At least 13 serotypes but B, C common in this
  country
• Based on capsular polysaccharide
• Nasopharyngeal colonisation
• Bacteraemia septicaemia
• Meningitis
• Clinical suspicion essential part of diagnosis

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Enterobacteriaceae

• Obligate pathogens
• Salmonella spp - S. typhi, S. paratyphi,
• Shigella spp - S. sonnei, S. boydii,
• Yersinia spp - Y. pestis
• Facultative pathogens
• Escherichia coli, Klebsiella spp., Proteus spp.,
  Enterobacter spp., Serratia spp., Morganella
  spp., Citrobacter spp., Providencia spp.

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Differentiation

• Gram stain - not helpful
• Motility
• Metabolic properties
• Lactose fermentation
• E. coli Vs Salmonella spp.

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Salmonella spp. and Shigella spp

• Salmonella spp.
• Motile non-lactose fermenting GNB
• S. typhi / S. paratyphi more invasive
• 60 serotypes
• Shigella spp. - dysentery
• non motile, non encapsulate, non lactose
  fermenting
• 40 serotypes

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E. coli

• Motile/non-motile GNB, lactose fermenting
• Common cause of infection
• UTI, bacteraemia, meningitis, intra-abdominal
  sepsis,
• Enteric infection e.g. Travellers diarrhoea,
  childhood diarrhoea, Haemolytic Uraemic Syndrome
  (E. coli O157),

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Pseudomonas aeruginosa

• Aerobic, motile GNB
• Oxidises rather than ferments carbohydrates
• Widely distributed - moist environment
• Antimicrobial resistance - intrinsic and acquired
• Diseases
• respiratory tract infection (cystic fibrosis,
  ventilated patients), bacteraemia
  (immunocompromised patients)

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Fastidious GNB

• Haemophilus influenzae
• Legionella pneumophila - Legionnaires
• Brucella spp - Brucellosis
• Bordetella pertussis - Whooping cough
• Franciella tularensis - Tularaemia
• Pasteurella spp - wound infection, meningitis
• Yersinia spp. - Plague

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H. influenzae

• Small non-motile
• Capsulated - 6 distinct types
• Requires supplementation for growth
• X and V i.e. protoporphyrins and nicotinamide
  adenine dinucleotide
• Diseases
• Bacteraemia, meningitis, epiglottitis, pneumonia,
  exacerbations of chronic obstructive pulmonary
  disease
• vaccination - H. influenzae type B

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Campylobacter spp.

• Zoonosis
• motile, non spore forming comma shaped GNB
• Microaerophilic
• Need selective techniques to isolate in
  laboratory and takes upto 48 hours
• Diseases
• gastrointestinal symptoms
• systemic infection

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Non-spore forming anaerobes

• Gram negative cocci
• Veillonella spp
• Gram negative bacilli
• Bacteroides spp.
• Fusobacterium spp.

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Other gram negatives - not normally classified
this way

• Spirochaetiaceae
• Treponema - T. pallidum Syphilis
• Borrelia - B. recurrentis Relapsing fever, B.
  burgdorferi Lyme Disease
• Leptospira - L. icterohaemorrhagiae Weils
  disease
• Rickettsiaceae
• Short coccoid gram negative rods
• Obligate intracellular bacteria
• R. prowazeki epidemic spotted fever (typhus)
• R. typhi murine spotted fever
• R. rickettsii Rocky mountain spotted fever