Content
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Staphylococcus |
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Streptococcal infections |
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Streptococcus pneumoniae, other Gram-positive cocci and the alpha-haemolytic streptococci |
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Listeria, Bacillus, Corynebacterium and environmental mycobacteria |
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Diphtheria, tetanus and pertussis |
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Pathogenic mycobacteria |
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Clostridium |
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Non-sporing anaerobic infections |
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Neisseria and Moraxella |
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Small Gram-negative coccobacilli: Haemophilus, Brucella, Francisella, Yersinia and Bartonella |
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Pathogenicity of enteric Gram-negative bacteria |
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Enterobacteriaceae clinical syndromes |
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Vibrio, Campylobacter and Helicobacter |
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Environmental pathogens: Pseudomonas, Burkholderia and Legionella |
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Chlamydia, Mycoplasma and Rickettsia |
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Spiral bacteria |
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Pseudomonas spp.
Most Pseudomonas spp. are environmental organisms that can
cause opportunistic infections in a healthcare environment.
Pseudomonas aeruginosa
This organism is widespread in the environment, but rare in the
flora of healthy individuals. Its carriage increases with hospitalization.
Moist places such as sink-traps, drains and flower vases can
harbour Pseudomonas.
Pathogenesis
- Produces cytotoxins and proteases (e.g. exotoxins A and S,
haemolysins and elastase).
- Isolates from patients with cystic fibrosis produce a polysaccharide
alginate that protects from opsonization, phagocytosis and
antibiotics in microcolonies.
- Alginate, pili and outer membrane protein mediate adherence.
- Alginate production is associated with hypersusceptibility to
antibiotics, lipopolysaccharide deficiency, non-motility and
reduced exotoxin production.
Clinical syndromes
- Chronic pulmonary infection in cystic fibrosis.
- Septicaemia, which has a high mortality and is a particular
threat to neutropenic patients.
- Rapidly progressive corneal infection and otitis externa.
- Colonization of burns, followed by septicaemia.
- Ecthyma gangrenosum, a destructive skin complication of
bacteraemia.
- Osteomyelitis, septic arthritis and meningitis.
Laboratory Diagnosis
- Culture on selective media containing cetrimide, irgasin and
naladixic acid.
- Identification by biochemical testing.
- Typing by pulse-field gel electrophoresis or multilocus sequence
typing (MLST).
Treatment
Organisms are often resistant; therefore, treatment is guided by
susceptibilities.
Prevention and control
Despite active research there is no effective vaccine available;
transmission of multiresistant strains should be controlled by the
methods described in Infection in the hospital environment
.
Burkholderia spp.
Burkholderia cepacia
- This organism can cause chronic pulmonary infection among
patients with cystic fibrosis.
- It can spread from patient to patient in cystic fibrosis clinics.
- It is naturally resistant to many antibiotics.
- Treatment is based on susceptibility tests and may include expandedspectrum
cephalosporins, carbapenems or ureidopenicillins.
Burkholderia pseudomallei
This organism is found in soil and water in the tropics. It causes
melioidosis that may present as a tuberculosis-like disease, as acute
septicaemia or as multiple abscesses. Septicaemia is associated
with a high mortality. The diagnosis is made by cultivating the
organism from blood or tissues. Treatment is with ceftazidime or
imipenem. B. mallei causes a similar infection in horses, known as
glanders, which can spread to humans.
Stenotrophomonas maltophilia and Acinetobacter spp.
These organisms are found in moist environments, are naturally
resistant to many antibiotics and can colonize patients who are
immunocompromised or in intensive care units Infection is transmitted
by staff or by contaminated shared equipment, such as
nebulizers, and is more likely to occur in patients who are receiving
antibiotics, have multiple cannulae or are intubated. Both organisms
have been implicated in outbreaks of multidrug-resistant
infection and systemic invasion leads to pneumonia, septicaemia,
meningitis or urinary tract infection. Treatment, when indicated,
is based on the results of susceptibility tests.
Legionella spp.
- There are more than 39 species of Legionella, but L. pneumophila is most frequently implicated in human disease.
- They are found in rivers, lakes, warm springs, domestic watersupplies,
fountains, air-conditioning systems, swimming pools and
jacuzzis.
- Multiplication occurs at temperatures between 20 and 40 �C
inside Acanthamoeba.
- Transmission is via aerosols generated from, for example,
showers and air-conditioning systems.
- Infection is associated with previous lung disease, smoking and
high alcohol intake, but previously healthy patients can be infected.
- Immunocompromised patients in hospital are vulnerable to
infection if the hospital air-conditioning system is not adequately
maintained.
Pathogenesis
- A major outer membrane protein that inhibits acidification of
the phagolysosome.
- Macrophage infectivity is required for optimal internalization.
- L. pneumophila expresses a potent exoprotease.
Clinical features
- A mild, influenza-like illness (Pontiac fever).
- Severe pneumonia (Legionnaires' disease), which can lead to
respiratory failure and high mortality.
- Patients may complain of nausea or vomiting and malaise before
lung symptoms become prominent.
- Cough, which is usually unproductive, and dyspnoea, which is
progressive.
- Confusion is common.
- Inappropriate naturetic hormone production may be associated
with low serum sodium.
Laboratory Diagnosis
- Culture of sputum or, preferably, bronchoalveolar lavage fluid.
- Rapid diagnosis by antigen detection in urine.
- Direct immunofluorescence or nucleic acid amplification test
(NAAT) of respiratory specimens.
- Serum antibodies can provide a retrospective diagnosis for epidemiological
purposes.
Treatment and Prevention
Effective regimens usually consist of a macrolide antibiotic
together with rifampicin.
Legionellosis is prevented by adequate maintenance of air-conditioning
systems and by ensuring that hot-water supplies are
above 45 �C to prevent multiplication. |