Pseudomonas

Pseudomonas are Gram-negative rod bacteria commonly found in soil, ground water, plants and animals. Pseudomonas aeruginosa is the most common cause of Pseudomonas infection.¹ Pseudomonas infection causes a necrotizing inflammation.

• Pseudomonas aeruginosa rarely affects healthy people and most community-acquired infections are associated with prolonged contact with contaminated water.
• P. aeruginosa is a major cause of healthcare-associated infections and also chronic lung infections in people with cystic fibrosis.
• P. aeruginosa can cause a wide range of infections, particularly among immunocompromised people (HIV or cancer patients) and persons with severe burns, diabetes mellitus or cystic fibrosis.²
• P. aeruginosa is increasingly resistant to many antibiotics. In hospitals the organism contaminates moist/wet reservoirs such as respiratory equipment and indwelling catheters.
• Infections can occur in almost every body site as well as bacteraemia.

• Although P.aeruginosa is an opportunistic pathogen, it can cause a wide range of infections, especially in immunocompromised people and people with severe burns, diabetes mellitus or cystic fibrosis²
• P. aeruginosa is a common causes of healthcare-associated infections. It is the most common pathogen isolated from patients who have been in hospital for longer than one week.

Respiratory tract

• Pneumonia is seen in patients with immunosuppression and chronic lung disease
• May be due to spread from the upper respiratory tract, especially in patients on mechanical ventilation, or from bacteraemic spread (often seen in patients with neutropenia following chemotherapy and in patients with HIV infection)
• Chronic infection of the lower respiratory tract with P. aeruginosa is prevalent among patients with cystic fibrosis.

Bacteremia

• May be acquired via medical devices in hospitals and nursing homes, and the mortality rate remains greater than 10%.
• Skin shows characteristic skin lesions (ecthyma gangrenosum), which are haemorrhagic and necrotic, with surrounding erythema and are most often found in the axilla, groin, or perianal area.

Endocarditis

• May infect heart valves in intravenous drug abusers and may also infect prosthetic heart valves
• Signs of thromboembolism, such as Janeway lesions, Osler nodes, and ecthyma gangrenosum, may occur.

Central nervous system

• May cause meningitis and intracranial abscesses
• Most infections result from direct spread from an ear, mastoid, paranasal sinus surgery or diagnostic procedures
• Haematogenous spread may also occur, especially from infective endocarditis

Ear

• Common cause of chronic otitis media.
• Malignant otitis externa is usually seen in patients with poorly controlled diabetes. Spread of infection can result in osteomyelitis of the temporal bone, cranial nerve palsies and central nervous system infection.

Eye

• Pseudomonas spp. are a common cause of bacterial keratitis, scleral abscess, and endophthalmitis in adults and ophthalmia neonatorum in children
• Local predisposing conditions are trauma and contact lens use
• Corneal lesions can progress to endophthalmitis and orbital cellulitis.

Bones and joints

• Most common affects the spine, pelvis, and the sternoclavicular joint
• Patients at risk include those with puncture wounds to the foot, peripheral vascular disease, intravenous drug abuse and diabetes.

Gastrointestinal

• Infection ranges from very mild to severe necrotizing enterocolitis.
• Severe pseudomonal diarrhoea can occur in neonates.
• Can cause enteritis, with patients presenting with prostration, headache, fever, and diarrhoea (Shanghai fever)
• Pseudomonas spp. typhlitis typically presents in patients with neutropenia resulting from acute leukaemia, with a sudden onset of fever, abdominal distension, and worsening abdominal pain.

Urinary tract infections

• Urinary tract infections are usually hospital-acquired and related to catheterization and surgery
• May be severe with renal abscess and bacteraemia

Skin

• Green nail syndrome is a paronychial infection that can develop in people whose hands are frequently immersed in water
• Secondary infections occur in patients with eczema, and tinea pedis. These infections may have a characteristic blue-green exudate with a fruity odour.
• Pseudomonas spp. are a common cause of whirlpool or swimming pool folliculitis:
  • Pruritic follicular, maculopapular, vesicular, or pustular lesions occur on any part of the body that was immersed in water
  • May also cause subcutaneous nodules, deep abscesses, cellulitis, and fasciitis
• Is an important cause of secondary infection of burns
• Suppurative thrombophlebitis may occur from having an intravenous venflon in situ

• Cultures: positive blood cultures may complicate IV venflon/catheter infections, urinary tract instrumentation, trauma, and surgery as well as endocarditis.
• Isolation of Pseudomonas from sputum and tracheal secretions might indicate airway colonization. (There is now a greater use of cultures obtained from protected bronchoalveolar lavage and protected specimen brushings obtained at bronchoscopy.)
• Local investigations, e.g. chest x-ray, stool, MSU, dependent on the site of infection.

• Most infections are susceptible to third generation cephalosporins (ceftazidime), ciprofloxacin (12% resistance in England and Wales in 2004²), carbapenems (imipenem and meropenem), aminoglycosides (gentamicin and tobramycin) and colistin. Serious infections are usually treated with ticarcillin or piperacillin, often in combination with an aminoglycoside.² The choice of antibiotic regime will depend on local guidelines and the results of laboratory sensitivities. Examples of recommended antibiotic regimes are:
  • Septicaemia and pneumonia: piperacillin plus gentamycin
  • Urinary tract infection: piperacillin or gentamycin
  • Endocarditis: gentamycin plus ceftazidime.
• The effectiveness of aerosol aminoglycoside or ceftazidime is controversial in lower respiratory tract infections but efficacy is greater in patients with cystic fibrosis
• Nebulised anti-pseudomonal antibiotic treatment has been shown to improve lung function in patients with cystic fibrosis. However the overall benefits and long term adverse effects are still uncertain.³
• Ceftazidime is very effective for pseudomonas meningitis because of its high penetration into the subarachnoid space
• Malignant otitis externa requires aggressive treatment with systemic combinations of antibiotics and surgery. Duration of treatment is 4-8 weeks, depending on the extent of involvement.
• Eye infections: in cases of small superficial ulcers, topical therapy, consisting of an ophthalmic aminoglycoside or quinolone antibiotic is an alternative. Endophthalmitis requires aggressive antibiotic therapy (parenteral, topical and intraocular).
• Urinary tract infections: piperacillin or an aminoglycoside are the antibiotics of choice for severe infection.⁴ Can be treated with a single agent, except in cases of bacteraemia and upper tract infections with abscess formation. Ciprofloxacin continues to be a preferred oral agent.
• Burn sepsis: requires aggressive surgical debridement, and avoidance of whirlpools.

Surgery

• Debridement of necrotic tissue
• Removal of infected medical devices if possible
• Malignant otitis requires surgery to debride granulation tissue and necrotic debris
• Surgery may be required for bowel necrosis, perforation, obstruction, or abscess drainage
• Vitrectomy may be needed in cases of endophthalmitis.

• Pseudomonal endocarditis may cause brain abscess, cerebritis, and mycotic aneurysms. Septic emboli to the lungs and spleen are not uncommon, and cardiac complications may include conduction blocks and congestive heart failure.
• Ear infections can cause perichondritis, sinusitis, mastoiditis, osteomyelitis of the temporal bones, cranial nerve involvement and thrombosis of the lateral and sigmoid sinuses. Meningitis and brain abscesses are relatively rare.
• Eye infections can result in corneal perforations, endophthalmitis, and orbital cellulitis
• Gastrointestinal infection can cause typhlitis, caecal perforation, and peritonitis
• Skin and soft tissue infections can cause massive necrosis and gangrene.

• Prognosis will depend on the site of infection and underlying health of the individual patient
• Acute fulminant infections, such as bacteraemic pneumonia, septicaemia, burn sepsis and meningitis are associated with significant mortality.

The following measures are important in all environments, but especially in hospitals and nursing homes:

• Strict adherence to rules of general hygiene
• Aseptic procedures, e.g. venflon and catheter insertion
• Strict isolation is required for patients with severe burns
• Proper cleaning, sterilization, and disinfection of reusable equipment
• Prophylactic antibiotics are not recommended as they result in the emergence of resistant strains of bacteria
• Potential vaccines, which may prevent infection withP.aeruginosa, are under development and if they provide effective prevention of P.aeruginosa infection they may improve outcome in people with cystic fibrosis.⁵