Pseudomonas Aeruginosa

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MICROBIOLOGY LEGEND

CYCLE 45 – ORGANISM 3

Pseudomonas aeruginosa

Pseudomonas aeruginosa is a common bacterium that can cause disease in animals, including humans. It is found in soil, water, skin flora, and most man-made environments throughout the world. It thrives not only in normal atmospheres, but also in hypoxic atmospheres, and has, thus, colonized many natural and artificial environments. It uses a wide range of organic material for food; in animals, the versatility enables the organism to infect damaged tissues or those with reduced immunity. The symptoms of such infections are generalized inflammation and sepsis. If such colonizations occur in critical body organs, such as the lungs, the urinary tract, and kidneys, the results can be fatal.

Because it thrives on most surfaces, this bacterium is also found on and in medical equipment, including catheters, causing cross-infections in hospitals and clinics. It is implicated in hot-tub rash. It is also able to decompose hydrocarbons and has been used to break down tar-balls and oil from oil spills.

Pathogenesis An opportunistic, nosocomial pathogen of immunocompromised individuals, P. aeruginosa typically infects the pulmonary tract, urinary tract, burns, wounds, and also causes other blood infections.

Infections Details and common associations High-risk groups Pneumonia Diffuse bronchopneumonia Cystic fibrosis patients Associated with a purple-black skin lesion Septic shock Neutropenic patients ecthyma gangrenosum Urinary tract infection Urinary tract catheterization

Gastrointestinal Premature infants and neutropenic Necrotising enterocolitis (NEC) infection cancer patients Skin and soft tissue Burns victims and patients with Haemorrhage and necrosis infections wound infections

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Identification It is a Gram-negative, aerobic, coccobacillus bacterium with unipolar motility. An opportunistic human pathogen, P. aeruginosa is also an opportunistic pathogen of plants. P. aeruginosa is the type species of the genus Pseudomonas (Migula).

P. aeruginosa strains produce two types of soluble pigments, the fluorescent pigment pyoverdin and the blue pigment pyocyanin. The latter is produced abundantly in media of low-iron content and functions in iron metabolism in the bacterium. Pyocyanin (from "pyocyaneus") refers to "blue pus", which is a characteristic of suppurative infections caused by Pseudomonas aeruginosa and is produced by many, but not all, strains of Pseudomonas aeruginosa.

Diagnosis Depending on the nature of infection, an appropriate specimen is collected and sent to a bacteriology laboratory for identification. As with most bacteriological specimens, a Gram stain is performed, which may show Gram-negative rods. P. aeruginosa produces colonies with a characteristic 'grape-like' odour on bacteriological media. In mixed cultures, it can be isolated as clear colonies on MacConkey agar (as it does not ferment lactose) which will test positive for oxidase. Confirmatory tests include production of the blue-green pigment pyocyanin on cetrimide agar and growth at 42°C. A TSI slant is often used to distinguish non-fermenting Pseudomonas species from enteric pathogens in faecal specimens.

Fig 1: Production of pyocyanin, water-soluble Fig 2: Gram negative bacilli P.aeruginosa Blue pigment of P. aeruginosa

Biofilms and treatment resistance

Biofilm production is an important mechanism for the survival of Pseudomonas aeruginosa and its relationship with antimicrobial resistance represents a challenge for patient therapeutics. Biofilms of P. aeruginosa can cause chronic opportunistic infections, which are a serious problem for medical care in industrialized societies, especially for immunocompromised patients and the elderly. They often cannot be treated effectively with traditional antibiotic therapy. Biofilms seem to protect these bacteria from adverse environmental factors. P. aeruginosa can cause nosocomial infections and is considered a model organism for the study of antibiotic-resistant bacteria. Researchers consider it important to learn more about the molecular mechanisms that cause the switch from planktonic growth to a biofilm phenotype and about the role of inter-bacterial communication in treatment-resistant bacteria such as P. aeruginosa. This should contribute to better clinical management of chronically infected patients, and should lead to the development of new drugs.

Treatment Many P. aeruginosa isolates are resistant to a large range of antibiotics and may demonstrate additional resistance after unsuccessful treatment. It should usually be possible to guide treatment according to laboratory sensitivities, rather than choosing an antibiotic empirically. If antibiotics are started empirically, then every effort should be made to obtain cultures (before administering first dose of antibiotic), and the choice of antibiotic used should be reviewed when the culture results are available. Antibiotics that may have activity against P. aeruginosa include:  aminoglycosides (gentamicin, amikacin, tobramycin, but not kanamycin)

 Quinolones (ciprofloxacin, levofloxacin, but not moxifloxacin)

 Cephalosporins (ceftazidime, cefepime, cefoperazone, cefpirome, ceftobiprole, but not cefuroxime, cefotaxime, or ceftriaxone)

 Antipseudomonal penicillins: carboxypenicillins (carbenicillin and ticarcillin), and ureidopenicillins (mezlocillin, azlocillin, and piperacillin). P. aeruginosa is intrinsically resistant to all other penicillins.

 Carbapenems (meropenem, imipenem, doripenem, but not ertapenem)

[54]  Polymyxins (polymyxin B and colistin)

 Monobactams (aztreonam)

Phage therapy against P. aeruginosa remains one of the most effective treatments, which can be combined with antibiotics, has no contraindications and minimal adverse effects. Phages are produced as sterile liquid, suitable for intake, applications etc.

Prevention Probiotic prophylaxis may prevent colonization and delay onset of pseudomonas infection in an ICU setting. Immunoprophylaxis against pseudomonas is being investigated.

References 1. http://en.wikipedia.org/wiki/Pseudomonas_aeruginosa 2. http://textbookofbacteriology.net/pseudomonas.htmlnosa

Questions 1. How would you identify a patient with P. aeruginosa infection in your lab? 2. Discuss the pathogenesis of P. aeruginosa? 3. Discuss the treatment of P. aeruginosa

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