Pseudomonas aeruginosa infection

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Etiology/Bacteriology

Taxonomy

| Domain = Bacteria | Phylum = Proteobacteria | Class = Gamma Proteobacteria | Order = Pseudomonadales | Family = Pseudomonadaceae | Genus = Pseudomonas | species = Pseudomonas aeruginosa

NCBI: Taxonomy Genome: Genome

Description

Pseudomonas aeruginosa is an opportunistic pathogen commonly found in the environment mainly in soil and water, but is also regularly found on plants and sometimes on animals, including humans. It is a Gram-negative, rod-shaped bacterium that is motile by means of a single polar flagellum and known to be highly antibiotic resistant and able to grow in a variety of generally inhospitable environments, often through its ability to form resilient biofilms[textbook of bacteriology]. The bacteria often produce the blue-green pigment pyocyanin, a redox-active phenazine, which is known to kill mammalian and bacterial cells through the generation of reactive oxygen intermediates [Hassett]. Pseudomonas infections often have a characteristic sweet odor and have become a substantial cause of infection in patients with immunodeficiencies. It is one of the main agents of hospital-acquired infections such as pneumonia, urinary tract infections (UTIs), and bacteremia [medscape].

Pathogenesis

P. aeruginosa is an opportunistic pathogen that rarely causes disease in healthy individuals. Most infections are able to take hold by the loss of the integrity of a physical barrier to infection (eg, skin, mucous membrane) or the presence of immune deficiency. This bacterium has also minimal nutritional requirements and can tolerate a wide variety of physical conditions like temperatures up to 41 degrees Celsius.

Transmission

Pseudomonas aeruginosa is a common inhabitant of soil, water, vegetation, and animals. It is found on the skin of some healthy persons and has been isolated from the throat (5 percent) and stool (3 percent) of nonhospitalized patients [medscape]. In some studies, gastrointestinal carriage rates increased in hospitalized patients to 20 percent within 72 hours of admission.

P. aeruginosa finds numerous reservoirs in a hospital setting such as disinfectants, respiratory equipment, food, sinks, taps, toilets, showers and mops. Because of its ubiquity, it is constantly reintroduced into the hospital environment on food, visitors, and patients transferred from other facilities. Transmission occurs from patient to patient on the hands of healthcare workers, by patient contact with contaminated reservoirs, and by the ingestion of contaminated materials.[textbook of bacteriology]

Infectious dose, incubation, and colonization

The infectious dose of P. aeruginosa is unknown, as it is an opportunistic pathogen that can colonize healthy hosts without disease. Likewise, the incubation period is disputed, as the infection can manifest in many ways depending upon the sight of infection. The pathogenesis of Pseudomonas is multifactorial and complex because Pseudomonas species are both invasive and toxigenic. The 3 stages are (1) bacterial attachment and colonization, (2) local infection, and (3) bloodstream dissemination and systemic disease [Pollack]. The importance of colonization and adherence is most evident when studied in the context of respiratory tract infection in patients that need complicate mechanical ventilation, such as those with cystic fibrosis. [medscape]

Epidemiology

Frequency

The Centers for Disease Control and Prevention (CDC) has estimated the overall prevalence of P. aeruginosa infections in US hospitals at approximately 4 per 1000 discharged patients (0.4%). P. aeruginosa accounts for 10.1% of all hospital-acquired infections and is also the fourth most commonly isolated nosocomial pathogen. [medscape]

Morbidity and Mortality

All P. aeruginosa infections are treatable and potentially curable, but fulminant infections, such as bacteremic pneumonia, sepsis, burn wound infections, and meningitis, generally have extremely high mortality rates. [medscape] These infections are a serious problem in patients with cancer, cystic fibrosis, and severe burns. The fatality rate in these patients is near 50 percent. [textbook of bacteriology]

Virulence Factors

Clinical features

Respiratory Tract

Nosocomially-acquired pneumonia often develops in patients with immunosuppression and chronic lung disease in the intensive care unit (ICU) setting, which can be primary, following aspiration of the organism from the upper respiratory tract, especially in patients on mechanical ventilation, and has a particularly high mortality rate [medscape, nature thing]. It may also occur as a result of a bacteremic infection spread to the lungs. This is observed commonly in patients following chemotherapy-induced neutropenia. P. aeruginosa is also commonly isolated from the respiratory tracts of cystic fibrosis patients and is often a cause of severe decline in these patients. Chronic lung colonization and infection also occur in patients with diseases affecting the airways of the lungs such as bronchiectasis and chronic obstructive pulmonary disease [nature thing].

Central Nervous System

A P. aeruginosa infection in the CNS can cause meningitis and brain abscess, most often following an extension from a contiguous parameningeal structure, such as an ear, a mastoid, paranasal sinus surgery, or diagnostic procedures [medscape]. In some patients, a CNS infection is due to hematogenous spread of the organism from infective endocarditis, pneumonia, or UTI. Patients with a CNS infection present with fever, headache, and confusion. The onset of disease may be fulminant or somewhat less severe, a characteristic that usually depends on the immune status of the patient.

Ear

P. aeruginosa can also cause swimmer’s ear, and patients present with pain, which is worsened by friction on the ear, itching, and ear discharge. It is also is a common cause of chronic otitis media (middle ear infection). Malignant otitis externa (severe outer ear infection) is an invasive infection observed mostly in patients with uncontrolled diabetes. It begins as a normal outer ear infection, but after failing to respond to antibiotic treatment, the infection worsens. Symptoms usually include persistent pain, swelling, and tenderness of the soft tissues of the ear, with discharge, and some patients present with a facial nerve palsy. Extension of the infection can result in osteomyelitis and cranial nerve palsies, which can possibly lead to a CNS infection.

Eye

The most common Pseudomonas infection in nonimmunocompromised patients is in the eye. By producing extracellular enzymes that create a rapidly destructive lesion, it can cause bacterial keratitis (infection of the cornea), scleral abscess, and endophthalmitis (infection of the intraocular cavity) in adults and ophthalmia neonatorum in children [medscape, nature thing]. Because the cornea, aqueous humor, and vitreous humor are a relatively immunocompromised environment, predisposing conditions such as trauma, contact lens use, preexisting ocular conditions, exposure to an ICU environment, and AIDS. Symptoms of an infection are pain, redness, swelling and impaired vision. Physical examination reveals swelling of the eyelid, redness and swelling of the conjunctiva, and a mucousal discharge.

Bones and Joints

Infections of the skeletal system most often involve the vertebral column, the pelvis, and the sternoclavicular joint. These infections are most often from either a blood-borne infection, which might stem from intravenous drug use, pelvic infections, or UTI, or contiguous from an open wound due to trauma, surgery, or a soft tissue infection. Those most at risk for these infections are those with puncture wounds to the foot, peripheral vascular disease, intravenous drug abuse, or diabetes. Skeletal infections manifest differently depending upon the location of the infection. Vertebral infections may involve the cervical spine, in which patients most often present with neck or back pain that can last from weeks to months and decreased range of motion. Patients with pyoarthrosis, or septic arthritis present with swelling and pain of the affected joint and a persistent fever. If a patient presents with neurological symptoms, spinal cord involvement is likely.

Diagnosis

Treatment

Prevention

Preventing transmission through medical equipment like catheters is an important way to prevent Pseudomonas infections. Aseptic techniques and sterile environments are important to prevent the spread of P. aeruginosa. Proper hygiene regarding medical devices like catheters is important to prevent opportunistic infection in a patient as well. Prophylactic use of antibiotics is not recommended to prevent the evolution of antibiotic-resistant strains of bacteria. Severe burn victims should be put into strict isolation to prevent unnecessary contact with potential pathogens. Care should be taken to seek help when there might be potential infection, such as with corneal scratches due to contact lenses.

Host Immune Response

References

Created by Lillian Flannigan, student of Tyrrell Conway at the University of Oklahoma.