Pseudomonas aeruginosa is a bacterium in the order Pseudomonadales. The pathogen can be pathogenic to humans. It is primarily known as a nosocomial germ.
What is Pseudomonas aeruginosa?
Pseudomonas aeruginosa is a rod-shaped bacterium of the genus Pseudomonas. The pathogen was discovered in 1900 by the German botanist Walter Emil Friedrich August Migula. Pseudomonas aeruginosa owes its name to the blue-greenish pus coloration that occurs during infections with the pathogen. Despite its fairly early discovery in 1900, the genome of the bacterium was not fully sequenced until 2000. It has a size of 6.3 Mbp and consists of more than 5500 genes. Pseudomonas aeruginosa is a Gram-negative bacterium. Gram-negative bacteria can be stained red in the Gram stain. In contrast to Gram-positive bacteria, they not only have a thin peptidoglycan layer of murein, but also an outer cell membrane. This difference plays a role in treatment. Gram-positive pathogens are treated with different antibiotics than Gram-negative pathogens. Pseudomonas aeruginosa is an obligate aerobic bacterium. It is therefore dependent on oxygen. In terms of external living conditions, Pseudomonas aeruginosa is extremely undemanding. The bacterium can survive for long periods under both humid and dry conditions. Typically, however, Pseudomonas aeruginosa prefers moist environments.
Occurrence, distribution, and characteristics
Pseudomonas aeruginosa is one of the nosocomial germs. Nosocomial infections are infections that occur during hospitalization or outpatient treatment. In nature, the bacterium is widespread. It lives in soil or water and prefers moist environments. Thus, the germ is found on moist soils, in surface waters, in tap water, showers, toilets, dishwashers or sinks. Medicines, dialysis equipment or even disinfectants can also be contaminated with Pseudomonas aeruginosa. The germ can even survive in distilled water. The prerequisite, however, is that small amounts of organic substances are present in the corresponding substance. In hospitals, Pseudomonas aeruginosa is also found on ventilation tubes, in humidifiers and incubators or in soap containers. Flower vases are also frequently contaminated. Infection with the pathogen occurs through direct contact. Infection is favored by a weakened immune system. Patients with skin or mucosal defects are at increased risk for infection. Pseudomonas aeruginosa is highly pathogenic. This considerable pathogenicity can be attributed to several virulence factors.
Diseases and symptoms
The bacteria attach to their target cells by means of so-called fimbriae. Fimbriae are filamentous adhesins that allow bacteria to attach to epithelial cells. At the target cell, the bacteria release exotoxins and enzymes such as alkaline protease or elastase. In interaction with various hemolysins that are also released, the cells and tissues are damaged by the bacteria. Since Pseudomonas aeruginosa have bacterial lipopolysaccharides on their surface, no opsonization can occur by the immune system. The bacteria are thus not recognized by the phagocytes and are accordingly attacked by the immune system only at a late stage. Pseudomonas aeruginosa is one of the most common pathogens of hospital infections. About 10 percent of all nosocomial infections are caused by Pseudomonas aeruginosa. Pseudomonas aeruginosa can cause pneumonia, especially in patients with cystic fibrosis or in patients in intensive care. Pneumonia is the inflammation of lung tissue. The inflammation causes an inflammatory fluid (exudate) to accumulate in the alveoli. This leads to a restriction of lung function and thus to shortness of breath. The patient’s respiratory rate increases. In addition, fever and cough occur. In patients with a permanent urinary catheter or in patients who have had urological surgery, a urinary tract infection often develops. Typical symptoms include pain and burning when urinating, frequent urination with small amounts of urine, or urgency to urinate without a void. In the case of upper urinary tract infections, for example renal pelvic inflammation, fever and pain in the kidney bed may also occur.In skin defects, Pseudomonas aeruginosa can cause skin infections. Burn victims are frequently affected here. Typical of skin infections with Pseudomonas aeruginosa is the green-blue pus. Other symptoms of a skin infection caused by Pseudomonas aeruginosa include rash and blistering. Newborns can also become infected with Pseudomonas aeruginosa in the hospital. Their immune system is not yet fully developed, so infections can take a drastic course. For example, neonatal sepsis can develop, especially in premature infants or in newborns with a low birth weight. This is a blood poisoning accompanied by shortness of breath, blue discoloration of the skin, bleeding into the skin, convulsions and drowsiness. In the worst case, septic shock can develop. This is usually fatal for the newborn. Other neonatal manifestations include meningitis (meningitis) and pneumonia (pneumonia). A typical site of manifestation of Pseudomonas aeruginosa is also the outer ear. Here, the pathogen causes otitis externa. This is also referred to as “swimmer’s ear”. In otitis externa, the skin and subcutaneous tissue in the area of the external auditory canal are inflamed. Middle ear infection (otitis media) can also be caused by Pseudomonas aeruginosa. In the absence of treatment or the wrong treatment, any infection with Pseudomonas aeruginosa is likely to cause sepsis. Treatment is usually with antibiotics. Since Pseudomonas aeruginosa can form so-called ß-lactamases, most cephalosporins and penicillins are ineffective. The pathogen has developed antibiotic resistance here. Instead, ceftazidime, piperacillin, and quinolones, among others, are used.
