Pseudomonas aeruginosa (Blue pus bacillus)

2021-08-19 06:34 PM

Blue pus bacillus is the main causative agent of nosocomial and opportunistic infections

Blue pus bacilli and Burkholderia pseudomallei belong to the family Pseudomonadaceae, which includes Gram-negative, aerobic, motile bacilli with one or more hairs at one end (except Burkholderia mallei which are not motile), which metabolize energy by morphogenesis. oxidized carbohydrates do not ferment sugars. There are oxidase enzymes and catalase enzymes. They are widely distributed in nature, with only a few species capable of causing disease in humans, animals, or plants.

Pseudomonas aeruginosa is commonly found in soil, water or on humans and animals. Blue pus bacillus is a major causative agent of nosocomial and opportunistic infections.

Biological characteristics

Shape

Gram-negative bacilli, usually small and slender, 1.5 - 3 m, usually in pairs and short chains, very motile, hairy at one end, rarely shelling and non-spore-forming.

Viral Culture

Aerobic bacteria grow easily on common culture media such as nutrient agar, blood agar, broth. Suitable temperature 30 - 37 0 C, but can grow at 410C. Suitable pH is 7.2 - 7.5. Colonies are usually large, clear, with even or irregular margins, may have a metallic luster, pale gray in color on a bluish, aromatic medium. Rough or mucilaginous colonies may also be encountered.

The characteristic properties of green pus bacilli are pigment and aromatic production. On a culture medium containing peptones, bacteria can secrete the following pigments:

Pyocyanin: is a type of phenazine pigment with blue color, soluble in water and chlorofoc, diffuses into the culture medium, making the medium and colonies green. This pigment is produced favorably in environments exposed to a lot of air. Only blue pus bacilli produce the pigment pyocyanin.

Pyoverdin: is a fluorescent pigment, emitting blue when irradiated with ultraviolet light with a wavelength of 400 nm, soluble in water but insoluble in chloroform. In addition to the blue pus bacillus, there are some other species of Pseudomonas that form this pigment.

Pyorubrin: pale pink pigment, only 1% of blue pus bacillus strains produce this pigment.

Pyomelanin: brown-black pigment, only 1-2% of blue pus bacillus strains produce this pigment.

About 5-10% of strains of blue pus bacilli do not produce pigment.

Biochemical properties

Blue pus bacillus is oxidase-positive, liquefying gelatin, reducing NO3 to N2. Using carbohydrates by oxidizing acids such as glucose, mannitol, glycerol, arabinose... Lactose negative, Citrate simmon positive, ADH positive; Urea negative, indole negative, H2S negative.

Antigen

Bacteria have heat-labile H hair antigens and heat-resistant O antigens. Based on the O antigen, up to now, people have divided green pus bacilli into 16 serotypes. Phage typing is also possible, but bacteriocins (pyocin) are usually identified in outbreaks.

Like enteric bacilli, the O-antigen of blue pus bacillus carries endotoxins of the glucose-lipid-protein nature. But in the pathogenesis more important is the exotoxin. Of the three bacterial exotoxins, exotoxin An is the major virulence factor, it is heat-labile, kills mice and rats, and interferes with protein synthesis similarly to diphtheria toxin.

Possibility to cause disease

Blue pus bacillus is a conditionally pathogenic bacterium. Therefore, infection with Pseudomonas aeruginosa is rare in the general population, except for secondary infections such as chronic otitis externa. Infection often occurs in people whose defense mechanisms are compromised such as long-term use of corticosteroids or antibiotics, severe burns, or intravenous drug injection... Common sites of infection are the urinary tract and open wounds. (especially burns). At the site of entry, they cause purulent inflammation (pus is green), in the body with reduced resistance, they can penetrate deeper into the body and cause inflammation of the internal organs such as pus-filled infections and pressures. vehicles in different parts of the human body. Cases of endocarditis, pneumonia and meningitis are rare but also occur or cause systemic disease (eg, sepsis, Infections in newborns or premature babies are often very serious). Sepsis, often fatal, occurs in debilitated individuals.

In recent years, bacilli infections have become important because treatment and prevention of other infections with antibiotics to which they are resistant, the use of corticosteroids, anti-metabolites, and immunosuppressive drugs have become increasingly important. decrease the body's resistance, use of examination instruments such as catheters and other instruments for probing have not been well disinfected, use more and more widely used blood and blood products cannot be disinfected while these substances can be contaminated with Pseudomonas. Blue pus bacillus is a notable nosocomial infection: postoperative infection and severe burns. Infection of the blue pus bacillus in such cases can be fatal. The mortality rate from sepsis can exceed 80%.

Pathophysiology

Some authors have demonstrated that blue pus bacilli cause disease due to:

A toxin is made up of a toxic mixture of: hemoglobin, protease, and lexitinase.

The mucus antigen around bacteria consists of a DNA attached to the gluxit-lipid - the protein of the bacteria's O (endotoxin) antigen. Antigens play an important role in bacterial virulence (comparable to the role of endotoxins).

Diagnose

Specimens are pus from infected wounds, bronchial fluid, urine, pleural fluid... In epidemiological diagnosis: transfusion fluid, wound washing fluid, surgical instruments... are samples. experience.

Specimens are inoculated on conventional media such as nutrient agar or inhibitor media such as Cetrimide medium. Incubate at 37 0C in a normal atmosphere.

Select colonies that are flat, large, irregular margins, metallic luster, soluble pigments that stain the colonies green, and the surrounding environment of the colonies green. Identification of bacteria is based on Gram-negative, non-spore-forming, oxidase-positive bacilli, which metabolize sugars in an oxidative fashion, especially colonies with aroma and pigment-producing cultures that stain the surrounding environment. For non-pigmenting strains, it is necessary to inoculate pigment-enhancing media such as King A (proliferative pyocyanin) and King B (proliferative pyoverdins). Various techniques can be used to identify the source of the blue pus bacilli strains in nosocomial infections.

Prevention and treatment

Infections caused by Pseudomonas aeruginosa are difficult to treat because they are resistant to many antibiotics. Common strains show that bacteria are usually resistant to 3 or more antibiotics. During treatment, you must make an antibiotic chart. Currently commonly used tobramycin, amikacin, carbenicillin, cefoperazone, ceftazidime. Recently, active and passive immunotherapy has been used in burn patients with good results. Local infections can be washed with 1% acetic acid or with Colistin or Polymyxin B ointment.