Morphology, Pathogenesis, Lab Diagnosis and Treatment of Pseudomonas aeruginosa

1. Dr. S. MEENATCHISUNDARAM
ASSOCIATE PROFESSOR
DEPARTMENT OF MICROBIOLOGY
SNMV COLLEGE OF ARTS AND SCIENCE
COIMBATORE
https://orcid.org/0000-0002-8691-449X
95496
https://scholar.google.com/citations?user=IkdZ5XsAAAAJ&hl=en
Pseudomonas aeruginosa

2. Pseudomonas aeruginosa
Gram negative
Motile
Aerobic
Nonfermentive
• Two forms
Planktonic
Biofilm
• Optimum growth
37˚C, can grow in 42 ˚C
Minimal nutritional requirements
• Three colony types
Rough
Smooth
Mucoid

3. Pseudomonas aeruginosa
Biofilm
Planktonic form

4. Cultural Characteristics
Small
rough
colonies
Large
smooth
colonies
Mucoid
colonies

5. Morphology
 It is a slender gram-negative bacillus, 1.5–3 μm × 0.5 μm,
actively motile usually with a single polar flagellum.
 Occasional strains have two or three flagella.
 It is nonsporing, noncapsulated but many strains have a
mucoid slime layer.

6. Cultural Characteristics
 It is a strict aerobe but can grow anaerobically if nitrate is available.
 Growth occurs at a wide range of temperatures, 6–42° C, the optimum being 37°C.
Optimum pH 7.4–7.6.
 It grows well on ordinary media and in the laboratory, it can be isolated on virtually
any medium.
 Nutrient agar: After aerobic incubation on nutrient agar at 37°C for 24 hours, the
colonies are large, 2–3 mm in diameter, smooth, translucent, irregularly round and emit
a characteristic fruity odor. This grape-like smell is due to the production of
aminoacetophenone from tryptophan.
 It grows on MacConkey and DCA media, forming nonlactose-fermenting colonies.
 Blood agar: Colonies on blood agar may be surrounded by a zone of hemolysis.
 In broth, it forms a dense turbidity with a surface pellicle.
 Cetrimide agar is selective medium for P. aeruginosa

7. Pigment Production
P. aeruginosa produces at least 4 distinct pigments:
 Pyocyanin:
It is a bluish-green phenazine pigment soluble in chloroform and water. This
pigment is not produced by other species of this genus. Demonstration of the
presence of the blue phenazine pigment pyocyanin is absolute confirmation of a
strain as P. aeruginosa.
 Pyoverdin (fluorescein):
The yellow/green pigment pyoverdin (fluorescein) is also produced by most strains,
giving the characteristic blue-green appearance of infected pus or cultures. It is
insoluble in chloroform but soluble in water.
 Pyorubrin: It is a bright red water soluble pigment and is insoluble in chloroform.
 Pyomelanin: It is a brown to black pigment and its production is uncommon.

8. Biochemical Reactions
 P. aeruginosa derives energy from carbohydrates by an oxidative rather than
a fermentative metabolism.
 Special media, such as the O–F medium of Hugh and Leifson must be used
for diagnostic tests.
 It utilizes glucose oxidatively with the production of acid only. Lactose and
maltose are not utilized. Indole, MR, VP and H2S tests are negative.
 However, all strains give a rapid positive oxidase reaction (within 30
seconds) and utilize citrate as sole source of carbon.
 It reduces nitrates to nitrites and further to gaseous nitrogen.
 It is catalase, arginine dihydrolase and gelatinase positive and lysine
decarboxylase andaesculin hydrolysis negative.

9. Resistance
 The bacillus is not particularly heat resistant, being killed at 55°C in one
hour but exhibits a high degree of resistance to chemical agents.
 It is resistant to the common antiseptics and disinfectants such as quaternary
ammonium compounds, chloroxylenol and hexachlorophene.
 It is sensitive to a 2% aqueous alkaline solution of glutaraldehyde (cidex),
acids, silver salts and strong phenolic disinfectants.
 P. aeruginosa possesses a considerable degree of natural resistance to
antibiotics.

10. Antigenic Characteristics
O antigens:
 P. aeruginosa possesses 19 distinct, group-specific 0 antigens.
 O antigens are heatstable.
H antigens:
 On the basis of slide agglutination, at least two heat-labile H antigens
have been recognized.

11. Virulence Factors
Most strains produce two exotoxins, exotoxin A and exoenzyme S, and a variety
of cytotoxic substances including proteases, phospholipases; rhamnolipids and
the blue-green pigment pyocyanin; an alginate-like exopolysaccharide.
1. Capsule: P. aeruginosa produces a polysaccharide capsule (also known as
mucoid exopolysaccharide, alginate coat, or glycocalyx) that has multiple
functions and is responsible for the mucoid phenotype.
2. Pili: Adherence of P. aeruginosa to host cells is mediated by pili and
nonpilus adhesins.
3. Lipopolysaccharide (LPS): It has endotoxin activity.
4. Pyocyanin: It mediates tissue damage through and also stimulates the
inflammatory response and impairs ciliary function.

12. Virulence Factors
5. Exotoxin A and Exotoxin S: Mechanism of action of exotoxin A is identical
to that of diphtheria toxin. Exotoxin S Inhibits protein synthesis and is
immunosuppressive.
6. Extracellular enzymes and hemolysins: P. aeruginosa produces proteases
(general protease, alkaline protease and elastase), hemolysins
(phospholipase C and heat-stable rhamnolipid) and lipase. These play a key
role in the formation of local lesions.
7. Antibiotic resistance: P. aeruginosa is inherently resistant to many antibiotics
and can mutate to even more resistant strains during therapy.

13. Diseases
 Endocarditis
 Respiratory infections
 Bacteremia and Septicemia
 Central Nervous System infections
 Ear infections including external otitis
 Eye infections
 Bone and joint infections
 Urinary tract infections
 Gastrointestinal infections
 Skin and soft tissue infections,
including wound infections, pyoderma
and dermatitis

14. Bacterial Endocarditis
• Pseudomonas aeruginosa
infects heart valves.
IV drug users
prosthetic heart valves.
(Implantation of prosthetic
cardiac valves – Valve
replacement)
• The organism establishes
itself on the endocardium by
direct invasion from the
blood stream.

15. Respiratory Infections
• Pneumonia
Bacteremic pneumonia commonly occurs in neutropenic cancer
patients undergoing chemotherapy.
• Lower respiratory tract colonization of cystic fibrosis patients

16. Cystic Fibrosis
• The most common lethal inherited disorder with an
incidence of approximately 1 in 2500 live births.
• Characteristics
• pancreatic insufficiency
• abnormal sweat electrolyte concentrations
• production of very viscid bronchial secretions
Cystic fibrosis is a disease passed down through families that causes thick, sticky
mucus to build up in the lungs, digestive tract and other areas of the body.

17. Bacteremia and Septicemia
Primarily in immunocompromised patients.
Predisposing conditions
hematologic malignancies,
immunodeficiency relating to AIDS
Neutropenia
diabetes mellitus
severe burns.

18. Bacteremia and Septicemia
Ecthyma gangrenosum:
Pseudomonas aeruginosa in neutropenic patients
Ecthyma gangrenosum is an infection of the skin typically caused by Pseudomonas aeruginosa. It
presents as a round or oval lesion, 1 cm to 15 cm in diameter

19. Central Nervous System Infections
• Pseudomonas aeruginosa
causes meningitis.
• Portal of Entry
• Inner ear or paranasal sinus
• Inoculated directly
• Surgery
• Invasive diagnostic procedures
• Spreads from a another site of
infection like the urinary tract

20. Ear infections
• External otitis
• "swimmer's ear"

21. Eye infections
It is one of the most
common causes of
bacterial keratitis, and
has been isolated as the
etiologic agent of
neonatal ophthalmia,
which occurs in 1-12% of
newborn infants.

22. Bone and Joint Infections
• Direct inoculation of the bacteria or the hematogenous spread
of the bacteria from other primary sites of infection.
• Blood-borne infections are most often seen in IV drug users, and in
conjunction with urinary tract or pelvic infections.
• Chronic contiguous osteomyelitis (Osteomyelitis is an acute or chronic
bone infection. Symptoms: Bone pain; Fever; General discomfort, uneasiness)
• The most common sites of involvement are the vertebral column, the
pelvis, and the sternoclavicular joint
• Osteochondritis - inflammation of bone and
cartilage
• puncture wounds of the foot

23. Urinary tract infections
• Usually hospital-acquired and related to urinary tract
catheterization, instrumentation or surgery.
•
• 3rd leading cause of hospital-acquired UTIs
• about 12 percent of all infections of this type.
• The bacterium is among the most adherent of common urinary
pathogens to the bladder uroepithelium.
• Pseudomonas can invade the bloodstream from the urinary
tract.
• source of nearly 40 percent of Pseudomonas bacteremias.

24. Gastrointestinal infections
It can produce disease in any part of the gastrointestinal tract.
Perirectal infections
Pediatric diarrhea
Gastroenteritis
Necrotizing enterocolitis.
The GI tract is also an important portal of entry in
Pseudomonas septicemia.

25. Skin and Soft tissue infections
• wound infections, pyoderma and dermatitis
• Pseudomonas aeruginosa can cause a variety of skin infections, both
localized and diffuse. It has also been implicated in folliculitis and
unmanageable forms of acne vulgaris.
• The common predisposing factors
• are breakdown of the integument
• Burns, trauma or dermatitis
• high moisture conditions
• ear of swimmers and the toe webs of athletes and combat troops, in the perineal region
and under diapers of infants, and on the skin of whirlpool and hot tub users
• AIDS

26. Reservoirs
• Ubiquitous to the soil, water, and
vegetation
• can be isolated from the skin,
throat, and stool of healthy
persons
• In a hospital, it can be found in:
• Disinfectants
• Respiratory
• Equipment
• Food
• Sinks
• Taps
• Mops

27. Transmission
• Patients usually become infected by contact spread, directly
or indirectly, from environmental sites.
Pseudomonas aeruginosa is a common inhabitant of soil, water, and vegetation.
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.

28. Laboratory Diagnosis
 Specimens: Pus, wound swab, urine, sputum, CSF or blood.
 Microscopy: Gram-negative rods are often seen in smears.
 Culture: They grow easily on common isolation media such as blood agar
and MacConkey agar. It may be necessary to use selective media, such as
cetrimide agar for isolation of P. aeruginosa from feces or other samples with
mixed flora, such as wound swab.
 Identification: The isolates are identified by their colonial morphology and
biochemical characters. The colonial morphology combined with the results
of selected rapid biochemical tests is sufficient for the preliminary
identification of these isolates.

29. Treatment
Pseudomonas aeruginosa is frequently resistant to many
commonly used antibiotics.
Although many strains are susceptible to gentamicin,
tobramycin, colistin, and amikacin, resistant forms have
developed.
The combination of gentamicin and carbenicillin is
frequently used to treat severe Pseudomonas infections.