Isolation Pseudomonas/entre
CAUTION: Handle with care with EACH UNKNOWN BACTERIA AS A PATHOGEN.
Pseudomonas aeruginosa and most other nonfermentative, gram-negative bacilli are oxidase-positive; all of the Enterobacteriaceae are oxidase-negative.
Pseudomonas aeruginosa produces a characteristic fruity or grape juice-like aroma due to production of an aromatic compound called aminoacetophenone.
ISOLATION AND IDENTIFICATION OF ENTEROBACTERIACEAE AND PSEUDOMONAS AERUGINOSA
A. ENTEROBACTERIACEAE: THE FERMENTATIVE, GRAM-NEGATIVE, ENTERIC BACILLI
Bacteria belonging to the family Enterobacteriaceae are the most commonly encountered organisms isolated from clinical specimens. The Enterobacteriaceae is a large diverse family of bacteria commonly referred to as the fermentative, gram-negative, enteric bacilli, indicating that they are gram-negative rods which can ferment sugars. Many are normal flora of the intestinal tract of humans and animals. Some infect the intestinal tract. Members of this family have the following five characteristics in common:
1. They are gram-negative rods
2. If motile, they possess a peritrichous arrangement of flagella
3. They are facultative anaerobes
4. They are oxidase negative
5. All species ferment the sugar glucose but otherwise vary widely in their biochemical characteristics.
Twenty-six genera and over 100 species of Enterobacteriaceae have been recognized. Some of the more common clinically important Aviculture/Avian genera of the family Enterobacteriaceae include:
Salmonella_ Enterobacter _ Escherichia_ Klebsiella
Several genera of Enterobacteriaceae are associated with gastroenteritis and food-borne disease. These include Salmonella, , certain strains of Escherichia coli. All intestinal tract infections are transmitted by the fecal-oral route.
Any infection caused by Salmonella is called a salmonellosis. The majority of Salmonella cause diarrhea.
Enterotoxigenc E. coli (ETEC) produce enterotoxins that cause the loss of sodium ions and water from the intestines resulting in a watery diarrhea.
These normal flora gram-negative bacilli, along with gram-positive bacteria such as Staphylococcus aureus (see Lab 15) and Enterococcus faecalis (see Lab 14), are among the most common causes of nosocomial infections. The four most common gram-negative bacteria causing nosocomial infections are Escherichia coli, Pseudomonas aeruginosa (discussed below), Enterobacter species, and Klebsiella pneumoniae.
In the outer membrane of the gram-negative cell wall (see Lab 6), the lipid A moiety of the lipopolysaccharide functions as an endotoxin. (see <This link's target cannot be found>) Endotoxin, especially when in the blood, can lead to inflammation, high fever, hypotension, capillary damage, intravascular coagulation, tissue degradation, and irreversible shock. Death is a result of what is called the shock cascade. As a result of the massive inflammatory response from an excessive endotoxin-induced production of such cytokines as TNF-alpha, Il-1, Il-6, and Il-8, the following sequence of events may occur:
 Blood vessels dilate and phagocytic WBCs called neutrophils adhere to capillary walls in massive amounts . Endotoxin and chemokines causes the neutrophils to release proteases and toxic oxygen radicals (the same chemicals they use to kill microbes) which now damage the capillary walls.
 Damage to the capillaries causes blood to leave the bloodstream and enter the tissue. Prolonged vasodilation and increased capillary permeability causes plasma to leave the bloodstream and enter the tissue. Vasodilation also leads to decreased vascular resistance. Activation of the blood clotting pathway causes clots to form within the blood vessels.
 The combination of blood and plasma leakage, decreased vascular resistance, and clot formation leads to hypotension and decreased volume of circulating blood.
 This, in turn, leads to acidosis and decreased cardiac output which can result in irreversible shock, organ failure, and death.
|