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This Sqadia video is the elucidation of Gram-Negative Rods Outside the Enteric Tract. These organisms are usually opportunistic pathogens that cause nosocomial infections, especially pneumonia and urinary tract infections. K. pneumoniae, Enterobacter cloacae, and Serratia marcescens are the species most often involved in human infections. They are frequently found in the large intestine but are also present in soil and water. These organisms have very similar properties and are usually distinguished on the basis of several biochemical reactions and motility. Of the three organisms, K. pneumoniae is most likely to be a primary, non-opportunistic pathogen; this property is related to its antiphagocytic capsule. Outbreaks of Serratia pneumonia have been associated with contamination of the water in respiratory therapy devices. Urinary tract infections and pneumonia are the usual clinical entities associated with these three bacteria, but bacteremia and secondary spread to other areas such as the meninges and liver occur. It is difficult to distinguish infections caused by these organisms on clinical grounds, with the exception of pneumonia caused by Klebsiella. Klebsiella produces a thick, bloody sputum and can progress to necrosis and abscess formation. Organisms of this group produce lactose-fermenting colonies on differential agar such as MacConkey’s or EMB. Although Serratia can produce a negative reaction. Because the antibiotic resistance of these organisms can vary greatly, the choice of drug depends on the results of sensitivity testing. Some hospital-acquired infections can be prevented by removing urinary catheters when they are no longer needed and taking proper care of respiratory therapy devices.
These organisms primarily cause urinary tract infections, both community and hospital-acquired. These gram-negative rods are distinguished from other members of the Enterobacteriaceae by their ability to produce the enzyme phenylalanine deaminase. Certain species are very motile and produce a striking swarming effect on blood agar. The cell wall O antigens of certain strains of Proteus, such as OX-2, OX-19, and OX-K, cross-react with antigens of several species of rickettsiae and can be used to detect the presence of antibodies against certain rickettsiae in patient’s serum. The organisms are present in the human colon as well as in soil and water. Production of the enzyme urease is an important feature of the pathogenesis of urinary tract infections by this group. Urease hydrolyzes the urea in urine to form ammonia, which raises the pH, producing an alkaline urine. The signs and symptoms of urinary tract infections caused by these organisms cannot be distinguished from those caused by E. coli or other members of the Enterobacteriaceae. P. vulgaris and P. mirabilis produce H2S, which blackens the butt of TSI agar, whereas neither M. morganii nor P. rettgeri does. Most strains are sensitive to aminoglycosides and trimethoprim-sulfamethoxazole, but because individual isolates can vary, antibiotic sensitivity tests should be performed. P. rettgeri is frequently resistant to multiple antibiotics. There are no specific preventive measures, but many hospital-acquired urinary tract infections can be prevented by prompt removal of urinary catheters.
Pseudomonas - I
Pseudomonas aeruginosa causes infections primarily in patients with lowered host defenses. It is the most common cause of ventilator-associated pneumonia. P. aeruginosa is also known as Burkholderia aeruginosa. Pseudomonas cepacia and Pseudomonas maltophilia also cause these infections, but much less frequently. Pseudomonads are gram-negative rods and are strict aerobes. They have been found growing in hexachlorophene-containing soap solutions, in antiseptics, and in detergents. P. aeruginosa produces two pigments useful in clinical and laboratory diagnosis: Pyocyanin and Pyoverdin. In the laboratory, these pigments diffuse into the agar, imparting a blue-green color that is useful in identification. P. aeruginosa is the only species of Pseudomonas that synthesizes pyocyanin. P. aeruginosa is found chiefly in soil and water, although approximately 10% of people carry it in the normal flora of the colon. Pathogenesis is based on multiple virulence factors: Endotoxins, Exotoxins, and Enzymes. The best known of the exotoxins is exotoxin A, which causes tissue necrosis. Strains of P. aeruginosa that have a “type III secretion system” are significantly more virulent than those that do not. This secretion system transfers the exotoxin from the bacterium directly into the adjacent human cell.
Pseudomonas - II
P. aeruginosa can cause infections virtually anywhere in the body, but urinary tract infections, pneumonia, and wound infections predominate. From these sites, the organism can enter the blood, causing sepsis. The bacteria can spread to the skin, where they cause black, necrotic lesions called ecthyma gangrenosum. Severe external otitis and other skin lesions occur in users of swimming pools and hot tubs in which the chlorination is inadequate. P. aeruginosa is the most common cause of osteochondritis of the foot. A typical metallic sheen of the growth on TSI agar, coupled with the blue-green pigment on ordinary nutrient agar and a fruity aroma are sufficient to make a presumptive diagnosis. Identification for epidemiologic purposes is done by bacteriophage or pyocin typing. Because P. aeruginosa is resistant to many antibiotics, treatment must be tailored to the sensitivity of each isolate and monitored frequently. The treatment of choice is an antipseudomonal penicillin and an aminoglycoside. Prevention of P. aeruginosa infections involves Keeping neutrophil counts above 500/mL, removing indwelling catheters promptly, and taking other similar measures to limit infection.
Bacteroides and Prevotella
Members of the genus Bacteroides are the most common cause of serious anaerobic infections. Bacteroides fragilis is the most frequent pathogen. Prevotella melaninogenica is also an important pathogen. Bacteroides and Prevotella organisms are anaerobic, non–spore-forming, gram negative rods. Of the many species of Bacteroides, two are human pathogens i.e. B. Fragilis and Bacteroides Corrodens. Because Bacteroides and Prevotella species are part of the normal flora, infections are endogenous. Predisposing factors such as surgery, trauma, and chronic disease play an important role in pathogenesis. The B. fragilis group of organisms is most frequently associated with intraabdominal infections, either peritonitis or localized abscesses. Prevotella intermedia is an important cause of gingivitis, periodontitis, and dental abscess. Bacteroides species can be isolated anaerobically on blood agar plates containing kanamycin and vancomycin to inhibit unwanted organisms. Members of the B. fragilis group are resistant to penicillins, first-generation cephalosporins, and aminoglycosides, making them among the most antibiotic resistant of the anaerobic bacteria. Metronidazole is the drug of choice, with cefoxitin, clindamycin, and chloramphenicol as alternatives.