Gram Negative Rods Related to the Respiratory Tract Subscribe
Date: 05. December 2017
In this lecture the educator explains about the Gram-Negative Rods Related to the Respiratory Tract. The educator has divided the lecture in 5 sections. In first section she explains about the Important Properties, Diseases, Pathogenesis, Clinical Findings, Laboratory Diagnosis, Treatment & Prevention.
The educator explains that influenzae used to be the leading cause of meningitis in young children, but the use of the highly effective “conjugate” vaccine has greatly reduced the incidence of meningitis caused by this organism. It is still an important cause of upper respiratory tract infections (otitis media, sinusitis, conjunctivitis, and epiglottitis) and sepsis in children. It also causes pneumonia in adults, particularly in those with chronic obstructive lung disease.
Influenzae infects only humans, there is no animal reservoir. It enters the body by the inhalation of airborne droplets into the respiratory tract, resulting in either asymptomatic colonization or infections such as otitis media, sinusitis, or pneumonia. The organism produces an IgA protease that degrades secretory IgA, thus facilitating attachment to the respiratory mucosa. After becoming established in the upper respiratory tract, the organism can enter the bloodstream (bacteremia) and spread to the meninges´.
Laboratory diagnosis depends on isolation of the organism on heated-blood (“chocolate”) agar enriched with two growth factors required for bacterial respiration, namely, factor X (a heme compound) and factor V (NAD). The blood used in chocolate agar is heated to inactivate nonspecific inhibitors of H. influenzae growth.
Bordetella – I
The educator explains Important Properties, Pathogenesis and Clinical Findings in section two. Pertussis is a small, coccobacillary, encapsulated gram-negative rod. Pertussis, a pathogen only for humans, is transmitted by airborne droplets produced during the severe coughing episodes. The organisms attach to the ciliated epithelium of the upper respiratory tract but do not invade the underlying tissue. Decreased cilia activity and subsequent death of the ciliated epithelial cells are important aspects of pathogenesis.
Whooping cough is an acute tracheobronchitis that begins with mild upper respiratory tract symptoms followed by a severe paroxysmal cough, which lasts from 1 to 4 weeks. The paroxysmal pattern is characterized by a series of hacking coughs, accompanied by production of copious amounts of mucus, that end with an inspiratory “whoop” as air rushes past the narrowed glottis. Despite the severity of the symptoms, the organism is restricted to the respiratory tract and blood cultures are negative. A pronounced leukocytosis with up to 70% lymphocytes is seen. Although central nervous system anoxia and exhaustion can occur because of the severe coughing, death is due mainly to pneumonia.
Bordetella – II
In section three the educator briefs about Laboratory Diagnosis, Treatment and Prevention. The organism can be isolated from nasopharyngeal swabs taken during the 386-paroxysmal stage. Bordet-Gengou1 medium used for this purpose contains a high percentage of blood (20%–30%) to inactivate inhibitors in the agar. Azithromycin is the drug of choice. Note that azithromycin reduces the number of organisms in the throat and decreases the risk of secondary complications but has little effect on the course of the disease at the “prolonged cough” stage because the toxins have already damaged the respiratory mucosa. Supportive care (e.g., oxygen therapy and suction of mucus) during the paroxysmal stage is important, especially in infants.
There are two types of vaccines: an acellular vaccine containing purified proteins from the organism and a killed vaccine containing inactivated B. The acellular vaccine contains five antigens purified from the organism. It is the vaccine currently used in the United States.
Legionella – I
Legionellae are gram-negative rods that stain faintly with the standard Gram stain. They do, however, have a gram-negative type of cell wall, and increasing the time of the safranin counterstain enhances visibility. Legionellae in lung biopsy sections do not stain by the standard hematoxylin-and-eosin (H&E) procedure; therefore, special methods, such as the Dieterle silver impregnation stain, are used to visualize the organisms.
Legionellae are associated chiefly with environmental water sources such as air conditioners and water-cooling towers. Outbreaks of pneumonia in hospitals have been attributed to the presence of the organism in water taps, sinks, and showers.
The clinical picture can vary from a mild influenza-like illness to a severe pneumonia accompanied by mental confusion, nonblood diarrhea, proteinuria, and microscopic hematuria. Although cough is a prominent symptom, sputum is frequently scanty and nonpurulent.
Legionella – II
Sputum Gram stains reveal many neutrophils but no bacteria. The organism fails to grow on ordinary media in a culture of sputum or blood, but it will grow on charcoal-yeast agar, a special medium supplemented with iron and cysteine. Azithromycin or erythromycin (with or without rifampin) is the treatment of choice.
Certain fluoroquinolones, such as levofloxacin and trovafloxacin, are also drugs of choice. Prevention involves reducing cigarette and alcohol consumption, eliminating aerosols from water sources, and reducing the incidence of Legionella in hospital water supplies by using high temperatures and hyperchlorination. There is no vaccine.