Genus Rhodococcus Lecture Notes PDF

Genus Rhodococcus V. MICRO 152 Precy D. Magtoto, DVM  Cellular characteristics Gram positive, pleomorphic (ranging from coccoid to bacillary forms) On solid media the form is usually coccoid; in fluids usually bacillary. Large non-motile Variably acid-fast...

Genus Rhodococcus V. MICRO 152 Precy D. Magtoto, DVM  Cellular characteristics Gram positive, pleomorphic (ranging from coccoid to bacillary forms) On solid media the form is usually coccoid; in fluids usually bacillary. Large non-motile Variably acid-fast & stains readily with other dyes. Non-sporeforming A lamellar capsule is usually present.  Cultural characteristics Aerobic, grows well on non-enriched/ordinary media Colonies: small, shiny, round, smooth, mucoid, raised, moist, translucent, and regular in outline non-hemolytic, larger mucoid and salmon pink in color with age Metachromatic granules can usually be demonstrated in cultures grown in milk  Biochemical characteristics Catalase positive usually oxidase (cytochrome) negative do not ferment carbohydrates reduces nitrates indole-negative Rhodococcus equi, blood agar  Rhodococcus equi, positive. CAMP-Phenomenon with Staph. aureus (SDA) Rhodococcus equi.Resembles Nocardia species. It is gram+ filamentous fragments into rods and cocci forms, may branch and are partially acid fast by MK Rhodococcus equi in sheep blood agar  Usual habitat Soil Intestinal tracts of animals Rhodococcus Main Disease(s) Natural equi host(s) habitat Foals (1-4 suppurative Soil and mos.old) bronchopneumonia feces of and pulmonary foals and abscessation other herbivores Horses Superficial As above abscessation Pigs (cattle) Mild cervical soil lymphadenopathy Cats Subcutaneous abscesses, mediastinal granulomas Suppurative bronchopneumonia of foals Major disease caused by R.equi (pyogenic organism) Affected foals (1-4 months of age) charac.by bronchopneumonia and lung abscessation Acquired by inhalation of dust contaminated with R.equi Granulomatous ulcerative enterocolitis and mesenteric lymphadenitis – when large #s of R. equi were swallowed from sputum Pathogenicity and Pathogenesis Foals under 4 mos. of age are the most susceptible – attributed to impaired cellular immunity of the lungs An intracellular pathogen – associated with specific surface antigens encoded in the DNA of a large plasmid surface antigens – temp.dependent and expressed at 34-41oC Capsular polysaccharides and mycolic acids in the cell wall – retards phagocytosis and various exoenzymes  Clinical signs Acute disease seen in one month-old foals Sudden onset of fever, anorexia, and signs of bronchopneumonia Disease is insidious in 2-4month old foals and lesions can be well advanced b4 it exhibits coughing, dyspnea, weight loss, exercise intolerance Charac.loud, moist rales – auscultation Occasionally , diarrhea  Disease Process § Bronchopneumonia with local abscessation § Formation and distribution of abscessation § Non pulmonary disorders Radiographic appearance of the chest of a normal foal. Radiographic appearance of the chest of a foal affected with Rhodococcus equi. Note the appearance of multiple abscesses within the lungs. Postmortem appearance of a foal that died as a consequence of Rhodococcus equi pneumonia. Note the presence of multiple coalescing large abscesses within the body of the lung. Appearance of lungs of a foal affected with Rhodococcus equi pneumonia. Notice that much of the lung has been affected by consumptive coalescing abscessation.  Appearance of the lungs of a foal that died as a consequence of Rhodococcus equi pneumonia Note the presence of multiple abscesses in several lung lobes.  Diagnosis Hx of the disease on the farm, age of the affected foal and clinical signs Auscultation and radiography of thorax Specimens for lab.exam include tracheal aspirates and pus from lesions BAP and MCA inoculated with suspect material incubated aerobically at 37OC for 1-2days  ID criteria isolates: - Colonies on blood agar – non-hemolytic, salmon-pink and mucoid - Absence of growth on MCA - CAMP test positive - Unreactive in the OF test and in sugar fermentation tests - Biochemical profile using commercially available kits Quantitative fecal culture on a selective medium demonstrating over 106 of R. equi of feces  Treatment and control Oral rifampin and erythromycin for 4 to 10 weeks Supportive tx – rehydration and the use of bronchodilatory agents or expectorants No vaccine available Foals shld. be kept under observation Foal manure should be removed from pastures at frequent intervals Foals and dams move regularly to fresh pasture Administer hyperimmune serum to foal at 1st month of life