Genus Rhodococcus V. MICRO 152

Genus Rhodococcus V. MICRO 152

• Rhodococcus is a genus of bacteria
• Gram-positive, pleomorphic bacteria (cocci to bacilli)
• Cocci on solid media; bacilli in fluids
• Large, non-motile
• Variably acid-fast, stains readily with dyes
• Non-spore-forming
• Lamellar capsule typically present

Cultural Characteristics

• Aerobic, grows well on non-enriched media
• Colonies: small, shiny, round, smooth, mucoid, raised, moist, translucent, regular outline
• Non-hemolytic, larger mucoid and salmon-pink in color with age
• Metachromatic granules often present in milk cultures

Biochemical Characteristics

• Catalase-positive
• Usually oxidase-negative (cytochrome)
• Does not ferment carbohydrates
• Reduces nitrates
• Indole-negative

Rhodococcus equi, Blood Agar

• A visual representation of Rhodococcus equi on blood agar
• Shows colonies and their characteristics

CAMP Phenomenon

• Rhodococcus equi is positive in the CAMP test with Staphylococcus aureus

Morphology (SDA)

• Resembles Nocardia species
• Gram-positive
• Filamentous fragments into rods and cocci forms
• May branch, partially acid-fast by MK

Rhodococcus equi in Sheep Blood Agar

• Visual representation of Rhodococcus equi culture on sheep blood agar
• Shows growth and characteristics

Usual Habitat

• Soil
• Intestinal tracts of animals

Diseases and Host

• Foals (1-4 months old): suppurative bronchopneumonia, pulmonary abscessation. Habitat is soil & feces of other herbivores.
• Horses: superficial abscessation. Habitat is as above.
• Pigs (cattle): mild cervical lymphadenopathy. Habitat is soil.
• Cats: subcutaneous abscesses, mediastinal granulomas

Suppurative Bronchopneumonia of Foals

• Major disease caused by Rhodococcus equi (pyogenic organism)
• Affected foals (1–4 months of age) characterized by bronchopneumonia and lung abscessation
• Acquired by inhalation of dust contaminated with R. equi
• Granulomatous ulcerative enterocolitis and mesenteric lymphadenitis when large numbers of R. equi swallowed from sputum

Pathogenicity and Pathogenesis

• Foals under 4 months are most susceptible due to impaired cellular immunity of the lungs
• Intracellular pathogen with specific surface antigens encoded in the DNA of a large plasmid
• Surface antigens are temp-dependent and expressed at 34–41°C
• Capsular polysaccharides and mycolic acids in the cell wall retard phagocytosis and exoenzyme activity

Clinical Signs

• Acute disease seen in one-month-old foals
• Sudden onset of fever, anorexia, and signs of bronchopneumonia
• Disease is insidious in 2–4-month-old foals; lesions advanced before coughing, dyspnea, weight loss, and exercise intolerance
• Characteristic loud, moist rales on auscultation
• Occasionally diarrhea

Disease Process

• Bronchopneumonia with local abscessation
• Formation and distribution of abscessation
• Non-pulmonary disorders

Radiographic Appearance

• Normal foal chest X-ray
• Foal chest X-ray affected with Rhodococcus equi showing multiple abscesses in the lungs

Postmortem Appearance

• Foal that died due to Rhodococcus equi pneumonia
• Shows presence of multiple coalescing large abscesses within the lung
• Image shows appearance of affected lungs

Diagnosis

• History of the disease on the farm, age of the affected foal, and clinical signs
• Auscultation and radiography of the thorax
• Specimens for laboratory examination (tracheal aspirates and pus from lesions)
• BAP and MCA inoculated with suspect material and incubated aerobically at 37°C for 1–2 days

Identification Criteria

• Colonies on blood agar—non-hemolytic, salmon-pink, and mucoid
• Absence of growth on MCA
• CAMP test-positive
• Unresponsive in the OF test and sugar fermentation tests
• Biochemical profile using commercial kits
• Quantitative fecal culture on a selective medium demonstrating over 106 R. equi/g of feces

Treatment and Control

• Oral rifampin and erythromycin for 4–10 weeks
• Supportive therapy (rehydration, bronchodilatory/expectorant agents)
• No vaccine available
• Foals should be kept under observation
• Remove foal manure from pastures at frequent intervals
• Foals and dams should move regularly to fresh pasture
• Administer hyperimmune serum to foals at 1 month of age

Explore the characteristics and morphology of the Rhodococcus genus in this quiz. Learn about its cultural and biochemical traits, including its appearance on blood agar and the CAMP phenomenon. This quiz is essential for understanding microbiology and bacterial classifications.