Mycobacterium Flashcards
Characteristics
Gram positive
Rod-shapedd
Acid-fast bacili
Slow growing (colonies only visible after 3-4 weeks of incubation)
Intracellular bacteria
Grows on which media?
Lowenstein Jensen and middlebrook’s media
Causes ?
Chronic, granulomatous infection
Important species?
M. tuberculosis, M. bovis, M. avium, M. paratuberculosis
Causes what important diseases?
Bovine tuberculosis, Johne’s disease, Avian tuberculosis
Virulence Factors (1)
Sulfolipids and Phosphatidyl inositol mannoside (PIM)
Prevent respiratoty burst and phagolysosomal fusion, interfere with function of reactive oxygen intermediates following ingestion by macrophage
Virulent factor (2)
Surface mycosides
Aid in ensuring bacterial survival within macrophages
Virulent Factor (3)
Waxes
Contained within cell wall, have adjuvant activuty, activate macrophages leading to granuloma formation
Virulent factors (4)
Alkyl hyroperoxidase reductase
Resistance to superoxides and reactive nitrogen, intermediates found within macrophage phagolysosomes.
Virulent factor (5)
Cord factor
Immobilize neutrohils, act as adjuvant, evokes granulomtous responses, cause mitochondrial disruption > disturbances in cellular respiration
Virulent factor (6)
Mycobactins and exochelins
Exochelins remove ferric iron from ferritin.
Mycobactin resides in cell membrane, responsible for transfer of iron from iron-exochelin complexes to the bacterium
Bovine Tuberculosis
Agent: M. bovis
Host: deer, pigs, people, domestic & wild animals
Case presentation: progressive emaciation and other non-specific signs
- Progressive development of granulomatous lesions or tubercles in multiple organs
- Tuberculous lesion, caseous in nature on organs
- Lung: chronic cough due to bronchopneumonia, dyspnoea in latter stager
- Common involves retropharyngeal, mediastinal
BT in deer
Subacute or acute
Often undetectable clinically
Emaciation (severly infected animal), small or large abscess in lymph node of head, thorax and abdomen, enlargement of superficial nodes may be apparent, more liquefactive than those in cattle, resemble a pyogenic iinfection
Transmission of BT
Inhalation of droplets
Ingesting raw milk from infected cows
Through movement of undetected infected domestic animals and contact with infected wild animals
Diagnosis of BT
Immunidiagnostics
- Tuberculin skin test (CFT or CCT)
- Serology (IFN GAMMA TEST)
Isolation and identification of bacteria
Polymerase chain reaction (pcr) - molecular detection
Mechanism of Tuberculin skin test
Cell-mediated hypersensitivity, acquired through infection.
Demonstrated by fever when given subcutaneous
Demonstrated by conjunctivitis when given conjuctival
Demonstrated by local swelling of dermis when given intradermal
CFT Technique - Positive cases in cattle:characterised by thickening and oedema >5mm swelling
False positive following sensitization of animals with other Mycobacterium spp
CCT
Injection site: skin of neck region
Positive: increase in skin thickness
M. bovis site is 4 mm or greater than thickness of m, Avium site
Immunodiagnostic of BT
Serology (interferon gamma testing/BOVIGAM)
- to detect immune response to bovine TB
- blood in heparinised tube transport at room temperature
- use freshly collected blood sample
- measure level of cytokine called IFN-gamma
- released by WBC infected with TB when stimulates with bovine and avian tuberculins
- Greater responses of IFN-gamma to bovine TB to avian Tb
JOHNE’S DISEASE
Agent: Mycobacterium paratuberculosis
Effects: chronic, infectious, granulomatous enteritis of domestic and wild ruminants
Clinical signs: chronic diarrhoea, progressive emaciation
Effects on cattle
@3 stages
- subclinical
excretory phase , without cs - Clinical phase
chronic diarrhoea, wasting, decrease milk production, oedema and infertility - Death as result
Effects on sheeps and goats
Emaciation, diarrhoea uncommon
Intermandibular eodema or bottle jaw resulting from Hypoproeinaemia especially in pregnant ewes, lethargy, depression and decrease parasite resistance in terminal stages
Avian Tuberculosis
Widest host range
Difficult to eradicate in cattle and pigs as infected animals with M.avium are sensitive to mammalian tuberculin and gives false positive
In birds; usually chronic, but in highly susceptible population is acute
Lesions at: liver and spleen
In cattle; Lesion usually confined in mesenteric lymph node. Majority infections are asymptomatic
Sheeps and goats
Resistant to M. avium although mesenteric node infections can be found (rarely)
Type of samples and sample preparation
Serology: plasma sample (lithium/heparin tube)
Isolation and identification: milk, tracheobronchial lavage, faeces, biopsy samples, organ samples especially retropharynheal lymph node, mediastinal lymph node, lung with nodules (tubercle), liver, spleen, intestinal lymph node, intestine with lesion
Dont freeze blood sample
Keep organ or fluid samples chill during long transportation (4-15c)
Organ or fluid samples need to be treated with 4% NaOH or 3% HCl or 5% oxalic acid for 15 to 30 minutes to decontaminate the sample. Tubercle bacili can survive the exposure
Lab diagnosis
Lowenstein-Jensen with glycerol – for M. tuberculosis, M.avium
Lowenstein-Jensen without glycerol for M. bovis
- malachite green as selective agent, inhibits contaminants
Middlebrook’s 7H10 agar (oleic acid-albumin media)
Incubation time: atleast 8 weeks, generation timesof tubercle bacill - 12 hours upwards at 37c, aerobic cond.
Acid fast or ziehl-neelsen staining technique
1. make smear
2. flood with concentrated carbol fuchsin
3. Heat until steam appears
4. Decolorize the smear with acid-alcohol
5. Counter stain with methhylene blue for one minute
6. Wash the slide with tap water, blot dry and observe under microscope
Expected findings
Colony morphology
- mammalian type: dry and crumbly
- avian type- dome shaped colony
Ziehl-Neelsen staining
- mycobacterium stains red, rod shape while others stain blue
Control and prevention
Identification and elimination of infected animals; test and slaughter
Post-mortem meat inspection (tubercles in lungs and lymph node, to prevent unsafe meat from entering the food chain, allows vet. service to trace back to the herd of origin of the infected animal for testing and eliminate if required), intensive surveillance (on-farm visits, systematic individual testing of cattle and removal of infected and in-contact animals, movement controls)
Pastereurization of milk for consumption
Vaccination for human
