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Questions and Answers
What is the main purpose of the Mantoux test in diagnosing latent tuberculosis?
What is the main purpose of the Mantoux test in diagnosing latent tuberculosis?
Why is a prolonged treatment course of 6-12 months necessary for tuberculosis?
Why is a prolonged treatment course of 6-12 months necessary for tuberculosis?
What type of environment is optimal for the growth of Mycobacterium leprae?
What type of environment is optimal for the growth of Mycobacterium leprae?
Which of the following is a first-line drug used in the treatment of tuberculosis?
Which of the following is a first-line drug used in the treatment of tuberculosis?
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What is the primary action of the Bacillus Calmette–Guérin (BCG) vaccine?
What is the primary action of the Bacillus Calmette–Guérin (BCG) vaccine?
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Which of the following statements correctly describes the Ziehl-Neelsen stain in the diagnosis of tuberculosis?
Which of the following statements correctly describes the Ziehl-Neelsen stain in the diagnosis of tuberculosis?
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What is a common characteristic of tuberculoid leprosy?
What is a common characteristic of tuberculoid leprosy?
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What complication does the caseous material present in tuberculosis treatment?
What complication does the caseous material present in tuberculosis treatment?
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What is the primary mode of transmission for Mycobacterium tuberculosis?
What is the primary mode of transmission for Mycobacterium tuberculosis?
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Which of the following is considered a significant clinical manifestation of pulmonary tuberculosis?
Which of the following is considered a significant clinical manifestation of pulmonary tuberculosis?
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What characteristic of Mycobacterium tuberculosis allows it to survive in dried sputum?
What characteristic of Mycobacterium tuberculosis allows it to survive in dried sputum?
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Which treatment strategy is recommended prior to starting antibiotic therapy for a Bacteroides infection?
Which treatment strategy is recommended prior to starting antibiotic therapy for a Bacteroides infection?
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What diagnostic method is most effective for staining Mycobacterium tuberculosis?
What diagnostic method is most effective for staining Mycobacterium tuberculosis?
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Which of the following describes the primary lesion formed during the first exposure to Mycobacterium tuberculosis?
Which of the following describes the primary lesion formed during the first exposure to Mycobacterium tuberculosis?
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Which factor makes Mycobacterium tuberculosis a major opportunistic pathogen?
Which factor makes Mycobacterium tuberculosis a major opportunistic pathogen?
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What cellular immunity response does Mycobacterium tuberculosis stimulate?
What cellular immunity response does Mycobacterium tuberculosis stimulate?
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Which clinical manifestation is specifically associated with the first stage of Lyme disease?
Which clinical manifestation is specifically associated with the first stage of Lyme disease?
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What is the drug of choice for treating all treponemal infections?
What is the drug of choice for treating all treponemal infections?
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Which of the following treatments is suitable for Stage III Lyme disease?
Which of the following treatments is suitable for Stage III Lyme disease?
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What is the primary method of diagnosing relapsing fever caused by Borrelia?
What is the primary method of diagnosing relapsing fever caused by Borrelia?
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Which stage of Lyme disease is most likely to include neurological disorders such as meningitis?
Which stage of Lyme disease is most likely to include neurological disorders such as meningitis?
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For patients allergic to penicillin, which of the following antibiotics is recommended for treating treponemal infections?
For patients allergic to penicillin, which of the following antibiotics is recommended for treating treponemal infections?
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How does the Borrelia organism evade the host's immune response during relapsing fever?
How does the Borrelia organism evade the host's immune response during relapsing fever?
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Which test serves as the sensitive screening tool for laboratory identification of Lyme disease?
Which test serves as the sensitive screening tool for laboratory identification of Lyme disease?
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Study Notes
Non-Enterobacteriaceae affecting GIT - Vibrio
- Vibrio are Gram-negative, comma-shaped, motile bacteria with a single polar flagellum
- They are facultative anaerobes and oxidase-positive
- Vibrio cholerae is the causative agent of cholera
- Vibrio cholerae is transmitted by drinking contaminated water and through food, especially sushi and sashimi in Asian countries like Japan
- Cholera causes profuse watery diarrhea (rice-water stools), vomiting, rapid heart rate, loss of skin elasticity, and low blood pressure
- Untreated cholera can lead to shock and death
Non-Enteric Gram-negative Rods
- These include:
- Pseudomonas aeruginosa
- Haemophilus
- Bordetella
- Brucella
- Legionella
- Bacteroides
1- Pseudomonas aeruginosa
- Pseudomonas aeruginosa is a free-living bacterium found in soil and water
- It is an opportunistic pathogen, primarily present in nosocomial infections
- It is a Gram-negative rod, motile and has simple nutritional requirements.
- It thrives in distilled water, signifying its minimal nutritional needs
- Pseudomonas aeruginosa is resistant to high salt concentrations, dyes, weak antiseptics, and many antibiotics
- Produces a blue-green pigment called pyocyanin
Virulence Factors of Pseudomonas aeruginosa
-
A) Adhesins:
- Fimbriae attach to epithelial cells in the upper respiratory tract
- Mucoid exopolysaccharide (alginate slime) protects bacteria from lymphocytes, phagocytes, and cilia
-
B) Siderophores:
- Pyochelin and pyoverdine are siderophores that accumulate iron vital for bacterial growth
-
C) Type III Secretion System (TTSS):
- Promoters of local invasion and distribution of the organism
-
D) Toxins and Extracellular Products:
- Cytotoxin, elastase, alkaline protease, exotoxin A (similar to diphtheria toxin), hemolysins, and LPS
Clinical Significance of Pseudomonas aeruginosa
-
Respiratory Infections:
- Pneumonia, commonly in cancer patients undergoing chemotherapy
-
Central Nervous System Infections:
- Meningitis and brain abscesses
-
Ear Infections:
- Commonly known as "swimmer's ear"
-
Eye Infections:
- Leading cause of bacterial keratitis
-
Urinary Tract Infections (UTIs):
- Often hospital-acquired from urinary tract procedures
2- Haemophilus influenzae
- Pleomorphic, ranging from small coccobacilli to long
- Fastidious; requires hemin (X factor) and nicotinamide adenine dinucleotide (NAD+) (V factor)
- Found in the upper respiratory tract, conjunctiva, and genital tract
- Two forms:
- Capsular (typable): The type b (Hib) form is a significant pathogen for young children
- Non-capsulated (non-typable): Can cause severe disease, particularly pneumonia, in older adults and individuals with chronic lung disease
- Transmitted by respiratory droplets
- High mortality in untreated patients, secondary to bacterial infection following an influenza virus infection
3- Bordetella pertussis
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The causative agent of whooping cough, an aerobic, small, encapsulated coccobacillus
-
Transmitted by respiratory droplets
-
Pertussis has three stages:
- Catarrhal phase: Non-specific symptoms
- Paroxysmal phase: Uncontrollable coughing fits followed by a "whoop" sound
- Convalescent phase: Lengthy, characterized by increasing risk of secondary infections
-
Involved Pathogenesis factors:
- Fimbriae/Filamentous hemagglutinin (FHA) for adhesion
- Pertussis toxin causing lymphocytosis, histamine sensitization, insulin production, and hypoglycemia
- Tracheal cytotoxin, hindering ciliary movement and regeneration
- Adenylyl cyclase toxin causing decreased chemotaxis and phagocytosis
- Dermonecrotic toxin causing vasoconstriction and ischemic necrosis
4- Brucella
- Brucella is primarily pathogenic to specific animal species (cattle, goats, sheep, swine, dogs) and is an aerobic, facultative intracellular parasite that survives within host phagocytes
- Infection, primarily from infected animals, typically occurs through contact with contaminated tissue or ingestion of unpasteurized milk
- The disease it causes, brucellosis * (undulant fever)*, is a zoonosis
- Symptoms are often nonspecific and flu-like, presenting with undulant fever
- Diagnosis often requires extensive history taking
5- Legionella
- Found in soil and water, with amoebas in water acting as reservoirs
- Legionella pneumophila causes Legionnaires' disease (severe pneumonia) and a milder form called Pontiac fever
- High mortality rate, particularly in immunocompromised individuals
- Transmitted through contaminated water and airborne dust, specifically through inhalation, or drinking untreated milk
6- Bacteroides
- A pleomorphic group of non-spore-forming anaerobic Gram-negative bacilli
- Bacteroides fragilis is a critical opportunistic pathogen causing abscess formation
- Surgical drainage of pus and elimination of necrotic tissue is crucial prior to treatment
A- Mycobacterium tuberculosis
- Nonmotile, strictly aerobic, slightly curved, non-spore-forming rods
- Grows very slowly (generation time 12-24 hrs)
- Requires special media (Lowenstein-Jensen)
- Acid-fast due to a mycolic acid cell wall (resistant to acid and alkali)
- Does not produce exotoxins/endotoxins
- Transmitted by droplets, causing pulmonary TB, or milk from infected cattle causing intestinal TB (rare)
- Clinical presentation includes pulmonary and other organ infections, typically disseminated through macrophages
B- Mycobacterium leprae
- Nonmotile, aerobic, rod-shaped bacteria with a waxy coating, unique to mycobacteria
- Affects the skin primarily, due its growth at low temperatures
- Grows in armadillo's footpads and mouse footpads, grows poorly in culture systems
- Causes leprosy
- Transmitted by prolonged close contact with infected individuals, particularly via nasal secretions and skin lesions from lepromatous leprosy patients
B- Rickettsia
- Gram-negative, small bacilli, staining poorly with Gram stains
- Cultivable in embryonated eggs and tissue cells but not on culture media
- All diseases are zoonoses (transmitted from animals).
- Example: Typhus and Rocky Mountain spotted fever
C- Coxiella
- Highly heat, UV, and drying-resistant
- Aerobic and Gram-negative
- Transmitted via airborne dust, including unpasteurized milk
- Example: Q fever, primarily infecting the lungs
D- Chlamydia
- Aerobic, Gram-negative, obligate intracellular bacteria
- Staining poorly with Gram stains
- Cultivate in embryonated eggs and cell culture systems
- Example: respiratory tract infections, ocular infections, and sexually transmitted infections
1. Spirochetes
-
Long, slender, helically curved, Gram-negative bacilli with axial fibrils or filaments for movement (corkscrew)
-
Lacking LPS (lipopolysaccharide) or endotoxin
-
Important types causing:
- Treponema pallidum: Syphilis
- Borrelia burgdorferi: Lyme disease
- Leptospira interrogans: Leptospirosis
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Transmission of Treponema pallidum (syphilis): is through sexual contact and congenital syphilis can be transmitted during pregnancy.
Atypical Bacteria (Mycoplasma and Ureaplasma)
- Extremely small, lacking a cell wall
- Require complex media for cultivation
- Important species:
- Mycoplasma pneumoniae: Respiratory infections
- Mycoplasma hominis: Genitourinary infections
- Ureaplasma urealyticum: Genitourinary infections
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