Miscellaneous Bacterial Infections of Skin and Soft Tissues: Anaerobic Infections including Gas Gangrene, Leprosy and Anthrax

Question 1

What are obligate anaerobes?

Answer 1

Organisms that cannot grow in the presence of oxygen

Question 2

List methods to achieve anaerobic conditions for culturing anaerobes

Answer 2

• McIntosh and Filde’s anaerobic jar
• GasPak system
• Anoxomat system
• Anaerobic glove box workstation
• Pre-reduced anaerobically sterilized (PRAS) media

Question 3

What is a key characteristic of obligate anaerobes’ culture media?

Answer 3

Medium with low redox potential

Question 4

Name examples of obligate anaerobes

Answer 4

• Clostridium (e.g., C. perfringens, C. tetani, C. botulinum, C. difficile)
• Bacteroides

Question 5

What are common clinical presentations of anaerobic infections?

Answer 5

• Infections adjacent to mucosal surfaces
• Predisposing factors (ischemia, tumor, penetrating trauma, foreign body)
• Spreading gangrene
• Foul smelling putrid pus
• Abscess formation
• Septic thrombophlebitis
• Toxemia and fever not marked
• Failure to respond to antibiotics

Question 6

What types of specimens are acceptable for anaerobic culture?

Answer 6

• Tissue bits
• Necrotic materials
• Aspirated body fluids or pus

Question 7

What is Robertson’s cooked meat (RCM) broth used for?

Answer 7

It is the most commonly used anaerobic media for culturing anaerobes.

Question 8

How does C. perfringens appear in RCM broth?

Answer 8

Turns meat particles pink and broth turbid

Question 9

What is the significance of Gram staining in anaerobic infections?

Answer 9

It helps in examining the characteristic morphology of the organisms.

Question 10

What are the various culture media used for anaerobic isolation?

Answer 10

• Anaerobic blood agar
• Neomycin blood agar
• Egg yolk agar
• Phenylethyl agar (PEA)
• BHIS agar
• Bacteroides bile esculin agar (BBE agar)

Question 11

What is the first-line treatment for anaerobic infections?

Answer 11

• Metronidazole plus penicillin
• Carbapenems
• Clindamycin (if penicillin allergy)

Question 12

True or False: Gas gangrene is caused solely by Clostridium perfringens.

Answer 12

False

Question 13

What are the established agents of gas gangrene?

Answer 13

• Clostridium perfringens
• Clostridium novyi
• Clostridium septicum

Question 14

What is the principle virulence factor of C. perfringens?

Answer 14

Alpha-toxin

Question 15

What are the clinical manifestations of gas gangrene?

Answer 15

• Sudden onset of excruciating pain
• Foul-smelling discharge
• Gas bubbles (crepitus)
• Brawny edema
• Shock and organ failure

Question 16

What is the incubation period for C. perfringens gas gangrene?

Answer 16

10-48 hours

Question 17

What type of specimens are ideal for diagnosing gas gangrene?

Answer 17

• Necrotic tissues
• Muscle fragments
• Exudates from deeper parts of the wound

Question 18

What is a key feature in the microscopy of C. perfringens?

Answer 18

Thick, boxcar-shaped gram-positive bacilli without spores

Question 19

What is the significance of the Nagler’s reaction in identifying C. perfringens?

Answer 19

Opalescence surrounding the streak line on egg yolk agar due to lecithinase activity

Question 20

What is the role of hyperbaric oxygen in treating gas gangrene?

Answer 20

It may kill obligate anaerobic clostridia like C. perfringens

Question 21

What organism causes leprosy?

Answer 21

Mycobacterium leprae

Question 22

What are the clinical signs of leprosy?

Answer 22

• Hypopigmented skin lesions
• Thinning of eyebrows
• Numbness in extremities

Question 23

What microscopy technique is used for diagnosing leprosy?

Answer 23

Modified acid-fast smear

Question 24

What are the laboratory diagnosis modalities for leprosy?

Answer 24

• Slit skin smear
• ZN technique staining
• Microscopy for acid-fast bacilli

Question 25

Fill in the blank: The incubation period for C. novyi gas gangrene is typically ____ days.

Answer 25

5-6

Question 26

What is the treatment for leprosy?

Answer 26

Combination of antibiotics based on susceptibility, typically including rifampicin and dapsone

Question 27

What is the causative agent of leprosy?

Answer 27

Mycobacterium leprae ## Footnote Mycobacterium leprae is known for causing leprosy, a chronic infectious disease.

Question 28

What type of cells are referred to as Virchow's 'lepra cells'?

Answer 28

Foamy macrophages ## Footnote These cells contain globi and are characteristic of leprosy infections.

Question 29

What is the appearance of live bacilli in a smear?

Answer 29

Uniformly stained with parallel sides and round ends; length is five times the width ## Footnote This indicates a healthy population of Mycobacterium leprae.

Question 30

What is the appearance of dead bacilli in a smear?

Answer 30

Less uniformly stained with fragmented and granular appearance ## Footnote This indicates a decline in the viability of Mycobacterium leprae.

Question 31

What is the Bacteriological Index (BI)?

Answer 31

Total number of bacilli (live and dead) seen per oil immersion field ## Footnote It quantifies the bacterial load in a smear.

Question 32

What does the Morphological Index (MI) represent?

Answer 32

Percentage of uniformly stained bacilli out of the total number of bacilli counted ## Footnote It assesses the health of the bacterial population.

Question 33

Which animal is used for cultivating Mycobacterium leprae?

Answer 33

Mice, specifically in the foot pad at 20°C for 6-9 months ## Footnote Mycobacterium leprae cannot be cultured in artificial media.

Question 34

What does the Lepromin test demonstrate?

Answer 34

Delayed hypersensitivity reaction and intact cell-mediated immunity against lepra antigen ## Footnote It is used to assess immune response in leprosy patients.

Question 35

What is the recommended treatment for leprosy according to WHO?

Answer 35

Multidrug therapy including Dapsone, rifampicin, and clofazimine ## Footnote This combination is effective in treating leprosy.

Question 36

What is the clinical manifestation of cutaneous anthrax?

Answer 36

Necrotic eschar surrounded by non-pitting indurated edema ## Footnote This is often referred to as malignant pustule.

Question 37

What is pulmonary anthrax also known as?

Answer 37

Wool sorter's disease ## Footnote It is characterized by hemorrhagic pneumonia and blood-stained sputum.

Question 38

What are the three modes of human infection with anthrax?

Answer 38

* Direct contact with spores * Inhalation of spores * Ingestion of carcasses ## Footnote These routes highlight the zoonotic nature of anthrax.

Question 39

What are the virulence factors of Bacillus anthracis?

Answer 39

* Anthrax toxin (edema factor, protective factor, lethal factor) * Anthrax polypeptide capsule ## Footnote These factors contribute to the pathogenicity of Bacillus anthracis.

Question 40

What does McFadyean's reaction demonstrate?

Answer 40

Polypeptide capsule surrounding blue bacilli ## Footnote This is visualized using a polychrome methylene blue stain.

Question 41

What type of colonies does Bacillus anthracis produce on nutrient agar?

Answer 41

Medusa head appearance ## Footnote This characteristic growth pattern is identifiable under low power microscopy.

Question 42

What is the appearance of Bacillus anthracis colonies on blood agar?

Answer 42

Dry, wrinkled, non-hemolytic colonies ## Footnote This is a typical growth pattern for Bacillus anthracis.

Question 43

What should be done with specimens suspected of anthrax?

Answer 43

Processed in appropriate biological safety cabinets ## Footnote This is to prevent laboratory-acquired infections.

Question 44

What is the treatment protocol for anthrax?

Answer 44

Ciprofloxacin or doxycycline plus clindamycin for 60 days ## Footnote Early treatment is critical for effective management of anthrax.