Anaerobic Infection

Question 1

Require complete absence of oxygen is?

Answer 1

Obligate/ strict anaerobe

Question 2

Classification of anaerobes?

Answer 2

1. Spore forming anaerobes
2. Non-spore-forming anaerobes
3. Spirochaetes

Question 3

Predisposing factors for Anaerobic Infections?

Answer 3

1. Trauma
2. Impaired blood supply
3. Presence of other organisms
4. Foreign bodies
5. Disruption of barriers

Question 4

Features of anaerobic infections?

Answer 4

1. Production of a large amount of foul-smelling pus.
2. Proximity of lesions to mucosal surface or portal of entry. 3. Failure to isolate organisms from pus by the usual aerobic methods (sterile pus).
3. Infection associated with necrotic tissue, deep seated abscesses or closed space , e.g. brain
   abscess.
4. Gas formation in the surrounding tissues detected as crepitations.
5. Failure to respond to conventional antimicrobial therapy. 7. Presence of special character, e.g. Sulphur granules seen by the naked eye in the pus in case of actinomycosis

Question 5

anaerobic infections Presence of special character?

Answer 5

Sulphur granules seen by the naked eye in the pus in case of actinomycosis

Question 6

Common types of anaerobic infections?

Answer 6

Respiratory tract infections

Central nervous system infections

Intra-abdominal and pelvic infection

Wounds and soft tissue infections

Bacteremia and endocarditis

Question 7

Laboratory diagnosis of Anaerobic Infections?

Answer 7

1. Specimen
   II. Macroscopic examination
   III. Microscopic examination
   IV. Culture

Question 8

Laboratory diagnosis of Anaerobic Infections

I. Specimen?

Answer 8

 Adequate clinical specimens are collected and transported, as soon as
possible, to the laboratory, preferably before antibiotic therapy.
 Best samples are taken by disposable closed syringe or on swab with
reduced transport media.
 The samples should be taken, as deep as possible , away from atmospheric
oxygen and as much sample as possible.

Question 9

Treatment of anaerobic infections

?

Answer 9

Surgical treatment:
Antimicrobial therapy:
3. Treatment of the aerobic organisms accompanying anaerobes, in a
mixed infection, is also necessary.

Question 10

drainage of pus from abscesses, debridement, and

removal of necrotic tissues may be sufficient. ?

Answer 10

Treatment of anaerobic infections

1. Surgical treatment

Question 11

Spore-forming Anaerobes ?

Answer 11

Clostridia

Question 12

•Large, Gram-positive, spore-forming bacilli.
•The position of the spore within the vegetative cells is useful
in identifying the species

Answer 12

Clostridium
 Microbiological features:
 Morphology:

Question 13

Clostridium Microbiological features?

Answer 13

-Morphology:

•Large, Gram-positive, spore-forming bacilli.
•The position of the spore within the vegetative cells is useful
in identifying the species

• Culture characteristics:

• Anaerobic

Question 14

Clostridium Natural habitat ?

Answer 14

 Soil  Intestinal tract of animals & humans

Question 15

Clostridium Important species?

Answer 15

 Clostridium perfringens: Gas gangrene & Food poisoning
 Clostridium tetani: Tetanus
 Clostridium botulinum: Botulism

 Clostridium difficile: (superinfection).

Question 16

Gram positive large rectangular bacilli
 Oval sub-terminal non bulging spores
 Spores are rarely seen

Answer 16

Clostridium perfringens Morphology

Question 17

Clostridium perfringens

Culture?

Answer 17

Anaerobic organism.

Colonies on blood agar are surrounded by complete haemolysis

Question 18

Biochemical reactions Clostridium perfringens

?

Answer 18

Ferments sugars with production of acid & gas.

Question 19

Clostridium perfringens

 Virulence factors?

Answer 19

Alpha-toxin: lecithinase

Theta-toxin: cytolysin

Others

Question 20

Clostridium perfringens Virulence factors:
 Alpha-toxin: lecithinase?  Theta-toxin: cytolysin
? Others?

Answer 20

Alpha-toxin: lecithinase
= It lyses cell membrane lecithin

Theta-toxin: cytolysin
= direct vascular injury

Others
= Haemolysins, collagenases, proteases, lipases

Question 21

Pathogenesis of Clostridium perfringens

?

Answer 21

All clostridial wound infections occur in an anaerobic tissue environment caused by
an impaired blood supply secondary to trauma, surgery, foreign bodies,
malignancy
 Usually polymicrobic because the source of wound contamination (faeces, soil) is
polymicrobic.

Question 22

Clostridium perfringens
 Clinical findings
?

Answer 22

A- Gas Gangrene (Clostridial myonecrosis)

B- Anaerobic Cellulitis

Question 23

Symptoms of Clostridium perfringens

?

Answer 23

As the clostridia multiply → exotoxins are liberated into the surrounding
tissue → more local tissue necrosis & systemic toxemia .  Infected muscle is discolored (purple mottling) & edematous & produces a
foul-smelling exudate & gas bubbles which cause crepitations.  Severe shock with massive hemolysis & renal failure is usually the ultimate
cause of death.

Question 24

Clostridium perfringens Diagnosis ?

Answer 24

Specimen: taken from the depth of the wound & examined rapidly.

Question 25

Clostridium perfringens Treatment & prevention:

?>

Answer 25

Correction of the anaerobic conditions:
• Drainage & Surgical removal of dead tissues
 Penicillin is the drug of choice
 Hyperbaric oxygen therapy may limit the spread of infection.

Question 26

Gram positive rod  Bulging terminal spore (drumstick appearance )  Most strains are motile

Answer 26

Clostridium tetani

Morphology

Question 27

Strict anaerobe
 Grows well on ordinary & cooked meat media.
 On blood agar, → swarm with surrounding zones of β-
hemolysis

Answer 27

Culture of Clostridium tetani

Question 28

Clostridium tetani

 Virulence factors:

Answer 28

Tetanospasmin toxin”

Question 29

Tetanus Pathogenesis?

Answer 29

Most cases result from lacerations or small puncture
wounds, contaminated with Cl. tetani spores.
 Ingestion of tetanus toxin does not produce the disease.
 The spores germinate , in the traumatized tissue, (the
blood supply is cut off & ischemia results, producing an anoxic
anaerobic environment, with low redox potential).
 A puncture wound can also cause spores to be injected
deeply into the tissue, offering anaerobic medium.
 The vegetative cells of Cl. tetani grow locally in the
necrotic tissue → release of tetanospasmin toxin.

Question 30

Tetanus Neonatal tetanus ?

Answer 30

mother lacks
immunity & the umbilical stump becomes
contaminated with Cl. tetani spores

Question 31

Tetanus Prevention?

Answer 31

I. Active immunization:
 Toxoid is given to infants in the first year of life: the triple
vaccine (DPT) is given at the age of 2, 4 & 6 months by IM injection.

II. Passive immunization Human tetanus immunoglobulin (HTIG)

Question 32

Non-spore-forming anaerobes

?

Answer 32

Bacteroides

Question 33

Gram-ve bacilli, highly pleomorphic  Capsulated (virulence factor)→ antiphagocytic.

Answer 33

Bacteroides

Question 34

The commonest pathogen among Bacteroides species

?

Answer 34

B. fragilis

Question 35

released from the colon into blood → multiplies rapidly →
?

Bacteroides

Answer 35

bacteremia

Question 36

If introduced into the abdominal cavity →

Bacteroides

Answer 36

abdominal abscess

Question 37

Drug resistance is common (beta lactamase production)  Preoperative antibiotics are given to prevent surgical wound
contamination with ?.

Answer 37

Bacteroides

Question 38

Gram+ve bacilli, having the typical morphology of diphtheroides.  Their metabolic products include propionic acid from which the
genus name is derived. ?

Answer 38

Propionibacterium Morphology

Question 39

Normally present in human skin, hair, oropharynx & GIT . It is the major contributor to the complex pathogenesis of acne vulgaris.
?

Answer 39

P. acne