Microbiology-Anaerobes

Question 1

Special precautions to take when handling anaerobes

Answer 1

Keep them protected from oxygen when taking them to diagnostics, otherwise they’ll die

Question 2

Characteristics of anaerobes

Answer 2

Can’t use O2 as final e- acceptor, unable to break down H2O2 because they lack catalase, in the presence of O2 (except bacteroides), superoxide accumulates because they lack superoxide dismutase (except bacteroides)

Question 3

Toxin-mediated anaerobic infections

Answer 3

Clostridia: C. botulinum (food-borne, infant, infection) is preformed. C. difficile, C. perfringens (gas gangrene and food poisoning) and C. tetani are formed in vivo.

Question 4

More common source of anaerobic infection? Where else can anaerobic infections come from?

Answer 4

Normal flora, although most infections are mixed. Regions of the body most susceptible have low O2, warm, moisture and substrate (like mucous membranes)Less common sources are exogenous where spores are kicked up in dirt or on contaminated foreign bodies that germinate on infection.

Question 5

What things create an opportunity for anaerobic infection?

Answer 5

Injury and poor perfusion (like in a dog bite)

Question 6

Why are anaerobic infections difficult to treat?

Answer 6

They are often mixed infections

Question 7

Areas in the body with high concentrations of anaerobes

Answer 7

GI tract

Question 8

Clinical characteristics of anaerobic infections

Answer 8

Aspiration, brain abscesses, foul-smelling pus, anaerobic sinusitis

Question 9

Anaerobic infections above the waist (like sinusitis)

Answer 9

Typically related to poor dentition and are more susceptible to antibiotics.

Question 10

Why is sinusitis commonly associated with anaerobic infection after a URI?

Answer 10

URI results in blockage of the sinuses from inflammation, decreases O2 content and allows for anaerobic growth.

Question 11

Anaerobic infections below the waist

Answer 11

Typically related to GI and GI. Less susceptible to antibiotics. Use metronidazole, clindamycin, augmentin.

Question 12

Which species of clostridia are shown below?

Answer 12

Left) Tetani Middle) Perfringens Right) Botulinum. Note that they are all gram + rods.

Question 13

Most common cause of invasive clostridial infections

Answer 13

C. perfringens (myonecrosis and gas gangrene). Often mixed with facultative organisms like E. coli that use up the oxygen in the environment that allow anaerobes to proliferate.

Question 14

C. perfringens virulence factors

Answer 14

Lecithinase: phospholipase that kills cells and hemolyzes RBCs (hemolytic and blood agar and egg yolk). This leads to muscle necrosis (reddish blue-black tissue) with ABSENT PMNs.

Question 15

What happens when you incubate C. perfringens with milk?

Answer 15

Stormy fermentation with lots of gas production.

Question 16

Pathogenesis of C. perfringens infection.

Answer 16

Contaminated wound -> Spores germinate where O2 is low -> Exotoxins (lecithinase) made -> Tissue necrosis and deeper penetration -> Rapid spread across fascial planes

Question 17

Anaerobe found in the oral flora that are gram-positive non-spore forming rods that grow in chains and in a molar formation.

Answer 17

Actinomyces

Question 18

Sulfur granules

Answer 18

Macro colonies that resemble grains of sand that are frequently seen in abscesses and sinus tracts. Associated with actinomyces.

Question 19

What microbe most likely caused this?

Answer 19

Note the suppurative and granulomatous inflammation of the cervico-facial region. This is most often due to poor oral hygiene after invasive dental surgery by actinomyces.

Question 20

Gram-positive, non-spore former that causes acne and infection of prosthetic devices

Answer 20

Propionibacterium

Question 21

Most common gram-negative non-spore forming rods

Answer 21

Bacteroides and fusobacterium. Bacteroides are commonly pathogenic after GI surgery because it is very prevalent in the colon and urogenital tract, causes intra-abdominal abscesses (below the waist!)

Question 22

Virulence factors of bacteroides fragilis

Answer 22

Polysaccharide capsule is anti-phagocytic.

Question 23

How do you treat bacteroides?

Answer 23

Not with penicillins because most below the waist anaerobes make beta lactamase

Question 24

Lab diagnosis of bacteroides

Answer 24

Grow in bile and turn bile black when they grow on it

Question 25

What bacteria played a role in periodontal disease?

Answer 25

Fusobacterium nucleatum. Note the long, thin gram-negative rods.

Question 26

What cancer is fusobacterium linked to?

Answer 26

Colorectal cancer. This is because it can be swallowed in the mouth an infect the GI tract.

Question 27

Major clinically significant non-spore-forming anaerobes

Answer 27

GRAM NEGATIVES RODS: Bacteroides (intra-abdominal), fusobacterium (oral). GRAM POSITIVE RODS: actinomyces (lumpy jaw), propionibacterium (prosthesis & acne).

Question 28

The usual antibiotics prescribed for above the waist anaerobic infections?

Answer 28

Penicillin + beta-lactamase inhibitor (amp/sulbactam, amox/clavulanate). Most normal flora are susceptible to normal beta-lactams.

Question 29

Good antibiotic for coverage of anaerobes mixed with enterococci and gram negatives like E. coli.

Answer 29

Carbapenems

Question 30

Antibiotic to give if you really need to get rid of toxin production

Answer 30

Clindamycin

Question 31

Antibiotic commonly used in deep abdominal infections

Answer 31

Metronidazole. Note that it will be combined to cover gram positives.

Question 32

A 3 year old presents with a neck abscess and was put on augmentin for 10 days with no resolution. He was later put on clarithromycin, it drained and he felt better. The drainage was cultured and positive for propionibacterium acnes and s. epidermidis. A month later he presents with inflammation on the other side and has torticollis. WBC is 17,000. CT is shown below. On culture small grey colonies grew out that smelled like bleach/locker room (Eikenella). Strep intermedius and prevotella oralis (bacteroides) also grew out. How do you treat him?

Answer 32

Note the vesicle overlying the abscess. The same infection happening 3x recently makes you suspicious for an anatomical cause. His culture shows mixed facultative aerobes and anaerobes. Prevotella is a beta-lactamase producer, so you treat with augmentin and clean out the branchial cleft cyst.

Question 33

Causes of adult deep neck infections

Answer 33

Dental, tonsils, trauma, foreign bodies

Question 34

Causes of pediatric deep neck infections

Answer 34

Dental, tonsils and congenital abnormality

Question 35

Facultative gram - bacillus that is commonly seen in bite wounds and boxers.

Answer 35

Eikenella corrodens

Question 36

What syndrome is a kid at risk for if he grows fusobacterium from a branchial cyst?

Answer 36

Lemierre’s syndrome: bacterial spread to lateral pharyngeal space and progresses to internal jugular vein, leading to vasculitis, septic emboli, metastatic infection and death.

Question 37

An 11 year old presents with abdominal pain, no bowel movements for the last 2 days, nausea, fever and the pain has migrated to the RLQ. CT shows thickening and fluid around the appendix. WBC is 11,200. Her appendix was removed and brown serous fluid was seen in the abdomen. How would you treat this patient?

Answer 37

E. coli, enterococcus faecalis, bacteroides fragilis, multiple anaerobic streptococci etc. are present in secondary peritonitis. Treatment is not culture based, you empirically treat with PCN + Beta-lactamase inhibitor, cefoxitin, carbapenems, 3rd generation cephalosporins or clindamycin.

Question 38

An 18 year old man presents with left sided neck swelling that was non-tender, not red, not warm, not boggy and it was nodular, firm and immobile. It started as a small nodule and has grown over the past 10 days. He reports having problems with the gums previously and hasn’t been to the dentist in a while. CT shows an expanding mass crossing fascial planes. All labs WNL. It started draining on its own and culture showed PMNs but no bacteria. What would you expect to see on culture? How would you treat?

Answer 38

Note how grainy the abscess is, this is typical of actinomyces. Treat with PCN + beta-lactamase inhibitor for 6 months to 1 year. On culture you would see filamentous organisms and sulphur granules, gram-positive, anaerobic bacteria.

Question 39

4 clinical forms of actinomyces

Answer 39

1) Cervicofacial (poor dentition) 2) Thoracic 3) Abdominopelvic (IUDs) 4) CNS (bacteremia, extension from oral cavity)