Anaerobic Infections

Question 1

Common aerobic microenvironments

Answer 1

Tonsils, gingiva, throat, skin, colon, vagina

Question 2

Aerotolerant

Answer 2

Survive in O2 but do not grow

Question 3

GNR Anaerobes (5)

Answer 3

• Bacteroides fragilis
• Other Bacteroides spp live in mouth and GU tracts. Less virulent than fragilis.
• Fusobacterium necrophorum
• Prevotella spp
• Porphyromonas spp

Question 4

Gram Positive Anaerobes (4)

Answer 4

• Peptostreptococcus
• Clostridia spp (spore-forming rods)
• Actinomyces spp (non-spore forming rods)
• Propionibacterium (non-spore forming rods)

Question 5

What is most common cause of anaerobic infections?

Answer 5

Bacteroides fragilis

Question 6

Bacteroides fragilis
Morphology
Known for?
Location of normal microbiota
Hallmark
Resistance

Answer 6

GNR
Most common cause of anaerobic infections.  
Normal microbiota of GI tract.  
Hallmark is abscess formation.  
Resistance due to beta-lactamases.

Question 7

Fusobacterium necrophorum
Morphology
Location
Virulence factor

Answer 7

Long thin rods (fusiform). Gram Neg.
Normal mouth / gingival flora.
May be found in lung and GI as well.
Secrete active endotoxin.

Question 8

Peptostreptococcus
Morphology
Known for?
Location

Answer 8

Gram Positive coccus.
2nd most common cause of anaerobic infections after B fragilis.
Found in mouth, lung, GI, and GU.

Question 9

Common anaerobes in oral cavity (6)

Answer 9

Bacteroides (non-fragilis), Fusobacterium, Prevotella, Peptostreptococcus, Actinomyces, and Porphyromonas

Question 10

Ludwig’s Angina

Answer 10

Deep soft tissue infection w/in the submandibular / sublingual space. May cause respiratory compromise by elevating floor of mouth and forcing tongue back into the airway.

Question 11

Lemierre’s Syndrome

Answer 11

Caused by Fusobacterium necrophorum.
Soft tissue infection of the lateral pharyngeal space w/ suppurative thrombophlebitis of the jugular vein → septic pulmonary emboli and bacteremia.

Question 12

Pyogenic brain abscess caused by?

Hematogenous brain abscess caused by?

Answer 12

Pyogenic - usually mixture of aerobes and anaerobes.

Hematogenous - usually NOT anaerobes. Often Staph aureus or pneumococcus.

Question 13

Anaerobes causing lung infections (4)

Answer 13

Prevotella, Fusobacterium, Peptostreptococci, Bacteroides

Question 14

What causes most pneumonias?

Answer 14

Aspiration

Question 15

Lung abscess
Speed of progression
Constitutional sxs
Hallmark
Tx

Answer 15

Slow / subacute.
Constitutional sxs include weight loss, anorexia, and night sweats
Hallmark is thick, fetid sputum
Tx w/ weeks / months of AB’s

Question 16

Pleural fluid characteristics of empyema
pH
Glucose
LDH
Tx

Answer 16

• Low pH, under 7.2, b/c bacteria produce acid
• Low glucose, under 60 b/c bacteria eat it
• High LDH, over 60
• Tx – Drainage (chest tube) + antibiotics. Possibly decortication (remove pleura)

Question 17

Anaerobes that cause intraabdominal infections (5)

How does normal microbiota usually prevent intraabdominal infections?

Answer 17

B fragilis, Prevotella, Fusobacterium, Peptostreptococcus, and Clostridia
Normally take up space and release enzymes to prevent infection. Also produce vitamin K and bile.

Question 18

Primary peritonitis

Answer 18

Infection of ascitic fluid seen in end-stage liver disease. Most often due to aerobic bacteremia that seeds the ascites

Question 19

Secondary peritonitis
Cause
Sxs
Tx

Answer 19

Usually caused by anaerobes following a breach in the GI mucosa.
Sxs include severe abdominal pain / rebound. Life-threatening.
Tx w/ surgery and AB’s.

Question 20

Liver abscess
Mechanism
Tx

Answer 20

Most common visceral abscess. Infection may spread from GI tract through biliary tract or through portal venous system. Tx w/ drainage of AB’s.

Question 21

Female GU anaerobes (4)

Answer 21

Prevotella, Peptostreptococcus, B fragilis, Clostridia

Question 22

Endometritis caused by which bug?

May follow what?

Answer 22

C perfringens

May follow incomplete abortions

Question 23

Tuboovarian abscess / PID
Caused by?
Complications?

Answer 23

Usually mixed infection

May cause scarring / infertility

Question 24

Vaginosis

Cause and sxs

Answer 24

Decline in acid-producing Lactobacilli (normal microbiota) and increase in anaerobes → vaginal discharge

Question 25

Anaerobes causing SSTI's (3) Examples Complication

Answer 25

Bacteroides, peptostreptococci, and Clostridia •Diabetic foot infections, pressure ulcers (often on sacrum), necrotizing fasciitis (ex includes Fournier’s gangrene), bites • Contiguous osteomyelitis – spreads from soft tissue infections, especially diabetic foot infections or pressure ulcers.

Question 26

What is most common anaerobe causing bacteremia?

Answer 26

Bacteroides fragilis

Question 27

Clostridia spp Where do they live? Morphology

Answer 27

Ubiquitous, found in soil, decaying vegetation, and GI tract. Large Gram Pos Rods that produce spores.

Question 28

``` C perfringens How common? Appearance Virulence factors Diseases (3) ```

Answer 28

Most common Clostridial isolate Characteristic "boxcar" appearance Toxins: lethicinase (alpha toxin) and hemolysin (phi toxin) Food poisoning, enteritis necroticans (small bowel necrotizing infection), and gas gangrene.

Question 29

What foods does C perfringens cause food poisoning in? Mechanism Sxs

Answer 29

Found in meats, poultry, and gravy Multiplies during cooling. Toxin is NOT preformed. Sxs start 8-16 hours after eating, including cramps and diarrhea (vomiting is rare).

Question 30

What causes gas gangrene? Sxs (5) Tx

Answer 30

Caused by C perfringens. Usually trauma-mediated. Sxs - Severe pain out of proportion to visual appearance, gas production in soft tissues (crepitus / subcutaneous emphysema), magenta / bronze color, hemorrhagic bullae, and dirty dishwater drainage Tx - debridement and AB's (penicillin + clindamycin to stop toxin production)

Question 31

``` C tetani Spore morphology Environment Toxin and mechanism Sxs Complications Diagnosis Tx Vaccine schedule ```

Answer 31

Spore, looks like a tennis racket. Found in soil and GI tracts. •Tetanospasmin (Tetanus Toxin) – exotoxin made at wound site. Enters nervous system via presynaptic terminals of lower motor neurons. Carried retrograde to CNS, inhibiting NT release from inhibitory cells → depol of motor neurons / sustained muscle contraction. •Descending pattern – trismus (lockjaw), neck stiffness, swallowing problems, abdominal rigidity, generalized. Spasms may be triggered by sensory stimuli. •Complications include airway obstruction, laryngospasms, fractures, autonomic hyperactivity, pulmonary embolism, and aspiration pneumonia. Toxin increases body temp, sweating, BP, and pulse. •Diagnosis is clinical •Tx – supportive (ventilation), muscle relaxants (benzos), HTIG (human tetanus immunoglobulin [passive]), metronidazole, and wound debridement. AB’s not great b/c sxs are toxin-mediated. •Childhood vaccine (DTaP), booster during adolescence (Tdap) and every 10 years during adulthood

Question 32

``` C botulinum Environment Spore characteristics Mechanism / sxs Causes (4) Clinical features Diagnosis Tx ```

Answer 32

* Found in soil / water worldwide. * Subterminal spore. Heat stable. * Neurotoxin prevents release of Ach → muscle weakness (flaccid paralysis) and autonomic dysfunction. * Causes * Foodborne (15%) – ingest PREFORMED toxin, acting w/in 36 hrs. Found in home-canned foods, fruits, fish products * Infant (65%) – ingest spores, found in honey, soil. Normal GI microbiota not established yet so infection is easier. * Wound (20%) * Inhalational – toxin, bioterrorism * Clinical features * Acute, bilateral cranial nerve dysfunction → Blurred vision, diplopia, dysphagia, facial and tongue weakness, drooping eyelids, slurred speech * Descending motor weakness * Afebrile * Diagnosis is clinical – stool, serum, and food * Tx – supportive (ventilation), trivalent antitoxin (A, B, E), wound debridement, AB’s (penicillin for wounds), human botulinum immune globulin for infants.

Question 33

What is most common cause of nosocomial diarrhea and unexplained leukocytosis in hospitalized pxs?

Answer 33

C difficile

Question 34

How can C diff b/c disinfected?

Answer 34

Bleach or UV light. NOT alcohol. Need to wash hands w/ soap and water.

Question 35

``` C difficile Virulence factors Population Diagnosis and problems w/ tests What if culture is positive? Tx ```

Answer 35

Spores infect colon. Exotoxin A and B cause mucosal damage --> diarrhea. More common in elderly •Diagnose w/ toxins in stool (using enzyme immunoassay, EIA), PCR, and endoscopy • Toxins break down quickly so it is important for stool sample to be fresh. • PCR may cause many false positives. •Name comes from being difficult to culture. Even when culture does grow, it doesn’t mean it’s a toxin-forming strain (most aren’t). •Tx – stop all unnecessary AB’s, do NOT use antiperistaltics. Use oral metronidazole for mild cases and oral vancomycin for moderate / severe cases. For life threatening cases, use oral / rectal vanco, IV metronidazole, IVIG, and possibly colectomy.

Question 36

Why do some pxs have recurrent C diff?

Answer 36

Lack IgG to toxins.

Question 37

Which AB's are generally considered "A+" for anaerobic infections? (5)

Answer 37

Metronidazole, carbapenems, beta-lactamase inhibitor combos, tigecyclin, moxifloxacin

Question 38

What does crepitus feel like? | What is this an indication of?

Answer 38

Skin feels bubbly / spongy/ like rice krispies. | Indicates anaerobic infection, often Clostridium perfringens for gas gangrene.

Question 39

What type of infection usually causes peritonitis?

Answer 39

Mostly mixed infections of aerobes and anaerobes.

Question 40

AB's for hospital acquired pneumonia

Answer 40

FQ or beta lactam (ceftriaxone) + macrolide

Question 41

What AB is used for anaerobic oral infections?

Answer 41

Clindamycin

Question 42

What are the 2 most common GNR's and GPC's to cause Anaerobic pneumonia? What do you use to treat?

Answer 42

GNR's: Prevotella and Fusobacterium GPC's: Peptostreptococcus and oral strep viridans. Tx w/ clindamycin or ampicillin / sulbactam