Anaerobic Bacteria and Clostridia Review

fifty flashcards covering key concepts from anaerobic bacteria, clostridia, and related toxins.

What is the role of superoxide dismutase (SOD) in oxygen metabolism?

Converts superoxide radicals (O2-) to hydrogen peroxide (H2O2).

What is the role of catalase in oxygen metabolism?

Converts H2O2 to water and oxygen.

Name a major virulence factor of Bacteroides fragilis that helps it avoid phagocytosis.

Polysaccharide capsule (anti-phagocytic).

True or False: Bacteroides fragilis tolerates oxygen because it has catalase and SOD.

True.

Which two enzymes help Bacteroides fragilis tolerate oxygen?

Catalase and superoxide dismutase.

What is a protease produced by B. fragilis that facilitates cell-to-cell contact?

A protease that stimulates cell-to-cell contact.

List sites where anaerobic infections commonly occur.

Colon, mouth, skin, and bone.

Why are anaerobic infections often foul-smelling?

Due to short-chain fatty acids produced during fermentation.

In anaerobic infections, what is often the relationship to normal flora?

Infections often due to expansion of normal flora.

Why are pathogenic anaerobes difficult to identify in cultures?

They form mixed infections that grow slowly on complex media.

What is the common Gram-negative anaerobic pathogen mentioned?

Bacteroides fragilis.

Characterize Clostridia in terms of Gram stain and oxygen requirements.

Gram-positive, spore-forming bacilli; obligate anaerobes or aerotolerant.

What are two pathogenic strategies of Clostridia?

Invasiveness and exotoxin production.

What toxin is associated with invasive C. perfringens infection?

Alpha toxin (phospholipase).

What disease is characteristic of histotoxic C. perfringens infection?

Gas gangrene (myonecrosis).

What toxin mediates tissue damage in C. perfringens infections?

Alpha toxin (phospholipase).

Which toxins cause antibiotic-associated GI disease by C. difficile?

Toxin A and Toxin B.

What is the enzymatic activity of C. difficile Toxin A and B?

Glucosyltransferases that glycosylate Rho GTPases, inactivating them.

Which Clostridium species cause tetanus and botulism?

C. tetani (tetanus toxin) and C. botulinum (botulinum toxin).

What type of paralysis is caused by tetanus toxin?

Spastic paralysis (lockjaw).

What type of paralysis is caused by botulinum toxin?

Flaccid paralysis.

Where does botulinum toxin act to cause its effect?

At the neuromuscular junction; cleaves SNAREs in motor neurons, inhibiting ACh release.

How does tetanus toxin reach the CNS?

Retrograde axonal transport to the cell body and inhibitory interneurons.

What is the net effect at the NMJ caused by TeNT?

Inhibits inhibitory interneurons, increasing ACh release and causing spastic paralysis.

Describe the structure of clostridial neurotoxins.

A 150-kDa single-chain protein cleaved into di-chain (A and B) linked by a disulfide; Zn-dependent protease; receptor binding and translocation.

What is the mechanism of action of clostridial neurotoxins?

Proteolytic cleavage of SNARE proteins, blocking synaptic vesicle fusion.

Do BoNT and TeNT share the same catalytic mechanism?

Yes; both cleave neuron-specific SNARE proteins.

What is the target of botulinum toxin (BoNT) at the neuron's level?

Motor neuron SNARE proteins at the NMJ; prevents acetylcholine release.

What is the target of tetanus toxin (TeNT) within the CNS?

Inhibitory interneuron SNARE proteins, leading to disinhibition of motor neurons.

Is there a licensed vaccine to prevent tetanus?

Yes, there is a licensed tetanus-containing vaccine.

What vaccines comprise DTaP and Tdap?

Diphtheria, tetanus, and acellular pertussis (DTaP/Tdap).

What is the DTaP vaccination schedule for children under 7?

Five doses at 2, 4, 6, 15-18 months, and 4-6 years.

What does the 'a' denote in DTaP and Tdap?

Acellular (pertussis component contains only part of the organism).

What do the letters D and T stand for in DTaP and Tdap?

Diphtheria toxoid and Tetanus toxoid.

What are the recommended management steps for suspected tetanus in the notes?

Administer tetanus immune globulin and vaccinate with Tdap; ICU care; darkened room; IV metronidazole; wound irrigation and debridement.

How many inpatient days and ICU days did the tetanus case involve?

57 days inpatient, including 47 days in the ICU.

What were the total inpatient charges for the tetanus case?

$811,929 (excluding air transport, rehab, and follow-up).

What is BabyBIG?

Botulism Immune Globulin IntraVenous, human-derived anti-botulism antibodies against serotypes A and B for infant botulism.

Are botulinum toxins contagious?

Not contagious and not transmitted person-to-person.

Why are BoNTs considered useful for therapy?

Dual neuron specificity and long half-life in neurons.

List some medical indications for BoNT beyond cosmetic use.

Blepharospasm, migraines, strabismus, hemifacial spasm, spasmodic torticollis, oromandibular dystonia, urinary retention, spasmodic dysphonia, stuttering, voice tremor, limb spasticity.

What infant botulism serotypes are treated with BabyBIG?

Serotypes A and B.

Which toxin is implicated in antibiotic-associated colitis?

C. difficile Toxin A and Toxin B.

What happens to normal flora during C. difficile infection?

Normal flora is reduced and endogenous/ingested C. difficile expands to produce toxins.

Are botulism toxins contagious?

No; not contagious and not transmitted person-to-person.

What is a typical sign of botulism treatment in infants?

Use of BabyBIG for serotypes A and B reduces hospital stay.

What is the typical odor characteristic of anaerobic infections?

Foul-smelling due to fermentation by anaerobes.

How do C. perfringens infections lead to tissue necrosis and gas formation?

Invasive infection with alpha toxin causing tissue damage and gas (gas gangrene).

What is the role of alpha toxin in C. perfringens pathology?

Phospholipase activity causing tissue damage and gas formation.

What organism is most associated with gas gangrene?

Clostridium perfringens.

What is a common management step for gas gangrene besides antibiotics?

Surgical excision or amputation when needed.

How dense is Bacteroides fragilis in human stool compared to facultative anaerobes?

B. fragilis ~10^11 bacteria/g stool; facultative anaerobes ~10^8 bacteria/g stool.

What metabolic lifestyle do anaerobes often use?

Fermentation-type metabolism.

What is a key feature of anaerobic infections on culture?

They are often mixed infections that grow slowly on complex media.

What is a hallmark of C. difficile's mechanism on host cells?

Glycosylation of Rho GTPases by glucosyltransferases A and B.

Which toxins are produced by C. difficile in GI disease?

Toxin A and Toxin B.

What is a major clinical feature of C. difficile infection?

Diarrhea and inflammation due to toxin-mediated damage.

What is the relationship between C. botulinum, C. tetani, and their toxins?

C. botulinum makes botulinum toxin; C. tetani makes tetanus toxin.

What is the difference between invasive and intoxication pathogenesis in Clostridia?

Invasive Clostridia invade tissue (e.g., C. perfringens); toxin-mediated disease (intoxication) from toxins like TeNT and BoNT.