Anaerobes and H. pylori Flashcards
Describe the normal gut microbiome
Each person has at least 160 different gut microbes
–57 shared by 90% of Europeans
–75 shared by 50%
–Two phyla account for 90% of the species
•Evidence that our core gut microbiome influences our body weight, CV health and tendency to develop of type II diabetes
What are the main anaerobic contributors to the gut microbiome?
Bacteriodes and Clostridia (note that anaerobes are the major players in the GI)
- Anaerobes are also prevalent in oral cavity, skin, colon, female genital tract
- Some (Clostridia) found in soil and air as spores
Why does oxygen kill anaerobes?
•Anaerobes lack SOD (superoxide dismutase) and catalase
–One of main reasons why the growth of anaerobes is inhibited by oxygen
–These enzymes eliminate the toxic compounds hydrogen peroxide and superoxide which are formed during production of energy by the organism
T or F. Anaerobic infections tend to stink
T. The odor is caused by metabolic end-products of the organisms which are mostly organic acids, but note that the lack of putrid smell does not rule out anaerobic infection
Also note that Special transport and culture are required fro anaerobes
When do anaerobes typically cause disease (abscesses)?
when they are introduced into normally sterile sites or when the balance of organisms is upset and pathogenic organisms overgrow
–Species found in abscesses often reflect the normal flora in that site.
T or F. Anaerobic infections are often polymicrobial (mixed anaerobic and facultative aerobic bacteria)
T.
Describe Bcteroides fragilis
This is a gram negative bacillus that is one of the most predominant organisms in the human colon and found in the vagina of 60% of women and represents the most common cause of serious anaerobic infections
Describe the pathogenesis of Bacteroides fragilis
–Infections usually arise from a break in a mucosal surface (Predisposing factors: surgery, trauma, chronic disease) and a Polysaccharide antiphagocytic capsule is the important virulence factor
–Host response to the capsule actually plays important role in abscess formation
How does Bacteroids fragilis infection present?
BF most commonly causes intra-abdominal infections marked by abscesses or peritonitis. Pelvic or peri-rectal abscesses, bacteremia, and infected decubitus ulcers can occur
In general, B. fragilis causes disease below the diaphragm, but are found in 25% of lung abscesses
–Enterotoxin producing strain can cause diarrhea
How is Bacteroides fragilis diagnosed?
anaerobic cultures
How is BF tx?
resistant to penicillin so tx with metronidazole, carbapenems, and combo beta/lactams with lactamase inhibitors
Describe Prevotella melaninogenica (formerly Bacteroides melaninogenicus)
This is a gram negative coccobacillus commonly found in the oral cavity, nasopharynx, GI tract, and vagina in compromised pts. (it is opportunistic! not commensal)
How does Prevotella melaninogenica present?
–Oral/periodontal abscesses
–Pulmonary abscesses/empyemas
–Chronic otitis
–Sinusitis
Describe Clostridium
Gram +, spore-forming rods (the ONLY anaerobic endospore-forming bacteria).
Note that Clostridium is resistant to both high heat and harsh environments (found in the colon and soil (as spores))
What is responsible for the pathogenesis of clostridium?
exotoxins and secreted hydrolytic enzymes
Describe Clostridium perfringens
this is a large, ‘boxcar’ gram+ bacilli found in soil and the colon
How does tetanus present?
The clinical presentation is marked by strong muscle spasms/spastic paralysis, first as trismus (lock jaw) resulting in a characteristic expression knwon as risus sardonicus. Reflexes become exaggergated and opisthotonos, pronounced arching of the back due to spasm of the strong extensor musles of the back (right) can occur. Respiratory failure typically follows.
