Anaerobic Infections

What is classical botulism?

a food-borne botulism, an intoxication due to consumption of contaminated food in which the bacterium has grown anaerobically and produced toxin -flaccid paralysis and respiraotry failure treatment: remove toxin from GI tract

What is clostridium dificile?

an example of an iatrogenic infection (caused by medical treatment) -begins when a patient is treated with an antibiotic for a bacterial infection

What bacteria is present in the colon?

because it is a completely anaerobic environment, obligate anaerobes outnumber facultative bacteria by a factor of 100 or 1000

how can obligate anaerobes survive and grow on the skin?

because they are growing in the skin and not on the skin *they are growing down in the sweat glands, the sebaceous glands, and hair follicles and beneath the dead keratinized cells of the stratum corneum, in environments that are shielded from oxygen

What are the most typical medications that produce clostridium dificile?

clindamycin or fluoroquinolones

What do aerotolerant anaerobes possess?

enzymes for detoxifying the toxic metabolites of oxygen, such as hydrogen peroxide, superoxide anion and hydroxyl radical

What is very informative of obligate anaerobes?

gram stain -often they will be seen in gram stain but no tin culture

What is wound botulism?

rarest form of the disease in the US -wound is infected with c. botulinum spores and the toxin is produced in vivo treatment: cleanse and give antitoxin

What is the pathogenesis of C. tetani?

spores enter wound, germinate, organisms multiply, produce toxin -need lowered oxidation-reduction potentail due to tissue damage and mixed bacterial flora

What is on thy dry areas of the skin?

staphylococcus epidermis is numerically predominant, although the obligate anaerobes of the genus propionibacterium are also present

What is present on the oily areas of the skin such as the nose, forehead and scalp?

the propionibacteria outnumber the staphylococci

Why do medications lead to clostridium dificile?

they disrupt the normal bowel flora nad open up an ecological niche for the overgrowth of antibiotic-resistant bowel flora, such as C. dificile

Why are anaerobes important part of our normal flora?

they help interfere with the colonization of pathogens by copeting for our nutrients and modulating the innate immune syste, they ferment carbohydrates and produce volitle fatty acids that can be used by the host for energy, they secrete Vitamin K and bile acids and they influence the development of an intact mucosa and the associated lymphoid tissue

What are anaerobes that are less strict with oxygen?

"aerotolerant" anaerobes -they can survive exposure to oxygen for a longer period of time and few may even be able to grow in very low concentrations of oxygen intermediate between atmospheric levels and full anaerobiosis

What are more sensitive to oxygen anaerobes?

"strict" anaerobes

What is clostridium?

-large anaerobic, Gram-positive, endospore-forming rods -prominent in soil and are also present in the gastrointestinal tracts of humans and animals -pathogenesis is based on the production of exotoxins, including cytolytic and histolytic enzymes which degrade tissue -typcially are exogenous infections caused by wounds, or food poisoning due to ingestion of preformed toxin

What is b. fragilis

-most important anaerobic pathogen in humans -it is obligately anaerobic, non-sporeforming, non-motile, Gram-negative, small pleomorphic rod, sometimes coccobacillus -resistnat to many common antibiotics -has a polysaccharide capsule which serves as an important virulence factor -it is antiphagocytic and promotes abscess formation (polysaccharide A) -has LPS but it has weak endotoxic activity -produces superoxide dismutase and catalase

What is c. botulinum?

-oval, subterminal spores -large, grayish colonies, hemolysis usually present

What does C. dificile do?

-produces large amounts of cytotoxin when it grows to high levels which causes diarrhea and which kills colon epithelial cells and results in the formation of necrotic pseudomembraneous plaques on the bowel mucosa; this can lead to bowel perforation, peritonitis and death

What is C. tetani?

-round terminal spores in long, narrow pleomorphic rods -motile (peritrichois flagella) -colonies with "ground-glass" appearance, hemolytic, thin, spreading growth

What is clostridium perfringes?

-very large rods, encapsulated within tissue, nonmotile -rapid growth, double zone of hemolysis on anaerobic blood agar plate -organisms ferment carbohydrate in muscles with gas production -many varied toxins are produced

What are obligate anaerobes?

1) bacteria which will not grow and cannot survive for very long in the presence of oxygen 2) they must be cultured in the absence of oxygen 3) they must obtain their energy from fermentation instead of respiration

What clinical signs are indicative of anaerobic inections?

1) infection site in proximity to mucosal surfaces normally harboring anaerobes 2) involvement of sites with tissue necrosis or abscess 3) foul odor 4) gram stain revels multiple morphotypes of bacteria indicating the presence of multiple species 5) presence of gas in the tissues 6) no growth in culture but lots seen on grma stain 7) failure of an injection to respond to antibiotics that are not active against anaerobes

How do you diagnose an infection of anaerobic bacteria by bacteriologic methods?

1) proper specimen collection 2) rapid transport to the microbiology lab 3) proper handling in the laboratory

What two categories can the anaerobic bacteria be divided into?

1) the genus Clostridium 2) anaerobic members of our resident microbial flora which have escaped their usual location and have invaded parts of the body that are normally sterile

What are the reasons why oxygen may be detrimental to obligate anaerobes?

1) they may not have the ability to deal with toxic byproducts produced in aerobic respiration > buildup would cause autoassassination 2) oxygen may react with sensitive targets in the cell oxidizing them to a form that is not functional and leading to cell death (iron sulfur centers)

What is infant botulism?

C. botulinum infects and colonizes the gastrointestinal tract of newborn infants and produces toxin in vitro -the source of C. botulinum is frequently honey containing viable spores

What are the important clostridiums?

-C. tetani -c. perfringens -C. botulinum C. dificile

What are bacteriodes?

-anaerobic gram-negative rods which are a major component of the normal flora in the colon and are also represented in the mouth -ressitant to the aminoglycoside antibiotics

What are the different pathogens of bacteriodes?

-b. fragilis -b. thetaiotamicron -b. melaninogenicus