ICL 2.16: Anaerobes

Question 1

what are the characteristics of aerobic bacteria?

Answer 1

aerobic bacteria require oxygen as a terminal electron acceptor and will not grow under anaerobic conditions

they usually have cytochrome systems for the metabolism of O2, superoxide dismutase to breakdown harmful oxygen radicals and catalase to breakdown H2O2

Question 2

what does SOD do?

Answer 2

SOD = superoxide dismutase

found in aerobic bacteria because it breaks down harmful oxygen radicals

O2- + O2- + 2H+ –> H2O2 + O2

Question 3

what does catalase do?

Answer 3

found in aerobic bacteria because it breaks down hydrogen peroxide that gets formed from SOD breaking down oxygen radicals

2H2O2 –> 2H2O + O2

Question 4

what are the characteristics of anaerobic bacteria?

Answer 4

they cannot use oxygen for growth and metabolism

instead they obtain energy from fermentation or respiration using non-oxygen terminal acceptors like SO4, NO3, S, etc.

they require reduced O2 tension for growth = they need low oxidation-reduction potential since critical enzymes must be reduced to work

obligate anaerobes usually lack SOD and catalase –> the ability of different anaerobes to survive in O2 usually correlates with their relative abilities to produce SOD and catalase

Question 5

what is a microaerophilic anaerobe?

Answer 5

they grow very poorly in the presence of air (21% oxygen)

they grow better anaerobically

Question 6

what are facultative anaerobes?

Answer 6

they can grow either aerobically or anaerobically so they possess both oxidative and fermentation machinery

during infections, facultative anaerobes can initially utilize O2, but after O2 is exhausted, can switch to anaerobic metabolism

this type of growth can create anaerobic conditions and subsequently allow contaminating anaerobic bacteria to grow and produce disease

ex. E. coli
ex. streptococcus sp, enterobacteriaceae

Question 7

what are the roles of anaerobes in normal tissues?

Answer 7

1. synthesize vitamin K and other co-factors
2. deconjugate bile acids which allows for fat absorption
3. give stool its color, smell, consistency, and weight because bacteria are necessary for normal bowel movements
4. provide stimulation critical for healthy immune system
5. prevent pathogenic organisms from invading the body because no two objects can occupy the same space at the same time

the case and point is that anaerobes are a normal and vital part of the human body and are generally not pathogenic as long as they stay where they belong!!

Question 8

are most anaerobic infections endogenous or exogenous?

Answer 8

most anaerobic infections are from endogenous sources, though some are exogenous

endogenous = a disease arising from an infectious agent already present in the body but previously asymptomatic

Question 9

what are the commonly encountered human anaerobes?

Answer 9

1. gram (-) cocci = veillonella
2. gram (+) cocci = peptostreptococcus
3. gram (-) rods = bacteroides, porphyromonas, prevotella, fusobacterium, parabacteroids
4. gram (+) rods = clostridium, actinomyces, propionibacterium, bifidobacterium, lactobacillus, mobiluncus

Question 10

where are anaerobes found in the body?

Answer 10

anaerobes are found in multiple areas of the body as normal flora

1. skin
2. mouth
3. URT
4. intestines
5. genitourinary tract

many of these areas are in direct contact with air, but even strict anaerobes can live there because the microenvironment may be relatively devoid of oxygen due to oxygen consumption by aerobes and facultative anaerobes

Question 11

what are some of the anaerobic sites of the body that would be good for anaerobic bacteria?

Answer 11

1. sebaceous glands of the skin
2. gingival crevices of the gums
3. ymphoid tissue of the throat
4. lumina of the intestinal and urogenital tracts

Question 12

what are the 4 main human niches for anaerobic bacteria?

Answer 12

1. skin/conjuctiva
2. oral cavity
3. GI tract
4. GU tract (female)

Question 13

what is the major anaerobe found in skin/conjunctiva?

Answer 13

propionibacterium acnes

it’s found in hair follicles and sebaceous glands in both “jungle” and “desert” areas

Question 14

which anaerobes are found in the oral cavity?

Answer 14

they’re located in the tongue crypts, tonsillar crypts, gingival crevices

1. bacteroides
2. prevotella,
3. porphyromonas
4. fusobacterium
5. actinomyces

Question 15

which anaerobes are in the stomach?

Answer 15

the stomach normally has few anaerobes …most of the ones you do find are of oral origin

but the number of anaerobes increases as you progress down the GI tract

Question 16

which anaerobes are in the colon?

Answer 16

bacteroides fragilis are the major potentially pathogenic anaerobe in the colon followed by clostridium and peptostreptococcus

anaerobes compromise the majority of colon pathogens

Question 17

which anaerobes are in the GU tract?

Answer 17

vagina = bacteroides, clostridium, prevotella

urethra = bacteroides, clostridium

Question 18

what are the two ways that anaerobes produce disease?

Answer 18

1. enter an area where they are not normally found and set up a purulent inflammatory response = endogenous infection

infection/abscess usually includes multiple species of bacteria – usually a mix of aerobic and anaerobic bacteria

ex. brain abscess, lung abscess, peritonitis, PID, diverticulitis, appendicitis, human bite
2. introduction into anaerobic condition causes toxin production that results in disease manifestations

often exogenous infection but some are endogenous

ex. botulism, tetanus, clostridium perfringens diseases, clostridium difficile colitis

Question 19

which factors predispose you to anaerobic infections?

Answer 19

1. GI surgery or disase/female GU surgery/disease
2. oral cavity disease or trauma to/from the area
3. immunocompromised state
4. prior therapy with anti-aerobic antibiotics

Question 20

what are the characteristics of an anaerobic infection?

Answer 20

1. foul smelling discharge due to short-chain fatty-acid products of anaerobic metabolism
2. gas in the tissues
3. abscess formation
4. specimens contain organisms that can be observed by gram stain, but can not be cultured aerobically
5. infection in proximity to a mucosal surface

Question 21

how do you diagnose an anaerobic infection?

Answer 21

it is key to get a high quality specimen directly from the infection site of pus/fluid

also the specimen needs to be processed quickly and protected from O2

a direct Gram-stained smear of sample demonstrating Gram-negative and/or Gram-positive bacteria of various morphologies is highly suggestive/diagnostic for anaerobic infection

cultures are really slow and prone to failure so gram stain of a tissue sample is more useful for diagnosis

Question 22

in what media do anaerobic bacteria grow?

Answer 22

anaerobic culture of specimens is very slow and prone to failure

media must contain reducing agents and often need growth factors

also the polymicrobial nature of most infections require selective media to protect slow-growing anaerobes from being overgrown by hardier facultative bacteria

Kanamycin (like all aminoglycosides) does not inhibit growth of obligate anaerobes, thus it permits them to proliferate without being overgrown by rapidly growing facultative anaerobes

Question 23

how do you treat anaerobic infections?

Answer 23

1. surgical drainage of pus from absecess is often needed – likewise wounds with dead tissue have to be debrided
2. antimicrobial therapy

approach usually involves selecting antibiotics based on the expected susceptibilities of the anaerobes known to produce infection at the site in question

anaerobic organisms derived from the oral flora are often susceptible to penicillin, but infections below the diaphragm are usually caused by fecal anaerobes, of which many are resistant to β-lactams

also since it’s usually a mixed bacterial species infection , multidrug regimens are often used

Question 24

which antibiotics have excellent anaerobic coverage?

Answer 24

1. metronidazole
2. imipenem/meropenem
3. extended sprecum penicillins (ampicillin-clavulanate or pipercillin-tazobactam)
4. chloramphenical
5. vancomycin

Question 25

which anaerobes is vancomycin used to treat?

Answer 25

gram positive anaerobes only

Question 26

which antibiotics have fair to good anaerobic coverage?

Answer 26

1. cefoxitin
2. clindamycin

but with this one, resistance is increasing especially by B. fragilis…

it’s also preferred for infections above the diaphragm

Question 27

what is the DOC for anaerobic infections?

Answer 27

metronidazole

Question 28

what are bacteroides?

Answer 28

bacteroides species are anaerobic, bile-resistant, non-spore-forming, gram-negative rods that are normal components of the human flora

B. fragilis is the major pathogen in the group

Question 29

what is the DOT group?

Answer 29

B. distasionis

B. ovatus

B. thetaiotaomicron

they’re all in the bacteroides species = anaerobic, bile resistant, non-spore forming, gram (-) rods

Question 30

where are bacteroides found in the body?

Answer 30

bacteroides species comprise ~25% of flora in gut

they first appear in neonates 10 days after birth

then numbers increase at the time of weaning

Question 31

what is the relationship of bacteroides with their human host?

Answer 31

mutualistic relationship

1. the bacteria ferments carbohydrates to produce pools of volatile fatty acids –> the FAs are reabsorbed through large intestine and utilized by the host as energy source!
2. germ-free animals that lack gut flora need 30% more calories to maintain body mass

microbiota of obese individuals contain more Firmicutes and less Bacteroidetes

when lose weight, see increase in Bacteroidetes and decrease in Firmicutes

Question 32

in what scenario would b. fragilis cause disease?

Answer 32

they’re normally benign commensals in the gut flora

but, these organisms can cause significant disease if introduced into surrounding tissues

B. fragilis is introduced into sterile tissues by “rupturing” event like the rupture of appendix, gallstones, intestinal diverticulum, perforated peptic ulcer, acute pancreatitis, chronic peritoneal dialysis surgery, bowel gangrene, post-operative leaks/infected catheters in abdomen, and general trauma

you also need the presence of facultative anaerobe that can use up most O2 in infection site, allowing anaerobic environment for B. fragilis

it’s the only bacterium shown to induce abscess formation as sole infecting organism

Question 33

how does b. fragilis cause infections?

Answer 33

it possess fimbriae and adhesins that allow establishment in tissues

it also produces short chain fatty acids that inhibit phagocytosis & oxidative killing

Question 34

what is the function of the B. fragilis capsule?

Answer 34

polysaccharide capsule is clearly linked to ability to form abscesses

in fact, the injection of capsule alone can induce abscesses

its unique structure causes T cell activation that leads to abscess formation and promotes pyogenic inflammation

it also confers resistance to complement-mediated killing and phagocytosis-killing

but if you have antibodies against the capsule, they can prevent ability to produce abscesses

Question 35

how do you treat B. fragilis?

Answer 35

so you also need the presence of facultative anaerobe that can use up most O2 in infection site, allowing anaerobic environment for B. fragilis

so to treat B. fragilis infection, you have to kill both B. fragilis and the facultative anaerobe (ex. E. coli)

gentamicin would kill the facultative anaerobe but not bacteroids

metronidazole would kill bacteroides but not the facultative anaerobe

so you have to use both to prevent both sepsis and abscess formation!

Question 36

how do you diagnose a B. fragilis infection?

Answer 36

gram stain of abscess fluid usually shows mixed bacteria types

preliminary ID of B. fragilis can be made from gram-stain and colony morphology or stimulated growth in 20% bile

Question 37

what is b. fragilis resistant to?

Answer 37

1. kanamycin
2. vancomycin
3. colistin

Question 38

how do you treat B. fragilis infection?

Answer 38

surgical drainage accompanied by antibiotics

antibiotics should address both facultative anaerobes and strict aerobes

also B. fragilis usually produces β-lactamase, so penicillin is not useful

use metronidazole, cefoxitin or cefotetan, imipenem, or β-lactam/ β-lactamase inhibitor combination – you can combine these with aminoglycoside for synergistic effect in mixed infection

Question 39

how do you prevent B. fragilis infections?

Answer 39

you can’t

there are no preventative measures or vaccines for these infections

Question 40

FLASHCARD: microbiology, pathology, epidemiology, clinical, diagnosis, and treatment of bacteroids fragilis

Answer 40

MICROBIOLOGY: Gram-negative rod, strict anaerobic, capsule, normal flora in gut

PATHOLOGY: Normal flora on mucosal surfaces. Mucosal damage allows bacteria to invade into deeper tissues. Their capsule promotes abscess formation, together with facultative anaerobes that maintain anaerobic environment. Bacterial LPS promotes inflammation, & can even cause sepsis.

EPIDEMIOLOGY: Part of “normal” flora on mucosal surfaces, particularly the intestine. Introduction is usually endogenous due to leakage from intestine (e.g. surgery or rupture).

CLINICAL:. Surgery or damage allows bacteria on mucosa to invade deeper tissues. Together with facultative anaerobes, cause mixed infection that leads to abscess formation near point of mucosal rupture. Abscess is very resistant to antibiotic penetration, so must drain abscess to remove bacteria and allow direct access by immune cells and antibiotics. Abscess material will be dark and foul-smelling. Peritonitis is common, and can develop sepsis.

DIAGNOSIS: Initially based on clinical symptoms and epidemiology. Abscess usually forms near mucosal surface. Gram-stain of abscess fluid shows polymicrobial mixture with Gram-negative pleomorphic rods with vacuoles. Bacteria will grow from abscess fluid only under anaerobic conditions, and can grow in high bile. Also resistant to kanamycin, vancomycin, and colistin.

TREATMENT: Must drain abscess to allow drug access to infection. Antibiotics should address both facultative anaerobes and strict aerobes. Metronidazole, cefoxitin or cefotetan, imipenem, or β-lactam/ β-lactamase inhibitor combination.

Question 41

what are the 6 major anaerobes in mixed infections?

Answer 41

1. prevotella species
2. fusobacterium necrophorym
3. fusobacterium nucleatum
4. porphyromonas
5. peptostreptococcus
6. bifidobacterium

Question 42

what is prevotella?

Answer 42

gram (-) anaerobic bacilli

P. bivia and P. disiens commonly seen in female genital tract

P. melaninogenica associated with upper respiratory tract

all can be found in brain and lung abscesses, in PID, and tube-ovarian abscess

Question 43

what is the microbiology of fusobacterium necrophorum?

Answer 43

pleomorphic, anaerobic gram (-) long rods with round ends and sometimes bizarre forms

Question 44

which diseases are associated with fusobacterium necrophorum?

Answer 44

can cause severe infections of head & neck = Lemierre’s disease

neck abscess leads to acute jugular vein thrombophlebitis that progresses to sepsis

also have metastatic abscesses in lungs, mediastinum, pleural space, & liver

mostly in older children & young adults, & associated with infectious mononucleosis

also in polymicrobial intra-abdominal infections

Question 45

what is the microbiology of fusobacterium nucleatum?

Answer 45

anaerobic, pleomorphic gram (-) long rods with tapered ends = need shaped

Question 46

which diseases are associated with fusobacterium nucleatum?

Answer 46

seen in pleuropulmonary infections, obstetric infections, chorioamnionitis, and in brain abscesses complicating periodontal disease

significant component of gingival microbiota

it’s also in genital, GI, and upper respiratory tracts

Question 47

which very serious disease is associated with fusobacterium nucleatum?

Answer 47

many colorectal tumors contain F. nucleatum

treatments to reduce F. nucleatum also reduce tumor growth

these strains match the strains the patient has as normal flora in mouth

Question 48

what is the microbiology of porphyromonas?

Answer 48

anaerobic, gram (-) bacilli

Question 49

what is porphyromonas?

Answer 49

found in normal oral flora and other sites

involved in gingival and periapical tooth infections

also involved in breast, axillary, perianal, male genital infections

Question 50

what is the microbiology of peptostreptococcus? where is it found in the body?

Answer 50

anaerobic, gram (+) cocci

it’s found in the normal flora of skin, oral cavity, URT, GI, and female genitourinary

Question 51

which infections is peptostreptococcus involved in?

Answer 51

opportunistic!

mixed infections in brain abscesses, pleuropulmonary, necrotizing fasciitis & other soft tissue, intra-abdominal

Question 52

what is the microbiology of bifidobacterium?

Answer 52

anaerobic pleomorphic gram (+) rod

associated with mixed infections associated with oropharyngeal or bowel flora

Question 53

what is PID?

Answer 53

an infection of the uterus, fallopian tubes and other reproductive organs

it causes lower abdominal pain, scarring of reproductive tract, ectopic pregnancy, etc.

Question 54

what causes PID?

Answer 54

PID is initiated when bacteria migrate from the vagina or cervix into the reproductive organs

although usually initiated by an STI, other causes include lymphatic, postpartum, postabortal (either miscarriage or abortion) or IUD related, and hematogenous spread

Question 55

which bacteria cause PID?

Answer 55

many different organisms can cause PID, but most cases are associated with gonorrhea and chlamydia

anaerobes, such as Peptococcus and Bacteroides species, can also cause PID

also up to 30-40% of acute PID cases are polymicrobial

like people will have an initial infection by N. gonorrhoeae or C. trachomatis that may compromise mucosa or spread to parametrial structures, allowing bowel and/or normal flora to invade tissues

Question 56

which groups are high risk for PID?

Answer 56

1. Sexually active women in their childbearing years are most at risk

those under age 25 are more likely to develop PID because the cervix of teenage girls and young women is not fully matured, increasing susceptibility to STDs linked to PID

2. women who douche may be at higher risk because douching changes the vaginal flora in harmful ways or it can force vaginal bacteria into the upper reproductive organs
3. women may have an increased risk of PID near the time of IUD insertion

Question 57

how do you treat PID?

Answer 57

because of the difficulty in identifying organisms infecting the internal reproductive organs and because more than one organism may be responsible for an episode of PID, PID is usually treated with at least two antibiotics that are effective against a wide range of infectious agents

must be effective against C. trachomatis and N. gonorrhoeae, as well as against gram-negative facultative organisms, anaerobes, and streptococci

regimens include cefoxitan, cefotetan + doxycycline, clindamycin + gentamicin, ampicillin and sulbactam + doxycycline, and ceftriaxone or cefoxitin plus doxycycline

Question 58

what is bacterial vaginosis?

Answer 58

it’s an abnormal vaginal condition that’s not usually dangerous but can result in disturbing or serious sequella

normally the vaginal tract contains Lactobacillus species that maintain a relatively low pH that inhibits growth of many bacteria/yeast

but if Lactobacillus numbers are significantly decreased, will see increase of pH in vaginal tract > 4.5

this results in overgrowth of atypical bacteria in the vagina

Gardnerella vaginalis is the bacteria that is most commonly associated with vaginitis – it forms a biofilm in the vaginal epithelium that serves as a “scaffolding” to which other bacterial species adhere in a symbiotic fashion

Question 59

which bacteria is most commonly associated with bacterial vaginosis?

Answer 59

gardnerella vaginitis

anaerobic bacteria

Question 60

what are the risk factors for bacterial vaginosis?

Answer 60

1. multiple/new sex partners
2. IUDs
3. recent antibiotic usage
4. vaginal douching
5. smoking

it’s a disease of women only; mostly AA women

BV rarely affects women who have never had sex –> you can’t get BV from toilet seats, bedding, or swimming pools

Question 61

what are the symptoms of bacterial vaginosis?

Answer 61

many women with BV do not have symptoms (84%)

if you do have symptoms you may notice:

1. thin white or gray vaginal discharge
2. pain, itching, or burning in the vagina
3. a strong fish-like odor, especially after sex
4. burning when urinating
5. itching around the outside of the vagina

Question 62

which health risks can bacterial vaginosis cause?

Answer 62

1. increasing your chance of getting HIV if you have sex with someone who is infected with HIV
2. if you’re HIV positive, it increases your chance of passing HIV to your sex partner
3. if you’re pregnant, it makes it more likely you’ll deliver your baby too early
4. it also increases your chance of getting other STDs like chlamydia and gonorrhea

then the problem is that these bacteria can sometimes cause pelvic inflammatory disease (PID), which can make it difficult or impossible for you to have children

Question 63

how do you diagnose bacterial vaginosis?

Answer 63

there’s no perfect test, but using the Amsel criteria, usually see at least 3 out of the 4 following:

1. thing white/gray coating on vaginal walls
2. pH of vaginal discharge shows low acidity ( ph > 4.5)
3. fishy odor when vaginal discharge is combined with a drop of KOH on a slide = Whiff test
4. clue cells visible on microscopic exam of vaginal discharge

you should also test to rule out yeast infection and trichomonas vaginalis

Question 64

which drugs are recommended to treat vacterial vaginosis?

Answer 64

1. metronidazole

2. clnidamycin cream

Question 65

what are the major anaerobic pathogens from previous lectures?

Answer 65

1. propionibacterium acnes = endogenous
2. actinomyces spp. = endogenous
3. clostridium botulinum = usually exogenous
4. clostridium tetani = usually exogenous
5. clostridium perfringens = exogenous or endogenous
6. clostridium difficile = exogenous or endogenous