Gram (+) Bacilli

Question 1

List the gram (+) bacilli (8)

Answer 1

Bacillus anthracis 
Bacillus cereus
Clostridium tetani
Clostridium botulinum 
Clostridium difficile 
Clostridium Perfringens
Corynebacterium diphtheriae
Listeria monocytogenes

Question 2

What does Bacillus anthracis look like?

Answer 2

Large gram (+) rods in chains

Question 3

What is Bacillus anthracis’ capsule made out of?

Answer 3

Protein - Poly D glutamate

Question 4

Black eschar

Answer 4

Black, necrotic cutaneous lesion with surrounding erythematous ring

Caused by Lethal Factor (LF) of Bacillus Anthracis

Question 5

Bacillus Anthracis respiration

Answer 5

Obligate aerobe

Question 6

Bacillus Anthracis transmission

Answer 6

BA is spore forming. It hibernates in a state with low metabolic activity.

Bc of it’s tough coat it can survive in many environments and withstand temp changes

Spores are small and tough. They grow back into metabolic state when environment is favorable.

Question 7

The 2 toxins produced by bacillus anthracis

Answer 7

Lethal Factor and Edema Factor

Question 8

Lethal Factor (LF)

Answer 8

toxin produced by Bacillus anthracis

Symptoms will not be caused unless Edema factor is ALSO present

Exotoxin that acts as a protease and cleaves MAP Kinase.

MAPK is a signal transduction protein involved in the control of cell growth.

LF leads to tissue necrosis (black eschar)

Question 9

Edema Factor (EF)

Answer 9

toxin produced by Bacillus anthracis

Symptoms will not be caused unless LF is ALSO present

It’s an adenylyl cyclase that raises cAMP intracellularly

The higher cAMP causes fluid to move into extracellular space, causing edema.

Edema limits host defenses and indirectly prevents phagocytosis.

Question 10

What are the 2 bacterial groups that form spores?

Answer 10

Bacillus and Clostridium

Question 11

Pulmonary anthrax

Answer 11

Wool-Sorter’s Disease

Spores last a long time so they can get into soil/wool and stay there. When people handle the wool, they inhale the spores which germinate in the lungs.

Causes mainly pulmonary symptoms

Starts out with nonspecific symptoms like cough. You must catch and treat early bc it quickly progresses to mediastinal lymph nodes.

Symptoms quickly progress to hemorrhagic mediastinitis, which is a pulmonary hemorrhage. It is close to 100% mortality when pulmonary hemorrhage is seen.

Chest XR shows widened mediastinum

Question 12

Tx for anthrax

Answer 12

Treat early

Fluoroquinolones

Doxycycline (2nd choice)

Question 13

Bacillus cereus respiration

Answer 13

Obligate aerobe

Question 14

What is bacillus cereus infection most associated with?

Answer 14

Food poisoning!!!

Someone who comes in with vomiting or diarrhea after eating reheated fried rice.

Reheating triggers germination of the spores and toxin formation.

Question 15

Clostridium respiration

Answer 15

obligate anaerobes

Question 16

Clostridium tetani transmission

Answer 16

Often found in soil, but tetani needs to get under skin into anaerobic environment to cause infection. Ideally, it gets in through a puncture wound that’s been closed off to air (rusty nails, barbed wire)

Foreign object with tetani punctures body. Spores embed in flesh, vegetate and stay at wound site. Produces toxin (Tetanus Toxin/Tetanospasmin). The toxin causes the symptoms.

Question 17

Neuromuscular symptoms of tetanus

Answer 17

Spastic paralysis (relentless muscle contraction leading to rigidity)

Rhesus sardonicus - an evil grin or Lock Jaw symptoms (tense masseters prevent jaw from opening)

Opisthotonus - Extension/arching of back due to strong spasms of back muscles.

Question 18

Tetanus toxin mechanism

Answer 18

Tetanus toxin (Tetanospasmin) is from C.tetani

Tetanus toxin travels retrograde from the motor axons to the spinal cord

Acts as a protease. It cleaves SNARE proteins which inhibits exocytosis of neurotransmitters into synapses.

Cleavage of SNARE inhibits release of GABA and Glycine from Renshaw cells (normally these guys are inhibitory nt’s)

This leads to uncontrolled neuronal firing leading to spasms.

Question 19

Tetanus vaccine

Answer 19

Toxoid vaccine - it’s a toxin conjugated to a protein to increase immunogenicity. This causes antibody responses to the toxin, but not to the bacteria.

Question 20

How is Clostridium Botulinum transmitted?

Answer 20

Through improper canning of foods

Improper/insufficient heating cycles when canning allows spores to survive. They then germinate and thrive in the anaerobic environment of the sealed can and make a ton of heat-stable toxin.

“A couple of family present with very similar symptoms (neuro symptoms)” - May have shared the same food!

Question 21

Clostridium Botulinum symptoms

Answer 21

Flaccid paralysis - going limp. Tough to keep body upright.

Caused by absence of muscle contraction

A descending paralysis (starts superiorly and goes down - NOT like Guillen-Barre)

First symptoms may be eye symptoms - Diplopia and ptosis

Question 22

Clostridium Botulinum toxin mechanism

Answer 22

The preformed toxin is absorbed in the gut and travels to peripheral nervous system via blood to cause symptoms

It only affects PNS, bc it CANNOT CROSS BBB

Toxin cleaves SNARE protein, which prevents fusion of vesicles with presynaptic nerve terminals (just like tetanus). The difference is that Botulism attacks motor neurons that release ACh. Ach normally excites and its release causes contractions. Its absence means no contractions which means flaccid paralysis.

Question 23

What is the difference between Botulinum toxin and Tetanus toxin?

Answer 23

The target:

Tetanus = GABA, Glycine releasing cells - spastic paralysis

Botulinum = ACh releasing cells - flaccid paralysis

Question 24

Floppy Baby Syndrome

Answer 24

Clostridium botulinum infection in babies.

Causes same flaccid paralysis, but the ingestion of the toxin is different.

Adults do not normally get sick from ingesting spores (we need the preformed toxin to get sick). The bacteria itself is weak.

In babies, they do not have robust GI flora yet. They have a perfect anaerobic environment without competition. Spores can germinate and produce toxin in babies.

The spores are normally ingested from honey. Infants should avoid honey.

Infantile botulism is more common than adult botulism

Question 25

What are the 2 toxins produced by Clostridium difficile?

Answer 25

Exotoxin A - binds to brush border enzymes of intestines and causes inflammation, cell death, and watery diarrhea Exotoxin B - depolymerizes actin to disrupt cytoskeleton integrity. Leads to enterocyte death and necrosis. Leads to yellow-ish gray exudate that forms a pseudomembrane that covers the colonic mucosa (pseudomembranous colitis)

Question 26

When do people typically contract a C. diff infection?

Answer 26

It's a nosocomial diarrhea. People get it while hospitalized. Spores are easily transmitted patient to patient without proper precautions (make sure to wash hands with soap and water...wiping shit down alone doesn't do enough here) C.Diff does not compete well with normal flora (like botulinum), but many patients in the hospital are on antibiotics so... that's a problem Common antibiotic that predispose to C.Diff is Clindamycin (Clinda + poor hand washing = copious diarrhea)

Question 27

Which antibiotic is most associated with C. diff infection?

Answer 27

Clindamycin (also Ampicillin)

Question 28

How can we know if diarrhea is from C.diff vs something else?

Answer 28

2 ways: 1) Visualize the pseudomembranes directly (histo/endoscope) 2) Look for toxin in stool with assays (PCR). We are looking for toxin in the stool, NOT the microbe. 1/3 of hospital pts are colonized for C.Diff (not that many infected) so bacteria in stool is just meh.

Question 29

Tx for C.Diff infection

Answer 29

Oral Vancomycin (not absorbed well in gut so it stays there to do its thing) - oral also lowers the typical side effects of vanco. IV is not useful. OR Metronidazole

Question 30

Which Clostridium species is most associated with motorcycle accidents or deep penetrating wounds from military combat?

Answer 30

C. Perfringens Both scenarios are instances where large amounts of flesh are exposed to dirt/dust - this is important bc C. Perfringens is spore forming and therefore likes the dirt/soil

Question 31

Gas Gangrene

Answer 31

One of 2 diseases classically caused by C. Perfringens "Claustridial myonecrosis" When claustridium enters the wound and causes infection a gas is produced under the infected tissue. This presents as crepitus (crackling sound on palpation) Gas is produced as organism consumes carbs. The myonecrosis is due to an alpha toxin called Lecithinase that cleaves lecithin (a phospholipase) and damages cell membranes. Lecithinase causes RBC hemolysis if RBC membranes are affected. On blood agar, it forms a double zone of hemolysis You need to plate C. Perfringens in anaerobic environment (this should give it away in the question) Tx = IV Penicillin G

Question 32

What toxin causes Gas Gangrene?

Answer 32

Lecithinase from C. Perfringens

Question 33

How do you treat Gas Gangrene?

Answer 33

IV Penicillin G

Question 34

Describe the food poisoning associated with C. Perfringens?

Answer 34

One of the 2 major illnesses linked to C. Perfringens Causes a late-onset watery diarrhea. Food poisoning is the result of ingesting a large amount of spores that must germinate in gut and then produce toxin (that's why it's not immediate). Does not usually require an antibiotic - it's a transient infection like most diarrheas. Unique bc all others needed a preformed toxin to infect adults. C. Perfringens does not.

Question 35

What does cornybacterium diphtheriae look like?

Answer 35

Club shaped Metachromatic granules that stain with aniline dye like methylene blue or toluidine blue (red granules with rest of cell blue) V or Y formation

Question 36

Diphtheria toxin

Answer 36

an exotoxin secreted by corynebacterium diphtheriae Has 2 subunits: Subunit A = active. Subunit B = Binding. Toxin causes ADP-ribosylation of elongation factor 2. This inhibits ribosome formation and therefore protein synthesis. This leads to cell death and formation of pseudomembranes (thick grayish exudate over mucosa of oropharynx) Throat and tonsils bc the infection is transmitted through respiratory droplets. Colonizes oropharynx and can spread to larynx and trachea causing airway obstruction. Can cause lymphadenopathy that looks like a characteristic neck thickening (Bulls Neck)

Question 37

What happens if diphtheria toxin makes it into blood?

Answer 37

Systemic effects in heart and NS Life threatening myocarditis - presents with arrhythmias and heart block Local paralysis beginning in posterior pharynx and may lead to other cranial nerve issues - caused by toxin damaging myelin of nerve fibers

Question 38

How do you diagnose a diphtheria infection?

Answer 38

Definitive dx requires a culture or a toxin assay Swab grayish membrane and plate them in 2 special agars: Tellurite agar Loeffler's Medium In vitro assay on filter paper that has anti-toxin on it. If toxin binds to it there's a rxn and we can say we have a toxic strain: Elek's Test.

Question 39

Elek's Test

Answer 39

Assay to determine Diphtheria infection

Question 40

What special agars are used to plate Corynebacterium diphtheriae?

Answer 40

Tellurite Agar and Loeffler's Medium

Question 41

Diphtheria vaccine

Answer 41

Toxoid vaccine - inactivated toxin bound to protein. Given routinely in USA. Often given with tetanus toxoid and acellular pertussis vaccine in TDaP Produces powerful IgG response

Question 42

How do you treat a patient with diphtheria who was never vaccinated?

Answer 42

Passive immunity via anti-toxoid Look out for patients who are immigrants! Kids are not vaccinated from many countries

Question 43

Listeria hemolysis

Answer 43

Narrow zone. B-hemolytic.

Question 44

Listeria respiration and motility

Answer 44

Facultative intracellular - can live and reproduce inside and outside of cells. When it's outside of cell, it uses its flagella for motility - It has "tumbling motility" extracellularly Inside the cell it rapidly polymerizes actin against the bacterial wall so it's propelled in opposite direction. They can even jump cell to cell like this - "Actin rockets"

Question 45

What environments are associated with Listeria?

Answer 45

Cold environments. It survives and multiplies in near-freezing temperatures.

Question 46

What food items are typically associated with Listeria contamination?

Answer 46

Unpasteurized milk Packaged meat Soft Cheeses

Question 47

Who is most at risk of contracting a Listeria infection?

Answer 47

Pregnant women are 20x more likely to get Listeria infections. They make up most cases. Infection early on can lead to termination of pregnancy. Later term infections lead to disease in the newborn. Pregnant women shouldn't eat soft cheeses. Listeria is 3rd most common cause of meningitis in newborns (GBS, E Coli) Listeria can also cause meningitis in elderly > 60

Question 48

Who is at risk of developing meningitis from Listeria?

Answer 48

Newborns, Older adults (>60)

Question 49

Tx for Listeria

Answer 49

Ampicillin Tx of meningitis in adults normally is vancomycin and cephtriaxone to cover gram(+) and gram(-) but in elderly add ampicillin to cover Listeria.