Gram- Bacilli

Question 1

this is the most common cause of food poisoning in humans, is self-limiting at 5-7 days, and presents with non-specific GI symptoms (ie, nausea, vomiting, abdominal cramps, bloody diarrhea)

Answer 1

campylobacter

Note: rare long-term complications include stimulation of the body’s immune response to destroy nerves (Guillan-Barre syndrome)

Question 2

Which of the following statements about the Campylobacter jejuni strain is FALSE?

A. the reservoir of human infections from this organism are found in contaminated food, usually poultry

B. it requires blood agar and antibiotics (to reduce other flora) to grow in vivo

C. some strains produce a secreted toxin and invasive strains posess a plasmid

D. it is unique from shigellosis in that it does not require adhesins to colonize the GI tract

E. treatment regimen includes fluid replacement and azithromycin

Answer 2

D.

On the contrary, adhesins are critical to the pathogenesis of all organisms that must be able to adhere to a surface that is in constant motion (ie, peristaltic GI tract, ciliated URT, etc.)

Question 3

gram-negative, curved or comma shaped bacteria that characteristically produce the enzyme urease and move about with flagella

Answer 3

helicobacter pylori

Question 4

Which of the following statements about H. pylori is INCORRECT?

A. it is the only known pathogen that can survive and grow in the stomach

B. it easily develops resistance and must be treated with triple antibiotic therapy - a PPI and 2 classes of antibiotics

C. its pathogenecity islands encode a type III secretion system that enables bacterial toxins to be delivered into host epithelial cells

D. it causes peptic ulcers and is linked to increased incidence of gastric carcinoma if left untreated

E. it produces a vacuolating cytotoxin (vacA) that causes vacuole formation in host epithelial cells, leading to necrosis

Answer 4

C.

H. pylori uses a type IV secretion system. A type IV secretion system is comprised of multiple core proteins that form a channel through which DNA and proteins can travel from the cytoplasm of the bacterial cell to the cytoplasm of the recipient cell. (see picture)

Question 5

Which of the following statements about Vibrio cholerae is FALSE?

A. It is gram negative and comma-shaped, like H. pylori

B. It has a single flagellum and is highly motile

C. It differs from the other gram negative bacilli in that it is alkaline and salt-intolerant

D. in the USA infections with this organism are associated with ingestion of contaminated raw seafood - in southeast Asia it is transmitted by drinking contaminated water.

E. these bacteria must be ingested in large quantitiy to cause disease

Answer 5

C.

The opposite is true. V. cholerae is alkaline and salt-tolerant and can grow at a wide range of temperatures and a relatively high pH.

Question 6

Strains of C. diphtheria, Bacillus anthracis, and V. cholerae all produce two-part toxins that belong to what family of toxins?

Answer 6

The AB toxins. The enzyme component of these toxins (A) enters the host cell through endosomes produced by the binding protein (B), and interferes with the cell’s function through ADP-ribosylation of G proteins.

Question 7

A school nurse at a local high school reported a high degree of absenteeism of the football team following a team dinner on the previous Saturday. Some players had been to the hospital with severe diarrhea and low-grade fever, others had reported vomiting but soon reocvered, others reported no symptoms at all. Stool samples from two hostpialized individuals yielded Gram-negative bacteria growing on Campy-bac agar at 42ºC. What organism is likely responsible for the outbreak, and how should it be managed?

A. H. pylori, and it should be managed with triple antibiotic therapy

B. Campylobactor jejuni, and it should be managed with fluid replacement only

C. V. cholerae, and it may be managed with antibiotics and fluid replacement

D. Campylobactor jejuni, and it should be managed with azithromycin and fluid replacement

E. Campylobactor jejuni, and it should be managed with vancomycin and fluid replacement

Answer 7

D.

Question 8

Which of the following statements about Enterobacteriaceae is FALSE?

A. They are all facultative anaerobes

B. They are all non-lactose utilizing

C. They all utilize glucose as their sole carbon and energy source

D. They are all generally transmitted via the fecal-oral route

E. They are all gram negative rod shaped bacteria

Answer 8

B

Shigella and Salmonella are non-lactose utilizing, but E. Coli does utilize lactose.

Question 9

Which pathogenic group of E. Coli are responsible for producing a toxin that may be disseminated from the GI tract to cause renal damage (ie, hemolytic uremic syndrome)?

A. ETEC

B. EIEC

C. EPEC

D. EHEC

Answer 9

D.

ETEC = Enterotoxigenic E. Coli

EIEC = Enteroinvasive E. Coli

EPEC = Enteropathogenic E. Coli

EHEC = Enterohemorrhagic E. Coli

Question 10

Which pathogenic group of E. Coli causes an infection that is clinically indistinguishable from shigellosis?

A. ETEC

B. EIEC

C. EPEC

D. EHEC

Answer 10

B

Question 11

Which pathogenic group of E. Coli causes an infection that is commonly referred to as traveler’s diarrhea through the production of two enterotoxins?

A. ETEC

B. EIEC

C. EPEC

D. EHEC

Answer 11

A.

The two toxins are a heat stable and a heat labile toxin. All symptoms are due to toxin production - there are no histological changes to the GI tract

Question 12

Which pathogenic group of E. Coli causes an infection that is associated with undercooked contaminated meat, and effects histological changes of the GI epithelia?

A. ETEC

B. EIEC

C. EPEC

D. EHEC

Answer 12

C

Question 13

Which pathogenic group of E. Coli produces shiga-like toxin, which binds to receptors on kidney cells, and may cause damage that leads to renal failure?

A. ETEC

B. EIEC

C. EPEC

D. EHEC

Answer 13

D.

Note: antibiotics are thought to make EHEC infections worse - renal dialysis is the treatment of choice.

Question 14

Which of the following statements about Salmonella is FALSE?

A. Salmonella growth is mediated by genes located on a pathogenicity island and a type III secretion system.

B. S. typhi causes human disease and is transmitted via infected livestock animals.

C. Salmonella are facultative intracellular pathogens.

D. Salmonella are easily killed by the gastric secretions of the stomach.

E. Salmonella has an incubation period of 6-24 hours (ie, it’s an infection, not an intoxication)

Answer 14

B.

Typhoidal strains of salmonella are pathogens of human reservoirs only.

Question 15

Which of the following statements about typhoid fever is FALSE?

A. incubation period may be up to 7 days

B. S. typhi bacteria grow within phagocytic cells and are disseminated throughout the body

C. patients with typhoid fever exhibit high fever and delirium, usually accompanied by watery diarrhea

D. the most widely accepted treatment of chronic typhoid infection is removal of the gallbladder.

E. S. typhi is the only strain of Salmonella that is encapsulated.

Answer 15

C.

Patients typically do not display GI symptoms.

Question 16

this organism is a gram neg lac neg enterobacteria that does not possess flagella and is attributed mainly in the US to daycare outbreaks

Answer 16

Shigella (particularly S. sonnei)

Like S. typhi, it is a human only pathogen!

Question 17

Which of the following is a way that Shigella is unlike Salmonella?

A. it is a facultative intracellular pathogen

B. it replicates in the cytosol of the host cell

C. it utilizes a type III secretion system

D. it produces micro ulcerations in the colonic mucosal epithelia, leading to pus and blood in the stools.

E. it multiplies intracellularly and then spreads laterally, invading neighboring epithelial cells

Answer 17

B.

This is an important differentiating characterisitinc between the intracellular growth of Shigella and Salmonella. S**almonella must remain within an intracellular vacuole of the host cell to replicate whereas Shigella, although originally internalized into a host cell via a phagocytic vacuole, must be released into the cytosol in order to replicate.

Question 18

the production of this toxin by Shigella dysenteriae strains is due to lysogenic conversion and may lead to hemolytic uremic syndrome

Answer 18

Shiga toxin

Note: lysogenic conversion is the phenomenon in which virulence genes being carred on a bacteriophage genome are integrated into the bacterial chromosome, following infection of the bacteria by the phage

Question 19

this opportunistic organism is gram-negative and rod-shaped with fermentative capability, produces copious amounts of mucus, and is associated with cystic fibrosis, severe burns and hospital-associated infections.

Answer 19

Pseudomonas aeruginosa

Question 20

burns infected with P. aeruginosa characteristically have greenish colored pus, do to production of these two types of blue/green pigments

Answer 20

pyoverdin and pyocyanin

Question 21

exotoxin produced by P. aeruginosa

Answer 21

exotoxin A

Question 22

this organism is derived from the normal flora, but posesses virulence factors like RTX and Pap to become the most common cause of community and hospital associated UTIs

Answer 22

E. Coli

Question 23

this member of the Enterobacteriaceae forms copious amounts of mucus, is lactose-fermenting like E. Coli, but is nonmotile

Answer 23

Klebsiella pneumoniae

Infection with Klebsiella is associated with a specific antigenic type of capsule (K1 serotype) and resistance to antibiotics is a major problem.

Question 24

this organism exhibits “swarming” on the agar plate due to its high motility, uses urease like heliobacter, and is the most common cause of kidney stone formation following infection

Answer 24

Proteus mirabilis

Question 25

A 10 year old girl was attending a fourth of July fireworks display with her parens when she wandered off into the area housing many fireworks. During the display, one firework landed in this area resulting in a massive explosion. The child was in close proximity to this explosion and suffered 2nd and 3rd degree burns on her arms and trunk. She was immediately transported to the hospital and started on IV therapy with prophylactic antibiotics and wound debridement. After 48 hours despite anitbiotic therapy, some of her wounds exhibited a greenish colored pus oozing from these sites. The girl developed a low-grade fever and became lethargic and her vital signs became quite unstable. What organism is the most likely cause of this infection?

A. K. pneumoniae

B. Proteus mirabilis

C. Pseudomonas aeruginosa

D. E. coli

E. S. pneumoniae

Answer 25

C.

P. aeruginosa is a common cause of infection in burn patients and produces two pigments (pyoverdin and pyocyanin) that give pus its greenish color.

Question 26

Which of the following statements about Bordatella pertussis is FALSE?

A. causes a highly contagious, violent respiratory illness in unvaccinated children, and prolonged coughing in vaccinated children

B. it is an aerobic, nutritionally fastidious organism that must be grown in very selective media

C. the incubation period is at least 1 week

D. antibodies to bordatella often appear in the serum during an acute infection and are used to diagnose whooping cough

E. it produces an AB toxin among many others

Answer 26

D.

Antibodies often do not appear in the serum until after an acute infection has resolved, making a definitive diagnosis generally retrospective.

Question 27

Which of the following statements regarding Haemophilus is INCORRECT?

A. in addition to its LOS endotoxin, it produces numerous exotoxins that mediate its pathogenesis

B. it is part of the normal flora on the mucosal surfaces of the URT

C. it is rarely invasive and is treated with beta lactams

D. conjugate vaccines that use a protein carrier attached to the polysaccharide capsule B have provided the best effectiveness against Hib

E. virulent strains produce neuraminidase and an IgA protease

Answer 27

A.

Haemophilus produces no demonstrable exotoxins, just an LOS endotoxin and an antiphagocytic polysaccharide capsule (Hib). Non b-capsule virulence factors are unknown.

Question 28

this organism produces similar types of infections as H**aemophilus, but is a diplococcus rather than a rod and is far less fastidious, growing on a wide range of mediums

Answer 28

Moraxella

These bacteria do not often cause progression to bacteremia are a marker for severe underlying disease. Since they produce beta-lactamase, must treat with a beta-lactam/beta-lactamase inhibitor combo, or a 2nd or 3rd generation cephalosporin

Question 29

Which of the following statements regarding Legionella pneumophila is FALSE?

A. Infections genereally occur in older generations and immunocompromised

B. They are aerobic organisms with many natural reservoirs of infection and exist in biofilms

C. They are facultative intracellular pathogens

D. It is a fast-growing organism and causes pneumonia-like iillness when inhaled via water droplets

E. Is best treated with macrolides (azithromycin)

Answer 29

D. This organism is slow growing (takes 3-7 days) and its colonies have a ground glass appearance. May cause serious illness (Legionnaires’ disease) or self-limiting milder disease (Pontiac fever).