Bacteria: Gram Negative Bacilli - Enteric Tract Flashcards
List the gram negative bacilli in the enteric tract
- Klebsiella Pnuemoniae
- Enterobacter spp
- Serratia Marcescens
- Salmonella Enteritidis
- Salmonella Typhi
- Shigella
- Escherichia Coli
- Yersinia Enterocoliticia
- Yersinia Pestis
- Camplyobacter Jejuni
- Vibrio Spp
- Helicobacter pylori
- Pseudomonas Aeruginosa
- Proteus Mirabilis
Enterobacter spp., Serratia marcescens, and Klebsiella pneumoniae bacteria
- gram-negative bacillus
- can cause pneumonia
- are common causes of UTIs
- are common nosocomial pathogens
- commonly exhibit multi drug resistance
- lactose fermenting bacteria
- form pink colonies on MacConkey agar
Enterobacter spp
- motile
- gram negative
- bacillus
Serratia marcescens
- gram negative
- bacillus
- motile
- produce a distinct red pigment
Klebsiella pneumoniae is common in
alcoholics, leads to abscesses, and often causes aspiration pneumonia
Klebsiella pneumoniae bacterial cells are surrounded by
a prominent polysaccharide capsule
The sputum produced by patients with Klebsiella pneumoniae is classically described as
“currant jelly sputum”
Klebsiella pneumoniae bacteria are
- gram negative
- bacillus
- immotile
- urease positive
Serratia marcescens produces a
distinct red pigment
Cavitary lesions resembling those in tuberculosis may develop in
Klebsiella pneumoniae pulmonary infections
Salmonella
- gram negative
- bacilli
- motile
- form black colonies on Hektoen enteric agar (HE) due to production of H2S (differentiating them from Shigella spp., which form green colonies on HE)
- encapsulated
- acid labile
- can cause osteomyelitis in sickle cell patients
- facultative intracellular within macrophages
Salmonella enteritidis and typhi bacteria form
black colonies on Hektoen enteric agar (HE) due to production of H2S (differentiating them from Shigella spp., which form green colonies on HE)
Chickens are the reservoir for
Salmonella enteritidis
Salmonella typhi colonizes
the gallbladder of chronic carriers
Typhoid fever
- caused by Salmonella typhi bacteria
- can present with a characteristic rash known as “rose spots”
- the khaki-green stools seen in typhoid fever are sometimes referred to as “pea soup” stools
Treatment for salmonella
fluoroquinolones are effective against Salmonella typhi (infections caused by Salmonella enteritidis typically do not require antibiotic therapy)
Vaccination for Salmonella typhi
a vaccination is available for Salmonella typhi only (the oral vaccine contains live attenuated Salmonella typhi, and the intramuscular vaccine includes a Salmonella typhi capsular antigen)
Salmonella enteritidis (and other nontyphoidal serotypes) most commonly cause
a self-limited gastroenteritis
Salmonella enteritidis and typhi bacteria possess
a type III secretion system that delivers effector proteins directly into host cells
Shigella
- gram negative
- bacilli
- immotile
- acid-resistant (a low inoculum is required to cause infection)
Shigella spp. bacteria form
green colonies on Hektoen enteric agar (HE) (differentiating them from Salmonella spp., which form black colonies on HE)
Shigella spp. invade
M cells in Peyer’s patches of the gastrointestinal mucosa (where they induce host cell apoptosis and manipulate actin filaments of the eukaryotic cytoskeleton to achieve intracellular motility)
Shigella spp. can
manipulate the eukaryotic cytoskeleton (primarily actin filaments) to achieve intracellular motility after invading M cells in Peyer’s patches of the gastrointestinal mucos
bloody diarrhea is a common symptom of
shigellosis
Shigellosis
- shigellosis can lead to gastroenteritis and diarrhea, characterized by the presence of leukocytes (predominantly neutrophils) in the stool
- bloody diarrhea is a common symptom
Shiga Toxin
Shiga toxin produced by Shigella dysenteriae can cause hemolytic uremic syndrome (HUS) due to cytotoxic effects on endothelial cells of the capillaries in glomeruli (leading to platelet adherence and aggregation → thrombocytopenia, microangiopathic hemolytic anemia, and acute kidney injury)
Microangiopathic hemolytic anemia (MAHA) often presents with
schistocytes in peripheral blood smear and is a component of hemolytic uremic syndrome (HUS) (caused by Shiga toxin producing strains of bacteria, such as Shigella dysenteriae)
Platelet adherence and aggregation in hemolytic uremic syndrome (HUS)
platelet adherence and aggregation in hemolytic uremic syndrome (HUS) (caused by Shiga toxin producing strains of bacteria, such as Shigella dysenteriae) occurs due to cytotoxic effects on endothelial cells of the capillaries in the glomerulus → thrombocytopenia, microangiopathic hemolytic anemia, and renal insufficiency
Young children are more commonly affected by
hemolytic uremic syndrome (HUS), which is caused by Shiga toxin producing strains of bacteria, such as Shigella dysenteriae
Shigella dysenteriae
produces Shiga toxin (virtually identical to the Shiga-like toxin of enterohemorrhagic E. coli) which inactivates the 60S ribosomal subunit
Shigella spp. bacteria possess
a type III secretion system that delivers effector proteins directly into host cells
E. coli
- gram-negative
- bacillus
- lactose fermenting
- form pink colonies on MacConkey agar
- encapsulated
- catalase positive
The K antigen of E. Coli is a
polysaccharide capsular antigen
E. coli bacteria form
characteristic metallic green colonies on eosin methylene blue (EMB) agar
The fimbriae of E. coli permit
adhesion to host cells
E. coli is the most common cause of
- urinary tract infections
2. gram negative sepsis
Only E. coli strains that possess the K1 capsular antigen cause
neonatal meningitis
Enterohemorrhagic E. coli (EHEC) is transmitted via
contaminated undercooked meat
Enterohemorrhagic E. coli (EHEC) can cause
bloody diarrhea
Escherichia coli O157:H7 can be differentiated from other strains of E. coli by
its inability to ferment sorbitol
Enterohemorrhagic E. coli (EHEC) produces a
Shiga-like toxin (virtually identical to the Shiga toxin of Shigella dysenteriae) which inactivates the 60S ribosomal subunit in host cells
Shiga-like toxin
(virtually identical to the Shiga toxin of Shigella dysenteriae) which inactivates the 60S ribosomal subunit in host cells
Platelet adherence and aggregation in hemolytic uremic syndrome (HUS) (caused by Shiga-like toxin producing bacteria, such as some strains of E. coli) occurs due to
cytotoxic effects on endothelial cells of the capillaries in the glomerulus → thrombocytopenia, microangiopathic hemolytic anemia, and acute kidney injury
Escherichia coli O157:H7 is an
enterohemorrhagic E. coli serotype that produces Shiga-like toxin, which can cause bloody diarrhea and hemolytic uremic syndrome (HUS)
Enterotoxigenic E. coli (ETEC) is a common cause of
“traveler’s diarrhea,” which often presents with watery diarrhea, abdominal cramping, nausea, and vomiting
Some strains of enterotoxigenic E. coli (ETEC) produce
- heat-labile toxin (LT), which overactivates adenylyl cyclase → increased cAMP → water and chloride efflux with decreased sodium reabsorption, resulting in watery diarrhea (secretory diarrhea)
- heat-stable toxin (ST), which overactivates guanylate cyclase → increased cGMP → decreased reabsorption of sodium and chloride, resulting in watery diarrhea (secretory diarrhea)
Enterotoxigenic E. coli (ETEC) is a common cause of “traveler’s diarrhea,” which often presents with
watery diarrhea, abdominal cramping, nausea, and vomiting
Yersinia enterocolitica
- gram negative
- bacillus
- Primarily transmitted via pet feces
- outbreaks are associated with daycare centers
- can be transmitted via contaminated milk and dairy products
Yersinia Pestis
- gram negative
2. bacillus
25°C is the optimal temperature for growth of
Yersinia enterocolitica bacteria (in contrast to Yersinia pestis, which is cultured most rapidly at 30°C)
Yersinia pestis and enterocolitica bacteria
- often exhibit bipolar (“safety pin”) staining on microscopy
- encapsulated
Yersinia enterocolitica infection can cause
bloody diarrhea
Yersinia enterocolitica infection can mimic
appendicitis (pseudoappendicitis)
rodents, such as rats and prairie dogs, are the main reservoir for
Yersinia pestis
fleas are the vector of
Yersinia pestis bacteria
intensely painful and swollen lymph nodes with overlying erythema (buboes) are characteristic of
Yersinia pestis infection
Disseminated Yersinia pestis infection can lead to
tissue necrosis and cutaneous hemorrhage, DIC, septic shock, and multiple organ dysfunction syndrome
Yersinia spp. bacteria possess
a type III secretion system that delivers effector proteins directly into host cells, such as Yersinia outer proteins (Yops)
_______ are effective against Yersinia spp.
- aminoglycosides (particularly streptomycin)
2. tetracyclines
An inactivated (killed) vaccine against Yersinia pestis is
available, though not routinely administered in the US
Campylobacter jejuni
- gram-negative
- curved bacillus
- thermophilic bacteria
- grows at 42°C
- oxidase positive
animals such as poultry, cattle, sheep, and dogs are common reservoirs for
Campylobacter jejuni
Campylobacter jejuniinfection can cause
bloody diarrhea
C. jejuni has a characteristic
“seagull wing” shape on microscopy
Campylobacter jejuni is an invasive pathogen and is able to
penetrate the intestinal epithelium, frequently leading to bloody diarrhea
Campylobacter jejuni infection is associated with
reactive arthritis
Guillain-Barre syndrome
can develop after a Campylobacter jejuni infection (characterized by progressive bilateral ascending weakness and loss of reflexes)
Vibrio cholerae
- gram-negative
- curved bacillus
- comma shaped bacilli
Cholera is endemic to
developing countries (outbreaks occur most commonly in southern Asia, Latin America, and Africa)
Vibrio cholerae can cause
profuse watery diarrhea, commonly referred to as “rice-water stool”
Transmission of Vibrio cholerae is
fecal-oral
The fimbriae of Vibrio cholerae
allow the bacteria to attach to (but do not invade) the intestinal mucosa and establish infection
Cholera toxin (choleragen) of Vibrio cholerae
activates adenylate cyclase in epithelial cells of the intestine → elevated cAMP, increased sodium and chloride efflux → profuse watery diarrhea (secretory diarrhea)
Cholera toxin permanently activates
Gs → overactivation of adenylate cyclase → elevated cAMP, increased sodium and chloride efflux → profuse watery diarrhea (secretory diarrhea)
Oral rehydration is the primary treatment of
cholera
Vibrio spp. bacteria preferentially grow in
alkaline media
Vibrio spp. bacteria are
- extremely acid-labile, and a high number of ingested organisms are required to cause infection
- oxidase positive
Vibrio parahaemolyticus and vulnificus infections are associated with
consumption of raw oysters
Helicobacter pylori is
- gram-negative
- curved bacillus
- motile
- urease positive
- oxidase positive
H. pylori’s ability to convert urea to ammonia and carbon dioxide is the basis of
the urea breath test
the development of gastric and duodenal ulcers is strongly associated with
Helicobacter pylori infection
Helicobacter pylori infection significantly increases the risk of developing
gastric adenocarcinoma
gastric mucosa-associated lymphoid tissue lymphomas (MALTomas) is associated with
Helicobacter pylori infection
Treatment of H. Pylori
- proton pump inhibitors are used in conjunction with clarithromycin and amoxicillin/metronidazole (triple therapy)
~90% of duodenal ulcers are associated with
Helicobacter pylori
Pseudomonas aeruginosa
- gram-negative
- bacillus
- thrives in aquatic environments
- oxidase positive
- catalase positive
- obligate aerobic pathogens
- encapsulated
- motile (Swarming motility)
Pseudomonas aeruginosa produces a
- characteristic blue-green pigment (pyocyanin and pyoverdin)
- a fruity grape-like odor when plated
Pseudomonas aeruginosa is a common cause of
nosocomial infections
Pseudomonas aeruginosa is a major cause of
lung infection and respiratory failure in cystic fibrosis patients
diabetics and IV drug users are at a higher risk of
Pseudomonas osteomyelitis
burn patients are at a higher risk of
Pseudomonas aeruginosa wound infections
Pseudomonas aeruginosa is associated with
indwelling catheters and is a common cause of nosocomial UTIs
Pseudomonas aeruginosa can cause a
- superficial infection of the hair follicle (characterized by a pruritic papulopustular rash) known as “hot tub folliculitis”
- otitis externa, or infections of the outer ear (also known as “swimmer’s ear”)
Pseudomonas aeruginosa sepsis can lead to
ecthyma gangrenosum, a rare cutaneous disease that presents with black, necrotic lesions
exotoxin A of Pseudomonas aeruginosa
inhibits elongation factor-2 by ADP ribosylation (a mechanism similar to that of diphtheria toxin)
the antipseudomonal antibiotics piperacillin and ticarcillin are effective against
Pseudomonas aeruginosa
fluoroquinolones can be used to treat
Pseudomonas aeruginosa infection
aminoglycosides can be combined with beta-lactam antibiotics to treat
Pseudomonas aeruginosa infection
Proteus mirabilis
- gram-negative
- bacillus
- swarming motility when plated
- urease positive
staghorn calculi (struvite stones composed of magnesium ammonium phosphate) are sometimes seen in cases of
urinary tract infection with urease-positive pathogens, such as Proteus mirabilis
struvite stones
precipitate in alkaline urine (the hydrolyzation of urea to ammonia by urease-positive organisms, such as Proteus mirabilis, increases urine pH to a neutral or alkaline level)
Proteus mirabilis causes
UTIs
Proteus mirabilis produces a
characteristic fishy odor
_____ are effective against Proteus mirabilis
sulfonamides
