Gram Negative Bacteria Flashcards
What are some of the distinctive characteristics of the Enterobacteriaceae family?
- Gram negative
- Facultative anaerobes
- Form Bacilli and Cocobacilli
- Many are commensals of the human colon that cause disease under certain circumstances
- Most can ferment glucose
- Oxidase (-)
Which members of the enterobacteriaceae family cannot ferment glucose?
Salmonella
Shigella
Proteus
Escherichia coli are… [Gram stain, metabolism, shape distinctive morphology]
Escherichia coli are gram negative, facultative aneroibic bacilli that are typically part of the normal flora of the human colon.
They are catalase (+) and ferment lactose
List the 5 subtypes of E. coli
ETEC = Enterotoxigenic
EHEC = Enterohermorrhagic
EPEC = Enteropathogenic
EIEC = Enteroinvasive
EAEC = Enteroaggregative
What is significant about an organism that turns MacConkey agar pink?
The organism ferments lactose
List the determinants of pathogenicity that apply to all E. coli subtypes
- Alpha-heymolysin: Pore-forming
- Aerobactin: Iron siderophore
- Polysaccharide capsulse: Inhibits phagocytosis
- Pili/fimbriae: Forms attachments
What dieseases are commonly associated with E. coli infection?
Meningitis
UTI
Septic Shock
Nosocomial infections
Diarrhea (5 types)
How is an E. coli infection diagnosed?
Culturable on routine media
EMB agar: appears metallic green
MacConkey agar: turns the agar pink due to ability to ferment lactose
How are UTI and kidney infections caused by E. coli treated?
Trimethoprim/sulfamethoxazol
nitrofuratoin
fosfomycin
What are the determinants of pathogenicity of ETEC?
2 toxins that are plasmid encoded and act on gut epithelial cells
- Heat labile (LT): An A-B Toxin, increases cAMP
- Similar to cholera toxin
- Heat stable (ST): Increases cGMP
Describe an ETEC infection
Enterotoxigenic diarrhea
- “traveller’s diarrhea”
- Watery stools
- 24-72 hr incubation period
- Spread through food and water contaminated with human wasta
How is ETEC infection diagnosed?
ETEC grows cultures from stools
ELISA PCR available for ST and LT, but is not commonly used
An E. coli strain positive for ST and LT is most likely..
ETEC
- Causes enterotoxigenic diarrhea
- “Traveler’s diarrhea”
- Watery stools
How is ETEC infection treated?
Rehydration
Ciprofloxacin or other fluroquinolone
How can ETEC infection be prevented?
Avoid raw veggies, pre-peeled fruit, unpasturized dairy, lukewarm cooked foods
Describe the Type III Secretion System
Type III secretion systems…
- Form attachment and effacement lesions
- Replace normal microvilli with pedastals at the point of attachment
- Inject bacterial proteins into the cytoplasm of host cells by…
- Secretion apparatus is embedded into the host cell membrane
- > Secretes toxins to the exterior of the bacterium - Several secreted proteins insert into the host cell membrane and form a translocation complex
- > Translocates toxins into the host cytoplasm - Toxins have enzymatic activity, act as effector proteins
What are the determinants of pathogenicity of EHEC?
- Type III Secretion Systems
- Injects toxin into host cell
- Shiga-like toxin
- Inhibits 60s unit of the human ribosome
- Fimbriae
- Forms attachment and effacement lesions
Describe an EHEC infection
Enterohemorrhagic diarrhea E. coli
- Bloody diarrhea
- Crampy
- Absent or low-grade fever
- May lead to hemolytic-uremic syndrome (10% of case)
What is hemolytic-uremic syndrome?
Accompanies ~10% of cases of EHEC; a result of shiga-like toxin
- Decrease in platelets
- Renal failure
- Toxin damages endothelial cells in glomerulus -> Clumps of platelets form -> Causes lysis of RBCs
- CNS dysfunction
What distinguises EHEC from other E. coli strains?
- Cannot ferment sorbitol
- Immunoassay for shiga-like toxin in stool
- O157:H7 serotype causes massive outbreaks
How is EHEC infection treated?
Rehydration
(do NOT use antibiotics)
How can EHEC infection be prevented?
Avoid undercooked meat and unpasteurized diary or juice
Infection with which E. coli subfamily is associated with consumption of raw meat?
EHEC (enterohemorrhagic)
Where is the reservoir for EHEC?
Cattle
Avoid infection by avoiding consumption of raw meat, unpasteurized dairy/juice
Describe an EPEC infection
Enteropathogenic E. coli
- Associated wtih childhood diarrhea in developing countries
- Fever, bloody diarrhea
What are the determinants of pathogenicity of EPEC?
Enteropathogenic E. coli
- Bundle-forming pili
- Responsible for initial attachment to intestinal epithelium
- Type III secretion system
- Injects Tir into cell membrane
- Acts as a receptor for intimin (an adhesin)
Describe the mechanism of action of EPEC infection
- Bacteria bind to intestinal epithelial cells using bundle-forming pili
- Disruption of the overlying mucosa
- Fever, bloody diarrhea
- Disruption of the overlying mucosa
Where are EPEC and EIEC most commonly found?
Outside of the United states
Causative agents of diarrhea in developing countries
Describe EAEC infection
Diarrhea in developing countries
(Rarely seen in the USA)
Which E. coli determinant of pathogenicity is associated with sepsis?
LPS
Salmonella enterica is a [Gram stain, metabolism, shape distinctive morphology]
- Salmonella enterica* is a gram negative, facultative intracellular, facultative aerobic, bacillus.
- Cannot ferment glucose or lactose
- Motile (has flagella)
- H2S (+)
- Acid labile (usually killed by stomach acid)
Which E. coli determinant of pathogenicity is associated with UTIs (bladder infections/lower UTI)
Type 1 fimbriae
Which E. coli determinant of pathogenicity is required to cause meningitis?
K capsule
Commonly causes meningitis in neonates
Which E. coli determinant of pathogenicity is associated with upper UTI/kidney infection?
P pili
What is the reservoir for Salmonella enterica serovar typhi?
Gallbladder of human carriers
What is the reservoir for Salmonella enterica serovar enteritidis?
Farm animals/uncooked chicken
Turtles and other reptiles
What are the determinants of pathogenicity of Salmonella enterica serovar enteritidis?
Unique to S. enteritidis:
- Type III Secretion systems
- SPI1 (Salmonella pathogenicity island 1)
- Causes ruffling on the surface of enterocytes
- Induces internalization of S. enteritidis
- SPI2
- involved in dissemination of the bacteria
- SPI1 (Salmonella pathogenicity island 1)
Common to S. enterica serovars:
- Large inoculum causes disease
- Bacteria survive and multiply in phagosomes of macrophages
- Causes bacteremia when disseminated in bloodstream
Which cells are most often inhabited by a Salmonella enterica infection?
Macrophages
What is the clinical presentation of a Salmonella enterica sevofar enteritidis infection?
24-48 hours after ingestion…
- Inflammatory diarrhea (food poisoning)
- Nausea, vomiting
- Fever in 50% of individuals
- Bacteremia in 8% of healthy individuals
What is unique about the diarrhea caused by Salmonella enteria serovar enteritidis, as compared to that caused by ETEC or EPEC?
Salmonella enteriditis is a bacteria of developed countries that causes ~15% of food-bourne illness in the USA
ETEC and EPEC are common in developing countries, and are often seen in the US in individals who have traveled to these countries
How is Salmonella enteritidis infection treated?
The infection is self-limiting but…
- Treat in immunocompromised patients or severe infections (bacteremia)
- Fluroquinolones or ampicillin
- Otherwise, antibiotics is not typically recommended because it may induce a carrier state
MacConkey agar culture: which enterobacteriaceae organisms might be growing on the left in this picture?
Any lactose fermentor
- E. coli
- Klebsiella
- Enterobacter
How is a Salmonella enterica infection diagnosed?
Routine stool culture (for S. enteritidis or S. typhi)
- Appears black on hektoen agar
- Motile
- H2S positive
- Acid labile (killed by acid)
Can also do blood culture for S. typhi
Which individuals are most susceptible to infection by Salmonella enterica?
Individuals with less stomach acid than normal
- Pts taking -prazole drugs (protone pump inhibitors)
- Pts. with H. pylori infection
- Elderly people
(Also pts who are immunocompromised)
(higher pH than normal)
In the United States, Salmonella typhi infection is most commonly seen in which individuals?
Travellers returning from Mexico, Latin America, Asia, India
What is the clinical presentation of an individual infected wtih Salmonella typhi?
Typhoid Fever
- Prolonged fever
- Persistent bacteremia
- Constipation or diarrhea
- if diarrhea, “pea soup”
- Abdominal pain
- Occasional rash (pale, pink macules)
- Occasional carrier state
- Reservoir in galstones, shed in feces
How is typhoid fever treated?
Always treat typhoid fever
- Antibiotics
- Fluroquinolone, ampicillin, chloramphenicol
- Note: Resistance is becoming more common
How are Salmonella enterica infections prevented?
S. enteritidis
- Don’t eat raw/undercooked chicken
- Hand hygiene if playing with farm animals
S. typhi
- Parenteral capsular vaccine
- Live attenuated oral vaccine
- Administerd in the United States for travelers to Central/South America, Asia, Africa
What are the determinants of pathogenicity of Salmonella typhi?
Unique to S. typhi serovars:
- Can induce a carrier state in human (Typhoid Mary)
- Reservoir in gallbladder; gallstones become infected
- Shed in feces
Common to S. enterica serovars:
- Large inoculum causes disease
- Bacteria survive and multiply in phagosomes of macrophages
- Causes bacteremia when disseminated in bloodstream
Yersinia pestis is [Gram stain, metabolism, shape, distinctive morphology]
Yersinia pestis is a gram negative, facultatively anaerobic, bacillus.
It is encapsulated and has a bipolar appearance on a gram stain (“closed safety pin)
What are the 3 medically relevant Yersinia species?
- Yersinia pestis - Bubonic plague
- Yersinia enterocolitica - Infectious diarrhea
- Yersinia pseudotuberculosis - Infectious diarrhea
Where is the environmental reservoir for Yersinia pestis?
What is the vector for human transmission?
Reservoir = rodents (prarie dogs in USA, rats historically)
Vector = fleas
What are the 3 infections that may be caused by Yersinia pestis?
Bubonic plague
Pneumonic plague
Primary septicemic plague
Describe the mechanism of Yersinia pestis infection from rodents to humans
Hms locus required for colonization in the flea foregut
- Flea bites rodent reservoir
- Y. pestis colonizes the foregut, inhibits swallowing
- Causes flea to regurgitate last blood meal (containing Y. pestis) into new prey
-> New prey has been inoculated with Y. pestis
What are the determinants of pathogenicity of Yersinia pestis?
- Adhesins Ail
- Chromosomally encoded adhesin
- Type III secretion system
- Secretes YOPS
- YOPS (effector proteins)
- Intoxicate host
- Disable macrophages and neutrophils
- Inhibition of phagocytosis and cytokind production
- Allows bacteria to multiply to large numbers very quickly
- Capsule: Fra1 (aka F1)
- Antiphagocytic
- Pla: Plasminogen activator
- Cleaves fibrin to prevent clot formation
- Allows for dissemination in the body
Which Yersinia pestis determinant of pathogenicity allows the bacteria to multiply in large numbers in the human body?
YOPS: The effector proteins secreted by the Type III Secretion system
- YOPS disable macrophages and neutrophils -> inhibits phagocytosis and cytokine produciton
Describe the clinical presentation of bubonic plague
After 2-6 day incubation period (following flea bite)
- Bubo forms (painful, swollen lymph node)
- Fever, chills, myalgias, arthralgias, headache
- Bubo enlarges; dry, erythematous
- If no treatment
- LPS release
- Septic shock (secondary septicemic plague)
- Necrosis of appendages
- Bacteria may invade macrophages of lungs
- Allows spread of disease via aerosols
Which Yersinia pestis-associated disease is caused by a flea bite?
Bubonic plague
(no bubo in pneumonic plague or primary septicemic plague)
Describe the clinical presentation of pneumonic plague
1-4 day incubation period after inhalation of Y. pestis aerosols
- Fever, chills, headache, myalgia, weakness
- Productive cough, may be bloody
- Dyspnea
- Very severe
- Contagious via aerosols
Describe the clnical presentation of primary septicemic plague
Follows direct inoculation of Y. pestis into bloodstream
- Gastroenteritis
- Nausea, vomiting, diarrhea, abdominal pain
- No bubo = late diagnosis
How is primary vs. secondary septicemic plague contracted?
Primary = direct inoculation of Y. pestis into bloodstream
Secondary = septic shock following bubonic plague
Which Y. pestis infection is most associated with gastroenteritis?
Primary septicemic plague
How is a Yersinia pestis infection diagnosed?
Blood cultures; Yersinia grows on normal lab media
If bubonic: culture bubo samples
If pneumonic: culture sputum samples
Giesma stain: Yersinia pestis has a bipolar appearance, like a closed safety pin
How is Yersinia pestis infection treated?
Choice: Streptomycin or gentamicin
Alternative: Doxycycline or chloraphenicol
How can Yersinia pestis infection be prevented?
There is a killed whole-cell vaccine, but it is not well tested and has unclear efficacy
It is not available in the USA
A patient with an inflammed dry, painful, erythmatous lymph node was hiking in Arizona last week.
What is your leading diagnosis?
How would you confirm your hypothesis?
Leading diagnosis: Bubonic plague caused by Yersinia pestis infection
Confirm with blood and bubo culture; look for bipolar/closed safety pin-shaped bacteria on a giemsa stain
What organism causes dysentery?
Shigella dysenteriae
What kind of bacteria appear in this image?
Yersinia pestis;
Bipolar/closed safety pin appearance
This is a Giemsa stain
Klebsilla pneumoniae is a [Gram stain, metabolism, shape, distinctive morphology]
Klebsilla pneumoniae is a gram negative, facultatively anaerobic bacillus.
Ferments lactose, immotile, urease positive
What diseases are caused by Klebsiella pneumoniae?
Nosocomial infections
- Hospital-acquired pneumonia
- UTIs (esp. catheterized patients)
- Blood infections
- Wound infections/sepsis
Community acquired infections in immunocompromised individuals
- Alcoholics
- Diabetics
- Patients with chronic respiratory disease
What are the determinants of pathogenicity of Klebsiella pneumoniae?
- Polysaccharide capsule
- Prevents phagocytosis
- Prevents complement deposition
- Makes siderophores
- Can scavenge iron
- Very resistant to antibiotics
What is the clinical presentation of a Klebsiella pneumoniae infection?
May cause pneumonia, UTI, or wound infection
Forms abscesses
Typically affect HADRs:
- Hospitalized patients
- Alcoholics
- Diabetics
- Indivdiuals with chronic Respiratory disesae
Haemophilus are [size, Gram stain, shape, metabolic]
Haemophilus are small Gram-negative coccibacilli that grow both aerobically and anaerobically
What symptoms does Haemophilius influenzae cause?
Otitis media, sinusitis, bronchitis, epiglottitis, pneumonia, and meningitis
Bortedella are [Gram stain, shape]
Bordetella are Gram-negative coccobacilli
Bordetella pertusis is [size, Gram stain, shape, metabolic]
Bordetella pertusis are tiny Gram-negative coccobacilli that are strict aerobes
What are the determinants of pathogenicity of Bordetella pertusis?
- Adhesins (pili, filamentous hemagglutinin, and pertactin)
- Endotoxin
- Exotoxins (4: pertussis toxin, adenylate cyclase toxin, dermonecrotic toxin, tracheal cytotoxin)
What are three adhesins used by Bordetella pertusis?
What do they do?
- Pili
- Filamentous hemagglutinin
- Pertactin
Allow adherence to ciliated epithelial cells in the upper airway
In addition to allowing adherence to ciliated epithelial cells in the upper airway, what does filamentous hemagglutinin (FHA) of Bordetella pertusis do?
Mediates adherence to PMNs
(BInding of pertussis toxin increases number of FHA receptors on the cell surface of PMNs, increasing FHA binding and bacterial internalization, which allows them to survive inside phagocytes)
What two types of toxins does Bordetella pertussis have?
- Endotoxin
- Exotoxins (4)