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 (-)
Escherichia coli are… [Gram stain, metabolism, shape distinctive morphology]
Escherichia coli are gram negative, facultative aneroebic bacilli that are typically part of the normal flora of the human colon.
They are catalase (+) and ferment lactose
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-hemolysin: Pore-forming
- Aerobactin: Iron siderophore
- Polysaccharide capsulse: Inhibits phagocytosis
- Pili/fimbriae: Forms attachments
What diseases 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
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
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 distinguishes 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)
Where is the reservoir for EHEC?
Cattle
Avoid infection by avoiding consumption of raw meat, unpasteurized dairy/juice
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 required to cause meningitis?
K capsule
Commonly causes meningitis in neonates
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 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
MacConkey agar culture: which enterobacteriaceae organisms might be growing on the left in this picture?
Any lactose fermentor
- E. coli
- Klebsiella
- Enterobacter
How is typhoid fever treated?
Always treat typhoid fever
- Antibiotics
- Fluroquinolone, ampicillin, chloramphenicol
- Note: Resistance is becoming more common
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)
Where is the environmental reservoir for Yersinia pestis?
What is the vector for human transmission?
Reservoir = rodents (prairie dogs in USA, rats historically)
Vector = fleas
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
How is Yersinia pestis infection treated?
Choice: Streptomycin or gentamicin
Alternative: Doxycycline or chloraphenicol
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
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
Bordetella pertussis 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 pertussis?
- Adhesins (pili, filamentous hemagglutinin, and pertactin)
- Endotoxin
- Exotoxins (4: pertussis toxin, adenylate cyclase toxin, dermonecrotic toxin, tracheal cytotoxin)
What does adenylate cyclase toxin of Bordetella pertussis do?
Inhibits leukocyte function by producing cAMP in the presence of host cell calmodulin
How communicable is Bordetella pertussis?
How is it transmitted?
Highly communicable
Via droplets
Most contagious during the catarrhal stage
What are the three stages of Bordetella pertussis infection?
- Incubation (2 weeks)
- Catarrhal stage: mild coughing and sneezing, patient is very infectious (most infectious stage)
- Paroxysmal stage: explosive cough followed by whoop during inhalation, may lead to exhaustion/cyanosis/vomiting/convusions, resolution is very slow
When is antibiotic treatment for Bordetella pertussis infection most effective?
What happens after this window?
What is true about antibiotic treatment after the onset of the paroxysmal stage of Bordetella pertussis infection?
Antibiotic treatment for Bordetella pertussis infection is most effective in the catarrhal stage, before the “whooping” symptoms begin
After the onset of the paroxysmal stage, antibiotic treatment is not as effective at altering the course of disease
tx is generally macrolides
Brucella spp. are [size, metabolic, Gram stan, shape]
Brucella are small aerobic Gram-negative coccobacilli
What cells can Brucella spp. survive in?
Macrophages
What is the clinical presentation of brucellosis?
undulating fever*, chills, malaise, anorexia, and drenching sweats
Infection can be chronic and last for weeks or months
What is the treatment for brucellosis?
- Doxycycline + rifampin/gentamicin/streptomycin
- Vaccine for animals not humans
Francisella tularensis are [size, metabolic, Grains stain, shape]
Francisella tularensis are small, metabolically facultative, Gram-negative coccibacilli
(similar in morphology to Brucella)
In which cells does Francisella tularensis multiply?
Macrophages
What is the clinical presentation of tularemia?
Site of innoculation is ulcerated
Regional lymphadenopathy
Fevers and chills
Possible pneumonia and dissemination to multiple organs
Pasteurella multocida are [size, Gram stain, shape, location where normally found]
Pasteurella multocida are small Gram-negative coccobacili that are part of the normal respiratory flora of some animals (especially cats and dogs)
How do humans become infected by Pasteurella multocida?
Cat or dog bite
Neisseria are [Gram-stain, shape]
Neisseria are Gram-negative diplococci
What antibiotics is Klebsiella pneumoniae resistant to?
All encode SHV Beta-lactamase on chromosome
- Resistant to ampicillin, amoxicillin
Some encode Extended-spectrum beta-lacatamase (ESBL)
- Resistant to all beta-lactams except carbapenem
Some encode Klebsiella pneumonia carbapenemase (KPC) or New Delhi Metalocarbapenemase (NDMC)
- Resistant to almost all beta-lactams inclucding carbapenem
What is notable about the polysaccharide capsule of Neisseria meningitidis?
Antiphagocytic and resists complement-mediated killing
Basis for serogrouping and target of vaccines
How does Neisseria gonorrheoae avoid immune clearance?
Produces pili that change their antigenic make-up during the course of infection (antigenic variation)
What kind of bacteria exhibit “swarming motility?”
Proteus spp
- Proteus mirabilis*
- Proteus vulgaris*
Which bacteria is associated with the formation of “struvite” kidney stones?
Why?
- Proteus* spp.
- Proteus* is urease positive
- Urease splits urea into ammonium hydroxide + CO2
- This raises urine pH (makes it more alkaline)
- This promotes the formation of struvite kidney stones
Which 3 members of Enterobacteraceae are associated with antibiotic resistant nosocomial respiratory infections, UTIs, and bloodstream infections?
- Enterobacter spp.
- Citrobacter spp.
- Serratia marcescens
Which bacteria is this likely to be?
Proteus spp.
Grows in this pattern due to swarming motility
What are the 6 medically-important gram-negative rods?
PAL-VCH
- Pseudomonas aeruginosa
- Acinetobacter baumanni
- Legionella pneumophila
- Vibrio cholerae
- Campylobacter jejuni
- Helicobacter pylori
A patient undergoing chemotherapy develops the following skin legion:
What is it called?
Which bacteria is causing the legion?
Ecthyma gangrenosum: A black eschar indicating cutaneous necrosis caused by Pseudomonas aeruginosa
The pre-med undergrad working in your lab forgot to label the bacterial cultures; your PI assigns you to determine which bacteria is growing in which plates.
What bacteria is this?
Pseudomonas Aeruginosa
Colors are due to pyocanain and pyoverdin (a siderophore)
May also have a grape-like odor
This is a picture of “coiling phagocytosis,” exhibited by which bacteria?
Legionella pneumophilia
This is a bacterial culture growing on BCYE agar
What bacteria is this?
What is in the agar helping the bacteria grow?
Legionella pneumophilia
- Not visualized on gram stain, overgrown by other respiratory flora on normal agar
BCYE agar = buffered charcoal-yeast extract agar
- Contains L-cysteine, agar, and antibiotics to prevent the growth of other bacteria
- Both an enrichment agar and a selective agar
This bacteria of the stomach is most likely…
Helicobacter pylori
Look for flagella and curved shape
What allows H. pylori to live in the acidic environment of the stomach?
Urease positive = cleaves ammonium hydroxide from urea. This creates a less acidic microenvironment in the mucus overlying the epithelium in which H. pylori grows, reproduces, and invades the stomach epithelium.
Pseudomonadas aeruginosa is a [Gram stain, metabolism, shape distinctive morphology]
Pseudomonas aeruginosa is a gram negative, obligate aerobic rod.
It is found in faucets, drains of hospitals and often has fluorescent pigments
It does not ferment; Catalase (+), oxidase (+)
What is exotoxin A?
Which bacteria secrets it?
Exotoxin A is secreted by Pseudomonas aeruginosa
It ADP-ribosylates EF-2 of the host ribosome. This inhibits protein synthesis and leads to cell death
(Functions similarly to diphtheria toxin)
What is quorum sensing?
Which bacteria have quorum-sensing abilities?
Quorum sensing allows bacteria to sense how many of them there are. Each bacteria secretes an autoinducer signal, and can sense the concentration of that signal.
Higher concentration => more bacteria are around => they secrete more toxins since there are enough of them to overpower host defenses
Pseudomonas aeruginosa has quorum-sensing abilities
Patient with which genetic disorder are likely to be infected with Pseudomonas aeruginosa?
Cystic Fibrosis
P. aeruginosa colonizes the lungs of CF patients; it causes repeat infections and is the most common cause of respiratory failure in this population
Which bacteria often causes skin infections in burn patients?
Pseudomonas aeruginosa
List the groups of patients and associated diseases that are likely caused by Pseudomonas aeruginosa
- Cystic Fibrosis patients -> Pneumonia
- Ventilated patients -> Pneumonia
- Burn patients -> Skin infection
- Catheterized patients -> UTI
- Neutropenic patients (undergoing chemo) -> Bacteremia
- IV drug users -> Osteomyelitis
- Diabetics -> Osteomyelitis
- Hot tub users -> Folliculitis
What causes Pseudomonas aeruginosa to appear fluorescent in cultures?
Siderophores
Pyocyanin and pyoverdin
How is Pseudomonas aeruginosa treated?
Very resistant to antibiotics; use 2 drugs until susceptibility is known
-
Choice: Aminoglycoside + beta-lactamase
- Piperacillin, ceftazidime, cefepime, ceftolozane-tazobactam, imipenem/peropenem, aztreonam
- Alternative: Quinolone + piperacillin
Note: Cephalosporins are not active against P. aeruginosa
Legionella pneumophilia is a [Gram stain, metabolism, shape distinctive morphology]
Legionella pneumophilia is a gram negative, obligate anaerobic, facultative intracellular, thin bacillus.
Oxidase (+)
Serogroup 1 causes 80% of disease
Infects amoebae
Where is Legionella pneumophilia found?
Natural bodies of water
Cooling towers of air-conditioning units
Water distribution systems
List the determinants of pathogenicity of Legionella pneumophilia
- Infects macrophages
- Type IV secretion system
- Phospholipase C
How does Legionella pneumophila infect macrophages?
Legionella pneumophila promotes coiling phagocytosis
- Promotes the formation of a long, thin, pseudopod by the macrophage
- The macrophage wraps around the bacterium, engulfs it in a coiled vesicle to create a phagosome
- This prevents the fusion of the phagosome with the lysosome
- Legionella pneumophilia recruits ribosomes to the phagosome and basically lives in the nice, new remodeled phagosome it has created
Describe the clinical presentation of Legionnaire’s disease
Nosocomial or community acquired pneumonia
Usually severe
- Fever >40.5 C (104 F)
- Respiratory symptoms
- Headache
- Change in neuro symptoms (headache and confusion)
- Nausea, vomiting, diarrhea
- Hyponatremia (low Na+ in blood)
- Patchy infiltrate in 1 lobe of lung (sometimes)
Pneumonia with respiratory symptoms, high fever >40.5 C, neurological symptoms, and GI symptoms is most likely caused by…
Legionella pneumophilia
Vibrio spp. is a family of [Gram stain, shape distinctive morphology]
Vibrio spp. are gram negative, curved rods that are “comma shaped”
Helicobacter pylori is a [Gram stain, metabolism, shape distinctive morphology]
Helicobacter pylori is a gram negative, slender, curved rod that grows best in microaerophilic environments (obligate aerobe that cannot survive in full oxygen)
Urease (+), Oxidase (+), Motile
List the determinants of pathogenicity of Helicobacter pylori
- VacA
- Urease (+)
- Flagella + Curved shape
- Adherence
- Type IV Secretion System
Describe the clinical presentation of an Helicobacter pylori infection
Peptic ulcer disease: Increased gastric acid production in the duodenum (caused by VacA, causes vacuolation)
Adenocarcinoma, non-Hodgkin lymphoma, MALT lymphoma: H. pylori is a risk factor. MALT lymphoma regresses in 50% of cases with antibiotic treatment
30% of people in the USA are infected with Helicobacter pylori
- Usually asymptomatic with GI inflammation
Campylobacter jejuni is a [gram stain, metabolism, shape]
Campylobatcer jejuni is a gram negative, obligate aerobe, that is a curved rod with a little twist
Which toxins ADP ribosylate EF-2?
Diphtheria toxin (Corynebacterium diphtheriae)
Exotoxin A (Pseudomonas aeruginosa)
What are some of the key differences that distinguish infection caused by Francisella tularensis and infection caused by Brucella spp.?
Type of fever
- F. tularensis = constant
- Brucella = undulant (rises and falls)
Type of animal that carries it
-
F. tularensis = Wild animals
- Rabbits, beavers, squirrels, muskrats
-
Brucella = Farm animals
- Cattle, goats, hogs
Distinguishing symptoms
-
F. tularensis = painful ulceration
- May lead to granuloma with caseating necrosis
-
Brucella = anorexia, arthralgia
- May lead to osteomyelitis, arthritis (esp. in sacroilliac joint)
