Gram Negative Bacteria Flashcards
How are samples of Bordetella pertussis collected and grown?
Collected from nasopharynx
Grown on Bordet-Gengou medium or charcoal-containing medium
How is Klebsiella pneumoniae infection diagnosed?
Culture specimen from infection on routine lab media
- Plump, gram (-) rods
- Hypermucoviscous strains overproduce capsule and have a hypermucoid appearance
On MacConkey agar
- Turns the agar pink (can ferment lactose)
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)
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
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)
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
Which E. coli determinant of pathogenicity is associated with upper UTI/kidney infection?
P pili
This is a picture of stomach epithellium:
What bacteria are also present?
What is allowing this bacteria to live in the acidic environment of the stomach?
Helicobacter pylori
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.
Why are patients with liver disease more sucesptible to life-threatening bacteremia due to Vibrio vulnificus infection?
Liver disease = iron overload
The bacteria grow really well when there is a lot of iron around
List the determinants of pathogenicity of Legionella pneumophilia
- Infects macrophages
- Dot - “Defect of Organelle Trafficking” genetic locus
- Type IV secretion system
- Phospholipase C
Why do patients with multiple UTIs often develop kidney stones?
UTIs caused by Proteus are associated with “struvite” kidney stones
- Proteus* is urease positive;
- Urease -> splits urea into ammonium hydroxide -> raises pH -> Kidney stone formation
How do humans become infected with Francisella tularensis?
Contact with rabbits, squirrels, muskrats, beavers, and deeper through tiny breaks in skin, exposure of mucous membranes, ingestion, or inhalation (also via ticks)
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
What is Dot?
Which bacteria posesses it?
Why is it important?
Dot stands for “defect of organelle trafficking”
It is a genetic locus posessed by Legionella pneumophilia
It carries the genes necessary to block phagosome/lysosome fusion, promote ribosome recruitment, and express a Type IV Secretion system
What is the clinical presentation of brucellosis?
Fever*, chills, malaise, and drenching sweats
Infection can be chronic and last for weeks or months
(Fever may be undulant; rise and fall)
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
Which bacteria often causes skin infections in burn patients?
Pseudomonas aeruginosa
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
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
What is tracheal cytotoxin of Bordetella pertussis?
Peptidoglycan fragment that inhibits/kills ciliated cells and is pro-inflammatory
What was the old vaccination strategy for pertussis?
Why was it discontinued?
Whole-cell killed vaccine combined with toxoid vaccines against tetanus and diphtheria
Poor long-term efficacy of pertussis component; seizures and hyporesponsive episodes; frequent side effects in kids
Which Y. pestis infection is most associated with gastroenteritis?
Primary septicemic plague
How is a Legionella pneumophilia infection diagnosed?
- Visualize with dieterle silver stain (Poorly visualized with gram stain)
- Grows on BYCE agar (but grows slowly)
- Direct fluorescent antibody
- Urinary antigen test
- Only detects serogroup 1
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)
Describe the clinical presentation of pontiac fever
Which bacteria is it caused by?
Fever and malaise
Usually self-limiting and not severe
Caused by Legionella pneumophilia
Neisseria are [Gram-stain, shape]
Neisseria are Gram-negative diplococci
List the determinants of pathogenicity of Pseudomonas aeruginosa
CASCQET - E (Like casket-y… kind of a stretch)
- Can survive at high temperatures (42 C)
- Adhesions
- Siderophore-producing
- Capsule
- Quorum Sensing
- Exotoxin A
- Type III Secretion System
- Endotoxin
What is the reservoir for Salmonella enterica serovar enteritidis?
Farm animals/uncooked chicken
Turtles and other reptiles
What virulence factor is linked to Traveler’s diarrhea?
LT
Heat Labile Toxin secreted by ETEC
What are the characterisitcs that define Enterobacteriaceae?
Gram negative rods that colonize or infect the GI tract
How does Legionella pneumopilia infect macrophages?
Legionella pneumophilia 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
Which cells are most often inhabited by a Salmonella enterica infection?
Macrophages
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
What antibiotics are used to treat Bordetella pertussis infection?
Macrolides
(TMP/SMX may also be effective)
How is ETEC infection treated?
Rehydration
Ciprofloxacin or other fluroquinolone
How is typhoid fever treated?
Always treat typhoid fever
- Antibiotics
- Fluroquinolone, ampicillin, chloramphenicol
- Note: Resistance is becoming more common
Where is the reservoir for EHEC?
Cattle
Avoid infection by avoiding consumption of raw meat, unpasteurized dairy/juice
Why is carbapenem used to treat Klebsiella pneumoniae?
Klebsiella pneumoniae is typically resistant to most early-line beta-lactam antibiotics
What diseases are associated with Enterobacter spp?
Often antibiotic resistant…
- Nosocomial respiratory infections
- UTIs
- Bloodstream infections
Which groups are more likley to be infected by Legionella pneumophilia?
- Smokers
- Alcoholics
- Elderly
- COPD patients
- Immunocompromised patients
Describe the clinical presentation of a Vibrio vulnificus infection
Severe gastroenteritis and/or wound infection following cuts exposed to sea water
Life-threatening bacteremia in anyone with iron overload (liver disease)
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)
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
How is Pseudomonas aeruginosa treated?
Very reisistant 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: Cefalosporins are not active against P. aeruginosa
Bordetella pertusis is [size, Gram stain, shape, metabolic]
Bordetella pertusis are tiny Gram-negative coccobacilli that are strict aerobes
What kind of bacteria appear in this image?
Yersinia pestis;
Bipolar/closed safety pin appearance
This is a Giemsa stain
Describe an EPEC infection
Enteropathogenic E. coli
- Associated wtih childhood diarrhea in developing countries
- Fever, bloody diarrhea
Brucella spp. are [size, metabolic, Gram stan, shape]
Brucella are small aerobic Gram-negative coccibacilli
A patient presents with this rash after spending a week at a ski lodge. He his typical day on this vacation included skiing, drinking beers, and sitting in the hot tub.
What do you think is causing this rash?
Pseudomonas aeruginosa
He likely acquired the bacteria from the hot tub
What kind of bacteria exhibit “swarming motility?”
Proteus spp
- Proteus mirabilis*
- Proteus vulgaris*
Campylobater jejuni is a [gram stain, metabolism, shape]
Campylobater jejuni is a gram negative, obligate aerobe, that is a curved rod with a little twist
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
Which serogroup of Neisseria meningitidis causes large outbreaks in Africa?
Serogroup A
What does dermonecrotic toxin of Bordetella pertusis do?
Localized tissue destruction in infection
Which E. coli determinant of pathogenicity is associated with sepsis?
LPS
How does Neisseria gonorrheoae avoid immune clearance?
Produces pili that change their antigenic make-up during the course of infection (antigenic variation)
What are the three stages of Bordetella pertusis infection?
- Incubation (2 weeks)
- Catarrhal stage: mild coughing and sneezing, patient is very infectious
- Paroxysmal stage: explosive cough followed by whoop during inhalation, may lead to exhaustion/cyanosis/vomiting/convusions, resolution is very slow
How is a Helicobacter pylori infection diagnosed?
Poorly visualized with gram stain, does not grow well in culture
- Endoscopy w/tissue biopsy
- Stain with giesma or silver stain
- Check urease activity using assay or breath test
- Serologic tests for specific IgG
- But IgG levels do not fall until 6 months after infection is cleared by abx
- Antibody test to detect H. pylori in stool
Describe the clinical presentation of an Helicobacter pylori infection
Peptic ulcer disease: Increased gastric acid production in the duodenum
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
Which Yersinia pestis-associated disease is caused by a flea bite?
Bubonic plague
(no bubo in pneumonic plague or primary septicemic plague)
Which diagnostic lab test finding is Bordetella pertussis infection associated with?
Atypical lymphocytosis
Acinetobacter baumannii is a [Gram stain, metabolism, shape distinctive morphology]
Acinetobacter baumannii is a gram negative, non-fermenting, bacillus or coccobacillus
What is the modern vaccination strategy for pertussis?
What is the booster?
Which group of people is recommended to receive Tdap and when?
DTap: uses acellular components of Bordatella pertussis (detoxified pertussis toxin, FHA, pertactin, fimbriae) to generate immunity
Tdap booster (reduced amounts of diphtheria and pertussis components)
Pregnant women should receive Tdap with each pregnancy
How is Neisseria gonorrhoeae transmitted?
What is the clinical presentation?
Sexually transmitted (gonorrhea)
Local infections such as urethritis and cervicits but can spread regionally to cause epididymitis and pelvic inflammatory disease or systemically to cause disseminated gonorrhea
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
This is a bacterial culture growing on BCYE agar
What bacteria is this?
What is in the agar helping the bactera 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
Where do Vibrio live?
Sea water, fresh water
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 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 do Brucella spp. cause?
Brucellosis in humans as well as cattle, goats, and hogs
What diseases are associated with Proteus spp?
UTIs (Hospital Acquired and Community Associated)
Also associated with nosocomial infections
A patient undergoing chemotherapy develops the following skin legion:
What is it called?
Which bacteria is causign the legion?
Ecthyma gangrenosum: A black eschar indicating cutaneous necrosis caused by Pseudomonas aeruginosa
How can Legionella pneumophilia infection be treated?
Disinfect hospital water systems
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
Which E. coli determinant of pathogenicity is associated with UTIs (bladder infections/lower UTI)
Type 1 fimbriae
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)
List the 5 subtypes of E. coli
ETEC = Enterotoxigenic
EHEC = Enterohermorrhagic
EPEC = Enteropathogenic
EIEC = Enteroinvasive
EAEC = Enteroaggregative
How can ETEC infection be prevented?
Avoid raw veggies, pre-peeled fruit, unpasturized dairy, lukewarm cooked foods
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