Gram-Negative Bacteria Flashcards
Enterobacteriaecea
- Escherichia coli*
- Shigella* spp.
- Salmonella enterica*
- Yersinia* spp.
large group of medically important Gram-negative, facultative anaerobic bacilli and coccobacilli
many are normal inhabitants of the human colon, some are pathogens and not part of the normal flora
Salmonella spp., Shigella spp., and Yersinia spp.
many are also opportunistic pathogens
Escherichia coli
part of normal flora of colon
frequent cause of urinary tract infections, uropathogenic E. coli (UPEC)
most common cause of Traveler’s diarrhea
five types of Escherichia coli that cause diseaes
enterotoxigenic E. coli (ETEC)
enterohemorrhagic E. coli (EHEC)
enteropathogenic E. coli (EPEC)
enteroinvasive E coli (EIEC)
enteroaggregative E. coli (EAEC)
Escherichia coli determinants of pathogenicity
alpha-hemolysin - a pore forming toxin
aeorbactin - iron siderophore
polysaccharide capsule - reduces phagocytosis (K1 capsule associated with meningitis and bacteremia)
pili - type I binding int he bladder and P pili binding in the upper urinary tract and causes pyelonephritis
ETEC
EPEC
EHEC
ETEC
heat labile toxin (LT)
- A-B toxin
- similar to cholera toxin
- stimulates adenylate cyclase in gut epithelial cells
- plasmid encoded
heat stable toxin (ST)
- stimulates guanylate cyclase in gut epithelial cells
- plasmid encoded
causes Traveler’s Diarrhea, spread through contaminated food and water, 24-72 hours incubation period
Escherichia coli
EPEC
Bundle-forming pili (BFP)
- initial attachment to intestinal epithelium
Intimin
- bacterial surface protein
- adhesin
Type II secretion system
Escherichia coli
Type III secretion systems
directly inject bacterial proteins int ocytoplasm of host cells
secretion apparatus in the bacterial cell envelope, secretes toxins to the exterior of the bacterium
translocation complex inserts into the host cell membrane and translocates toxins into the host cell cytoplasm
effector proteins are toxins
Escherichia coli
pathogens that harber type III secretion systems
- P. aeruginosa*
- Salmonella*
- Shigella*
- Bordetella*
- Yersinia*
- Chlamydia*
EPEC
EPEC Type III Secretion
cause attachment and effacement lesions due to loss of normal microvilli structure and pedestal formation
secretes a number of proteins including Tir, which inserts into the host cell membrane and acts as a receptor for intimin, which allows for tight adherence
EHEC
type III secretion system, also forms attachment and effacement lesions
Shiga-like toxin, similar to toxin made by Shigella spp., HUS (hemolytic uremic syndrome)
O157:H7 is the most frequent serotype
cattle are reservoir, acquire from undercooked meat, unpasteurized milk, and juices
bloody diarrhea, abdominal pain, and usually no fever or low-grade fever
leads to HUS in 10% of cases - hemolytic anemia, decreased platelets, renal failure, CNS dysfunction, 3-5% mortality
Escherichia coli
Escherichia coli clinical disease
UTIs, 90% of bladder infections and ppyelonephritis in healthy individuals
meningitis in neonates
nosocomial infections such as pneumonia, UTI, bacteremia, and intra-abdominal infections
EPEC, EIEC, and EAEC
causes Diarrhea in developing countries
Escherichia coli
Escherichia coli diagnostic laboratory tests
growth on routine media, differentiated from other enterobacteriaceae by biochemical tests
ETEC - ELISA and PCR assays for ST and LT
EHEC - can differentiate O157:H7 strains from commensal E. coli in that the former fail to ferment sorbitol
enzyme immunoassay for Shiga-like toxin in stool
lactose fermentation
MacConkey Agar
test used to differentiate bacteria
Lactose fermentors - Escherichia, Klebsiella, Enterobacter
Lactose non-fermentors - Proteus, salmonella, SHigella, Yersinia
Escherichia coli treatment
ETEC - rehydration, tetracycline/doxycycline, trimethoprim/sulfamethoxazole (TMP-SMX), bismuth subsalicylate (Pepto-Bismol), but increasing resistance, ciprofloxacin drug of choice in some countries
EHEC - no antibiotics
Uropathogenic E. coli - TMP-SMX, nitrofurantoin, ciprofloxacin
Escherichia coli prevention
avoid raw vegetables, fruits you do not peel yourself, unpasteurized dairy products, undercooked foods, tap water
rifaximin or bismuth subsalicylate if avoidance of illness is crucial
EHEC - avoid undercooked meat or unpasteruized milk or juices
Shigella spp.
S. dysenteriae, S. flexneri, S. boydii, S. sonnei
cause dysentery - cramps, painful straining to pass stools (tenesmus), and frequent, small-volume, bloody, mucoid stools
Salmonella enterica
formerly, many species
now known that all constitude a single species
former species designations now called serovars
facultative intracellular pathogens
common cuase of diarrhea in the US (15% of food-borne illness)
causes gastroenteritis
farma nimals (especially chickens) and turtles and other reptiles are reservoirs
serovar Typhi causes typhoid fever
Salmonella enterica determinants of pathogenicity
SPI-1 type III secretion system induces ruffling of enterocytes -> bacterial internalization
survive and multiply in phagosomes
leads to strong inflammatory response and diarrhea
occasionally disseminates to bloodstream, SPI-2 type III secretion system
serovar typhi capable of surviving inside macrophages -> aids in dissemination
Salmonella enterica clinical disease
majority of bacteria killed by acid in stomach, so large inoculum required for disease
diarrhea, nausea, vomiting 24048 hours after ingestion
usually, self-limited, lasts 7 days
fever in 50%
bacteremia in 8% of normal healthy patients
typhoid fever
typhoid fever
prolonged fever
persistent bacteremia
constipation or diarrhea
abdominal pain
occasionally a rash consisting of a few pink macules (rose spots) is observed
occasionally, carrier state develops and gallstones get infected, leads to shedding in feces, sometimes for years
Salmonella enterica
Salmonella enterica diagnostic laboratory tests
growth on agar with routine stool culture
typhoid fever, culture organism from blood
Salmonella enterica treatment
diarrhea is usually self-limited and has no treatment
treatment may predispose to carrier state
treat immunocompromised patients or severe infections
fluoroquinolones, ampicillin, chloramphenicol
always treat typhoid fever and bacteremia
Salmonella enterica prevention
prevent typhoid fever with parenteral capsular vaccine
live attenuated oral vaccine
recommended for travelers to Central and South America, Asia, and Africa who plan to stay for >4 weeks or live in conditions of poor hygiene
Yersinia spp.
- Yersinia enterocolitica* causes infectious diarrhea
- Y. pestis* causes plague
Yersinia pestis
cuase of plague (“The Black Death”)
infection acquired in three ways:
1) transmission from rats/fleas (bubonic plague)
2) human-to-human transmission by aerosols (pneumonic plague)
3) direct contact with infected animal tissues (primary septicemic plague)
endemic cases still occur in the US (about 15 cases/year)
usually hikers or hunters who acquire the illness from wild animals
90% of US cases occur in NM, AR, CO, and CA
- Yersinia pestis* determinants of pathogenicity
hms locus (hemin storage locus) - bacterial colonization of flea foregut
multiplies in flea foregut, blocks passage of blood meals, leads to regurgitation of blood meal along with bacteria
bacteria inoculated into host and travel to nearest lymph node
bacteria multiply and form bubos, leak into blood stream and releases LPS and causes septic shock and DIC
eventually, make their way to macrophages in the lungs
spread of disease to close contacts by aerosols
adhesins - Ail, chromosomally encoded, type III secretion system (on plasmid) - secretes several Yops (Yersinia outer proteins) - YopE and YopH
Fra1 - antiphagocytic protein that forms part of a capsule around Y. pestis
Pla - plasminogen activator -> cleaves fibrin clots -> dissemination
Ail
chromosomally encoded adhesin
Yersinia pestis
Fra1
antiphagocytic protein that forms part of a capsule
Yersinia pestis
Pla
plasminogen activator -> cleaves fibrin clots -> dissemination
Yersinia pestis
Yersinia pestis clinical disease
bubonic plague
pneumonic plague
primary septicemic plague
bubonic plague
2-6 day incubation period, bubo develops near site of flea bite
fevers, chills, myalgias, arthralgias, and headache
bubo becomes progressively enlarged, painful, and arythematous
sepsis and death
Yersinia pestis
pneumonic plague
1-4 day incubation period
sudden onset of chills, fever, headache, myalgias, and weakness
productive cough (sometimes bloody) and dyspnea
particularly severe and associated with high mortality rates
may result in aerosol spread of the organism from person to person
Yersinia pestis
primary septicemic plague
follows direct inoculation of the organism into the bloodstream
nausea, vomiting, diarrhea, and abdominal pain
diagnosis often not made until late in the course of the illness
Yersinia pestis
Yersinia pestis diagnostic laboratory tests
blood cultures
bubo aspirates for bobnic plague
sputum samples for pneumonic plague
grows on commonly used laboratory media such as sheep blood agar
Giemsa stain - characteristic bipolar appearance - “closed safety pins”
Yersinia pestis treatment
streptomycin or gentamicin
tetracycline/doxycycline or chloramphenicol are alternatives
Yersinia pestis prevention
avoidance of sick or dead animals in endemic areas
antibiotic prophylaxis for direct contact with pneumonic plague
tetracycline, doxycycline, and trimethoprim-sulfamethoxazole
whole-cell vaccine
unclear efficacy
not routinely recommended
Gram-negative Bacilli
- Pseudomonas aeruginosa*
- Legionella pneumophila*
- Vibrio cholerae*
- Heliobacter pylori*
- Campylobacter jejuni*
Pseudomonads
aerobic Gram-negative rods
use a broad variety of organic compounds for growth
inhabit many different environments such as soil, water, and man-made solutions
Pseudomonas aeruginosa is the most medically important
Pseudomonas aeruginosa
found in most environments including faucets and drains in hospitals
capable of using many different organic compounds for growth
Pseudomonas aeruginosa determinants of pathogenicity
Pili - adherence
Exotoxin A - similar to diphtheria toxin -> ADP ribosylates EF-2
Alginate
LasA and LasB
proteases that act together to degrade elastin
type III secretion system - kill cells and distrupt action cytoskeleton
quorum-sensing - system by which bacteria determine their numbers
endotoxin
exotoxin A
acts similarly to diptheria toxin -> ADP-ribosylates EF-2
Pseudomonas aeruginosa
alginate
exopolysacharide, “mucoidy” phenotype in CF patients
antiphagocytic
Pseudomonas aeruginosa
LasA and LasB
proteases that act together to degrade elastin
alginate
quorum sensing
system by which bacteria determine their numbers
Pseudomonas aeruginosa
Pseudomonas aeruginosa Clinical Disease
opportunistic pathogen
colonizes the majority of adult cystic fibrosis patients - impossible to clear from cystic fibrosis lungs once established
leads to repeated bouts of respiratory exacerbations
nosocomial infections - pneumonia (ventillated patients and necrotizing) and urinary tract infections, wound infections
bacteremia and sepsis in cancer patietns with decreased numbers of neutrophils in their blood
characteristic skin lesions are called ecthyma gangrenosum
hot tub folliculitis
Pseudomonas aeruginosa diagnostic laboratory tests
grows on many types of laboratory media
produces a grape-like odor
produce fluorescent pigments
oxidase positive
Pseudomonas aeruginosa treatment
intrinsic and acquired resistance to multiple antibiotics
serious infections should be treated with two drugs at least until susceptibilities are known
aminoglycosides, piperacillin, ceftazidime, imipenem, aztreonam, fluoroquionolones
most other penicillins and cephalosporins are not active against this bacteria
Pseudomonas aeruginosa prevention
tap water should not be used to wash respiratory equipment
has been found contaminating many different hospital sites and solutions, including some disinfectants
Legionella
thin Gram-negative rods
L.pneumophila - most medically significant
17 other species of Legionella have been associated with human disease
Legionella pneumophila
aerobic Gram-negative bacilli
cause of Leionarre’s Disease
inhabits natural bodies of water as well as cooling towards and water distribution systems, where they parasitize amoebae
greater than 10 serogroups - serogroup 1 causes 80% of disease
Legionella pneumophila determinants of pathogenicity
facultative intracellular pathogen
primarily infects macrophages
attaches to macrophages and provokes a novel form of phagocytic uptake called “coiling phagocytosis”
entails the formation of a long, thin pseudopod by the macrophage
wraps around the bacterium
engulfs it in a coiled vesicle
fusion of vesicle (phagosome) with lysosomes is blocked, and ER membranes with ribosomes are recruited to the phagosome
baceria survive and multiply in the phagosome and eventually lyse macrophage and infects the new cells
dot locus
phospholipase C
dot locus (defect in organelle trafficking)
necessary for the blockage of phagolysosome fusion and ribosome recruitment
encodes a type IV secretion system - another delivery system by which bacteria inject toxins directly into host cells
Legionella pneumophila
phospholipase C
hydrolyzes phosphatidyl choline in eukaryotic membranes
Legionella pneumophila
Legionella pneumophila clinical disease
airconditioning cooling towers and water faucets are the primary source of organism in human infection
infection can occur by aspiration of water or inhalation of aerosol - vegetable mister in the produce department of a supermarket
no-human-to-human transmission
nosocomial outbreaks are important, but community-acquired disease also occurs
causes a pneumonia that is often severe - fever exceeding 40.5 degrees C occurs in 20% of patients
respiratory symptoms accompanied by - headach, changes in mental status, nausea, vomiting, diarrhea, hyponatremia
Legionella pneumophila diagnosis
poorly stained by Gram’s method
visualized by using Dieterle silver staining
grows on buffered charcoal-yeast aextract (BYCE) agar, which contains L-cysteine, a required amino acid
antibiotics are used to suppress growth of other bacteria in respiratory samples
direct fluorescent antibody test (nto very sensitive)
urinary antigen test (sensitive and specific but only serogroup 1)
Legionella pneumophila treatment
macrolides and ciprofloxacin
rifampin is added iun severe disease
Legionella pneumophila prevention
disinfection of hospital water systems may be helpful in preventing nosocomial cases
Vibrios
commonly live in salt water and freshwater
often cuase infections associated with exposure to seawater
- Vibrio cholerae* comma-shaped rod that causes cholera, a severe form of diarrhea
- V. vulnificus* causes gastroenteritis, causes wound infections following cuts that are exposed to seawater, may also cause life-threatening bacteremia, especially in individuals with liver disease or iron-overload states
helicobacter
Gram-negative, slender, spiral-shaped organisms
Helicobacter pylori is responsible for most human infections, though other species cause similar infections in animals
Helicobacter pylori
grows best under microaerophilic conditions
common cause of peptic ulcer disease
Helicobacter pylori determinants of pathogenicity
grows in mucus that overlies gastric mucosa
urease
flagella and curved shape allows motility through mucus that lines the stomach, adherence to gastric epithelial cells
VacA
Type IV secretion
urease
splits ammonia from urea -> alkaline microenvironment -> allows organism to survive the acid conditions of the stomach
Helicobacter pylori
VacA
cytotoxin, causes vacuolation of cultured epithelial cells
patients with ulcers are more likely to be infected with isolates that have detectable VacA activity
Helicobacter pylori
Type IV secretion
stimulates inflammation
Helicobacter pylori
Helicobacter pylori clinical disease
approximately 30% of peopl in the US are infected, usually asymptomatic, gastric inflammation is nearly always present
major cause of peptic ulcer disease
risk factor for adenocarcinoma, non-Hodgkin’s lymphoma, and low-grade B cell mucosa-associated lymphoid tissue (MALT) lymphoma of the stomach
approximately half of the cases of MALT lymphomas regress upon antibiotic treatment
Helicobacter pylori diagnostic laboratory tests
endoscopy -> histologic examination of tissue biopsy
giemsa or silver stains are used to visualize the organisms, though culturing H. pylori is difficult
urease test: biopsy specimens are assayed for urease activity
urea breath tests - patient drinks a radio-labeled urea solution and look for exhalation of radio-labeled CO2
serological tests for igG are simple and sensitive, levels do not decrease for six months after following usccessful antibiotic therapy
antibody tests detect bacterial antigens in stool
Helicobacter pylori treatment
treatment requires multiple drugs
two popular regimens:
proton-pump inhibitor + clarithromyin + amoxicillin
protin-pump inhibitor + amoxicillin + metronidazole
Helicobacter pylori prevention
no vaccine currently available
Campylobacter
curved Gram-negative rod
frequent cause of gastroenteritis leading to diarrhea
Haemophilus
small Gram-negative cocobacilli
facultative anaerobe
H. influenzae - otitis media, sinusitis, bronchitis, epiglottitis, pneumonia, meningitis
sexually transmitted disease similar to syphilis
Bordetella pertussis
tiny, gram-negaive coccobacilli
strict anaerobes
cause of Whooping Cough
Bordetella pertussis determinants of pathogenicity
Pili, filamentous hemagglutinin (FHA), pertactin - allows adherence to ciliated epithelial cells in the upper airway, FHA mediates adherence to epithelial cells by binding to galactose residues and to PMNs by binding CR3
pertussis toxin
adenylate cyclase, makes cAMP in the prosence of host cell calmodulin - inhibits leucocyte function
capsule - only encapsulated organisms are virulent
endotoxin
Pertussis toxin
A-B toxin that exists as a hexamer with subunits S1-S5
S2 through S4 mediate toxin adherence to host
S1 has enzymatic activity, ADP-ribosylates a host cell G protein, which ultimately causes a rise in cAMP levels
S5 acts as a scaffold to position other subunits
action of toxin increases number of CR3 molecules on the cell surface, which increases FHA binding and bacterial internalization, bacteria survive inside phagocytes
also blocks recruitment of neutrophils
Bordetella pertussis clinical disease
Whooping cough
highly communicable
transmission by droplets
infects upper airway
1) incubation
2) Catarrhal stage - mild coughing and sneezing, patient very infectious
3) paroxysmal stage - explosive cough followed by “whoop” during inhalation, leads to exhaustion, cyanosis, vomiting, and convulsions, resolution very slow
Bordetella pertussis diagnostic laboratory tests
samples collected from the nasopharynx
grown on Bordet-Gengou medium or charcoal-containing medium
after 4 weeks of symptoms, cultures are rarely positive
new PCR test
Bordetella pertussis treatment
antibiotic treatment after onset of paroxysmal stage and is not as effective in altering clinical course
macrolides are the treatment of choice
TMP/SMX is an alternative
Bordetella pertussis pervention
whole-cell kileld vaccine - given with tetanus and diphtheria toxoid vaccines (DTP)
immunity wanes after 2 years - no protection is present after 12 years
concern over CNS side-effects
increased incidence of side-effects in adults - not to be given after childhood
acellular vaccines - also given with tetanus and diphtheria toxoid vaccines (DTaP)
detoxified pertussis toxin, FHA, pertactin, pili to generate protection against pertussis
associated with fewer side-effects
currently licensed for children
formulation with reduced concentrations licensed for adolescents and adults
Brucella
Brucella abortus, B. melitensis, and B. suis
small, coccobacillary, aerobic, Gram-negative bacteria
cause disease in humans as well as cattle, goats, and hogs
acquire infection through contact with mucous membranes, cuts, inhalation, consumption of unpasteurized milk or other diary products
veterinarians, meat inspectors at particular risk
able to survive inside macrophages
Brucellosis
fever, chills, malaise, and drenching sweats
symptoms last for weeks or months
diagnosis - isolation of the organism from the blood or biopsy specimens, serological tests
treatment - doxycycline + (rifampin or gentamicin or streptomycin)
prevention - animal vaccine but no human vaccine
zoonotic infection
Francisella tularensis
causes tularemia
small, metabolitcally facultative, Gram-negative coccobacillus
similar in morphology to Brucella
infects rabbits, squirrels, muskrats, beavers, and deer
human infection follows contact with inty breaks in the skin, exposure to mucous membranes, ingestion, inhalation, or tick bite
pathogenesis - multiplies within macrophages
clinical disease of Francisella tularensis
site of inoculation often becomes ulcerated
regional lymphadenopathy
fevers and chills
pneumonia and dissemination to multiple organs
difficult to grow, requires special media
serological assay is available
Pasteurella multocida
Pasteurella multocida is a small gram-negative coccobacillus
part of normal mouth and respiratory flora of some animals (cats and dogs)
humans usually become infected from a cat or dog bite
Neisseria
Gram-negative diplococci
neisseria meningitidis - meningitis and sepsis
N. gonorrhoeae - STD
Moraxella catarrhalis
morphologically and metabolically resembles Neisseria spp.
at one time was classified int he genus Neisseria
small, Gram-negative cocci or coccobacilli
causes otitis media, sinusitis, bronchitis, and pneumonia
Gram-Negbative Anaerobes
many are members of the normal flora of the GI tract, respiratory tract, and female genital tract
opportunistic pathogens
common anaerobic Gram-negative rods include Bacteriodes spp, Prevotella spp., and Fusobacterium spp.
