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Flashcards in Gram-Negative Bacteria Deck (86):


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






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



Bundle-forming pili (BFP)

  • initial attachment to intestinal epithelium


  • 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








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



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



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



chromosomally encoded adhesin

Yersinia pestis



antiphagocytic protein that forms part of a capsule

Yersinia pestis



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



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


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



exotoxin A

acts similarly to diptheria toxin -> ADP-ribosylates EF-2

Pseudomonas aeruginosa



exopolysacharide, "mucoidy" phenotype in CF patients


Pseudomonas aeruginosa


LasA and LasB

proteases that act together to degrade elastin



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



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



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



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


flagella and curved shape allows motility through mucus that lines the stomach, adherence to gastric epithelial cells


Type IV secretion



splits ammonia from urea -> alkaline microenvironment -> allows organism to survive the acid conditions of the stomach

Helicobacter pylori



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



curved Gram-negative rod

frequent cause of gastroenteritis leading to diarrhea



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



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 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



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



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.