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