Transcript Bacterial Pathogens

Bacterial Pathogens
ENVR 421
Mark D. Sobsey
Spring Semester, 2008
Some Important Enteric Bacterial Pathogens and Their Sources
Bacterium/Group
Salmonella spp.
(except S. typhi)
Campylobacter spp.
Escherichia coli
Helicobacter pylori
Aeromonas hydrophila
Yersinia enterocolitica
Listeria monocytogenes
Vibrio cholerae
some other Vibrio sp.
Shigella spp.
Animal Feces
yes
no
yes
yes
unknown
yes
yes
yes
yes
no
Non-fecal sources
no
no
yes
no
unknown
yes
yes
yes
yes
no
Enterobacteriaceae Family
 Small gram-negative rods (2-5 by 0.5 microns)
 Most motile with peritrichous flagella
• Shigella and Klebsiella are nonmotile
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Oxidase-negative facultative anaerobes
Reduce nitrate
Ferment glucose and other carbohydrates
Many genera
• Escherichia, Salmonella, Shigella, Klebsiella, Proteus,
Enterobacter, Yersinia, etc.
 Some strains opportunistic pathogens
 Some strains true pathogens
• Salmonella, Shigella, Yersinia, some strains of E. coli
Distinguishing Properties of All
Enterobacteriaceae
 Ferment glucose
 Reduce nitrates
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NO3 to NO2 or all the way to N2
 Oxidase negative
Distribution of Pathogenicity within Enteric Bacteria
E. coli
Shigella
Salmonella
Citrobacter
Klebsiella
Erwinia
Serratia
Yersinia
Proteus
based on this distribution, virulence is the derived state
Pathogens have virulence genes not present in non-pathogenic relatives,
and this distribution suggests that bacteria evolve to become pathogens
by acquiring virulence determinants
Bacterial Toxins
ENDOTOXIN
EXOTOXIN
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Released from the cell before
• or after lysis
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Protein
Heat labile
Antigenic and immunogenic
Toxoids can be produced
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Specific in effect on host
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Produced by gram-positive and
gram-negative organisms
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Integral part of cell wall
Endotoxin is LPS; Lipid A is toxic
component
Heat stable
Antigenic
Toxoids cannot be produced
Many effects on host
• Fever
• activate complement
• kinin and clotting factors
Produced by gram-negative
bacteria only
Genes for pathogenic traits can get transferred laterally
Transduction:
via bacteriophage
Conjugation:
direct contact
Transformation:
integrating free DNA
or plasmids
(from Redfield, Nat. Rev. Genet. 2001)
Typical Procaryotic Cell
Gram Negative Outer Cell Membrane (Wall)
and Lipopolysaccharide Structure
Shigellosis - Illness
• Persistent diarrhea with frequent and painful passage of
stools consisting mostly of blood, mucus and pus
– accompanied by fever and stomach cramps.
• Blood and mucus in stools are likely signs of shigellosis
• Shigella infect, invade cells lining the large intestine (colon)
• Cause breaks (ulcers) in mucous membrane lining of intestine
– Inflammation and tissue damage
– Causes painful straining to pass stools;
• can lead to rectal prolapse
– Ulcers commonly in the rectum
– results in increased production of mucus
– loss of blood and serum proteins into intestinal cavity
• Result: symptoms of dysentery: blood and mucus in the stool
(bloody diarrhea); fever is also common
Shigella and Shigellosis
• Gram-negative rods; do not ferment lactose
• Biochemistry and genetics are similar to E. coli
• Fecal-oral transmission
– person-to-person, fomites, food, water, ect.
• Waterborne and water-washed
• Reservoirs: humans and primates
• Infectious dose: low; as few as 10 cells to infect
• Incubation period: 1 to 7 days; typically, 1-3 days
• Duration of illness:
– untreated: severe symptoms for about two weeks
– Antibiotic treatment shortens illness and prevent spread
to others
Shigellosis - Epidemiology
• Four species of Shigella: flexneri, sonnei, dysenteriae, boydii
• Major public health problem in many developing countries
– causes about 5 to I0% of childhood diarrhea
– up to 25% of all diarrhea-related deaths attributed to Shigella
Developing countries:
• Sh. flexneri is endemic (always present) in most communities
• Sh. dysenteriae type 1 often occurs in an epidemic pattern
– organism can be absent for a number of years, then reappear and infect a
large proportion of the population.
• These two species generally produce the most severe illness.
Developed countries:
• Sh. sonnei is the most common and is the least virulent
• Sh. boydii causes disease of intermediate severity
– Least common, except in the Indian sub-continent
Shigellosis - Epidemiology
• Worldwide distribution; infections occur throughout year
• Mostly in children aged under five
• Rates of infection are highest where sanitation is poor
– As few as 10 cell can initiate infection
• Transmission influenced by:
– nutritional status
– environmental factors affecting transmission:
• rainfall and temperature
• Water-washed as well as Waterborne
• Incidence highest in dryer climates in hot and dry weather
– Scarcity of water limits handwashing and other hygiene
measures to reduce transfer of the few bacteria that cause
infection
• Incidence in wet climates is often highest in rainy season
Shigellosis - Complications
• Severe anorexia (loss of appetite)
• Hypoproteinaemia (a low concentration of blood
protein)
• Hyponatraemia (a low concentration of blood sodium)
• Dilation of the large intestine
• Seizures
• Anaemia
• Kidney damage
• Persistent diarrhea
• Weight loss and malnutrition
• Rectal prolapse
Shigellosis - Treatment, Control and Prevention
Treatment:
• Continue to eat (feed)
– to prevent weight loss and hypoglycemia
• include foods rich in potassium (bananas)
• Replace fluids
– Oral or IV rehydration with fluids and electrolytes
• Treat with antibiotics:
– trimethoprim/ sulfamethoxazole
– ampicillin
Prevention and Control:
• Handwashing, especially after defacation
• Improved sanitation and hygiene
– improve water, waste treatment/disposal and food sanitation
– reduce overcrowding, etc.
• No effective vaccine
Escherichia - Taxonomy and Biochemistry
Five accepted species:
• E. coli, E. blattae, E. fergusonii, E. hermanii and E. vuneris
Can be differentiated on the basis of the following reactions:
• Indole, citrate, lysine decarboxylase, growth in KCN and
malonate utilization
Biochemistry:
• frequently produce indole (except E. blattae and E. vulneris)
• ferment glucose by mixed acid fermentation
• do not produce H2S, phenylalaninedeaminase or urease, do not
utilize citrate as sole carbon source (except some strains of E.
blattae , and E. fergusonii. )
• Most are motile, ferment a variety of carbohydrates and
decarboxylae arginine, lysine and/or ornithine.
E. coli Genetics and Serology
Genetics:
• Single, circular DNA molecule, ~4 x 106 base pairs
• Molecular weight of 4 x 109
• Total length of about 1.4mm.
• Some strains completely sequenced and genomic
organization is now being characterized
– many of the genes have been mapped.
Serology:
• E. coli can be subdivided by somatic (cell-wall) or O
antigens and flagellar or H antigens.
– >160 recognized O types and 55 recognized H types
– over 8000 possible OH serotypes.
– also capsular (K) and fimbrial antigens.
Some Virulence Properties of E. coli
Enterotoxins:
• at least two types: Heat Stable (ST) and Heat Labile (LT)
• Verotoxins or Shiga-like toxins (interchangeable terms):
– Verotoxin term is based on the reactions of toxins on Vero cells
– at least two families of these toxins:
• VT1 (SLT I): similar to Siga-toxin (produced by some strains of
Shigella dysenteriae)
• VT2 (SLT II) which is only about 50% realted Shiga toxin.
• Other Toxins:
– Cytolethal distending toxin (CLDT), VirCytotoxin, Cytotoxic necrotising
factors (CNF), a possible Enteropathogenic E. coli (EPEC) enterotoxin and
a possible E. coli Sudden Infant Death Syndrome (SIDS)-toxin.
• Haemolysins:
– extracellular haemolysin known as alpha-haemolysin (many strains)
– cell-associated haemolysin, beta-haemolysin, (some strains)
– enterohaemolysin: extracellular; Enterohaemorrhagic E. coli (EHEC)
Virulence Properties of E. coli
• Fimbriae: CFAI/CFAII, Type 1 fimbriae, P fimbriae, S fimbriae
– Most important: K88, K99 and CFA fimbriae associated with
enterotoxigenic E. coli (ETEC).
– p-fimbriae: associated with urinary tract pathogens.
– E. coli also produce common fimbriae not associated with
virulence.
• Adhesins:
– Intimin: non-fimbrial adhesin; causes the intimate association
with target cells in enteropathogenic and
enterohaemorrhagic E. coli .
• Associated with the 'attachment and effacement' phenomenon
• Causes destruction of the intestinal surface cells.
• Other outer membrane proteins can act as adhesins.
Pathogenic E. coli
Enteric Infections:
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Enteroadherent E. coli (EAEC)
Enteroaggregative E. coli (EAggEC)
Enterohaemorrhagic E. coli (EHEC)
Enteroinvasive E.coli (EIEC)
Enteropathogenic E. coli (EPEC)
Enterotoxigenic E. coli (ETEC)
Extraintestinal Infections:
• Uropathogenic E. coli (UPEC): urinary tract infections
• Neonatal Menigitis E. coli (NMEC).
Enterohemorrhagic E. coli
Harbor genes for one or more of the virulence attributes known
to associated with the EHEC.
• Shiga toxin(s)
• Adherence factor(s)
• Enterohemolysin
• Somatic antigens characteristic of many EHEC serogroups,
such as O111 or O157.
• An E. coli must cell carry a sufficient number of such genes
to cause disease.
• Magnitude of exposure or size of infectious dose is also
important.
– Dose is very small in comparison with those for most other
enteric pathogens; a few bacteria per dose has high
probability of causing infection and illness
Enteropathogenic E. coli
• Cause infantile gastroenteritis.
• Certain serotypes and serogroups are
associated with infantile diarrhea.
– Infantile gastroenteritis with dehydration is an
important problem.
• EPEC have declined in the developed world as
major causes of infantile diarrhea
• EPEC remain very important in the developing
world.
• EPEC adhere to the intestinal mucosa to
produce a characteristic "attaching and
effacing" lesion in the brush border
microvillous membrane.
Enterotoxigenic E. coli
• Major cause of travellers' diarrhea (Montezuma’s revenge,
Delhi belly, Aztec two-step, etc.) and of diarrhea in children
in the developing world
• Produce an enterotoxin similar to cholera toxin.
– They are involved with a condition known as "Non-Vibrio cholerae
cholera-like diarrhoea".
• Produce one or both of two enterotoxins:
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heat stable enterotoxin (ST) : survives boiling for 30 minures
heat labile enterotoxin (LT): does not survive such boiling
LT response is sensitive to acid pH; ST was not.
LT is closely related to choleragen (CT) the enterotoxin of V.
cholerae.
• Most ETEC isolated from humans produce colonization
factor antigens which are human specific fimbrial antigens
– also a common cause of diarrhea in young animals.
Enteroinvasive E. coli (EIEC)
• Cause positive reaction in the Sereny test (ability to cause
keratoconjunctivitis in guinea pig eyes).
– a characteristic shared with strains of Shigella
• By DNA probes the invasiveness plasmids of both E. coli and
Shigella are identical.
– 120-140 mD invasiveness plasmids encode all the genes
necessary for the virulence of the EIEC.
• Many EHEC are non-motile and anaerogenic.
• Account for only a small proportion of diarrhea in non-tropical
countries
– but, cause high proportions of illness and death, mostly in
warmer seasons
• Also important causes of dysentery-like diarrhea in tropical
countries.
Enteroadherent E. coli (EAEC)
• Different patterns of adherence to cultured epithelial
cells.
• Localized adherent E. coli (LAEC) by some serotypes
– form adherent microcolonies on HEp-2 cells
– associated with acute, non-bloody diarrhoea in
children.
• Diffusely adhering E. coli (DAEC)
– a cause of diarrhea in some studies
Enteroaggregative E. coli (EAggEC)
• 3rd type of adherence: enteroaggregative adherence
• Bacteria align in parallel rows to cells or glass ('stacked
brick-like’).
• persistent childhood diarrhea in South America and India
• Illness lasts >14 days.
• Produce a heat-labile toxin antigenically related hemolysin
but not hemolytic
• Produce plasmid-encoded heat stable toxin (EAST1)
unrelated to the heat stable enterotoxin of ETEC.
Uropathogenic E. coli (UPEC)
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Common cause of urinary tract infections (UTI).
Severity: from asymtomatic to bacteriuria, cystitis and pyelonephritis.
Women more frequently affected than men.
Same serotypes are found in feces and urine of patients, but, UPEC
have virulence factors which enhance their ability to cause infection.
• Only some O groups cause UTI
• Only some K antigens cause UPEC
• Certain pili (fimbrae), the p-pili, are an important virulence factor
– bind to the P-antigen, a blood grouping antigen
– bind more to uroepithelial cells of persons with the P or P2 phenotype
– other adhesins may also be involved.
• Production of alpha-haemolysin
• Production of aerobactin
• Several virulence factors enhance an E. coli's ability to cause UTI
– an infecting strain may only express some of them to cause infection.
Neonatal Meningitis E. coli (NMEC)
• Neonatal menigitis in about 1/2500 live births.
• Up to 80% of cases of neonatal menigitis are due to E. coli.
• ~80% of the isolates possess the K1 capsular antigen.
– masks the underlying structures of the bacterial cell surface, preventing
specific antibody responses and the activation of the alternate complement
system from being activated.
– poor immunogen, maybe due to it resembling extracellular matrix proteins.
– serotypes isolated from meningitis cases often found in maternal feces;
probable source; infection occurs at birth.
• Reasons for susceptibility of neonates to NMEC is not known.
Salmonella and Salmonellosis
• In Enterobacteriaceae family
• Gram-negative bacilli; facultative and flagellated (motile).
• 3 major antigens:
– "H" or flagellar antigen (phase 1 & 2)
– "O" or somatic antigen (part of the LPS moiety)
– "Vi" or capsular antigen (called "K" in other
Enterobacteriaceae).
• Posess LPS endotoxin characteristic of Gram-negative bacteria
– Evoke fever and can activate complement, kinin and clotting
factors.
Salmonella Illness
Gastroenteritis or salmonellosis: less severe disease
• Contaminated food or water
• Often from contaminated poultry (turkeys and chickens).
• S. enteritidis or S. choleraesuis: most commonly isolated
species
Enteric fever: more severe disease
• Transmitted from person to person
• S. typhi (no animal reservoirs)
• Reservoirs:
– Contaminated food or water with human feces
– asymptomatic human carrier
• “Typhoid Mary”, a food service worker who infected many patrons
Salmonella enteritidis
Salmonella typhi
Salmonella typhimurium DT 104
• A commonly reported phage type of S. typhimurium
• Resistant to many antibiotics: ampicillin, chloramphenicol,
streptomycin, sulphonamides, and tetracyclines.
– also some additionally resistant to trimethoprim and to
quinolone antibiotics such as ciprofloxacin
• Antibiotic resistance emerged as a result of widespread use
both prophylactically and therapeutically.
– Effective antibiotics to control its spread is severely limited.
• Associated with cattle, pigs and chickens and other animals.
– May infect animals without showing any signs of illness.
– Spreads from farm to farm by raw water and other sources
– Once a farm becomes contaminated it is hard to eradicate
• Survives in dry as well as in wet environments
• Illness is more difficult to treat than from other salmonellae
• Has a higher mortality rate
Campylobacters
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Gram-negative
Curved (spiral) rod
about 1.5-3 microns
motile via polar flagella
Microaerophilic
– Prefer high CO2
• C. jejuni:
– Highly prevalent
– Relatively fragile
– But, persistent in feces
and water
– Adapted to birds
Campylobacteriosis
• Due to Campylobacter jejuni or sometimes C. coli.
• Normal intestinal flora of many warm-blooded animals
– chickens and turkeys; also in raw water and raw milk.
– Illness in sheep (abortion), dogs and cats (gastroenteritis)
• Causes illness in humans
– Cause 5-11% of all diarrhea cases in the United States.
• Symptoms: from mild to severe:
– bloody diarrhoea is the most characteristic symptom)
– also fever, nausea, abdominal cramps and (seldom) vomiting
– duration of illness usually 2-10 days
• abdominal cramps, may recur for up to 3 months after infection
– Complications such as septicaemia, may arise.
• The infectious dose may be very low, i.e. 100s of cells
• Infants, young children and debilitated people at highest risk
Campylobacteriosis
• Campylobacter enteritis or
gastroenteritis.
• Illness is watery or sticky
diarrhea
– Contain blood and fecal
leukocytes.
• Other symptoms:
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Fever
Abdominal pain
Nausea
Headache
Muscle pain.
Campylobacteriosis Epidemiology
• Illness typically occurs 2-5 days after ingestion of
contaminated food or water
– Generally lasts 7-10 days.
– Most infections are self-limiting; not treated with antibiotics
• C. jejuni
– Infectious at low dose
• 400-500 cells have high probability of causing
illness
– Major cause of bacterial diarrhea in the U.S
• An estimated 2.1 - 2.4 million cases per year
• Most retail chicken is contaminated with C. jejuni
– Most chickens in commercial operations are
colonized by 4 weeks of age
Campylobacteriosis Epidemiology, Continued
• C. jejuni infection is most frequent in children under 5
years and young adults (15-29)
• Transmission is usually not person-to-person
– but it can occur if the infected person is a child or is producing a
large volume of diarrhea
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Illness can occur in single, sporadic cases
Also occurs as outbreaks
Hyperendemic in some countries (New Zealand)
Increased human infections caused by antimicrobialresistant strains of C. jejuni
– Makes clinical management of cases more difficult.
• Antimicrobial-resistant enteric infection rates are highest in
the developing world
– Antimicrobial use in humans and animals is relatively unrestricted
C. jejuni pathogenicity
• Many likely virulence factors
• Suspected determinants of pathogenicity:
– chemotaxis and motility (flagella) for attachment,
invasion and colonization
• After colonization, other possible virulence
determinants are: iron acquisition, host cell
invasion, toxin production, inflammation and
and epithelial cell lysis
Complications and Sequelae of Campylobacteriosis:
Guillain-Barré Syndrome (GBS)
• Develop a rare disease of the nervous system beginning several weeks
after the diarrheal illness.
• A demyelinating disorder resulting in acute neuromuscular paralysis.
– Also called Acute Post Infective Polyneuritis
• Person's immune system is "triggered" to attack the body's own nerves
• Peripheral nerves show the presence of mononuclear cells,
demyelination, and macrophages.
– Pathology is most severe in spinal roots.
• Can lead to paralysis lasting several weeks; usually requires intensive
care
• About 1 per 1000 reported campylobacteriosis cases leads to GBS.
• Perhaps 40% of Guillain-Barrsyndrome cases in this country may be
triggered by campylobacteriosis.
Ang CW, Jacobs BC, Laman JD. (2004)
The Guillain-Barre Syndrome: a true
case of molecular mimicry. Trends in
Immunology. 25(2):61-66
“Carbohydrate mimicry between human
ganglioside GM1 and Campylobacter
jejuni lipooligosaccharide causes
Guillain–Barre ́ syndrome” Yuki, N. et
al (2004) PNAS Vol. 101 No. 31 p.
11404-11409.
GBS
• Immune system destroys the protective covering of the peripheral
nerves (myelin sheath)
– disables the nerves from transmitting signals to the muscles.
– the primary cause of the symptoms elicited by GBS.
• Begins with paresthesias in the toes and fingertips, followed by rapidly
advancing weakness and areflexia
• Weakness reaches a plateau within 4 weeks, then recovery begins.
• Some cases are fulminant, evolving in one or two days
– muscles become unable to respond to nerve commands
– Weakness, numbness or paralysis may occur.
– The brain also receives fewer sensory signals, resulting in the
inability to feel heat, cold, pain and other sensations.
– Many patients are completely paralyzed and unable to breathe.
– Approximately 5% of patients die from respiratory paralysis,
cardiac arrest, sepsis, and other complications.
– 10% of those who recover have residual weakness
Campylobacteriosis Prevention and Control
• Proper food handling and kitchen hygiene
practices
• Thorough cooking of all poultry and other
foods of animal origin
• Reduction of endemicity in food animals like
poultry and sheep
– Probiotics: colonize the intestinal tract of the
animals with other bacteria to prevent or
overcome colonization by campylobacters
Some Readings and References
– http://www.cdc.gov/ncidod/eid/vol5no1/altekruse.htm
– http://www.cdc.gov/ncidod/dbmd/diseaseinfo/campylobacter_g.htm
– http://www.cfsan.fda.gov/~mow/chap4.html
– http://www.mayoclinic.com/health/guillain-barresyndrome/DS00413/DSECTION=1