Enteric Gram Negative Rods

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Enterobacteriae

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gram negative motile rods, peritichous flagellae do not form spores

tolerate bile detergents such as deoxycholate and grow well on selective agars

grow aerobically and anaerobically

ferment sugars to produce gase

carry out a wide variety of biochemical reactions

cytochrome oxdiase (-)

acquire and exchange genetic material encoding resitance to anitbiotics on plasmids transposons by conjugation and by bacteriophage

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Functional properties

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all of the enteric pathogens are killed by heat, temperatures about 65 C will kill

pasteurization

almost all enteric pathogens survive freezing and thawing

all of the enteric pathogens remain susceptible to chlorine

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Coliforms

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lactose fermenting gram negative rods

considered a fecal marker for contamination in beaches and well water

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detection of lab enteric pathogens

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selective agar, macconkey hektoen, XLD and others

selective means the addition of chemicals to inhibt growth of gram positive bacteria such as deoxycholate detergent, crystal violet

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MacConkey

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lactose fermenters are pink

non lactose fementers are white

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E. coli serotyping

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serotyping system based on antigens present on the external surface of bacteria

O or somatic antigens are in the LPS

H are flagellar antigens, K antigens are capsular

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Diarrheagenic e. coli

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enterotoxigenic e.coli ETEC

enteropathogenic EPEC

Shiga toxigenic STEC

Enteroaggregative EAEC

Enteroinvasive

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ETEC

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most common cause of travelers diarrhea worldwide

one of the leading causes of diarrhea in children in developing countries

strains may produce but the the heat liable and heat stable toxin

LT stimulates cAMP ST stimulates cGMP in host

not detectable in routine stool

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ETEC Lt

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closely resembles cholera toxin in its structure and has identical action ot increase AC function

cross reacts with choler

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Cholera Toxin and E.coli LT

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A subunit of both toxins enters the host cell and is an enzyme that catalyzes the transfer of an ADP ribose group from NAd to the host cel G-protein, Gs-alpha activating adenylyl cyclase prudcues cAMP

B subunity binds to ganglioside on the host to mediate internalization

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Heat stable toxins ST

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small peptide toxin of 18 to 19 AAs, not immunogenic

endogenous analogs are the peptide hormones guanylin and uroguanylin

binds to and activates guanylyl cyclase this is not the form that responds to NO

increased cAMP and cGMP, both activate kinases that phospho CFTR

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EPEC

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enteropathogenic e. coli

another common cause of watery, non-bloody diarrhea in children in develop countries

diarrhea may be long lasting and is oftern associated with fever and vomiting

does not produce any known toxins

not invasive ahdeere to the small intestinal cells (LOCAL ADHERENCE)

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Intimin

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adherence gene encoded by eae

e.coli gene

attaching and effacing the villi because microvili are lost

dense mats of adherent EPEC bacteria on intestinal walls

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LEE

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pathogenicity island

encodeds many virrulant genes

"Locus for Eneterocyte Effacement"

leading diarrhea theory is that it releases ATP which when converterd to adensonie both causes secretions

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STEC

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more common in industrialized countries

linked to foods, juices and other produce

person to person transmission is possible

cattle are the main reservour for STEC

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Shiga-toxigenic E.coli

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strain O157:H7 is the most notorious and may be more virulent

over 50 serotypes

clinically hallmark is bloody diarrhea, usually without fever followed by hemolytic uremic syndrom in 10%

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Shiga toxin

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extra-intestinal effects are due to absroption of Shiga toxins from the gut lumen

cells of the body are sensitive to Stx 1 and 2 anre endothelium esp in childern and elferly in the brain and kidney

teenager and middle-aged rarely get HUS

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Mechanism of STX action

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B subunit binds to Gb3 a neutral sphingolipid that helps in host absorption

A subunit enters the host cell and is site specific for an RNA direct nuclease; cleaves a partucular adenine resiude from 16S rRNA halting protein synthesis

same as plant toxin ricin

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Detection

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need to be able to detect the O157:H7 strain in NYS to prevent outbreak

in other states it may not be mandated

in germany contaminated fenugreek seeds were the cause

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STEC infections

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antibiotics are considered contra indicated in STEC

antibiotics increase Stx toxins with Stx2 being more inducible then I

antibiotics MOST likely will worsen the course of STEC are quinolones and trimethloprim

if you had to give one give azithro

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EAEC

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enteroaggregative E.Coli

afftect children in developing countries, adult travelers and patients with AIDS

loser adherence and stacked brick apperance, adherence to glass slide

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EAEC virulence factors

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pet plasmoid encoded toxin a member of the SPATE family of toxins

EAST enteroaggregative E. coli stable toxin like ST execept 48 AAs in size

Flagellin = very inflammatory when in contact wiht epithelila cells

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Pathogenic E. coli adherence patterns

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Localized adherence = EPEC

Aggregative adherence = EAEC

diffuse adherence is not definitely established as a pathogen

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Enteroinvasive E.coli

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true invasive diseas like Shigella, rarest type of diarrheagenic e. coli worldwide and especially rare in the US

not emphazied

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Salmonella and Shigella

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protypical for invasive enteric infectious organisms

invasive means the pathogen penetrates through the epithelium at least into the submuc

diarrheal illness characterized by inflammation, invasion of mucosa, and often blood mucos and leukocytes

shigella - dysentary (tenesmus and feequent small mucus and blood rich)

both are unable to ferment lactose, colonies are white on MacConkey and cna be detecte in stool

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XLD

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useful for Salmonella

thiosulfate is reduced by Salmonella which produces H2S which reacts with other minerals and produces black

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Infectious doses

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low inoculum organisms, below 10^2

intermediate 100-1,000,000

high inoclume at least a million pathogens

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Characteristics of high vs low

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high = vehicle is very contaminated and at permissive temp, secondary cases rare under reasonable sanitation

low - may be transmitted by bodily contact swimming in a pool of infected patient or ice cubes, secondary cases are common may be spread in families or day care ceners

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S. enterica

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nomenclature

until a few years ago, every serotype was designated a new species

no there are two spieces (enterica, and bongori)

S. enterica Newport

s. typhi is considered its own species due to differences in path

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s. enterica general

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1st or 2nd most common causes of gastroenteritis/food poisoning in the US after campylotbacter jejuni

salmonella exceeds campylobacter in the SE US

sources of infection are eggs poultry and reptiles

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Typhoid fever

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disease produced by paratyphi/typhi

prolonged febrile illenss without diarrhea

uncommon among returning western tourists

can be seen in VFR's

us patients usually have acquirewd it in one of 3 countires india pakistan or bangladesh

best test for dx is easlly in illness is blood culture

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Typhoud sx

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prolonged fever, headache, mental slowness

enlarged liver and or spleen

live salmonellae survive in macros

rose spots at peak of illness on trunk in fair skinned individuals

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typhoid rx

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ANTIBIOTICS are ceftriaxone cipro azithro

chloramphenicol, ampicillin and TMP/SMX used in developing countries because of lower price but resistance to these agents is common

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Typhoid vaccines

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Ty21a live attenuated oral salmonella typhi vaccine longest lasting protection

typhoid Vi polysaccharide vaccine I.M injection

old heat killed whole cell s. typhi vaccin no longer available

does not protect agains paratyphi

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Shigella

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s. sonnei most common

s. flexneri named after med educator

s. boydii common in india

s. dysenteria, only shigella that produces shiga toxin

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Yersinia enterocolitica and y. pseudotuberculosis

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zoonoses acquired from farm animals or from undercooked meat products

most commonly implicated foods are undercooked pork sausage and pork chit lins

symptoms are fever and abdominal pain

diarrhea may be low volume high or absent

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Vibrios

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V. cholerae

motile oxidase (+) GNR with polar flagellae found in warm brachish coastal water worldwide, live as commensals with crustaceans

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Cholera toxin

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ADP ribosylates Gs-alpha, a G protein which activates adenyly cyclase, Gs becaomes locked in the on position and so adenylyl cyclases remains active

opens chloride channels

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Cholera detection

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can grow on sucrose others cant

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Cholera vaccine

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2 made, none available in th eUS

dukoral in Canada

shancol bivalent inactivated vaccine cotaning killed whole cells

neither vaccine contains any live bacteria

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V. parahaemoliticus

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most common identified cause of food poisoning/ gastroenteritis in Japan

often assoc'd with eating raw fish or shellfish

not invasvie but diarrhea may be bloody

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Aeromonas hydrophilia

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member of vibrionacea family

lives in fresh water and is often a pathogen of cold blooded vertebrate animals such as

frogs, salamanders, fish, salmon and trough

also an obligate intestinal symbiont of leeches

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Campylobacter

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C. jejuni is the 1st or 2nd leading food posioner

about 2/3 of grocery store chicken has culturable or PCR identified c. jejuni

spectrum of illness varies from watery ro severe diarrhea with blood and fever

isolates in SE asia have developed alarming rates of resistance to quiniolone antibiotics with as high as 90% resistance

may trigger Guillain Barre syndrome

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C. jejuni growth req

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10% co2 prefers 42

blood or chocolate agar

grows very slowly

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campylobacter disease

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ordinary water to blood with fever to sever colitis

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Guillain Barre syndrome

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evidence of a preceding campylobacter infection is found in 25% of patients

campylobacter infection usually preceds GBS by 2-3 weeks

less then.1% go on to develop GBS

weakness of the limbs triggered by infection