EnterobacteriaceaeOpportunistic pathogens

Escherichia coli

Klebsiella pneumoniae

Enterobacter aerogenes

Serratia marcescens

Proteus spp.

Providencia spp.

Citrobacter spp.

Obligate pathogens

Salmonella spp.

Shigella spp.

Yersinia spp.

Some E. coli strains

Sepsis

Meningitis

UTI

Diarrhea

Pneumonia

Morphology and Physiology

Short gram-negative rods.

Facultative anaerobes.

Grow readily and rapidly

on simple media.

K. pneumoniae

Klebsiella spp. have large capsule

(form large and very mucoid coloni

es); those of Enterobacter have sm

aller capsule; the others produce di

ffusible slime layers (form circular,

convex and smooth colonies).

Proteus spp.

Some enteric bacteria are

motile. Klebsiella species are

not motile, while Proteus

species move very actively by

means of peritrichous flagella,

resulting in "swarming" on solid

medium.

Some strains of E. coli

produce hemolysis on blood

plates.

Enterobacteriaceae is characterized biochemically by the a

bility to reduce nitrates to nitrites and to ferment glucose.

Cytochrome oxidase-negative.

Enterobacteriaceae species differ in their ability to ferment

lactose. Some ferment lactose rapidly, some does it slowly

and the others (e.g., Salmonella and Shigella) do not

ferment lactose at all.

Some Enterobacteriaceae pathogens (e.g., Salmonella and

Shigella) are resistant to bile salts, and this property can be

used to select them from commensal organisms that are

inhibited by bile salts.

Antigenic StructureO antigens

O-specific polysaccharides located in LPS. Heat-stable and resistant to alcohol. A single organism may carry several O antigens.

(Core polysaccharide of LPS: enterobacterial common antigen)

K antigens

External to O antigens in some strains. Mostly are capsular antigens (polysaccharides). K antigens of Klebsiella can be identified by capsular swelling test.

H antigen

Flagellin. Heat-labile and denatured by alcohol. May be absent or undergo phase variation in different species.

ECA

O antigen

Pathogenesis and ImmunityCommon virulence factors

Type III secretion systems: possessed by some Enterobacteriaceae

pathogens, e.g., E. coli, Yersinia, Salmonella, and Shigella;

facilitate transport of bacterial virulence factors directly into host

cells.

Endotoxin (Lipid A of LPS)

Capsule

Antigenic phase variation

Acquisition of growth factors (e.g. Fe)

Resistance to serum killing

Antimicrobial resistance

Toll-like receptor 4(TLR-4)

Pathogenesis of sepsis caused by gram-negative bacteria

Pathophysiological effects of LPS

Activation of complement, release of cytokines, fe

ver, leukocytosis, thrombocytopenia, impaired org

an perfusion, disseminated intravascular coagulati

on (DIC), hypotension, shock and death.

Escherichia coli

Sepsis

For people with inadequate host defenses, e.g. the newborns. Usually originates from UT or GI infections. Many of this type of infection are endogenous.

Pathogenesis and clinical diseases

Meningitis

E. coli (particularly K1 strains) and S. agalactiae are the leading causes of meningitis in neonates.

Bacteremia

Urinary tract infection

E. coli is the most common cause of urinary tract infection.

Community- vs. hospital-acquired UT infection

Most infections originate from colon; the bacteria contaminate t

he urethra, ascend into the bladder, and may migrate into the

kidney or prostate.

Symptoms: urinary frequency, dysuria, hematuria, and pyuria.

Can result in bacteremia and sepsis.

Many uropathogenic E. coli strains produce P (pyelonephritis-a

ssociated) pili, which is associated with renal colonization, and

hemolysin HlyA.

Escherichia coli

Pathogenesis and clinical diseases

Escherichia coliPathogenesis and clinical diseases

Gastroenteritis (Diarrhea)

Caused by various virotypes:

Enterotoxigenic E. coli

Enteroaggregative E. coli

Enteropathogenic E. coli

Enterohemorrhagic E. coli

Enteroinvasive E. coli

Table 30-2

EAST & PET

STx

Escherichia coliPathogenesis and clinical diseases

Enterotoxigenic E. coli (ETEC): major causal agent of Traveler's diarrhea.

These strains express:

a) Heat-labile (LT-1) enterotoxins: an A-B toxin. Subunit A causes intense and prolonged hyper-secretion of chloride ions and inhibits the reabsorption of sodium and chloride. The gut lumen is distended with fluid, and hypermotility and secretory diarrhea occur, lasting for several days. It stimulates the production of neutralizing antibodies, and cross-reacts with cholera toxin (Vibrio cholerae enterotoxin).

b) Heat-stable (STa) enterotoxin: also stimulates fluid secretion; poorly immunogenic; short onset.

c) Colonization factors (CFAs): facilitate the attachment of E. coli strains to intestinal epithelium. Usually are pili in nature.

ADP-ribosylation

Enhance chloride secretion

Decrease sodium and chloride absorption

Escherichia coliPathogenesis and clinical diseases

Enteropathogenic E. coli (EPEC): causes infant diarrhea in poor countries. Watery diarrhea results from microvilli destruction. Spread by person-to-person contact.

Enteroinvasive E. coli (EIEC): closely related to Shigella in pathogenic properties.

Enteroaggregative E. coli (EAEC): causes chronic diarrhea and growth retardation in infants in developing countries.

Escherichia coliPathogenesis and clinical diseases

Enterohemorrhagic E. coli (EHEC)

The most common strains producing disease in developed countries.

These strains are associated with hemorrhagic colitis and hemolytic uremic syndrome (HUS: acute renal failure, microangiopathic hemolytic anemia and thrombocytopenia; 5-10% infected children).

Serotpe O157:H7 is most commonly isolated.

Cattle is a reservoir, and hamburger, unpasteurized milk, fruit juices, and uncooked vegetables (contaminated spinach in USA’s outbreak in 2006) are common sources of human infection.

Induces A/E lesions on enterocytes. Diarrhea and HUS may be associated with the Shiga toxins, which are A-B toxins that bind to 28S rRNA and disrupt protein synthesis.

歐洲腸菌元凶 疑來自埃及2011-7-1〔編譯陳成良／綜合報導〕歐洲腸道出血性大腸桿菌（ O104:H4）疫情的罪

魁禍首，又出現了新的元凶！據歐洲科學家初步調查，埃及出口至法國與德國的香苜蓿（ fenugreek ，又稱葫蘆巴）種子，可能是引爆歐洲 48 人死亡的腸道出血性大腸桿菌疫情的元凶。

5 月初爆發的這一波奪命大腸桿菌疫情，至今已造成歐洲及北美地區 4000 多人感染，幾乎所有病患都是居住在德國或最近曾往當地旅遊。德國的疫情以及法國波爾多地區的較小群聚感染，都被認為與發芽的種子有

關。 歐洲疾病預防管制中心（ ECDC ）與歐洲食品安全局（ EFSA ）表示，初步

調查顯示，芽菜的食用，疑為德國與法國的大腸桿菌食物中毒疫情的感染媒介，目前的追查結果顯示，其源頭有可能是 2009 年及去年從埃及進口的香苜蓿種子。聲明指出， 2009 年埃及出口的種子與法國疫情有關，去年出口的種子則與德

國疫情有關。但該局也強調，相關檢驗仍未出現陽性結果，還需要進行更多調查，才能確定元凶。這兩大機構已要求緊急調查這兩批種子在德國及歐洲的銷售情形，並警告說，

種子可能是在生產、運輸、包裝及分銷此一漫長又複雜供應鏈的任何一階段受到污染，不排除還有受污染貨品仍在歐盟甚至世界其他地區流通。

Klebsiella

K. pneumoniae and K. oxytoca are the most commonly isolated.

Can cause community-acquired primary lobar pneumonia (frequently involves necrotic destruction of alveolar space), and infections of wound, soft tissue, and urinary tract.

Risk factors for pneumonia: alcoholism; compromised pulmonary function.

*In Taiwan: liver abscess is commonly seen in infection of diabetes patients by K. pneumoniae.

K. granulomatis may cuase granuloma inguinale, a sexually transmitted disease, in some countries.

K. rhinoscleromatis: granulomatous disease of the nose.

K. ozaenae: chronic atrophic rhinitis.

Other opportunistic Enterobacteriaceae

Proteus

Most common isolates: P. mirabilis.

Cause urinary tract infections and bacteremia.

Produce urease, making the urine of the patients of UT infection with Proteus alkaline, promoting kidney stone formation by precipitating Mg and Ca.

Enterobacter, Citrobacter, Morganella, Serratia

Opportunistic pathogens causing nosocomial infections in neonates and immunocompromised patients.

These genera, particularly Enterobacter, are resistant to multiple antibiotics.

Escherichia coli and other opportunistic

EnterobacteriaceaeLaboratory diagnosis

Smears: the Enterobacteriaceae pathogens resemble each othe

r. The presence of large capsules is suggestive Klebsiella.

Culture: blood agar and selective differential media (e.g., MacC

onkey agar), the latter is useful for preliminary identification. Co

mmercial biochemical test systems can be used for identificatio

n of Enterobacteriaceae members.

Serologic tests are used for determining the clinical significance

of an isolate and for epidemiologic purpose.

Treatment

Diarrhea patients usually need only symptomatic relief.

Antibiotic treatment may prolong the fecal carriage or

increase the risk of secondary complications.

Treatment of bacteremia and septic shock: prompt

antibiotic treatment, restoration of fluid and electrolyte

balance, and treatment of disseminated IV coagulation.

Variation in drug susceptibility is great in opportunistic

infections, and antibiotic sensitivity tests are essential.

E. coli and other opportunistic Enterobacteriaceae

Prevention and control

Enterobacteriaceae are a major part of normal flora and

a common contaminant of the environment. Food safety

plays an important role in prevention of GI infections.

In hospitals, opportunistic Enterobacteriaceae are comm

only transmitted by personnel, instruments, or parenteral

medications. Their control depends on hand washing, rig

orous asepsis, sterilization of equipment, disinfection, re

straint in IV therapy, and strict precautions in keeping the

urinary tract sterile.

E. coli and other opportunistic Enterobacteriaceae

Salmonella

Classification of salmonellae into groups and species is traditionall

y based on serogrouping and serotyping of O and H antigens (> 2,

500 serotypes). However, Salmonellae have been reclassified bas

ed on DNA homology. Therefore, the correct name of S. typhi is S.

enterica, serovar. Typhi or S. Typhi. They can be identified by bioc

hemical tests and serogrouping and serotyping.

Salmonella spp. do not ferment lactose.

Most species of Salmonella are motile with peritrichous flagella.

Some Salmonellae have capsular antigens; that of S. Typhi is refer

red to as Vi antigen.

SalmonellaEpidemiology

S. Typhi and S. Paratyphi are primarily infective for humans.

Other salmonellae are chiefly pathogenic in animals (poultry, pigs, rodents, cattle, pets etc.) that constitute the reservoir for human infection.

Humans usually become infected by ingestion of contaminated food or drink (mean infective dose: 106-108, but that of S. typhi is lower). In children, infections can result from direct fecal-oral spread.

The most common sources of human infections: poultry, eggs, dairy products, and foods prepared on contaminated work surfaces. However, the major source of infection for enteric fever is the carriers (convalescent or healthy permanent).

SalmonellaPathogenesis and Immunity

Invasion

Acid tolerance response (ATR) gene protects the organism from gastric acid.

The bacteria invade into (by inducing membrane ruffling) and multiply in the M cells and enterocytes of the small intestine. They can also be transported across the enterocytes and released into the blood and lymphatic circulation.

Inflammatory response confines the infection to the GI tract in non-typhoid salmonellosis.

Survival in macrophages

Salmonellae are facultative intracellular pathogen.

Salmonella

Clinical diseases

1. Enteritis

Incubation period: 6-48 hours.

Symptoms: nausea, headache, vomiting, nonbloody prof

use diarrhea, with few leukocytes in the stools. Low-grad

e fever, abdominal cramp, myalgia, and headache are al

so common. Episode resolves in 2-7 days.

Inflammatory lesions of the small and large intestine are

present. Stool cultures remain positive for several weeks

after clinical recovery.

SalmonellaClinical diseases

2. Bacteremia

Most common causal species: S. Choleraesuis, S Typhi

and S. Paratyphi.

Symptoms: like sepsis caused by other gram-negative b

acteria. 10% of patients may have localized suppurative i

nfections, e.g., osteomyelitis, endocarditis, arthritis, etc.

High risk population: pediatric and geriatric patients; AID

S patients.

SalmonellaClinical diseases

3. Enteric fever (typhoid fever)

Causal species: S. Typhi, S. Paratyphi A, S. Schottmuelleri,

and S. Hirschfeldii.

Mouth small intestine lymphatics and bloodstream

infect liver, spleen and bone marrow mul

tiply and pass into the blood second and heavier bactere

mia onset of clinical illness colonization of ga

llbladder invasion of the intestine typhoid ulcers a

nd severe illness.

Chronic carriers (1%-5% of patients): bacteria persist in the g

allbladder and the biliary tract for more than one year.

Symptoms: incubation time: 10-14 days. Gradually increasing fever, malaise, headache, myalgias, and anorexia, which persist for a week or longer. In severe cases: intestinal hemorrhage and perforation.

Principal lesions: hyperplasia and necrosis of lymphoid tissue, hepatitis, focal necrosis of the liver, and inflammation of the gallbladder, periosteum, lungs and other organs.

SalmonellaTreatment

Enteric fever and bacteremia require antibiotic treatment: chlo

ramphenicol, ampicillin, trimethoprim-sulfamethoxazole. Surg

ical drainage of metastatic abscesses may be required.

Salmonella enterocolitis needs only supportive therapy (antibi

otic treatment may prolong the symptoms and excretion of th

e salmonellae). Drugs to control hypermotility of the gut shou

ld be avoided because it is easy to transform a trivial gastroe

nteritis into a life-threatening bacteremia by paralyzing the bo

wel.

Chronic carriers of S. Typhi may be cured by antibiotics alone

or combined with cholecystectomy.

Salmonella

Prevention and control

Sanitary measures.

Carriers must not be allowed to work as food handlers.

Strict hygienic precautions for food handling.

Vaccines against S. Typhi:

Purified Vi antigen

Oral, live attenuated vaccine.

National salmonella death toll rises to 7(Staff writer Ridgely Ochs contributed to this story. January 24, 2009)

A seventh death was linked Friday to a nationwide outbreak of salmonella associated with tainted peanut butter and paste sourced to the Peanut Corp. of America's plant in Blakely, Ga., authorities confirmed.

Although their exact causes of death have not been determined, all seven people have died after being infected with the bacterial strain Salmonella Typhimurium, the Centers for Disease Control and Prevention said on its Web site.

There have been 493 cases reported in 43 states and one Canadian province of people sickened, though authorities stress the numbers sickened are likely far in excess of that as many cases go unreported. Known patients ranged in age from 1 to 98, and 22 percent of the those have been hospitalized.

Another 10 firms Friday recalled products that use PCA peanut butter or paste - bringing to roughly 360 the number of products affected - as it emerged that the Peanut Corp. of America's plant in Blakely, Ga. laid off most of its roughly 50 workers. The outbreak has triggered a congressional inquiry and renewed calls for reform of food safety laws.

http://www.newsday.com/services/newspaper/printedition/saturday/health/ny-lisalm246010666jan24,0,5876138.story

ShigellaS. dysenteriae, S. flexneri , S. sonnei , & S. boydii: bacillary dysentery

> 45 O serotypes; have no H antigen; do not ferment lactose.

Pathogenesis and Immunity

Shigellosis is primarily a pediatric disease, and is restricted to the GI tract.

Mean infective dose: 103.

Mouth colon invade M cells and subsequently spread to mucosal epithelial cells cause microabscess in the wall of colon and terminal ileum necrosis of the mucous membrane, superficial ulceration, bleeding, and formation of pseudomembrane.

Shiga toxin

An A-B toxin inhibiting protein synthesis.

Damages intestinal epithelium and glomerular endothelial cells (associated with HUS) .

Internalized shigellae induce apoptosis of macrophage and release of the bacteria

Attracted by the cytokines released by macrophage

Destablize the intestinal wall

Activates the invasion genes on the virulence plasmid

M cell

Shigella

Clinical diseases

Incubation period: 1-3 days

Sudden onset of abdominal pain, fever and watery diarrhea

number of stools increase, less liquid, often contain mucus

and blood, rectal spasms with resulting lower abdominal pain (t

enesmus) symptoms subside spontaneously in 2-5 days in

adult cases, but loss of water and electrolytes frequently occur

in children and the elderly a small number of patients rem

ain chronic carriers.

Some cases were accompanied by hemolytic uremic syndrom

e (HUS).

Shigella

Laboratory diagnosis

Specimens: fresh stool, mucus flecks, and rectal swabs. Large

numbers of fecal leukocytes and some RBC may often be seen

microscopically.

Culture: differential and selective media as used for salmonellae.

Treatment

Antibiotic treatment: chloramphenicol, ampicillin, tetracycline, an

d trimethoprim-sulfamethoxazole. Drug resistance is common.

Opiates should be avoided.

Shigella

Prevention and control

Humans are the only reservoir for shigellae.

Transmission of shigellae: water, food, fingers, feces, and flies.

Most cases occur in children under 10 years of age.

Prevention and control of dysentery:

1. Sanitary control of water, food and milk; sewage disposal;fly control.

2. Isolation of patients and disinfection of excreta.

3. Detection of subclinical cases and carriers.

Yersinia Y. pestis: plague ("black death")

Y. pseudotuberculosis and Y. enterocolitica: gastroenteritis

Grows more rapidly in media containing blood or tissue fluids an

d fastest at 30 oC. Some species (e.g. Y. enterocolitica) can gro

w in refrigerated food.

Pathogenesis

The Yersinia pathogens are able to resist phagocytic killing by se

creting proteins into the phagocyte and result in inhibition of killin

g by phagocyte, apoptosis of macrophage, and suppression of c

ytokine production.

Y. pestis produces a protein capsule (Fraction 1) and Pla (plasmi

nogen activator protease) that degrades C3b, C5a and fibrin clot

(enhances spread of bacteria into blood stream).

Yersinia pestisCauses zoonotic infections; humans are accidental hosts.

Three major pandemics have occurred in 541 AD, 1320s and 1860s.

Two forms of infections:

Urban plague

Rats as natural reservoirs.

Spread among rats or between rats and humans by infected flea.

Can be eliminated by effective control of rats and better hygiene.

Sylvatic plague: infections of rodents and domestic cats.

Y. pestis are widely distributed in mammalian reservoirs and flea vectors and produces fatal infections in animal reservoirs.

Human infections are acquired by contacting the reservoir population.

Yersinia pestisPathogenesis

Bubonic plague

Y. pestis enters a flea when it feeds on an infected animal the bacteria multiply in the gut of the flea flea becomes hungry and bites ferociously the bacteria passes from the flea into the bite wound bacteria are phagocytised, but can multiply intracellularly or extracellularly bacteria reach the lymphatics, and an intense hemorrhagic inflammation develops in the enlarged lymph nodes, which may undergo necrosis the bacteria may reach the blood stream and disseminated. Hemorrhagic and necrotic lesions may develop in all organs.

Primary pneumonic plague

Results from inhalation of infective droplets (usually from a coughing patient), with hemorrhagic consolidation of the lung, sepsis and death.

Yersinia pestisClinical Diseases

Bubonic plague

Incubation period: 2-7 days.

High fever and painful lymphoadenopathy with greatly enlarged, tender lymph nodes (buboes) in the groin and axilla sepsis (early stage: vomiting and diarrhea; late stage: hypotension, renal and cardiac failure; terminal stage: pneumonia and meningitis). Mortality: 75% if untreated.

Pneumonic plague

Incubation time: 2-3 days.

Fever and malaise, pulmonary signs develop within 1 day. Patients are highly infectious. Mortality: 90% if untreated.

Yersinia pestisTreatment

Patients have to be promptly treated with antibiotics (drug of choice: streptomycin).

Epidemiology and control

Plague is an infection of wild rodents that still occurs in many parts of the world (enzootic areas: India, Southeast Asia, Africa, and North and South America).

Control of plague requires surveys of infected animals, vectors, and human contacts, and by destruction of infected animals.

All patients with suspected plague should be isolated.

Contacts of patients with suspected pneumonic plague should receive tetracycline as chemoprophylaxis.

Y. enterocolitica and Y. pseudotuberculosisCause zoonotic infections.

Y. enterocolitica is a common cause of enteritis in cold areas during the cold months. Y. pseudotuberculosis infection is relatively uncommon.

They are found in the intestine of a variety of animals, and are transmissible to humans through contaminated food, drink or fomites, resulting in diarrhea, fever and abdominal pain that last for 1-2 weeks or, in some cases, months. Most are self-limited.

Y. enterocolitica infection can cause pseudoappendicitis (enlarged mesenteric lymph nodes) in children, and blood-transfusion related sepsis in those who used blood products stored for at least 4 weeks.

Y. enterocolitica grows slowly at 37 oC and prefers cooler temperatures. The fecal specimen can be mixed with saline and then stored at 4 oC for 2 weeks or more to facilitate isolation of this organism (cold enrichment).

How does Proteus swarm?

Back

Lipopolysaccharide (LPS)

is also called endotoxin.

LPS is composed of lipid A, cor

e polysaccharide, and O-specif

ic polysaccharide.

Lipid A anchors LPS in the lipid

bilayer of outer membrane. It c

auses symptoms associated wi

th endotoxin.

O-specific polysaccharide can

be used to identify certain spec

ies and strains.