ENTEROBACTERIACEAE B.A.Fontanilla, MD Department of Microbiology and Parasitology

ENTEROBACTERIACEAE

B.A.Fontanilla, MDDepartment of Microbiology and

Parasitology

GENERAL CHARACTERISTICS

• Taxonomy• Morphology• Physiology• Antigenic Structure• Determinants of Pathogenicity• Clinical Infection

ENTEROBACTERIACEAE

• Large number of closely related species- found in soil, water, decaying matter- found in large intestines of human, animals and

insects ----”enterics” or “enteric bacilli” - includes causative agents of gastrointestinal

diseases- causative agents of nosocomial infections

ENTEROBACTERIAECEAETAXONOMY

• Cedecea• Citrobacter• Edwardsiella• Enterobacter• EscherichiaEscherichia• Ewingella• Hafnia• KlebsiellaKlebsiella• Kluyvera• Morganella

• ProteusProteus• Providencia• Rhanella• SalmonellaSalmonella• Serratia• ShigellaShigella• YersiniaYersinia• Enteric group

ENTEROBACTERIACEAEMORPHOLOGY

• Small 0.5 x 3.0 µ• Gram-negative• non-spore-forming bacilli• May be motile or non-motile If motile – peritrichous flagella nonmotile – Shigella and Klebsiella

ENTEROBACTERIACEAE

• Biochemically diverse• Facultative organisms• When grown in anaerobic or low O2

- ferment carbohydrates• When grown in sufficient O2

- utilize the TCA cycle and the electron transport system for energy production

ENTEROBACTERIACEAEPHYSIOLOGY

• Ferment glucose• Reduce nitrates to nitrite• Do not liquify alginate• Oxidase negative• Basis for speciation within a family

- differences in carbohydrate they ferment- variations in end-product production

- variation in substrate utilization

ENTEROBACTERIACEAECULTURAL CHARACTERISTICS

• On non differential or nonselective media blood agar or infusion agar

- no species distinction- appear as moist, smooth, gray colonies

• Selective media -To isolate Shigella and salmonella from fecal matter

• Differential media – selectively inhibit gram-positive organisms and to separate enterics in broad categories

ENTEROBACTERIACEAEANTIGENIC STRUCTURE

• In serologic typing, antigenic structures are used for classification and epidemiologic studies

- Capsular (K) antigens- Flagellar (H) antigens- Somatic (O) antigens


• Capsular (K) antigens- Klebsiella species has a well defined

polysaccharide capsule- in other genera, amorphous slime layer

surrounding the bacterial cell - in E.coli – proteins and form fimbriae not capsules - Vi antigen of Salmonella typhi


• Flagellar antigens- proteins-antigenic variation is due fo differences in amino acid sequences-antigenic typing of Salmonella is based on serologic typing of flagellar antigens


• Somatic antigens- O antigens is the most external part of the cell wall lipopolysaccharide (LPS)- may enhance the establishment of the organism in the host.


• Flagellar (H) antigens - proteins- antigenic variation of various flagellar

types due to differences in amino acid sequences

- serologic typing of flagellar antigens – basis for antigenic typing of Salmonella typhi

ENTEROBACTERIACEAEDETERMINANTS OF PATHOGENICITY

1. ENDOTOXIN- LPS (review structure p. 26 Jawetz)- resides in the lipid A portion of the LPS- produces, fever, fatal shock, leukocytic

alterations, regression of tumors, alteration in host response to infection

- pooling of blood in the microcirculation - causing cellular hypoxia and metabolic failure due to inadequacy of blood in vital organs

ENTEROBACTERIACEAEDETERMINANT OF PATHOGENICITY

2. ENTEROTOXIN-Toxins that affect the small intestines- transduction of fluid in the lumen –diarrhea

3. SHIGA TOXINS AND SHIGALIKE TOXINS (Verotoxins) – actions on Vero (African green monkey) tissue culture cells- Shigella – toxin that interferes with protein synthesis of cells- E.coli – hemolytic diarrhea

ENTEROBACTERIACEAEDETERMINANTS OF PATHOGENICITY

4. COLONIZATION FACTORS- cellular surface factors:

capsule – Klebsiella pneumoniae “Vi” antigen – S. typhi5. Other Factors

- ability to penetrate epithelial lining – E.coli - Shigella - Salmonella

ESCHERICHIA

ESCHERICHIA

• Includes 6 species• 5 species associated with human disease

Escherichia blattaeEscherichiaEscherichia colicoli

Escherichia fergusonii Escherichia hermanii Escherichia vulneris

ESCHERICHIA COLI

• Grows well on commonly used media• On enteric isolation media – lactose fermenting colonies• On blood agar – β-hemolytic (assoc with UTI)• Majority – non-pigmented, motile– Produce lysine decarboxylase, use acetate as

carbon source, hydrolysis of tryptophan to indole

ESCHERICHIA COLI

• Serologic typing is based on the determination of the O antigen type, the H antigen type and when applicable the K antigen type.- 164 O antigens- 100 K antigens- 50 H antigens

Example: Serotype O157:H7 – hemorrhagic colitis Serotype O124:H30 –enteroinvasive; bacillary dysentery

ESCHERICHIA COLIDETERMINANTS OF PATHOGENICITY

1. Surface Factorsa. K1 capsule – E.coli with K1 capsule cause neonatal meningitisb. O antigenc. S fimbriae

2. Enterotoxins –produces watery diarrhea caused by the outpouring of fluids and electrolytes

- plasmid mediated


2. Enterotoxin – produces watery diarrhea- plasmid mediated

a. LT enterotoxin - similar to enterotoxin of Vibrio cholera

- stimulates adenylate cyclase in the epithelial cells of the small intestines, increasing perrmeability of the intestinal lining, resulting to loss of fluids and electrolytes


2. Enterotoxinb. ST enterotoxin – ST producing E.coli do not cause diarrhea

3.Verotoxins (Shigalike Toxins)- associated with 3 human syndrome:

- diarrhea, hemorrhagic colitis, hemolytic uremic syndrome

- inhibit protein synthesis similar to Shigatoxin

ESCHERICHIA COLIDETERMINANT OF PATHOGENICITY

4. Other factorsa. Enteroinvasiveness – strains have large plasmids that encode for O antigensb. Hemolytic – strains are nephropathogenic

ESCHERICHIA COLICLINICAL MANIFESTATION

1. Pulmonary infections – nosocomial pneumonia- most patients are 50 yrs or oldeer- with underlying chronic disease- main source: endogenous aspiration of oral secretions containing E.coli

2. Neonatal meningitis – with subsequent neurologic or developmental abnormalities


3. Wound infections – especially occurring in the abdomen

4. Sepsis – can invade the bloodstream from any of the primary infection sites

ESCHERICHIA COLICLINICAL MANIFESTATIONS

5. Diarrheal diseasea. Enteropathogenic E.coli (EPEC)

- cause of infantile diarrhea- adhere to mucosal cells of small bowell- loss of microvilli- produce watery diarrhea


5. Diarrheal diseaseb. Enterotoxigenic E.coli – common cause of travelers diarrhea- some strains produce LT, plasmid mediated- toxin activates adenylyl cyclase

- intense and prolonged hypersecretion of water and chlorides and inhibits reabsorption of sodium


5. Diarrheal diseasec. Enterohemorrhagic E. coli (EHEC)

- produces verotoxin- associated with hemorrhagic colitis and hemolytic uremic syndrome- serotype O157:H7 – most common


5. Diarrheal diseasesd. Enteroinvasive E. coli (EIEC)

- cause bacillary dysentery in all age groups

- disease is very similar to shigellosis- occurs most commonly in children- invade intestinal mucosal cells


5. Diarrheal diseasesf. Enteroaggregative E.coli (EAEC)

- causes acute and chronic diarrhea in persons in developing countries

- produce ST-like toxins

To be continued….

KLEBSIELLA

KLEBSIELLATAXONOMY

Klebsiella pneumoniae (Friedlander’s bacillus)Klebsiella oxytoca – Klebsiella ozeana –Klebsiella rhinoscleromatis

KLEBSIELLABIOCHEMICAL AND CULTURAL CHARACTERISTICS

- Appear as lactose fermenting colonies on differential enteric media

- Non-motile- Large capsule – colonies appear large, moist

and mucoid

KLEBSIELLAANTIGENIC STRUCTURE

- Possess O and K antigens- K antigens are most useful in serologic typing

KLEBSIELLADETERMINANTS OF PATHOGENICITY

1. Capsule – resist phagocytosis- encapsulated strains are more virulent

2. Endotoxin3. Enterotoxin – isolated in patients with tropical

sprue- similar to E.coli ST and LT- plasmid mediated

KLEBSIELLACLINICAL INFECTION

1. Klebsiella pneumoniae- cause primary community-acquired

pneumonia - typical patient: middle or older aged with underlying medical problems – alcoholism, chronic bronchopulmonary disease, diabetes mellitus- most patients – thick, non-putrid bloody sputum – necrosis and abscess formation

KLEBSIELLACLINICAL INFECTION

1. Klebsiella pneumonia- can cause urinary tract infection-wound infections, bacteremia,

meningitis2. Klebsiella oxytoca – causes chronic atrophic

rhinitis – fetid odor3. Klebsiella rhinoscleromatis – infects nose and

pharynx; produces granulomatous inflammation

ENTEROBACTER

ENTEROBACTER

Enterobacter cloacaEnterobacter aerogenes

- Non motile- Isolated less frequently than Klebsiella and E.coli- Capable of infecting any tissue in the body- Frequently associated with urinary tract infection

ENTEROBACTER

- Most infections occur in patients with underlying problems

- Usually nosocomial- Among elderly- Risks for development of Enterobacter

bacteremia- long hospitalization, placement of

intravenous catheters, respiratory colonization, use of antibiotics

ENTEROBACTER

Enterobacter cloacaEnterobacter aerogenes

ENTEROBACTERBIOCHEMICAL AND CULTURAL CHARACTERISTICS

- Motile- Grows on media used for the isolation of

enterics- Rapid lactose fermenters and produce

pigmented colonies

ENTEROBACTERANTIGENIC STRUCTURE

- Antigenic subgrouping not as developed as E.coli and Klebsiella

ENTEROBACTERCLINICAL INFECTION

- Isolated less frequently than E. coli and Klebsiella

- Capable of infecting any tissue- Most frequently associated with urinary tract

infection- Most infections occur in patients with

underlying problems – nosocomial- Risks: long term hospitalization, plac ement of intravenous catheters,

respiratory colonization; prior use of antibiotics,

SERRATIA

SERRATIA

Serratia marcescensSerratia liquifaciens

- Can be differentiated from other members of the Enterobacteriaceae by:- ability to produce extracellular deoxyribonuclease (Dnase),

lipase and gelatinase - resistance to colistin and cephalosporin

SERRATIA

- O and A antigens are important epidemiologic markers

- All Serratia infections – associated with underlying disease, changing physiologic patterns, immunosuppressive therapy or mechanical manipulations

- 90% are hospital acquired: UTI, wound infections, pneumonia, septicemia

PROTEUS

PROTEUS

• Proteus mirabilis• Proteus vulgaris

PROTEUSCULTURAL CHARACTERISTICS

- Produce a translucent sheet of growth on non-selective media such as blood agar

- swarming

PROTEUSBIOCHEMICAL CHARACTERISTICS

- Distinguished from other enterics – produce phenylalanine deaminase

- All species produce urease:urea = ammonia + CO2

- Proteus mirabilis does not hydrolyze tryptophan to indole – basis of grouping into indole-positive and indole-negative

PROTEUSANTIGENIC STRUCTURE

- All members possess O, H and K antigens- certain P. vulgaris strains share antigens with

Rickettsia – used as -antigens for the detection of rickettsial antibodies in Weil_Felix test

- ( OX-19, OX-K, OX-2)

PROTEUSCLINICAL INFECTION

Proteus mirabilis-2nd leading cause of community acquired UTI- major cause of nosocomial infection- urease formation causes urine to become alkaline – stone formation- rapid motility – invasion of urinary tract

PROVIDENCIA

PROVIDENCIA

Providencia rettgeri – previously ProteusProvidencia alcalifaciensProvidencia stuartii

- Members of the normal intestinal flora- All cause urinary tract infections- Often resistant to antimicrobial therapy

CITROBACTER

CITROBACTER

Citrobacter freundii – isolated from patients with diarrhea

Citrobacter diversus- neonatal meningitis and brain abscesses

TO BE CONTINUED…..

SHIGELLA

SHIGELLATAXONOMY

Shigella – genetically indistinguishable fromE.coli

- divided into 4 serogroups given species nameserogroup A – Shigella dysenteriaeserogroup B – Shigella flexneriserogroup C – Shigella boydiiserogroup D – Shigella sonnei

SHIGELLABIOCHEMICAL PROPERTIES AND CULTURAL

CHARACTERISTICSFactors that distinguish from Salmonella- Appear as non-lactose fermenting colonies- Non-motile- Do not produce H2S- Do not produce gas from glucose (except S.

flexneri)

SHIGELLARESISTANCE TO PHYSICAL AND CHEMICAL AGENTS

- Less resistant than most enterics to physical and chemical agents

- Susceptible to most common disinfectants- Can tolerate low temperatures if adequate

moisture is present- Can survive for more than 6 months in water

and room temperature

SHIGELLAANTIGENIC STRUCTURE

-Shigella are divided into 4 major O antigenic groups – A, B, C, Dsubgrouping – based on minor O antigensex: 12 serologic types of group A

6 serologic types of group B 18 serologic types of group C

- No H antigens - nonmotile

SHIGELLADETERMINANTS OF PATHOGENESIS

1. Surface properties – due to O antigens- Survive the passage through upper GIT,

2. Invasiveness - attach to colonic cells and penetrate the epithelial cells by induced phagocytosis, escape from phagocytic vacuole, multiply and spread inside the cytoplasm and passage to adjacent cells.

SHIGELLADETERMINANTS OF PATHOGENICITY

3. Toxins-Shiga toxin interferes with protein synthesis- inactivates the 60S ribosomal unit

bacillary dysentery is a 2-stage diseaseShigella multiply in a noninvasive manner in the

jejunum- and produce the toxin which is taken up by small bowel receptors- result in an activated secretory process

second phase – involve the large intestines

SHIGELLATOXINS

1. Endotoxin- from the LPS- causes irritation of the bowel wall

2. Shigella dysenteriae exotoxin- neurotoxic –meningisimus, coma

- enterotoxic – produces diarrhea

SHIGELLAPATHOGENESIS

Spectrum of diseaseasymptomatic infection to severe bacillary dysentery with high fever, chills, convulsions, abdominal cramps, tenesmus and frequent bloody stools

Organisms rarely penetrate the intestinal wall and spread to other parts of the body

For children and elderly - dehydration

SHIGELLADIAGNOSTIC LABORATORY TESTS

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ENTEROBACTERIACEAE B.A.Fontanilla, MD Department of Microbiology and Parasitology