enterobacteriaceae

ENTEROBACTERIACEAE

The Enterobacteriaceae are usually considered to be only transiently ,present in the normal oral cavity ,and when their found their numbers are so small ,so that it unlikely play any important role in the mechanisms of the biological balance in the oral ecosystem

General Characteristic :

1-Gram negative, rods ,bacilli or coccobacilli. 2- most genus are motile ( Peritrichous flagella ) except Shigella , Yersinia & Klebisella. 3- Non spore forming . 4- Grow aerobically of facultative anaerobic. 5- Catalase ( + ) , oxidase ( - ) . 6-All reduce nitrates to nitrites 7-all species are fermentation glucose . 8- all Enterobacteriaceae produce similar growth on blood agar and chocolate agar are large, gray and smooth colonies , klebisella and Enterobacter are mucoid colonies.

Virulence and Antigenic Factors of Enterobacteraceae

Ability to colonize, adhere, produce various toxins and invade tissuesSome possess plasmids that may mediate resistance to antibioticsMany enterobactereaceae possess antigens that can be used to identify groupsO antigen – somatic, heat-stable antigen located in the cell wallH antigen – flagellar, heat labile antigenK antigen – capsular, heat-labile antigen


Based on clinical infections produced, enterobacteraceae are divided into two groups:Opportunistic pathogens – normally part of the usual intestinal flora that may produce infection outside the intestinePrimary intestinal pathogens – Salmonella, Shigella, and Yersinia sp.

Classification the family depending to the lactose fermentation on MacConkey agar : 1-Lactose fermentation.EX : E . coli, Klebisella spp. Colonies appear pink.2- Non – lactose fermentation.EX : Salmonella spp. , Shigella spp. .

Escherichia coli

Most significant species in the genus Important potential pathogen in humans Common isolate from colon flora

Escherichia coli :

Escherichia coli
InfectionsWide range including meningitis, gastrointestinal, urinary tract, wound, and bacteremiaGastrointestinal Infectionsdiarrhoeal diseases.Diarrhoeal –producing E.coli can be divided into five types: Enteropathogenic (EPEC) – primarily in infants and children; stool has mucous but not blood; identified by serotyping

Escherichia coli

Enterotoxigenic (ETEC) – “traveler’s diarrhea”; watery diarrhea without blood; self-limiting; usually not identified.Enteroinvasive (EIEC) – produce dysentery with bowel penetration, invasion and destruction of intestinal mucosa; watery diarrhea with blood; do NOT ferment lactose.

Escherichia coli (cont’d) Enterohemorrhagic (EHEC serotype 0157:H7) – associated with hemorrhagic diarrhea and hemolytic-uremic syndrome (HUS), which includes low platelet count, hemolytic anemia, and kidney failure; potentially fatal, especially in young children; does NOT ferment sucrose; identified by serotyping

Escherichia coli

Enteroaggregative (EaggEC) – cause diarrhea by adhering to the mucosal surface of the intestine; watery diarrhea; symptoms may persist for over two weeksUrinary Tract InfectionsE. coli is most common cause of UTI and kidney infection in humansUsually found in the large intestineAble to adhere to epithelial cells in the urinary tract

Escherichia coli

Septicemia & MeningitisE. coli is one of the most common causes of septicemia and meningitis among neonates; acquired in the birth canal before or during deliveryE. coli also causes bacteremia in adults, primarily from a genitourinary tract infection or a gastrointestinal sourceEscherichia hermannii – yellow pigmented; isolated from CSF, wounds and bloodEscherichia vulneris - wounds

Culture

1-Mac Conkey agar : Pink colonies due to the lactose fermentation 2-Blood agar : Some strains show beta haemolysis 3-Eosin methylene blue agar ( EMB ) : green to black with metallic sheen.


2. Klebisella Spp.
Characteristics : G- , thick to short rod, non motile, capsulated, ( polysaccharide ). Biochemical reaction : Catalase ( + ) . oxidase ( - ) , LF , Urease ( + ) , IMVIC : - - + +

Culture :

Blood agar : mucoid colonies . MacConkey agar : large mucoid, pink colonies ( mucoid because accumulation of capsule ) .

pathogenicity

K. pneumoniae is mostly commonly isolated species Possesses a polysaccharide capsule, which protects against phagocytosis and antibiotics AND makes the colonies moist and mucoid Frequent cause of nosocomial pneumonia urinary tract infection, septicemia and meningitis

Table to differentiate between E. Coli & klebisella .

klebisella
E. Coli
* capsulated
* non capsulated
* thick and short
* Slender and long
* non motile
* motile
* IMVIC - - + +
* IMVIC + + - -
* Urease ( + )
* Urease ( - )
* mucoid Colonies
* Colonies not mucoid

3. Salmonella spp.

Characteristics :G- , rod , motile , All species except S.typhi are Non –capsulate , non sporing .Biochemical reaction :Catalase ( + ) . oxidase ( - ) , fermentation many carbohydrate forming acid and gas , IMVIC : - + - + .

Species S. typhi typhoid fever S.paratyphi A,B,C Paratyphoid fever S. typhimurium food posining

Typhoid Fever

Salmonella typhi Pathogenesis contaminated food or water Bacteria spread in the body and infect the small intestine and invade the blood stream 1-3% recovered patients become carriers, harboring Salmonella in their gallbladder Symptoms: severe fever/headache weakness, abdominal pain and rash


Diagnosis of typhoid fever Blood cultures are positive during the first week and after the second week Stool cultures and sometimes urine cultures are positive after the second week The Widal test is a serological test for antibodies against Salmonella typhi. rise in titer .

Culture :Mac Conkey agar : Colonies colourless ( NLF )Salmonella – Shigella agar : brown colonies with black center ( SS agar ) .

S. typhi produce H2S : 1-S release from sodium thiosulfate by bacteria enzyme action . 2-Coupling S with H ( found on media ) to form H2S . 3-Delecting H2S by iron lead to produce heavy sulfides that appear black precipitate. H2S + FeSo4 FeS black

Bismuth Sulfate agar :

To differentiate between the species of salmonella S. typhi black colonies Other species of salmonella brown colonies

4. Shigella spp. 
Characteristics :G- , rods , non motile , non capsulated .Biochemical reaction :Catalase ( + ) . oxidase ( - ) , TSI K/A with NO gasUrea –Motility -All ferment mannitol except S. dysenteriaeS. sonnei may show delayed lactose fermentation .


Species :
Contains four species that differ antigenically S. dysenteriae S. flexneri S. Boydii S. sonnei .

Shigella

Clinical significance Causes shigellosis or bacillary dysentery. Transmission is via the fecal-oral rout under crowded conditions. The infective dose required to cause infection is very low (10-200 organisms). There is an incubation of 1-7 days followed by fever, cramping, abdominal pain, and watery diarrhea (due to the toxin)for 1-3 days.

The severity of the disease depends upon the species which infected with it. S. dysenteria is the most pathogenic followed by S. flexneri, S. sonnei and S. boydii.

Culture

MacConkey agar : Pale colonies except Sh. sonnei after 48hr . SS agar : Colourless without black center .

5. Proteus spp. 

Characteristics : G- , motile , swarming present only in the absence of bile salt , . Biochemical reaction : Catalase ( + ) . oxidase ( - ) , urease ( + ) , NLF .

Culture

1-nutrient agars produce swarming, fishy odor 2-urea agar.

Species : P. vulgaris . P. mirabilis . P. morganii . P. rettgeri .. P. mirabilis and P. vulgaris are widely recognized human pathogens Isolated from urine, wounds, and ear and bacteremic infections Virulence factors Urease , the ammonia produced may damage the epithelial cells of the UT Clinical Significance UT infections, as well as pneumonia, septicemia, and wound infections


6. Citrobacter :

Species :

C.freandii C.koseri C.amalonaticus Pathogenicity : U. T. I . C.koseri associated with meningitis and brain abscesses in infant

.7. Enterobacter :

Species :
E.aergenes E.clocae E.taylorae Pathogenicity Gastroenteritis Septecemia Liver Abscesses UTI Endocarditis Meningitis Pneumonia Diarrhea

EMB PLATE: E. coli is seen on the left and E. aerogenes on the right

8.Serratia spp.
Seven species, but S. marcescens is the only one clinically important Frequently found in nosocomial infections of urinary or respiratory tracts Characteristics : G- , bacilli, Ferments lactose slowly Produce characteristic red pigment, especially when cultures are left at room temperature vp( + ) . gelatinase ( - ) , citrate( + ) ,

Species

S.marcescens S.odorifera S.grimesii Pathogenicity : Meningitis Wound infection UTI, URTI Endocarditic


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