Enterobacteriaceae[Lactose Fermenters] Flashcards
Properties of enterobacteriaceae
1—Gram neg rods whose natural habitat are in the intestinal tract of humans and animals
2—some are normal flora and incidentally cause disease e.g E.coli while some are regularly pathogenic for humans e.g salmonella and shigella
3— either motile with peritrichous flagella or non motile, non sporing, non acid fast and can either be capsulated or non capsulated
4— simple nutritional requirements hence can grow on an ordinary media e.g mac conkey agar
5— they are aerobes and facultative anaerobes and ferment a wide range of carbohydrates
6— catalase positive and oxidase negative
7— reduce nitrate to nitrite
Ewing’s 1986 classification into 8 classes based on biochemical characteristics
- Escharichieae — E.coli and Shigella
- Edwardsielleae — Edwardsiella
- Salmonelleae — Salmonella
- Citrobactereae — Citrobacter
- Klebsielleae — Klebsiella, Enterobacter and Serratia
- Proteeae — Proteus
- Yersinieae — Yersinia
- Erwinieae — Erwinia
Biochemical tests for enterobacteriaceae
- Indole test
- Voges - proskauer test
- Methyl red test
- Citrate utilization test
- Urease test
- Hydrogen sulphide production
Escherichia Coli properties & Cultural Properties
Gram negative, motile, aerobic and facultative anaerobic bacilli
Its a marker of fecal contamination as large amounts are excreted from man and animal feces
[Cultural Properties]
Optimal temp for growth 37 degrees celsius
Grows on ordinary media, nutrient agar and mac conkey agar (appears pink on mac conkey cause of the lactose fermentation)
Yellow on CLED and Metallic green sheen on EMB agar
A complete zone of hemolysis surrounds its growth on blood agar
Biochemical reactions for E.coli
Methyl red positive
Indole positive
Ornithine decarboxylase positive
Lysine decarboxylase positive
Voges - proskauer negative
Citrate negative
Urease negative
H2S production negative
[TSI Test] assesses acid and gas production and fermentation of 3 sugars( glucose 0.1 lactose 1 sucrose 1)
The phenol red sensitive dye senses the acid by fall in ph and converts it from red to yellow ( fermentation is indicated by acid production which makes ph fall and color change
[Indole production]
The bacteria demonstrates the ability to convert amino acid Tryptophan using enzyme Tryptophanese to produce Indole, Pyruvic acid and Ammonium.
Virulence properties and Pathotypes
The virulence properties include 1 Verocytotoxin 2 siderophore 3 Enterotoxin 4 Hemolysin O somatic antigens H Flagella antigens F fimbrial antigens K capsular antigens
Pathotypes include
1 ETEC ENTEROTOXIGENIC E COLI 2 EPEC ENTEROPATHOGENIC E COLI 3 EHEC ENTEROHAEMORRHAGIC E COLI 4 EIEC ENTEROINVASIVE E COLI 5 EAEC ENTERO AGGREGATIVE E COLI 6 DAEC DIFFUSE ADHERENT E COLI
Entero Toxigenic E Coli
Causative agent of Traveller’s diarrhea
2 types of enterotoxins namely HLT and HST ( heat labile toxins and heat stable toxins)
Heat labile toxin destroyed at a temperature of 65 degree for 30 minutes and it has 2 sub groups A and B
B subgroup is the one responsible for its binding to the intestinal tract within the intestinal brush border at the ganglioside receptor
Upon binding it facilitates the entry of subgroup A which Facilitates ADP RIBOSYLATION that occurs before the formation of CAMP
The LT toxin activates ADENYLATE CYCLASE resulting in the production of CAMP(cyclic adenosine monophosphate)
Accumulation of CAMP in the Git leads to hypersecretion of fluids and electrolytes in the lumen
Heat stable toxin is not destroyed by Heat, it activates Guanylate cyclase in intestinal wall causing increased production of cGMP(cyclic guanosine monophospate) and thus subsequent hypersecretion of fluids and electrolytes
Diarrhea of ETEC is similar to cholera
Entero Pathogenic E Coli
Causes Infantile Diarrhea
Mechanism of action not clear but after attachment to GIT the microvilli is lost, epithelial degeneration and inflammation is seen
No ST or LT toxin and it’s moderately invasive
Entero Hemorrhagic E coli (AKA E coli O157 H7)
Produces Verocytotoxin referred to as shiga-like toxin(toxic to african green monkey kidney cells)
Can be neutralized by antibodies formed against Shiga toxin
Consist of somatic capsular and fimbrial antigen( somatic is heat stable and capsular is heat labile)
Outcome is initial watery diarrhea followed by grossly bloody diarrhea with abdominal cramps
May progress to HUS(hemolytic Uremic syndrome) THROMBOCYTOPENIA ,ACUTE RENAL FAILURE, HEMOLYTIC ANEMIA
Enteroinvasive E.coli
Illness resemble bacillary dysentry (Shigellosis)
Common diseases associated with E.coli
1 Sepsis
2 UTI( most common cause of cystitis pyelonephritis and prostatis)
3 Gastroenteritis(5 out of the 6 pathotypes)
4 Neonatal Meningitis
5 Post operative wound infections
6 Intra abdominal infections
7 Respiratory tract infection
Treatments for E.coli infections
Cephalosporins
Aminoglycoside
Carbapenem
Piperacillin - tazobactam
KLEBSIELLA SPECIES PROPERTIES
It is the most common cause of a variety of community and hospital acquired infections
Klebsiella pneumoniae being the most common, klebsiella oxytoca too
Rare in immunocompetent normal host but more commonly encountered in hospital settings as opportunistic infections
Clinical presentation sudden high fever, hemoptysis and abnormal chest radiograph with multiple abscesses
Rhinoscleroma is a rare granulomatous disease causes by Klebsiella Rhinoscleromatie. There’s granulomatous infiltration of the respiratory mucosa
Non sporing, non motile, encapsulated & mucoid, lactose fermenting gram neg bacilli
Catalase positive and oxidase negative
Ferment glucose and lactose
Cultural characteristics of Klebsiella
Grow well on ordinary media
Optimal temp 37 degree
Colonies appear large mucoid and red on Macconkey agar
The presence of the capsular antigen enables it resist complement mediated killing
Biochemical Properties of Oxytoca and Pneumoniae
P. O
Indole Neg. Pos.
Methyl red. Neg. Variable
Vp. Positive. Variable
Citrate. Positive. Pos/neg
Urease Positive. Positive
Lactose. Positive Positive
