Enterobacteriaceae - MICRO Flashcards
1
Q
Enterobacteriaceae are large ………. Group of ……….?
A
Enterobacteriaceae are large herterogenous group of gram negative rods whose natural habitat is the intestinal tract of humans and animals
2
Q
Properties of Enterobacteriaceae ?
A
- Gram Negative Rods, that are either motile with peritrichous flagella or non motile
- Non sporing and non acid-fast
- can be capsulated or uncapsulated
- Can readily grow on peptone/or ordinary media e.g MacConkey (simple nutritional requirement)
- Carbohydrate fermenters
- facultative anaerobes/aerobes
3
Q
In terms of Fermentation, Enterobacteriaceae……..?
A
- Are glucose fermenters with acid +/- gas production
- Some are lactose fermenters with acid and gas production. some are non-lactose fermenters
4
Q
Biochemical properties of Enterobacteriaceae?
A
- Catalase positive and Oxidase negative
- They reduce Nitrate to Nitrite
5
Q
Ewing classification of Enterobacteriaceae is based on?
A
Based on biochemical characters, they are classified into **8 families*
6
Q
Erwin’s 8 families of Enterobacteriaceae and examples under each?
A
- Escharichieae - E.coli, Shigella
- Edwardsielleae - Edwardsiella
- Salmonelleae - salmonella
- Citrobactereae - Citrobacter
- Klebsielleae - klebsiella, enterobacter, serratia
- Proteeae - protease, providencia
- Yersinieae - Yersinia
- Erwinieae - Erwinia
7
Q
E. Coli features ..?
A
- Gram negative, Motile, aerobic and facultative anaerobic bacilli
- most infections are endogenous
- mostly enteric (some arise from extra intestinal)
- Large numbers are excreted in feces and animal feces
- marker of fecal contamination
8
Q
Cultural characteristics of E.coli..?
A
- Lactose fermenting
- Optimal temperature for growth is 37•c
- Grows on ordinary media (MacConkey agar, nutrient agar)
- Pink colony on MacConkey agar
- Yellow colony on CLED agar
- Matellic green sheen on EMB agar
- Beta Hemolysis (complete zone of hemolysis surrounds units growth in blood agar
9
Q
Biochemical reactions of E. coli?
A
Methyl red - positive
Ornithine decarboxylase - positive
Lysine decarboxylase - positive
Voges-proskauer - negative
Citrate - Negative
Urease - negative
H2S production - negative
10
Q
Use of TSI for E.coli ?
A
fermentation is indicated by acid production, hence the ph falls and then is picked by the indicator (phenol red) as a colour change from yellow to red
11
Q
Indole test- production by E.coli
A
It possesses the ability to convert amino acid tryptophan using
tryptophanase enzyme to produce indole, pyruvic acid and ammonium
12
Q
Virulence factors of E.coli ?
A
O antigens - somatic Antigens
K antigens - capsular antigens
H antigens - Flagella antigens
F antigens - Fimbrial antigens
Enterotoxin
Hemolysis
Verocytotoxin
Siderophore
13
Q
Pathotypes of E. coli ?
A
Enterotoxigenic E.coli (ETEC)
Enteropathogenic E.coli (EPEC)
Entero-haemorrhagic E.coli (EHA)
Entero-invasive E.coli (EIEC)
Entero-aggregative E.coli (EAEC)
Diffuse adherent E.coli (DAEC)
14
Q
The causative E.coli pathotype for Travellers diarrhea is
A
Enterotoxigenic E.coli
15
Q
Mention the toxins produced by Enterotoxigenic E.coli ?
A
Heat Labile (LT) and Heat stable (ST) toxins
16
Q
LT toxin can be destroyed by…..??
and subunits, and MOA?
A
Heat labile toxins (LT) are destroyed at a temperature of 65•c at 30mins
- B sub-units; Binding in the intestinal tract, at the ganglioside receptor within the intestinal brush border
- A sub-unit; Which facilitates, ADP ribosylation that occurs before CAMP production
- (LT) activates Adenylase Cyclase and then cause production of CAMP (cyclic adenosine monophosphate)
17
Q
Diarrhea in ETEC is caused by ….?
A
Accumulation of CAMP being produced causes hypersecretion of fluids in the GIT lumen (diarrhea is similar to that of cholera)
18
Q
Enteropathogenic E.coli causes ?
A
Infantile diarrhea
19
Q
Mechanism at which EPEC cause diarrhea?
A
- They attach to the gut lumen and causes loss of microvilli, epithelial degeneration and inflammatory changes are seen
- They have no toxins, and are moderately invasive
20
Q
Another name for EHEC?
A
Entero-hemorraghic E.coli is also know as E.coli O157 H7
21
Q
What toxin does EHEC produce and why the name?
A
Verocytotoxin - Shiga-like toxin (similar to shigella toxin)
Toxin is toxic to vero (African green monkey kidney cells )
22
Q
Function of EHEC toxin?
A
- It disrupts protein synthesis and also causes the destruction of intestinal microvilli
- This causes decreased absorption with watery diarrhea followed by grossly bloody diarrhea (Hemorrhagic colitis) with abdominal cramp
23
Q
Symptoms of enterohemorrhagic E. coli?
A
- Abdominal cramps
- Watery diarrhea
- Hemorrhagic colitis
-
Hemolytic uraemic syndrome;
acute renal failure, thrombocytopenia, hemolytic anemia
24
Q
EIEC pathogenesis ? ?
A
- Illness caused by EIEC resembles that of bacillary dysentery (shigellosis)
- It enters into the cell, there’s intracellular multiplication and intra/intercellular spread and then host cell death
- it causes ulcerative colonic lesions, submucosal and mucosal Edema and infiltration by PMNs
- Symptoms; abdominal cramps, watery diarrhea may progress to dysentery with scanty bloody stools, severe inflammation and fever
25
The most common isolated **Gram negative rod** in **sepsis** is?
Escherichia coli
26
Diseases associated with E.coli
UTIs - Cystitis, pyelonephritis, prostatitis
Sepsis
Gastroenteritis - at least 5 different pathogenic groups
Neonatal meningitis
Intra abdominal infections
Post operative wound infections
Respiratory tract infections
27
In neonatal Meningitis, what statins of E.coli is usually implicated?
Statins of E.coli carrying the **K1 capsular antigen**
28
What’s the usually organism implicated in **Post operative infections** ?
Escherichia coli
29
Treatment of UTI caused by Ecoli?
Nitrofurantoin and topical TMP
30
Treatment of hospital acquired infections caused by E.coli
Usually **drug resistant strains of E.coli**
Requires **cephalosporin**, **carbapenams**, **aminoglycosides**, **piperacillin- Tazobactam**
31
The most common cause of Hospital and community acquired infections include?
Klebsiella species
32
An important emerging pathogen in community acquired live abscess worldwide is ?
Klebsiella pneumoniae
33
Klebsiella and immunocomoetence?
- Rare in immunocompetent normal hosts.
- Mostly encountered in **hospital settings** as **opportunistic infections**
34
Risk factors for severe infection with Klebsiella
Alcohol , Diabetes , COPD
35
An important cause of **Friedlanders pneumonia** is ?
AKA Community acquired pneumonia, which is —— **Klebsiella**
36
Clinical manifestation is Fried lander pneumoniae is ?
- Sudden high fever
- Hempotysis (red currant belly)
- Chest radiograph showing multiple lung abscesses
37
Which klebsiella specie is associated with a granulomatous infection?
**K. rhinoscleromatis** which causes **rhinoscleroma**
38
Features of rhinoscleroma?
There’s **granulomatous infiltration of the respiratory mucosa**
39
The two leading species in most klebsiella infections are ?
K.**pneumoniae** and K.**oxytoca**
40
Properties of klebsiella
- **Glucose** and **lactose fermenter**
- facultative anaerobe and aerobe
- non sporing, non motile, Encapsulated and mucoid
- **Gram negative bacilli**
- **Catalase positive and oxidase negative**
- Species; **Oxytoca, pneumoniae, aerogenes, rhinoscleromatis, Ozaenae**
41
Cultural characteristic of Klebsiella?
- Grow well on ordinary media (macConkey agar)
- Optimal temperature for growth is 37•c
- Colonies appear **Red, Large, mucoid** on **MacConkey agar**
42
Structural properties of klebsiella?
- **Capsular antigen** (k antigen) enables it to **resist complement mediated killing**
- **O antigens** make them **resistant to phagocytosis**
- There are over 80 known Capsular antigens and at least 5 known O antigens in klebsiella.
43
The only Klebsiella species that’s **positive to indole test** is ?
K. oxytoca
44
Biochemical properties of Klebsiella
Negative to Ornithine decarboxylase
Lactose fermenters (apart from Rhinoscleromatis)
45
Rhinoscleromatis is only positive to ?
- Methyl red test
- **Aerogenes** is negative for MP
46
What drugs are Klebsiella species resistant to ?
- **Ampicillin and other penicillins**
- They are mostly MDR organisms
- Treatment should be done according to local sensitivity data
47
Epidemiology of Enterobacter
- 5th leading Cause of nosocomial infections (burn & wound infection, pneumoniae)
- 3rd leading cause of nosocomial pneumoniae….
- from contaminated enteral feeding, respiratory equipment
48
Properties of enterobacter??
- They are facultative anaerobes /aerobes.
- They are **catalase positive** and **oxidase negative**.
- They **ferment glucose** and **lactose.**
- They are **motile and unlikely to be capsulated** like Klebsiellia
- They **reduce nitrate to nitrite**
- They are endowed with virulence factors such as adhesion, endotoxin, siderophores
• They utilize **citrate. (positive)**
• **Voges -proskauer - positive**.
• They **do not produce HaS**.
• Indole negative
• Methyl red negative
• **Ornithine decarboxylase positive**
49
Risk factors for enterobacter infection
- Indwelling lines
- Recent invasive procedure
- Diabetes
- Neutropenia
- Recent dialysis
- Frequent course of antibiotic use.
50
Enterobacter species are resistant to what class of drugs ?
**First generation cephalosporins** and readily develop resistance to **2nd and 3rd generation cephalosporins**
51
What’s the mainstay of treatment of enterobacter ?
The use of **Carbapenams**
52
Two groups of patients at risk of developing **citrobacter** infections?
**Neonates** and **Elderly**
53
What are the possible infection sites of citrobacter?
Meninges, bone, endocardium, wounds, respiratory, urinary, blood, surgical
54
Biochemical properties of Citrobacter
**Ferment glucose** and **lactose** with **gas production**
Citrate **positive**
Methyl red **positive**
Vp **positive**
The **slowly hydrolyze urea**
They are **motile**
Produces **hydrogen sulphide (H2S)** and can be mistaken for salmonella
55
Treatment of Citrobacter infections?
They are **MDR organisms**.
Treatment options includes
- use of **quinolones**
- use of **carbapenams**
- use of **aminoglycosides**
- use of **anti-pseudomonas penicillin**
56
Shigella infection is called?
**Shigellosis.** ——- **bacillary dystentry**
Shigella is only found in the stool of infected people, contaminated water and surface (**not a normal flora** of the GIT)
57
Shigella is divided into ____ serogroups?
**4 serogroups** with different serotypes
A - S. dysenteriae (12 serotypes)
B - S. flexneri (6 serotypes)
C - S. boydii (18 serotypes)
D - S. sonnei ( 1 serotype)
58
Cultural properties of Shigella?
- FA/Aerobes
- Non motile, not capsulated, non flagellated
- Temp for growth is 10-40•c optimal (37•c )
- Grows in blood, XLD agar, and;
- MacConkey - **colourless** (**Non lactose fermenter**) **pink - sonnei**
- DCA; Seletive media for isolating Shigella. **Colourless colony with no blackening**
- SS agar; highly selective media (**salmonella shigella agar**)
- Selenite F enrichment agar - inhibits other GIT coliforms and **recovers SS**
- presence of **sodium thiosulphate** as a good source of **H2S and ferric citrate**
59
Bacteria that produces hydrogen sulphide are detected how?
Presence of a **black precipitate** formed with ferric citrate
60
Which of the shigella species are catalase negative?
**S. dysenteriae 1** is Catalase negative
61
All shigella species are non lactose fermenters apart from ?
**S. sonnei** (hence why it appears pink on MacConkey and DCA agar)
62
The hallmark for shigella infection is??
**Invasion**, **Intracellular replication**, **and toxin production**
63
Pathogenesis of Shigella infection ?
- They invade the large bowel with varying level of **inflammation** and **capillary thrombosis**.
- The organism continues to **multiply within epithelia cell**, causes **cell death** due to cytotoxicity of the endotoxin and **ulcers are formed**
- Enterotoxin - Diarrhea similar to E coli
- Exotoxin: **Neurotoxin - meningismus, coma** is observed.
- Symptoms may begin as early as 12hrs after ingestion.
64
S. dysenteriae 1 produces what type of toxin?
- **Endotoxin** - Verocytotoxin similar to EHEC
- **Exotoxin** - Neurotoxin
65
Infective dose of shigella is?
**10-100 organisms**
- **Humans are the only natural host**, they get infected by ingesting contaminated water or food ( mechanical carriers (flies) or poor hand hygiene)
66
Symptoms of shigellosis ?
- The **typical symptoms** are **abdominal pain, vomiting, fever, tenesmus, mucus in stool, and diarrhea which is often bloody**.
• Severe symptoms are seen in S dysenteriae infection - **marked prostration, toxic megacolon, convulsions and HUS**.
• Complications - **arthritis, toxic neuritis and intussusception** after S dysenteriae 1 infection.
67
Diagnosis of shigellosis?
- History
- Physical examination.
- **Sample** : **Fresh stool**
- Micrcoscopy : **Demonstration of blood and neutrophils**
- Stool culture.
- EIA
- Rapid techniques eg **PCR**
- Ancillary test **FBC, E/U/Cr**
68
Treatment of shigellosis?
- Most cases are mild and self limiting.
- Oral rehydration - to replace fluid loss
- **Beta lactams**: Ampicillin, amoxicillin, 3rd gen cephalosporins
- **Quinolones**: Ciprofloxacin, ofloxacin.
- **Macrolides** Azithromycin
- Others : **Sulfonamides**, **co-trimoxazole**
- Appropriate infection control measures to prevent spread of infection
