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Pathology And Pharamcology > Enterobacteriaceae - MICRO > Flashcards

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

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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
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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
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4
Q

Biochemical properties of Enterobacteriaceae?

A
  • Catalase positive and Oxidase negative
  • They reduce Nitrate to Nitrite
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5
Q

Ewing classification of Enterobacteriaceae is based on?

A

Based on biochemical characters, they are classified into **8 families*

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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
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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
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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
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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

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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

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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

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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

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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)

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14
Q

The causative E.coli pathotype for Travellers diarrhea is

A

Enterotoxigenic E.coli

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15
Q

Mention the toxins produced by Enterotoxigenic E.coli ?

A

Heat Labile (LT) and Heat stable (ST) toxins

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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)
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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)

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18
Q

Enteropathogenic E.coli causes ?

A

Infantile diarrhea

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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
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20
Q

Another name for EHEC?

A

Entero-hemorraghic E.coli is also know as E.coli O157 H7

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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 )

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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
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23
Q

Symptoms of enterohemorrhagic E. coli?

A
  • Abdominal cramps
  • Watery diarrhea
  • Hemorrhagic colitis
  • Hemolytic uraemic syndrome;
    acute renal failure, thrombocytopenia, hemolytic anemia
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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
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25
Q

The most common isolated Gram negative rod in sepsis is?

A

Escherichia coli

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26
Q

Diseases associated with E.coli

A

UTIs - Cystitis, pyelonephritis, prostatitis
Sepsis
Gastroenteritis - at least 5 different pathogenic groups
Neonatal meningitis
Intra abdominal infections
Post operative wound infections
Respiratory tract infections

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27
Q

In neonatal Meningitis, what statins of E.coli is usually implicated?

A

Statins of E.coli carrying the K1 capsular antigen

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28
Q

What’s the usually organism implicated in Post operative infections ?

A

Escherichia coli

29
Q

Treatment of UTI caused by Ecoli?

A

Nitrofurantoin and topical TMP

30
Q

Treatment of hospital acquired infections caused by E.coli

A

Usually drug resistant strains of E.coli
Requires cephalosporin, carbapenams, aminoglycosides, piperacillin- Tazobactam

31
Q

The most common cause of Hospital and community acquired infections include?

A

Klebsiella species

32
Q

An important emerging pathogen in community acquired live abscess worldwide is ?

A

Klebsiella pneumoniae

33
Q

Klebsiella and immunocomoetence?

A
  • Rare in immunocompetent normal hosts.
  • Mostly encountered in hospital settings as opportunistic infections
34
Q

Risk factors for severe infection with Klebsiella

A

Alcohol , Diabetes , COPD

35
Q

An important cause of Friedlanders pneumonia is ?

A

AKA Community acquired pneumonia, which is —— Klebsiella

36
Q

Clinical manifestation is Fried lander pneumoniae is ?

A
  • Sudden high fever
  • Hempotysis (red currant belly)
  • Chest radiograph showing multiple lung abscesses
37
Q

Which klebsiella specie is associated with a granulomatous infection?

A

K. rhinoscleromatis which causes rhinoscleroma

38
Q

Features of rhinoscleroma?

A

There’s granulomatous infiltration of the respiratory mucosa

39
Q

The two leading species in most klebsiella infections are ?

A

K.pneumoniae and K.oxytoca

40
Q

Properties of klebsiella

A
  • 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
Q

Cultural characteristic of Klebsiella?

A
  • Grow well on ordinary media (macConkey agar)
  • Optimal temperature for growth is 37•c
  • Colonies appear Red, Large, mucoid on MacConkey agar
42
Q

Structural properties of klebsiella?

A
  • 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
Q

The only Klebsiella species that’s positive to indole test is ?

A

K. oxytoca

44
Q

Biochemical properties of Klebsiella

A

Negative to Ornithine decarboxylase
Lactose fermenters (apart from Rhinoscleromatis)

45
Q

Rhinoscleromatis is only positive to ?

A
  • Methyl red test
  • Aerogenes is negative for MP
46
Q

What drugs are Klebsiella species resistant to ?

A
  • Ampicillin and other penicillins
  • They are mostly MDR organisms
  • Treatment should be done according to local sensitivity data
47
Q

Epidemiology of Enterobacter

A
  • 5th leading Cause of nosocomial infections (burn & wound infection, pneumoniae)
  • 3rd leading cause of nosocomial pneumoniae….
  • from contaminated enteral feeding, respiratory equipment
48
Q

Properties of enterobacter??

A
  • 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
Q

Risk factors for enterobacter infection

A
  • Indwelling lines
  • Recent invasive procedure
  • Diabetes
  • Neutropenia
  • Recent dialysis
  • Frequent course of antibiotic use.
50
Q

Enterobacter species are resistant to what class of drugs ?

A

First generation cephalosporins and readily develop resistance to 2nd and 3rd generation cephalosporins

51
Q

What’s the mainstay of treatment of enterobacter ?

A

The use of Carbapenams

52
Q

Two groups of patients at risk of developing citrobacter infections?

A

Neonates and Elderly

53
Q

What are the possible infection sites of citrobacter?

A

Meninges, bone, endocardium, wounds, respiratory, urinary, blood, surgical

54
Q

Biochemical properties of Citrobacter

A

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
Q

Treatment of Citrobacter infections?

A

They are MDR organisms.
Treatment options includes
- use of quinolones
- use of carbapenams
- use of aminoglycosides
- use of anti-pseudomonas penicillin

56
Q

Shigella infection is called?

A

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
Q

Shigella is divided into ____ serogroups?

A

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
Q

Cultural properties of Shigella?

A
  • 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
Q

Bacteria that produces hydrogen sulphide are detected how?

A

Presence of a black precipitate formed with ferric citrate

60
Q

Which of the shigella species are catalase negative?

A

S. dysenteriae 1 is Catalase negative

61
Q

All shigella species are non lactose fermenters apart from ?

A

S. sonnei (hence why it appears pink on MacConkey and DCA agar)

62
Q

The hallmark for shigella infection is??

A

Invasion, Intracellular replication, and toxin production

63
Q

Pathogenesis of Shigella infection ?

A
  • 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
Q

S. dysenteriae 1 produces what type of toxin?

A
  • Endotoxin - Verocytotoxin similar to EHEC
  • Exotoxin - Neurotoxin
65
Q

Infective dose of shigella is?

A

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
Q

Symptoms of shigellosis ?

A
  • 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
Q

Diagnosis of shigellosis?

A
  • 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
Q

Treatment of shigellosis?

A
  • 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

Pathology And Pharamcology (7 decks)

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