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Flashcards in Microbiology Enteric Infections Deck (72):
1

Common

• Campylobacter ep.,
• Salmonella sp. (food poisoning)
• Shigella sp,.
• E.Coli

2

Less common

• Paratyphi (enteric fevers)
• Virbio parahaemolyticus
• Vibrio cholera
• C.Diff
• C. perfringens
• Listeri
• Helicobacter pylori
• Aeromonas sp.,
• Plesiomonas sp.

3

Performed Toxins

• Staphylococcis aureus
• Bacillus cereus (rice)
• Clostridium botuinum
• Perfringens

4

Common Gastroenteritis Viruses:

• Rotavirus (most common)
• Calciciviruses (Norovirus, Sapovirus)
• Adenoviruses
• Astrovirusus
• (Hepatitis A and E)
• Many others found in GI tract as part of systemic infection

5

Parasites

Protoazoa:
• Giardia intestinals
• Cryptosporidium parvum
• Entamoeba histolytica

Helminths
• Ascaris lumbricoides
• Hookworms
• Tapeworms

6

Acute gastroenteritis in USA


>30 million episodes/yr
1.5 million OPD visits/yr
200,000 hospitalisations/yr
Around 300 deaths/yr

7

Developing Countries diarrhoea

Is a common cause of death in under 5’s – 2 million deaths per year

8

Oral Rehydration Therapy

Diarrhoea secretory (Chloride or calcium mediated) +/- osmotic (damage to villous brush border)
Success of ORS relies on coupled transport of sodium and glucose into enterocytes so that water follows the gradient.

9

Common Presenting Features

Diarrhoea (uncomplicated or collities) – D & V may be first stages of UTI, meningitis
Vomiting
Fever
Recent contact environmental link
Epidemiology

10

Types of enteric infection

Type 1: Non-inflammatory (Watery diarrhoea) e.g. toxin mediated (c. perfringens, B. cerues, S. aureus), Giardia, Cryptosporidium, Rotavirus, Norovirus, ETEC, EPEC

Type 2: Inflammtory (dysentery, faecal leukocytes, lactoferrin) e.g. Shigella, VTEC, C. difficile, C. jejuni, S.enteritidus, Entamoeba.

Type 3: Penetrating (Enteric Fever) e.g. S. Typhi, yersinia

11

Standard Management

Often uncomplicated an self-limiting
Mainstay of treatment is supportive
• Rehydration
• Little role for anti-diarrhoeal agents
Specific: therapy may be required
• Some bacteria and some parasites require antimicrobial therapy

12

Assessment of Dehydration

Correct, early assessment essential
Infants more prone as higher body surface to volume ratio, smaller fluid reservoir, dependent on others for fluids
Signs

13

Signs of severe dehydration

Apathy, tachycardia (bradycardia if extreme), weak pulse, deep breathing, deep sunken eyes, no tears, parched mouth, skin recoil >2 secs, minimal urine output.

14

Basic Diagnosis

Rarely possible on clinical features alone
Epidemiology (e.g. par of outbreak)
Microbiological investigation
• Rarely necessary unless dehydration, febrile, blood or pus in stool, or part of outbreak
• Stoll +/- blood culture, selective, indicator growth media (diagnostic yield Stool culture – 5%)
• Microscopy of stool for ova, cysts, parasites
• Specific typing

15

Prevention

Avoidance of risk
• Don’t travel?
• Basic Hygiene, hand washing
• Clean water, clean food, adequate cooking
• Immunisation (Typhoid, rotavirus)
• Hospital infection control

16

E.Coli
Description

• E.coli is a major part of normal gut flora.
• Until recently role uncertain as difficult to distinguish pathogens from commensals

17

Pathogenic forms of E.Coli

• Enterotoxigenic E. Coli (ETEC)
• Verocytotoxic (VTEC) or Enterohaemorrhagic (EHEC)
• Enterinasive (EIEC)
• Enteropathogenic (EPEC)

18

Pathogenicity of ETEC

Produce 2 main types of toxin
• Polypeptide, like cholera toxin
• Stimulates hypersecretion

19

Pathogenicity of VTEC

Or Haemmohagic
• Cytotoxin, Kills cells, like Shigella toxin
• Haemorrhagic colitis and HUS (Haemolytic uremic syndrome)

20

Spread ecoli

All Faecal-oral, direct, food or water

21

ETEC epidemiology

Commonest cause bacterial diarrhoea in children in areas of poor hygiene, uncommon W Europe, important cause traveller’s diarrhoea.
Reservoir-human GI tract

22

VTEC Epidemiology

Several types, commonest O157, now common cause of acute renal failure in Western countries.
Reservoir-GI tract of healthy cattle
Contaminated food/animal carcasses (hamburgers0, unpasteurised milk, farms, paddling pools person to person rare e.g. nurseries

23

E.Coli
Clinical Features (general)

Incubation usually 1-5 days (up to 14)
Abrupt onset vomiting and diarrhoea – later profuse watery diarrhoea only
Mild fever, little pain
Similar to viral gastroenteritis/salmonellosis (early stage but complications)

24

E.Coli
Severe complications

Haemorrhagic Colitis
Haemolytic Uraemic Syndrome

25

E.Coli
Haemorrhagic Colitis

• May complicated O157 infection in children and adults 699 positive stool cultures in 2004
• Typical diarrhoea progressing to bloody with abdominal pain
• Fever usually low
• May be mistaken for acute inflammatory bowel disease (as the preceding infection not severe)

26

E.Coli
Haemolytic Uraemia Syndrome

• May accompany colitis as a complication – 10% children in outbreaks
• Rising urea and creatinine, haemolytic anaemia and thrombocytopaenia
• Raising BP, fitting
• More than half need haemodialysis, almost all caes recover (most deaths in elderly, fatal <5%)
• Preceding GI illness may be unrecognised
• Mucosal damage and microangiopathic haemolytic anaemia and renal vascular disease

27

E.Coli
Laboratory Diagnosis

• Difficult – pathogen and normal flora are same species
• O157 phage typing
• O157 doesn’t ferment sorbitol
• Immunological cytotoxin detection
• PCR detection of cytotoxin gene

28

E.Coli
Management

• Supportive
• Many E.coli resistant to broad spectrum penicillins, cephalosporins, trimethoprim
• Ciprofloxacin 500 mg BD, 3-5 days
• Avoid antibiotics in HUS
• Anti-motility drugs probably increase change of HUS through delayed clearance of toxin

29

Salmonella → Description

Food Poisoning
• Infect humans and other animals
• >2000 serotypes

30

Salmonella →Commonest serotypes

S. enteritidis
S. typimurism
S. Virchow

Typhoid and paratyphoid fevers
Exclusive human pathogens – more torpical causes

31

Salmonella → Source

Contaminated poultry/ dairy products common source – not usually from food handlers or person-to-person spread. Reservoire – GI tract of birds, reptiles, amphibians

32

Salmonella → Seasonally timing

Commoner in summer/hot weather – 11,415 positive stool isolates In 2004

33

Salmonella → Microbiology

Identified on specific media by biochemical features:
1. Non-lactose fermenter
2. Produces H2s
LPS is O antigen, flagellae H antigen, defines serotype

34

Salmonella Food poisoning

Infection of gut epithelium
• Does not extend beyond membrane
• Excessive fluid secretion from ileum/jejunum
• If transported through cells, leads to systemic infection
Survives in macrophages

35

Clinical Features salmonella

Incubation 12-72 hrs
Malaise
Nausea
Vomiting
Fever
Watery brown diarrhoea follows rapidly
Abdominal Pain common but not severe
Often resolves in several days, some cases last several weeks
Children and elderly at risk of hypovolaemia

36

Salmonella Complications

• Salmonella Collitis (Up to 10% colic and bloody stools)
• Bacteraemia – seeding to bones/ joints (sickle-cell), aneurysms
• Post-infectious reactive arthritis
• Prolonged excretion – diverticulosis, IBO, HIV

37

Salmonella Microbiology

Stool cultre, blood culture if high fever/very unwell
Selective agar to inhibit normal flora and indicator, often lactose red resulting in pink colonies due to fermentation of lactose and acid production

38

Salmonella Typing

Bacteriophage
Antiobiotic panels

39

Salmonella Management

Rehydration
Antibiotics if no recovery after 8 rs, shock, high risk (valve disease/prosthesis), bacteraemia
Ciprofloxacin first line (alternative is cefotaxime)

40

Shigellosis (Bacillary dysentery) → Epi


• Worldwide problem
• Western countries endemic Shigellae usually cause mild illness
• Tropical strains tend to be more severe and persistent
• Person to person spread and via contaminated food and water → Reservoir – human GI tract
• Fw thousand cases/yr in UK Commonest S. sonneir, others flexneri, boydii, dysenteriae

41

Shigellosis (Bacillary dysentery) → Invasion

• Invade gut by destroying submucosa, infecting enterocytes, spread from cell to cell
• S.dysenteriae type 1 produces exotosin (shiga toxin)

42

Shigellosis (Bacillary dysentery) → Clinical Features

Incubation 1-7 days
High fever, high WBC, fever resolves and diarrhoea and colic begin sonnei and boydii mild, rarely colitis
Flexneri and dysenteriae more severe, mucus and blood in stools, marked cells
Asymptomatic excretion

43

Shigellosis (Bacillary dysentery) → Microbiology

Like E.coli (difficult to differentiate)
-Non-lactose fermenters
Non-motile
Serotype on basis of I antigens

44

Shigellosis (Bacillary dysentery) → Management

Symptomatic, antispasmodics, rehydrate
Abx in severe cases, ciprofloxacin (trimethoprim may be active, ceftriaxone also alternative)

45

Campylobacter: Epi


Commonest causes of food poisoning >50,000 cases/yr UK
Mostly sporadic, undercooked poultry, bird pecked milk – large food/waterbourne outbreaks can occur

46

Campylobacter: Incidence

Higher in summer

47

Campylobacter: Spread

Person-person spread uncommon

48

Campylobacter: Pathogen type

Animal Pathogen; several species infect humans – C.jejuni, coli, fetus, lari

49

Campylobacter: C. Jejuni

Low infective dose
Cell-wall LPS (Lipopolysaccarides)
Enterotoxin and cytotoxin

50

Campylobacter: Clinical Features

• Incubation period 2-5 days (up to 9)
• 24 hr prodrome, fever, headache
• Watery diarrhoea, can be bloody, vomiting
• Pain significant, constant, not colicky
• Pain with little diarrhoea may occur – like acute abdomen
• Systemic infection rare
• Commonest antecedent infection identified in Guillain Barre Syndrome (a post-infectious peripheral neuropathy).

51

Campylobacter: Microbiology

• Selective media with antibiotics
• 43oC may improve selection
• Gull wing morphology

52

Campylobacter: Management

• Mild cases self-limiting
• Severe/ prolonged, use 3-4 day course oral erythromycin
• Ciprofloxacin active/ erythromycin

53

Campylobacter: Clinical presentation

• Asymptomatic carriage
• Antibiotic – associated diarrhoea
• Antibiotic-associated colitis

54

Campylobacter: Complications

• Acute abdominal syndrome/ toxic megacolon, colonic perforation, pseudomembranous colitis, recurrence ( in 20%)

55

Clostridium difficile: Risk Groups



>65 years
Antibiotic treamtnet (esp. clindamycin, cephalosporins, penicillins)
GI surgery/manipulation
Long stay in hospital/residential care
Immunosuppression

56

Clostridium difficile: Management

Confirm diagnosis (C.Diff toxin testing)
Stop or change antiobiotics if possible
Fluid/electrolyte replacement
Avoid antiperistaltics
If above not possible or unsuccessful, treat with metronidazole (2nd line vancomycin)
Infectino contorl

57

Viral Gastroenteritis: Epi

Commonest cause of symptomatic intestinal infection in Western World
Rarely severe or fatal in UK
Significant cause of infant mortality in resource poor countries

58

Viral Gastroenteritis: Management

|All self-limiting in the normal host
Rehydration is the key
Prevention of spread
• Faecal-oral, person-person, food
Antiviral therapy not used/available

59

Viral Gastroenteritis: Diagnosis

Rarely possible on clinical grounds
Epi
Stool electron microscopy, ‘catch all’
Stool enzyme imunoassays (e.g. rotavirus)
Molecular diagnosis – stool PCR
Outbreak typing and molecular epi
None of these viruses can be grown in cell culture

60

Rotavirus: Epi

Commonest cause of viral gastroenteritis in young children
• 1 mllion eaths/yr worldwide
• >10,000 cases/yr UK, under-reported

61

Rotavirus:Peak incidence

6-24 months, uncommon >5 yrs but adult infection occurs and can be symptomatic – may cause outbreaks in elderly care homes
Seasonal, late winter – march/april

62

Rotavirus:Virology

Reovirus:
• Segmented dsRNA genome
• No envelope
• Seven serogroups (A-G)
• Gp A human, others infect different animals e.g. pigs
• Genomes can reassert (like flu A), possibility of new human strains
Reservoir GI tract humans: 1 billion viruses/ml faeces, only 10 needed for infection

63

Rotavirus: Clinical

Incubation around 1 day
Abrupt onset D and V (D-V)
Mild fever, short-lived
Recovery in 48 hrs usual (D for up to a week)
Blood in stool can ovvur – investigate further
Gross dehydration and shock
Adults may have mild disease, transient vomiting
Persistent diarrhoea may occur in immunosuppressed

64

Rotavirus: Rotavirus Vaccine

Original tetravalent rhesus monkey/human reassortment vaccine 9Rotashield) withdrawn over concerns regarding intussusception
New live attenuated vaccines (Rotarix and Rota Teq) highly effective against severe disease
Protection severe disease not necessarily against infection
Rotarix added to UK Chidhood immunization programme in 2013-2 dosease given at 2 months and 3 months of age

65

Caliciviruses: Types



Norovirus
Sapovirus (SRSV)
IEM demonstrated Norwalk virus as vomiting agent (winter vomiting) +ssRNA, non-enveloped, does not grow in routine cell culture
Reservoir human GI tract – may be concentrated in bivalve molluscs (osyters)

66

Norovirus Gastroenteritis clinically

Incubation 10-50 hrs
Asymptomatic to explosive vomiting and diarrhoea
Headache and abdominal cramps
Lasts 24-48 hrs

67

Norovirus outbreaks

Common defined outbreak – Closed communities/hospitals/cruise ships
Breathe in aerolised vomit/faeces and swallow
Infectious dose low

68

Enteric Adenoviruses

Second most common cause of infantile diarhhoea in temperate climates

69

Adenovirus causing disease

Non-enveloped, dsDNA
Subgrou[s A-F, Gastroenteritis agents are gp F types 40,41
Poor growth in cell culture

70

Adenovirus Standard clinical picture

Incubation period up to 10 days, watery diarrhoea, mild fever, illness may last longer in general (3-11 days)

71

Astroviruses

Infants and elderly exhibit significance illness
• Severity lower than other agents
• Often co-infection with rotavirus/norovirus

72

Astrovirus epi

<5% hospitalised cases viral gastroenteritis
Winter time
+ssRNA, non-enveloped, 5-6 pointed star
Several Serotypes

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