1. Infections that require large infective dosage
Food Borne Illness
Infections that require large infective dosage

2. Infections that require large infective dosage
Bacteria  Salmonella spp.  Yersinia enterocolitica and Yersinia pseudotuberculosis  Vibrio parahaemolyticus and other vibrios  Escherichia coli -             Enterotoxigenic (ETEC)             Enterohemorrhagic             HUS
Campylobacter jejuni
Listeria

3. Enterobacteriaceae Classification – more than15 different genera
Lactoes Ferm +ve
Escherichia
Enterobacter
Citrobacter
Klebsiella
Pectinobacterium
Lactoes Ferm –ve
Shigella
Edwardsiella
Salmonella
Hafnia
Serratia
Proteus
Providencia
Morganella
Yersinia
Erwinia
Classification – more than15 different genera

4. Enterobacteriaceae Morphology and General Characteristics
Gram-negative, non-sporing, rod shaped bacteria
Oxidase –
Ferment glucose and may or may not produce gas in the process (aerogenic vs anaerogenic)
Reduce nitrate to nitrite (there are a few exceptions)

5. Enterobacteriaceae Are facultative anaerobes
If motile, motility is by peritrichous flagella
Many are normal inhabitants of the intestinal tract of man and other animals
Some are enteric pathogens and others are urinary or respiratory tract pathogens
Differentiation is based on biochemical reactions and and differences in antigenic structure

6. Enterobacteriaceae
Most grow well on a variety of lab media including a lot of selective and differential media originally developed for the the selective isolation of enteric pathogens.
Most of this media is selective by incorporation of dyes and bile salts that inhibit G+ organisms and may suppress the growth of nonpathogenic species of Enterobacteriaceae.
Many are differential on the basis of whether or not the organisms ferment lactose and/or produce H2S.

7. Antigenic Structure of Enterobacteriaceae

8. Escherichia coli Normal inhabitant of the G.I. tract.
Some strains cause various forms of gastroenteritis.
Is a major cause of urinary tract infection and neonatal meningitis and septicemia.

9. E. coli May be hemolytic on CBA – more common in pathogenic strains
KEY tests for the normal strain:
TSI is A/A + gas
LIA K/K
Urea –
Indole +
Citrate –
Motility +
There is an inactive biotype that is anaerogenic, lactose – , and nonmotile.

10. Escherichia coli Virulence factors
Toxins
Enterotoxins and Shigella like Toxins
Enterotoxins causes a movement of water and ions from the tissues to the bowel resulting in watery diarrhea.
There are two types of enterotoxin: LT and ST

11. E. Coli Enterotoxins
LT – is heat labile and LT – is heat labile and alters the activity of sodium and chloride transporters producing an ion imbalance that results in fluid transport into the bowel.
ST – is heat stable and binds to specific receptors with the same results as with LT.

12. Shiga-type toxins
Shiga-type toxin – also called the verotoxin -produced by enterohemorrhagic strains of E. coli (EHEC)
– is cytotoxic, enterotoxic, neurotoxic, and may cause diarrhea and ulceration of the G.I. tract.

13. E. coli infections
Gastroenteritis – there are several distinct types of E. coli that are involved in different types of gastroenteritis:
enterotoxigenic E. coli (ETEC),
enteroinvasive E. coli (EIEC),
enteropathogenic E. coli (EPEC) ,
enteroaggregative E. coli (EAEC), and
enterohemorrhagic E. coli (EHEC).

14. Shigella
Shigella
Contains four species that differ antigenically and, to a lesser extent, biochemically.

15. Shigella species Biochemistry S. dysenteriae (Group A)
S. flexneri (Group B)
S. boydii (Group C)
S. sonnei (Group D)
Biochemistry
TSI K/A with NO gas
LIA K/A
Urea –
Motility -
All ferment mannitol except S. dysenteriae
S. sonnei may show delayed lactose fermentation

16. Shigella species Virulence factors
Shiga toxin – is produced by S. dysenteriae and in smaller amounts by S. flexneri and S. sonnei.
Acts to inhibit protein synthesis This plays a role in the ulceration of the intestinal mucosa.

17. Shigella Clinical significance
Causes shigellosis or bacillary dysentery.
Transmission is via the fecal-oral route.
The infective dose required to cause infection is very low ( 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.
This may be followed by frequent, scant stools with blood, mucous, and pus (due to invasion of intestinal mucosa).
It is rare for the organism to disseminate.
The severity of the disease depends upon the species one is infected with.
S. dysenteria is the most pathogenic followed by S. flexneri, S. sonnei and S. boydii.

18. Salmonella Salmonella
Classification has been changing in the last few years.
There is now 1 species: S. enteritica, and 7 subspecies: 1, 2 ,3a ,3b ,4 ,5, and 6.
Subgroup 1 causes most human infections
2000 sub species

19. Salmonella
Clinically Salmonella isolates are often still reported out as serogroups or serotypes based on the Kauffman-White scheme of classification.
Based on O and H (flagella) antigens
The H antigens occur in two phases; 1 and 2 and only 1 phase is expressed at a given time.
Polyvalent antisera is used followed by group specific antisera (A, B, C1, C2, D, and E)
Salmonella typhi also has a Vi antigen which is a capsular antigen.

20. Salmonella Biochemistry Virulence factors
TSI K/A + gas and H2S: S. typhi produces only a small amount of H2S and no gas , and S. paratyphi A produces no H2S
LIA K/K with H2S with S. paratyphi A giving K/A results
Urea –
Motility +
Citrate +/-
Indole -
Virulence factors
Endotoxin – may play a role in intracellular survival
Capsule (for S. typhi and some strains of S. paratyphi)
Adhesions – both fimbrial and non-fimbrial

21. Salmonella
Clinical Significance – causes two different kinds of disease: enteric fevers and gastroenteritis.
Both types of disease begin in the same way, but with the gastroenteritis the bacteria remains restricted to the intestine and with the enteric fevers, the organism spreads
Transmission is via a fecal-oral route, i.e., via ingestion of contaminated food or water.

22. Enterobacteriaceae Proteus, Providencia, and Morganella
Are all part of the NF of the GI tract (except Providencia).
All motile, with Proteus swarming
PA +
Lysine deamination + (LIA R/A)
Urea + for most, strongly + for Proteus
TSI variable (know the reactions for each in the lab!)
Indole – only P. mirabilis is -

23. Proteus, Providencia, and Morganella
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

24. Enterobacter sakazakii
a Gram-negative rod-shaped pathogenic bacterium.
It is a rare cause of invasive infection with historically high case fatality rates (40–80%) in infants.
From contaminated infant formulas
E. sakazakii as a now classified into a new genus, Cronobacter, comprising five species
For survivors, severe lasting complications can result including neurological disorders.

25. Three ways infant formula get contaminated with Cronobacter sp. ?
a) Through the raw material used for producing the formula;
b) through contamination of the formula or other dry ingredients after pasteurization; and
c) through contamination of the formula as it is being reconstituted by the caregiver just prior to feeding.
Can other foods also be contaminated?
Cronobacter sp. has been detected in other types of food, but only powdered infant formula has been linked to outbreaks of disease.

26. Most frequent notified enteric disease
Campylobacter
Campylobacteriosis
Most frequent notified enteric disease
The organism – G-ve, motile, spiral rod
C. jejuni & C. coli
Thermophile (25 to 43 deg. C)

27. Campylobacter
Exponential
Slender, curved shaped growth
morphology

28. Campylobacter Characteristics - thermophile, survives > 1 hour on
hands & moist surfaces
- survives refrigeration
- can revert to VBNC

29. Campylobacter The illness - incubation – 2 to 5 days
- febrile prodrome
- watery/bloody diarrhoea,
abdominal pain & nausea

30. Campylobacter The illness, continued
- infective dose – to cells
- any age group; infants < 1 year & young
adults; males up to 45 years
- Rx – fluids, ? erythromycin
(resistance)

31. Campylobacter Sources - human – faecal-oral person-to-person
- animal – ruminants, cats, dogs, flies,
birds

32. Campylobacter jejuni

33. Campylobacter Sources - food – raw poultry, raw milk, offal, red
meat
- environment – faeces from infected
animals contaminate soil &
water

34. Yersinia enterocolitica
Yersiniosis
The organism – small G-ve rods of family Enterobacteriaceae
Geographical variation in pathogenic serotypes
Serotype O:3 in NZ

35. Yersinia enterocolitica
Characteristics
- grows at wide range of temperatures
(0 to 44 0 C), aerobically & anaerobically
- withstands freezing & survives in damp
soil

36. Yersinia enterocolitica
The illness
- incubation – 7 days
- abdominal pain (confused with appendicitis)
- headache, fever, diarrhoea, nausea &
vomiting (children – watery, mucoid diarrhoea)

37. Yersinia enterocolitica
The illness, continued
- infective dose – unknown
- children < 4 years & adults years
- Rx – antibiotics when serious

38. Yersinia enterocolitica
Sources
- human – person-to-person, hospitals
- animal – primary source is pigs (tongue &
tonsils), companion animals, rats &
insects
- food – pork & pork products
- environment – drinking & surface water,
sewage sludge

39. Yersinia enterocolitica

40. Listeria monocytogenes
Listeriosis
(invasive disease & non-invasive enteritis)
The organism – G+ve ovoid to rod-shaped bacterium
Widespread in environment
and a non-invasive gastroenteritis.

41. Listeria monocytogenes
Characteristics
- grows in wide range of temperatures (1 to 45o C)
- survives freezing
- aerobic & anaerobic
conditions

42. Listeria monocytogenes
The illness – invasive form
- incubation – 30 days
- flu’-like symptoms, diarrhoea,
vomiting, meningitis, septicaemia,
spontaneous abortion

43. Listeria monocytogenes
The illness – invasive form, continued
- infective dose – 100 to cells
- pregnant women, newborn babies, the elderly & AIDS patients
- Rx – penicillin, ampicillin +/- gentamicin

44. Listeria monocytogenes
The illness – non-invasive
- incubation – 18 hours
- diarrhoea, fever, muscle pain,
headache, abdominal cramps &
vomiting

45. Listeria monocytogenes
The illness – non-invasive
- infective dose – > 100 thou. cells/gm
- all individuals susceptible
- Rx - penicillin, ampicillin +/-
gentamicin

46. Listeria monocytogenes
Sources
- human – person-to-person rare
- animal – diseased animals shed in faeces,
contamination of red meat; silage
- food – ready-to-eat cooked food with long
shelf-life
- raw foods
- environment – widespread in soil, water & sewage
(Hospitals & occupational exposure)

47. Listeria monocytogenes

48. Vibrio, Aeromonas & Plesiomonas

49. General Characteristics of Vibrio, Aeromonas and Plesiomonas
Similarities to Enterobacteriaceae
Gram-negative
Facultative anaerobes
Fermentative bacilli
Differences from Enterobacteriaceae
Polar flagella
Oxidase positive
Formerly classified together as Vibrionaceae
Primarily found in water sources
Cause gastrointestinal disease
Shown not closely related by molecular methods

50. Morphology & Physiology of Vibrio
Comma-shaped (vibrioid) bacilli
V. cholerae, V. parahaemolyticus, V. vulnificus are most significant human pathogens
Broad temperature & pH range for growth on media
18-37C
pH (useful for enrichment)
Grow on variety of simple media including:
MacConkey’s agar
TCBS (Thiosulfate Citrate Bile salts Sucrose) agar
V. cholerae grow without salt
Most other vibrios are halophilic

51. Vibrio spp. (Family Vibrionaceae) Associated with Human Disease

52. Epidemiology of Vibrio spp.
Vibrio spp. (including V. cholerae) grow in estuarine and marine environments worldwide
All Vibrio spp. can survive and replicate in contaminated waters with increased salinity and at temperatures of 10-30oC
Pathogenic Vibrio spp. appear to form symbiotic (?) associations with chitinous shellfish which serve as an important and only recently recognized reservoir
Asymptomatically infected humans also serve as an important reservoir in regions where cholera is endemic

53. Taxonomy of Vibrio cholerae
>200 serogroups based on somatic O-antigen
O1 and O139 serogroups are responsible for classic epidemic cholera
O1 serogroup subdivided into
Two biotypes: El Tor and classical (or cholerae)
Three serotypes: ogawa, inaba, hikojima
Some O1 strains do not produce cholera enterotoxin (atypical or nontoxigenic O1 V. cholerae)
Other strains are identical to O1 strains but do not agglutinate in O1 antiserum (non-cholera (NCV) or non-agglutinating(NAG) vibrios) (non-O1 V.cholerae)
Several phage types

54. Epidemiology of Vibrio cholerae
Cholera recognized for more than two millennia with sporadic disease and epidemics
Endemic in regions of Southern and Southeastern Asia; origin of pandemic cholera outbreaks
Generally in communities with poor sanitation
Seven pandemics (possible beginning of 8th) since 1817 attributable to increased world travel
Cholera spread by contaminated water and food
Human carriers and environmental reservoirs

55. Recent Cholera Pandemics
7th pandemic:
V. cholerae O1 biotype El Tor
Began in Asia in 1961
Spread to other continents in 1970s and 1980s
Spread to Peru in 1991 and then to most of South & Central America and to U.S. & Canada
By 1995 in the Americas, >106 cases; 104 dead
8th pandemic (??)
V. cholerae O139 Bengal is first non-O1 strain capable of causing epidemic cholera
Began in India in 1992 and spread to Asia, Europe and U.S.
Disease in humans previously infected with O1 strain, thus no cross-protective immunity

56. Pathogenesis of V.cholerae
Incubation period: 2-3 days
High infectious dose: >108 CFU
CFU with achlorhydria or hypochlorhydria (lack of or reduced stomach acid)
Abrupt onset of vomiting and life-threatening watery diarrhea (15-20 liters/day)
As more fluid is lost, feces-streaked stool changes to rice-water stools:
Colorless
Odorless
No protein
Speckled with mucus

57. Pathogenesis of V.cholerae (cont.)
Cholera toxin leads to profuse loss of fluids and electrolytes (sodium, potassium, bicarbonate)
Hypokalemia (low levels of K in blood)
Cardiac arrhythmia and renal failure
Cholera toxin blocks uptake of sodium & chloride from lumen of small intestine
Death attributable to:
Hypovolemic shock (due to abnormally low volume of circulating fluid (plasma) in the body)
Metabolic acidosis (pH shifts toward acid side due to loss of bicarbonate buffering capacity)

58. Treatment & Prevention of V. cholerae
Untreated: 60% fatality
Treated: <1% fatality
Rehydration & supportive therapy
Oral
Sodium chloride (3.5 g/L)
Potassium chloride (1.5 g/L)
Rice flour (30-80g/L)
Trisodium citrate (2.9 g/L)
Intravenous (IV)
Doxycycline or tetracycline (Tet resistance may be developing) of secondary value
Water purification, sanitation & sewage treatment
Vaccines

59. Laboratory Identification of Vibrios
Transport medium - Cary-Blair semi-solid agar
Enrichment medium - alkaline peptone broth
Vibrios survive and replicate at high pH
Other organisms are killed or do not multiply
Selective/differential culture medium - TCBS agar
V. cholerae grow as yellow colonies
Biochemical and serological tests

60. Characteristics and Epidemiology of Aeromonas (Family Aeromonadaceae)
Gram-negative facultatively anaerobic bacillus resembling members of the Enterobacteriaceae
Motile species have single polar flagellum (nonmotile species apparently not associated with human disease)
16 phenospecies: Most significant human pathogens A. hydrophila, A. caviae, A. veronii biovar sobria
Ubiquitous in fresh and brackish water
Acquired by ingestion of or exposure to contaminated water or food

61. Clinical Syndromes of Aeromonas
Associated with gastrointestinal disease
Chronic diarrhea in adults
Self-limited acute, severe disease in children resembling shigellosis with blood and leukocytes in the stool
3% carriage rate
Wound infections
Opportunistic systemic disease in immunocompromised
Putative virulence factors include: endotoxin; hemolysins; eneterotoxin; proteases; siderophores; adhesins

62. Afimbriated Aeromonas hydrophila
Nonadherent Afimbriated Bacterial Cells and Buccal Cells

63. Fimbriated Aeromonas hydrophila
Adherent Fimbriated Bacterial Cells and Buccal Cells

64. Characteristics of Plesiomonas
Formerly Plesiomonadaceae
Closely related to Proteus & now classified as Enterobacteriaceae despite differences:
Oxidase positive
Multiple polar flagella (lophotrichous)
Single species: Plesiomonas shigelloides
Isolated from aquatic environment (fresh or estuarine)
Acquired by ingestion of or exposure to contaminated water or seafood or by exposure to amphibians or reptiles
Self-limited gastroenteritis: secretory, colitis or chronic forms
Variety of uncommon extra-intestinal infections

65. Characteristics of Aeromonas and Plesiomonas Gastroenteritis
Epidemiological Features
Aeromonas
Plesiomonas
Natural Habitat
Source of Infection
Fresh or brackish water
Contaminated water or food
Fresh or brackish water Contaminated water or food
Clinical Features
Diarrhea
Vomiting
Abdominal Cramps
Fever
Blood/WBCs in Stool
Present
Absent
Pathogenesis
Enterotoxin (??)
Invasiveness