Bacterial diarrhea and dysentery

1. Bacterial diarrhea and dysentery
Dr. Dinesh Kr Jain, MD.,
Assistantprofessor,
Department of Microbiology,
SMS Medical college, Jaipur

2. • Diarrhoea: Passage of three or more loose or liquid stools per day,
in excess than the usual habit for that person(WHO). (>10 mL
stool/kg body weight/day).
• Gastroenteritis or infectious diarrhea: An inflammation of the
mucous membrane of stomach and intestine resulting in
combination of diarrhoea, vomiting and pain abdomen with or
without mucus/blood/ fever/ dehydration.
• Dysentery : Diarrhoea with increased blood and mucus, often
associated with fever, abdominal pain and tenesmus.
• Food poisoning: Major cause of gastroenteritis acquired through
consumption of food or drink contaminated either with
microorganisms, or their toxins.
INTRODUCTION

3. Bacteria causing diarrhea

4. Gram -positive cocci Gram-positive bacilli Gram- negative bacilli
Escherichia coli
• Enteropathogenic
• Enterotoxigenic
• Enteroaggregative
• Enterohemorrhagic
• Enteroinvasive
Vibrio cholera,Vibrio
parahemolyticus
Shigella species
Staphylococcus aureus Bacillus cereus Salmonella species
Clostridium perfringes, botulinum,
difficile
Campylobacter jejuni
Aeromonas hydrophila
Pleisomonas shigelloides
Yersinia enterocolitica
Listeria monocytogenes

5. Infectious agents of acute diarrhea and underlying
mechanism

7. Cell adherence
• Attachment within or close to mucosal cells.

8. Enterohemorrhagic E.coli(EHEC)
• Serotypes associated with EHEC are:
 0 157:H7 (most common serotype)
 Other serotypes are rarely associated such as 026:H11, 06, 055,
091, 0103, 0111 and 0113.
• EHEC is usually transmitted by contaminated food, i.e.
consumption of lettuce, spinach, sprouts and undercooked
ground beef.
• It is prevalent mainly in industrialized countries (in contrast to
other diarrheagenic E. coli which are common in developing
regions).
• Low infective dose: the infective dose of EHEC is very low. Only
few organisms (<102 bacilli) are required to initiate the infection.

9. • Pathogenesis:
• Produces verocytotoxin or Shiga-like toxin
• It is so named because it is cytotoxic to vero
cell lines and it resembles shiga toxin in its
structure and function.
• Detection of VT:
Serologically- Latex agglutination, ELISA
Molecular methods-using specific DNA
probe
Cytotoxicity on Vero and Hela cell lines

10. • Manifestations:
i. HC (hemorrhagic colitis). Gross bloody diarrhea, abdominal pain and fecal
leukocytosis but no fever.
ii. Hemorrhagic uremic syndrome (HUS): Injury to small vessels often kidney
and brain, which can lead to bloody diarrhea, thrombocytopenia,
renal failure and encephalopathy but no fever. More common in children.
• Diagnosis:
 Sorbitol MacConkey agar: EHEC, in contrast to other E. coli, does not ferment
sorbitol and produces pale colonies.
 Rainbow agar: 0157 strain appear as black colonies as they are negative for p-
glucuronidase.
 Toxin detection:
Demonstration of cytotoxicity in Vero cell lines (goldstandard method)
Fecal toxin detection by ELISA or rapid tests
PCR can be used to differentiate genes coding for Stx1 and Stx2.

11. Mechanism of action

12. Enteropathogenic
E.coli(EPEC)
• EPEC frequently causes infantile diarrhea (outbreaks) esp in tropical
countries.
• Occasionally cause sporadic diarrhea in adults.
• Person-to-person spread is seen.
• It is non toxigenic and non invasive.
• Common serogroups- O26, O55, O86, O111, O114, O119, O125, O126,
O127, O128, O142, O158
Pathogenesis:- Plasmid mediated.
 Strains which carry plasmid factor pEAF are called typical EPEC(tEPEC)
 Strains without this plasmid are termed as ‘atypical’ EPEC (aEPEC)

13. EPEC
adhere to
HEP-2 cells
form
Localised adhesion clusters
(mediated by plasmid PEAF)
Colonisation of upper part of small intestine
Brush border microvilli are lost
Attaching and effacing lesion
pedestals
bacteria
Increased secretions
and watery
diarrhea.

14. Neurotoxin
• Neurotoxins are toxins that are destructive to nerve
tissue (causing neurotoxicity).
• They are exogenous chemical neurological insults that
can adversely affect function in both developing and
mature nervous tissue
• They inhibit neuron control over ion concentrations
across the cell membrane,or communication between
neurons across a synapse.
• Neurotoxins can also cause glial cell damage, central
nervous system damage such as intellectual
disability persistent memory impairments, epilepsy,
and dementia.

15. Staphylococcus aureus
• Secretes enterotoxin which acts as neurotoxin.
• It is a preformed toxin.
• Incubation period: 1- 6 hours.
• Causes food poisioning.
• Site of action:
– toxin stimulates the vagus nerve and the vomiting center of the brain.
– also stimulate the intestinal peristaltic activity.
• Symptoms: nausea, vomiting , diarrhea, hypotension, and dehydration (no
fever),resolve within 8- 10 hours.
• Source of infection: food handler(carrier of S. aureus).
• Most common food items involved are milk products, bakery food,
custard, potato salad, or processed meats.
• Heat stable toxin and resistant to gastric juice.

16. Bacillus cereus
• Normal habitant of soil.
• It produces several toxins implicated in the diarrheal
symptoms, including hemolysin BL (HBL), nonhemolytic
enterotoxin (Nhe), and cytotoxin K (CytK; also referred to
as hemolysin IV).
• The three toxins are believed to act synergistically, with
Nhe responsible for the major symptoms in the diarrheal
presentation of the infection.
• B. cereus group “food poisoning” is associated with the
ingestion of a wide variety of foods including meats,
vegetables, desserts, sauces, and milk.
• A higher incidence is seen after the ingestion of rice dishes.
• After ingestion, patients present with one of two types of
symptoms: diarrhea and abdominal pain within 8 to 16
hours, or nausea and vomiting (emetic food poisoning)
within 1 to 5 hours.

17. Clostridium botulinum
• Anaerobic bacteria.
• Causes botulism.
• Distributed as saprophyte in soil, animal manure, vegetables and
sea mud.
• Non invasive.
• Transmission: spores ingested or inhaled.
• Pathogenesis: due to production of powerful neurotoxin
‘botulinum toxin’(BT).
• BT:
– 150 kDa zinc dependent protein consisting of 100 kDa heavy chain and a 50
KdA light chain.
– Produced intracellularly and appears outside only after autolysis of
bacterial cell
• 8 serotypes- A, B, C1, C2, D, E, F and G (most severe A)

18. • Common source: home made canned food(since growth requires
low oxygen content).
• Food borne botulism: results from food contaminated with
preformed botulinum toxin.
• After ingestion of toxin, within 24 hr or less there is progressive
paralysis affecting occulomotor and oropharyngeal muscles
followed by vomiting, diarrhea, abdominal swelling.
• Mechanism of action:After ingestion
of food
BT transported via blood to peripheral cholinergic
nerve terminal
Binds to acetylcholine receptors at NMJ
Blockage of release of Acetylcholine
Flaccid paralysis

19. Enterotoxin
• An enterotoxin is a protein exotoxin released by
a microorganism that targets the intestines.
• Enterotoxins are frequently cytotoxic and kill cells
by altering the apical membrane permeability of
the mucosal (epithelial) cells of the intestinal
wall.
• They are mostly pore-forming toxins (mostly
chloride pores), secreted by bacteria, that
assemble to form pores in cell membranes which
causes the cells to die.

20. Vibrio Cholera
• Pathogenesis of Cholera Both V. cholera O1 and 0139 are
capable of producing cholera toxin, thus resulting in cholera.
• Mode of transmission: V. cholerae is transmitted by ingestion
of contaminated water or food.
• Infective dose: Since V. cholerae is extremely acid labile; a high
infective dose of 10 bacilli is required to bypass the gastric
barrier.
• Factors promoting transmission: These include all those
conditions where gastric acidity is reduced, such as
hypochlorhydria, use of antacids, etc.
• Mechanism of action- similar to heat labile enterotoxin of
E.coli.

22. • Gene for cholera toxin (CTX):- CTXФ
• ToxR gene: It regulates the expression of CT and is itself regulated by
environmental factors, such as heat shock response.
• Chromosomes: V. cholerae has two circular chromosomes, one large and one
small.
 Large chromosome- growth and intestinal survival.
 Small chromosome- environmental survival.
• Other virulence factors include:
 Zona occludens toxin: It disrupts the light junctions between mucosal cells.
 Accessory cholera enterotoxin: Phage packaging and secretion.
 Vero cell toxin: It is analogous to the toxin produced by Shigella dysenteriae 1.
It is important for the survival of the bacilli in aquatic environment.
 Accessory colonization factors: help in adhesion and colonization.
 Siderophore: for iron acquisition .

23. Clinical Manifestations of Cholera
V. cholerae 01 or O139 infections produce a range of clinical
manifestations such as:
1. Asymptomatic infection (75% of cases)
2. Mild diarrhea or cholera (20% of cases)
3. Sudden onset of explosive and life-threatening diarrhea
(cholera gravis, in 5% of cases).
• Incubation period varies from 24 to 48 hours.
• The usual manifestations include:
 Watery diarrhea
 Rice water stool:
 Vomiting
 No fever
 Muscle cramps

24. Complications are directly proportional to the fluid loss
resulting in loss of body weight.

25. Epidemiological Determinants
• Reservoir: Humans.
• Source: either asymptomatic cases or carriers.
• Carriers: healthy people who shed the bacilli in feces.
• Cholera season: high temperatures, heavy rainfall and flooding.
• Risk factors:
– Poor sanitation, poverty, overcrowding, population
mobility.
– Lack of pre-existing immunity
– Persons with 'O' blood group are at greater risk, while
those with type AB
blood group are at least risk.
– Malnutrition

26. Treatment
• Fluid replacement: to correct hypovolemia and thereafter to be
maintained to replace the ongoing fluid losses.
• In mild to moderate fluid loss: Oral rehydration solution (ORS) should
be given.
• In severe cases: Intravenous fluid replacement with Ringer's lactate (or
normal saline) should be carried out till the consciousness arrives.
Thereafter replaced by ORS
• Antibiotic therapy:

27. vaccines
• Injectable Killed Vaccines
They are no longer in use, as they provide little
protection, cause adverse effects and fail to induce a
local intestinal mucosal immune response
• Oral Cholera Vaccines (OCV)
Oral cholera vaccines are currently in practice. two types
of oral vaccines are available.
 Killed Whole-cell vaccine:
two preparations are available:
1. Whole-cell (WC) vaccine: It is composed of killed
whole cells of V.cholerae O1 (classical and El Tor, Inaba
and Ogawa).
2. Whole-cell recombinant B subunit cholera
vaccine(WC/rBS) (Dukoral): Composition is same as that of
WC vaccine, in addition it has recombinant cholera toxin B
subunit

28. • Schedule:
Two doses are given orally, at 7 days gap except for children 2- 5
years (3 doses). Its not licensed for children less than 2 years.
• WHO recommends for using vaccine during epidemics and out
breaks in the community but not during inter epidemic period.
Oral Iive attenuated vaccines (OCV): Several live OCV are under
trial such as:
CVD 103-HgR, Peru-15 and V. cholerae H38 for classical and/ or El
Tor biotypes of V. cholerae 01.
• CVD-112 and Bengal-15 vaccine for V. cholerae 0 139.
• CVD 103-HgR vaccine (Orochol) contains a live attenuated strain
derived from reference strain 569 B (classical, 0 1, Inaba), given as
single dose. Its protection starts after 8 days.

29. • Use of OCV is recommended to limit the risk
of:
 Occurrence of cholera outbreaks in
displaced populations in endemic areas.
Spread and incidence of cholera during an
outbreak.
NICED: National reference Center for
cholera in India is located at National
lnstitute of Cholera and Enteric Diseases
(NICED), Kolkata.

31. Vibrio parahemolyticus
• Though V. parahemolyticus was first reported from Japan
(1953), the incidence of infection has greatly increased in
several countries including Japan since 1993. In India, it has
been reported from Kolkata.
ClinicalManifestations
• Food-borne gastroenteritis is the most common
presentation.
• Occurs following raw or uncooked sea food (e.g. oyster)
intake.
• It commonly presents as watery diarrhea or rarely as
dysentery with abdominal cramps

32. Pathogenesis:
• Virulence factors:
• Polysaccharide capsule which prevents the bacilli from
phagocytosis.
• Hemolysin (thermo -stable)
• Urease enzyme (in few strains): It breaks down urea from food
to release ammonia that buffers gastric acidity.
• It possesses two type III secretion systems in cell wall, which
directly inject toxic bacterial proteins into host cells.
Serotype: V. parahaemolyticus has 13 0 somatic
antigens and more than 60 K capsular antigens. Most
of the infections are caused due to serotypes 03:K6,
04:K68, and 01:K-untypable.

33. Enterotoxigenic
E.coli(ETEC)• ETEC is the most common cause of traveller's diarrhea causing 25- 75% of cases.
• Occurs in temperate industrialized countries to tropical regions of Asia, Africa, and
Central and South America
• It causes acute watery diarrhoea in infants and adults.
• Responsible for community acquired diarrheal disease in areas of poor sanitation.
• Common serotypes associated are -06, 08, 015, 025, 027, 0153, 0159,etc
• lt is toxigenic, but non invasive .
• Pathogenesis:-by
 Attachment to intestinal mucosa by fimbrial protein called CFA (colonization factor
antigen)
 Toxin production

34. • Produces: 1)heat labile toxin LT
It resembles cholera toxin in its structure and function, but it is less
potent than the latter.
• Detection of LT:
In vivo test
 Ligated rabbit ileal loop test is positive (fluid accumulation in the
loop) only after 18 hours.
 Adult rabbit skin test is positive
In vitro tests:
Tissue culture tests:
 Steroid production in Y'1 mouse adrenaI cell culture.
 Elongation in Chinese hamster ovary cells

35. 2)-heat stable toxin ST
• Detection of ST:
In vivo tests:
 ligated rabbit ileal loop test ...positive (fluid accumulation) at 6 hours.
 Infant mouse intra gastric test is positive at 4 hours.
In vitro tests:
 Tissue culture tests are negative when compared to both labile toxin
and verocytotoxin
Note: ST and LT can also be detected and differentiated from each other
by
 Serological tests- such as latex agglutination and ELISA.
 Molecular methods- using LT and ST specific DNA probe

36. Mechanism of
action

37. Enteroaggregative
E.coli(EAEC)
• It is so named because it adheres to HEp-2 cells in a distinct pattern, layering of the
bacteria aggregated in a stacked-brick fashion.
• Most strains are "O" untypeable but "H” typeable.
• Manifestations: Persistent and acute diarrhea are commonly seen; especially in
developing countries.
• Pathogenesis:
 Intestinal colonization is mediated by aggregative adhesion fimbriae I (regulated by
aggR gene).
 It also produces EAST 1 toxin (entero aggregative heat stable enterotoxin 1).
E. coli 0104: H4 -It is an enteroaggregative strain that has caused major outbreaks in
Germany in 2011. One peculiar feature of this strain is, it produces Shiga- like toxin
and can cause HUS

38. SALMONELLA
• Elberth-Gaffky bacillus or Eberthella typhi.
• Clinical classification:
– Typhoidal : serotypes S. typhi and S. paratyphi, cause
typhoid fever.
– Non typhoidal : food borne gastroenteritis and
septicemia.
• Antigenic classification: Kauffmann-White Scheme:
– Based on presence somatic(O) and flagellar(H) antigens
– Detected by agglutination
• Molecular classification: based on DNA hybridization:
– Salmonella enterica
– Salmonella bongori

39. Non typhoidal salmonellosis
• Most common and widely distributed food borne disease.
• Caused by:
• S. typhimurium
• S. enteritidis
• Incidence is higher in rainy season(tropical) and warmer
months(temperate).
• Morbidity and mortality highest among elderly, infants, and
immunocompromised.
• Multiple animal reservoirs.
• Transmission:
– Animal food products: eggs, poultry, undercooked ground meat, dairy
products

40. MECHANISM OF ACTION

41. • Clinically varies from self limiting gastroenteritis
to septicemia:
– Nausea, vomiting and diarrhea after 6-48 hrs of
ingestion.
– Abdominal cramping and fever
– Loose, non bloody stool of moderate volume.
• Reference centre for Salmonella:
• National Centre for Salmonella phage typing- Lady Hardinge
Medical College , New Delhi.
• National Salmonella Refrence Centre – Central Research
Institute, Kasauli.
• National Salmonella Refrence Centre for animal origin-
Izatnagar.

42. Clostridium difficile
• Causes unique colonic disease- pseudomembranous colitis(PMC)
and antibiotic associated diarrhea(AAD).
• Associated with:
– prolonged antibiotic use like cephalosporins (ceftriaxone),
clindamycin, ampicillin and fluoroquinolones (ciprofloxacin)
– prolonged hospital stay.
• Pathogenesis: toxin mediated, produces 2 powerful exotoxins-
– Toxin A (enterotoxin)
– Toxin B (cytotoxin)

43. MECHANISM OF ACTION
Toxins A and B
Secreted in intestine
Glycosylate the GTP binding protiens that regulate cellular actin
cytoskeleton
Disruption of cytoskeleton and epithelial cell barrier
Results in loss of cell shape, adherence
Diarrhea
Peusdomembrane formatiom

44. • Clinically:
– Diarrhea, fever, abdominal pain and leukocytosis.
– Pseudomembrane:
• Whitish yellow plaque of ranging from 1-2 mm to large
enough to spread over entire colonic mucosa.
• Composed of necrotic leukocytes, fibrin , mucus and cellular
debris, attaches to underlying mucosa.

45. Clostridium perfringes
• Commensal in large intestine.
• Saprophyte in soil, dust and air.
• Invasive and toxigenic.
• Virulence factor:
– 4 major toxins-alpha(food poisioning), beta, epsilon and iota,
– 8 minor toxins- gamma, delta, lambda, kappa, theta, eta, mu, and nu,
– Heat labile entertoxin.
• Food poisioning-
– Types A enterotoxin(coded by cpe gene).
– Consumption of improperly cooked contaminated meat.
– Infective dose:108 viable vegetative bacilli.
– Enterotoxin act by forming pore in intestinal mucosal
membrane.

46. Campylobacter jejuni
• Primarily diarrhea causing accounting for 80-90% cases.
• Mode of transmission:
– By raw or undercooked food products, ingestion of contaminated
poultry , raw unpasteurized milk or untreated water.
– Direct contact with infective animals,
– Travelling to developing countries can cause traveller’s diarrhea
– Oral-anal sexual route.
• Most common in children.
• Incidence peaks during summer and early autumn.

47. • Pathogenesis :
– Motility of strain
– Capacity to adhere to host tissues
– Toxins: enterotoxin(heat labile) and cytotoxins (cytolethal
distending toxin)
– Protienaceous capsule like structure(S-layer)-prevent
complement mediated killing and opsonisation.
• Clinically :
– Inflammatory diarrhea(several loose stools to groosly bloody
stools),
– Abdominal pain,
– Fever.

48. Aeromonas hydrophilia
• Gram-negative facultatively anaerobic bacillus resembling
members of the Enterobacteriaceae.
• Motile species have single polar flagellum.
• Ubiquitous in fresh and brackish water.
• Acquired by ingestion of or exposure to contaminated water or
food.
• Associated with gastrointestinal disease:
– Watery diarrhea, vomiting, fever and rarely dysentery and peritonitis.
– Self-limited acute, severe disease in children resembling shigellosis
with blood and leukocytes in the stool.
– 3% carriage rate.
– Mainly in immunocompromised.

49. CYTOTOXIN

50. SHIGELLA
• Most important agent of bacillary dysentery.
• CDC classification :
• Japanese microbiologist KIYOSHI SHIGA, isolated first
member S. dysenteriae serotype-1(the shiga bacillus) in
1896 from epidemic dysentery.
• Diarrheal stool contains 106 to 108 shigellae per gram.

51. Antigens and serotyping of Shigella:
• Somatic O polysacchride antigen-
1. S. dysenteriae (group A)- 15 serotypes, does not
ferment mannitol.
– Serotype 1 (s. shigae): only shiga toxin producing shigella,
catalse negative and indole negative.
– Serotype 2 (s. schmitzi): forms indole and ferments sorbitol
and rhamnose.
– Serotype 3-7( formerly called large sachs group).
2. S. flexneri(group B) -6 serotypes, indole negative
– Based on gas production from sugars 3 biotypes-
manchester, newcastle and boydd 88,
– Based on bacteriophage typing -123 phage types
– Fimbrial antigens present.

52. Pathogenesis :
• Mode of transmission-
– Ingestion through contaminated fingers(most common), food and water.
– Homosexual transmission
• Minimum infective dose- 10-100 bacilli.
• Resistance to low ph conditions allows shigellae to survive passage
through gastric barrier.
• Toxins:
– Exotoxins : Shigella enterotoxin
– Shiga toxin( S. dysenteriae): cytotoxin, similar to verocytotoxin
of EHEC.
– Endotoxins : induce intestinal inflammation and ulcerations.
Shet1 (S. flexneri2a): structurally
similar to cholera toxin.
Shet2 (S. flexneri): iron uptake

53. Mechanism of action

54. Shigellosis(5 phases)
• Incubation period: 1-4 days
• Initial phase:
– Watery diarrhea with fever, malaise, anorexia, vomiting.
• Phase of dysentery: (self limiting)
– Bloody mucopurulent stools,
– Increased tenesmus,
– Abdominal cramps,
– Endoscopically edematous and hemorrhagic mucosa with ulcerations.
• Phase of complications: (less than 5 years of age):
– Intestinal: toxic megacolon, perforations and rectal prolapse.
– Metabolic: hypoglycemia, hyponatremia and dehydration.
– EKIRI SYNDROME / toxic encephalopathy.
• Post infectious phase: only after S. flexneri infection, characterized
by reactive arthritis, ocular inflammation and urethritis(patients
expressing HLA-B27).

55. • Risk factors:
– Overcrowding,
– Poor hygiene,
– Children less than 5 years.
• Cases caused by S. dysenteriae type 1 are
associated with high mortality.
• Natural host- human.
• Source of infection- cases

56. INVASION

57. Enteroinvasive E.coli(EIEC)
• biochemically, genetically and pathogenically closely related to
Shigella .
• Manifestations: ulceration of bowel, dysentery (diarrhea with mucus
and blood, called bacillary dysentery (resembling shigellosis).
• Common serotypes associated with EIEC -028,0112,0114,O124,0136,
0 152,etc.
• Pathogenesis: not toxigenic, but invasive. The
epithelial cell invasion is mediated by a plasmid coded antigen called
virulence marker antigen (VMA)
• Diagnosis:
 Detection of VMA by ELISA
 HeLa cell invasion assay
 Sereny test (inoculation of bacterial suspension into guinea pig eyes produces
conjunctivitis)

58. Plesiomonas shigelloides
• Antigenically related to S.sonnie.
• Closely related to Proteus & now classified as Enterobacteriaceae
despite differences:
 Oxidase positive
 Multiple polar flagella.
 Saprophyte in water and Soil.
• Causes Self-limited gastroenteritis, secretory colitis .
• Risk factors:
– Consumption of untreated water and fresh-water sources.
– Immunocompromised persons.

59. • Putative virulence factors include: endotoxin; hemolysins;
eneterotoxin; proteases; siderophores; adhesins.
• Pathogenicity:
– Tissue adherence mediated by adhesions such as S- layer and
fimbriae.
– Capsular polysaccharide ( prevents phagocytosis).
– Exotoxins such as aerolysin, phospholipases, hemolysins,
enterotoxin and cytotoxin similar to Shiga toxin.
– Endotoxin or LPS.

60. Yersinia enterocolitica
• Causes yersinosis.
• Due to consumption of contaminated food such as raw pork,
milk etc.
• More common in children and colder climates.
• Characterized biochemically into 6 biotypes and antigenically
based on somatic O Antigen into 60 biotypes.
• Infection due to O:3 and O:9.
• Virulence factors:
– Invasion protein ( inv)- binds to B-1 integrins on M cells of GI mucosa
and helps in invasion,
– Ail protein ( attachment and invasion),
– Yersinia adhesin A ( Yad A),
– Myf antigen( fimbrial),
– Heat stable toxin,
– Ph6 antigen.

61. • Clinically:
– Self limited gastroenteritis
– Intestinal complications in older children ( terminal
ileitis and mesenteric adenitis).
– May mimic pseudoappendicitis

62. Listeria monocytogenes
• Food borne pathogen.
• Ubiquitous saprophyte.
• Human infection due to serotypes 1/2a, 1/2b and 4.
• Mode of transmission: contaminated food followed by vertical
transmission.
• Common among extremes of age, pregnant women and
immunocompromised.
• Sources: stored food especially ages soft cheeses, packaged meats,
milk and cold salads.

63. • Pathogenesis:
– Entry into intestinal epithelium by host surface protein
internalins.
– Intracellular survival due to inhibition and lysis of phagosome by
forming pores ( listeriolysin O).
– Direct cell to cell spread: with surface protein Act A, that
mediates the nucleation of host actin filaments which in turn
helps in bacterium to reach cell membrane and migrate further(
listeriopods).
• Clinically causes gastroenteritis.

64. Klebsiella Oxytoca
• Causes Antibiotic associated diarrhea.
• Antibiotic- penicillin like antibiotic
• Virulence factor:
– Outer membrane composed of lipopolysaccharides(LPS) with O
antigen(endotoxins),
– Capsules,
– Resistance to multiple antimicrobial agents.
• Clinically bloody diarrhea with severe abdominal cramps

65. FOOD POISIONING

67. Laboratory diagnosis
• Specimen and collection: Feces-
– passed into clean bedpan,
– Unmixed with urine or disinfectant
– Container: 25 ml screwcapped, wide-mouthed glass or
plastic bottle, preferably with a spoon projecting from
underside of the cap.
– Collect 1-2 ml of stool on spoon into bottle.
– Transmit quickly.
– If delay unavoidable, collect in a container holding 6 ml
buffered glycerol saline transport medium.
– Note: rectal swab is unsatisfactory unless it is heavily
charged and visibly stained with feces collected from
rectum.

68. Universal container for stool

69. • Microscopy :
– With naked eye: consistency, whether formed or fluid,
presence of mucus or pus and blood,
– Hanging drop preparation: darting motility of vibrio,
– Gram stain:
• Comma shaped bacilli: Vibrio cholerae

70. • Culture: fecal suspension is prepared in 1 in 10 dilution in 2-3 ml of
phosphate-buffered saline(ph 7.3) or 0.1% peptone water.
– Shigella :
• Enrichment broth- Selenite F Broth, Tetrathionate broth and Gram
Negative broth, after 24 hrs subculture onto selective media.
• Selective media-
o Mildly selective: Macconkey agar
o Highly selective(increased bile salts as inhibitory): Deoxycholate
Citrate Agar, Xylose Lysine Deoxycholate, Salmonella Shigella Agar
and Hektoen Enteric Agar.
– Salmonella:
• Highly selective: Deoxycholate Citrate Agar, Xylose Lysine
Deoxycholate, Salmonella Shigella Agar and Wilson Blairs’s bismuth
sulphite medium( jet black colonies).
– Campylobacter:
• Selective media: skirrows’s selective medium, Butzler’s selective
medium, Campy BAP selective media( contains lysed blood agar,
vancomycin, polymyxin B, trimethoprim, cephalothin and
amphotericin B)

71. • Vibrio cholerae:
Transport media: VR medium, Cary·Blair medium,
Enrichment broth: APW; Monsur's taurocholate tellurite peptone
water,
Selective media: Bile salt agar, Monsur's GTTT agar, TCBS agar
(yellow colonies),
MacConkey agar

72. • Clostridium difficile: (whenever there is severe, blood stained
diarrhea and toxemia in patient who has been receiving antibiotics)
– Selective media: cefoxitin cycloserine fructose agar(CCFA) or
cefoxitin cycloserine egg yolk agar(CCYA).
• Aeromonas hydrophila:
– Selective media: sheep blood agar with 15 mg ampicillin/litre,
after incubation flood the plate with 1% sodium dimethyl-p-
phenylenediamine monohydrochloride(oxidase reagent) gives
purple black color with narrow zone of hemolysis.

73. • Food poisoining bacteria: for outbreak examine for:
– Clostridium perfringes:
• 106 or more C. perfringes per gram reported as significant.
• Media : Robertson cooked meat broth,Egg yolk agar.
– Staphylococcal aureus:
• in an outbreak identity of phage type among the isolates from
several patients and food stuffs is fair evidence.
• Reverse passive latex agglutination for detection of staphylococcal
enterotoxin.
– Bacillius cereus:
• Selective media: MYPA (mannitol, egg yolk, polymyxin, phenol red
and agar), PEMBA( Polymyxin B, ehh yolk, mannitol, bromothymol,
blue agar).
– Vibrio parahemolyticus:
• Wagatsuma agar- beta hemolysis
• TCBS- green colonies,
• Blood agar- swarming seen

74. • Appropriate biochemical tests
• Antibmicrobial susceptibility test: various drugs for
sensitivity testing are- amikacin, ciprofloxacin,
cotrimoxazole, chloramphenicol, ceftriaxone, imipenam,
tetracycline, furazolidine.
• Tissue culture: for E.coli
• Molecular methods: PCR assays.
• Toxin detection: ELISA and PCR

76. THANKYOU