This document provides an overview of Salmonella, including Salmonella enterica and Salmonella bongori. It discusses Salmonella serotyping based on surface structures. The pathogenesis and immunity of Salmonella is described, noting how it attaches and invades the intestines. Two pathogenicity islands regulate these processes. Epidemiology sections explain the animal reservoirs and most common sources of human infections like poultry, eggs and dairy. Clinical diseases caused include gastroenteritis, septicemia, enteric fever and asymptomatic colonization. Laboratory diagnosis focuses on culturing Salmonella from blood, feces or bone marrow. Biochemical tests are used to identify isolates.
The genus Shigella exclusively infects human intestine.
Shigella dysenteriae is the causative agent of bacillary dysentery or shigellosis in humans.
It is a diarrheal illness which is characterized by frequent passage of blood stained mucopurulent stools.
The four important species of the genus Shigella are:
Shigella dysenteriae
Shigella flexneri
Shigella sonnei
Shigella boydii.
The genus Shigella exclusively infects human intestine.
Shigella dysenteriae is the causative agent of bacillary dysentery or shigellosis in humans.
It is a diarrheal illness which is characterized by frequent passage of blood stained mucopurulent stools.
The four important species of the genus Shigella are:
Shigella dysenteriae
Shigella flexneri
Shigella sonnei
Shigella boydii.
Microbiology of E coli giving basic of Escherichia coli, its morphology, cultural and biochemical characteristics, Antigenic character, pathogenesis, laboratory diagnosis, prevention and control
Cholera is a serious bacterial disease that usually
causes severe diarrhea and dehydration. The disease is typically spread through contaminated water.
Modern sewage and water treatment have effectively eliminated cholera in most countries. It’s still a problem in countries like Asia, America and Africa. Mostly in India.
Countries affected by war, poverty, and natural disasters have the greatest risk for a cholera outbreak.
Taxonomy:
class : Gamma Proteobacteria
Order: Vibrionales
Family: Vibrionaceae
Genus: Vibrio
Species: v.cholerae, v.parahaemolyticus,
v. vulnificus, v. alginolyticus
MORPHOLOGY:
Gram negative, actively motile, short, rigid curved bacilli
Resembling letter “V”
about 34 genus
most common in water
1.5µ X 0.2 -0.4 µ in size
polar flagellum , strongly aerobic
Smear – fish in stream appearance
PATHOGENESIS:
Source: Ingestion of contaminated water, food,
fruits and vegetables etc.,
Incubation periods: 1-5 days
Symptoms: Watery diarrhoea, vomiting, thirst, dehydration, muscle cramps
Complications: muscular pain, renal failure, pulmonary edema, cardiac arrhythrnias
DIAGNOSIS:
Specimen: stool sample, water sample(envt)
Microscopy: a) Hanging drop : +ve
b) Gram stain :-ve
Culture: Mac conkey Agar :colourless to light pink
TCBS : yellow colonies
Serology: serological tests are no diagnostic value
TREATMENT:
Adequate replacement of fluids and electrolytes.
Oral tetracycline reduces the period of vibrio excreation.
PREVENTION:
Drink and use bottled water
Frequent washing
Sanitary environment
Defecate in water
Cook food thoroughly
Microbiology of E coli giving basic of Escherichia coli, its morphology, cultural and biochemical characteristics, Antigenic character, pathogenesis, laboratory diagnosis, prevention and control
Cholera is a serious bacterial disease that usually
causes severe diarrhea and dehydration. The disease is typically spread through contaminated water.
Modern sewage and water treatment have effectively eliminated cholera in most countries. It’s still a problem in countries like Asia, America and Africa. Mostly in India.
Countries affected by war, poverty, and natural disasters have the greatest risk for a cholera outbreak.
Taxonomy:
class : Gamma Proteobacteria
Order: Vibrionales
Family: Vibrionaceae
Genus: Vibrio
Species: v.cholerae, v.parahaemolyticus,
v. vulnificus, v. alginolyticus
MORPHOLOGY:
Gram negative, actively motile, short, rigid curved bacilli
Resembling letter “V”
about 34 genus
most common in water
1.5µ X 0.2 -0.4 µ in size
polar flagellum , strongly aerobic
Smear – fish in stream appearance
PATHOGENESIS:
Source: Ingestion of contaminated water, food,
fruits and vegetables etc.,
Incubation periods: 1-5 days
Symptoms: Watery diarrhoea, vomiting, thirst, dehydration, muscle cramps
Complications: muscular pain, renal failure, pulmonary edema, cardiac arrhythrnias
DIAGNOSIS:
Specimen: stool sample, water sample(envt)
Microscopy: a) Hanging drop : +ve
b) Gram stain :-ve
Culture: Mac conkey Agar :colourless to light pink
TCBS : yellow colonies
Serology: serological tests are no diagnostic value
TREATMENT:
Adequate replacement of fluids and electrolytes.
Oral tetracycline reduces the period of vibrio excreation.
PREVENTION:
Drink and use bottled water
Frequent washing
Sanitary environment
Defecate in water
Cook food thoroughly
Bacteria of the genus Salmonella are highly adapted for growth in both humans and animals and cause a wide spectrum of disease.
The growth of S. Typhi and S. Paratyphi is restricted to human hosts, in whom these organisms cause enteric (typhoid) fever.
The remaining serotypes (non-typhoidal Salmonella or NTS) can colonize the gastrointestinal tracts of a broad range of animals, including mammals, reptiles, birds and insects.
Foodborne, commonly called food poisoning, and waterborne illnesses are conditions caused by eating or drinking food or water that is contaminated by microbes or the toxins they produce. They typically cause gastrointestinal symptoms such as abdominal pain, nausea, vomiting, and diarrhea.
A detailed description of HIV covering virology, morphology, pathogenesis, clinical stages and manifestations, laboratory diagnosis, and diagnostic strategy, and therapeutic options and prevention.
Basic discussion on Coccidian parasites with a focus on Cryptosporidiosis -morphology, life cycle, pathogenesis, clinical manifestations, and laboratory diagnosis and management.
Morphology, Life cycle, Clinical manifestations and laboratory diagnosis of E. histolytica from Clinical and Microbiological point of view for UG and PG Students.
Basic discussion on Clinical and Microbiological Aspects of Food Poisoning caused by various bacteria, viruses, protozoa, and Fungi along with their clinical and laboratory diagnosis and basic management.
Basic description of Infective Endocarditis from a Clinical and Microbiological point of view with description on Pathogenesis, Clinical Manifestations, Clinical and Laboratory diagnosis.
Basic description of Lyme disease from Microbiological and Clinical point of view with discussion on Pathology, Clinical Features and, Laboratory Diagnosis.
A basic description of Leishmania spp. along with Old and New world Leishmaniasis regarding Parasite morphology, Life Cycle, Pathogenesis, Clinical manifestations, Laboratory Diagnosis and Treatment.
Detailed description of malarial parasites especially P. falciparum with regards to their Morphology, Life cycle, Pathogenesis, Epidemiology, Clinical manifestations and complications and Laboratory diagnosis including modern methods and treatment.
Concise discussion on Fialrial worms including Morphology, Life cycle, pathogenesis, clinical manifestations and laboratory diagnosis including newer techniques for UG and PG students.
Title: Sense of Taste
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the structure and function of taste buds.
Describe the relationship between the taste threshold and taste index of common substances.
Explain the chemical basis and signal transduction of taste perception for each type of primary taste sensation.
Recognize different abnormalities of taste perception and their causes.
Key Topics:
Significance of Taste Sensation:
Differentiation between pleasant and harmful food
Influence on behavior
Selection of food based on metabolic needs
Receptors of Taste:
Taste buds on the tongue
Influence of sense of smell, texture of food, and pain stimulation (e.g., by pepper)
Primary and Secondary Taste Sensations:
Primary taste sensations: Sweet, Sour, Salty, Bitter, Umami
Chemical basis and signal transduction mechanisms for each taste
Taste Threshold and Index:
Taste threshold values for Sweet (sucrose), Salty (NaCl), Sour (HCl), and Bitter (Quinine)
Taste index relationship: Inversely proportional to taste threshold
Taste Blindness:
Inability to taste certain substances, particularly thiourea compounds
Example: Phenylthiocarbamide
Structure and Function of Taste Buds:
Composition: Epithelial cells, Sustentacular/Supporting cells, Taste cells, Basal cells
Features: Taste pores, Taste hairs/microvilli, and Taste nerve fibers
Location of Taste Buds:
Found in papillae of the tongue (Fungiform, Circumvallate, Foliate)
Also present on the palate, tonsillar pillars, epiglottis, and proximal esophagus
Mechanism of Taste Stimulation:
Interaction of taste substances with receptors on microvilli
Signal transduction pathways for Umami, Sweet, Bitter, Sour, and Salty tastes
Taste Sensitivity and Adaptation:
Decrease in sensitivity with age
Rapid adaptation of taste sensation
Role of Saliva in Taste:
Dissolution of tastants to reach receptors
Washing away the stimulus
Taste Preferences and Aversions:
Mechanisms behind taste preference and aversion
Influence of receptors and neural pathways
Impact of Sensory Nerve Damage:
Degeneration of taste buds if the sensory nerve fiber is cut
Abnormalities of Taste Detection:
Conditions: Ageusia, Hypogeusia, Dysgeusia (parageusia)
Causes: Nerve damage, neurological disorders, infections, poor oral hygiene, adverse drug effects, deficiencies, aging, tobacco use, altered neurotransmitter levels
Neurotransmitters and Taste Threshold:
Effects of serotonin (5-HT) and norepinephrine (NE) on taste sensitivity
Supertasters:
25% of the population with heightened sensitivity to taste, especially bitterness
Increased number of fungiform papillae
Anti ulcer drugs and their Advance pharmacology ||
Anti-ulcer drugs are medications used to prevent and treat ulcers in the stomach and upper part of the small intestine (duodenal ulcers). These ulcers are often caused by an imbalance between stomach acid and the mucosal lining, which protects the stomach lining.
||Scope: Overview of various classes of anti-ulcer drugs, their mechanisms of action, indications, side effects, and clinical considerations.
The prostate is an exocrine gland of the male mammalian reproductive system
It is a walnut-sized gland that forms part of the male reproductive system and is located in front of the rectum and just below the urinary bladder
Function is to store and secrete a clear, slightly alkaline fluid that constitutes 10-30% of the volume of the seminal fluid that along with the spermatozoa, constitutes semen
A healthy human prostate measures (4cm-vertical, by 3cm-horizontal, 2cm ant-post ).
It surrounds the urethra just below the urinary bladder. It has anterior, median, posterior and two lateral lobes
It’s work is regulated by androgens which are responsible for male sex characteristics
Generalised disease of the prostate due to hormonal derangement which leads to non malignant enlargement of the gland (increase in the number of epithelial cells and stromal tissue)to cause compression of the urethra leading to symptoms (LUTS
- Video recording of this lecture in English language: https://youtu.be/lK81BzxMqdo
- Video recording of this lecture in Arabic language: https://youtu.be/Ve4P0COk9OI
- Link to download the book free: https://nephrotube.blogspot.com/p/nephrotube-nephrology-books.html
- Link to NephroTube website: www.NephroTube.com
- Link to NephroTube social media accounts: https://nephrotube.blogspot.com/p/join-nephrotube-on-social-media.html
These simplified slides by Dr. Sidra Arshad present an overview of the non-respiratory functions of the respiratory tract.
Learning objectives:
1. Enlist the non-respiratory functions of the respiratory tract
2. Briefly explain how these functions are carried out
3. Discuss the significance of dead space
4. Differentiate between minute ventilation and alveolar ventilation
5. Describe the cough and sneeze reflexes
Study Resources:
1. Chapter 39, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 34, Ganong’s Review of Medical Physiology, 26th edition
3. Chapter 17, Human Physiology by Lauralee Sherwood, 9th edition
4. Non-respiratory functions of the lungs https://academic.oup.com/bjaed/article/13/3/98/278874
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Report Back from SGO 2024: What’s the Latest in Cervical Cancer?bkling
Are you curious about what’s new in cervical cancer research or unsure what the findings mean? Join Dr. Emily Ko, a gynecologic oncologist at Penn Medicine, to learn about the latest updates from the Society of Gynecologic Oncology (SGO) 2024 Annual Meeting on Women’s Cancer. Dr. Ko will discuss what the research presented at the conference means for you and answer your questions about the new developments.
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Title: Sense of Smell
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the primary categories of smells and the concept of odor blindness.
Explain the structure and location of the olfactory membrane and mucosa, including the types and roles of cells involved in olfaction.
Describe the pathway and mechanisms of olfactory signal transmission from the olfactory receptors to the brain.
Illustrate the biochemical cascade triggered by odorant binding to olfactory receptors, including the role of G-proteins and second messengers in generating an action potential.
Identify different types of olfactory disorders such as anosmia, hyposmia, hyperosmia, and dysosmia, including their potential causes.
Key Topics:
Olfactory Genes:
3% of the human genome accounts for olfactory genes.
400 genes for odorant receptors.
Olfactory Membrane:
Located in the superior part of the nasal cavity.
Medially: Folds downward along the superior septum.
Laterally: Folds over the superior turbinate and upper surface of the middle turbinate.
Total surface area: 5-10 square centimeters.
Olfactory Mucosa:
Olfactory Cells: Bipolar nerve cells derived from the CNS (100 million), with 4-25 olfactory cilia per cell.
Sustentacular Cells: Produce mucus and maintain ionic and molecular environment.
Basal Cells: Replace worn-out olfactory cells with an average lifespan of 1-2 months.
Bowman’s Gland: Secretes mucus.
Stimulation of Olfactory Cells:
Odorant dissolves in mucus and attaches to receptors on olfactory cilia.
Involves a cascade effect through G-proteins and second messengers, leading to depolarization and action potential generation in the olfactory nerve.
Quality of a Good Odorant:
Small (3-20 Carbon atoms), volatile, water-soluble, and lipid-soluble.
Facilitated by odorant-binding proteins in mucus.
Membrane Potential and Action Potential:
Resting membrane potential: -55mV.
Action potential frequency in the olfactory nerve increases with odorant strength.
Adaptation Towards the Sense of Smell:
Rapid adaptation within the first second, with further slow adaptation.
Psychological adaptation greater than receptor adaptation, involving feedback inhibition from the central nervous system.
Primary Sensations of Smell:
Camphoraceous, Musky, Floral, Pepperminty, Ethereal, Pungent, Putrid.
Odor Detection Threshold:
Examples: Hydrogen sulfide (0.0005 ppm), Methyl-mercaptan (0.002 ppm).
Some toxic substances are odorless at lethal concentrations.
Characteristics of Smell:
Odor blindness for single substances due to lack of appropriate receptor protein.
Behavioral and emotional influences of smell.
Transmission of Olfactory Signals:
From olfactory cells to glomeruli in the olfactory bulb, involving lateral inhibition.
Primitive, less old, and new olfactory systems with different path
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2 Case Reports of Gastric Ultrasound
2. Introduction
The genus Salmonella is composed of motile bacteria that
conform to the definition of the family Enterobacteriaceae.
The genus Salmonella is composed of two species,
Salmonella enterica and
Salmonella bongori (formerly subspecies V).
Salmonella enterica has been subdivided into six subspecies:
A. S. enterica subsp. enterica, designated subspecies I;
B. S. enterica subsp. salamae, subspecies II;
C. S. enterica subsp. arizonae, subspecies IIIa;
D. S. enterica subsp. diarizonae, subspecies IIIb;
E. S. enterica subsp. houtenae, subspecies IV; and
F. S. enterica subsp. indica, subspecies VI.
3.
4. Introduction
The type species is S. enterica subsp. enterica.
Subspecies I strains are commonly isolated from humans and warm-
blooded animals.
Subspecies II, IIIa, IIIb, IV, and VI strains and S. bongori are usually
isolated from coldblooded animals and the environment.
Salmonella Serotypes
Salmonella serotyping is a subtyping method based on the immunologic
characterization of three surface structures:
O antigen, which is the outermost portion of the LPS layer that covers the
bacterial cell;
H antigen, which is the filament portion of the bacterial flagella; and
Vi antigen, which is a capsular polysaccharide present in specific
serotypes.
Serotyping of Salmonella is commonly performed to facilitate surveillance
for Salmonella infection and to aid in the recognition of outbreaks.
5.
6.
7.
8.
9.
10.
11.
12.
13. Pathogenesis and Immunity
After ingestion and passage through the stomach, salmonellae attach to the
mucosa of the small intestine and invade into the M (microfold) cells located in
Peyer patches, as well as into enterocytes.
The bacteria remain in endocytic vacuoles, where they replicate. The bacteria can
also be transported across the cytoplasm and released into the blood or lymphatic
circulation.
Regulation of the attachment, engulfment, and replication is controlled primarily
by two large clusters of genes (pathogenicity island I and II) on the bacterial
chromosome.
Pathogenicity island I encodes salmonella-secreted invasion proteins (Ssps)
and a type III secretion system that injects the proteins into the host cell.
Pathogenicity island II contains genes that allow the bacteria to evade the host’s
immune response and a second type III secretion system for this function.
14.
15.
16. Epidemiology
Salmonella can colonize virtually all animals, including poultry, reptiles,
livestock, rodents, domestic animals, birds, and humans.
Animal-to-animal spread and the use of Salmonella-contaminated
animal feeds maintain an animal reservoir.
Serotypes such as Salmonella Typhi and Salmonella Paratyphi are
highly adapted to humans and do not cause disease in nonhuman
hosts.
In addition, in contrast with other Salmonella serotypes, strains that are
highly adapted to humans (i.e., Salmonella Typhi, Salmonella Paratyphi)
can survive in the gallbladder and establish chronic carriage.
17. Epidemiology
Most infections result from the ingestion of contaminated food products and,
in children, from direct fecal-oral spread.
The incidence of disease is greatest in children younger than 5 years and adults
older than 60 years who are infected during the summer and autumn months,
when contaminated foods are consumed at outdoor social gatherings.
The most common sources of human infections are poultry, eggs, dairy
products, and foods prepared on contaminated work surfaces (e.g., cutting
boards where uncooked poultry was prepared).
Salmonella Typhi infections occur when food or water contaminated by
infected food handlers is ingested. There is no animal reservoir.
It is estimated that 21 million Salmonella Typhi infections and 200,000 deaths
occur each year worldwide.
18. Epidemiology
The infectious dose for Salmonella Typhi infections is low, so
person-to-person spread is common.
In contrast, a large inoculum (e.g., 106 to 108 bacteria) is required
for symptomatic disease to develop with most other Salmonella
serotypes.
The organisms can multiply to this high density if contaminated
food products are improperly stored (e.g., left at room temperature).
The infectious dose is lower for people at high risk for disease
because of age, immunosuppression or underlying disease
(leukemia, lymphoma, sickle cell disease), or reduced gastric
acidity.
19.
20.
21. Clinical Diseases
The following four forms of Salmonella infection exist:
gastroenteritis, septicemia, enteric fever, and asymptomatic
colonization.
Gastroenteritis-
Gastroenteritis is the most common form of salmonellosis in the
United States.
Symptoms generally appear 6 to 48 hours after the consumption of
contaminated food or water, with the initial presentation consisting
of nausea, vomiting, and nonbloody diarrhea.
Fever, abdominal cramps, myalgias, and headache are common.
Colonic involvement can be demonstrated in the acute form of the
disease.
Symptoms can persist from 2 to 7 days before spontaneous
resolution.
22. Clinical Diseases
Septicemia
All Salmonella species can cause bacteremia, although infections
with Salmonella Typhi, Salmonella Paratyphi, and Salmonella
Choleraesuis more commonly lead to a bacteremic phase.
The risk for Salmonella bacteremia is higher in pediatric and
geriatric patients and in immunocompromised patients (HIV
infections, sickle-cell disease, congenital immunodeficiencies).
The clinical presentation of Salmonella bacteremia is like that of
other gram-negative bacteremias; however, localized suppurative
infections (e.g., osteomyelitis, endocarditis, arthritis) can occur in
as many as 10% of patients.
23. Clinical Diseases
Enteric Fever
Salmonella Typhi produces a febrile illness called typhoid
fever.
A milder form of this disease, referred to as paratyphoid
fever, is produced by
Salmonella Paratyphi A,
Salmonella Paratyphi B), and
Salmonella Paratyphi C).
The bacteria responsible for enteric fever pass through the
cells lining the intestines and are engulfed by macrophages.
They replicate after being transported to the liver, spleen, and
bone marrow.
24. Clinical Diseases
Ten to 14 days after ingestion of the bacteria, patients
experience
gradually increasing fever, with
nonspecific complaints of headache, myalgias, malaise,
and anorexia.
These symptoms persist for 1 week or longer and are
followed by
gastrointestinal symptoms. This cycle corresponds to an
initial bacteremic phase that is followed by colonization of
the gallbladder and then reinfection of the intestines.
Enteric fever is a serious clinical disease and must be
suspected in febrile patients who have recently traveled to
developing countries where disease is endemic.
25. Clinical Diseases
Enteric fever is a misnomer, in that the hallmark features of this
disease—fever and abdominal pain—are variable.
Although fever is documented at presentation in >75% of cases,
abdominal pain is reported in only 30–40%.
Thus a high index of suspicion for this potentially fatal systemic
illness is necessary when a person presents with fever and a history
of recent travel to a developing country.
The incubation period for S.Typhi averages 10–14 days but
ranges from 3 to 21 days, with the duration likely reflecting the
inoculum size and the host’s health and immune status.
The most prominent symptom is prolonged fever (38.8°–40.5°C;
101.8°–104.9°F), which can continue for up to 4 weeks if
untreated.
S. Paratyphi A is thought to cause milder disease than S.Typhi, with
predominantly gastrointestinal symptoms.
26. Clinical Diseases
Symptoms reported on initial medical evaluation included
headache (80%),
chills (35–45%),
cough (30%),
sweating (20–25%),
myalgias (20%),
malaise (10%), and
arthralgia (2–4%).
Gastrointestinal symptoms included
anorexia (55%),
abdominal pain (30–40%),
nausea (18–24%),
vomiting (18%), and
diarrhea (22–28%) more commonly than constipation (13–16%).
27. Clinical Diseases
Physical findings included
coated tongue (51–56%),
splenomegaly (5–6%), and
abdominal tenderness (4–5%).
Early physical findings of enteric fever include
rash (“rose spots”),
hepatosplenomegaly (3–6%),
epistaxis, and
relative bradycardia at the peak of high fever.
28. Clinical Diseases
Rose spots make up a faint, salmon-colored,
blanching, maculopapular rash located primarily
on the trunk and chest.
The rash is evident in ∼30% of patients at the end
of the first week and resolves without a trace after
2–5 days.
Patients can have two or three crops of lesions,
and Salmonella can be cultured from punch
biopsies of these lesions.
The faintness of the rash makes it difficult to
detect in highly pigmented patients.
29. Clinical Diseases
Complications of Enteric Fever-
1. Gastrointestinal bleeding
2. Intestinal perforation (usually of terminal ileum
3. Encephalopathy accompanied by hemodynamic shock
4. Hepatitis
5. Cholecystitis
6. Pneumonia (may be due to secondary infection with other
organisms such as Streptococcus pneumoniae)
7. Myocarditis
8. Acute kidney injury, nephritis
30. Clinical Diseases
Complications of Enteric fever-
1. Deep-seated abscess (e.g., spleen, large joint, bone)
2. Anemia
3. Meningitis
4. Neurological disturbance (cerebellar ataxia)
5. Miscarriage
6. Psychiatric disturbance
7. Disseminated intravascular coagulation
8. Chronic carriage (fecal or urinary carriage for 1 yr)
9. Carcinoma of gallbladder
31. Clinical Diseases
Asymptomatic Colonization
The strains of Salmonella responsible for causing
typhoid and paratyphoid fevers are maintained by
human colonization.
Chronic colonization for more than 1 year after
symptomatic disease develops in 1% to 5% of patients,
the gallbladder being the reservoir in most patients.
Chronic colonization with other species of Salmonella
occurs in less than 1% of patients and does not
represent an important source of human infection.
34. Laboratory diagnosis of Enteric Fever
Diagnostic tests are needed for the diagnosis of-
invasive Salmonella infections,
for the detection of convalescent and chronic fecal carriage of typhoidal
Salmonella,
and to estimate the burden of disease for public health assessment.
It may be important to be able to detect both Salmonella serovar Typhi and
Salmonella serovar Paratyphi A infections, as they cannot be distinguished
from each other clinically.
Microbial culture is the mainstay of diagnosis.
Antibody and antigen detection and nucleic acid amplification tests have
limitations, as described below.
35. Laboratory diagnosis of Enteric Fever
The test of choice depends on the duration of
disease-
Duration of disease Specimen Positivity (%)
1st week Blood culture 90
2nd week Blood Culture
Feaces culture
Widal test
75
50
Low titre
3rd week Widal test
Blood culture
Feaces culture
80-100
60
80
36.
37. Laboratory diagnosis of Enteric Fever
The definitive diagnosis of enteric fever relies on the
isolation of Salmonella enterica from normally sterile
clinical samples, usually blood and bone marrow.
Culture confirms the diagnosis and provides an isolate for
antimicrobial susceptibility testing, epidemiologic typing,
and molecular characterization.
Blood culture-
Blood cultures are positive in approx. 90% of cases in the
first week of fever, 75% in the second week and 60% in the
third week.
Positivity rates decline thereafter and blood cultures remain
positive in 25% cases till the subsidence of pyrexia.
38. Laboratory diagnosis of Enteric Fever
10 mL of blood is collected under aspectic conditions
into blood culture bottles(Glucose and Taurocholate
broth).
Before transferring the blood into blood culture bottles,
caps of these bottles should be thoroughly cleansed
with spirit. Blood should be transferred through a hole
in a cap by inserting the needle, thus avoiding
contamination from external environment.
The dilution ratio is 1: 10 for blood culture( 5 mL blood
in 50 mL blood culture bottles.)
The blood culture bottles are incubated at 370 C.
39. Laboratory diagnosis of Enteric Fever
In areas of endemicity where antimicrobials are frequently taken before
evaluation, the yield from blood culture can be as low as 40%, and in this setting,
bone marrow aspirate culture is usually considered the reference standard
method, with a sensitivity of 80%.
The optimum period for detecting organisms circulating in the bloodstream is
considered to be in the first or second week of the illness, although cultures can
still remain positive in the third week in the absence of antimicrobial exposure.
It is possible that if a sufficiently large volume of blood is taken for culture using
modern media and systems, blood culture may be as sensitive as bone marrow
culture.
Rose spot culture has been reported to be positive in 70% of patients,
although in practice rose spots are rarely present.
Cerebrospinal fluid culture is usually positive only in very young children.
40. Laboratory diagnosis of Enteric Fever
Blood culture bottles are sub-cultured in Blood and MacConkey
agar and pale lactose non-fermenting colonis are selected for
Biochemical and serological identification.
Clot Culture-
It is an alternative to blood culture. 5 mL of blood is withdrawn
aseptically into a sterile container and allowed to clot.
The serum is separated and used for Widal test.
The clot is broken up with a sterile glass rod and added to bile broth
containing streptokinase (100 units/ml.) which digests the clot and
bacteria is released from the clot.
41. Laboratory diagnosis of Enteric Fever
Faeces Culture-
Salmonella is shed in the feaces throughout the diseaes and even in the
convalescence.
Hence, feacal culture may be helpful in patients and also in detection of
carriers. It is also valuable during antibiotic therapy when blood cultures
become negative.
Successful culture depends on the use of Enrichment and Selective media.
Feacal samples are inoculated into one tube each of Selenite and
Tetrathionate broth(Both enrichment media) and also plated directly
MacConkey agar, DCA/ XLD and Wilson-Blair Media.
Salmonella appear as pale yellow colonies on MacConkey agar and DCA
media. On W-B medium, S. typhi form large black colonies with metallic
sheen whereas S. paratyphi A produces green colonies due to lack of H2S
production.
Enrichment broths are incubated for 6-8 hrs. before subculture to
MacConkey and DCA agar and incubated overnight for 370 C.
42. Laboratory diagnosis of Enteric Fever
Biochemical Identification of Isolates-
Tests S. typhi S. Paratyphi
Catalase +ve +ve
Oxidase -ve -ve
Nitrate
Reduction
+ve +ve
Glucose +ve (Acid only) +ve( Acid and
Gas)
Mannitol +ve (Acid only) +ve( Acid and
Gas)
Lactose -ve -ve
46. Laboratory diagnosis of Enteric Fever
Serological Identification of Isolates-
A loopful of the growth from a nutrient agar slop is emulsified in 2
different drops of saline,
one acts a control ( check for Autoagglutination), another is tested
by Polyvalent O & H antisera.
Positive agglutination confirms identification of salmonella genus.
Further typing can be done in a Reference lab. Like National
Salmonella Reference Center , Kasauli.
47. Laboratory diagnosis of Enteric Fever
Demonstration of Antibodies-
Widal Test-
It is an agglutination test for detection of agglutinins (H and O) present
in patients with enteric fever. Antibodies start appearing at the end of the
1st week and rise sharply at 3rd week.
Procedure-
Two types of tubes are used for this test- Dreyer’s Tube (narrow tube
with a conical bottom) and Felix tube ( Short, round bottom).
Equal vol. (0.4 ml) of serial dilutions of serum (1:10 to 1:640) and H
and O antigengs ( for S. Typhi) and AH & BH antigens (for S.
Paratyphi) are mixed and incubated in a water bath at 370C for 4 hours
and read after overnight refrigeration at 40C.
Control tubes containing the antigen and normal saline are included to
check for autoagglutination.
48. Laboratory diagnosis of Enteric Fever
Interpretation of Widal Test-
1. The test may be negative in early part of first week.
2. Single test is usually of not much value
3. A rise in titer between two sera specimens is more meaningful
than a single test.
4. If the first sample is taken late in the disease, a rise in titer may
not be demonstrable. Instead, there may be a fall in titer.
5. Baseline titer of the population must be known before
attaching significance to the titers.
6. The antibody levels of healthy individuals in population of a
given area give the baseline titer.
7. A titer of 100 or more for O antigen is considered significant
and a titer in excess of 200 for H antigens is considered
significant generally.
49. Laboratory diagnosis of Enteric Fever
Interpretation of Widal Test-
1. Patients already treated with antibiotics may not show any rise
in titer, instead there may be fall in titer.
2. Patients treated with antibiotics in the early stages may not give
positive results.
3. Patients who have received vaccines against Salmonella may
give false positive reactions.
4. This can be differentiated from true infection by repeating the
test after a week. True untreated infection results in rise in titer.
5. Those individuals with past infections may develop anti-
Salmonella antibodies during an unrelated or closely related
infection…. “anamnestic response” …..differentiated from
true infection by lack of any rise in titer on repetition after a
week.
50.
51.
52. Laboratory diagnosis of Enteric Fever
Other Serological Tests-
1. ELISA
2. Reverse Passive Haemagglutination Test (RPHA)
3. The TyphiDot is a DOT enzyme immunoassay (Typhidott and
Typhidot-Mt)
4. TUBEX (IDL Biotech, Sollentuna, Sweden) is a
semiquantitative test that uses polystyrene particle
agglutination to detect IgM antibodies to the O9 antigen.
5. S. Typhi antigen can be detected in the urine of some typhoid
patients by co-agglutination and ELISA
53.
54.
55.
56. Laboratory diagnosis of Enteric Fever
Molecular Diagnosis-
Targets for Salmonella serovar Typhi PCR-based assays have included
theHdflagellin gene fliC-d,
the Vi capsular gene viaB,
the tyvelose epimerase gene (tyv) (previously rfbE),
the paratose synthase gene (prt) (previously rfbS),
groEL,
the 16sRNA gene ,
hilA (a regulatory gene in Salmonella pathogenicity island 1 [SPI-1]), the gene
encoding the 50-kDa outer membrane protein ST50
The food industry has used PCR technology for several decades and guidelines
are published for quantitative detection of Salmonella in food by PCR.
Studies using single or nested PCR primers for fliC of S. Typhi have reported
good results from PCR.