Gastro-Intestinal Bacterial Infections Flashcards
Describe characteristics of the causative agents (including virulence properties), pathogenesis, clinical features, diagnosis, treatment & prevention of the following: Shigellosis Salmonellosis Typhoid/enteric fever Non typhoidal Salmonella Cholera
Types of Infectious Bacterial Diarrhoea
Salmonella enterica ser Typhi
(Salmonella Typhi)
Salmonella spp.
Shigella sonnei
Shigella boydii
Shigella dysenteriae
Shigella flexneri
Vibrio cholera
Shigella:
Epidemiology
Shigella species are closely related to E. coli
Strictly human pathogen, no animal reservoir
Not members of the normal GI microbiota
Transmission: Faecal-oral. Also spread by
food or water contaminated by humans
Outbreaks: Poor personal hygiene standards
- Very young
- Very old
All can cause Bacillary dysentery
Microscopy of Shigella
Gram-negative bacilli (rods)
Non-motile
Unencapsulated
Facultative
Non-fastidious
Bile-tolerant
Non lactose-fermenter (NLF)
They do not produce H_2S
Types of Shigella
Shigella dysenteriae – serogroup A
S. flexneri – serogroup B
S. boydii – serogroup C
S. sonnei – serogroup D
Shigella:
Pathogenesis
Highly infectious - very small inoculum required 101
– 102 organisms
Acid-resistant- survives passage through the stomach to reach the intestine
Invasion of the wall of the large bowel - Intense
inflammatory response involving neutrophils and
macrophages
Patches of necrotic epithelium are sloughed and ulcers form
Many strains have been shown to produce an exotoxin -cause secretion of water and electrolytes by cells of the small bowel
Shiga toxin (Stx) that affects both the gut and the central nervous system
Antibiotic use increases shiga toxin = HUS
Shigella:
Clinical Presentation
Initial symptoms appear
approximately 24 to 48 hours after
ingestion of the organisms
Fever, chills, abdominal cramps, and
pain accompanied by tenesmus
Frequent, small-volume, bloody,
mucoid fecal discharge
S. dysenteriae causes dysentery ->severe disease
Infants: convulsions, meningeal
irritation
Transient bacteraemia
Septicaemia rare->immunosuppressed pts
Bacilli in stools-short period
Chronic carriers-recurrent episodes
Do not use Imodium = ↑ toxin absorption
Shigella:
Diagnosis
Readily isolated using selective differential media (eg, Hektoen enteric agar, XLD agar)
Isolates are identified with further
biochemical tests
Slide agglutination tests using O groupspecific antisera (A, B, C, D) confirm
both the Shigella genus and the
species
Shigella:
Tx
Usually self-limiting
Supportive therapy
Treatment reserved for the
immunocompromised, those with
severe/complicated disease as well in
outbreak setting
IV antibiotic Rx + REHYDRATION:
- Ciprofloxacin
- Ceftriaxone
- Azithromycin
Shigella:
Px
Standard practices such as
sewage disposal and water
chlorination.
Handwashing and proper
cooking of food, are highly
protective
No vaccines
Salmonella:
Epidemiology
1400 serotypes infect humans
2 groups: Humans are the only known source of Salmonella enterica ser Typhi
infections
Typhoid fever caused by:
- Salmonella enterica ser Typhi
- Salmonella paratyphi A and B
Typhoid (enteric) fever- severe, higher fatality rate
Paratyphoid fever- less severe, lower fatality rate
Non-typhoid salmonellae (NTS)
Salmonella:
Microscopy
Gram-negative bacilli
Motile
All except S. enterica ser Typhi are unencapsulated
Salmonella:
Pathogenesis
- Ingestion
- Small intestine
- Macrophage
- MLNs-Mesenteric Lymph Nodes
- Lymph duct
- Transient bacteraemia
- Replication in RES»»Septicaemia»>Fever Kidneys Other organs
- Gallbladder»»Cholecystitis and Carrier state
- Bile to 2
- (2.) Inflamation, ulceration: Peyer
- Diarrhoea Bleeding Perforation
Salmonella:
Clinical Presentation
1) Typhoid (enteric) fever, paratyphoid fever-Caused by S.enterica ser Typhi & S. Paratyphi
2) Acute gastroenteritis, enterocolitis-Caused by non-typhoid salmonellae (NTS)
3) Extra-intestinal infections-Bacteraemia
4) Asymptomatic colonization-carrier state
Typhoid(Enteric) Fever:
Epidemiology
NOTIFIABLE MEDICAL CONDITION
S. enterica ser Typhi + S. paratyphi colonise only humans
Transmission: close contact: typhoid fever pt. OR carrier
Infection acquired via ingestion of contaminated food: faecal-oral route
Endemic in developing countries:due to poor socio-economic conditions + sanitation
-SE Asia
-South + Central America
-Africa SALMONELLA:
CLINICAL FEATURES-ENTERIC FEVER
Typhoid/Entreric Fever:
Clinical Presentation
Multiorgan infection characterized by prolonged fever, sustained bacteraemia and involvement of MLNs, liver and spleen
Mean incubation period is 13 days
First sign of disease is fever associated with a headache
Fever rises in a stepwise fashion over the next 72 hours and can persists for weeks in untreated patients
A faint rash (rose spots) may appears during the first few days on the abdomen and chest
Many patients are constipated, although perhaps one-third of patients have a mild diarrhea
As the untreated disease progresses, an increasing number of patients complain of diarrhea
Chronic infection of the bloodstream is serious
Effects of endotoxin can lead to myocarditis, encephalopathy, or
intravascular coagulation
Persistent bacteremia can lead to infection at other sites
Biliary tree, with reinfection of the intestinal tract and diarrhea late in the disease
Urinary tract infection and metastatic lesions in bone, joint, liver, and meninges may also occur
Most important complication is hemorrhage from perforations through
the wall of the terminal ileum or proximal colon at the site of necrotic Peyer patches
In patients whose disease has been progressing for 2 weeks or more
Typhoid/Enteric Fever:
DIagnosis
Collect BEFORE antibiotic therapy is initiated
Non invasive specimen: Stools
Invasive specimens: Blood Culture, Bone marrow
S. enterica ser Typhi: 90% of pts. have positive BC in first week of illness otherwise positive in the 2nd, 3rd week
Ideally blood and stool cultures should be submitted simultaneously
Bone marrow may remain positive even after 5 days of antibiotics
Urine and stool culture positive in weeks 2 & 3 Specimen culture followed by agglutination with specific antisera including Vi antigen
Serology: Widal->Antibodies against O and H antigens may be suggestive
but not confirmatory. Does not provide information on antibiotic resistance
Typhoid/Enteric Fever:
Complications
2–5 wks after onset:
Intestinal perforation
Intestinal haemorrhage
Myocarditis
Osteomyelitis
Meningitis, Relapse, Death
10% mortality if untreated
Relapse in 10% of pts.
Carriers: NB source-permanent,
asymptomatic
Typhoid/Enteric Fever:
Treatment
Positive BC:
- Ceftriaxone
- Ciprofloxacin
Empiric Rx:
- Ciprofloxacin
- Ceftriaxone
- Cefotaxime
Carriers:
- Ciprofloxacin
- Ceftriaxone
Non Typhoid Fever
Gastroenteritis»contaminated food
Animal origin
- Poultry
- Meat
- Eggs
- Dairy products
Proper cooking necessary
Outbreaks occur – common source
GIT infection - does not need antibiotics
Non-Typhoid Salmonella Gastroenteritis/Enterocolitis:
Clinical Presentation
S. enteritidis
Acute salmonella gastroenteritis: mild to severe
Most cases are self-limiting
Symptoms may appear 8 to 36 hours after ingestion of contaminated food
Nausea, vomiting, fever, and chills, accompanied by watery diarrhea and abdominal pain
Sometimes bacteraemia, bacteriuria, occult abscess
The infection may be more severe in very young children, elderly adults, and
patients with other underlying disease
Dissemination occasionally occur and in such cases, antimicrobial therapy is required
Non-Typhoid Salmonella Gastroenteritis/Enterocolitis:
Lab Diagnosis
Depends on culture and ID of organism from stools
Non-Typhoid Salmonella Gastroenteritis/Enterocolitis:
Treatment
Severe illness-extreme of ages
Patient septic and/or sick enough to be
hospitalized
Immune compromised
Sick enough to hospitalize
HIV & sickle cell anaemia is a risk factor for invasive
infections
Empiric treatment if indicated: -Ciprofloxacin -Ceftriaxone -Cefotaxime
Non-Typhoid Salmonella Gastroenteritis/Enterocolitis:
Prevention
Sanitation + hygiene
Cook food thoroughly
Carriers: do not handle or prepare food
Vaccination (travelers) only for S typhi protection moderate not absolute
Salmonella:
Bacteremia
Can be with or without extraintestinal foci of infection
Characterized primarily by prolonged fever and intermittent bacteremia
Serotypes most commonly associated with bacteremia are S. enterica ser Typhi, Paratyphi, and Choleraesuis
Young children may experience fever and gastroenteritis with brief episodes of bacteremia
Adults, may experience transient bacteremia during episodes of gastroenteritis or develop symptoms of septicemia without gastroenteritis
The risk of metastatic complications could be more severe than the bacteremia itself, even in individuals who do not have underlying diseases
Cases of septic arthritis can also occur in patients who had asymptomatic salmonellosis
Salmonella: Carrier State
Individuals who recover from infection may harbor the organisms in the
gallbladder
Such individuals excrete the organisms in their feces either continuously
or intermittently
They become an important source of infection for susceptible persons
The carrier state may be terminated by antimicrobial therapy if
gallbladder infection is not evident
Otherwise, cholecystectomy has been the solution to the chronic state of
enteric carriers
SALMONELLA
CARRIER STATE-TYPHOID MARY
Mary Mallon (Mallone): Irish-born cook USA
Worked as housekeeper for various families
“Dishes to die for” People became sick; fatal cases
Health authorities carrier When confronted aggressive
In isolation hospital for 3 yrs
Public outcry released
5 yrs later: typhoid outbreak
Died in isolation at age 69
Could have been
prevented:
WASHING OF
HANDS
Salmonella Carrier State-TyphoidMary
Mary Mallon (Mallone): Irish-born cook
USA
Worked as housekeeper for various families
“Dishes to die for”
People became sick; fatal cases
Health authorities»carrier
When confronted»aggressive
In isolation hospital for 3 yrs
Public outcry»released
5 yrs later: typhoid outbreak
Died in isolation at age 69
Could have been prevented:WASHING OF HANDS
Vibrio cholera:
Microscopy and Epidemiology
Curved Gram-negative rod
Non spore forming
Motile by means of single polar flagellum
Salt (NaCl) tolerant - halophilic
Grow in alkaline conditions - aquatic environments
0139 serogroups
Somatic antigens O1 and O139_ produce the toxin that causes cholera V. cholerae O1 3 serotypes, 2 biotypes Poor sanitation and hygienic conditions Contaminated rivers, warmer climates
Vibrio cholera:
Classification
Genus
Vibrio
Vibrio choleraeSEROVAR O:1* SEROVAR O:139* NON O:1 Non-agglutinating vibrios (NAV)
Non Cholera Vibrios (NCV) OTHER SEROVARS Non-agglutinating vibrios (NAV)
Non-cholera vibrios (NCV)
Biotypes Classic El Tor Serotypes
Ogawa Inaba
Hikojima OTHER SPECIES V. parahaemolyticus
V.vulnificus
Vibrio cholerae
CLASSIFICATION
Vibrio cholera:
Pathogenesis
Virulence factors:
- Mucinase, adhesins , enterotoxin
- Cholera toxin
- Consist of A-B subunits
- Binds to intestinal epithelium
- Binds to ganglioside receptors activating adenyl cyclase
- Overproduction of cAMP
- Massive watery diarrhoea
Vibrio cholera:
Clinical Manifestations
Incubation period: 2–3 days Mainly through contaminated water Improperly preserved and handled foods, including fish and seafood, milk, ice cream, and unpreserved meat, have been responsible for outbreaks
Acute onset: Profuse watery diarrhoea Tenesmus Abdominal pain Sometimes vomiting Neither white cells nor blood in the stools-Non inflammatory Fever: < 5% of ptsRice water stools 10–30 per day up to 20 liter 10% of cases: rapid, severe dehydration Electrolyte imbalance Metabolic acidosis, hypovolaemic shock Renal damage, death Without rehydration: Mortality rate 40–60% WITH REHYDRATION: < 1% Vibrio cholerae
Vibrio cholera:
Diagnosis
Clinical diagnosis in outbreaks & endemic areas
Alkaline peptone water (enrichment media
before subculturing on the TCBS)
Grow in thiosulfate citrate bile salts
sucrose (TCBS) medium to form yellow
colonies (V. cholerae)-ferments sucrose
Biochemical tests, Oxidase positive
Grow under aerobic and anaerobic
conditions
Specific antisera required for complete
identification-Polyvalent 01
Vibrio cholera:
Treatment and Prevention
Rx: rehydration NB NB NB NB
Mild cases usually Oral Rehydration Therapy
Severe cases: IV
Role of antibiotics – shortens symptoms & carriage of organisms:
- Azithromycin, ampicillin, tetracyclines, trimethoprim, and chloramphenicol
- Most strains are susceptible to doxycycline or ciprofloxacin
Boiling and chlorination of water during epidemics are required
Adequate cooking
