2ba Flashcards
Closely related to Escherichia – both belong to the same tribe, Escherichieae
Shigella
– not members of the GI microbiota, and are considered as “primary pathogens”
Shigella
Shigella
All species causes
dysentery (bloody diarrhea with mucus, blood, and leukocytes)
Shigella
Biochemical characteristics:
§ fermenters
§ motile?
§ Anaerogenic, except____
§ Do not hyrdrolyse____
§ Do not produce____
§ Do not___ lysine
§ Do not use ______as carbon source
Non-lactose
Non-motile
Shigella flexneri
urea
H2S
decarboxylate
acetate or mucate
Biochemically inert
Shigella
Shigella
– unique member of the genus
§ Ability to ferment lactose slowly (LLF)
producing pink colonies on MAC agar only after 48 hours of incubation
§ ONPG positive
Shigella sonnei
Shigella species – fragile and susceptible to various effects of physical and chemical
agents:
§ Disinfectants
§ High concentrations of acids and bile
Differentiate sonnei with other members of the genus
LLF
are susceptible to the acid pH of
the stool. Feces suspected of containing ____ spp., must be immediately inoculated to primary culture media to increase recovery of the organisms
Shigella
All Shigella species – possess____ antigens, and certain strains possess___ antigens
O
K
if present, interfere with the detection of the O antigen during serologic grouping.
K antigens (capsular)
Does shigella have H antigen?
No! Non motile!
Shigella
Serotypes based on their O antigen
Subgroup A–
Subgroup B–
Subgroup C–
Subgroup D–
S. dysenteriae (Dysentery bacillus)
S. flexneri (Strong’s bacillus)
S. boydii (S. ambigua)
S. sonnei
Shigella sp (-) for Mannitol fermentation
S. dysenteriae
Shigella sp (+) Ornithine decarboxylase
S. sonnei
Shigella
Mode of Transmission
(2)are the only known reservoir!
Humans and other large primates
Shigella
Mode of Transmission
Mode of transmission:
May also be transmitted by
…plays a major role in the transmission
direct person-to-person contact,
fecal-oral-route with carriers as the source.
flies, fingers, and food and water contaminated by infected persons
Personal hygiene
cause all types of bacillary dysentery– painful type of diarrhea characterized by watery feces w/ mucus, blood streaks & pus cells
Shigella species
Shigella
Infective dose: as low as____ bacilli are needed to initiate the disease in some healthy individuals.
100
– predominant in the U.S and other industrialized countries
– affects mostly young children. Leading isolate of gastroenteritis among ^men who have sex with men.* HIV infections increases this risk.
§ ____ and ____are the most common isolates in developing countries.
_____remains the most virulence of all the species with a significantly high
morbidity and mortality rate
§ S.sonnei
§ S. flexneri
S.dysenteriae type 1 and S.boydii
S.dysenteriae type 1
– attach to and invade the M cells located in Peyer patches.
Shigella
The organism secretes four invasion-plasmid antigen (Ipa)
proteins into epithelial cells and macrophages that induce
membrane ruffling on the target cell, leading to engulfment
of bacteria. These proteins include:
§ IpaA
§ IpaB
§ IpaC
§ IpaD
Shigella
– lyses the phagocytic vacuole and replicate in the cytoplasm.
Shigella
The rearrangement of actin filaments in the host cells propel the bacteria through the cytoplasm through the adjacent cells where cell- to-cell passage occurs.
§ Cell-to-cell passage protects it from immune-mediated clearance.
§ They survive phagocytosis by inducing apoptosis. Apoptotic phagocytes release IL1B that acts as a chemoattractant for
PMNs into the infected tissues. This destabilizes the integrity of the intestinal wall and allows bacteria to reach the deeper epithelial cells
Shigella
– produces shiga toxins, similar to the verotoxins produced by EHEC.
Shigella dysenteriae
Shigella dysenteriae – produces shiga toxins, similar to the verotoxins
produced by EHEC.
______binds to the host cell glycolipid Gb3 receptor and facilitate the transfer of the A subunit into the cell.
The______ cleaves the 28S rRNA in the 60S ribosomal subunit, resulting in the disruption of protein synthesis resulting in cell damage and death.
The B subunit
A subunit
High concentrations of____ are found on intestinal villi and renal endothelial cells.
This results in hemorrhagic
diarrhea and hemolytic uremic syndrome (HUS)
Gb3
– enrichment medium for the isolation of Salmonella spp., and Shigella species from heavily contaminated specimens such as stool.
Selenite broth
Many_____ serotypes are typically found in cold-blooded animals as well as in rodents and in birds, which serve as their natural hosts.
Salmonella
On selective and differential media –______ produce clear, colorless, non-lactose fermenting colonies.
§ Colonies with black centers are seen in
media with sodium thiosulfate such as
HEA, SSA, and XLD
§ Black precipitates indicate H2S production.
Salmonellae
Salmonella
– Non-motile
All are NLF –except for_____
All are aerogenic – except_____
All are H2S positive –except_____
S.pullorum and S. gallinarum
Salmonella Arizona -LLF
Salmonella Typhi
Salmonella Paratyphi
Salmonella
Antigenic Structures and Virulence Factors
______: Stable to boiling and acid alcohol
______: More stable
______ are the primary antigenic structures
______: Virulence Ag (K antigen); occurs in Salmonella serotype Typhi and a few strains of Salmonella serotype Cholerasius
§ Plays a role in preventing phagocytosis
O Ag
H Ag
§ O and H
Vi Ag
Salmonella
- invasiveness (enables them
to traverse the intestinal mucosa);
endotoxin, enterotoxins, intracellular
capability
– for adhesion
Surface Ag’s
Fimbriae
Salmonella
Classification
Formerly, there are only 3 known species:
S.enteritidis
S. cholerasius
S.typhi
– also known as the Gardner’s bacillus;
formerly S.typhosa is also known as the Eberth’s bacillus
S.enteritidis
S.typhi
Salmonella
Genetic studies have shown that the three previously named species are genetically related and that
there are only 2 designated species;
_______ (Type species of the genus); and with 6 subspecies.
_______(rare isolate) – initially isolated from a lizard and is usually isolated from cold-blooded
animals and the environment
§ S.enterica
§ S,bongori
Typhoid fever, the most severe form of enteric fever, caused by_______, and
enteric fevers caused by other serotypes such as (2)
Salmonella serotype Typhi
Salmonella serotype Paratyhpi and Salmonella serotype Cholerasius.
§ Except for (2), Salmonella infect animals that serve as their
reservoir
§ (2)have no known animal reservoirs and infections only occurs in humans. Carriers are often the source of infection
Salmonella Typhi and Salmonella Paratyphi
Salmonella Typhi and Salmonella Paratyphi
Salmonella
Source of infection have been attributed to poultry, milk, eggs, and egg products, as well as to handling pets.
Insufficiently cooked eggs and domestic fowl, such as chicken, turkey, and duck and common sources of infection.
Gastroenteritis
Salmonella
Outbreaks associated with consumptions of foodstuffs such as
peanut butter, cantaloupe, puffed rice and wheat cereals, corn-and vegetable-coated snacks, vegan cheese, alfalfa sprouts, cucumber, and raw tomatoes.
Cross –contamination through cooking utensils also occur
Gastroenteritis
Salmonella
Also known as_____ – a febrile disease that results from the ingestion of food contaminated with organisms originating from infected individuals or asymptomatic carriers.
Enteric Fever
typhoid fever
Salmonella
When organisms are ingested – they are resistant to gastric acid
Upon reaching the proximal end of the small intestine, they invade and penetrate the intestinal mucosa – patients suffer constipation instead of diarrhea
Organisms gain entrance to the lymphatic system and are sustained in the mesenteric lymph nodes. They eventually reach the blood stream and spread to the liver, spleen, and bone marrow, where they are immediately engulfed by mononuclear phagocytes.
Organisms multiply intracellularly inside phagocytes and are released in the
blood stream for the second time.
This results to febrile episode and the organism can be easily isolated from bloo
ENTERIC FEVER 1st Week of infection
Salmonella
Patient generally sustained fever with prolonged bacteremia
The organism invade the gall bladder and the Peyer’s patches of the bowel.
They also reach the intestinal tract via the biliary tract.
“Rose-spots” - blanching rose-colored papules around the umbilical region also appear during the second week of fever.
Involvement of the biliary system initiates GI symptoms as the organisms reinfect the intestinal tract.
The organism now exists in large number in the bowel and may be isolated from the stool
ENTERIC FEVER
2nd and 3rd Weeks of Infection
Salmonella
For asymptomatic carriers, the gallbladder becomes the foci of long-
term carriage of the organism
From the gallbladder of carriers, the organism is occasionally/intermittently shed in the feces which then result in
the spread of infection via fecal-oral route.
They become important sources of infections for susceptible persons
Enteric Fever
Asymptomatic Carriers
Salmonella
Specimen Collection and Laboratory Diagnosis
– 1st and 2nd week
– 3rd and subsequent weeks
– can be used indefinitely as clinical
specimen
NOTE:_____ is the best diagnostic procedure to identify Salmonella
Blood
Urine/Stool
Stool
Culture
: “Metallic colonies with a black ring” on BSA
S. Typhi
Serologic test that detects the presence of antibodies in the person’s serum against O and H antigens of Salmonella Typhi.
Widal Test
Widal Test
Interpretation:
Titer of______ or more for O agglutinins and_____ or more for H agglutinin should be considered clinically
significant as these indicate active infection.
1:100
1:200
