Salmonella enterica Flashcards
characteristics of salmonella enterica
- gram negative, non-sporulating, facultative anaerobic motile rods
- mesophilic, optimum growth temperature between 35C and 37C, but generally have a growth range of 5-54C
- easily killed by pasteurization, sensitive to low pH (4.5-9.5), and do not multiply below A-w 0.94
- can survive under frozen or dried states for a long time
- multiplication in several food types does not effect acceptance qualities
why is it that salmonella contaminating cocoa beans is such a problem?
cannot inactive salmonella using heat, since the heat required to kill Salmonella at the low Aw present in the chocolate (high sucrose) would “burn” the sucrose containing chocolate (giving it a burnt taste)
why does Salmonella contaminating chocolate, make a great opportunity for outbreaks?
in the low a-w of the chocolate, salmonella can survive for years at room temperature
what subspecies of Salmonella cause illness in humans?
Salmonella enterica subspecies enterica
which serovars are most commonly associated with foodborne illness?
Typhimurium and Enteriditis
how can salmonella serotyping be done?
through reactions with antisera, but now it is much more common to serotype based on whole genome sequence
how are serovars generally named?
after their geographic origin
what serotype do many food animals and pets harbor?
serotype Typhimurium
how can salmonella be transmitted through eggs?
serotype enteriditis infecting the ovaries of poultry. in this way, the interior of the egg is infected prior to shell development
besides pets and eggs, what are other food sources of salmonella?
fruits and vegetables
what are the symptoms of salmonella? when do they begin to occur?
- symptoms generally occur 8-72 hours after ingestion. generally resolve within 5 days
- illness is self-limiting, non-bloody diarrhea, and abdominal pain
- uncomplicated cases only require supportive therapy such as fluid and electrolyte replacement
why are antibiotics not a good idea to treat salmonella?
prolongs the carrier state and increase AMR so they generally are not used
why is non-typhoidal salmonella dangerous in immunocompromised people?
can manifest as an invasive disease, characterized by bacteremia and a high mortality rate
what is the overview of salmonella infection?
salmonella exploits phagocytic intestinal cells, such as antigen-sampling M cells and DCs, but also forces its own uptake into non-phagocytic epithelial cells. Salmonella adheres to intestinal cells via fimbriae
once across the epithelium, salmonella can efficiently invade further epithelial cells from the basolateral side
usually remain localized to intestinal tissues - inflammatory response responsible for the symptoms of gastroenteriditis
significance of SPIs
contain virulence factors that salmonella requires during infection
not all strains have the same SPIs
what does salmonella activate after it is ingested?
the acid tolerance response (ATR) to maintain intracellular pH in the acidic stomach
how does salmonella attach to the host’s epithelial cells?
by means of adhesins, such as those encoded within SPI-3 and SPI-4
what does SPI-3 encode?
MisL which binds to the fibronectin on epithelial cells, it also encodes MgtCB which is involved in intramacrophage survival
what does SPI-4 produce?
SiiE, which mediates attachment to epithelial cells, although its receptor is unknown
what does SPI-1 encode?
a type 3 secretion system that delivers a cohort of virulence effector proteins into host cells
what do T3SS virulence factors do?
drive the forced uptake of the pathogen by non-phagocytic cells, and also manipulate host cell signalling pathways, especially those involved in the inflammatory response.
the released effectors also induce rearrangements of the host cell actin cytoskeleton, leading to the production of large surface protrusions termed membrane ruffles
what do ruffles produced by the T3SS do?
engulf the pathogen into large vesicles called Salmonella-containing vacuoles (SCVs)
where are SCVs located? and why?
near the Golgi apparatus, to intercept vesicles and obtain nutrients
what about Salmonella leads to diarrhea?
host responses and inflammation, due to bacterial invasion of the intestinal cells, caused by the immune system –> lead to diarrhea
what can SCVs do in immunocompromised individuals?
SCVs can migrate to the basolateral side of the intestine and have direct blood access, thus causing a systemic infection
what is the structure’s function of the T3SS?
the needle-like structure is used as a sensory probe to detect the presence of eukaryotic cells. it can inject effector proteins into the eukaryotic cell which exerts a number of effects that help the pathogen to survive and to escape an immune response
define Pyroptosis?
a highly inflammatory form of programmed cell death that occurs most frequently upon infection with intracellular pathogens and is likely to form part of the antimicrobial response
what is SPI-2 important for?
intracellular replication (epithelial cells and macrophages) inside the SCVs
what does SPI-5 encode? what do these proteins do?
SopE, SopE2, and SigD. lead to cytoskeletal remodeling and induction of the proinflammatory response
what does the inflammatory response that SPI-5 causes, do?
results in gastrointestinal dysbiosis
why does inflammation favor salmonella growth over commensal bacteria?
respiratory electron acceptors are produced, which provides an energetic growth advantage to facultative anaerobes such as Salmonella
how is the electron acceptor, tetrathionate produced?
neutrophils release reactive oxygen species which react with thiosulfate in the gut which is what forms tetrathionate
what does SPI-2 encode?
the ttr operon which allows Salmonella to use tetrathionate as a terminal electron acceptor, which allows salmonella to outgrow its anaerobic competitors
how does diarrhea occur? how does salmonella cause it?
subcellular alterations disrupted which is caused by both extracellular and intracellular pathogens
Salmonella can modify tight junctions by regulating actin filament dynamics to induce membrane ruffling. the proteins responsible for ruffling are instrumental in altering the integrity of tight junctions
what are the four likely effectors Salmonella uses to disrupt tight junctions?
SipA, SopB, SopE and SopE2
Antibiotics for Salmonella:
only recommended for those who are severely ill, and for cases of bloodborne infection
routinely used in feed and food animals and birds, and this has resulted in an increase in multidrug resistant (MDR) Salmonella strains
genes for the virulence factors as well as for antibiotic resistance can occur on the same plasmid
Salmonella Post-acute Sequelae:
- IBS and Reactive arthritis
- IBS may occur in between 7.4-31.6% of Salmonella infections
- some evidence of reactive arthritis lasting over 5 years post-infection also exists
Difference between Typhoid vs Non-Typhoid Serovars
Typhi serovars are human restricted - causes enteric fever: fever, abdominal pain, transient diarrhea or constipation, and a salon-colored maculopapular rash on the trunk
Non-Typhoid serovars have a broad host-range - causes gastroenteritis: abdominal pain, vomiting, and inflammatory diarrhea
while non-typhoid Salmonella mostly stays in the GI tract, Typhoid spreads wider and results in systemic illness
how does Salmonella ser. Typhi spread throughout the body?
uses immune cells to traffic the lymphatic system (spleen, bone marrow, liver, and gall bladder) where they hide out and lead to an extended shedding period
who was Typhoid Mary?
an irish immigrant worker who cooked for affluent families in New York.
she was the first person identified as being an asymptomatic carrier of Salmonella ser. Typhi. when they found out she was responsible for getting several families sick through her cooking, she was forced into isolation for three years. she was supposed to not cook anymore but she did eventually and caused more fever outbreaks
when do symptoms begin to occur in Salmonella ser. Typhi
7-28 days
what is the significance of the asymptomatic carrier state in Salmonella ser. Typhi
generally follows the active infection, allowing transmission from human-to-human
what is treatment for Salmonella ser. Typhi
based on supportive therapy, and antibiotics to relieve the systemic infection
includes Chloroamphenicol, ampicillin, or trimethoprim-sulfamethoxazole
what are some methods of prevention for salmonella
- buy graded eggs, eggs should be refrigerated with clean and uncracked shells
- avoid handling food while ill
- prevent cross-contamination in your kitchen
- defrost meats in the refrigerator, defrosting at room temperature allows bacteria to grow
- cook breaded chicken products to an internal temperature of 74C
- do not microwave to cook frozen breaded chicken products
- before cutting a melon, always wash and scrub the entire melon with warm water
- wash your hands well with soap after handling pets, pet food, changing cat litter, scooping after your dog, or cleaning your pet’s habitat
Key points and review of Salmonella enterica
- leading cause of foodborne bacterial illness in humans
- salmonella are generally grouped according to serovar, based on antibody reactions with somatic (O) antigen (LPS), and the flagellar (H) antigens
- most salmonella infections are localized to the intestine and cause diarrhea
- salmonella ser. Typhi and Paratyphi can cause systemic infection (other serotypes may cause systemic infection in immunocompromised individuals)
