Salmonella enterica

Question 1

characteristics of salmonella enterica

Answer 1

• 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

Question 2

why is it that salmonella contaminating cocoa beans is such a problem?

Answer 2

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)

Question 3

why does Salmonella contaminating chocolate, make a great opportunity for outbreaks?

Answer 3

in the low a-w of the chocolate, salmonella can survive for years at room temperature

Question 4

what subspecies of Salmonella cause illness in humans?

Answer 4

Salmonella enterica subspecies enterica

Question 5

which serovars are most commonly associated with foodborne illness?

Answer 5

Typhimurium and Enteriditis

Question 6

how can salmonella serotyping be done?

Answer 6

through reactions with antisera, but now it is much more common to serotype based on whole genome sequence

Question 7

how are serovars generally named?

Answer 7

after their geographic origin

Question 8

what serotype do many food animals and pets harbor?

Answer 8

serotype Typhimurium

Question 9

how can salmonella be transmitted through eggs?

Answer 9

serotype enteriditis infecting the ovaries of poultry. in this way, the interior of the egg is infected prior to shell development

Question 10

besides pets and eggs, what are other food sources of salmonella?

Answer 10

fruits and vegetables

Question 11

what are the symptoms of salmonella? when do they begin to occur?

Answer 11

• 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

Question 12

why are antibiotics not a good idea to treat salmonella?

Answer 12

prolongs the carrier state and increase AMR so they generally are not used

Question 13

why is non-typhoidal salmonella dangerous in immunocompromised people?

Answer 13

can manifest as an invasive disease, characterized by bacteremia and a high mortality rate

Question 14

what is the overview of salmonella infection?

Answer 14

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

Question 15

significance of SPIs

Answer 15

contain virulence factors that salmonella requires during infection

not all strains have the same SPIs

Question 16

what does salmonella activate after it is ingested?

Answer 16

the acid tolerance response (ATR) to maintain intracellular pH in the acidic stomach

Question 17

how does salmonella attach to the host’s epithelial cells?

Answer 17

by means of adhesins, such as those encoded within SPI-3 and SPI-4

Question 18

what does SPI-3 encode?

Answer 18

MisL which binds to the fibronectin on epithelial cells, it also encodes MgtCB which is involved in intramacrophage survival

Question 19

what does SPI-4 produce?

Answer 19

SiiE, which mediates attachment to epithelial cells, although its receptor is unknown

Question 20

what does SPI-1 encode?

Answer 20

a type 3 secretion system that delivers a cohort of virulence effector proteins into host cells

Question 21

what do T3SS virulence factors do?

Answer 21

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

Question 22

what do ruffles produced by the T3SS do?

Answer 22

engulf the pathogen into large vesicles called Salmonella-containing vacuoles (SCVs)

Question 23

where are SCVs located? and why?

Answer 23

near the Golgi apparatus, to intercept vesicles and obtain nutrients

Question 24

what about Salmonella leads to diarrhea?

Answer 24

host responses and inflammation, due to bacterial invasion of the intestinal cells, caused by the immune system –> lead to diarrhea

Question 25

what can SCVs do in immunocompromised individuals?

Answer 25

SCVs can migrate to the basolateral side of the intestine and have direct blood access, thus causing a systemic infection

Question 26

what is the structure's function of the T3SS?

Answer 26

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

Question 27

define Pyroptosis?

Answer 27

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

Question 28

what is SPI-2 important for?

Answer 28

intracellular replication (epithelial cells and macrophages) inside the SCVs

Question 29

what does SPI-5 encode? what do these proteins do?

Answer 29

SopE, SopE2, and SigD. lead to cytoskeletal remodeling and induction of the proinflammatory response

Question 30

what does the inflammatory response that SPI-5 causes, do?

Answer 30

results in gastrointestinal dysbiosis

Question 31

why does inflammation favor salmonella growth over commensal bacteria?

Answer 31

respiratory electron acceptors are produced, which provides an energetic growth advantage to facultative anaerobes such as Salmonella

Question 32

how is the electron acceptor, tetrathionate produced?

Answer 32

neutrophils release reactive oxygen species which react with thiosulfate in the gut which is what forms tetrathionate

Question 33

what does SPI-2 encode?

Answer 33

the ttr operon which allows Salmonella to use tetrathionate as a terminal electron acceptor, which allows salmonella to outgrow its anaerobic competitors

Question 34

how does diarrhea occur? how does salmonella cause it?

Answer 34

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

Question 35

what are the four likely effectors Salmonella uses to disrupt tight junctions?

Answer 35

SipA, SopB, SopE and SopE2

Question 36

Antibiotics for Salmonella:

Answer 36

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

Question 37

Salmonella Post-acute Sequelae:

Answer 37

- 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

Question 38

Difference between Typhoid vs Non-Typhoid Serovars

Answer 38

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

Question 39

how does Salmonella ser. Typhi spread throughout the body?

Answer 39

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

Question 40

who was Typhoid Mary?

Answer 40

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

Question 41

when do symptoms begin to occur in Salmonella ser. Typhi

Answer 41

7-28 days

Question 42

what is the significance of the asymptomatic carrier state in Salmonella ser. Typhi

Answer 42

generally follows the active infection, allowing transmission from human-to-human

Question 43

what is treatment for Salmonella ser. Typhi

Answer 43

based on supportive therapy, and antibiotics to relieve the systemic infection includes Chloroamphenicol, ampicillin, or trimethoprim-sulfamethoxazole

Question 44

what are some methods of prevention for salmonella

Answer 44

- 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

Question 45

Key points and review of Salmonella enterica

Answer 45

- 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)