Enterobacteriaceae/Salmonella

Question 1

Enterobacteriaceae- where do they live?

Answer 1

Important pathogens of mammals, birds and humans
a number are zoonotic: foodborne, water borne, vector borne
typical habitat: intestinal tract of vertebrates

Question 2

Enterobacteriaceae- general characteristics

Answer 2

gram negative rods or coccobacilli
usually MOTILE and flagellated
facultative anaerobes
Fermentative organisms: produce acid and gas
Oxidase negative- distinguished from non-fermenters
Grow well on MAC agar
Lactose fermenters: E. coli, Klebsiella
NLF: Salmonella, Proteus, Yersinia

Question 3

ID of enterobacteriaciae

Answer 3

E. coli resists action of bile salts. Produce acidic reaction which lowers pH and a color change results (pink). If NLF, colonies are colorless or yellow (increased pH)
E. coli is hemolytic on sheep blood agar

Question 4

Subdivision/serotyping of enterobacteriaceae

Answer 4

All species subdivided using a scheme based on O (somatic) and H (flagellar) antigens
Different pathoypes cause different types of disease.

Question 5

Enterobacterial surface antigens

Answer 5

Flagella: H antigen
Fimbriae/pili: F (K) antigen
LPS: O antigen- on outside of LPS, chain of sugars which is variable–> antigenically variable–> use serotypes to recognize antigen with generation of antibodies.
Capsule: K antigen (kelbsiella and E. coli have capsules)

Question 6

Salmonella-general characteristics

Answer 6

Non-lactose ferementers, pathogens of warm blooded-animals, commensals of cold blood animals. Reptiles and amphibs. carry organisms but may cause disease also.
Generally infection via fecal-oral route.
Salmonella are invasive (get inside epithelial, endothelial cells and macrophages)
Facultative intracellular pathogens.

Question 7

Important salmonella syndromes

Answer 7

1. enteritis resulting in diarrhea- reistricted to gut tissue- organisms generally don’t invade beyond mesenteric LN- acute diarrheal disease with inflammation of ileum or colon— enteritis is often zoonotic
2. septicemia-organisms spread through body may lead to abortion or joint infections or pneumonia- may or may not be accompanied by diarrhea–septicemia is generally NOT zoonotic
   After recovery, chronic infection and carrier state may follow- organism persists in body, transmits infection to other animals, humans and/or environment.

Question 8

Salmonella “species”

Answer 8

S. enterica; 1. subspecies >1300 serotypes isolated- infects warm blooded animals
S. enterica II, IIIa,IIIb, IV, VI and S. bongori all infect cold blood animals and account for less than 1% of clinical isolates.
NB: s. tymphimurium=S. enterica subspecies I serotype typhimurium
Distinct antigen differences for over 2500 serotypes of salmonella.

Question 9

Salmonella species

Answer 9

Only 2- s. enterica and S. bongori

S. enterica subdivided by O and H antigens into serotypes

Question 10

Serotypes of Salmonella enterica

Answer 10

O antigens identified using sera against LPS denoted as 1,2,3 etc (1-13)
Similar O types are grouped into serogroups A, B, C and D
Can produce one of two types of antigenically distinct flagella
Phase I H antigen
Phase II H antigen
Capsules present on only a few salmonella serovars

Question 11

Non-host specific (non-host adapted serovars)

Answer 11

broad host range e.g. S. typhimurium, S. enteritidis
cause enteritis, mainly of young animals
v. important cause of food poisoning in humans

Question 12

Host-specific (host-adapted) serotypes

Answer 12

often cause systemic infection, young or adult animals

i.e. s. gallinarum, s. abortusovis and S. typhi

Question 13

Host-restricted serovars

Answer 13

preferentially infect one host but can infect others
S. dublin: cattle- septicemia, enteritis, abortion, meningitis, joint ill, terminal dry gangrene- also found in pigs
S. cholerasuis: pigs- septicemia, simialr to swin fever- can also be found in cattle.
Both CAN, but rarely infect humans; infectiosn are serious. systemic–> causes focal infections in organs.

Question 14

Chronic salmonellosis

Answer 14

S. dublin, calf post-septicimia–> necrotic ear tips

peripheral vascular shutdown. tissue went gangrenous, surgically removed, dry gangrene at periphery.

Question 15

Septicemic salmonellosis

Answer 15

S. cholerasuis: acute speticemia, periphery becomes cyanotic in favor of blood supply to critical organs- get disseminated vascular coagulation
Pig with megacolon resulting from rectal stricture, S. typhimurium- eventual peritonitis–> die of overwhelming infection.

Question 16

Pathogenesis of Salmonella infection- enteritis

Answer 16

Organism ingested–> reaches gut–> invades cell through epithelium/enterocytes into submucosa or via M cell. If non-host adapted, neutrophils into lamina propria–> massive inflammatory response. Acute neutrophil infiltration results in diarrhea and enteritis.

Question 17

Pathogenesis of Salmonella infection- septicemia

Answer 17

preferentially attracts macrophages to lamina propria. infection doesn’t stop at gut. Macrophages go to mediastinal LNs. Bacteria grow in macrophages–> go around body–> liver and spleen (reticulo-endothelial system) –> septicemia.

Question 18

Salmonella attachment: fimbriae

Answer 18

each serotype can produce many different types of fimbriae/pilli. S. tymphimurium has genes for 13 different types of pili, except fimbriae aren’t well expressed in the lab so we don’t know which of the 13 is responsible for adhesion in the gut.

Question 19

Salmonella membrane ruffling

Answer 19

Adhesion via fimbriae to cell–> contacts host cell–> molecular syringe is produce–> engulfment by host. Bacteria mediates its own engulfment via membrane ruffling.

Question 20

Type III secretion systems (TTSS)

Answer 20

molecular syringes produced by TTSS. Molecular syringe injects host cell. Effector proteins bring out ruffling.

Question 21

Pathogenicity islands

Answer 21

Large chromosomal regions (30-200 kb) that encode virulence genes (toxins, adhesins, invasins, secretion systems)
Have a different G+C component in comparison to the rest of the chromosomal DNA- come from another organism through evolution
Acquired horizontally: from another organism–> have phage remnants

Question 22

Patho. islands for salmonella

Answer 22

All genes required for membrane rufflin on SPI 1
SPI 1: TTSS, invasion of epithelial cells, enteritis
SPI 2: important for survival in macs should organism go systemic- TTSS, survival in macs

17 PIs identified in salmonella, strain may not have all PIs
Expressed in different environments
SPI I expressed in gut
SPI2 expressed in tissue of reticuloendothelial system

Question 23

SPI 1: invasion of epithelial cells

Answer 23

Salmonella contacts surface via fimbriae–> SPI 1 TTSS produces molecular syringe and injects effector proteins–> membrane ruffling–> bacteria goes into phagosome–> delivered to basal lateral surface of enterocyte–> within lamina propria, attracts n’phils –> inflammation

Question 24

Salmonella enteritis- what causes destruction of epithelium?

Answer 24

Destruction of epithelium is largely d/t inflammatory response marked by massive n’phil influx elicited by salmonella. Leads to diarrhea (nb: diarrhea is very efficient for transmission and dissemination of salmonella). H2O absorption is prevented–> tissue damage may result in diarrhea with blood

Question 25

Is gut inflammation beneficial to salmonella?

Answer 25

Inflammation induced is important for clearing out normal flora. if you get rid of normal flora by ABX, animal is susceptible to salmonella. antimicrobial peptides and n’phils flush out normal flora in diarrhea, but not necessarily salmonella

Question 26

Survival strategies of salmonella species in macrophages

Answer 26

normally, fusion of phagolysosome kills organisms, however, bacteria prevents the fusion of the phagolysosome. salmonella can then survive and grow in macrophages. it remodels the vacuole (mediated by SPI 2) and allows replication within the vacuole.
SPI 2 is essential for replication in the macrophage, but there are also many other genes important for survival in the macs.

Question 27

Salmonella Zoonosis

Answer 27

CDC estimates ~70k americans have contracted salmonella from a reptile
Veggies (due to manuring with infected feces)/meat can also carry salmonella infection