Staphylococcus aureus

Question 1

what are the bacterial cell characteristics of Sa?

Answer 1

• gram positive cocci
• either exist as single cells or grape-like clusters
• nonmotile, noncapsular
• non-spore forming, sensitive to heat treatment
• facultative anaerobes but grow rapidly under aerobic conditions
• mesophiles and can grow between 7-48C, and rapidly between 20-37C
• can grow at relatively low Aw (0.86), low pH (4.8) and under high salt and sugar conditions
• can grow under several adverse conditions, but are poor competitors against other organisms, therefore they do very well when adverse environments give them a competitive advantage

Question 2

foodborne illness is usually an …

Answer 2

intoxication

Question 3

what do strains of Sa that cause foodborne illness carry?

Answer 3

an enterotoxin

Question 4

how is Sa characterized based off of sequence type or allelic profile?

Answer 4

multilocus sequencing typing, based on the sequences of 7 housekeeping genes found in all strains of Sa

Question 5

how are groups of sequence types defined if groups share at least 5 of 7 alleles?

Answer 5

defined as a clonal complex (CC)

Question 6

how is Sa distributed among the hosts they are able to infect?

Answer 6

distributed ubiquitously among mammalian, reptile, and avian hosts

certain lineages are specific to certain hosts

Question 7

what clonal complexes are bovine infections commonly caused by?

Answer 7

CC20, CC188, CC8, CC97, and CC151

Question 8

what are the predominant CC’s in human colonization and infection?

Answer 8

CC1, CC5, CC8, CC30, and CC45
most strains capable of producing the enterotoxin are from the human CCs

Question 9

what is the Sa accessory genome made up of?

Answer 9

several mobile genetic elements which can be transferred horizontally (20% of the genome)

Question 10

how is horizontal gene transfer inhibited in Sa lineages?

Answer 10

due to a very advanced restriction modification system in Sa, preventing HGT between different clonal complexes

Question 11

how many prophage genomes do Sa genomes carry?

Answer 11

1-4, phage genomes have enterotoxins

Question 12

what genetic elements are many of the enterotoxins located on?

Answer 12

mobile genetic elements

Question 13

definition of enterotoxin:

Answer 13

a toxin that acts on the GI tract

Question 14

definition of endotoxin:

Answer 14

a toxin that is structurally associated with the bacterial cell (LPS)

Question 15

definition of exotoxin:

Answer 15

a toxin that is usually secreted into the extracellular fluid but can be intracellular or injected directly into eukaryotic cells

Question 16

definition of exfoliative toxins:

Answer 16

dermolytic exotoxins produced exclusively by Sa that cause the symptoms of impetigo or scalded skin syndrome

Question 17

all Sa enterotoxins are also ….

Answer 17

exotoxins

Question 18

how are all Sa enterotoxins similar?

Answer 18

all have a high degree of homology, and all cause gastroenteritis

Question 19

what growth phase are enterotoxins primarily made during?

Answer 19

exponential growth phase

Question 20

how can enterotoxin production be inhibited?

Answer 20

by the presence of glucose

Question 21

what other function can enterotoxins of Sa be involved in?

Answer 21

quorum sensing

Question 22

how does Sa compare to the rest of the non-spore forming pathogens?

Answer 22

it is one of the most resistant to environmental stress. it is also very osmotolerant which is problematic because there are few bacteria that can compete with it in these environments

Question 23

staphylococcal enterotoxins are primarily produced during …

Answer 23

the late exponential or early stationary phase

Question 24

what system are some SE’s regulated by?

Answer 24

the agr system that is a density-sensing sytem in Sa

Question 25

what are the proteins that form a quorum-sensing system

Answer 25

AgrA - AgrD

Question 26

what is the auto-inducing peptide?

Answer 26

peptide produced to be recognized by quorum-sensing system, specifically AgrC to initiate signal transduction pathways

Question 27

what happens once AgrC recognizes AIP?

Answer 27

AgrC then phosphorylates AgrA and activate the expression of RNAIII

Question 28

how are SEB and SEC regulated?

Answer 28

regulation via agr can be translational or transcriptional - SEB and SEC are regulated at the transcriptional level. Repressor of Toxin (ROT) negatively regulates transcription of SEB by binding to the promoter region (RNAIII binds to ROT and causes degradation thus up-regulating SEB)

Question 29

how does SarA up-regulate SEB?

Answer 29

binds to several promoters including agr and upregulates RNAIII

Question 30

what is SEA linked to?

Answer 30

the life cycle of temperate phage: - has two promoters, one immediately upstream of the sea gene and the other at the phage-related latent promoter - during stress induced phage induction, both promoters are activated resulting in lots of production of SEA

Question 31

what is the main environmental source of Sa?

Answer 31

people - we have it on our skin, the interior of the nose is the main site, it spreads by direct contact, skin fragments, and respiratory droplets - also found in erupted acne - able to invade our cells and live intracellularly

Question 32

what environments are Sa able to survive in?

Answer 32

a variety of extreme environments and is isolated from air, dust, sewage, and water. can also acquire resistance to heavy metals and antibiotics

Question 33

how does Sa affect animals?

Answer 33

- often a cause of bovine mastitis, and a variety of infections in agricultural animals

Question 34

what is the impact on farms when a cow has bovine mastitis?

Answer 34

when milked, the bacteria can contaminate milk and dairy products. this cow can also contaminate other batches of milk. if the toxins resulting from this contamination can grow, the toxins may survive pasteurization

Question 35

in cases of food contamination with Sa, where is it mostly traced back to?

Answer 35

humans, during food preparation

Question 36

what are the contributing factors of Sa food-contamination?

Answer 36

- inadequate refrigeration - preparing foods too far in advance - poor personal hygiene - inadequate cooking - prolonged use of warming plates (i.e. buffet)

Question 37

Characteristics of Sa disease:

Answer 37

- very quick onset (30 min), mean incubation is 4.4 hours, 10 hrs is maximum time to onset - self-limiting and recovery in 24-48 hours - most cases not reported - outbreaks are seasonal, many of the cases/outreaks occur during the summer - there is never any fever - almost everyone vomits, other symptoms can have nausea, diarrhea, and abdominal pain - death is very rare - purified toxin is considered a bioterrorism agent

Question 38

what is methicillin-resistant Sa (MRSA)? where is it found?

Answer 38

- strains that carry the mecA gene - causative agent of soft tissue and skin infections, along with necrotizing fasciitis - found in cows, pigs, and 0.4-12% of retail meat (carrying the enterotoxin gene)

Question 39

prevention of Sa?

Answer 39

- hand washing, glove wearing, and avoidance of hiring food prep workers with active skin infections - adequate refrigeration, or continued heating of prepared food. re-heating is not helpful - preservatives could be used to kill or arrest growth of the organism