Staphylococci and Related Gram Positive Cocci 9/2/15

Question 1

What are the key characteristics of Staphylococci?

Answer 1

-Gram + cocci -Grape-like clusters ***Catalase positive -Fac anaerobes

Question 2

What are some important species of Staphylococci?

Answer 2

-S. aureus -S. epidermidis -S. lugdunensis -S. saprophyticus “Achy epidermis, loose skin”

Question 3

Where are S. aureus typically found?

Answer 3

-Skin and mucous membranes (i.e. anterior nares)

Question 4

What factors predispose to serious Staphylococcus aureus infection?

Answer 4

1. Defects in leukocyte chemotaxis (Down syndrome, DM, or RA)
2. Defects in opsonization
3. Defects in intracellular killing (leukemia)
4. Skin injury (burns, sports)
5. Presence of foreign bodies (sutures, IV)
6. Infection with other agents (influenza)
7. Chronic underlying disease (malignancy)
8. Use of antibiotics to which the infecting S. aureus is not susceptible

Question 5

What are the usual sites of infection for S. aureus?

Answer 5

Skin

Nose

Throat

GI tract

Urethra

Vagina

Question 6

What are some diseases caused by Staphylococcus aureus?

Answer 6

1. Pyoderma: pyogenic skin disease (the baby pic)
2. Furuncle (boil): infected hair follicle, filled with pus and dead tissue, painful
3. Carbuncle: Abscess larger than a boil, openings draining pus onto the skin, common on nape of neck
4. Toxin-mediated infections: Scalded skin syndrome (the babies), TSS, Food poisoning
5. Disseminated infections: infection metastasis resulting in: sepsis, pneumonia, osteomyelitis, endocarditis

Question 7

What are some of the major virulence factors of Staph aureus?

Answer 7

• Components interfering with phagocytosis: Capsules, protein A, PVL, COAGULASE +
• Hemolysins: alpha and beta mostly (others exist)
• Toxins
• Enzymes
• Superantigens: pyrogenicity, superantigenicity, enhance effects of endotoxin, induce polyclonal T cell proliferation

Question 8

What are some effects of toxins produced by S aureus

Answer 8

• Exfoliatins/epidermolytic toxins: Dissolves muco-polysaccharide matrix of epidermis (scalded skin syndrome)
• Enterotoxins: heat-stable, responsible for Staph food poisoning (quick onset, quick recovery)

Question 9

What are some examples of pyrogenic toxin superantigens?

Answer 9

• TSST-1 (S. aureus mediated)
• SPE -Streptococcal superantigens

Question 10

What are the coagulase positive Staphylococci species?

Answer 10

STAPH AUREUS = pathogenic

Question 11

What species of Staphylococci can be detected via Latex Agglutination?

Answer 11

A coagulase test of Staph aureus

Question 12

Is Staphylococcus epidermidis coagulase positive or negative?

Answer 12

Negative

Question 13

What types of infections are associated with Staph epidermidis?

Answer 13

• Infections of indwelling devices
• Infections involving biofilms

Question 14

What Staphylococcus species is responsible for acute UTI in young women?

Answer 14

Staph saprophyticus

Question 15

How can one ID Staph saprophyticus?

Answer 15

-Negative coagulase

-Resistance to Novobiocin

Question 16

Which bacterial strains would be resistant and which would be susceptible to a Novobiocin disc?

Answer 16

R = S. saprophyticus

S = Other Staph and Micrococcus

Question 17

Which bacterial strains are resistant and which are susceptible to Furozolidone?

Answer 17

R = Micrococcus S= Staphylococcus

Question 18

Describe characteristics of Staphylococcus lugdunensis “The Lug Bug”.

Answer 18

• Coagulase negative
• Colonizes human inguinal area

-ONLY species that is both PYR and Ornithine positive

-Causes same infections as Staph aureus: meningitis, abscesses, oral infections, osteomyelitis, etc.

Question 19

List six settings that have been associated with community-acquired MRSA outbreaks

Answer 19

• Sports participants: MPSM
• Correctional facilities
• Military recruits
• Daycare and other institutions
• Newborn nurseries and other healthcare settings
• MSM

Question 20

List 5 severe syndromes in which MRSA should be considered in the differential diagnosis.

Answer 20

• Severe diseases compatible with S. aureus infection:
  1. Sepsis
  2. Osteomyelitis
  3. Necrotizing pneumonia
  4. Septic arthritis
  5. Necrotizing fasciitis

Question 21

Describe effective infection prevention measures to control MRSA infections in the hospital.

Answer 21

• Careful hand hygiene for all pt interactions
• Standard precautions: gowns, gloves, masks
• Effective cleaning of pt environment
• Clean shared/dedicated equipment: Stets, remotes, BP cuffs, etc.
• Appropriate use of antibiotics
• Active surveillance