Lecture 5: Gram positive bacteria -Staphylococci

Question 1

Staphylococci

• found where?
• 3 major pathogenic species

Answer 1

• Lives in nasopharynx and skin of 50% people
• 3 major pathogenic species
  1) Staphylococcus aureus
  2) Staphylococcus epidermis
  3) Staphylococcus saprophyticus

Question 2

Identifying Staphylococci

• Gram (+) or Gram (-)?
• Lines or Clusters
• Catalase (+) or (-)
• Culture
• Coagulase

Answer 2

-Gram (+)
-Clusters
-Catalase (+)
-Culture: S.aureus is B-hemolytic
S. aureus -golden pigment on sheep blood agar
-Coagulase: S.aureus is (+) activates pro-thrombin

Question 3

What do you see on a positive catalase test?

Answer 3

Bubbles, indicating H2O2 being broken down into O2 and H2O

Question 4

Staphylococcus aureus

-characteristics

Answer 4

• a microcapsule surrounds its huge peptidoglycan cell wall, which in turn surrounds a cell membrane containing penicillin binding proteins called transpeptidase
• numerous powerful defensive and offensive protein weapons protrude out of the microcapsule or excreted from the cytoplasm

Question 5

Proteins that disable the immune defenses (6x)

Answer 5

PROTEIN A -has sites that bind the Fc portion of IgG
-protects the bacteria from opsonization and phagocytosis
COAGULASE -can lead to fibrin formation around the bacteria, protecting from phagocytosis
HEMOLYSINS -alpha, beta, gamma, and delta, destroy RBCs, neutrophils, macrophages, and platelets
LEUKOCIDINS -destroy leukocytes (WBCs)
PENICILLINASE -secreted form of beta-lactamase that disrupts the beta-lactam ring of penicillin
NOVEL PENICILLIN BINDING PROTEIN -also called tanspeptidase, necessary for peptidoglycan formation *some strains have resistant novel PBP

Question 6

Proteins that tunnel through tissue (4x)

Answer 6

HYALURONIDASE -breaks down proteoglycans in connective tissue
STAPHYLOKINASE -lyses formed fibrin clots (similar to streptokinase)
LIPASE -degrades fats and oils that often accumulate on the surface of our body
-facilitates S.aureus colonization of sebaceous glands
PROTEASE -destroys tissue proteins

Question 7

Exotoxins (3x)

Answer 7

EXFOLIATIN
-a diffusible exotoxin that causes skin to slough off (scalded skin syndrome)
ENTEROTOXINS
-exotoxins that cause food poisoning, resulting in vomiting and diarrhea
TOXIC SHOCK SYNDROME TOXIN (TSST-1)
-analogous to pyrogenic toxin by streptococci, but is far more deadly

Question 8

S. Aureus

• Diseases
  - >Exotoxin release

Answer 8

1) Gastroenteritis
2) Toxic shock syndrome
3) Scalded skin syndrome

Question 9

S. Aureus

• Diseases
  - >Direct organ invasion

Answer 9

1) Pneumonia
2) Meningitis
3) Osteomyelitis
4) Acute bacterial endocarditis
5) Septic arthritis
6) Skin infections
7) Bacteremia/sepsis
8) Urinary tract infection

Question 10

Gatroenteritis

Answer 10

S.aureus can grow in food and produce exotoxin. Ingestion of contaminated food causes peristalsis of intestine, nausea, vomiting, diarrhea, abdominal pain lasting 12-24 hrs

Question 11

Toxic Shock Syndrome

-S.aureus

Answer 11

manifested in different sites

• tampons, infected sutures in surgical wounds, cutaneous and subcutaneous infections and infections following childbirth or abortion
• symptoms are like a hybrid between food poisoning (enterotoxins) and streptococcal pyrogenic toxin that produces scarlet fever. Desquamation of palms and soles, multi-organ system failure

Question 12

Staphylococcal Scalded Skin Syndrome

Answer 12

pathogenesis similar to TSS
-S.aureus strain that produces exfoliative toxin A and B establishes a localized infection and releases a diffusible toxin exerting distant effects

Question 13

Pneumonia

-S.aureus

Answer 13

S. aureus is a rare but severe cuase of community acquired pneumonia
-usually follows a viral influenza (flu) upper respiratory illness

Question 14

Meningitis, Cerebritis, Brain Abscess

Answer 14

patients present with high fever, stiff neck, headache, coma, and focal neurological signs

Question 15

Osteomyelitis

Answer 15

bone infection occurring in boys under 12

Question 16

Acute Endocarditis

-S. aureus

Answer 16

violent destructive infection of heart valves with sudden onset of high fever (103-105F), chills and myalgias
-endocarditis caused by S.viridans and group D streptococci has a more gradual onset

Question 17

Septic Arthritis

Answer 17

S. aureus invades the synovial membrane resulting in a closed infection of joint cavity

• patients complain of acute painful red swollen joint with decreased range of motion
• therapy requires drainage of joint and antimicrobial therapy
• most common in pediatrics and 50+

Question 18

Skin Infections (5x)

Answer 18

Minor skin infections are caused by either Streptococcus pyogenes or Staphylococcus aureus

(1) Impetigo - usually occurs on the face. Small vesicles lead to pustules, which crust over to become honey colored, wet, and flaky
(2) Cellulitis - deeper infection of the cells. Tissue becomes hot, red, shiny, and swollen
(3) Local Abscesses, Furuncles & Carbuncles - infection of a hair follicle produces an abscess that can penetrate deep into subcutaneous tissue to become a furuncle. These bore through to produce painful lesions communicating under the skin called carbuncles
(4) Wound infections - any skin wound can be infected with S.aureus resulting in an abscess, cellulitis, or both
(5) Blood and catheter infections - S.aureus can migrate from the skin and colonize central venous catheters resulting in bacteremia, sepsis, septic shock, and endocarditis

Question 19

Methicillin-Resistant Staphylococcus aureus (MRSA)

Answer 19

• most staphylococci secrete penicillinase and are resistant to penicillin
• methicillin, nafcillin, and other penicillinase resistant penicillins kill most strains of S.aureus
• *MRSA is a strain of S.aureus that has acquired multi drug resistance, even against methicillin and nafcillin
• resistance is mediated by an acquired chromosomal DNA segment (mecA) encoding a new penicillin binding protein 2A

Question 20

What is used to treat MRSA infections?

Answer 20

Vancomycin

Question 21

What is a common route of the spread of MRSA?

Answer 21

Nasal carriage

Question 22

Staphylococcus epidermis

• found where?
• Coagulase (+) or (-)
• causes what?

Answer 22

• Normal bacterial flora widely found on the body
• Coagulase (-)
• compromised hospital patients with urine catheters and intravenous lines can become infected
• frequent skin contaminant of blood cultures
• causes infections of prosthetic devices such as joints, heart valves, and peritoneal dialysis catheters by forming biofilms

Question 23

Staphylococcus saprophyticus

• causes what?
• classified as?
• acquired where?
• Coagulase (+) or (-)
• treatment?

Answer 23

-Leading cause (second only to E.coli) of UTI infections in sexually active young women
-facultative anaerobe
-commonly (not hospital) acquired
-Coagulase (-)
TX: penicillin