Staphylococcus Flashcards
1
Q
What are the general characteristics of Staphylococcus spp.?
A
- Gram +
- Cocci in clusters
- Facultative Anaerobes
- Grow in HIGH Salt concentrations (7.5 - 10%)
- Catalase Positive (differentiate from streptococcus)
2
Q
What disease does S. aureus cause?
A
- Mastitis in cattle, sheep, and goats
3
Q
What disease does S. pseudintermedius cause?
A
- Pyoderma, Otitis externa, endometritis, cystitis in Dogs
4
Q
What disease does S. hylcus cause?
A
- Exudative or Exfoliative dermatitis “Greasy pig disease” in Pigs
- Skin infections in other animals
5
Q
What are the diagnostic characteristics of Staphylococcus aureus?
A
- Double Zone hemolysis
- Ferments Mannitol
- Turns Mannitol Salt Agar Yellow
6
Q
Where can S. aureus be found?
A
- Commensals on the skin and mucous membranes
- Nostrils are a major site
7
Q
What are the Virulence Factors of S. aureus?
A
- Divided in 3 categories:
- Cell-Associated Components
- Exoenzymes
- Exotoxins
8
Q
What are the Cell-Associated Components of Virulence Factors?
A
- Surface Proteins:
- Protein A
- Adhesins
- Capsular polysaccharides
- peptidoglycan and teichoic acid
9
Q
What does Protein A do?
A
- Virulence Factor
- Binds to Fc region of IgG
- disrupts opsonization and phagocytosis
10
Q
What do Adhesins do?
A
- Virulence Factor
- Surface proteins that promote attachment to the host proteins
- Fibronectin-binding protein
- Collagen-Binding protein
11
Q
What are capsular polysaccharides?
A
- Serologically distinct capsule types
- Interfere with host defense mechanisms by inhibiting attachment of antibodies, induce the release of cytokines
- Mediate cell binding to epithelial and endothelial cells
12
Q
What does peptidoglycan and teichoic acid do?
A
stimulate cytokine production
13
Q
What are the Exoenzymes
A
- Coagulase
- Lipase
- Hyaluronidase
- Proteases
14
Q
What does Coagulase do?
A
- Converts fibrinogen to fibrin
15
Q
What does Lipase do?
A
- Hydrolyzes lipid molecules that the host produces in response to infections
16
Q
What does Hyaluronidase do?
A
- Digests hyaluronic acid present in connective tissue and promotes spread of the infection
17
Q
What do Proteases do?
A
- Breakdown antibodies, antimicrobial peptides, tissue proteins
18
Q
What do Proteases do?
A
- Breakdown antibodies, antimicrobial peptides, tissue proteins
19
Q
What are Exotoxins in staphylococcus spp.
A
- Toxic Shock Syndrome Toxin
- Enterotoxins
- Exfoliative or Epidermolytic toxins
- Hemolysins
20
Q
What is toxic shock syndrome toxin?
A
- Act as super-antigens
- rarely seen in infections
21
Q
What are Enterotoxins?
A
- Foodborne infections in humans
- Act as a super-antigen
- produced in contaminated food
- Resistant to proteases and heat stable, hence not inactivated by cooking
- Toxin is ingested with food d in the stomach the toxin stimulates vagus nerve endings to induce vomiting and abdominal pain
22
Q
What is staphylococcal Food Poisoning?
A
- Gastroenteritis: Nausea, vomiting, stomach cramps, diarrhea
- Salty food like ham
- Contaminated milk and cheeses
- Contact with food workers who carry the bacteria
- Fast acting toxins can cause illness in as little as 30 min
- Symptoms usually develop within 1-6 hours after eating contaminated food
- Illness usually mild, recovery in 1-3 days
23
Q
What is staphylococcal Food Poisoning?
A
- Gastroenteritis: Nausea, vomiting, stomach cramps, diarrhea
- Salty food like ham
- Contaminated milk and cheeses
- Contact with food workers who carry the bacteria
- Fast acting toxins can cause illness in as little as 30 min
- Symptoms usually develop within 1-6 hours after eating contaminated food
- Illness usually mild, recovery in 1-3 days
24
Q
What is staphylococcal Food Poisoning?
A
- Gastroenteritis: Nausea, vomiting, stomach cramps, diarrhea
- Salty food like ham
- Contaminated milk and cheeses
- Contact with food workers who carry the bacteria
- Fast acting toxins can cause illness in as little as 30 min
- Symptoms usually develop within 1-6 hours after eating contaminated food
- Illness usually mild, recovery in 1-3 days
25
What are Exfoliative or Epidermolytic toxins?
* ETA and ETB
* Cause skin infections
* Exfoliative dermatitis in pigs: *S. hyicus*
* Pyoderma in dogs: *S. pseudintermedius*
26
What are Exfoliative or Epidermolytic toxins?
* ETA and ETB
* Cause skin infections
* Exfoliative dermatitis in pigs: *S. hyicus*
* Pyoderma in dogs: *S. pseudintermedius*
27
What are Exfoliative or Epidermolytic toxins?
* ETA and ETB
* Cause skin infections
* Exfoliative dermatitis in pigs: *S. hyicus*
* Pyoderma in dogs: *S. pseudintermedius*
28
What are Hemolysins?
* Protein toxins that lyse RBCs
* Produced by *S. aureus, S. pseudintermedius, **NOT** a. hyicus*
* *S. aureus* produced 4 different hemolysins:
* **α, β, γ, δ,**
* Differ antigenically, biochemically, and in their effects on the RBC of animals species
29
What are Alpha Hemolysins
* **Membrane-damaging (pore-forming)** toxin
* Produces a zone of complete hemolysis
* Human platelets and monocytes are also susceptible to the toxin
* Release of **cytokines triggering production of inflammatory mediators**
* Responsible for the symptom of septic shock
30
What are Beta Hemolysins?
* a sphingomyelinase, damages membranes ring in sphingomyelin lipid
* Incomplete hemolysis of sheep/cattle erythrocytes
* AKA “Hot-cold hemolysin”
* Pathogenic role is not known
31
What is Gamma hemolysin?
* AKA “Leukotoxin” “Leukocidin” “Panton-Valentine Leucocidin”
* Not al *S. aureus* strains produce
* **pore-forming** toxin
* gene located on a prophage
32
What is the pathogenesis and pathogenic mechanism of staphylococcus spp?
* Cause **pyogenic** **or suppurative** lesions
* Predisposing factors: skin injury or immune suppression
* Virulence factors promote:
* **Tissue colonization*****:*** Protein A and adhesins
* **Immune evasion**: Capsular polysaccharide, teichoic acid, protein A, catalase, and coagulase interfere with opsonization ang phagocytosis
* **Spread:** hyaluronidase, lipase, proteases
* **Tissue destruction:** exotoxins
* Minor local skin infections to life-threatening septicemic conditions
33
What are the general characteristics of Staphylococcus spp.?
* Gram +
* Cocci in clusters
* Facultative Anaerobes
* Grow in **HIGH Salt** concentrations (7.5 - 10%)
* Catalase Positive (differentiate from streptococcus)
34
What diseases does staphylococcus cause
* Mastitis in Dairy Cows
* Dermatitis and Joint infections in chickens
* Exudative dermatitis in pigs
* Pyoderma in Dogs
35
How does staphylococcus cause Mastitis?
* The Route of infection is via the teat
* Organisms travel through the teat canal to enter the secretory mammary tissue and attach to ductular and alveolar epithelial cells
* Milk is a good medium for multiplication of staphylococci and production of toxins cause infiltration of the mammary gland by neutrophils
* Aggregation of neutrophils cause clots in the milk and intravascular edema
* Neutrophils obstruct the lobules, which begin to involute
* Accumulation of fibroblast, macrophages, and leukocytes results in the expansion of the intravascular connective tissue
* Infection can spread from Cow to Cow with contaminated hands/milking machines or through feces
* Ranges in severity from mild to gangrenous
36
What percentage of mastitic infections are due to staphylococcus spp?
25-30%
37
How do you diagnose Bovine Mastitis?
* Isolation of coagulase-positive or -negative staphylococci from bulk tank milk samples
* Colonies on blood agar with double zone hemolysis
* Confirmed by additional biochemical tests
* Herds with subclinical mastitis are diagnosed based on somatic cell count (SCC) or total bacterial count (BCC) in milk samples
* Increase in somatic cells is because of increased leukocytes
37
How do you diagnose Bovine Mastitis?
* Isolation of coagulase-positive or -negative staphylococci from bulk tank milk samples
* Colonies on blood agar with double zone hemolysis
* Confirmed by additional biochemical tests
* Herds with subclinical mastitis are diagnosed based on somatic cell count (SCC) or total bacterial count (BCC) in milk samples
* Increase in somatic cells is because of increased leukocytes
38
What is the treatment for Bovine Mastitis?
* Intra-mammary administration of antibiotics
* B-lactamase-resistant antibiotics, such as Ceftiofur, Cephalosporin (2nd or 3rd gen), or Cloxacillin
* Systemic antibiotics are employed to achieve effective concentrations of antibiotics in the mammary tissue
* No vaccines are available
39
What is Dry Cow Therapy?
Administration of antibiotics at the beginning of the dry period, to treat or prevent staphylococcus mastitis
40
What diseases does Staphylococcus produce in Poultry
* Dermatitis, osteomyelitis, arthritis, and synovitis, and occasionally bacteremia or septicemia
* “Bumblefoot”
* Lameness has a significant economic impact
41
What does *S. hyicus* cause in pigs?
* Exudative Dermatitis
* by exfoliative toxin
* Predisposing factor: breach in epidermis
42
How does Exudative Dermatitis progress?
* Initially. yellowish brown crusts on the face and ears
* Severe cases:
* Skin feels greasy and moist, becomes covered in dark brown coating which entraps dirt
* Crusty lesions heal or progress to increased exudation with crusts becoming more confluent, blackened, and hard with cracks and furrows.
* Death from dehydration duet to electrolyte and fluid loss
43
How is Exudative Dermatitis diagnosed?
* Characteristic skin lesions
* Bacterial isolation
44
How is Exudative Dermatitis treated?
* Antibiotics in early stages
* Ceftiofur, enrofloxacin, lincomycin, or sulfadimethoxizole/trimethoprin
* Severely affected animals do not respond
* *S. hyicus* strains develop resistance, susceptibility testing is recommended
* Other treatments include spraying pigs with disinfectants (chlorhexidine, iodine, etc) or antibiotics (novobiocin)
45
What is Canine Pyoderma?
* Caused by *S. pseudintermedius*
* **Dermatitis and folliculitis**, rarely systemic
* Lesions start as papular (small reddened) eruptions progressing to pustules and small intradermal abscesses
* Deep skin lesions, “furuncles” (large hemorrhagic bullae), may rupture to become fistulous tracts with pus
46
How is Canine Pyoderma treated?
* Beta-lactams
* Antimicrobial susceptibility testing
* Amoxicillin plus clavulanic acid
* Oxacillin
* Erythromycin
* Cephalosporins
47
What is Methicillin Resistant *S. aureus* (MRSA)?
* *S. aureus* resistant to Beta-lactam antibiotics
* Penicillins, cephalosporins, and carbapenems
* No more virulent than other strains
* Resistance makes it more difficult to treat with standard antibiotics, therefore more serious
48
How is *S. aureus* resistant to methicillin?
* Resistance is conferred by a gene called, *mecA*, which encodes for a variant of penicillin-binding protein (PBP), called PBP2a
* Acquisition of *mecA* confers resistance to all B-lactam antibiotics in addition to methicillin
49
What contributes to MRSA infections?
* Contributing factors: Close skin-to-skin contact, openings in the skin such as cuts or abrasions, contaminated items and surfaces, crowded living conditions, and poor hygiene.
* Hospital-Acquired (HA-MRSA) infections: Wound or surgical sites
* Community-Associated (CA-MRSA) infections: Athletic facilities, Dorms, Military barracks, Correctional facilities, Day care centers
50
Is there MRSA in animals?
* Reported in all animals
* particularly cattle and pigs
* Zoonotic transfer from animal to human or humans to animals (Reverse Zoonosis)
* Livestock-Associated (LA-MRSA) infections
