Staphylococcus

Question 1

gram stain of Staphylococcus

Answer 1

Gram positive

Question 2

Size of Staphylococcus

Answer 2

~1um in diameter

Question 3

morphology of Staphylococcus

Answer 3

tend to occur in irregular clusters resembling bunch of grapes

Question 4

growth requirements of Staphylococcus

Answer 4

• highly resistant
  
  • Growth in NaCl
  • Not fastidious
    Facultative anaerobes
    grow on non enriched media

Question 5

catalase test of Staphylococcus

Answer 5

Catalase +

Question 6

Colony morphology of Staphylococcus

Answer 6

Moderately-sized white or golden colonies

Question 7

What is coagulase

Answer 7

• Conversion of fibrinogen to fibrin
• Fibrin deposition may shield staphylococci from phagocytic cells

Question 8

Major groups of Staphylococcus

Answer 8

S. aureus
S. pseudintermedius
S. hyicus

Question 9

Minor groups of Staphylococcus

Answer 9

all of which can cause infections like UTIs & ear infections in companion animals

• S. intermedius
• S. schleiferi
• S. delphini

Question 10

Define MRSA

Answer 10

• Methicillin resistant staphylococcus aureus
• has acquired resistance to methicillin & all other beta-lactam antibiotics
• resistance typically arises when the bacterium acquires the MecA gene (sometimes MecC or MecB)
• While there are a few recent derivates of beta-lactams that still be effective
  • Most penicillin-based drugs become useless against MRSA

Question 11

Major types of MRSA

Answer 11

Health-associated MRSA (HA-MRSA)
Community associated MRSA
Livestock associated MRSA (LA-MRSA)
MRSA in companion animals (dogs & cats)
MRSA in horses

Question 12

Describe Health Associated MRSA

Answer 12

• highly drug resistant
  
  • Often multi-drug resistant
  • Primarily found circulating in hospitals, nursing homes & even vet hospitals

Question 13

Virulence & infections caused by HA-MRSA

Answer 13

• Generally less virulent compared to community-associated strains but are very difficult to treat with some becoming untreatable
• frequently causes infections such as wound infections, bacteraemia & sepsis, especially P undergoing invasive procedures

Question 14

Transmission of HA-MRSA

Answer 14

• Transmission often occurs via healthcare workers who may carry the bacteria in their noses & on their hands, then pass it to P
  • Hand hygiene important in controlling spread
  • Nasal carriage: major risk factor for infection, particularly before surgery

Question 15

Describe Community associated MRSA

Answer 15

these strains are found in the general community & are typically less resistant to other classes of antimicrobials than HA-MRSA

Question 16

Virulence of CA-MRSA

Answer 16

• strains are generally highly virulent
  
  • Especially those producing the Panton-Valentine Leukocidin (PVL) toxin
  • These PVL-positive strains like ST93 cause very vicous infections, leading to cell damage, impaired phagocytosis & inflammation

Question 17

Major types of MRSA in animals

Answer 17

Livestock associated MRSA (LA-MRSA)
MRSA in companion animals (dogs & cats)
MRSA in horses

Question 18

Transmission of MRSA in animals

Answer 18

transmission can occur through direct contact with animals, handling contaminated meat or through contact in hospital settings

Question 19

Carriers of LA-MRSA in animals

Answer 19

Pigs & veal calves more likely carriers than chickens & turkeys

Question 20

Zoonosis of LA-MRSA

Answer 20

• Although LA-MRSA is less problematic for humans than community-associated strains
  
  • Can still cause infection in people who work with animals

Question 21

Development of LA-MRSA

Answer 21

• Clone originated as MSSA in humans but when humans working with pigs passed this MSSA to pigs
  • Bacteria acquired the MecA gene (likely from other bacteria due to heavy b-lactam use in the pig industry), transforming it into MRSA
  • while adapting to pigs, ST398 often lose its ability to effectively colonise humans but acquired resistance to other antimicrobials like tetracycline

Question 22

MRSA in companion animals (dogs & cats)

Answer 22

• MRSA ST22 clone: most common in human hospitals but also commonly found in dogs & cats
• ST22 strain in companion animals is also fluoroquinolone resistant
• CA MRSAST93: positive, highly virulent

Question 23

Strain of MRSA in horses

Answer 23

common strains found in horses include ST8 & ST612

Question 24

Staphylococcus as pathogens

Answer 24

• occurs as commensals on skin & mucous membranes
  
  • may acts as opportunistic pathogens causing pyogenic infections

Question 25

Describe S. aureus

Answer 25

- variety of diseases in a wide range of animals, from livestock to elephants & monkeys - In dairy cows, predominant cause of mastitis - Can be acute or chronic & is a serious infection - Chronic infections can also be seen in birds, rodents & guinea pigs - Particularly causing bumble foot or isolated pododermatitis

Question 26

S. pseudintermedius infected animals

Answer 26

predominantly seen in dogs & occasionally in cats where it is a primary pathogen

Question 27

S. pseudintermedius cause of what diseases

Answer 27

major cause of skin diseases such as surface pyodermas, superficial pyodermas & deep pyodermas Deep pyodermas can be particularly challenging to treat Can also colonise & cause ear infections & otitis

Question 28

Cause of greasy pig disease

Answer 28

S. hyicus

Question 29

greasy pig disease describe

Answer 29

known as exudative dermatitis which affects pigs aged 5-60 days old

Question 30

Onset of greasy pig disease

Answer 30

is sudden onset & can lead to significant production losses & high mortality rates, ranging from 5-90%

Question 31

When will infection of S. hyicus occur

Answer 31

- notable that S. hyicus cannot penetrate intact skin - Infection typically occurs when the skin is compromised

Question 32

Byproduct of S. hyicus infection

Answer 32

Produces an exudative toxin that can make the skin appear mushy

Question 33

Infections caused by S. aureus in humans

Answer 33

Pyoderma Septicaemia Osteomyelitis Pneumonia Wounds & surgical site infections Nosocomial infections Food poisoning Toxic shock syndrome

Question 34

Describe pyoderma caused by S. aureus

Answer 34

& skin infections: common manifestations with S. aureus causing pyogenic (pus-forming) infections & a variety of skin diseases

Question 35

Describe Septicaemia caused by S. aureus

Answer 35

1. Blood poisoning 2. serious bloodstream infection where bacteria enter & spread throughout the body 3. Trigger sepsis

Question 36

Describe Osteomyelitis caused by S. aureus

Answer 36

1. Bone infection 2. can be acute or chronic

Question 37

Pneumonia

Answer 37

lung infection

Question 38

Describe Wounds & surgical site infections caused by S. aureus

Answer 38

1. S. aureus commonly causes infections in hospitals, particularly wound & surgical site infections 2. Risk of S. aureus infection, including MRSA, is significantly increased in individuals undergoing surgery, especially if they are already colonised with the bacteria

Question 39

Importance of MRSA ST398

Answer 39

- major livestock-associated MRSA clone - evolved from MSSA in humans - MRSA ST398 while adapting to pigs, often loses a prophage (SA3) which is a factor that enhances S. aureus to colonise human epithelium - its ability to colonise humans effectively will be reduced

Question 40

Main diseases infections caused by S. pseudintermedius

Answer 40

Surface pyodermas Superficial pyodermas (e.g. folliculitis) Deep pyoderma

Question 41

MRSP =

Answer 41

Methicillin-Resistant Staphylococcus pseudintermedius (MRSP)

Question 42

clinical implications of MRSP infections in dogs.

Answer 42

Hard to treat - Dogs that have prior antimicrobial treatments are 3x more likely yo have MRSP from surgical site infections - Makes dealing with MRSP cases very challenging if there is hx of abx use

Question 43

Define S. pseudintermedius

Answer 43

Commensal organism found on most mammals, colonising areas like skin, glands, nares & perineum & typically opportunistic

Question 44

Define MRSP

Answer 44

emerges when MSSP(methicillin susceptible S. pseudintermedius) acquires the MecA gene gene typically carried on a gene cassette (SEC Mec) that jumps into the bacterium’s genome

Question 45

List major staphylococcus spp. that cause mastitis in cow

Answer 45

- Staphs ( & Strep agalactiae): most common cause - S. aureus - Peracute gangrenous mastitis - Acute mastitis - Chronic(subclinical) mastitis - S. epidermis - occasionally chronic mastitis - more often a contaminant from poor sampling

Question 46

list major staphylococcus spp. that cause bumble foot in birds

Answer 46

- S. aureus - ulcerative pododermatitis (bumble foot) in guinea pigs, rat & birds