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STAPHYLOCOCCUS Flashcards

Gram positive bacterias

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1
Q

What does the term “aureus” mean in relation to S. aureusmean

A

The term “aureus” means “golden.” It refers to the characteristic golden-yellow color of the colonies produced by S. aureus when grown on agar plates.

the colonies of S. aureus are golden in colour

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2
Q

What is the significance of Staphylococcus spp. in humans?

A

Staphylococcus spp. are part of the normal microbial community (flora) that naturally reside in and on the human body. They can be found on the skin, in the nasal passages, and other mucous membranes.

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3
Q

How many recognized species of staphylococci exist?

A

There are currently over 40 recognized species of staphylococci, each with its unique characteristics

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4
Q

Which staphylococci are commonly associated with human infections?

A
  1. S. aureus (Staphylococcus aureus): Known for causing a wide range of infections, from skin infections to more severe conditions like pneumonia and bloodstream infections.
  2. S. epidermidis (Staphylococcus epidermidis): Often found on the skin and mucous membranes, it is less virulent but can cause infections in immunocompromised individuals or those with medical devices (e.g., catheters).
  3. S. saprophyticus (Staphylococcus saprophyticus): Primarily associated with urinary tract infections (UTIs) in young sexually active females.
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5
Q

What color are the colonies of S. aureus?

A

The colonies of S. aureus are often golden in color, which is why the species is named “aureus.”

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6
Q

How does the presence of S. aureus impact human health

A

S. aureus can cause various infections, ranging from mild skin conditions (like boils) to severe systemic infections (such as sepsis).

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7
Q

Why is S. epidermidis less virulent compared to S. aureus?

A

S. epidermidis lacks certain virulence factors that make S. aureus more aggressive. It is typically considered a commensal (harmless) bacterium unless it enters sterile sites (e.g., during surgery or with medical implants).

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8
Q

base on the classification of staphylococci, describe them based on coagulase production

A
  1. Coagulase positive: Eg- S. aureus
  2. Coagulase negative: Eg- S. epidermidis, S. saprophyticus
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9
Q

What is the significance of coagulase production in Staphylococcus?

A

Coagulase production distinguishes Staphylococcus aureus (coagulase positive) from other species (coagulase negative)

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10
Q

Which bacteria are examples of coagulase-negative staphylococci?

A

Examples include Staphylococcus epidermidis and Staphylococcus saprophyticus.

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11
Q

What is the common pathogen associated with human infections

A

Staphylococcus aureus is a common pathogen causing various infections

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12
Q

what shapes do staphylococcusmosly mostly occurs with

A

like a bunch of grape formation, due to the cells dividing into two planes

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13
Q

what are characteristics of staphylococcus

A
  1. Non-motile
  2. Non sporing
  3. Facultative anaerobes
  4. Oxidase Negative
  5. Resistant to dry conditions and high salt concentrations
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14
Q

What does it mean for S. aureus to be a commensal?

A

Being a commensal means that S. aureus naturally resides in or on the human body without causing harm.

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15
Q

What percentage of the population carries S. aureus in their nose?

A

Approximately 20-30% of the population carries S. aureus in their nasal passages.

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16
Q

What are the carrier rates of S. aureus among hospital patients and staff?

A

Carrier rates can be as high as 80% among hospital patients and staff.

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17
Q

Where else can S. aureus be carried as a commensal?

A

S. aureus can also be carried on the skin as a commensal in 10-15% of the population.

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18
Q

Why is the skin of hospital personnel and patients a common site for S. aureus colonization?

A

Hospital personnel and patients are frequently exposed to S. aureus in healthcare settings, leading to colonization on their skin

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19
Q

What is the significance of cross-infection in hospitals?

A

Cross-infection refers to the transmission of infections from one person to another within a hospital. It emphasizes the importance of proper hygiene practices, including thorough hand washing.

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20
Q

What are cytolytic toxins, and how do they function?

A

Cytolytic toxins act on host cell membranes and mediate cell destruction. They can cause damage to the cell membrane, leading to cell lysis.

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21
Q

what are the examples of cytolytic toxins

A
  1. Hemolysins (alpha, beta, gamma, and delta)
  2. Leucocidin (Panton-Valentine toxin), which specifically mediate the destruction of phagocytes.
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22
Q

What is the role of enterotoxin?

A

Enterotoxins are toxins produced by certain bacteria that affect the intestines. They can lead to symptoms such as diarrhea, vomiting, and abdominal pain. Their primary role is to cause gastrointestinal disturbances.

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23
Q

What is the function of exfoliative (epidermolytic) toxin?

A

Exfoliative (epidermolytic) toxin is responsible for causing skin exfoliation. It leads to the detachment of the top layer of the skin, resulting in conditions like staphylococcal scalded skin syndrome (SSSS)

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24
Q

Mention toxins and enzymes that mediate tissue invasion and survival of stypheloccoci at the infextion site

A
  1. Hemolysins
  2. Enterotoxin
  3. Toxic shock syndrome toxin (TSST)
  4. Exfoliative (epidermolytic toxin)
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25
Q

outline the steps of pathogenesis and spectrum of disease in order

A
  1. cocco gain access to damaged skin, mucosal or tissue site
  2. colonize by adhering to cells or extracellularmatrix
  3. Evade the host defence mechanismand multiply
  4. cause tissue damage
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26
Q

difference between pyogenic and toxic-mediated infection

A

pyogenic infection is any infection that causes pus to be produced while Toxin-mediated infections occur when microorganisms produce toxins that cause illness

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27
Q

what are examples of pyogenic infections caused by S. Aureus

A
  1. Boils
  2. Impetigo
  3. Wounds
  4. Septicaemia
  5. Osteomyelitis
  6. Septic arthritis
  7. Pneumonia
  8. Endocarditis
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28
Q

what are toxic mediated infections caused by S. Aureus

A
  1. Scalded skin
  2. Food poisoning
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29
Q

waht are boils

A

are localised, pyogenic skin infection

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30
Q

Who is most commonly affected by boils

A

Boils commonly occur in otherwise healthy individuals without any specific predisposing factors.

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31
Q

What might recurrent boils indicate?

A

Diabetes
Poor hygiene
Nasal carriage of a particularly virulent strain of bacteria.

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32
Q

what does a boil typically involves

A

it involves an infected hair follicle

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33
Q

What is a furuncle?

A

A furuncle is an isolated cutaneous abscess or boil. It typically occurs as a localized infection in a hair follicle or oil gland

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34
Q

How do furuncles differ from carbuncles?

A

Furuncles are single abscesses or boils, whereas carbuncles result from several adjacent furuncles coalescing (coming together). Carbuncles are deeper and involve multiple hair follicles or oil glands.

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35
Q

Define a carbuncle

A

A carbuncle is a more severe condition than a furuncle. It results from multiple furuncles coming together. Unlike furuncles, systemic features of infection (such as fever) are commonly observed in carbuncles.

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36
Q

What is Impetigo?

A

Impetigo is a superficial skin infection.

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37
Q

Which part of the body is impetigo usually confined to?

A

Impetigo is usually confined to the face

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38
Q

Who is most commonly affected by impetigo?

A

Impetigo is most common in children

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39
Q

Where around the face is impetigo especially seen?

A

Impetigo is especially seen around the mouth.

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40
Q

Describe the progression of impetigo lesions.

A

Impetigo lesions initially become purulent (filled with pus) and then crusty.

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41
Q

In what setting are outbreaks of impetigo common?

A

Outbreaks of impetigo are common in schools.

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42
Q

Which group of individuals is predisposed to impetigo

A

Children with eczema are predisposed to impetigo.

also known as atopic dermatitis, is a chronic skin condition characteriz

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43
Q

What is a wound infection?

A

A wound infection occurs when the physical integrity of the skin is compromised, allowing microorganisms to enter and cause an infection.

44
Q

What are some predisposing factors for wound infections?

A

Nasal carriage: Carrying bacteria in the nasal passages.
Presence of a foreign body: Objects or materials within the wound that can promote infection.

45
Q

What are the signs of a wound infection?

A
  1. Erythema (redness) around the wound.
  2. Warmth of the affected area.
  3. Tenderness when touched.
  4. Swelling at the wound site.
  5. Purulent exudate (pus) draining from the wound.
  6. Post-operative fever* (fever after surgery)*
46
Q

What is septicaemia?

A

Septicaemia, also known as blood poisoning, occurs when an infection spreads via the blood from a primary site of infection.

47
Q

What types of primary infections can lead to septicaemia?

A

Primary infections that may lead to septicaemia include wound infections and abscesses.

48
Q

What are some predisposing conditions for septicaemia?

A
  1. Diabetes: Individuals with diabetes are at higher risk.
  2. Presence of a foreign body: especially an IV cannula (intravenous catheter).
49
Q

What are the signs and symptoms of septicaemia?

A
  1. Fever.
  2. Changed mental state (confusion, altered consciousness).
  3. Multi-organ failure, which can ultimately lead to death.
50
Q

What is osteomyelitis?

A

Osteomyelitis is an infection of the bone

51
Q

What are the causes of osteomyelitis?

A
  1. Osteomyelitis is caused by bacteria or other pathogens that invade the bone.
  2. Predisposing conditions include diabetes and intravenous drug use (IVDU)
52
Q

How does osteomyelitis affect bone tissue

A

Osteomyelitis leads to progressive destruction of bone.

53
Q

What are the common signs and symptoms of osteomyelitis?

A

Fever
Bone pain
Local swelling
Tenderness

54
Q

What is septic arthritis?

A

Septic arthritis is a bacterial infection of a joint.

55
Q

Which bacterium is responsible for 90% of septic arthritis cases?

A

Staphylococcus aureus (S. aureus) is the primary causative agent.

56
Q

What are the predisposing conditions for septic arthritis?

A

Pre-existing joint disease
Osteomyelitis
Chronic systemic diseases (e.g., cancer)
Intravenous drug use (IVDU)

57
Q

What type of arthritis is commonly associated with septic arthritis?

A

Monoarthritis (as opposed to rheumatoid arthritis, which is usually symmetrical).

58
Q

Which joints are most commonly affected by septic arthritis?

A

Knee
Hip
Ankle
Wrist
Shoulder
Elbow

59
Q

differences between infueza and pneumonia

A

Influenza is a highly contagious viral infection that spreads easily from person to person, often through coughing or sneezing.
Pneumonia is a serious infection or inflammation of the lungs, where the air sacs fill with pus and other fluids, hindering oxygen exchange

60
Q

What is infective endocarditis (IE)

A

Infective endocarditis is an infection of the heart valves

61
Q

Which group of patients is most affected by IE

A

IE can affect patients with no risk factors, including otherwise healthy individuals.

62
Q

What is the most virulent cause of IE?

A

The most virulent cause of IE is Staphylococcus aureus.

63
Q

What are the clinical features of IE

A
  1. Rapid onset: IE symptoms develop quickly.
  2. Fever and malaise: Patients experience fever and a general feeling of illness.
  3. Cardiac murmur: Abnormal heart sounds due to valve damage.
  4. Cardiac failure: Heart failure can occur due to destruction of heart valves.
  5. Vague symptoms: IE symptoms can be nonspecific, making laboratory diagnosis essential.
64
Q

What is Scalded Skin Syndrome?

A

Scalded Skin Syndrome (SSS) is a bacterial skin infection caused by exotoxins that lead to the exfoliation (peeling) of the upper layers of the skin

65
Q

What is the initial site of infection in SSS?

A

The initial site of infection in SSS is usually a minor or localized lesion.

66
Q

What follows after the initial infection in SSS

A

After the initial infection, there is rapid skin colonization by the causative bacteria.

67
Q

Which population group is predominantly affected by SSS?

A

SSS is predominantly seen in neonates (newborns).

68
Q

Describe the skin changes in SSS

A

In SSS, the upper layers of the skin wrinkle and separate, leading to the formation of large sheets of skin that eventually peel off, leaving a raw and tender surface

69
Q

What is the primary causative agent of food poisoning described in the text?

A

The primary causative agent is Staphylococcus aureus.

70
Q

How many types of enterotoxins does S. aureus produce?

A

enterotoxin A
enterotoxin B
enterotoxin C
enterotoxin D
enterotoxin E

71
Q

What is the mechanism of food poisoning caused by S. aureus

A

Food poisoning occurs due to preformed toxins in the food. These toxins are heat-stable.

72
Q

What are the common symptoms of S. aureus food poisoning

A
  1. Nausea
  2. Vomiting
  3. Diarrhea (Occasionary)
73
Q

explain enterotoxin A, enterotoxin B, enterotoxin C
enterotoxin D ,enterotoxin E.

A

1.Enterotoxin A (SEA):
Produced by Staphylococcus aureus. Common cause of food poisoning. Symptoms include severe diarrhea, nausea, and intestinal cramping. Remains active even after bacteria are killed. Can withstand boiling at 100°C for a few minutes.
2. Enterotoxin B (SEB):
Also produced by Staphylococcus aureus.
Another common cause of food poisoning.
Similar symptoms as SEA: diarrhea, nausea, and cramping. Stable and heat-resistant.
3. Enterotoxin C (SEC):
Produced by certain bacteria. Targets the intestines.
Associated with gastrointestinal symptoms such as cramps, nausea, vomiting, or diarrhea.
4. Enterotoxin D (SED):
Produced by Staphylococcus aureus. Contributes to Staphylococcal Food Poisoning. Causes severe diarrhea and other gastrointestinal symptoms.
5. Enterotoxin E (SEE):
Also produced by Staphylococcus aureus. Implicated in food poisoning cases. Symptoms include diarrhea and vomiting

74
Q

what is the source of food poisoning infection

A

Source of infection is infected lesions on the hands of food handler

lesion refers to any pathological or traumatic discontinuity of tissue

75
Q

what causes rapid onset food poisoning

A

due to preformed toxins in food that are heat-stable

76
Q

state the specime requred in the diagnosis of the following infections
1. boil
2. impetigo
3. wound
4. septicaemia
5. osteomyelitis
6. septic arthritis
7. pneumonia
8. infective endocarditis
9. scalded skin
10. food poisoning

A
  1. boil ~pus
  2. impetigo ~no lab dignosis
  3. wound ~ pus
  4. septicaemia ~blood
  5. osteomyelitis ~blood
  6. septic arthritis ~blood
  7. pneumonia ~ sputum
  8. infective endocarditis ~blood
  9. scalded skin ~skin
  10. food poisoning ~stool, voming, food
77
Q

outline the laboratory diagnosis process for bacteria

A
  1. gram stain from specimen
  2. culture
  3. gram stain from culture
  4. biochemical tests
78
Q

what is gram staining

A

Gram staining is a fundamental technique in microbiology that helps differentiate bacteria into Gram-positive and Gram-negative based on their cell wall properties.

79
Q

what is the difference between gram-positive bacteria and gram negative based on their staining properties

A

~Gram-positive bacteria have a thick layer of peptidoglycan in their cell walls, which retains the Crystal Violet-Iodine complex, appearing blue or purple.

~Gram-negative bacteria have a thinner peptidoglycan layer and an outer lipid layer. The Crystal Violet-Iodine complex gets washed off during decolorization, and they appear red after counterstaining with safranin

80
Q

what is the principle of gram staining

A

~When bacteria are stained with the primary stain (Crystal Violet) and fixed by a mordant (Iodine), some bacteria retain the stain, while others are decolorized by alcohol.
~Gram-positive bacteria have a thick layer of peptidoglycan in their cell walls, which retains the Crystal Violet-Iodine complex, appearing blue or purple.
~Gram-negative bacteria have a thinner peptidoglycan layer and an outer lipid layer. The Crystal Violet-Iodine complex gets washed off during decolorization, and they appear red after counterstaining with safranin.

81
Q

what is the procedure for gram staining

A
  1. Prepare a clean slide with a bacterial smear.
  2. Apply Crystal Violet for 30 seconds to 1 minute and rinse with water.
  3. Add Gram’s iodine for 1 minute and wash.
  4. Decolorize with 95% alcohol or acetone for 10-20 seconds and rinse.
  5. Counterstain with safranin for 1 minute and wash.
    Air dry, blot dry, and observe under a microscope.
82
Q

what is the procedure of acid fast stain

A

~ Acid-fast staining helps differentiate bacteria based on their cell wall properties.
~ Acid-fast bacteria have a thick, waxy cell wall containing mycolic acids.
~ The Ziehl–Neelsen stain uses carbol fuchsin as the primary stain, which penetrates the cell wall of acid-fast bacteria.
~After decolorization with acid alcohol, acid-fast cells retain the stain, appearing bright red.
~Non-acid-fast bacteria lose the stain and appear colorless.

83
Q

examples of acid fast bacterias

A
  1. Mycobacterium tuberculosis: Causes tuberculosis (TB).
  2. Mycobacterium leprae: Causes leprosy.
  3. Other acid-fast bacteria include some species of Nocardia and Cryptosporidium.
84
Q

In acid fast staining what will happen if we replace ziehl-neelsen stain with with crystal violet

A

1.Acid-fast bacteria will not retain the crystal violet stain.
2. Non-acid-fast bacteria will still take up the crystal violet stain.
3. The overall staining pattern will not differentiate acid-fast from non-acid-fast bacteria.

85
Q

what is the functio of crystal violet and what is its reason in gram staining

A

function: Crystal violet is the primary stain used in Gram staining.
reason:
It enters the peptidoglycan layer of bacterial cell walls.
Binds to negatively charged components in the cell.
Stains all bacteria purple/violet initially.

86
Q

what is the function of grams iodine and reason it is used in gram staining

A

function: iodine acts as a mordant (fixative) in gram staining process
reason:
~Forms a complex with crystal violet, making it larger.
~Enhances retention of the stain within the peptidoglycan layer

87
Q

what is the function and reason of use of alcohol (ethanol or acetone) in gram stain

A

functions: Alcohol serves as the decolorizing agent
reasons for use:
1. Removes the stain from some bacterial cells.
2. Critical step in distinguishing Gram-positive from Gram-negative cells.
3. Gram-positive cells retain the stain; Gram-negative cells lose it.

88
Q

what is the function and reason of use of safranin

A

function: Safranin is the counterstain used after decolorization
reason for use:
~Stains cells that lost the primary stain (crystal violet).
~Gram-negative cells appear pink/red due to safranin uptake.

89
Q

what are fulcutative anaerobes

A

anaerobes that can grow either with or without free oxygen.
It adjusts its metabolic pathways depending on oxygen availability

90
Q

explain the biochemical tests used to identify styphylococci aureus

A

gram positive cocci
we do catalase test to identify if bacteria is catalase positive or negative
coagulase positive (S. aureus) and coagulase negative will indicate coagulase negative styphylococci (CNS)

91
Q

outline the biochemical tests in stepls

A

gram positive
catalase positive or catalase negative
from catalase pos. =coagulase positive (S. aureus) coagulase negative will mean (CNS)

92
Q

What is the purpose of the catalase test?

A

The catalase test helps differentiate between Staphylococcus spp. and Streptococcus spp. based on their ability to produce the enzyme catalase.

93
Q

Which bacterial genus produces catalase, and which one does not

A

Staphylococcus spp. produce catalase.
Streptococcus spp. do not produce catalase.

94
Q

What is the function of the catalase enzyme

A

The catalase enzyme catalyzes the breakdown of hydrogen peroxide (a waste product) into water and oxygen.

95
Q

The catalase enzyme catalyzes the breakdown of hydrogen peroxide (a waste product) into water and oxygen.

A

A positive reaction is observed as the immediate production of bubbling when hydrogen peroxide is added to the bacterial sample.

96
Q

What is the purpose of the coagulase test

A

The coagulase test is used to determine whether the organism present is Staphylococcus aureus (S. aureus) after a positive catalase test has indicated the presence of Staphylococcus spp.

97
Q

Which bacterial species produces coagulase, and which ones do not

A
  1. S. aureus produces the enzyme coagulase.
  2. Other Staphylococcus spp. do not produce coagulase.
98
Q

What is the role of coagulase in the test?

A

Coagulase causes plasma to clot by converting fibrinogen to fibrin.

99
Q

What is the difference between staphelococci aureus and ataphylococci epidermidis in terms of coagulase

A

S. aureus produses coagulase while epidermidis does not

100
Q

What is the typical outcome for most boils and superficial staphylococcal abscesses?

A

Most boils and superficial staphylococcal abscesses resolve spontaneously without antimicrobial therapy.

101
Q

Which antibiotic is considered the most effective for treating S. aureus infections if the strain is sensitive?

A

Penicillin is the most effective antibiotic for sensitive S. aureus strains.

102
Q

What antibiotics are used against beta-lactamase producing strains of S. aureus?

A

Cloxacillin or Methicillin are used against beta-lactamase producing strains.

103
Q

What treatment is recommended for infections caused by Methicillin Resistant Staphylococcus aureus (MRSA) strains

A

: Infections with MRSA strains are treated with Vancomycin.

104
Q

Ways of preventinf staphylococci infections

A
  1. Education of food handlers
  2. Hand washing by HCWs
  3. Isolation & treatment of MRSA patients
  4. Avoid indiscriminate usage of antibiotics
105
Q

laboratory diagnosis of staphylococci epidermidis

A
  1. GPC (gram positive cocci) in clusters, indistinguishable from S. aureus
  2. Rapid growth of white colonies
  3. Catalase positive
  4. Coagulase negative
  5. Usually reported as CNS
106
Q

treatment of staphylococci saprophyticus

A

Treatable with trimethoprim

Microbiology 1 (27 decks)

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