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Medical Microbiology > Wound Infections > Flashcards

Wound Infections Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
0
Q

Name three.

A

S. aureus (important human pathogen) epidermidis (normal skin flora, disease under special circumstances) saprophyticus (UTI’s in young females).

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1
Q

Describe what staphylococci is.

A

Facultative, non-sporulating, non-motile, gram positive cocci. Divides in 3 planes where daughter cells don’t fully separate but form clusters.

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2
Q

What are the characteristics of S. aureus?

A

Gram positive coccus, forms grape-like clusters, common on skin and nose: grows in high salt. When grown on sheep blood agar it forms golden-coloured colonies.

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3
Q

What results are received from the coagulase and catalase test for each Staphylococci?

A

S. aureus - cat. Positive, co. Postive.
S. epidermidis - cat. Positive, co. Negative
S. saprophyticus - cat. Positive, co. Negative.

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4
Q

What is the epidemiology for S. aureus?

A

Reservoir - humans.
Asymptomatic carriage sites: rectum, pharynx, perineum (area between anus and genitals) and nares (nostrils or nasal passages).
Transmission - person to person.

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5
Q

What are the staphylococci associated infections cause?

A

Liver disease, neoplasia (benign growth), diabetes, renal failure, skin disease (increased colonisation). Healthy people are not normally affected by staph infection.

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6
Q

What are the patterns of disease for S. aureus?

A

Invasion with tissue destruction.

Toxin mediated: toxic shock syndrome, scalded skin syndrome, staphylococcal food poisoning.

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7
Q

What are the four skin issues related to bacterial infection with staphylococcus aureus?

A

Foruncle starts with Follicilitus (infection of hair follicle)
Causes form and tender red nodule which is painful. It drains spontaneously.

Carbuncle found at the nape of the neck, is larger than furuncle, extends into subcutaneous fat, creates firm and inelastic skin.

Impetigo: superficial infection of skin by S. aureus and streptococcus pyogenes. Cases seen in children during hot weather.

Cellulitis: acute, spreading infection involving both skin and subcutaneous tissues. Prior trauma to skin. Feels warm and erethematous.

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8
Q

What is the cause of food poisoning?

A

Toxigenic strain of S. aureus growing in contaminated food. Produces enterotoxin B which is heat stable.
Person to Person transmission whereby organism is seen in person involved in meal preparation who passes it into food.

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9
Q

What are the food associated with staph food poisoning?

A

Custard filled bakery goods, canned food, potato salad, ice cream.
Food appears normal in appearance, odor and taste.

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10
Q

What are the clinical features of food poisoning?

A

Incubation period: 2-6 hours. The enterotoxin stimulates intestinal peristalsis and CNS causing salivation, nausea and vomiting, abdominal cramps and watery diarrhoea. Symptoms disappear in 8 hours.

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11
Q

Name the drug used for treatment.

A

Penicillin.

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12
Q

How has MRSA become resistant?

A

Produces beta lactamase which breaks down the beta-lactam ring of penicillin. Serious MRSA infections require treatment with vancomycin.

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13
Q

What are the characteristics of pseudomonas?

A

Gram negative rod shaped. Colonies produce green fluorescence (pyocyanin).

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14
Q

Where can pseudomonas be found?

A

Soil, decaying matter, moist environments.

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15
Q

What are the virulence factors for pseudomonas?

A

Adhesins, toxins, and a polysaccharide capsule.

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16
Q

What is the pathogenesis?

A

Infection can occur in burn victims where the bacteria grow under the surface of the burn. The bacteria kills cells, destroys tissues and triggers shock.

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17
Q

How can you diagnose infection?

A

Pyocyanin discolouration indicates massive infection.

18
Q

What about treatment?

A

Naturally resistant to penicillins and other drugs.

19
Q

What are the characteristics of clostridium spps?

A

Anaerobic, spore-forming, gram positive bacilli.

20
Q

Where can they be found?

A

Soil, human and animal intestine, water, decaying animal and plant matter.

21
Q

What is the pathogenesis?

A

Produce potent toxins.

22
Q

Why do they form spores?

A

Spores are formed under adverse conditions. Spores are a survival mechanism. C. perfringens and C. botulinum have ovoid subterminal spores whereas C. tetani have round terminal spores.

23
Q

What are the biochemical lab characteristics?

A

Saccharolytic: ferments sugars, with a reddening of Robertson’s meat medium with a rancid smell.
Proteolytic: enzymes that digest proteins, blackening of Robertson’s meat medium with a foul smell.
Toxins: exotoxins produced by C. tetani and C. botulinum which is highly toxic.
Antibiotic sensitivity: penicillin, metronidazole, erythromycin.
Resistant to aminoglycosides: kanamycin and streptomycin.

24
Q

Name four clostridium species.

A

C. botulinum, perfringens, tetani, difficile.

25
Q

What is the pathogenicity for C. perfringens?

A

Gas gangrene: wounds associated with necrosis of muscle may become infected with C. perfringens which will grow rapidly in anaerobic tissue.
Food poisoning: when ingested in large numbers some strains of C. perfringens produce an enterotoxin in the gut, causing diarrhoea and other symptoms.

26
Q

What methods are used in diagnosis?

A

Grows rapidly in culture (nagler reaction). Characteristic forms seen on gram stain.

27
Q

Describe the nagler reaction.

A

C. perfringens produces alpha toxin, lecithinase. On a medium containing egg yolk (lecithin), enzyme activity can be detected as opacity around the line of growth. If anti-alpha toxin is applied to the surface of the plate, the action of the toxin is inhibited (seen as transparent).

28
Q

Treatment, prevention and control.

A

Rapid treatment is essential for serious infections. High doses of penicillin. Proper wound care and use of prophylactic antibiotics will prevent most infections.

29
Q

What is the pathogenicity for Clostridium tetani?

A

Tetanus: a classic toxin mediated disease in which C. tetani in a wound produces a powerful neurotoxin which spreads and acts on CNS causing muscle spasms.

30
Q

What are the characteristics?

A

Have prominent terminal spores (tennis racket appearance). Strict anaerobe (vegetative cells are extremely oxygen sensitive), when growth is detected on agar media, it typically appears as a film over the surface of the agar rather than discrete colonies.

31
Q

What are the virulence factors?

A

Spore formation. Tetanospasmin (heat-labile neurotoxin; blocks release of neurotransmitters for inhibitory synapses.

32
Q

What is the epidemiology?

A

Spores are found in most soils and can colonise gastrointestinal tract of humans and animals. Exposure to spores is common, but disease is uncommon except in underdeveloped countries where there is poor vaccination compliance and medical care is inadequate. Risk is greatest for people with inadequate vaccine induced immunity. Disease does not induce immunity.

33
Q

What are the methods used for diagnosis?

A

Microscopy and culture with poor sensitivity. Neither tetanus toxin nor antibodies are typically detected.

34
Q

Treatment, prevention and control.

A

Metronidazole. Vaccination with tetanus toxoid.

35
Q

What are the clinical forms of tetanus?

A

Generalised: difficulty swallowing, irritability, opisthotonos (spasm of the muscle causing backward arching of the head, neck and spine).
Cephalic: primary infection in head, very poor prognosis.
Localised: involvement of muscles in area of primary injury, favourable prognosis.
Neonatal: infection typically originates from umbilical stump. Very poor prognosis in infants whose mothers are nonimmune.

36
Q

What is the pathogenicity for C. botulinum?

A

Botulism: rare but very severe form of food poisoning in which symptoms are neurological rather than intestinal. It is caused by ingestion of preformed toxin in food contaminated with C. botulinum.

37
Q

What are the characteristics?

A

Strict anaerobe. Very attentive growth requirements. Can produce seven distinct botulinum toxins. Strains associated with human disease produce lipase, digest milk proteins, hydrolyse gelatin, and ferment glucose.

38
Q

What are the virulence factors?

A

Spore formation. Botulinum toxin (prevents release of neurotransmitter acetylcholine).
Binary toxin.

39
Q

What is the epidemiology?

A

Found everywhere in soil. Infant botulism more common than other forms.

40
Q

What methods are used for diagnosis?

A

Botulism confirmed by isolating the organism or detecting the toxin in food products or faeces or serum.

41
Q

Treatment, prevention and control.

A

Metronidazole or penicillin.
Spore germination in foods prevented by maintaining food in an acid pH, by high sugar content or by storing the foods at 4C or colder. Toxin is heat-liable so can be destroyed by heating of food for 20 minutes at 80C. Infants younger than 1 should not be given honey or foods containing it.

42
Q

What are the characteristics for C. perfringens?

A

Large, gram-positive rods, non-motile, grows rapidly in tissues and in culture, haemolytic.

43
Q

What are the three types of botulism?

A

Foodborne- ingest contaminated food, signs include blurred vision, dilated pupils, dry mouth.

Infant botulism- caused by neurotoxin production in vivo by C. botulinum colonising the gastrointestinal tract of infants. Signs include weak cry, constipation.

Wound botulism- develops from toxin production in contaminated wounds.

Medical Microbiology (8 decks)

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