Flashcards in Micro 6: Examples of Bacteria Deck (119)
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Case 6
• A 45 y/o male has a motorcycle accident in which he is ejected from his motorcycle, lands in mud in a ditch on the side of the road, and suffers a severe compound fracture of his right lower extremity.
He is found approximately 18 hours after his accident, and is rushed to Regional One. He is taken to the OR immediately for RLE repair.
Vascular injury and ischemia of his RLE are found in the OR. Vasculature is repaired. There is a dusky appearance to his tissues in the OR.
• His RLE pain worsens and his leg became very discolored, almost black. Exam of the leg reveals crepitus (crackling or popping sound when palpating the soft tissues). He is taken back to the OR urgently where significant necrotic tissue is found. Extensive debridement (cleaning of necrotic tissue) is done.
Case 6
• A 45 y/o male has a motorcycle accident in which he is ejected from his motorcycle, lands in mud in a ditch on the side of the road, and suffers a severe compound fracture of his right lower extremity.
He is found approximately 18 hours after his accident, and is rushed to Regional One. He is taken to the OR immediately for RLE repair.
Vascular injury and ischemia of his RLE are found in the OR. Vasculature is repaired. There is a dusky appearance to his tissues in the OR.
• His RLE pain worsens and his leg became very discolored, almost black. Exam of the leg reveals crepitus (crackling or popping sound when palpating the soft tissues). He is taken back to the OR urgently where significant necrotic tissue is found. Extensive debridement (cleaning of necrotic tissue) is done
92
The lab is asked to perform both aerobic and anaerobic cultures. Why might this be?
crepitus indicates gas in the tissue (assumedly from anaerobic bacteria) and he was found in ditch where anaerobes are found commonly
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Gram stain of the OR specimens reveals large Gram positive bacilli. Aerobic culture is negative, anaerobic culture grew colonies on BAP that produced clear hemolysis. This was consistent with Clostridium perfringens.
• What are the dual benefits of debridement in anaerobic infections?
you get rid of devitalized tissue and only leave behind good tissue and
you get rid of the toxin produced by the bacteria
94
• Crepitus indicates the presence of gas in tissues and this is a case of “gas gangrene,” which is an invasive infection.
1) How might the gas be produced?
2) What type of virulence factor do you suppose is causing the necrotic infection?
1) fermentation (bad smelling is a characteristics of anaerobic infection)
2) cell-lysing exotoxin
95
1) What feature of some Gram positive organisms would allow it to survive long periods of time in the soil?
2) If infection is initially by spores, what patient factor favored development of this invasive infection?
1) spores
2) the time in the soil allow the spores to reactivate
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What is Gas gangrene?
a dreaded disease that begins as a contaminated wound infection but can quickly lead to shock and death in just a few hours. Traumatic injury allows the introduction of spores from the soil.
If the injury is not attended to in a timely way, the spores can germinate in oxygen-poor tissue and lead to infection.
Hydrogen and carbon dioxide production is the result of fermentation of carbohydrates in the infected tissues.
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In Gas genrene, bacterial growth is accompanied by what?
Bacterial growth is accompanied by the production of **alpha-toxin**, a phospholipase (lecithinase) that lyses cells. Shock is attributable to the spread of alpha-toxin to the bloodstream
Clostridia are not found at the distal sites, just the toxin.
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How is gas gangrene treated?
Gas gangrene is a medical emergency and requires surgical debridement, often radical, and high doses of penicillin G. You can give desensitizing doses of penicillin G if they are allergic.
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What is the causative bacteria of gas gangrene?
Clostridium perfringens
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What are some characteristics of Clostridium perfringens?
• Anaerobic, spore-forming Gram positive bacilli that are large with square ends – “box cars”
• Produce double zone of hemolysis on BAP
• Present in soil and colon of humans and animals
• Gas gangrene or food poisoning
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What kinds of important virulence factors do Clostridium perfringens have?
• Virulence factors
– Spore formation
– Alpha toxin (lecithinase) in gas gangrene that lyse cells
Pore-forming enterotoxin in food poisoning (5% of strains)
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What is the difference between gas gangrene and food poisoning?
Food poisoning: spores survive cooking, germinate during reheating to form toxin. Food poisoning is self-limiting, requiring only fluid replacements.
Not caused by the alpha-toxin that causes gas gangrene
103
Case 7
• A 1-month-old girl presents with a diffuse, “sandpaper-like” rash. Her mother noticed the rash while nursing her daughter. The girl does not appear to be severely ill, but is feverish and dehydrated. The rash soon worsens, with widespread loss of skin, with the epidermis appearing to come off in sheets. Hospitalization is required.
• Blood cultures from the girl were negative, but a sample taken from the oral cavity grew Staphylococcus aureus. No S. aureus was cultured from any of the sites of skin loss. Combined with the clinical presentation, this indicated a case of staphylococcal scalded skin syndrome (SSSS).
Case 7
• A 1-month-old girl presents with a diffuse, “sandpaper-like” rash. Her mother noticed the rash while nursing her daughter. The girl does not appear to be severely ill, but is feverish and dehydrated. The rash soon worsens, with widespread loss of skin, with the epidermis appearing to come off in sheets. Hospitalization is required.
• Blood cultures from the girl were negative, but a sample taken from the oral cavity grew Staphylococcus aureus. No S. aureus was cultured from any of the sites of skin loss. Combined with the clinical presentation, this indicated a case of staphylococcal scalded skin syndrome (SSSS).
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If the cultured bacteria were Gram stained, what would have been seen?
gram-positive cocci in grape-like clusters
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What would the catalase and coagulase results been?
catalase- positive
coagulase- positive
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How might the girl have been infected with S. aureus (does the site of isolation suggest anything)?
breast feeding
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How can you explain systemic features if S. aureus was not present in the blood or affected tissues?
toxin dissemination
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Why didn’t the mother have SSSS?
Antibodies and maybe better renal clearance
109
What is SSSS (staph. aureus skin syndrome)? .
it is only one form of S. aureus (very virulent) infection. It is typically found in children under the age of 5, and is often transmitted in daycare settings.
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What is the cause of SSSS?
Two exfoliative toxins (ETA and ETB) cleave desmoglein-1, a cell-to-cell attachment protein of the superficial epidermis (no scarring).
These exotoxins are phage-encoded and found in only about 5% of S. aureus isolates.
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What are the types of presentation of SSSS?
SSSS has two types of presentation: the generalized exfoliation described here and a more localized, blistering form occurring at the site of infection.
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What is the treatment for SSSS?
SSSS treatment includes rehydration therapy, topical wound care, and nafcillin or oxacillin.
If MRSA is involved, then vancomycin or linezolid should be used.
Clindamycin can be used to inhibit toxin production.
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What are some of characteristics of Staphylococcus aureus?
• Gram positive coccus in grape-like clusters that form golden colonies
– Catalase positive, coagulase positive
– Often beta-hemolytic; growth on mannitol salts agar
• Normal flora of the nose (10-30%)
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What are some of the virulence factors of Staph. aureus?
• Virulence factors
– Numerous degradative exoenzymes
– Numerous exotoxins (enterotoxins, cytotoxins, exfoliative toxins, TSST)
– Protein A
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What are some of the things St. aureus cause?
• S. aureus is a prolific pathogen
– Food poisoning
– Pyogenic skin infections (bullous impetigo, folliculitis, styes, carbuncles)
– Toxic shock syndrome
– Necrotizing pneumonia
– Meningitis
– Acute endocarditis
– Osteomyelitis
– Organ abscesses
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What is the treatment for a Staph. aureus infection?
Treatment with methacillin or oxacillin, but MRSA is increasing (vancomycin used)
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How would you treatment Gonorrhea?
Ceftriaxone
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How would you treat Clamydia?
Azithromycin
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