Methicillin resistant staphylococcus aureus history and symptoms: Difference between revisions
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'''Is it difficult to detect oxacillin/methicillin resistance?''' | '''Is it difficult to detect oxacillin/methicillin resistance?''' | ||
Accurate detection of oxacillin/methicillin resistance can be difficult due to the presence of two subpopulations (one susceptible and the other resistant) that may coexist within a culture of staphylococci. All cells in a culture may carry the genetic information for resistance, but only a small number may express the resistance in vitro. This phenomenon is termed heteroresistance and occurs in staphylococci resistant to penicillinase-stable penicillins, such as oxacillin. | Accurate detection of [[oxacillin]]/[[methicillin]] resistance can be difficult due to the presence of two subpopulations (one susceptible and the other resistant) that may coexist within a culture of staphylococci. All cells in a culture may carry the genetic information for resistance, but only a small number may express the resistance in vitro. This phenomenon is termed heteroresistance and occurs in staphylococci resistant to penicillinase-stable penicillins, such as oxacillin. | ||
Cells expressing heteroresistance grow more slowly than the oxacillin-susceptible population and may be missed at temperatures above 35°C. This is why CLSI recommends incubating isolates being tested against oxacillin, methicillin, or nafcillin at 33-35° C (maximum of 35°C) for a full 24 hours before reading. | Cells expressing heteroresistance grow more slowly than the oxacillin-susceptible population and may be missed at temperatures above 35°C. This is why CLSI recommends incubating isolates being tested against oxacillin, methicillin, or [[nafcillin]] at 33-35° C (maximum of 35°C) for a full 24 hours before reading. | ||
==History and Symptoms== | ==History and Symptoms== | ||
S. aureus most commonly colonises the anterior nares (the nostrils) although the respiratory tract, open wounds, intravenous catheters and urinary tract are also potential sites for infection. MRSA infections are usually asymptomatic in healthy individuals and may last from a few weeks to many years. | S. aureus most commonly colonises the anterior nares (the nostrils) although the respiratory tract, open wounds, intravenous catheters and urinary tract are also potential sites for infection. MRSA infections are usually asymptomatic in healthy individuals and may last from a few weeks to many years. | ||
Symptoms in MRSA infections depend upon the infection caused by MRSA: | |||
* [[Furuncles]] - painful pus filled tender lumps, [[fever]] is present | |||
* [[Carbuncles]] - painful and pus draining onto the skin, [[fever]] is present | |||
* [[Abscess]] - [[fever]], [[pain]], [[tenderness]] | |||
Revision as of 16:58, 14 August 2012
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
According to Betsy McCaughey, founder of the Committee to Reduce Infection Deaths, MRSA can be detected in asymptomatic patients by a blood test. Combined with extra sanitary measures for those in contact with infected patients, screening patients admitted to hospitals has been found effective in minimizing spread of MRSA in hospitals in Denmark, Finland and the Netherlands.
Is it difficult to detect oxacillin/methicillin resistance?
Accurate detection of oxacillin/methicillin resistance can be difficult due to the presence of two subpopulations (one susceptible and the other resistant) that may coexist within a culture of staphylococci. All cells in a culture may carry the genetic information for resistance, but only a small number may express the resistance in vitro. This phenomenon is termed heteroresistance and occurs in staphylococci resistant to penicillinase-stable penicillins, such as oxacillin.
Cells expressing heteroresistance grow more slowly than the oxacillin-susceptible population and may be missed at temperatures above 35°C. This is why CLSI recommends incubating isolates being tested against oxacillin, methicillin, or nafcillin at 33-35° C (maximum of 35°C) for a full 24 hours before reading.
History and Symptoms
S. aureus most commonly colonises the anterior nares (the nostrils) although the respiratory tract, open wounds, intravenous catheters and urinary tract are also potential sites for infection. MRSA infections are usually asymptomatic in healthy individuals and may last from a few weeks to many years.
Symptoms in MRSA infections depend upon the infection caused by MRSA:
- Furuncles - painful pus filled tender lumps, fever is present
- Carbuncles - painful and pus draining onto the skin, fever is present
- Abscess - fever, pain, tenderness