The Effects of Salt Concentration and Growth Phase on MRSA Solar and Germicidal Ultraviolet Radiation Resistance

Author(s): 
Jennifer L. Sheldon, MSc; Tyler A. Kokjohn, PhD; and Eugene L. Martin, PhD, JD

A ntimicrobial drugs are used continuously and extensively all over the world. While much of their use is warranted, considerable employment of these agents is inappropriate. The Centers for Disease Control and Prevention (CDC) estimates in the US that many prescriptions are unnecessary: 30% are prescribed for ear infections, 50% for sore throats, and the majority for the common cold.1 Drugs are overused in animal and poultry feed and also greatly misused in over-the-counter sales in much of the world. All of this contributes greatly to the development of drug resistance. One organism that is becoming an increasing problem worldwide is methicillin-resistant Staphylococcus aureus (MRSA).2

With the widespread emergence of organisms like MRSA, emphasis has increased on the need to develop alternative treatments for chronic wounds such as diabetic ulcers and pressure ulcers. One such alternative treatment method employs ultraviolet (UV) radiation. Ultraviolet radiation can be conveniently categorized into germicidal (UV C, with a wavelength of 190 nm to 290 nm) and solar (UV B and UV A, with wavelength ranges of 290 nm to 320 nm and 320 nm to 400 nm, respectively). Although essentially all UV C radiation is screened out by the stratospheric ozone layer, substantial UV A and B radiation still reaches the Earth’s surface.3 A range of in vitro and in vivo studies has been conducted involving germicidal and solar UV radiation as an adjunctive therapy to the use of antimicrobials in the treatment of various skin disorders.2,4-8 Taken together, these studies reveal the potential of UV radiation as an adjunctive treatment. The authors extended these studies by quantifying UV inactivation rates under differing physicochemical and growth conditions. In addition, the response of MRSA and the Gram-negative bacterium, Pseudomonas aeruginosa, a common cause of wound and burn infections, was compared.

Literature Review

For the last 20 years or so, outbreaks of MRSA have been associated with healthcare facilities such as hospitals and nursing homes. During this time span, this problem has been become much more prevalent. Recent studies document the situation.9–16 In hospital neurosurgical populations, MRSA infection is a growing problem; most cases are hospital-acquired, are often associated with extended lengths of stays, and many involve wound infections. Often these MRSA patients are discharged before eradication of the infection was achieved.9 The results of one study, conducted after MRSA was observed in a tertiary hospital and a geriatric institution where isolates were recovered from pressure ulcers, suggested nosocomial acquisition and highlight the need for epidemiological analysis to control dissemination of MRSA in such facilities.10 Another report documented the frequent transmission of MRSA from colonized hospital employees to their households.11

References: 

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