Methicillin-resistant Staphylococcus Aureus (MRSA)

Droplet Contamination

Synopsis of Methodology

This work simulated droplet contamination of MRSA that represents a sneeze or splash. Inoculations of MRSA and EMRSA (an epidemic strain) were made onto copper, brass and stainless steel coupons. The inoculations consisted of 10⁷ colony-forming units (CFUs) suspended in 20ul of medium onto coupons with dimensions of 1 cm by 1 cm. The inoculated coupons were then incubated at either 22°C or 4°C for various time periods and surviving bacteria enumerated by standard culture techiques and EDIC/epifluorescent microscopy (to confirm cell death).

Key Findings

• On pure copper surfaces at 22°C, inoculations of MRSA, EMRSA-1 and EMRSA-16 were completely killed after 45 min, 60 min and 90 min, respectively. At 4°C, complete kill was achieved on pure copper for all three strains within six hours.
• In contrast, viable organisms for all three strains were detected on stainless steel (grade 304) after 72 hours at 22°C. The results demonstrate an antimicrobial effect of copper on MRSA, EMRSA-1 and EMRSA-16 in contrast to stainless steel.
• Results for brass (80% Cu) at 22°C are still significant with regards to viability reduction, although not to the same extent as those for pure copper. Complete kills were achieved for MRSA and EMRSA-1 after 4.5 hours of exposure, with both strains producing similar viability curves over time. The effect of brass on EMRSA-16 viability was less than a 100-fold reduction over six hours.
• Epifluorescent images of copper coupons showed there were no respiring cells remaining after 45, 60 and 90 min of exposure for MRSA, EMRSA-1 and EMRSA-16, respectively. In contrast, images of inoculated stainless steel coupons after 72 h of incubation at 22 C clearly show the presence of respiring cells for all three strains tested. This confirms cell-death rather than sub-lethal damage.

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Dry Touch Contamination

Synopsis of Methodology

This study simulated a dry fingertip contamination event, using the same number of bacteria as the droplet contamination test (10⁷) per coupon but this time suspended in just 1ul which dried within seconds. As fingertip touch will also contaminate a surface with biomolecules transferred from the skin surface,  the medium used to suspend the bacteria contained a complex
mixture of proteins, salts, and sugars. Survival of MRSA, EMRSA and meticillin-sensitive strain of S. aureus (MSSA) were assessed on 1cm x 1cm coupons of pure copper, copper-nickel, cartridge brass and stainless steel at 21°C. Bacterial survival at various time points was enumerated.

Key Findings

• A 5-log reduction of a hardy epidemic strain of MRSA (EMRSA-16) was observed following 10 minutes contact with copper, and a 4-log reduction was observed on copper nickel (90% Cu) and cartridge brass (80% Cu) alloys within 15 minutes.
• A methicillin-sensitive strain (MSSA), from an osteomyelitis patient, was killed on copper surfaces in 15 minutes and a 4-log and 3-log reduction occurred within 20 minutes contact with copper nickel (90% Cu) and cartridge brass (80% Cu), respectively.
• Bacterial respiration was found to be compromised on copper surfaces and superoxide generated as part of the killing mechanism.
• In addition, destruction of genomic DNA was confirmed to occur on copper and brass surfaces, allaying concerns about horizontal gene transfer and copper resistance.
• Cells exposed to stainless steel surfaces displayed intact DNA and active respiration.

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MRSA Facts

What is it?

Staphylococcus aureus (S. aureus) is a  gram-positive bacterium that commonly colonises human skin and mucosa without causing any harm but if it enters the body it can cause a range of illnesses ranging from mild to life-threatening.These include skin and wound infections, infected eczema, abscesses or joint infections, infections of the heart valves (endocarditis), pneumonia and bacteraemia (blood stream infection).

Most strains of S. aureus are sensitive to the more commonly used antibiotics, and infections can be effectively treated but some bacteria are more resistant. Those resistant to the antibiotic meticillin are termed meticillin resistant Staphylococcus aureus (MRSA) and require different types of antibiotic to treat them. Those that are sensitive to meticillin are termed meticillin susceptible Staphylococcus aureus (MSSA).

• Epidemic MRSA is defined as MRSA isolated from two or more patients in at least two hospitals. This first epidemic strain, designated EMRSA-1, was recognized in 1981 and continued to cause outbreaks in hospitals until the late 1980s.
• EMRSA-15 and EMRSA-16 are highly transmissible and durable. They gained a reputation as ‘super’ EMRSA. They are the most prevalent strains found in the UK and have also been found in a number of European countries as well as the US.

How is it contracted?

• According to the US Centers for Disease Control and Prevention (CDC), anyone can get MRSA through contact with an infected wound or from contaminated hands, usually those of health care workers (HCWs), via broken skin or a medical procedure.
• According to the authors of the study, hand hygiene remains the single most effective strategy for preventing crosscontamination via HCWs. However, door handles and commonly touched surfaces may be important secondary reservoirs for cross-contamination between HCWs and patients.
• People who carry MRSA may not show any signs of infection, but can easily spread the bacteria to others and potentially cause an infection.

Where is it prevalent?

• According to the CDC, one in three (33%) people carry staph in their nose, usually without any illness. When it comes to MRSA, two in 100 people carry the bacteria.
• MRSA infections occur both in communities and healthcare facilities. In communities, MRSA most commonly causes skin infections. While in medical facilities, MRSA can cause life-threatening bloodstream infections, pneumonia and surgical site infections.