Research Paper on Methicillin-resistant Staphylococcus Aureus

Characteristics of the microorganism

Methicillin-resistant Staphylococcus aureus (MRSA) is caused by bacterium called staph aureus (S. aureus). Under the microscope, staph aureus resembles a cluster of grapes (1). The microorganism is both anaerobic (oxygen fearing) and aerobic (oxygen loving). It is also a gram-positive bacterium and has a coccal shape. S aureus is catalase positive and facultative-anaerobic. MRSA infections are unresponsive to methicilin, oxacillin, amoxicillin and penicillin treatment. S. aureus produces coagulase adhesion which causes conversion of fibrinogen to fibrin. The tight coat of fibrin that cover the S. aureus bacteria make it more virulent than other staph strains. Test to determine methicillin resistance includes taking a swab from the infected body part (1). The obtained sample is observed for colonization by the pathogen that lack mecA. The test also involves incubation of MSA plates for 48 hours at 37 degrees Celsius. After the incubation, the fermenting colonies are sub-cultured at 37 degree Celsius on trypticase soy agar plates (1). Finally, diffusion discs are used to screen S. aureus isolates for methicillin resistance.

In a clinical setting, MRSA presents itself as a puss-filled cavity with a yellow or white head. The cavity is easily drainable with a syringe (1). A culture can be obtained using fluid drainage or biopsy of the affected area. MRSA commonly manifests itself as skin infections, but can also be manifest in the lungs only. In such a case, a sputnam culture is obtained through respiratory lavage or bronchoscopy (1). Other manifestations of MRSA may require blood or urine samples. Unfortunately, MRSA is extremely difficult to detect as a cultures can have antibiotic resistant and non-resistant S. aureus. At 33 to 35 degrees Celsius resistant cultures will grow slowly and specifically, while no growth will be noticed at temperatures above 35 degree Celsius (1).

Disease, Signs and Symptoms

As seen earlier, MRSA can infect different parts of the body. The symptoms of MRSA manifest themselves differently depending on the part of the body that is infected (2). Some manifestations include sores, boils and mild skin infections. However, severe blood, lung and urinal tract infections have been reported (4). The majority of MRSA cases are not life-threatening although some can be very serious. Unlike other strains of staphylococcus aureus, MRSA is harder to treat and manage as it is resistant to common antibiotics (2).

Transmission, Morbidity and Mortality

MRSA is caused by common bacteria that are found on many peoples bodies. According to the Centre for Disease Control (CDC), most people act as host for s. aureus but never get infected by the bacteria (2). However, infections occur when the s. aureus get into the body mostly through a cut. People infected with the MRSA can infect others although the risk of cross infection is low. Infections can occur through touching surfaces like bed-rails, medical equipment, bed-linens and touching hands of infected individuals (2). Formite contact and lack of sanitation significantly increases the risk of transmission of MRSA (4).

According to the CDC, MRSA is responsible for 18,000 annual deaths in the US alone. Some victims of MRSA have resulted to amputation to remove parts of the body infected by the bacteria (2). Globally, MRSA account for 50 per cent of staph aureus infections recorded in hospitals. Innovative hygiene in the Netherlands has been able to keep MRSA infection at only 2% of all s. aureus infections (2).

Control and Treatment

In some cases MRSA can be treated using antibiotics. Generally, patients require medical attention for their abscess to be drained (3). When MRSA present itself as small skin boil, careful draining by a doctor is enough. When MRSA spread to infection is more serious bacterium and vancomycin can be administered intravenously (5). The best control method for MRSA is good personal hygiene; hands are always clean and washed (2). Wounds should also be drained and covered at all times. Sharing of personal items should also be avoided to keep MRSA infections in control.

Article Summary

Florescu et al sought to compare the safety and efficacy of tigecycline with linezolid and vancomycin as treatment option for serious cases of vancomycin-resistant enterococci (VRE) or MRSA respectively (5). The authors linked MRSA and VRE to an increase in nosocomial infections. The researchers hypothesized that tigecycline would be more effective and safer as a treatment option for MRSA than vancomycin. Acccording to Florescu et al, new strains of MRSA that are resistant to vancomycin have emerged and thus there is need to change to tigecycline (5). The authors argue that Tigecycline a new glycylcycline antibiotic has mechanisms that can enable it overcome tetracycline resistance (ribosomal protection and efflux pumps) and remains unaffected by other mechanism used by bacteria to develop resistance. The authors indicated that the safety and efficacy of tigecycline against VRE and MRSA pathogens had already been demonstrated in other studies (5). However, no study has compared the drug efficacy and safety to either Vancomycin or tigecycline when treating MRSA or VRE.

Methods

Florescu et al was a Phase 3, multicentre, randomized, double-blind study in which hospitalized patients diagnosed with VRE or MRSA were treated with either vancomycin, linezolid or tigecycline (5). The study involved 15 VRE patients and 157 patients diagnosed with MRSA in over 50 sites across 14 countries. The participants were required to attend treatment session for 7-28 days. After 12 to 27 days of receiving the last treatment, participants were required to take a test-of-cure test (5). Clinical responses at the endpoint to evaluate efficacy of treatment could either be failure, cure or indeterminate.

Results

For MRSA treatment (n=117) a 81.4 per cent cure rate was reported for patients treated with tigecycline. On the other hand, patients treated with vancomycin reported a 83.6 per cent clinical cure rate (5). MRSA Patients suffering from complicated skin and skin structure infections reported statistically similar cure rates for both vancomycin and tigecycline (86.9% and 86.4% respectively). Side effects were less frequent with vancomycin than with tigecycline (17.9% versus 41.0%). Patients treated with tigecycline were more likely to experience nausea or vomiting (5). However, the researchers reported that the side effects were mild and only three patients discontinued treatment. On the other hand, the researchers found higher VRE cure rate for patients treated with vancomycin than those treated with linezolid. In patients diagnosed with VRE (n=15), 2 out of 3 in the microbiologically evaluable group were cured by linezolid, while all 3 out of 3 treated with tigecycline were cured (5).

Conclusion

This study shows there is hope for the treatment of MRSA although the disease is developing resistance to vancomycin (5). Tigecycline an effective and safe treatment option is now available for the treatment of strains of MRSA that are resistant to the vancomycin.

Works Cited

Maor, Yasmin, et al. "Clinical features of heteroresistant vancomycin-intermediate Staphylococcus aureus bacteremia versus those of methicillin-resistant S. aureus bacteremia." The Journal of infectious diseases 199.5 (2009): 619-624.

Centers for Disease Control and Prevention (CDC) MRSA infections. (2010). Available online: http://www.cdc.gov/mrsa/index.html.

Kallen AJ, et al. Health care-associated invasive MRSA infections, 2005-2008. JAMA (2010): 304(6): 641-647.

Liu C, et al. Clinical practice guidelines by the Infectious Diseases Society of America for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children. Clinical Infectious Diseases (2011): 52(3): 285-292.

Florescu, I., et al. "Efficacy and safety of tigecycline compared with vancomycin or linezolid for treatment of serious infections with methicillin-resistant Staphylococcus aureus or vancomycin-resistant enterococci: a Phase 3, multicentre, double-blind, randomized study." Journal of Antimicrobial Chemotherapy 62.suppl_1 (2008): i17-i28.