GUEST WRITER

SARWAT ALI RAJA/PROF DR MUHAMMAD ASHRAF

Methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen emerged over half a century causing a number of disseminated lethal diseases. This superbug not only present in human but harbour animals as well resulting its spread from animals to humans and vice versa. It has now turned to be a pathogen of interest globally and considered a major public threat resulting in high morbidity and mortality.

More alarming is that the epidemic clones of this superbug harbouring the hospitals have now transferred to the community and can very swiftly migrate from one geographic region to the other. Another astonishing fact is that not only the hospital acquired strains are prevalent in the community but infections with MRSA emerging in greater number even in individuals with no previous history of exposure to any health-care settings producing strains of Community acquired-MRSA presented with higher risks of disease complications and transmission.

This superbug is now reported in increased frequency in Pakistan not only in healthcare settings but reports from the community also increasing. As these epidemic strains remain endemic in the environment can result in sporadic outbreaks as previously reported in USA, Europe, Japan and Australia in 1970s.

MRSA is critically important as it is resistant to multiple existing anti-microbials and treatment is very difficult. Currently the major rising issue is clinical infections due to Methicillin resistant Staphylococcus aureus with decreased susceptibility to Vancomycin are increasing and this led to increased use of linezolid as alternative.

This growing resistance to previously sensitive anti-microbials is resulting into increase in treatment failure and complicating the management of such patients presented with multiple drug resistant infections.

Keeping in view the above facts, a research project was designed to characterise the resistant strains of Staphylococcus aureus in our hospitals and community and to identify their origin and focused on screening for new therapeutic options from indigenous medicinal plants essential oils against such evolving multidrug resistant Staphylococcus aureus.

The results of this study indicated prevalence of MRSA not only from patients but associated health care workers and first time from the healthy community in Pakistan as carriers of this superbug called MRSA.

It was observed that MRSA was most prevalent in healthy community followed by health care workers endorsing them as reservoirs and their transmission from hospitals to the community. The present study reports an overall increase in the antibiotic resistance as compared to those reported previously in Pakistan.

Currently no such studies were available synchronously on all the three sampling groups together highlighting important differences in drug resistance pattern in all three sampling groups - patients, healthcare workers and community.

Overall increased resistance was observed against many available antibiotics with almost 100 % resistant to lincomycin, tetracycline and fusidic acid. Increased resistance was also observed against Vancomycin 33.3%. Previously no linezolid resistant strains were reported but in present study overall 25.6 % isolates were resistant to Linezolid with maximum resistance shown by community isolates. All the MRSA isolates were multiple drug resistant. Many were extended drug resistant but none were pan-resistant.

Resistance to linezolid, vancomycin and teicoplanin has increased due to over prescribing and extensive utilization in both inpatient and outpatient settings. Lincomycin, fusidic acid, tetracycline, azithromycin and clindamycin absolutely should not be considered for the treatment in patients presented with postsurgical MRSA infections in the intensive care units. Tigecyclin was found to be most effective.

To establish the fact of flow of hospital acquired MRSA in the community, molecular level studies were performed. Surface proteins were isolated and analyzed. Upon protein profiling, it was observed that many polypeptides were found common among the three sampling groups. Only few were specific to just one sampling group and completely absent in the other.

An overall cluster analysis of MRSA surface proteins was performed and five clusters were identified which were showing an overall substantial association with each other explaining the fact that all these isolates were interlinked and further strengthening the fact of flow of hospital acquired MRSA in the community and vice versa.

This analysis also gave an insight in explaining the fact of horizontal transmission of infection. Further the differences in surface protein isolation from the MRSA isolates from the three sampling groups, explained the differences observed in the susceptibility patterns of various antibiotics tested.

The present study then focused on screening of indigenous medicinal plants essential oils for their bioactive molecules with anti-MRSA activity. Five medicinal plants were selected and were screened for the characterization of bioactive constituents in their essential oils and their different fractions possessing antibacterial activity against selected multiple drug resistant Staphylococcus aureus.

Among all the five essential oils tested, Carum copticum (Ajwain) essential oil was the most effective with lowest minimum inhibitory concentration values (effective dose) against multi-drug resistant Staphylococcus aureus isolates as compared to the commercially available standards (Vancomycin and Linezolid).

Upon fractionation, seven fractions were eluted. All were tested for their anti-MRSA activity and fortunately one of the fractions was even more potent than pure essential oil and the two commercial standards.

None of the previous studies are available specifically regarding such fractionation pattern of this essential oil and reporting their effective doses against multiple drug resistant Staphylococcus aureus.

Upon characterization of bioactive constituents of C. copticum essential oil the method used for analysis eluted so far the maximum number of constituents than previously reported. The solvent combination used for fractionation of essential oil allowed elution of only those constituents with high antimicrobial activity against MDR - SA.

The effective fraction contained mainly phenolic monoterpenes with monoterpene hydrocarbons which together represented a synergistic combination and enhanced antibacterial activity.

Finally the C. copticum essential oil and its effective fraction were evaluated for their toxic potential using genotoxic assays. None of the studies available previously reported toxicity of C. copticum essential oil and its effective fraction using COMMET Assay and Ames Test.

Upon toxicity studies, C. copticum essential oil and its effective fraction were found safe at many folds of MIC doses (effective doses) causing no DNA damage rather possessed additional property as strongly anti-mutagenic, i.e. resists any damage to DNA.

From this study, it is concluded that 1-Superbug-MRSA is emerging a real threat from hospitals 2-Resistance against its drugs of choice (Vancomycin and Linezolid) is increasing 3-Awjwine essential oil is a novel alternate treatment for this pathogen.

The writers belong to Department of Pharmacology and Toxicology, University of Veterinary and Animal Sciences, Lahore.