New insights: mupirocin resistance among methicillin-resistant Staphylococcus aureus (MRSA) infection in southern Indian region

Introduction

Staphylococcus aureus is a well-known ubiquitous microorganism that able to colonize the anterior nares and skin surface, normally cause no infection in healthy individuals. Still, if invades the systemic circulation, can cause various serious infections. Currently antibiotic therapy remains difficult because of the circulation of multi-drug resistant methicillin-resistant Staphylococcus aureus (MRSA) strains. MRSA has been recognized as a major mode of origin of multi-drug resistant among nosocomial pathogens, causing high risk infections in patients.^[1]

Decades after, Staphylococcus aureus remains to be a notoriously dangerous organism against human individuals. The rate of community-acquired as well hospital-acquired staphylococcal infection has increased drastically, with negligible impact on overall mortality.^[2] The success of S. aureus as a human pathogen with its ability to impact with wide range of implications as a result of dominant virulence factors and toxins. The increased resistance of this S. aureus to broad-spectrum antimicrobial agents, addition as a prevalent nosocomial pathogen is of great threat for global health sector. The resistant phenotypes mostly associated with the persistence of S. aureus in the hospitals leads to the emergence of resistant strains against methicillin.^[1], ^[3]

Studies pertaining to Indian set up including present study reveals all the MRSA isolates found to be sensitive to vancomycin. But, antibiotics such as Cotrimoxazole, Erythromycin, Gentamicin, Penicillin and Cephalosporin found to be resistant, correlating to the present study.^[4], ^[5], ^[6] In late nineteen century wide range antibiotics were effective in treating bacterial infections. But the emancipation of the clinical strains resistance toward broad antibiotics and emergence of bacterial population with rise in antimicrobial resistance is possible due to various factor such irrational use of antimicrobials and drugs usage in animal feed as an enhancers.^[7], ^[8] At present, resistance is firmly established towards penicillin for the most clinical S. aureus isolates. Resistance against Beta-lactam antibiotics such as methicillin and penicillin causing MRSA infections too difficult to treat. MRSA strains related to hospital infection predominantly is of multi-drug resistant, causing reserved drug to be the only final option.^[9]

A promising action plan taken into consideration to avert hospital related staphylococcal infections by using mupirocin, a decolonizing regime.^[10] With an urgent need to curb MRSA infection, there is a possibility with increased use of mupirocin against MRSA infection as nasal decolonization regime. To determine the usage of mupirocin as a decolonization regime in clinical setting, there is a need to commiserate the clinical significance, pathogenesis, and epidemiology of resistance towards mupirocin, this may be a leaping step for the controlling emergence of MRSA strains.^[9], ^[10] The increased irrational use of some antibiotics added with the endemic outbreaks because of the presence of resistant MRSA strains (low level and high level) causing the emergence of resistance against mupirocin. However, the spread of low-level resistance is becoming significant and it is less possibly has major impact on clinical practice.^[10] Implementations are formulated in order restrict the rise in mupirocin resistance in MRSA strains should express the vitality of monitored use of mupirocin in clinical practice. The goal of the present study is to understand the susceptibility and resistance pattern among the clinical isolates of MRSA strains to mupirocin and to ascertain the minimum inhibitory concentration (MIC) against MRSA strains using E-strips.

Materials and Methods

Results

Out of 65 MRSA strains shown drastic variability in a distribution of the staphylococcal infection as per site, ward and type of sample collected ([Table 1]).

Antimicrobial susceptibility showed the MIC value of 0.5μg/ml to vancomycin of all 65 samples as per CLSI guidelines, which is considered to be sensitive. Linezolid 2μg/ml was sensitive to all MRSA isolates. Antimicrobial agents such as gentamycin, erythromycin as well as clindamycin reported to be sensitive against MRSA isolates. The resistance towards mupirocin determined by Kirby Bauer’s disc diffusion test using mupirocin disc (5 μg/ml), zone of inhibition observed in all the MRSA isolates except five (8%) samples and remaining other sixty (92%) samples shown sensitivity zone with more than 18mm ([Table 2]). The MIC determined by using mupirocin E-strip on Muller Hinton agar. All isolates found to have MIC of < 4 μg/ml, 23 isolates between 0.05 μg/ml and 0.19 μg/ml, 12 isolates MIC ranged between 0.125 μg/ml and 0.640 μg/ml. However, five MRSA isolates not found to be present with any zone against mupirocin E-strip (0.0064 - 1024 μg/ml). ([Table 2])

Present study report that the majority of the MRSA isolates coincide with surgical ward followed by geriatric ward. The clinical history revealed that the majority of the MRSA isolates were obtained from the individuals with Diabetes Mellitus, breast abscess and Sepsis. All the five mupirocin resistant strain were isolated from the pus sample.

Discussion

In present study out of 65 MRSA isolates five were resistant to mupirocin. The antibiotic resistance pattern among these five samples correlated with emergence of resistance for mupirocin in S aureus isolates detected in various parts of world. This brings to grave concerns towards antibiotic therapy, as the most effective drugs are at the brink of development of resistance. In present work 92% of bacteria were sensitive to mupirocin, which is a helpful finding. However, various studies shows the evident interrelation between development of low rate of mupirocin resistance and reduced usage.^[11]

One study revealed that 5µg mupirocin discs resistant towards all MRSA isolates (n=25). MIC breakpoint range suggest heterogeneous variability towards methicillin resistance. The mupirocin low level resistance using 5µg discs in MRSA isolates present with no clinical relevance. This pattern of resistance is drastically at rise in United Kingdom and south East Asia. A Study with a duration of 10 year at SJMCH laboratory, revealed that the resistance towards mupirocin is of 8.3% to 10% when 5µg mupirocin disc was used against MRSA isolates.^[12]

Another study carried out for a period of three months in a tertiary care hospital to detect the occurrence of high level and low level mupirocin resistance (MuL) among staphylococcus isolates, in which 5 µg and 200 µg mupirocin discs were used by means of agar dilution method. The rate of high level mupirocin resistance (MuH) detected to be 2% among MRSA and 28% methicillin resistance CONS species. The suggested strains with low level resistance mupirocin can be effectively treated with use of mupirocin, however the high level resistance towards mupirocin need to eradicate with other treatments.^[13] The utilization of topical application of mupirocin, the elimination of MRSA strains in healthcare workers studied earlier. Additionally, some previous studies carried out previously in which decimation of MRSA infection in 25% patients by using mupirocin was evident and 18% of them treated with placebo amalgamated with chlorohexidine baths. This study revealed that application of mupirocin intra nasally is effective in expunging of MRSA infection among patients.^[14]

Present study accord with one of the study carried out in India which shows similar results of mupirocin resistance among 5% isolates in which three found to be high level mupirocin resistant isolates and two strains found to be low level resistance strains. But the present work discloses the complete resistant among five MRSA isolates possibly because of point mutation in ileS genes.^[15]

In present study 92% of isolates were sensitive to mupirocin which still gives hope that mupirocin is promising in elimination of MRSA strains. MRSA predominantly found in individuals with diabetes and breast abscess. Hence, extermination of such strains is essential added with preventive and control measures among such individuals.

Conclusions

Present work revealed that the use of 5µg mupirocin disc economical as compared to mupirocin E-strips. Mupirocin discs can be used in low resourceful clinical set up. However, present study gives evidence of no difference in sensitivity for the both E-strip and disc method.

Sources of Funding

None.

Conflict of Interest

None.