European Journal of Cardiovascular Medicine

Staphylococcus aureus  is a predominant pathogen responsible for skin and soft-tissue infections (SSI) across community and healthcare settings, with methicillin-resistant strains (MRSA) posing significant threat in nosocomial setting.(1) Mupirocin, an antibiotic derived from Pseudomonas fluorescens, is frequently used topically to manage SSI and decolonize MRSA, especially within nasal passages.(2) However, random use of mupirocin has paralleled a rise in mupirocin-resistant MRSA (MuRMRSA) strains globally, particularly among healthcare workers and patients subjected to routine mupirocin application.(3). This resistance is largely due to the mupA gene, which confers high-level mupirocin (MuH) resistance and is often plasmid-borne, enabling both clonal and horizontal spread.(4,5) Studies have identified MuRMRSA prevalences in countries: 2% in Ireland, 12.4% in New Zealand, 24% in the USA, 44.1% in Trinidad and Tobago, and 0–38.6% in India.(6,7) Given this resistance trend, the efficacy of mupirocin in decolonization is under threat, especially in healthcare settings, where MRSA carriage is prevalent.

In India, studies have shown varying mupirocin resistance levels, suggesting a substantial but incomplete understanding of regional patterns.(8) Notably, West Bengal lacks comprehensive data on high-level mupirocin resistance among methicillin-resistant Staphylococcus isolates from wound infections, both for Staphylococcus aureus and coagulase-negative Staphylococcus (CoNS). Given that MRCoNS are increasingly implicated in nosocomial infections, understanding resistance in both MRSA and MRCoNS is critical for effective infection control measures.(9) Despite its clinical importance, local studies have focused on MRSA, with MRCoNS resistance patterns relatively underexplored.(9) Addressing this knowledge gap could lead to improved decolonization strategies and antibiotic stewardship protocols, especially in high-risk hospital environments, where staphylococcal infections are common.

The primary aim of this study was to ascertain and compare the prevalence of high-level mupirocin resistance in methicillin-resistant Staphylococcus aureus  (MRSA) and methicillin-resistant coagulase-negative Staphylococcus (MRCoNS) isolated from wound infections in a tertiary care hospital in West Bengal. This study employed a cross-sectional design to analyze wound swabs and pus samples for both MRSA and MRCoNS isolates, followed by mupirocin susceptibility testing. This comparative approach will allow us to evaluate resistance trends within staphylococcal species and provide insights into the utility of mupirocin as a decolonization agent in our hospital setting. By addressing the prevalence of MuH resistance in MRSA and MRCoNS, this study sought to inform infection control strategies specific to the local healthcare context and contribute valuable data to the growing body of evidence on mupirocin resistance in India and beyond.

Study setting

This study was conducted at Burdwan Medical College, Purba Bardhaman, West Bengal, a tertiary care teaching hospital that serves a large and diverse patient population from both urban and rural areas. Located in an agriculturally prominent region, the hospital caters to numerous patients from the surrounding underserved communities, where healthcare access and infection control practices are often limited. The institution provides comprehensive inpatient and outpatient care, including wound management, and operates within a high burden setting for nosocomial infections. This geographical and clinical context allows for a robust assessment of mupirocin resistance patterns among MRSA and MRCoNS isolates, providing insights that may inform regional infection control protocols.

Study design

We conducted a hospital-based cross-sectional study at Burdwan Medical College, a tertiary-level teaching hospital in Purba Bardhaman, West Bengal.

Study population

In this study, clinical samples including pus, tissues and wound swabs, were collected from a diverse patient population, including both inpatients and outpatients, spanning various age groups and genders, across multiple medical and surgical specialties. These specimens, submitted to our department, subsequently yielded Staphylococcus species upon isolation.

Sample size

The investigation, conducted over a nine-month period, considered 653 separate patients who provided samples including pus, tissues, and wound swabs that grew Staphylococcus species.

Study procedure

In this study, detailed patient information, including duration of hospital admission, presenting symptoms and any prior hospitalizations or surgeries, was carefully recorded before sample collection. All samples including pus, tissues and wound swabs were screened for Staphylococcus aureus  and Coagulase negative Staphylococcus species and they were subjected for screening of MRSA, MRCoNS and high level mupirocin resistance.

Detection of MRSA & MRCoNS

To identify MRSA and MRCoNS, cefoxitin disc (30 µg) was utilized. Staphylococcus aureus  and coagulase-negative Staphylococcus isolates were categorized as methicillin-sensitive if they exhibited inhibition zones of 22 mm and 25 mm or larger, respectively, indicating cefoxitin susceptibility. Conversely, Staphylococcus aureus and Coagulase negative Staphylococcus isolates displaying inhibition zones measuring 21 mm and 24mm or less, respectably were deemed methicillin-resistant.(10)

Detection of High Level Mupirocin Resistance

Testing for high-level mupirocin resistance was performed by the Kirby-Bauer disc diffusion method using a 200 μg mupirocin disc. High-level mupirocin resistance was detected in the  presence of light growth within the zone of inhibition after careful examination with transmitted light. However, presence of any zone of inhibition surrounding the 200 μg mupirocin disc signified absence of high-level mupirocin resistance.(10)

Data collection

Standardized case report forms were used to document clinical information, including patient characteristics, medical background, length of hospital stay, and infection location. These forms also incorporated the laboratory findings.

Microsoft Excel was employed for data input, with a secondary researcher verifying the entered information for precision. The database incorporates automated checks to identify outliers and missing entries, thereby ensuring data completeness and consistency. Furthermore, 5% of the records underwent double-entry verification.

These methodical approaches to data gathering, entry, and validation are crucial for producing reliable and replicable results. Such rigor was essential for conducting an accurate comparative analysis between high-level mupirocin resistance in MRSA and MRCoNS strains.

Data analysis

Statistical analyses were performed using SPSS version 16 (SPSS for Windows; SPSS Inc., Chicago, IL, USA). Medians and interquartile ranges were used for continuous variables, which were compared using the Mann-Whitney U test. Categorical variables were compared using Fisher’s exact test. Statistical significance was set at p < 0.05.

Human participant protection

This research was approved by the Institutional Human Ethics Committee (IHEC) of Burdwan Medical College in West Bengal. Participants provided informed consent, and measures were taken to protect their privacy and confidentiality. The investigation strictly followed the approved protocol without any deviations.

Demographic characteristics

The demographic characteristics of patients with wound infections exhibiting high-level mupirocin resistance among the MRSA (n=7) and MRCoNS (n=5) isolates are presented in Table 1. The median age was similar between the two groups, with 28 years (range, 21–35 years) for MRSA and 26 years (range, 20–31 years) for MRCoNS. Male patients constituted the majority in both groups, representing 71.4% (5/7) of the MRSA cases and 60% (3/5) of the MRCoNS cases. Female patients accounted for 28.6% (2/7) and 40% (2/5) of the groups, respectively. No statistically significant differences were observed between the MRSA and MRCoNS groups with respect to age or sex distribution (p =1) (Table 1).

Table 1: Demographic characteristics of patients with wound infections having high level mupirocin resistance among MRSA and MRCONS isolates

Distribution of high level mupirocin resistance among Staphylococcus species isolated from wound infections

In this study, the overall prevalence of high-level mupirocin resistance (MuH) among the 130 Staphylococcus isolates was 25.3% (33/130). Among the 90 Staphylococcus aureus  isolates, 21.2% (7/33) of methicillin-resistant Staphylococcus aureus  (MRSA) and 24.6% (14/57) of methicillin-sensitive Staphylococcus aureus  (MSSA) exhibited MuH. Similarly, among the 40 coagulase-negative Staphylococcus (CoNS) isolates, MuH was identified in 33.3% (5/15) of methicillin-resistant CoNS (MRCoNS) and 28% (7/25) of methicillin-sensitive CoNS (MSCoNS) isolates.

Notably, MRCoNS demonstrated the highest prevalence of MuH at 33.3% (5/15), followed by MSCoNS at 28% (7/25). Among the S. aureus isolates, the rates of resistance were slightly lower, with MSSA having a slightly higher resistance rate than MRSA. These findings suggest a significant variability in MuH rates across different Staphylococcus species and resistance phenotypes (Table 2).

Table 2: Distribution of high-level mupirocin resistance among Staphylococcus species isolated from wound infection

The comparison of high-level mupirocin resistance between MRSA (MuHMRSA) and MRCoNS (MuHMRCONS) is summarized in Table 3. Although a higher proportion of high-level mupirocin resistance was observed in MRCoNS than in MRSA, the difference was not statistically significant (p > 0.05).

Table 3: Comparison of high-level mupirocin resistance among MRSA (MuHMRSA) & MRCONS (MuHMRCONS)

Antimicrobial susceptibilities of MuHMRSA and MuHMRCONS isolates

Table 4 presents the antimicrobial susceptibilities of MuHMRSA (n=7) and MuHMRCONS (n=5) isolates. Both the groups exhibited 100% susceptibility to vancomycin, linezolid, and teicoplanin.

For azithromycin, susceptibility was noted in 57.1% (4/7) of the MuHMRSA isolates and 80% (4/5) of the MuHMRCONS isolates. Ciprofloxacin susceptibility was lower at 28.6% (2/7) for MuHMRSA and 40% (2/5) for MuHMRCONS. Doxycycline showed high susceptibility, especially in MuHMRCONS, where all isolates (5/5) were sensitive compared to 71.4% (5/7) of MuHMRSA isolates.

Gentamicin susceptibility was greater in MuHMRSA (57.1%, 4/7) than in MuHMRCONS (20%, 1/5); however, the difference was not statistically significant (p > 0.05). Both groups showed variable susceptibility to other antibiotics such as tetracycline, clindamycin, and cotrimoxazole, with no significant differences.

Table 4: Antimicrobial susceptibilities of MuHMRSA and MuHMRCONS isolates

S1: Sensitive, R2: Resistant. 3P value: The resistance rates of antibiotics among MuHMRSA compared with those among MuHMRCONS

This study highlights significant findings regarding the prevalence of high-level mupirocin resistance (MuH) among methicillin-resistant Staphylococcus aureus  (MRSA) and methicillin-resistant coagulase-negative Staphylococcus (MRCoNS) isolated from wound infections. The results underscore the varying resistance patterns between these bacterial groups, with MRCoNS exhibiting a higher prevalence of MuH than MRSA. These observations are discussed in the context of their clinical implications, antimicrobial susceptibility profiles, and in the light of comparative insights from existing literature.

Prevalence and Demographics

Demographic analysis revealed that patients with high-level mupirocin resistance (MuH) among MRSA and MRCoNS isolates were predominantly male with no significant differences in age or sex distribution. This aligns with studies by Jayakumar et al. (2013), where male predominance was observed in staphylococcal wound infections, likely due to higher exposure to occupational hazards.(11) The median age preponderance suggested that young adults are disproportionately affected, potentially due to greater wound contamination risks.(11) The lack of statistical significance indicates that demographic characteristics alone may not influence MuH emergence, warranting the exploration of alternative contributing factors.

Distribution of high level mupirocin resistance among Staphylococcus species isolated from wound infections

We observed that high-level mupirocin resistance (MuH) was more prevalent among methicillin-resistant coagulase-negative Staphylococcus (MRCoNS) isolates than among methicillin-resistant Staphylococcus aureus  (MRSA) isolates. This aligns with previous studies reporting a higher propensity for resistance in CoNS due to their role as reservoirs for resistance genes, such as ileS-2, which confer mupirocin resistance.(12,13) For instance, a study by Oommen et al. (2010) found that MRCoNS isolates exhibited significantly higher mupirocin resistance compared to MRSA, potentially attributed to their increased genetic plasticity and frequent association with indwelling medical devices, providing selective pressure for resistance.(8)

Interestingly, despite the higher prevalence of MuH in MRCoNS patients in our study, the difference was not statistically significant. This finding contrasts with some reports, such as those by Oommen et al. (2010), which highlighted a substantial difference in the prevalence of resistance between MRCoNS and MRSA isolates. The lack of significance in our results could stem from the limited sample size or regional variations in antimicrobial use practices, warranting further investigations.

Among S. aureus isolates, we observed a slightly higher prevalence of MuH in methicillin-sensitive Staphylococcus aureus  (MSSA) than in MRSA. This was unexpected, as methicillin resistance often correlates with a broader resistance profile, as reflected in the findings of a study by Chaves et al. (2004), where MRSA isolates exhibited higher resistance rates than MSSA.(14) This discrepancy suggests that mupirocin resistance may not strictly co-evolve with methicillin resistance but could arise independently through distinct selective pressures, such as topical mupirocin overuse in outpatient settings.

Antimicrobial susceptibilities of MuHMRSA and MuHMRCONS isolates

The antimicrobial susceptibility patterns in MuH isolates revealed 100% susceptibility to vancomycin, linezolid, and teicoplanin across both the MRSA and MRCoNS groups. This concurs with global reports indicating the preserved efficacy of these antibiotics against resistant staphylococcal strains, underscoring their importance in managing severe infections.(15,16)  However, variable susceptibility to other antibiotics, such as ciprofloxacin, azithromycin, and doxycycline, reflects the ongoing challenge of evolution of resistance, particularly in the context of widespread empirical use.

An intriguing finding was the slightly higher susceptibility of MRCoNS to doxycycline compared to that of MRSA, although this finding was not statistically significant. This finding was in contrast with the findings of the study by Elsahn et al. (2010) which reported all MRSA isolates were susceptible to tetracycline, while MRCoNS isolates were not consistently sensitive to tetracycline.(17) While MRCoNS is traditionally viewed as less virulent than MRSA, its role as a pathogen in immunocompromised individuals is growing.(18–20) This differential susceptibility raises hypotheses about variations in exposure to doxycycline between MRSA and MRCoNS. Further genomic studies are required to elucidate the mechanisms underlying these observations.

The susceptibility to gentamicin was higher in MRSA than in MRCoNS, although the difference was not statistically significant. This finding also observed in the study by Elsahn et al. (2010) where it was reported that all MRSA isolates were susceptible to gentamicin, while only 65% of MRCoNS isolates were susceptible.(17) This finding warrants hypothesis generation regarding the role of aminoglycoside-modifying enzymes, which may be more prevalent in MRCoNS owing to their frequent colonization of medical devices and biofilm formation. Investigating this hypothesis through molecular studies could enhance our understanding of resistance mechanisms.

The overall prevalence of MuH (25.3%) among Staphylococcal species and (23.3%) among Staphylococcus aureus  isolates in our study population is concerning and highlights the need for stringent antimicrobial stewardship. Compared with global estimates, our findings align with regions where mupirocin is commonly used, emphasizing the role of local prescribing practices in resistance emergence. (21,22)The slightly higher MuH rates in MSSA and MSCoNS also suggest that surveillance should not be restricted to methicillin-resistant strains alone, as resistance determinants may spread horizontally among staphylococcal species.

The findings also emphasize the critical role of infection control measures in preventing the dissemination of resistant strains, particularly in resource-limited settings where therapeutic options are already constrained.(23,24) Strategies such as restricted mupirocin use, routine screening for resistance, and enhanced hand hygiene compliance are essential to mitigate the spread of resistance.

Implications of the findings

In summary, our study provides valuable insights into the prevalence and susceptibility patterns of high-level mupirocin-resistant Staphylococcus isolates in a tertiary care hospital setting. This raises critical questions regarding the dynamics of mupirocin resistance, particularly the higher prevalence of MSSA and MRCoNS. These findings should inform future research, including larger multicenter studies and molecular investigations, to unravel the mechanisms driving resistance and to guide effective interventions.

Strengths of the study

The strength of this study lies in its feasibility; it was conducted in a tertiary care hospital with diverse patient demographics and clinical presentations, offering a representative snapshot of high-level mupirocin resistance (MuH) in the region. This comparative approach, focusing on methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative Staphylococcus (MRCoNS), provides novel insights into the resistance dynamics between these clinically significant pathogens. The ethical rigor of the study is evident in adherence to institutional guidelines and ensuring patient confidentiality. Its relevance is underscored by the escalating global threat of antimicrobial resistance and the critical role of mupirocin in decolonization strategies, making these findings highly pertinent to clinical practice and infection control policies.

Limitations of the study

However, this study has certain limitations. The relatively small sample size, particularly for MRCoNS isolates, may limit the generalizability of the findings. Additionally, the cross-sectional design precludes conclusions regarding temporal trends or causality. Another limitation is the lack of molecular characterization of resistance mechanisms, such as the presence of ileS-2 or other genetic determinants, which would provide deeper mechanistic insights. These limitations may affect the robustness of the conclusions and highlight areas for further exploration.

Therefore, future studies should focus on larger multicenter cohorts to validate these findings and to provide a broader epidemiological perspective. Longitudinal designs could elucidate the trends in MuH prevalence and resistance dynamics over time. Molecular studies, including whole-genome sequencing, would be invaluable for identifying the genetic mechanisms underlying resistance and exploring their potential transmissibility between staphylococcal species. These efforts would enhance our understanding of mupirocin resistance and inform more effective strategies for antimicrobial stewardship and infection control.

This study highlights the concerning prevalence of high-level mupirocin resistance (MuH) in methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative Staphylococcus (MRCoNS) isolates from wound infections. These findings underscore the need for judicious mupirocin use and robust antimicrobial stewardship to mitigate resistance emergence, aligning with the study objectives of understanding resistance patterns and informing infection-control strategies. Routine surveillance, molecular studies to identify resistance mechanisms, and strict antimicrobial stewardship programs are essential to address high-level mupirocin resistance. Future research should evaluate intervention strategies such as optimized mupirocin usage policies and alternative decolonization agents to mitigate resistance and improve infection control in tertiary care settings.

Conflicts of Interest

The authors declare no conflicts of interest.

Acknowledgement

I express my heartfelt thanks and gratitude to the administration, faculty members, and staff of the Department of Microbiology, Burdwan Medical College and Hospital, for allowing me to conduct the study.

Funding

Funding: This study was supported by the authors.

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