European Journal of Cardiovascular Medicine

Staphylococcus aureus, a major cause of skin and soft-tissue infections (SSTIs), poses substantial challenges in both community and healthcare settings due to its association with high morbidity and, at times, severe complications.(1,2) Among the primary topical treatments for superficial skin infections, mupirocin, a naturally derived antibiotic from Pseudomonas fluorescens, has proven efficacious since its introduction in the 1980s.(3) Mupirocin has been widely used in formulations for impetigo, wound infections, and the nasal eradication of methicillin-resistant Staphylococcus aureus  (MRSA) among healthcare personnel and patients and often indiscriminate use of mupirocin has led to a concerning rise in resistance, particularly high-level mupirocin resistance (MuH), which complicates treatment protocols and reduces therapeutic options .(4–7)

Globally, mupA gene been documented in various regions, with reported prevalence rates indicating geographical variability—ranging from as low as 2% in Ireland to as high as 44.1% in Trinidad and Tobago, underscoring the need for region-specific surveillance.(8,9) In India, mupirocin resistance Staphylococcus aureus  isolates vary significantly across states, with local studies revealing a prevalence rate between 2% to 16.6%, suggesting disparities that may stem from differences in prescribing practices and infection control measures.(10–12) The mechanism of resistance primarily involves mutations in the native ileS gene, leading to low-level mupirocin resistance (MuL), and plasmid-borne mupA genes for high-level resistance, which can be clonally and horizontally disseminated, thereby facilitating resistance transfer within and between healthcare facilities. (13–17)

The issue of mupirocin resistance is increasingly relevant, implications for infection control and the potential for failed decolonization protocols.(7) High-level mupirocin resistance (MuH) is particularly problematic, as it is associated with limited success in eradicating S. aureus colonization, which is essential for preventing the spread of MRSA in healthcare environments. Moreover, as mupirocin resistance correlates with resistance to clindamycin, tetracycline, and erythromycin, it poses further challenges for clinicians in managing multidrug-resistant infections.(18–20) Locally, mupirocin has been extensively used for the empirical treatment of skin infections at our tertiary care hospital. However, data on the prevalence and resistance patterns of S. aureus strains remain limited, creating an essential knowledge gap in our understanding of the burden of resistance and its impact on patient outcomes.

Hence, this study aimed to determine the prevalence of high-level mupirocin resistance among Staphylococcus aureus  isolates from wound infections in a tertiary care hospital in West Bengal. By focusing on MuH among S. aureus, this study sought to establish baseline data that can inform infection control practices and guide empirical treatment decisions. Data from this study will contribute to actionable insights into local and regional antimicrobial resistance for clinicians and policymakers aiming to optimize mupirocin use and effectively manage the spread of resistant S. aureus strains. Through this investigation, we aimed to bridge the current knowledge gap on mupirocin resistance, offering data-driven recommendations for mupirocin stewardship and enhancing infection control strategies within the healthcare setting.

Study setting

This study was conducted at Burdwan Medical College and Hospital, a tertiary care teaching hospital in Purba Bardhaman, West Bengal. The hospital serves as a referral center for rural and urban populations across several districts of southern Bengal, catering to diverse demographics with varying healthcare access. It provides comprehensive healthcare services, including specialized surgical and wound care management, making it an ideal setting for investigating Staphylococcus aureus  wound infections. The region's high burden of antimicrobial resistance, compounded by widespread mupirocin use, underscores the importance of this study in providing region-specific resistance data.

Study design

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

Study population

In this study, clinical specimens such as pus, tissues, and wound swabs were obtained from a diverse group of patients, encompassing both inpatients and outpatients across various age groups and sexes, representing a wide range of medical and surgical specialties. These samples were submitted to our department and processed, and samples that contained Staphylococcus species were included.

Sample size

The study, spanning nine months, examined 653 individual patients who submitted various samples, including pus, tissues, and wound swabs, which yielded Staphylococcus species upon cultivation.

Study procedure

This research involved meticulous documentation of comprehensive patient data, including length of hospitalization, initial symptoms, and any previous hospital stay or operation, prior to obtaining samples. All the collected specimens, including pus, tissue samples, and wound swabs, were examined for the presence of Staphylococcus aureus. These samples were subsequently evaluated for methicillin-resistant Staphylococcus aureus  (MRSA) and high-level mupirocin resistance (MuH).

Detection of MRSA

For the detection of MRSA, a 30 µg cefoxitin disc was used. Staphylococcus aureus  strains were classified as methicillin-sensitive when they showed inhibition zones of 22 mm or greater, demonstrating susceptibility to cefoxitin. In contrast, Staphylococcus aureus  isolates with inhibition zones measuring 21 mm or smaller were considered methicillin-resistant.(21)

Detection of High Level Mupirocin Resistance

The Kirby-Bauer disc diffusion technique was employed to assess high-level mupirocin resistance using a disc containing 200 μg mupirocin. The presence of high-level mupirocin resistance was identified by observing slight growth within the inhibition zone when carefully examined under transmitted light. Conversely, the absence of high-level mupirocin resistance was indicated by the presence of any inhibition zone around the 200 μg mupirocin disc.(21)

Data collection

This study employed a systematic approach for data collection, entry, and validation to assess the prevalence of high-level mupirocin resistance among Staphylococcus aureus  isolates from wound infections in a tertiary care hospital in West Bengal.

Clinical specimens including pus, wound swabs, and tissue samples were collected from both inpatient and outpatient departments across diverse medical and surgical specialties. Standard aseptic techniques were followed during specimen collection to minimize contamination. The specimens were promptly transported to the microbiology laboratory under the appropriate conditions to maintain their integrity. S. aureus was isolated and identified using conventional microbiological methods, including Gram staining, colony morphology on basal and selective media, and biochemical tests, including catalase and coagulase tests. High-level mupirocin resistance was determined using the Kirby-Bauer disc diffusion method with mupirocin discs (200 µg) according to CLSI guidelines.

Laboratory results, including patient demographics, clinical diagnosis, specimen type, and antibiotic susceptibility patterns, were documented using a structured data-collection sheet. The data were then entered into a secure password-protected electronic database using Microsoft Excel. A unique identifier code was assigned to each specimen to ensure its anonymity and traceability.

Rigorous validation procedures were performed to ensure data accuracy and reliability. Random cross-checks were conducted by a second researcher to verify the consistency between the laboratory records and electronic database. Discrepancies were resolved through reevaluation of the original laboratory documentation. Statistical outliers were identified and reassessed to confirm authenticity. All data analyses were conducted only after completing these validation steps to ensure high-quality data for the accurate interpretation of the results.

Data analysis

The collected data were analyzed using SPSS version 16 (SPSS for Windows; SPSS Inc., Chicago, IL, USA). Descriptive statistics were used to summarize the prevalence rates, with categorical variables expressed as frequencies and percentages. 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. The prevalence of high-level mupirocin resistance (MuH) among Staphylococcus aureus  isolates was calculated. Statistical significance was set at p < 0.05.

Human participant protection

This study was conducted in accordance with ethical guidelines and was approved by the Institutional Human Ethics Committee (IHEC) of Burdwan Medical College and Hospital. Written informed consent was obtained from all participants. Patient confidentiality was maintained strictly. The investigation strictly followed the approved protocol without any deviations.

Demographic characteristics

Among the 21 patients with wound infections caused by Staphylococcus aureus isolates exhibiting high-level mupirocin resistance (MuH SA), the median age was 31 years (range: 22–36). The majority of patients were male (13/21, 61.9%), and 38.1% (8/21) were female. This demographic pattern highlights the predominance of younger males affected by MuH-SA-associated wound infections. (Table 1)

Table 1: Demographic characteristics of patients with wound infections having high level mupirocin resistance among Staphylococcus aureus  isolates(MuH SA)

Distribution of high level mupirocin resistance among Staphylococcus aureus  isolates obtained from wound infections

Among the 90 Staphylococcus aureus  isolates obtained from wound infections, 21 (23.3%) exhibited high-level mupirocin resistance (MuH SA). Of these, 7 of 33 methicillin-resistant Staphylococcus aureus  (MRSA) isolates (21.2%) and 14 of 57 methicillin-susceptible Staphylococcus aureus  (MSSA) isolates (24.6%) showed MuH SA. The prevalence of MuH was slightly higher in MSSA compared to MRSA, but the difference was not statistically significant (p = 0.7173).(Table 2)

Table 2: Distribution of high level mupirocin resistance among Staphylococcus aureus  isolates obtained from wound infections

Antimicrobial susceptibilities of MuHMRSA and MuHMSSA isolates

The antimicrobial susceptibility patterns of the MuHMRSA (n=7) and MuHMSSA (n=14) isolates showed notable variations. All the isolates were uniformly susceptible to vancomycin, linezolid, and teicoplanin. Among the fluoroquinolones, ciprofloxacin resistance was higher in MuHMRSA (5/7, 71.4%) than in MuHMSSA (8/14, 57.1%). Clindamycin resistance was more frequent in MuHMRSA (3/7, 42.9%) than MuHMSSA (2/14, 14.3%). Trimethoprim-sulfamethoxazole (TMP/SMX) resistance was higher in MuHMRSA (5/7, 71.4%) than in MuHMSSA (4/14, 28.6%). Resistance to aminoglycosides such as gentamicin and netilmicin was higher in MuHMRSA (3/7, 42.9% and 5/7, 71.4%, respectively) than in MuHMSSA (5/14, 35.7% and 6/14, 42.9%, respectively). Tetracycline resistance was identical in both groups (MuHMRSA: 1/7, 14.3%; MuHMSSA: 2/14, 14.3%).(Table 3)

Table 3: Antimicrobial susceptibilities of MuHMRSA and MuHMSSA isolates

S^1: Sensitive, R²: Resistant. ³P value: The resistance rates of antibiotics among MuHMRSA compared with those among MuHMSSA

Antimicrobial susceptibilities of MuH SA and MRSA isolates

 The antimicrobial susceptibility patterns of high-level mupirocin-resistant Staphylococcus aureus  (MuH SA) and methicillin-resistant Staphylococcus aureus  (MRSA) isolates revealed notable variations. Among the 21 MuH SA isolates, resistance was the highest for levofloxacin (14/21, 66.6%), netilmicin (13/21, 61.9%), and azithromycin (13/21, 61.9%). Ciprofloxacin resistance was observed in 9/21 (42.9%) isolates, whereas 12/21 (57.1%) showed resistance to trimethoprim-sulfamethoxazole (TMP/SMX). Among the 33 MRSA isolates, the highest resistance was observed against ceftriaxone (29/33, 87.9%), followed by levofloxacin (22/33, 66.6%) and gentamicin (24/33, 72.7%). A statistically significant difference was observed in susceptibility to doxycycline (p = 0.03), where 10/21 (47.6%) MuH SA isolates were susceptible compared with 25/33 (75.8%) MRSA isolates. Similarly, ceftriaxone resistance was significantly higher in the MRSA group (p = 0.010). All isolates of both MuH SA and MRSA were susceptible to vancomycin, linezolid, and teicoplanin, reinforcing their potential as effective treatment options. (Table 4)

Table 4: Antimicrobial susceptibilities of MuH SA and MRSA isolates

S^1: Sensitive, R²: Resistant. ³P value: The resistance rates of antibiotics among MuH SA compared with those among MRSA

The present study highlights the substantial prevalence of high-level mupirocin-resistant Staphylococcus aureus (MuH SA) in wound infections. The findings highlight the distinct resistance patterns observed between these bacterial groups, with MSSA showing a higher incidence of MuH than MRSA, although this difference was not statistically significant. An analysis of these observations is presented, considering their clinical relevance, profiles of antimicrobial susceptibility, and comparative insights drawn from current scientific literature.

Prevalence and Demographics

The demographic characteristics of patients with high-level mupirocin-resistant Staphylococcus aureus (MuH SA) infections in our study revealed a predominance of younger males, consistent with reports from other studies.(10) This trend may be attributed to increased exposure to wound-prone environments and differential healthcare-seeking behavior. The median age of affected patients aligns with findings from South Indian cohorts, emphasizing the role of occupational risks.(22) The absence of significant sex-based differences in resistance patterns warrants further investigation into potential genetic or behavioral factors contributing to MuH SA acquisition and persistence.

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

The distribution of high-level mupirocin resistance (MuH) among Staphylococcus aureus isolates revealed a slightly higher prevalence in methicillin-susceptible strains (MSSA) than in methicillin-resistant strains (MRSA), although the difference was not statistically significant. However, several studies have reported a higher prevalence of mupirocin resistance in MRSA than in MSSA. For instance, Chaves et al. (2004) reported that 14.8% of MRSA isolates exhibited mupirocin resistance, compared to only 0.6% of MSSA isolates.(23) Similarly, González-Domínguez et al. (2016) found a high proportion (27.2%) of high-level mupirocin-resistant MRSA isolates in their study. (24) This disparity in our study could result from excessive mupirocin use in outpatient settings, where MSSA is more common. Unexpectedly, the lower resistance of MRSA may indicate selective pressure favoring alternative resistance pathways, warranting molecular studies to explore the genetic determinants of MuH evolution.

Antimicrobial susceptibilities of MuHMRSA and MuHMSSA isolates

The antimicrobial susceptibility patterns of high-level mupirocin-resistant Staphylococcus aureus (MuH SA) isolates showed notable variations between methicillin-resistant (MuHMRSA) and methicillin-susceptible (MuHMSSA) Staphylococcus aureus strains. Ciprofloxacin resistance was notably higher in MuHMRSA (71.4%) than in MuHMSSA (57.1%), consistent with prior studies indicating fluoroquinolone resistance as a common trait in MRSA due to mutations in DNA gyrase and topoisomerase IV.(25–27) Clindamycin resistance was also more frequent in MuHMRSA (42.9%) than in MuHMSSA (14.3%), suggesting a possible linkage between methicillin resistance and inducible macrolide-lincosamide-streptogramin B (iMLSB) resistance mechanisms.(28)

Trimethoprim-sulfamethoxazole (TMP/SMX) resistance was significantly higher in MuHMRSA (71.4%) than in MuHMSSA (28.6%), reflecting findings from global surveillance reports highlighting increased resistance to this drug combination among MRSA isolates due to dihydrofolate reductase mutations.(29) Aminoglycoside resistance, particularly to netilmicin (71.4% in MuHMRSA vs. 42.9% in MuHMSSA), aligns with previous studies demonstrating aminoglycoside-modifying enzymes as a key resistance mechanism in MRSA strains.(30)

Interestingly, tetracycline resistance was identical between MuHMRSA (14.3%) and MuHMSSA (14.3%), an unexpected finding that suggests the possible absence of widespread tetracycline resistance genes in these isolates, warranting further molecular investigations.(31) Encouragingly, all isolates remained susceptible to vancomycin, linezolid, and teicoplanin, reinforcing their role as effective treatment options. This study underscores the urgent need for continued antimicrobial stewardship and molecular characterization of resistance determinants to inform treatment guidelines and infection control policies.

Antimicrobial susceptibilities of MuHSA and MRSA isolates

The antimicrobial susceptibility patterns of high-level mupirocin-resistant Staphylococcus aureus (MuH SA) and methicillin-resistant Staphylococcus aureus (MRSA) isolates demonstrated significant resistance to multiple antibiotics. Among MuH SA isolates, the highest resistance was observed against levofloxacin (66.6%), netilmicin (61.9%), and azithromycin (61.9%). These findings align with studies from abroad reporting high fluoroquinolone resistance in S. aureus due to efflux mechanisms and target site mutations.(32,33) Similarly, high azithromycin resistance suggests widespread macrolide resistance genes, such as ermC and msrA, in these isolates.(34)

Among the MRSA isolates, resistance was notably high against levofloxacin (66.6%) and gentamicin (72.7%). The significantly higher ceftriaxone resistance in MRSA compared to MuH SA (p = 0.01) aligns with prior findings linking methicillin resistance to enhanced β-lactam resistance via PBP2a-mediated mechanisms.(35,36) Furthermore, the lower susceptibility of MRSA to gentamicin compared to MuH SA (p > 0.05) is consistent with previous reports linking aminoglycoside-modifying enzymes to gentamicin resistance in MRSA strains.(37)

Interestingly, MRSA isolates exhibited higher susceptibility to doxycycline (75.8%) than to MuH SA (47.6%, p = 0.03). Liu et al. (2009) mentioned that mupirocin resistance is mediated by plasmids carrying the mupA gene, which is distinct from the mechanisms of tetracycline resistance. This could potentially explain why mupirocin resistance doesn't necessarily correlate with increased resistance to other antibiotics like doxycycline.(38)

Despite widespread resistance, all isolates remained susceptible to vancomycin, linezolid, and teicoplanin, reinforcing their critical role in last-line therapy. However, the emergence of MuH SA with multidrug resistance highlights the need for continuous surveillance and judicious antibiotic use to mitigate further resistance development.

Implications of the findings

The findings of this study highlight the growing challenge of mupirocin resistance among S. aureus isolates from wound infections. Despite high resistance to multiple antibiotic classes, all MuH SA and MRSA isolates remained susceptible to vancomycin, linezolid, and teicoplanin. These findings reinforce the continued efficacy of glycopeptides and oxazolidinones for treating mupirocin-resistant S. aureus infections. However, reliance on these last-resort antibiotics raises concerns about the potential emergence of resistance in the future. This establishes the need for stringent antibiotic stewardship programs, targeted infection control measures, and further research to elucidate genetic mechanisms underlying high-level mupirocin resistance.

Strengths of the study

This study provides significant insights into the prevalence of high-level mupirocin resistance (MuH) among Staphylococcus aureus isolates from wound infections in a tertiary care hospital in West Bengal. One of the key strengths of this study is its feasibility, as it was conducted in a high-burden setting, ensuring robust data collection and generalizability within similar hospital environments. Furthermore, the novelty of this study is evident in its focus on a relatively underexplored aspect of antimicrobial resistance, particularly in India, where mupirocin resistance among S. aureus remains an emerging concern. This study was conducted in accordance with standard microbiological and ethical guidelines, ensuring patient anonymity and minimizing the risks associated with antimicrobial resistance research. Its relevance is underscored by the increasing global concern regarding mupirocin resistance, particularly in hospital settings where Staphylococcus aureus is a major pathogen associated with nosocomial infections. These findings have direct clinical implications, as they provide valuable data for revising empirical treatment strategies and implementing effective antimicrobial stewardship programs.

Limitations of the study

However, the limitations of this study must be acknowledged. This study was conducted in a single tertiary care hospital, which may limit the broader applicability of the findings to other geographical regions. Additionally, molecular characterization of the resistance genes was not performed, which could have provided a deeper understanding of the underlying genetic mechanisms driving MuH. Furthermore, patient-related factors, such as comorbidities and prior antibiotic exposure, which may influence resistance patterns, have not been extensively analyzed.

To address these limitations, future research should focus on multi-centre studies to enhance generalizability. Additionally, molecular studies should be conducted to identify specific resistance determinants, aiding targeted interventions. A prospective cohort approach incorporating patient history and antibiotic usage patterns would further strengthen our understanding of the MuH dynamics. These efforts will contribute to more effective infection control measures and antibiotic policies in the healthcare setting.

This study highlights a concerning prevalence (23.3%) of high-level mupirocin resistance (MuH) among Staphylococcus aureus isolates from wound infections in a tertiary care hospital in West Bengal. Resistance was observed in both MRSA and MSSA strains, necessitating vigilant antimicrobial stewardship. Continued surveillance and molecular characterization of resistance mechanisms are essential for developing effective infection control strategies. Routine surveillance and antimicrobial stewardship programs must be strengthened to mitigate high-level mupirocin resistance in S. aureus. Future studies should focus on the molecular characterization of resistance mechanisms. Regular monitoring of mupirocin usage and the efficacy of infection control measures should be implemented to evaluate intervention effectiveness and curb further development of resistance.

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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