European Journal of Cardiovascular Medicine

Staphylococcus aureus (S. aureus) is one of the most common pathogens affecting human health. It has shown remarkable adaptability, acquiring resistance to multiple antibiotics, making it a primary cause of both hospital-acquired and community-associated infections.(1) These infections range from minor skin conditions to severe, potentially fatal conditions such as septicemia and endocarditis.(2)Methicillin-resistant S. aureus (MRSA) was first identified in 1961, only a year after methicillin's introduction, and has since become one of the most critical nosocomial pathogens worldwide, especially over the past two decades.(3)

MRSA is now endemic to India, with healthcare and community settings experiencing outbreaks. However, the prevalence of MRSA varies geographically, with reports from India indicating an incidence ranging from 25% in the western regions to approximately 50% in the southern regions, illustrating significant regional variability.(4) Infections by these superbugs have serious implications because of limited treatment options and increased healthcare costs. They pose a substantial challenge not only because of its methicillin resistance but also due to cross-resistance to several commonly used antibiotics, necessitating reliance on more expensive drugs like vancomycin, linezolid, and teicoplanin.(5) Additionally, there are emerging reports of vancomycin resistance in MRSA, which further limits therapeutic options.(6) The high incidence of MRSA in Indian healthcare facilities necessitates ongoing surveillance and analysis to inform effective antimicrobial policies and control measures.

On the other hand, methicillin-resistant coagulase resistant Staphylococcus (MRCoNS) have become a predominant pathogen in hospitalized patients, with infections caused by these organisms increasing dramatically resulting in significant morbidity and mortality rates. The increasing resistance of MRCoNS to multiple antibiotics complicates treatment options and necessitates regular surveillance and monitoring of antibiotic sensitivity patterns.(7,8)

In West Bengal, MRSA surveillance data are relatively sparse, particularly concerning methicillin-resistant coagulase-negative staphylococci (MRCoNS), which have also been reported as significant nosocomial pathogens. While numerous studies have focused on MRSA, few have included MRCoNS, which play a crucial role in healthcare-associated infections due to their antimicrobial resistance patterns. Identifying the local prevalence and susceptibility patterns is essential for addressing regional gaps in knowledge and providing data that can aid in developing targeted antimicrobial stewardship practices.

This study aimed to compare the prevalence and antimicrobial susceptibility profiles of MRSA and MRCoNS in a tertiary care hospital in West Bengal. By analyzing clinical isolates, this study seeks to enhance our understanding of the epidemiology and resistance profiles of these pathogens in a regional context.

Study setting

This study was conducted at Burdwan Medical College, a tertiary care hospital located in Purba Bardhaman, West Bengal. Serving a population from both urban and rural backgrounds, the institution provides critical healthcare services to diverse patient populations, facilitating extensive interactions between healthcare-associated and community-acquired infections. The regional context is marked by variations in antimicrobial resistance, particularly among methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative staphylococci (MRCoNS), due to high antimicrobial use. Given the high patient influx and extensive use of antimicrobial therapies, Burdwan Medical College presents an optimal setting to assess the prevalence and antimicrobial resistance patterns of MRSA and MRCoNS. This context provides valuable insights into regional antimicrobial resistance trends, aiding in the formulation of localized infection control and treatment protocols.

Study design

This was a hospital-based, cross-sectional study.

Study population

The study included both hospitalized and ambulatory patients who provided clinical samples to our department at Burdwan Medical College and Hospital. These patients were from various medical and surgical units, encompassing all age groups and sexes. The samples were those from which Staphylococcus aureus was isolated.

Sample size

The research, spanning a nine-month duration, included 694 distinct Staphylococcus aureus isolates.

Study procedure

This investigation involved the meticulous documentation of patient data prior to specimen collection. The Kirby-Bauer disk diffusion technique was used to assess the antimicrobial susceptibility of all Staphylococcus aureus clinical isolates. The antibiotics tested included using azithromycin (10 μg), ciprofloxacin (5 μg), levofloxacin (300 μg), clindamycin (2 µg), cotrimoxazole (25 μg ), doxycycline (30 μg ) amikacin (30 µg), netilmicin (30  μg), gentamicin (10 μg), ceftriaxone (10 μg) vancomycin (30 µg), linezolid (30 µg), teicoplanin (30 µg), amoxicillin clavulanic acid (20/10 μg), and nitrofurantoin (300 µg).(10)

Detection of MRSA & MRCoNS

Cefoxitin discs (30 µg) were used to identify MRSA and MRCoNS. 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)

Data collection

Standardized case report forms were used to document clinical information, including patient demographics and laboratory results.

Microsoft Excel was employed for data entry, with a second researcher verifying the accuracy of the entered information.

To ensure data quality, the database incorporates automated checks to identify outliers and missing entries, thereby promoting completeness and consistency. Furthermore, 5% of the records underwent double-entry verifications.

These methodological approaches to data collection, input, and validation were crucial for generating reliable and replicable results, which were essential for conducting an accurate comparative analysis between MRSA and MRCoNS isolates.

Data analysis

Demographic characteristics and symptom profiles were summarized as frequencies and percentages. All statistical analyses were performed using the SPSS software (version 16.0; SPSS Inc., USA). The antimicrobial susceptibilities of MRSA and MRCoNS strains were compared using the chi-square test. Statistical significance was set at p < 0.05.

Human participant protection

This study was approved by the Institutional Human Ethics Committee (IHEC) at Burdwan Medical College, West Bengal. All participants provided informed consent and their privacy and confidentiality were safeguarded. The investigation was conducted in strict compliance with the approved protocol, without any deviations.

Demographic characteristics

A total of 317 isolates were analyzed, comprising 261 methicillin-resistant Staphylococcus aureus (MRSA) isolates and 56 methicillin-resistant coagulase-negative Staphylococcus (MRCoNS) isolates. The median age of the patients was similar between the two groups: 46 years (range: 19–75 years) for MRSA and 42 years (range: 20–72 years) for MRCoNS (p = 0.82). Regarding sex distribution, male patients constituted 153/261 (58.6%) of MRSA cases and 37/56 (66.1%) of MRCoNS cases (p = 0.367). Female patients accounted for 108/261 (41.4%) patients in the MRSA group and 19/56 (33.9%) patients in the MRCoNS group (Table 1).

Table 1: Demographic characteristics of patients having MRSA and MRCONS isolates

Distribution of MRSA and MRCoNS according to different collected clinical samples

A total of 261 MRSA and 56 MRCoNS isolates were analyzed from various clinical samples. Among the MRSA isolates, the most common sample was pus (64/261; 24.5%), followed by urine (55/261; 21.1%) and wound swabs (53/261; 20.3%). Similarly, in MRCoNS, pus was the leading sample source (12/56; 21.4%), followed by urine (10/56; 17.9%) and wound swabs (8/56; 14.3%).

Blood samples contributed to 25/261 (9.6%) of MRSA and 3/56 (5.4%) of MRCoNS isolates. Sputum accounted for 6/261 (2.3%) MRSA cases and 3/56 (5.4%) MRCoNS cases. Tracheal aspirates were uncommon in both groups, representing 4/261 (1.53%) MRSA and 2/56 (3.6%) MRCoNS isolates, respectively.

Interestingly, other sample types collectively accounted for 54/261 (20.7%) of MRSA and a notably higher proportion of 18/56 (32.1%) of MRCoNS isolates, although the difference was not statistically significant (p = 0.06) (Table 2).

Table 2: Distribution of MRSA and MRCoNS according to different collected clinical samples

Antimicrobial susceptibilities of MRSA and MRCoNS isolates

Among 261 MRSA isolates, vancomycin and linezolid showed excellent efficacy, with 100% and 99% susceptibility, respectively (259/261 for linezolid). Similarly, all 56 MRCoNS isolates were sensitive to vancomycin and 98% (55/56) were sensitive to linezolid.

Clindamycin was effective against 162/261 (62%) MRSA isolates and showed even better activity against MRCoNS, with 45/56 (80%) being sensitive (p < 0.05). Ciprofloxacin susceptibility was significantly lower in MRCoNS (18/56; 32%) than in MRSA (155/261; 59.3%) (p < 0.05).

Nitrofurantoin displayed better activity against MRSA, with a susceptibility of 47% (123/261) compared to 29% (16/56) for MRCoNS (p < 0.05).

Amikacin and tetracycline demonstrated higher efficacy against MRCoNS, with susceptibilities of 84% (47/56) and 71% (40/56), respectively, compared to 19.5% (51/261) and 52% (137/261) for MRSA (p < 0.05).

Ceftriaxone was less effective against both groups, with a sensitivity of 14% (36/261) for MRSA and 38% (21/56) for MRCoNS (p < 0.05) (Table 3).

Table 3: Antimicrobial susceptibilities of MRSA and MRCoNS isolates

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

This study highlights key differences in the prevalence and antimicrobial susceptibility patterns of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative Staphylococcus (MRCoNS) isolated from diverse clinical specimens. While both groups exhibited significant resistance to commonly used antibiotics, their susceptibility profiles varied markedly, with vancomycin and linezolid remaining highly effective. These findings underscore the need for targeted antimicrobial stewardship and infection control measures to address these resistant pathogens in tertiary care settings.

Prevalence and Demographics

In this study, we analyzed 317 isolates, including 261 methicillin-resistant Staphylococcus aureus (MRSA) and 56 methicillin-resistant coagulase-negative staphylococci (MRCoNS). The median ages of the MRSA and MRCoNS cases were comparable (46 vs. 42 years), with no statistically significant difference. This aligns with other studies that reported similar age distributions among patients infected with methicillin-resistant Staphylococcus species, reflecting the widespread nature of these pathogens across all age groups​. (11,12) Male predominance in both groups (58.6% in MRSA, 66.1% in MRCoNS) may be linked to higher occupational exposures or comorbidities common in males. This trend is consistent with studies on methicillin-resistant staphylococcal infections, which suggest that males might have increased exposure to nosocomial environments​​. However, sex-specific biological factors influencing susceptibility remain underexplored and could form the basis for future hypothesis-driven research.

Sample Sources

The distribution of isolates from various clinical samples revealed that pus was the most common source of both MRSA (24.5%) and MRCoNS (21.4%), followed by urine and wound swabs. This pattern is consistent with findings from other tertiary care centers in India, where pus and wound swabs are frequently reported as the predominant sources of MRSA and MRCoNS isolates. (11,13,14) The higher prevalence in pus samples underscores the role of these pathogens in skin and soft tissue infections. Unexpectedly, a higher proportion of MRCoNS in "other samples" compared to MRSA could be an artifact of the study or it could be due to opportunistic colonization tendency of MRCoNS in diverse body sites, especially among immunocompromised patients or those with invasive devices, which ultimately warrants further investigation.

Antimicrobial Susceptibility Patterns

Vancomycin and linezolid exhibited excellent efficacy against both MRSA and MRCoNS isolates, with susceptibility rates of 100% and 99%, respectively. These findings are in line with those of studies from other regions in India, which have reported high susceptibility rates to these antibiotics. (11,15–17) The sustained effectiveness of vancomycin and linezolid is crucial as  limited therapeutic options available for treating methicillin-resistant staphylococcal infections.

Clindamycin showed a significantly higher susceptibility rate in MRCoNS (80%) than in MRSA (62%) (p < 0.05). This reason of this disparity should be examined in some other studies. However, the potential for inducible clindamycin resistance, particularly in MRSA isolates, requires caution and further testing prior to clinical use. (11,18–20)

Ciprofloxacin susceptibility was notably lower in MRCoNS (32%) than that in MRSA (59.3%) (p < 0.05). This finding was comparable with some study and also contrasts with some studies that have reported higher resistance rates to ciprofloxacin in MRSA isolates.(11,21,22) The observed variability in resistance patterns may reflect differences in local antibiotic prescription practices and selective pressures that they impose.

Amikacin and tetracycline demonstrated higher efficacy against MRCoNS, with susceptibilities of 84% and 71%, respectively, compared to 19.5% and 52% in MRSA (p < 0.05). These differences contradicts with existing data from various studies and may be due to varying resistance mechanisms.(23–25)

Ceftriaxone was less effective against both groups, with sensitivity rates of 14% for MRSA and 38% for MRCoNS (p < 0.05). This low efficacy is consistent with the known resistance of methicillin-resistant staphylococci to beta-lactam antibiotics, including cephalosporins.(11) Consequently, ceftriaxone is not recommended for treating infections caused by resistant organisms.

The antimicrobial susceptibility patterns observed in this study were generally consistent with the findings from other regions of India. For instance, a study conducted in Mangalore reported similar susceptibility rates for vancomycin and linezolid among MRSA isolates.(11)

However, variations in susceptibility to other antibiotics, such as ciprofloxacin and clindamycin, highlight the importance of local antimicrobial stewardship and the need for region-specific treatment guidelines.(21,22)

An unexpected finding in this study was the significantly higher susceptibility of MRCoNS to amikacin and tetracycline compared to MRSA. This observation raises questions regarding the underlying genetic and environmental factors that contribute to these differences. Further research is warranted to explore the molecular mechanisms of resistance in MRSA and MRCoNS isolates, which could inform targeted therapeutic strategies and help mitigate the spread of resistance.

Implications of the findings

This study provides valuable insights into the prevalence and antimicrobial susceptibility patterns of MRSA and MRCoNS in a tertiary care hospital in West Bengal. These findings underscore the continued efficacy of vancomycin and linezolid against these pathogens, while highlighting the variable susceptibility to other antibiotics. The observed differences in susceptibility patterns between MRSA and MRCoNS emphasize the need for ongoing surveillance and tailored antimicrobial stewardship programs to effectively manage infections caused by resistant organisms.

Strengths of the study

This comparative analysis of MRSA and MRCoNS in a West Bengal tertiary care hospital stands out for its feasibility, novelty, and adherence to the ethical standards. Conducted in a single centre, this study ensured controlled data collection and efficient resource use. This study uniquely contributes insights specific to the region by filling a critical data gap. Its relevance lies in aiding infection control strategies and optimizing empirical antibiotic therapy, thereby positively influencing patient care practices.

Limitations of the study

The limitations of this study include its single-centre design, which may restrict the generalizability of the findings to other settings and temporal constraints that could overlook variations in antimicrobial resistance patterns over time. Additionally, the absence of molecular typing limits the identification of specific strains, hindering insights into transmission dynamics. Not testing susceptibility to newer antibiotics may also omit potential treatment options, affecting the comprehensiveness of the study. To advance the understanding of MRSA and MRCoNS, future research should adopt multicentre designs for broader applicability, longitudinal studies to track trends over time, molecular typing for detailed genetic insights, and expanded antibiotic testing to identify novel treatments. These strategies will enhance the depth and impact of the findings and support better infection control and patient care.

This study highlights the comparative prevalence and antimicrobial susceptibility patterns of MRSA and MRCoNS in a tertiary care hospital in West Bengal, India. It provides valuable data on antimicrobial susceptibility patterns, revealing that vancomycin and linezolid remain effective and play a critical role in therapy. Variations in resistance patterns emphasize the need for targeted antimicrobial stewardship and infection control strategies tailored to local epidemiology and resistance profiles. To address the emerging antimicrobial resistance, future studies should focus on the molecular mechanisms of resistance and epidemiological dynamics of MRSA and MRCoNS. Regular surveillance programs and antimicrobial stewardship interventions are essential to monitor resistance trends, evaluate clinical outcomes, and optimize empirical treatment protocols 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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