Antimicrobial resistance (AMR) is a major global public health concern that threatens the effective prevention and treatment of infectious diseases. Antimicrobial resistance arises when microorganisms develop mechanisms that enable them to withstand the effects of antimicrobial agents, leading to treatment failure, prolonged illness, and increased mortality. The World Health Organization recognizes AMR as one of the top global health threats, with healthcare settings serving as key reservoirs for the emergence and spread of resistant pathogens.

CoNs are among the most abundant bacterial species colonizing the human anterior nares. While S.aureus is a well-known pathogen, CoNs are part of the normal flora but have increasingly been implicated in opportunistic infections, particularly in hospitalized and immunocompromised patients [1]. Nasal carriage of these organisms is clinically significant, as it serves as a reservoir for both endogenous infections and transmission to vulnerable patients.

Healthcare workers (HCWs) are at increased risk of colonization due to frequent exposure to patients and the hospital environment. Nasal carriage of CoNs among HCWs plays a critical role in the epidemiology of healthcare-associated infections, as colonized individuals can act as reservoirs and vectors for transmission within healthcare settings [1][2]. Determining the prevalence of nasal carriage among HCWs is therefore essential for understanding the burden and potential transmission dynamics of these organisms, particularly in high-risk units such as neonatal and intensive care units.

The growing concern surrounding these organisms is largely driven by their ability to develop antimicrobial resistance. CoNS have demonstrated increasing resistance to commonly used antibiotics, limiting treatment options and complicating infection management [3]. CoNS, in particular, are recognized as important reservoirs of resistance genes that can be transferred to more pathogenic species, further amplifying the AMR problem [4]. Assessing the antimicrobial resistance profiles of these isolates is crucial in guiding appropriate therapy and informing antimicrobial stewardship programs.

A key mechanism of resistance in staphylococci is mediated by the mecA gene, which confers resistance to methicillin and other beta-lactam antibiotics through the production of an altered penicillin-binding protein (PBP2a) [5]. The presence of this gene is associated with methicillin-resistant S.aureus (MRSA) and methicillin-resistant CoNS (MR CONs), both of which are of significant clinical concern. Detection of the mecA gene provides a more accurate understanding of the genetic basis of resistance compared to phenotype methods alone.

Despite the clinical importance of staphylococcal colonization and resistance, there is limited data on the prevalence, antimicrobial resistance patterns, and genetic determinants such as mecA among HCWs in many low- and middle-income settings, including Makueni County. Most available studies in Kenya have focused on phenotypic resistance, with minimal emphasis on molecular characterization [6]. This gap in knowledge limits the ability to fully understand the role of HCWs as reservoirs of resistant organisms and to implement targeted infection prevention and control strategies.

Numerous studies have extensively examined nasal colonization by S.aureus and the occurrence of methicillin resistance among healthcare workers (HCWs). However, CoNS has increasingly been recognized as a significant HAI pathogen in recent years, particularly in association with device-related and bloodstream infections. In addition to their pathogenic potential, CoNS serve as important reservoirs of antimicrobial resistance determinants, including the mecA gene, which mediates methicillin resistance and may be transferred to S.aureus [7]. The epidemiology of CoNS in healthcare settings is substantially less studied than it is for S.aureus. Furthermore, recent studies have demonstrated a high prevalence of nasal carriage of MR-CoNS among HCWs, with reported rates of approximately 45.9% in a tertiary care hospital setting [8]. Similar findings have been reported in other populations exposed to healthcare environments, where MR-CoNS colonization was found to exceed that of MRSA, highlighting their epidemiological importance [9]. In addition, evidence indicates that CoNS colonization is common in the nasal cavities of HCWs and plays a role in the transmission of multidrug-resistant organisms within healthcare settings [10]. Therefore, in the present study, the nasal carriage of CoNS among HCWs was high, with 258 out of 294 HCWs (87.8%) colonized, and 71.3% were MR CONs. In comparison to a recent study in which 343 nasal samples (73.3%) were positive for CoNS, and only 10 (2.1%) were identified as MR-CoNS [8].

Furthermore, another study by Soma Kanta Baral et al. [8] reported a high prevalence of CoNS (66.2%) and MR-CoNS (45.9%), further supporting the widespread occurrence of resistant CoNS in healthcare settings. Similarly, a study by Neelima Kulshrestha et al. [11] reported CoNS in 148 (69.2%) and MR-CoNS in 76 (35.5%) of healthcare workers, which, although lower than the present study, still indicates a substantial burden of CoNS colonization and methicillin resistance in hospital settings.

The high prevalence of CoNS among HCWs is consistent with their status as normal commensals of the nasal mucous membrane and skin, which enables them to persist in the anterior nares. While CoNS are generally considered less virulent than S.aureus, they can act as opportunistic pathogens, particularly in immunocompromised patients or those with invasive devices. The high prevalence of MR-CoNS is of particular concern, as these organisms can serve as reservoirs of resistance genes that may be transferred to more pathogenic bacteria. Healthcare workers carrying MR-CoNS may inadvertently transmit these resistant strains to patients, highlighting the critical need for strict infection prevention and control measures and robust antimicrobial stewardship to limit the risk of HAIs, especially among vulnerable patient populations. The variations observed in the prevalence of nasal carriage of CoNS and MR-CoNS across different studies may be explained by differences in study populations, sampling techniques, or microbiological detection methods, geographical distribution of bacterial strains, disparities in infection prevention and control practices across healthcare settings, as well as differences in study periods and populations.

The distribution of CoNS and MR-CoNS was relatively uniform across different cadres and varying durations of work experience. This suggests that colonization is widespread and not limited to specific professional groups or levels of exposure within the healthcare setting. The findings may indicate that CoNS, being a normal commensal of the skin and nasal mucous membrane, are easily acquired and maintained regardless of role or experience. It also highlights the possibility that common environmental exposure and shared infection prevention practices within the hospital contribute to similar colonization patterns among HCWs.

High resistance was observed across most antibiotics, with complete resistance to penicillin (100%) and very high resistance to ampicillin (96.6%). Moderate resistance was noted for ciprofloxacin (65%), gentamicin (63.5%), and co-trimoxazole (61.1%), while erythromycin showed comparatively lower resistance (30%). The high cefoxitin resistance (71.3%) further indicates a substantial burden of methicillin-resistant CoNS (MR-CoNS), and overall, the isolates demonstrated a multidrug resistance pattern. These findings are comparable to a 2016 Indian study, which also reported 100% resistance to penicillin and similar resistance to co-trimoxazole (63%) and erythromycin (56%) among MR-CoNS isolates [12]. However, resistance levels to ciprofloxacin (65%) and gentamicin (63.5%) in the present study are higher than those reported by Agarwal et al. [12], who documented 22% and 40% resistance, respectively. In addition, a study conducted at a tertiary care hospital by Baragundi Mahesh reported high resistance to penicillin (84.48%), co-trimoxazole (72.41%), ofloxacin (68.96%), and erythromycin (67.24%), with MR-CoNS strains showing higher resistance to most antibiotics, which is in agreement with the multidrug resistance pattern observed in the present study [13].

Overall, the dominance of ciprofloxacin and penicillin in most resistance combinations highlights strong selective pressure against β-lactams and fluoroquinolones, which are commonly used in clinical settings. The frequent addition of gentamicin resistance further indicates reduced effectiveness of aminoglycosides, limiting therapeutic options. Although sulfamethoxazole and clindamycin resistance were less common, their presence in multidrug combinations reflects progressive accumulation of resistance determinants among MR-CoNS isolates.

These findings demonstrate that MR-CoNS in this setting exhibit diverse but overlapping multidrug resistance profiles, with a core resistance backbone mainly driven by penicillin and ciprofloxacin. This pattern is concerning as it suggests continued selection and dissemination of resistant strains within the healthcare environment, emphasizing the need for strict antimicrobial stewardship and infection control measures.

mecA gene carriage was detected in 87.6% of MR-CoNS isolates, confirming that methicillin resistance is largely mediated by this gene. This prevalence is comparable to the 90% reported in the University of Nairobi study [14] and the 82% reported by Tluanpuii et al. [15], indicating a consistently high contribution of mecA to resistance across different settings. However, the absence of the mecA gene in 12.4% of phenotypically identified MR-CoNS in the present study suggests that alternative resistance mechanisms may be involved, such as the presence of mecA or other modifications in penicillin-binding proteins. This highlights that while mecA is the driver of methicillin resistance, reliance on phenotypic methods alone may not fully capture the underlying genetic mechanisms, emphasizing the importance of molecular characterization.

In conclusion, this study demonstrated a high prevalence of CoNS colonization among healthcare workers, with a substantial proportion identified as methicillin-resistant (MR-CoNS), indicating that these organisms serve as important reservoirs of antimicrobial resistance in healthcare settings. The resistance pattern showed widespread multidrug resistance, including very high resistance to commonly used antibiotics such as penicillin and ampicillin, thereby limiting therapeutic options. Furthermore, the high prevalence of the mecA gene among MR-CoNS isolates confirms its central role in mediating methicillin resistance, although its absence in a minority of isolates suggests the involvement of alternative resistance mechanisms. Overall, these findings underscore the need for continuous surveillance, strengthened infection prevention measures, and rational antibiotic use to control the spread of resistant CoNS.

Based on the findings of this study, routine screening of healthcare workers for CoNS and MR-CoNS colonization should be considered to identify potential reservoirs of multidrug-resistant organisms. Strengthening infection prevention and control measures, including proper hand hygiene and adherence to standard precautions, is essential to limit transmission within healthcare settings. In addition, antimicrobial stewardship programs should be reinforced to promote the rational use of antibiotics and reduce selective pressure that drives resistance.