Research Article Aparna Shil, Sushmit Mukherjee, Prerona Biswas, Sudipta Majhi, Sima Sikdar, Biswadev Bishayi, Mausumi Sikdar (née Bhakta)* Catharanthus roseus (L.) G. Don counteracts the ampicillin resistance in multiple antibiotic- resistant Staphylococcus aureus by downregulation of PBP2a synthesis https://doi.org/10.1515/biol-2022-0718 received March 18, 2023; accepted August 11, 2023 Abstract: It is essential to revisit the global biodiversity, search for ethnopharmacologically relevant plants, and unveil their untapped potential to overcome the complica- tions associated while treating infections triggered by mul- tiple antibiotic-resistant Staphylococcus aureus. Catharanthus roseus (L.) G. Don of the Apocynaceae family is a medicinal plant used for remedial purposes against infectious diseases from ancient times. In this study, we intended to evaluate the mechanism by which the ethanolic extract of C. roseus root (EECRR) causes the reversal of ampicillin resistance in S. aureus. To achieve this goal, we have stained EECRR-treated S. aureus with acridine orange, analysed DNA damage by comet assay, and studied the alteration of plasmid band pat- tern and expression of penicillin-binding protein 2a (PBP2a) protein. Experiments revealed better S. aureus killing effi- ciency of EECRR at its minimum inhibitory concentration (MIC) doses due to DNA damage and reducing plasmid band intensities along with a decline in the expression of PBP2a in EECRR-treated cells at half-MIC dose. EECRR proved to be an efficient growth inhibitor of S. aureus that reduces the expression of PBP2a. Therefore, EECRR can also render ampicillin-resistant S. aureus susceptible to the antibiotic. Keywords: Staphylococcus aureus, ethanol extract of Catharanthus roseus root, ampicillin resistance, peni- cillin-binding protein 2a, comet assay 1 Introduction Staphylococcus aureus, a well-known commensal microbe found in human skin and mucous membranes, is known to cause bacterial infections upon gaining an opportunity to invade these physical barriers. According to a case study report by Cai et al., a patient with atypical hip pain had developed systemic sepsis due to an infection caused by S. aureus and ultimately died of multiple organ failure [1]. It can also colonize in urinary stents and cause urinary tract infection (UTI) in renal transplant patients [2]. Peni- cillin was initially used to treat these infections, which was replaced by methicillin due to the appearance of penicillin- resistant mutants, as was primarily reported in 1946 [3]. Even- tually, methicillin-resistant S. aureus (MRSA) appeared in 1961, and the treatment of MRSA infection became more difficult gradually due to its multidrug-resistant properties. One of the reasons behind the emergence of antibiotic-resistant mutants of S. aureus is the improper use of antibiotics [4]. Acquisition of the mecA gene in MRSA enables them to exhibit resistance against β-lactam antibiotics. Penicillin-binding protein 2a (PBP2a), the product of the mecA gene, confers a lower affi- nity for all β-lactam antibiotics and restricts their thera- peutic use [5]. Vancomycin and teicoplanin have reduced effectiveness on many MRSA strains since they have acquired resistance against those drugs [6]. New drugs, such as line- zolid, daptomycin, dalfopristin, fidaxomicin, and tigecycline, are used to treat the infection as an alternative to those anti- biotics. However, the dynamic changes in the susceptibilities of S. aureus to these antibiotics have also been reported [7]. The number of currently approved drugs is insufficient to Aparna Shil, Sushmit Mukherjee, Prerona Biswas, Sudipta Majhi, Sima Sikdar: Microbiology, Nutrition and Dietetics Laboratory, Physiology Unit, Department of Life Sciences, Presidency University, Kolkata 700073, India Biswadev Bishayi: Department of Physiology, Immunology Laboratory, University of Calcutta, University Colleges of Science and Technology, Kolkata 700009, India  * Corresponding author: Mausumi Sikdar (née Bhakta), Microbiology, Nutrition and Dietetics Laboratory, Physiology Unit, Department of Life Sciences, Presidency University, Kolkata 700073, India, e-mail: mausumi.dbs@presiuniv.ac.in Open Life Sciences 2023; 18: 20220718 Open Access. © 2023 the author(s), published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 International License.