Decreased expression of femXAB genes and fnbp mediated biofilm pathways in OS-MRSA clinical isolates

Abstract

Methicillin-Resistant Staphylococcus aureus (MRSA) is a significant threat to human health. Additionally, biofilm forming bacteria becomes more tolerant to antibiotics and act as bacterial reservoir leading to chronic infection. In this study, we characterised the antibiotic susceptibility, biofilm production and sequence types (ST) of 74 randomly selected clinical isolates of S. aureus causing ocular infections. Antibiotic susceptibility revealed 74% of the isolates as resistant against one or two antibiotics, followed by 16% multidrug-resistant isolates (MDR), and 10% sensitive. The isolates were characterized as MRSA (n = 15), Methicillin-sensitive S. aureus (MSSA, n = 48) and oxacillin susceptible mecA positive S. aureus (OS-MRSA, n = 11) based on oxacillin susceptibility, mecA gene PCR and PBP2a agglutination test. All OS-MRSA would have been misclassified as MSSA on the basis of susceptibility test. Therefore, both phenotypic and genotypic tests should be included to prevent strain misrepresentation. In addition, in-depth studies for understanding the emerging OS-MRSA phenotype is required. The role of fem XAB gene family has been earlier reported in OS-MRSA phenotype. Sequence analysis of the fem XAB genes revealed mutations in fem × (K3R, H11N, N18H and I51V) and fem B (L410F) genes. The fem XAB genes were also found down-regulated in OS-MRSA isolates in comparison to MRSA. In OS-MRSA isolates, biofilm formation is regulated by fibronectin binding proteins A & B. Molecular typing of the isolates revealed genetic diversity. All the isolates produced biofilm, however, MRSA isolates with strong biofilm phenotype represent a worrisome situation and may even result in treatment failure.

Carvacrol Targets SarA and CrtM of Methicillin-Resistant Staphylococcus aureus to Mitigate Biofilm Formation and Staphyloxanthin Synthesis: An In Vitro and In Vivo Approach

“…aureus biofilm encoded by the ica operon and expression of the ica operon is under the control of SarA. Apart from PIA, SarA also controls adhesion proteins FnbA and FnbB. − As a downstream effect of SarA downregulation, expressions of icaA , icaD , fnbA , and fnbA were also decreased by carvacrol treatment. On the other hand, interaction of carvacrol with CrtM, the first enzyme of the staphyloxanthin biosynthetic pathway, was investigated using molecular docking analysis as prior studies reported CrtM as an efficient drug target to inhibit staphyloxanthin synthesis. ,, Results revealed the strong binding of carvacrol with CrtM through hydrogen bonding.…”

Recent Developments in Phenotypic and Molecular Diagnostic Methods for Antimicrobial Resistance Detection in Staphylococcus aureus: A Narrative Review

“…If an OS-MRSA is wrongly identified as MSSA and beta-lactam antibiotics are given, the oxacillin resistance subpopulation will be selected and will be responsible for treatment failure [ 90 ]. In another study, 11 OS-MRSA isolates were isolated from ocular infections [ 91 ]. Boonsiri et al analyzed 43 OS-MRSA clinical isolates and found that cefoxitin performed better (19/43 isolates correctly identified as MRSA) than the automated system or the Etest in managing OS-MRSA, but was still not optimal, so a confirmatory PCR might be required [ 92 ].…”

Emergence of a NDM-1-producing ST25 Klebsiella pneumoniae strain causing neonatal sepsis in China

“…Experiments were performed in triplicate and results were presented as 10.3389/fmicb.2022.980191 Frontiers in Microbiology 04 frontiersin.org mean ± SD. The data were analyzed as described before (Brahma et al, 2019).…”