A random forest model based on core genome allelic profiles of MRSA for penicillin plus potassium clavulanate susceptibility prediction

Antimicrobial resistance in methicillin-resistant staphylococcus aureus

In the medical community, antibiotics are revered as a miracle because they stop diseases brought on by pathogenic bacteria. Antibiotics have become the cornerstone of contemporary medical advancements ever since penicillin was discovered. Antibiotic resistance developed among germs quickly, placing a strain in the medical field. Methicillin-resistant Staphylococcus aureus (MRSA), Since 1961, has emerged as the major general antimicrobial resistant bacteria (AMR) worldwide. MRSA can easily transmit across the hospital system and has mostly gained resistance to medications called beta-lactamases. This enzyme destroys the cell wall of beta-lactam antibiotics resulting in resistance against that respective antibiotic. Daptomycin, linezolid and vancomycin were previously used to treat MRSA infections. However, due to mutations and Single nucleotide polymorphisms (SNPs) in Open reading frames (ORFs) and SCCmec machinery of respective antibody, MRSA developed resistance against those antibiotics. The MRSA strains (USA300, CC398, CC130 etc.), when their pan-genomes were analyzed were found the genes involved in invoking resistance against the antibiotics as well as the epidemiology of that respective strain. PENC (penicillin plus potassium clavulanate) is the new antibiotic showing potential in treatment of MRSA though it is itself resistant against penicillin alone. In this review, our main focus is on mechanism of development of AMR in MRSA, how different ORFs are involved in evoking resistance in MRSA and what is the core-genome of different antimicrobial resistant MRSA.

The NaHCO3-Responsive Phenotype in Methicillin-Resistant Staphylococcus aureus (MRSA) Is Influenced by mecA Genotype

Methicillin-resistant Staphylococcus aureus (MRSA) strains are a leading cause of many invasive clinical syndromes, and pose treatment difficulties due to their in vitro resistance to most β-lactams on standard laboratory testing. A novel phenotype frequently identified in MRSA strains, termed ‘NaHCO₃-responsiveness’, is a property whereby strains are susceptible in vitro to many β-lactams in the presence of NaHCO₃. Specific mecA genotypes, repression of mecA/PBP2a expression and perturbed maturation of PBP2a by NaHCO₃ have all been associated with this phenotype. The aim of this study was to define the relationship between specific mecA genotypes and PBP2a substitutions, on the one hand, with NaHCO₃-responsiveness in vitro. Mutations were made in the mecA ribosomal binding site (RBS -7) and at amino acid position 246 of its coding region in parental strains MW2 (NaHCO₃-responsive) and C36 (NaHCO₃- nonresponsive) to generate ‘swap’ variants, each harboring the other’s mecA-RBS/coding region genotypes. Successful swaps were confirmed by both sequencing, as well as predicted swap of in vitro penicillin-clavulanate susceptibility phenotypes. MW2 swap variants harboring the nonresponsive mecA genotypes became NaHCO₃-nonresponsive (resistant to the β-lactam, oxacillin [OXA]), in the presence of NaHCO₃. Moreover, these swap variants had lost NaHCO₃-mediated repression of mecA/PBP2a expression. In contrast, C36 swap variants harboring the NaHCO₃-responsive mecA genotypes remained NaHCO₃-nonresponsive phenotypically, and still exhibited nonrepressible mecA/PBP2a expression. These data demonstrate that in addition to the mecA genotype, NaHCO₃-responsiveness may also depend on strain-specific genetic backgrounds.