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Hanzada T Nour El-Din,1 Aymen S Yassin,1 Yasser M Ragab,1 Abdelgawad M Hashem1,2 1Department of Microbiology and Immunology, Faculty of Pharmacy, Cairo University, Cairo, 11562, Egypt; 2Department of Microbiology and Immunology, Faculty of Pharmacy, British University in Egypt, El-Sherouk City, Cairo, 11837, EgyptCorrespondence: Aymen S YassinDepartment of Microbiology and Immunology, Faculty of Pharmacy, Cairo University, Kasr Eleini Street, Cairo, 11562, EgyptTel +2-02-23620122Fax +2-02-23620122Email aymen.yassin@pharma.cu.edu.egIntroduction: Methicillin-resistant Staphylococcus aureus (MRSA) presents a profound hazard to public health. MRSA colonizing skin, mucous membranes, and the anterior nares without clinical symptoms is termed “colonizing MRSA”. Upon manifestation of clinical symptoms, it is termed “infectious MRSA”. Here, we characterize and differentiate colonizing and infectious MRSA, and analyze the phenotypic-genotypic and antibiotic susceptibility correlations.Methodology: Clinical MRSA isolates were recovered from intensive care units (ICUs) of two major Egyptian hospitals and their biofilm formation ability was tested. Antibiograms against 16 antibiotics were determined, in addition to the minimum inhibitory concentrations (MICs) of vancomycin and linezolid. The entire collection was typed by enterobacterial repetitive intergenic consensus (ERIC)-PCR, as well as multi-locus sequence typing (MLST). Representative resistance and virulence genes were detected by PCR amplification.Results: Forty-nine isolates were confirmed as MRSA, of which 30 isolates were infectious and 19 were colonizing. Versatile resistance patterns were observed in both groups of isolates. We report a higher tendency for biofilm-formation and borderline minimum inhibitory concentrations among infectious isolates. A Positive antibiotic correlation was observed between susceptibility to protein synthesis inhibitors and cell wall inhibitors. Positive correlations were observed between isolation site and rifampicin resistance: nasal samples were enriched in rifampicin-resistant isolates, while urine and blood samples were enriched in susceptible ones. Furthermore, biofilm formation ability was slightly associated with amikacin resistance, and an association between teicoplanin resistance and the presence of the Panton-Valentine leukocidin gene was the only significant phenotype-genotype correlation observed. Finally, ERIC typing and MLST had congruent results.Conclusion: Linezolid and vancomycin are still the most convenient choice for MRSA treatment. ERIC PCR and MLST show promising typing combination that could be easily used periodically for tracking the genotypic changes of MRSA, especially within the healthcare facilities. Several correlations were established between groups of antibiotics and the genotypes/phenotypes of the selected isolates.Keywords: methicillin-resistant Staphylococcus aureus, MRSA carriage, MRSA colonization, multi-drug-resistant bacteria, virulence, phenotype correlations