Background: Staphylococcus aureus is a common hospital acquired infections pathogen. Multidrug-resistant Methicillin-resist- ant Staphylococcus aureus represents a major problem in Egyptian hospitals. The over-expression of efflux pumps is a main cause of multidrug resistance. The discovery of efflux pump inhibitors may help fight multidrug resistance by sensitizing bacteria to antibiotics. This study aimed to investigate the role of efflux pumps in multidrug resistance. Methods: Twenty multidrug resistant S. aureus isolates were selected. Efflux pumps were screened by ethidium bromide agar cartwheel method and polymerase chain reaction. The efflux pump inhibition by seven agents was tested by ethidium bromide agar cartwheel method and the effect on sensitivity to selected antimicrobials was investigated by broth microdilu- tion method. Results: Seventy percent of isolates showed strong efflux activity, while 30% showed intermediate activity. The efflux genes mdeA, norB, norC, norA and sepA were found to play the major role in efflux, while genes mepA, smr and qacA/B had a minor role. Verapamil and metformin showed significant efflux inhibition and increased the sensitivity to tested antimicrobials, while vildagliptin, atorvastatin, domperidone, mebeverine and nifuroxazide showed no effect. Conclusion: Efflux pumps are involved in multidrug resistance in Staphylococcus aureus. Efflux pump inhibitors could increase the sensitivity to antimicrobials. Keywords: Staphylococcus aureus; multidrug resistance; efflux pump inhibitors.

Surgical site infections are the most common post-operative infections even in hospitals with most modern facilities complications and standard protocols of pre-operative preparation and antibiotic prophylaxis. Staphylococci stay as our natural flora and yet sometimes threaten our life as tenacious pathogens. In addition to their ability to evade our immune system, the multi-drug resistance phenotype makes Staphylococci the most intractable pathogenic bacteria in the history of antibiotic chemotherapy. Staphylococci are among the leading causes of nosocomial infections such as surgical site infections. Increasing resistance to β-lactams and the glycopeptides complicates treatment of infections caused by Stahpylococci. The aim of this study is to investigate the antibiotic resistance profile of Staphylococci isolated from surgical site infection. Staphylococci isolates were identified morphologically, by Gram stain and biochemical tests. Antimicrobial susceptibility testing was done by the Kirby-Bauer standard disk diffusion method. One hundred Staphylococci isolates were recovered from one hundred and ninety samples isolated from surgical site infections. Staphylococcus aureus was the most predominant one. From 100 isolates, Staphylococcus aureus was found in 91 isolate and coagulase-negative Staphylococci (CoNS) in 9 isolates. Staphylococcus aureus isolates were highly resistant to tigecycline, oxacillin, ampicillin and ampicillin-sulbactam antibiotics. They showed intermediate resistance to daptomycin, amikacin, azithromycin, levofloxacin, clindamycin, sulfamethoxazole-trimethoprime, doxycycline and gatifloxacin, while they showed low resistance to vancomycin, linezolid and imipenem. On the other hand, CoNS isolates were highly resistant to doxycycline, oxacillin, ampicillin and ampicillin-sulbactam antibiotics. They showed intermediate resistance to daptomycin, levofloxacin, clindamycin, sulfamethoxazoletrimethoprime, gatifloxacin, vancomycin, tigecycline, linezolid and imipenem, while they showed low resistance to amikacin and complete sensitivity to azithromycin. Eighty four isolates were multi-drug resistant. Percentage of multi-drug resistant Staphylococci isolates were very high. This may be attributed to the misuse of antibiotics. To minimize resistance, strict antimicrobial prescription policy should be applied.

The appearance of persister cells with low metabolic rates are key factors leading to antibiotic treatment failure. Such persisters are multidrug tolerant and play a key role in the recalcitrance of biofilm-based chronic infections. Here, we present the genomic analyses of three distinct Pseudomonas aeruginosa Egyptian persister-isolates recovered from chronic human infections. To calculate the persister frequencies, viable counts were determined before and after treatment with levofloxacin. The susceptibilities of isolates to different antibiotics were determined using the agar-dilution method. To determine their recalcitrance, the levofloxacin persisters were further challenged with lethal concentrations of meropenem, tobramycin, or colistin. Furthermore, the biofilm formation of the persister strains was estimated phenotypically, and they were reported to be strong biofilm-forming strains. The genotypic characterization of the persisters was performed using whole genome sequencing (WGS) followed by phylogenetic analysis and resistome profiling. Interestingly, out of the thirty-eight clinical isolates, three isolates (8%) demonstrated a persister phenotype. The three levofloxacin-persister isolates were tested for their susceptibility to selected antibiotics; all of the tested isolates were multidrug resistant (MDR). Additionally, the P. aeruginosa persisters were capable of surviving over 24 h and were not eradicated after exposure to 100X-MIC of levofloxacin. WGS for the three persisters revealed a smaller genome size compared to PAO1-genome. Resistome profiling indicated the presence of a broad collection of antibiotic-resistance genes, including genes encoding for antibiotic-modifying enzymes and efflux pump. Phylogenetic analysis indicated that the persister isolates belong to a distinct clade rather than the deposited P. aeruginosa strains in the GenBank. Conclusively, the persister isolates in our study are MDR and form a highly strong biofilm. WGS revealed a smaller genome that belongs to a distinct clade.