BackgroundFluoroquinolone resistance in Pseudomonas aeruginosa may be due to efflux pump overexpression and/or target mutations. We designed this study to investigate the efflux pump mediated fluoroquinolone resistance and check the increasing effectiveness of fluoroquinolones in combination with an efflux pumps inhibitor among P. aeruginosa isolates from burn wounds infections.Materials and MethodsA total of 154 consecutive strains of P. aeruginosa were recovered from separate patients hospitalized in a burn hospital, Tehran, Iran. The isolates first were studied by disk diffusion antibiogram for 11 antibiotics and then minimum inhibitory concentration (MIC) experiments were performed to detect synergy between ciprofloxacin and the efflux pump inhibitor, carbonyl cyanide-m-chlorophenyl hydrazone (CCCP). Then to elucidate the inducing of multi drug resistance due to different efflux pumps activation in Fluoroquinolone resistant isolates, synergy experiments were also performed in random ciprofloxacin resistant isolates which have overexpressed efflux pumps phenotypically, using CCCP and selected antibiotics as markers for Beta-lactams and Aminoglycosides. The isolates were also tested by polymerase chain reaction (PCR) for the presence of the MexA, MexC and MexE, which encode the efflux pumps MexAB-OprM, MexCD-OprJ and MexEF-OprN.ResultsMost of the isolates were resistant to 3 or more antibiotics tested. More than half of the ciprofloxacin resistant isolates exhibited synergy between ciprofloxacin and CCCP, indicating the efflux pump activity contributed to the ciprofloxacin resistance. Also increased susceptibility of random ciprofloxacin resistant isolates of P. aeruginosa to other selected antibiotics, in presence of CCCP, implied multidrug extrusion by different active efflux pump in fluoroquinolones resistant strains. All of Ciprofloxacin resistant isolates were positive for MexA, MexC and MexE genes simultaneously.ConclusionIn this burn hospital, where multidrug resistant P. aeruginosa isolates were prevalent, ciprofloxacin resistance and multidrug resistance due to the overexpression of fluoroquinolones mediated efflux pumps has also now emerged. Early recognition of this resistance mechanism should allow the use of alternative antibiotics and use an efflux pumps inhibitor in combination with antibiotic therapy.

Background & Objective: Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA), represent serious nosocomial and community infections. Biofilm formation as an important virulence factor may be affected by sub-inhibitory levels of antibiotics. Few studies examined the effects of all therapeutic antimicrobial agents on clinical S.aureus. The current study aimed at observing the inducing and reducing effects of antibiotics, commonly used to treat staphylococcal infections on the production of staphylococcal biofilm. Methods: Four MRSA (1ATCC and 3 clinical) and 1 methicillin-susceptible Staphylococcus aureus (MSSA) strains with biofilm forming ability, evaluated by the Congo red agar (CRA) plate test, were employed. Biofilm formation was measured by crystal violet microtiter plate assay. Cefazolin, rifampicin, vancomycin, oxacillin, clindamycin, cotrimoxazole, minocycline, linezolid, azithromycin, and clarithromycin were added to wells ranging from 0.06to 128 µg/mL (1× to 1/1024 MIC dependent on the MIC value of each strain). Results: The current study showed that azithromycin and vancomycin had a significant inducing effect on biofilm formation. In contrast, linezolid, cefazolin, and clarithromycin, and in the second place, clindamycin and minocycline could inhibit the level of biofilm production in the sub-minimal inhibitory concentrations. Conclusion: The findings demonstrated that the biofilm formation as an important virulence factor may be affected by the subinhibitory levels of antibiotics.

Background: Enterococcus spp. are part of the normal flora of humans and animals. The nosocomial pathogenicity of Enterococcus spp. has emerged in recent years and has caused great concern due to developing of resistance to many antimicrobial agents. Objectives: The current study aimed to determine the resistance pattern and the type of virulence genes in Enterococcus spp. isolated from Milad hospital of Tehran, Iran. Materials and Methods: The current observational study was conducted from Apr 2014 to Feb 2015 on a total of 149 Enterococcus species isolated from Milad hospital in Tehran, Iran. The antibiotic susceptibility pattern of the bacteria was determined by the disc diffusion method for eight antibiotics. Minimum inhibitory concentration (MIC) of vancomycin was also done using agar-dilution assay by clinical and laboratory standards institute (CLSI) recommendations. The sodA, esp, cyl, ace and gelE genes were detected by polymerase chain reaction (PCR) assay. Results: About 37.5%, 73%, 86.6%, 35.8%, 69%, 60.8%, 45% and 79% of the isolates were resistant to vancomycin, tetracycline, gentam-

Objectives: In Iran as well as throughout the world Enterococci have been rated as the important cause of urinary tract and nosocomial infections. The aim of this study was to evaluate the relationship between high antimicrobial resistance activity and harboring the virulence factors among clinical Enterococcus isolates. Materials and Methods:Clinical strains were isolated from hospitalized patients. Prevalence of different virulence genes was evaluated by PCR method and the relation between resistance to antibiotics and harboring virulence genes was evaluated by statistical analysis. Results:The results showed that E. faecalis (60%) is more prevalent than E. faecium (26%) and harboring more virulence factors. The highest resistance was related to gentamicin in both E. faecalis and E. faecium isolates with the rate of 88.7% and 93.5% respectively. Harboring esp, ace and cylA are significantly related to resistance to different antibiotics. Conclusion:The antimicrobial resistance and virulence pattern of Enterococcus must be constantly monitored in order to choose the best antimicrobial treat and prevent nosocomial infections. Keywords: antimicrobial resistance, virulence factors, enterococcus, IranHighlights: The E. faecalis is more prevalent than E. faecium among hospitalized patients. The E. faecalis harboring more virulence factors rather than E. faecium. Gentamicin was detected as the most resistance antibiotics among all isolates. The significant correlation between harboring esp, ace and cylA and resistance to antibiotics has been detected.