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In this study, mechanisms of carbapenem resistance in carbapenem-resistant but cephalosporin-susceptible (Car-R/Ceph-S) Pseudomonas aeruginosa were investigated. A total of 243 P. aeruginosa isolates were studied. The disk diffusion and agar dilution methods were used for determination of antibiotic susceptibility patterns. AmpC and efflux pump overproductions were detected by phenotypic methods. The presence of carbapenemase-encoding genes was detected by polymerase chain reaction (PCR). The expression of OprD, MexAB-OprM, and MexXY-OprM efflux pumps was assessed by real-time PCR. According to disk diffusion method, altogether 116 P. aeruginosa isolates (47.7%) were carbapenem-resistant and among them, 23 isolates (19.8%) were cephalosporin-susceptible. Carbapenemase producer was not detected. Overexpression of AmpC was detected in one (4.3%) isolate that was ceftazidime-susceptible but cefepime-resistant. Overexpression of MexAB-OprM and MexXY-OprM efflux pumps was detected in 12 (60.9%) and 16 (68.8%) of isolates, respectively. A total of 16 (68.8%) isolates showed decreased expression of OprD. The Car-R/Ceph-S P. aeruginosa did not develop by carbapenemase production. The resistance to carbapenem was mediated in our clinical isolates by decreased expression of OprD and overexpression of MexAB-OprM and MexXY-OprM efflux systems or the combination of these mechanisms.

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The resistance of Bacteroides fragilis to the most antimicrobial agents has been reported in the world. Identification of the microbial resistance mechanisms can play an important role in controlling these resistances. Currently, B. fragilis is resistant to most antibiotics. The multi-drug efflux pumps have been shown to underlie the antimicrobial resistance in B. fragilis strains. Two types of these efflux pumps including RND and MATE can be regarded as main structures responsible for antibiotic resistance. Therefore, the strategy for suppressing of this efflux system may be useful in the treatment and control of the multidrug-resistant B. fragilis. The purpose of this study is to review the B. fragilis efflux pumps and their functions in the resistance to antibiotics.

The increasing prevalence of antimicrobial-resistant microorganisms is presently known as a global challenge. An effective alternative is critical to guarantee an operative paradigm shift in the epidemic of resistance. The antimicrobial effects of grape seed extract (GSE) have been reported against a broad range of microbes. This study is an updated overview of the antimicrobial effect of GSE against different pathogens. The available reports from various studies retrieved from PubMed, Scopus, and Google Scholar databases regarding the antimicrobial effect of GSE was evaluated. The GSE is rich sources of phenolic compounds. GSE can inhibit the growth of a broad spectrum of Gram-negative and Gram-positive bacteria depended on its concentrations, phenolic content, and tested bacterial species. The GSE is more effective against Gram-positive bacteria than Gram-negative bacteria. It has also been shown to have inhibitory effects against several clinically important viruses and fungi. The antibiofilm effect of GSE also has been described in some studies. The significant side effects of GSE have not reported and it is almost safe. GSE may be a promising source for new generations of antimicrobial agents in the food industry and clinical setting.

Background: The ever-increasing resistance to antimicrobial agents among bacteria associated with nosocomial infections indicate the necessity of new antimicrobial therapy. The nanoparticles are considered as new drug delivery systems to increase the efficiency and decrease the unfavourable effects of the antimicrobial agents. Methods: Herein we report the preparation and characterization of mesoporous silica nanoparticles (MSNs) loaded with meropenem against carbapenem-resistant Enterobacteriaceae. The antimicrobial effect of meropenem-loaded MSNs was determined against Enterobacteriaceae using the minimum inhibitory (MIC) method. The biocompatibility of meropenem-loaded MSNs was studied by the impact on the haemolysis and sedimentation rates of human red blood cells (HRBCs). Cytotoxicity of the meropenem-loaded MSNs was studied by the MTT test (hBM-MSC cell viability). Results: The meropenem-loaded MSNs have shown antibacterial activity on all isolates at different MIC values lower than MICs of meropenem. Free MSNs did not show any significant antibacterial effect. Meropenem-loaded MSNs have no significant effect on haemolysis and ESR of HRBCs. The viability of hBM-MSC cells treated with serial concentrations of meropenem-loaded MSNs was 92-100%. Conclusion: Due to the desirable biocompatibility, low cytotoxicity and the improved antibacterial effect, MSNs can be considered as a promising drug delivery system for meropenem as a potential antimicrobial agent.