In vitro synergistic effects of a short cationic peptide and clinically used antibiotics against drug-resistant isolates of Brucella melitensis.

PURPOSE: In the last few decades, increasing microbial resistance to common antibiotics has attracted researchers' attention to the development of new classes of antibiotics such as antimicrobial peptides. Accordingly, the aim of the current study was to evaluate antimicrobial effects of the CM11 peptide alone and combined with common antibiotics against drug-resistant isolates of Brucella melitensis. METHODOLOGY: A total of 50 pathogenic samples of B. melitensis were isolated from patients and their antibiotic susceptibility pattern was evaluated by E-test. Then, the synergistic reaction of the peptide with selected antibiotics was evaluated using a chequerboard procedure. RESULTS: Based on the susceptibility pattern of isolates, ciprofloxacin, rifampin, streptomycin and co-trimoxazole were used for synergistic study. According to the results, synergic effect was observed for streptomycin and co-trimoxazole in combination with the peptide while ciprofloxacin and rifampin showed partial synergy and additive effect, respectively. Consistent with these results, in the time-killing assay, a decrease in colony counts for streptomycin-peptide and co-trimoxazole-peptide was >2 Log10 while for ciprofloxacin-peptide and rifampin-peptide it was about 1.5 Log10 and <2 Log10, which represents synergy, partial synergy and additive interaction, respectively. CONCLUSION: These results showed that by antibiotic-CM11 combination, their effective dose can be reduced particularly for drug-resistant isolates. In conclusion, considering the importance of brucellosis caused by B. melitensis in the Middle East beside reports on antibiotic resistance strains, especially against rifampin, which may literally lead to an increase in resistant strains of Mycobacterium tuberculosis in endemic areas, our findings can be used to develop a suitable alternative treatment for brucellosis, and with less risk.

Insights into Pyrazinamidase and DNA Gyrase Protein Structures in Resistant and Susceptible Clinical Isolates of Mycobacterium tuberculosis.

BACKGROUND: Mutations in pncA and gyrA genes cause pyrazinamide (PZA) and fluroquinolone resistance in Mycobacterium tuberculosis (MTB). In the present study, structures of pyrazinamidase (PZase) and DNA gyrase proteins were studied in resistant and susceptible clinical isolates of MTB. MATERIALS AND METHODS: Sixty clinical isolates of MTB were used in this study. Polymerase chain reaction (PCR) amplification of pncA and gyrA genes was accomplished on purified DNA. Sequence of the fragments was determined by an Applied BiosystemsTM apparatus. Bioinformatic analysis was performed by online software and three-dimensional (3D) structures of proteins was predicted using Molegro Virtual Docker (MVD) Modeler software. RESULTS: Amplified 744 and 194 bp fragments of pncA and gyrA genes, respectively were yielded suitable sequence results. Predicted 3D structures of proteins showed some differences between wild-type and mutant structures. Mutation in amino acid No.31 (T92C) caused an increase in distance from metal ion position to enzyme active site, but it was considered as a polymorphism. Docking results by MVD revealed a relationship in quinolone resistance-determining regions (QRDR) amino acids in interaction with antibiotic. T92C mutation in PZase from non-polar aliphatic amino acid Ile (ATC) to polar aliphatic amino acid threonine (ACC) was a polymorphism. CONCLUSION: Structural changes in two important proteins related to drug resistance were proven in clinical isolates of MTB.

Genotyping of vancomycin resistant enterococci in arak hospitals.

BACKGROUND: Enterococcal species have emerged as important pathogens in Iran as well as throughout the world. With the increased use of vancomycin, Vancomycin-Resistant Enterococci (VRE) has become an important nosocomial pathogen. OBJECTIVES: The aim of the present study was to determine the incidence and antimicrobial susceptibility pattern of VRE and also to determine the most important genes that cause resistance to vancomycin in clinical samples in Arak, Iran. MATERIALS AND METHODS: In total, 200 enterococci samples were collected from clinical specimens of Arak hospitals. Enterococcal species were identified using standard biochemical tests. Antibiotic susceptibility was tested by the Clinical and Laboratory Standards Institute (CLSI) disk diffusion. Minimum Inhibitory Concentration (MICs) was determined by broth micro dilution. All of the VRE isolates were examined by PCR to detect the presence of VRE genes. RESULTS: Disk diffusion agar showed that 96 strains (48%) were resistant to gentamicin, 89 (44.5%) to ciprofloxacin, 127 (63.5%) to erythromycin, 142 (71%) to tetracycline, 11 (5.5%) to teicoplanin, 32 (16%) to vancomycin, none to linezolid and 96 (48%) to co-trimoxazole. The MICs of the resistant isolates were as follows; 88 strains had MIC ≥ 32 µg/mL to vancomycin and 59 strains had MIC ≥ 32 µg/mL to teicoplanin. Molecular studies revealed that 59.09% of VRE contained VanA genes and 7.95% of VRE contained the VanB genes. None of the strains had vanC1 and vanC2/3 gene. CONCLUSIONS: According to the results of this study, rates of vancomycin-resistance in enterococci, in Iran like other parts of the world, is increasing. Therefore accurate methods are required for identifying strains that possess resistance genes because many cases of hospital infections are caused by these strains.