Time-kill study and morphological changes of Proteus mirabilis cells exposed to ethyl acetate crude extract of Lasiodiplodia pseudotheobromae IBRL OS-64

@#Aims: To investigate time-kill curve and morphological changes of Proteus mirabilis cells exposed to ethyl acetate crude extract of endophytic fungus, Lasiodiplodia pseudotheobromae IBRL OS-64, isolated from Ocimum sanctum. Methodology and results: Inhibitory effect of the fungal extract against the test bacteria via disc diffusion assay showed a fair antibacterial activity with diameter of inhibition zone was 12.0 ± 0.4 mm. The Minimal Inhibition Concentration (MIC) and Minimal Bactericidal Concentration (MBC) values of the ethyl acetate extract against P. mirabilis was 250 and 500 µg/mL, respectively. The value of MBC which is two-fold higher than MIC value indicated that the fungal extract exerted bactericidal effect on bacterial cells of P. mirabilis. Time-kill curve study revealed that the bactericidal effect of the crude extract towards test bacteria was both dose and time dependent. Scanning electron microscope (SEM) observation revealed that the bacterial cells of P. mirabilis exposed to fungal crude extract resulted in formation of pits, irregular shape of the bacterial cell and ultimately cell death beyond repair. Conclusion, significance and impact of the study: The time-kill curve study, and cell morphological changes suggested the potential of ethyl acetate extract of L. pseudotheobromae IBRL OS-64 against P. mirabilis infection by formation of cavities, irregular bacterial cell that leads to ultimate cell death and the extract may have pharmaceutical potential to be develop as antibacterial agent.

In vitro Antimicrobial Synergy against Imipenem-Resistant Acinetobacter baumannii / 대한진단검사의학회지

BACKGROUND: Most imipenem-resistant Acinetobacter baumannii (IRAB) isolates are multiresistant, leaving few options for an effective antimicrobial therapy. We purposed to select possible candidates for the combinations of antimicrobials that are synergistic in vitro for inhibitory or bactericidal activities against IRAB and evaluate the usefulness of double disk synergy test (DDS) in predicting synergistic bactericidal activity. METHODS: Fifty-five IRAB isolates recovered from patients during the period from August 1999 to November 2000 were tested for susceptibilities to amikacin, gentamicin, tobramycin, piperacillin, piperacillin/tazobactam, cefotaxime, cefepime, cefoperazone/sulbactam (C/S), imipenem, meropenem, ciprofloxacin, levofloxacin, trimethoprim/sulfamethoxazole, chloramphenicol, minocycline, and colistin by the Clinical and Laboratory Standard Institute agar dilution method. Three isolates showing different susceptibility profiles were tested for antimicrobial synergy by DDS and then by timekill study (TKS) using DDS-positive combinations. RESULTS: Colistin, C/S, and minocycline were active in 50 (90.9%), 50, and 44 (80.0%) isolates, respectively, and all the other drugs were active in less than 20% of isolates. Minocycline-imipenem, minocycline-C/S, minocycline-amikacin, imipenem-tobramycin, C/S-amikacin, and C/S-tobramycin combinations showed synergistic inhibitory or bactericidal activity by TKS when the same combinations were synergistic in DDS; however, C/S-imipenem was found synergistic on DDS, but not by TKS. CONCLUSIONS: Colistin, C/S, and minocycline were relatively active against IRAB. DDS might help predict the synergistic antimicrobial effect of TKS if one of the combinations was susceptible.

In vitro Efficacy of Antibiotic Combinations against Multidrug-resistant Streptococcus pneumoniae / 감염

BACKGROUND: Penicillin- and multidrug-resistant Streptococcus pneumoniae became a global problem during recent decades. Multidrug resistance poses a serious threat to clinical medicine due to restriction of selecting appropriate antimicrobial agents to treat with. Current data suggest that any single antimicrobial agent cannot be a satisfactory option to treat pneumococcal infections caused by multidrug-resistant strains, particularly in meningitis. The aim of the study was to assess in vitro efficacy of several antimicrobial combinations that are commonly used in clinical practice, and to obtain reasonable candidate regimens that can be applied to in vivo model. METHODS: We performed time-kill studies of antimicrobial combinations including penicillin, cefotaxime, vancomycin, gentamicin, imipenem and ampicillin against five multidrug-resistant strains and two penicillin-susceptible strains. Penicillin, cefotaxime and vancomycin were combined with gentamicin, respectively. Cefotaxime plus vancomycin, imipenem plus vancomycin, and cefotaxime plus ampicillin combinations were also tested. Synergy was defined as a >or =100-fold or 2-log decrease in colony count at 24 h by the combination compared with that by the most active single agent. RESULTS: Penicillin plus gentamicin, cefotaxime plus gentamicin, and vancomycin plus cefotaxime combinations were demonstrated to have in vitro synergistic activities against multidrug-resistant strains. CONCLUSION: Three combinations showed in vitro synergism against penicillin- resistant pneumococci. Experimental animal study is warranted to determine the clinical relevance of the in vitro results.