Aim: The flavonol galangin, an antimicrobial constituent of the traditional medicines propolis and Helichrysum aureonitens, is being assessed as part of an ongoing investigation into the antibacterial activity of flavonoids. The present study sought to establish whether galangin has any aggregatory effect on bacterial cells. Methods and Results: In preparatory time‐kill assays, 50 μg ml−1 of galangin was found to reduce colony counts of c. 5 × 107 CFU ml−1Staphylococcus aureus NCTC 6571 by approximately 15 000‐fold during 60 min of incubation. Subsequent light microscopy studies demonstrated significant increases in the number of large clusters of bacterial cells in populations treated with the flavonol. Conclusion: Data presented here show that galangin causes aggregation of bacterial cells. Significance and Impact of the Study: The finding that galangin causes bacterial cells to clump together may implicate the cytoplasmic membrane as a target site for this compound’s activity. More importantly, this observation indicates that decreases in CFU numbers detected in time‐kill and minimum bactericidal concentration (MBC) assays in previous investigations were at least partially attributable to this aggregatory effect. This raises the possibility that galangin is not genuinely bactericidal in action, and calls into question the suitability of time‐kill and MBC assays for determining the nature of activity of naturally occurring flavonoids.
The postantibiotic effect (PAE) of meropenem was determined for 11 strains, both clinical isolates and reference strains of members of the family Enterobacteriaceae. The study compares PAE results obtained by five methods used to monitor bacterial regrowth, including viable counting, alone and in combination with impedance; bioluminescence, alone and in combination with impedance; and a morphological technique. After exposure of the test organisms to meropenem (0.1 x to 100 x MIC) for 2 h, concentration-dependent differences in counts by bioluminescence and viable counts were observed, the latter always being lower. The differences varied with the test organism. For example, after exposure ofProvidentia stuartii NCTC 10318 to 0.1 x MIC, the counts were 5.5 x 105 and 2.0 x l05 whereas after exposure of Citrobacter freundii MR76 to 0.1x MIC of meropenem the counts were 2.3 x 106 and 6.8 x 103 by bioluminescence and viable counting, respectively. The discrepancies were probably due to the relative inability of the viable counting procedure to detect fragile aberrant morphologies and resulted in differences in the calculated PAE values. With methods which do not detect fragile morphologies, the PAE may be underestimated. A general trend was observed for the order of magnitude of the PAEs by the following methods (in order of decreasing magnitude of PAE): (i) morphological technique, (ii) bioluminescence technique alone, (iii) bioluminescence in combination with impedance, (iv) viable counting in combination with impedance, and (v) viable counting alone. It is our opinion that of the methods examined in this study, bioluminescence in combination with impedance best reflects the true values for PAEs, and these results were examined more closely.Postantibiotic effect (PAE), the delayed regrowth of bacteria after antibiotic exposure, is now a well-established phenomenon that was first described almost 50 years ago (1). The effect appears to be a feature of virtually all antimicrobial agents and has been observed for a wide variety of bacteria and yeasts. It is, however, the specific antimicrobial agent-organism combination which determines the presence and duration of the PAE. Investigators using both old and new ,-lactams have consistently observed a PAE with gram-positive cocci (2). In contrast, after exposure of gram-negative bacilli to ,-lactams, PAEs, if any, are of short duration or have a negative value. PAE values obtained are, however, very dependent on the methods used to quantify the effect (8, 12). Bearing in mind that gram-negative bacilli generally form fragile spheroplasts when exposed to meropenem, the suitability of performing viable counts on these cell forms has been questioned, and it was found that an underestimation of the number of cells by viable counting led to an underestimation of the PAE (9,13,15). This study extends these observations of some members of the family Enterobacteriaceae by using an impedance technique (3) in conjunction with a bioluminescence assay of bacterial ATP (6) and compa...
The postantibiotic effect (PAE) of the carbapenem antibiotic meropenem was determined for the reference strains of Escherichia coli NCTC 4174 and E. coli NCTC 12210. Regrowth of bacteria after antibiotic exposure was determined by viable counting and bioluminescence alone and in combination with an impedance technique and a morphological technique was also employed. Different methods of calculating the PAE were also used. After exposure of E. coli to 0.1-100 x MIC of meropenem for 2 h, concentration dependent differences in counts by bioluminescence, and viable counting were observed, the latter always being lower. The unexposed control of E. coli NCTC 4174 yielded counts of 1.1 x 10(6) +/- 1.1 x 10(5) and 1.3 x 10(6) +/- 4.7 x 10(5) by viable counting and bioluminescence respectively and E. coli NCTC 12210 gave counts of 4.2 x 10(6) +/- 1.8 x 10(6) and 1.1 x 10(7) +/- 4.3 x 10(6) by the same methods. After exposure to 100 x MIC of meropenem, NCTC 4174 yielded counts of 1.28 x 10(3) +/- 5.35 x 10(2) and 2.59 x 10(5) +/- 8.61 x 10(4) and NCTC 12210 gave counts of 5.22 x 10(3) +/- 9.74 x 10(2) and 5.21 x 10(6) +/- 1.45 x 10(6) by viable counting and bioluminescence, respectively. The discrepancies were due to the inability of the viable counting procedure to detect spheroplasts. Falsely low post exposure counts led to falsely low determinations of PAE by viable counting alone and in combination with the impedance technique.(ABSTRACT TRUNCATED AT 250 WORDS)
Purpose – The purpose of this paper is to report the results of a study of voters' online behaviour conducted during the 2011 Scottish parliamentary election campaign. Design/methodology/approach – The study used an interactive, electronically-assisted interview method, where 64 citizens were observed and questioned while they searched for, browsed and used information on the web sites and social media sites of political parties and candidates standing for election to the Scottish Parliament. Findings – While online campaign sites were generally regarded as serving a useful purpose, as being easy to use and understand, relatively interesting and likely to be visited again, there was very little evidence in this study to indicate that they had any significant impact on voting behaviour during the 2011 Scottish campaign. Rather, the participants' comments suggest that more traditional information sources, particularly print and broadcast media, coupled with long-established campaign techniques, such as leaflet deliveries and door knocking, continue to be more influential in determining Scottish voters' democratic choices. Research limitations/implications – The paper presents results obtained from a sample of 64 citizens of North-east Scotland. As such, the authors would lay no claims to the results of the study being applicable outwith the Scottish setting. Practical implications – The findings have implications for those candidates successfully elected to the Scottish Parliament, who may have to significantly modify their information practices on entering parliament. The study also has implications for the broader, international, political and information research communities, as it has added to a rather sparse body of qualitative work on voters' online election information needs. The voter-centred methodological approach used in the study has the potential to be used or adopted more widely, to aid our understanding of the use and impact of online campaign tools. Originality/value – This study forms part of an ongoing series of investigations by the authors, which has examined the use of the internet by political parties and candidates during parliamentary election campaigns in Scotland. These are the only such studies which have looked specifically at the Scottish political arena. Internationally, most studies of users of online campaign resources have been largely quantitative in nature. The qualitative research discussed in this paper is, therefore, particularly timely and potentially significant.
The effects of pretreatment with colistin (polymyxin E) on the sensitivity of Proteus mirabilis, P. vulgaris and P. morganii strains to tris and sodium deoxycholate (DOC) have been studied. Pretreatment of two P. mirabilis strains (NCTC 60 and 4199) with low conc.ntrations (0.25 -1 #g/ml) of colistin rendered them sensitive to lysis by tris (0.05 M) or DOC (250-1,000 ,ug/ml) although DOC induced lysis of control (non colistin-treated) suspensions also. In contrast, the other P. mirabilis strains, as well as the P. vulgaris and P. morganii strains were little affected by tris (0.2 M) or DOC (10,000 /cg/ml) even after exposure of the cells to high colistin concentrations (up to 500 aug/ml). Colistin-pretreated or control cells of P. mirabilis NCTC 60 rapidly lost viability when suspended in water but not when held in 0.16 M sodium chloride solution. Ethylenediamine tetraacetate-pretreated cells of stra ns 60 and 4199 were fairly sensitive to tris, although the extent of the lysis was less than when c )listin was used as pretreating agent. One strain of P. vulgaris (NCTC 4175) became sensitive to tris and to DOC following exposure of the cells to ampicillin.
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