Postantibiotic effects of imipenem and enoxacin against S. typhimurium and S. enteritidis and the influence on their surface hydrophobicity

Aggregation of Lactobacilli and Bifidobacteria with Escherichia coli O157

A total of 5 Bifidobacterium spp. isolated from pig and children' feces and 6 Lactobacillus spp. from chicken feces were examined for expression of aggregation, cell surface hydrophobicity (CSH) and adherence to intestinal mucin. Co-aggregation activity was seen in 3 strains of auto-aggregative bifidobacteria and 4 auto-aggregative strains of Lactobacillus spp. with 2 enterohemorrhagic E. coli (O157). CSH correlated with Lactobacillus auto-aggregating activity and adherence to mucin but the correlation between Bifidobacterium adherence to mucin and CSH was not confirmed.

Influence on Enterobacter cloacae metabolism, cell-surface hydrophobicity and motility of suprainhibitory concentrations of carbapenems

The impact of postantibiotic effect (PAE) of carbapenems (imipenem, meropenem) on the metabolism (biosynthesis of macromolecules, respiration), cell-surface hydrophobicity and motility of a clinical isolate of Enterobacter cloacae was examined. The metabolism was evaluated after 16 h and after 1 d of cultivation using 2x and 4x minimum inhibitory concentrations (MIC) of both antibiotics for the induction of PAE. Imipenem at 4 x MIC did not induce PAE. After a 16-h cultivation (in the postantibiotic phase of both carbapenems), inhibition of nucleosynthesis and protein synthesis was found; after a 1-d cultivation, during regrowth stimulation of mainly 14C-leucine incorporation was found. The presence of the exogenous intermediates of citrate cycle, viz. 2-oxoglutarate, increased the respiratory activity of the cells. The cell-surface hydrophobicity (evaluated by three methods--bacterial adhesion to hydrocarbon, nitrocellulose-filter test and salt-aggregation test) decreased after PAE of both carbapenems; meropenem was more effective. Motility (an important virulence factor) was inhibited in the postantibiotic phase of both carbapenems; the 4 x MIC caused a higher inhibition.

Aggregation of animal lactobacilli with O157 enterohemorrhagic Escherichia coli

The effect of selected autoaggregative lactobacilli on enterohemorragic O157 Escherichia coli was studied. A total of 27 Lactobacillus sp. strains were examined for expression of autoaggregation and cell surface hydrophobicity. Autoaggregative isolates were obtained from the crops of chickens and vaginas of calves. Aggregative activity was seen between eight autoaggregative lactobacilli and six strains of enterohemorrhagic E. coli O157. The presence of aggregation-promoting factor (apf gene) was confirmed by polymerase chain reaction (PCR). We propose that autoaggregative lactobacilli that aggregate with enterohemorrhagic E. coli can express a class of APF proteins that exhibit the function of an aggregative mediator. The results of this study suggest that APF-producing lactobacilli could represent a further mechanism in the interaction of comensal microflora with enterohemorrhagic E. coli.

Effects of subinhibitory concentrations of nitroxoline on the surface properties of Escherichia coli

Nitroxoline (5-nitro-8-quinolinol; NIQ) at subinhibitory concentrations (sub-MIC) decreased the adherence of uropathogenic Escherichia coli to catheter surface and significantly enhanced cell surface hydrophobicity. The surface hydrophobicity increased in the presence of sub-MIC of NIQ and also in an excess of Mg2+. The effect of NIQ on the cell surface was not related to the bacteriostatic effect of this agent. The increase in nitrogen and decrease in phosphate content in the cell surface was found in the presence of NIQ. NIQ did not inhibit the expression of fimbriae.

Postantibiotic effects of gentamicin and netilmicin on Serratia marcescens: effects on hydrophobicity and motility

The impact of postantibiotic effect (PAE) of aminoglycosides (gentamicin, netilmicin) on cell-surface hydrophobicity and motility of a clinical isolate Serratia marcescens was evaluated. For the induction of PAE 2x and 4xMIC concentrations of both antibiotics were used. Gentamicin and netilmicin induced a PAE of similar duration after 2xMIC concentration (2.7 and 2.8 h, respectively). Both aminoglycosides demonstrated concentration-dependent PAE. At a concentration of 4xMIC they produced PAEs of 5.9 and 8.2 h, respectively. The evaluation of hydrophobic properties of S. marcescens after affecting PAE showed that both aminoglycosides inhibited adherence to xylene. This inhibition was also concentration-dependent. More expressive was netilmicin which inhibited the adhesion by 70.5% at 2xMIC and by 85.2% at 4xMIC. Netilmicin inhibited also the adhesion to nitrocellulose filter by 34.7% at 4xMIC. Exposure of the bacterial cells to suprainhibitory concentrations of both aminoglycosides resulted only in moderate inhibition of motility of strain tested compared to the unexposed cells.

Some biological properties of new quinoline-4-carboxylic acid and quinoline-4-carboxamide derivatives

The antimicrobial and morphogenetic effects of fourteen newly synthesized 2-substituted derivatives of quinoline-4-carboxylic acid and quinoline-4-carboxamide were studied using G+ and G- bacteria, yeasts and filamentous fungi. The highest antimicrobial effects were found with substituted quinoline-4-carboxylic acid derivatives. Quinoline-4-carboxamides only weakly influenced the growth of the tested microorganisms. Some derivatives of quinoline-4-carboxylic acid elicited profound changes in the morphology of hyphal tips of Botrytis cinerea, mainly their branching and the release of the cytoplasmic content. Quinoline derivatives, which elicited morphological changes, increased also the permeability of the plasmalemma of plant cells.