Action of penicillin onSerratia marcescens

The action of penicillin onSerratia marcescens was studied. In culture media containing sucrose (0.33m) and in the presence of magnesium ions, cell wall lesions occurred giving rise to osmotically fragile spheroplasts. However, in the absence of sucrose and magnesium ions it was still possible to induce some spheroplast formation. Quantitative aspects of the conversion of rods into spheroplasts were studied as well as physical properties of the spheroplasts.     

Effect of suprainhibitory concentrations of quinolones on hydrophobicity and motility of Serratia marcescens

The effect of suprainhibitory concentrations of quinolones (ciprofloxacin, enoxacin and norfloxacin) on the growth, hydrophobicity and motility of a nosocomial pathogen Serratia marcescens was studied. A postantibiotic effect (PAE) was induced by 2x of 4x MIC concentrations for 0.5 h. By using the 2x MIC concentrations all three quinolones induced equally long PAE approximately 1 h. The longest PAE of 5.4 h at 4x MIC concentration was induced by enoxacin. The results obtained showed that suprainhibitory concentrations of quinolones significantly stimulated the adhesion of S. marcescens to xylene, with the exception of enoxacin, which inhibited the adhesion to 61.2% at 4x MIC concentration. These results correlated with those in the salt aggregation test. The adhesion of strains to nitrocellulose filters did not influence the aftereffect of suprainhibitory concentrations of quinolones. Exposure of bacterial cells to suprainhibitory concentrations of ciprofloxacin and norfloxacin caused a reduction in motility, while this effect was more distinct at 4x MIC concentration. The results suggest that any consideration of postantibiotic effects should include the residual antibiotic effects on virulence factors, in addition to the defined suppression of bacterial regrowth.     

Postantibiotic effects of imipenem and enoxacin againstS. typhimurium andS. enteritidis and the influence on their surface hydrophobicity

The influence of the postantibiotic effect (PAE) and the postantibiotic sub-MICs effect (PA SME) of imipenem and enoxacin on the surface hydrophobicity ofS. typhimurium andS. enteritidis strains were studied by evaluating Congo red binding and the aggregation in molar solutions of ammonium sulfate (SAT). A PAE was induced by 2× and 4× MIC of antibiotics tested for 0.5 h. Suprainhibitory concentrations of imipenem againstS. typhimurium induced a short PAE (0.3–0.6 h) compared toS. enteritidis (6.0–9.7 h). Suprasubinhibitory concentrations of imipenem did not allow a regrowth ofS. enteritidis. Similar results were also found for enoxacin. Evaluation of surface hydrophobic properties of the salmonellas after affecting both PAEs and PA SMEs has shown that imipenem at concentrations 4×MIC and 4×MIC+0.3×MIC partially influenced the hydrophobicity ofS. typhimurium. S. enteritidis was more susceptible toward both antibiotics tested.     

Nephrotoxicity of gentamicin and netilmicin in the rat. Quantification and qualification of glomeruli

The application via i.v. jugular, in rats, of two fluorochromes (rhodamine 6GO and phosphine 3R) with a 10 min interval, allows the direct observation of nephronal corpuscles using an epifluorescent microscopical technique, as well as their eventual quantification and qualification into normal or semifunctional corpuscles. In rats previously treated by i.p. injection of gentamicin or netilmycin a decrease of the active nephronal population as well as an increase of the percentage of semifunctionality has been noticed.     

Alpha-chymotrypsin: effects of bicyclic substrate geometry and hydrophobicity on reactivity

The α-chymotrypsin-catalyzed hydrolysis rates of p-nitrophenyl cyclopentane-carboxylate (I), p-nitrophenyl indan-2-carboxylate (II), and p-nitrophenyl spiro-[4.4]nonane-2-carboxylate (III) were measured at pH 8.1 in 20% methanol. After correction for variations in reactivity owing to stereoelectronic effects inherent to the substrates, the deacylation rate constants (k_c)_n of I and II are not significantly different. In $\text{(}\text{k}{}_{\mathrm{c}}\text{K}{}_{\mathrm{m}}\text{)}{}_{\mathrm{n}}$ II is 50 times more reactive than I, which demonstrates that the aromatic ring of the former substrate contributes significantly to its reactivity. The nearly equal reactivities of II and III indicate that the enzyme is rather insensitive to the geometry of the nonester-bearing ring of these compounds.     

Isolation of pigmented and nonpigmented mutants of Serratia marcescens with reduced cell surface hydrophobicity

Enrichment for nonhydrophobic mutants of Serratia marcescens yielded two types: (i) a nonpigmented mutant which exhibited partial hydrophobic characteristics compared with the wild type, as determined by adherence to hexadecane and polystyrene; and (ii) a pigmented, nonhydrophobic mutant whose colonies were translucent with respect to those of the wild type. The data suggest that the pronounced cell surface hydrophobicity of the wild type is mediated by a combination of several surface factors.     

Effects of Oxygen on Aerosolized Serratia marcescens

Suspensions of Serratia marcescens (ATCC strain 14041) in water were aerosolized in a rotating drum in the presence of various concentrations of oxygen. The colony-forming ability of aerosolized organisms was rapidly destroyed by contact with 0.25% or more oxygen at 40% relative humidity (RH) and 25 C, but was almost unimpaired for at least 5 hr in nitrogen containing not more than 10 ppm of oxygen. Completely hydrated organisms were insensitive to oxygen at pressures up to 100 psi for 4 hr. No loss in viability occurred in aerosols of washed cells in air at 97% RH. It is proposed that dehydration of the aerosolized cell results in sensitization to lethal effects of oxygen, but is not the primary cause of death. Mn(++), Co(++), glycerol, and thiourea enhanced the biological stability of aerosols in air. Numerous similarities between the effects of oxygen in this system and in systems using freeze-dried or irradiated organisms or cell-free enzymes support the hypothesis that closely related mechanisms are involved.     

Increased cell surface hydrophobicity of a Serratia marcescens NS 38 mutant lacking wetting activity.

The cell surface hydrophobicity of Serratia marcescens appears to be an important factor in its adhesion to and colonization of various interfaces. The cell surface components responsible for mediating the hydrophobicity of S. marcescens have not been completely elucidated, but may include prodigiosin and other factors. In the present report we have investigated the potential role of serratamolide, an amphipathic aminolipid present on the surfaces of certain S. marcescens strains, in modulating cell surface hydrophobicity. The hydrophobic properties of a serratamolide-producing strain (NS 38) were compared with those of a serratamolide-deficient mutant (NS 38-9) by monitoring the kinetics of adhesion to hexadecane. Serratamolide production was monitored by thin-layer chromatography and the wetting activity of washed-cell suspensions on polystyrene. Wild-type NS 38 cells were far less hydrophobic than the serratamolide-deficient mutant cells were; the removal coefficients were 48 min-1 for the mutant, as compared with only 18 min-1 for the wild type. The data suggest that the presence of serratamolide on S. marcescens cells results in a reduction in hydrophobicity, presumably by blocking hydrophobic sites on the cell surface.     

Postantibiotic effects and postantibiotic sub-MIC effects of ciprofloxacin, pefloxacin and amikacin on the biological properties ofSalmonella strains

The postantibiotic effect (PAE) and the postantibiotic sub-MIC effect (PASME) of ciprofloxacin, pefloxacin and amikacin were studied forSalmonella typhimurium andS. enteritidis strains. PAE was induced by 2× and 4×MIC of antibiotics studied for 0.5 h. After PAE and PASME their effect on prophage induction of a lysogenicS. typhimurium strain and on Congo red binding for both strains as a marker of their surface hydrophobicity was examined. The longest PAE was found after treatment with ciprofloxacin, higher values being observed withS. typhimurium. PAEs of pefloxacin and amikacin were much lower, except for the suprainhibitory concentration 4×MIC of amikacin withS. enteritidis (6.9 h). PASMEs of ciprofloxacin did not allow any regrowth of either strain. For other antibiotics the PASME's were different while concentrations of 2×MIC+0.2×MIC and 0.3×MIC, and of 4×MIC+0.1×MIC, 0.2×MIC and 0.3×MIC of amikacin did not allow any regrowth ofS. enteritidis. PAEs of the antibiotics tested did not affect the Congo red binding by bothSalmonella strains, but the PAEs of ciprofloxacin and pefloxacin expressively induced a prophage of lysogenicS. typhimurium strain. We noted the influence of Congo red binding after applying 4×MIC+0.1×MIC, 0.2×MIC and 0.3×MIC of amikacin forS. typhinurium and 2×MIC+0.1×MIC forS. enteritidis.     

Influence of temperature on biofilm formation by Listeria monocytogenes on various food-contact surfaces: relationship with motility and cell surface hydrophobicity

Aims:  To assess the ability of Listeria monocytogenes to form biofilm on different food-contact surfaces with regard to different temperatures, cellular hydrophobicity and motility.
Methods and Results:  Forty-four L. monocytogenes strains from food and food environment were tested for biofilm formation by crystal violet staining. Biofilm levels were significantly higher on glass at 4, 12 and 22°C, as compared with polystyrene and stainless steel. At 37°C, L. monocytogenes produced biofilm at significantly higher levels on glass and stainless steel, as compared with polystyrene. Hydrophobicity was significantly ( P  < 0·05) higher at 37°C than at 4, 12 and 22°C. Thirty (68·2%) of 44 strains tested showed swimming at 22°C and 4 (9·1%) of those were also motile at 12°C. No correlation was observed between swimming and biofilm production.
Conclusions:  L. monocytogenes can adhere to and form biofilms on food-processing surfaces. Biofilm formation is significantly influenced by temperature, probably modifying cell surface hydrophobicity.
Significance and Impacts of the Study:  Biofilm formation creates major problems in the food industry because it may represent an important source of food contamination. Our results are therefore important in finding ways to prevent contamination because they contribute to a better understanding on how L. monocytogenes can establish biofilms in food industry and therefore survive in the processing environment.     

Influence onEnterobacter 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 ofEnterobacter cloacae was examined. The metabolism was evaluated after 16 h and after 1 d of cultivation using 2× and 4× minimum inhibitory concentrations (MIC) of both antibiotics for the induction of PAE. Imipenem at 4×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 mainly¹⁴C-leucine incorporation was found. The presence of the exogeneous 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×MIC caused a higher inhibition.     

Surfactin and iturin A effects on Bacillus subtilis surface hydrophobicity

The synthesis of extracellular molecules such as biosurfactants should have major consequences on bacterial adhesion. These molecules may be adsorbed on surfaces and modify their hydrophobicities. Certain strains of Bacillus subtilis synthesize the lipopeptides, which exhibit antibiotic and surface active properties. In this study the high-performance liquid chromatography (HPLC) analysis of the culture supernatants of the seven B. subtilis strains, showed that the lipopeptide profile varied greatly according to the strain. Among the three lipopeptide types, only iturin A was produced by all B. subtilis strains. Bacterial hydrophobicity, evaluated by the water contact angle measurements and the hydrophobic interaction chromatography, varied according to the strain. Two strains (ATCC 15476 and ATCC 15811) showing extreme behaviors in term of hydrophobicity were selected to study surfactin and iturin A effects on bacterial hydrophobicity. The two lipopeptides modified the B. subtilis surface hydrophobicity. Their effects varied according to the bacterial surface hydrophobic character, the lipopeptide type and the concentration. Lipopeptide adsorption increased the hydrophobicity of the hydrophilic strain but decreased that of the hydrophobic. Comparison of lipopeptide effects on B. subtilis surface hydrophobicity showed that surfactin was more effective than iturin A for the two strains tested.     

Hemagglutination (fimbriae) and hydrophobicity in adherence ofSerratia marcescens to urinary tract epithelium and contact lenses

The capacity of 59 isolates of Serratia marcescens, obtained from urinary tract infections, wounds, and contact lenses or their paraphernalia, to agglutinate erythrocytes from different animal species was tested. Three main patterns were found: mannose-sensitive agglutination of guinea-pig, fowl or horse erythrocyte; mannose-resistant agglutination of chicken or pigeon erythrocytes alone or in combination with mannose-sensitive agglutination; and no agglutination. Hemagglutination capacity was associated with isolates from urinary tract infection, but not with isolates associated with contact lenses. Adherence to human urinary tract epithelium did not correlate with the hemagglutination patterns nor with the origin of the isolates. Some strains of different hemagglutination pattern were selected for the study of hydrophobicity and adherence to contact lens polymers. Hydrophobicity, as determined by degree of partition in hexadecane and water (BATH-values), correlated neither with degree of adherence to contact lens polymers nor with the hemagglutination pattern. For a representative strain there was an excellent correlation (r2 = 0.98) between adherence and the water content (hydrophobicity) of the lens polymers. These results suggest that, as with tissues, other factors interact with hydrophobicity in causing adherence to plastics.     

Putative role of a 70 kDa outer-surface protein in promoting cell-surface hydrophobicity of Serratia marcescens RZ

Serratia marcescens RZ has been previously shown to possess pronounced cell-surface hydrophobicity, as evidenced by its affinity for hydrocarbons and polystyrene. The present report suggests the involvement of a 70 kDa protein, serraphobin, in this phenomenon. The 70 kDa protein was recovered from both the cell surface and culture supernatant of hydrophobic wild-type cells, but was either totally absent or present in minor quantities in hydrophobicity-deficient mutants. Similarly, loss of hydrophobicity of RZ cells following growth at 39 degrees C was accompanied by loss of the protein. Serraphobin was capable of binding to hexadecane droplets following a brief mixing procedure, and could be desorbed by solidifying and melting the hexadecane phase.     

Biochemical and morphological effects of gentamicin in human proximal tubular cells: effects on lipid and lipoprotein metabolism

The effects of gentamicin, an antibiotic used extensively for antimicrobial therapy on the ultrastructure, binding, internalization, degradation, and cholesterol esterification of low-density lipoproteins, were investigated in cultured human proximal tubular cells. Cells were incubated with 0.3 mM gentamicin for 21 days with the following observations. Cells treated with gentamicin contained numerous "myeloid bodies." The binding, internalization, and degradation of 125I-labeled low-density lipoproteins ([125I]LDL) in cells treated with gentamicin was twofold lower than control cells. Pulse-chase experiments demonstrated that gentamicin did not impair the internalization of receptor-bound LDL and their subsequent transport to the lysosome. The relative amounts of [125I]LDL displaced by increasing concentrations of unlabeled LDL were the same in both gentamicin-treated and control cells. This pattern was reflected in the cell surface binding, internalization, and degradation of [125I]LDL. Gentamicin did not alter the degradation of [125I]LDL in cell homogenates at 4.0. The data suggest that gentamicin decreases the receptor-mediated endocytosis of LDL and subsequent lipid metabolism.     

Tumour invasion: effects of cell adhesion and motility

Metastasis is the major cause of failure in cancer therapy. Recent studies of the molecular cell biology of the metastatic process have provided new insights into the mechanisms of cell-cell adhesion, cell-substrate adhesion and cell motility that underly invasion by tumour cells. In this review, Van Roy and Mareel discuss the role of proteins with invasion-promoting and invasion-suppressing functions in metastasis.     

Covalently linked gramicidin channels: effects of linker hydrophobicity and alkaline metals on different stereoisomers

The direct role of the dioxolane group on the gating and single-channel conductance of different stereoisomers of the dioxolane-linked gramicidin A (gA) channels reconstituted in planar lipid bilayers was investigated. Four different covalently linked gA dimers were synthesized. In two of them, the linker was the conventional dioxolane described previously (SS and RR channels). Two gAs were covalently linked with a novel modified dioxolane group containing a retinal attachment (ret-SS and ret-RR gA dimers). These proteins also formed ion channels in lipid bilayers and were selective for monovalent cations. The presence of the bulky and hydrophobic retinal group immobilizes the dioxolane linker in the bilayer core preventing its rotation into the hydrophilic lumen of the pore. In 1 M HCl the gating kinetics of the SS or RR dimers were indistinguishable from their retinal counterparts; the dwell-time distributions of the open and closed states in the SS and ret-SS were basically the same. In particular, the inactivation of the RR was not prevented by the presence of the retinal group. It is concluded that neither the fast closing events in the SS or RR dimers nor the inactivation of the RR are likely to be a functional consequence of the flipping of the dioxolane inside the pore of the channel. On the other hand, the inactivation of the RR dimer was entirely eliminated when alkaline metals (Cs(+) or K(+)) were the permeating cations in the channel. In fact, the open state of the RR channel became extremely stable, and the gating characteristics of both the SS and RR channels were different from what was seen before with permeating protons. As in HCl, the presence of a retinal in the dioxolane linker did not affect the gating behavior of the SS and RR in Cs(+)- or K(+)-containing solutions. Alternative hypotheses concerning the gating of linked gA dimers are discussed.     

Solute effects on Lagenidium giganteum: zoospore motility and bioassay reproducibility

The zoospores of Lagenidium giganteum rapidly lose motility when dispersed in deionized water. Several organic solutes were tested for the ability to prolong zoospore activity. Peptone at 0.2 and 0.05 g/liter was more effective than methionine and glucose, individually or in combination. The use of 0.2 g/liter of peptone as a medium for bioassays of L. giganteum against 3-day-old Aedes aegypti reduced the mean LD₅₀ to 12.9 zoospores/ml as compared to 133 with field water and 124 with deionized water. The use of peptone also dramatically improved the reproducibility of the assays and the goodness of fit of the resultant probit regression lines. The mean χ² values were 7.4 for 0.2 g/liter of peptone, 26.8 for field water, and 47.8 for deionized water. It is suggested that the erratic results obtained from use of deionized water are due to variation in the osmotic stress to which the zoospores were exposed, depending on the amount of debris that is introduced into the assays along with the mosquito larvae.