Effects of Growth in the Presence of Subinhibitory Concentrations of Dicloxacillin on Staphylococcus epidermidis and Staphylococcus haemolyticus Biofilms

Low concentrations of antibiotics can inhibit microbial adherence to medical device surfaces. However, little is known about the changes that occur in the physiology of bacteria within biofilms formed in the presence of subinhibitory (sub-MIC) concentrations of antibiotics. In this study, the densities and matrix compositions ofbiofilms formed by two coagulase-negative Staphylococcus species in the absence and in the presence of sub-MIC concentrations of dicloxacillin were evaluated. Biofilms formed in the presence of sub-MIC concentrations of dicloxacillin contained less biomass, and there were notable changes in the composition of the biofilm matrix. Changes in the spatial structure were also verified by confocal scanning laser microscopy, indicating that biofilms grown in the presence of sub-MIC concentrations of dicloxicilln had a lower cell density. Physiological alterations in the bacteria within biofilms grown in the presence of subinhibitory concentrations of the antibiotic were also evaluated. The results showed that there were differences in bacterial surface characteristics when cultures were grown in the presence of sub-MIC concentrations of dicloxacillin, including decreased hydrophobicity and decreased expression of the exopolysaccharide poly-N-acetylglucosamine. The elemental composition of the cell surface was also analyzed, and whereas in Staphylococcus epidermidis there were decreases in the oxygen and nitrogen contents, in Staphylococcus haemolyticus there were increases in these two parameters. Additionally, increases in resistance to several antibiotics were observed for the cells within biofilms formed in the presence of dicloxacillin.     

In vitro activity of allicin against Staphylococcus epidermidis and influence of subinhibitory concentrations on biofilm formation

AIMS: The aim of this study is to determine the in vitro activity of allicin against Staphylococcus epidermidis and to evaluate the influence of allicin on biofilm formation. METHODS AND RESULTS: In vitro activity of allicin (diallyl thiosulphinate) against 38 strains of S. epidermidis was investigated. The activity of allicin was similar against S. epidermidis methicillin susceptible and methicillin resistant strains [minimum inhibitory concentration (MIC)90=8 mg l(-1)]. In general, subinhibitory concentrations (sub-MIC) of allicin diminished biofilm formation in the five strains analysed. CONCLUSION: The results confirm the antibacterial effect of allicin. Sub-MICs of allicin also diminished the biofilm formations by S. epidermidis. SIGNIFICANCE AND IMPACT OF THE STUDY: The present study shows that allicin is active in vitro against S. epidermidis and that sub-MICs of allicin may play a role in the prevention of adherence of this bacteria to medical devices.     

The evaluation of lipolytic activity of strains of Staphylococcus epidermidis and Staphylococcus haemolyticus

A total of 103 isolates of CNS (66 strains of S. epidermidis and 37 strains of S. haemolyticus) were investigated. Lipolytic activity of staphylococcal strains was determined by Tryptic Soy Agar containing Tween 20 or Tween 60. The 95.4% strains of staphylococci demonstrated the lipolytic activity on Tween 20 agar and the 89.4% of strains of staphylococci degradation ester of fatty acids on Tweens 60 agar. We detected that S. epidermidis strains (respectively 95,4%, 89,4%) produced lipases more frequently than S. haemolyticus strains (respectively 72,9%, 59,4%). Studies suggest that source of isolation from clinical materials (blood, wound and pus) does not have an influence on the ability hydrolysis esters.     

Anomalous growth of Staphylococcus epidermidis in the presence of Silastic and glycopeptide antibiotics

Abstract In the presence of supra-inhibitory concentrations of the glycopeptide antibiotics vancomycin and teicoplanin, biofilms of Staphylococcus epidermidis on a Silastic surface produce anomalous growwth. This takes the form of macroscopic, cohesive aggregates of cocci bound together with slime. This phenomenon was intermittent, independent of antibiotic concentrations between 20 and 50 μg ml⁻¹, occured more often with teicoplanin, and was found both with slime-negative strains.     

Viscoelastic properties of Staphylococcus aureus and Staphylococcus epidermidis mono‐microbial biofilms

The viscoelastic properties of mono‐microbial biofilms produced by ocular and reference staphylococcal strains were investigated. The microorganisms were characterized for their haemolytic activity and agr typing and the biofilms, grown on stainless steel surface under static conditions, were analysed by Confocal Laser Scanning Microscopy. Static and dynamic rheometric tests were carried out to determine the steady‐flow viscosity and the elastic and viscous moduli. The analysed biofilms showed the typical time‐dependent behaviour of viscoelastic materials with considerable elasticity and mechanical stability except for Staphylococcus aureus ATCC 29213 biofilm which showed a very fragile structure. In particular, S. aureus 6ME biofilm was more compact than other staphylococcal biofilms studied with a yield stress ranging between 2 and 3 Pa. The data obtained in this work could represent a starting point for developing new therapeutic strategies against biofilm‐associated infections, such as improving the drug effect by associating an antimicrobial agent with a biofilm viscoelasticity modifier.     

MicroDSC study of Staphylococcus epidermidis growth

Background  

A microcalorimetric study was carried out using a Staphylococcus epidermidis population to determine the reproducibility of bacterial growth and the variability of the results within certain experimental parameters (temperature, bacterial concentration, sample thermal history). Reproducibility tests were performed as series of experiments within the same conditions using either freshly prepared populations or samples kept in cold storage. In both cases, the samples were obtained by serial dilution from a concentrated TSB bacterial inoculum incubated overnight.     

Electric current-induced detachment of Staphylococcus epidermidis biofilms from surgical stainless steel

Biomaterial-centered infections of orthopedic percutaneous implants are serious complications which can ultimately lead to osteomyelitis, with devastating effects on bone and surrounding tissues, especially since the biofilm mode of growth offers protection against antibiotics and since removal frequently is the only ultimate solution. Recently, it was demonstrated that as a possible pathway to prevent infections of percutaneous stainless steel implants, electric currents of 60 to 100 microA were effective at stimulating the detachment of initially adhering staphylococci from surgical stainless steel. However, initially adhering bacteria are known to adhere more reversibly than bacteria growing in the later stages of biofilm formation. Hence, the aim of this study was to examine whether a growing Staphylococcus epidermidis biofilm can be stimulated to detach from surgical stainless steel by the use of electric currents. In separate experiments, four currents, i.e., 60 and 100 microA of direct current (DC) and 60 and 100 microA of block current (50% duty cycle, 1 Hz), were applied for 360 min to stimulate the detachment of an S. epidermidis biofilm that had grown for 200 min. A 100-microA DC yielded 78% detachment, whereas a 100-microA block current under the same experimental conditions yielded only 31% detachment. The same trend was found for 60 microA, with 37% detachment for a DC and 24% for a block current. Bacteria remaining on the surface after the current application were less viable than they were prior to the current application, as demonstrated by confocal laser scanning microscopy. In conclusion, these results suggest that DCs are preferred for curing infections.     

Antimicrobial activities of YycG histidine kinase inhibitors against Staphylococcus epidermidis biofilms

Staphylococcus epidermidis has become a significant pathogen causing infections due to biofilm formation on surfaces of indwelling medical devices. Biofilm-associated bacteria exhibit enhanced resistance to many conventional antibiotics. It is therefore, important to design novel antimicrobial reagents targeting S. epidermidis biofilms. In a static chamber system, the bactericidal effect of two leading compounds active as YycG inhibitors was assessed on biofilm cells by confocal laser scanning microscopy combined with viability staining. In young biofilms (6-h-old), the two compounds killed the majority of the embedded cells at concentrations of 100 microM and 25 microM, respectively. In mature biofilms (24-h-old), one compound was still effectively killing biofilm cells, whereas the other compound mainly killed cells located at the bottom of the biofilm. In contrast, vancomycin was found to stimulate biofilm development at the MBC (8 microg mL(-1)). Even at a high concentration (128 microg mL(-1)), vancomycin exhibited poor killing on cells embedded in biofilms. The two compounds exhibited faster and more effective killing of S. epidermidis planktonic cells than vancomycin at the early stage of exposure (6 h). The data suggest that the new inhibitors can serve as potential agents against S. epidermidis biofilms when added alone or in concert with other antimicrobial agents.     

Modulation of poly-N-acetylglucosamine accumulation within mature Staphylococcus epidermidis biofilms grown in excess glucose

PNAG is a major component of Staphylococcus epidermidis biofilms involved in intercellular adhesion as well as in the interaction of the biofilm with components of the host immune response. Synthesis of PNAG has been found to be regulated by several environmental factors. In the present study, the effect of glucose metabolism-dependent culture medium acidification in PNAG accumulation was evaluated. Established S. epidermidis biofilms were allowed to grow in excess glucose with or without maintained pH conditions. PNAG accumulation in these biofilms was determined by flow cytometry and fluorescence microscopy using wheat germ agglutinin as a fluorescent probe. Biofilms grown in maintained pH conditions presented significantly higher amounts of this polymer as well as higher icaA expression than biofilms grown in acidic pH conditions. Moreover, PNAG accumulation in biofilms grown in non-maintained pH conditions occurred in association with cell death. Overall, we show that glucose metabolism by decreasing the culture pH affects biofilm physiology in respect to PNAG production and cell death. The reported in vitro modulation of PNAG accumulation within S. epidermidis biofilms further highlights the role of environment on determining the biofilm physiological state.     

The Effects of Low-Frequency Ultrasound on Staphylococcus epidermidis

Low frequency ultrasound (LFUS) significantly enhances skin permeability to a variety of drugs; however, its bacterial effects have not been well studied. Staphylococcus epidermidis organisms were grown and standardized to 10⁵ cfu/ml 24 h prior to investigation and suspended in normal saline. LFUS was applied with two probes immersed in the bacterial suspensions over a range of suspension volumes, intensities, and exposure times. The suspension temperature was measured, and a sample was removed, streaked onto blood agar plates, and incubated at 37°C for 24 h. Quantitative bacterial counts were then obtained. LFUS resulted in significant reductions in bacterial counts that correlated with fluid temperature. Probe size and ultrasound intensity appeared to affect bacterial counts, but were also correlated with temperature. Bacterial growth was minimal with temperatures exceeding 45°C. While LFUS can reduce bacterial counts, these conditions have the potential to cause burns in humans. Received: 21 August 1998 / Accepted: 29 September 1998     

Dependence of Staphylococcus epidermidis on non-transferrin-bound iron for growth

The ability of Staphylococcus epidermidis strains to grow in the presence of human transferrin and varying amounts of ferric iron was studied. At initial bacterial densities up to 10(4) cfu ml(-1), none of the three strains grew when transferrin iron saturation was below the full saturation point, whereas the bacteria grew consistently when transferrin was fully iron-saturated and there was non-transferrin-bound iron in the medium. Precultivation of the bacteria under iron-restricted conditions to induce siderophore production did not abolish the growth dependence on non-transferrin-bound iron. At initial bacterial densities of 10(6) cfu ml(-1), the bacteria proliferated consistently also in the presence of partially saturated transferrin. The results indicate that at low bacterial densities, S. epidermidis cannot utilise transferrin-bound iron for growth and that its proliferation is dependent on non-transferrin-bound iron.     

The effects of subinhibitory concentrations of costus oil on virulence factor production in Staphylococcus aureus

Aim: To determine the antimicrobial activity of costus (Saussurea lappa) oil against Staphylococcus aureus, and to evaluate the influence of subinhibitory concentrations of costus oil on virulence‐related exoprotein production in staph. aureus. Methods and Results: Minimal inhibitory concentrations (MICs) were determined using a broth microdilution method, and the MICs of costus oil against 32 Staph. aureus strains ranged from 0.15 to 0.6 μl ml^?1. The MIC₅₀ and MIC₉₀ were 0.3 and 0.6 μl ml^?1, respectively. Western blot, haemolytic, tumour necrosis factor (TNF) release and real‐time RT‐PCR assays were performed to evaluate the effects of subinhibitory concentrations of costus oil on virulence‐associated exoprotein production in Staph. aureus. The data presented here show that costus oil dose dependently decreased the production of α‐toxin, toxic shock syndrome toxin 1 (TSST‐1) and enterotoxins A and B in both methicillin‐sensitive Staph. aureus (MSSA) and methicillin‐resistant Staph. aureus (MRSA). Conclusion: Costus oil has potent antimicrobial activity against Staph. aureus, and the production of α‐toxin, TSST‐1 and enterotoxins A and B in Staph. aureus was decreased by costus oil. Significance and Impact of the Study: The data suggest that costus oil may deserve further investigation for its potential therapeutic value in treating Staph. aureus infections. Furthermore, costus oil could be rationally applied in food products as a novel food preservative both to inhibit the growth of Staph. aureus and to repress the production of exotoxins, particularly staphylococcal enterotoxins.     

In vitro activity of alpha-mangostin in killing and eradicating Staphylococcus epidermidis RP62A biofilms

Applied Microbiology and Biotechnology - Alpha-mangostin (α-MG) has been reported to be an effective antibacterial agent against planktonic cells of many Gram-positive bacteria. However, the...     

Laser desorption 7.87 eV postionization mass spectrometry of antibiotics in Staphylococcus epidermidis bacterial biofilms

This paper describes the development of laser desorption 7.87 eV vacuum UV (VUV) postionization MS to detect antibiotics within intact bacterial colony biofilms. As >99% of the molecules ejected by laser desorption are neutrals, VUV photoionization of these neutrals can provide significantly increased signal as compared to the detection of directly emitted ions. Postionization with VUV radiation from the molecular fluorine laser single photon ionizes laser desorbed neutrals with ionization potentials below the 7.87 eV photon energy. Antibiotics with structures indicative of sub-7.87 eV ionization potentials were examined for their ability to be detected by 7.87 eV laser desorption postionization MS. Tetracycline, sulfadiazine, and novobiocin were successfully detected neat as dried films physisorbed on porous silicon oxide substrates. Tetracycline and sulfadiazine were then detected within intact Staphylococcus epidermidis colony biofilms, the former with LOD in the micromolar concentration range.     

表皮葡萄球菌对大鼠变应原敏感性的影响

目的 筛选具有较好抑制金黄色葡萄球菌效果的表皮葡萄球菌,研究通过鼻腔进行表皮葡萄球菌调节观察大鼠对变应原敏感性的效果。方法 由鼻腔拭子稀释液分离筛选得到的9株表皮葡萄球菌（Staphylococcus epidermidis）,使用上清液抑制法选取抑制金黄色葡萄球菌效果最好的表皮葡萄球菌做体内实验。将Wistar大鼠分为阴性组、模型组、表葡调节组。模型组、表葡调节组使用OVA建立呼吸道炎症模型,使用表皮葡萄球菌DMSA16001进行滴鼻调节2周,同时用PBS进行滴鼻对照。统计抓鼻和喷嚏数,用ELISA进行肺灌洗液（BALF）和外周血IgE的检测。结果 （1）不同株的表皮葡萄球菌均对金黄色葡萄球菌有抑制作用,表皮葡萄球菌DMSA16001对金黄色葡萄球菌的抑制率最高。（2）与模型组相比,表葡调节组的抓鼻数显著下降（t=2.173,P=0.049）,喷嚏数有下降趋势,表葡调节组的肺灌洗液和外周血血清的IgE水平均呈现下降趋势。结论 对金黄色葡萄球菌有抑制作用的表皮葡萄球菌能使OVA造模的哮喘大鼠对变应原敏感性降低。