Bacterial adhesion onto materials with specific surface chemistries under flow conditions

Staphylococcus epidermidis adhesion onto materials with specific chemical functionalities, under flow, was investigated by using surfaces prepared by self-assembly of alkyl silane monolayers on glass. Terminal methyl (CH(3)) and amino (NH(2)) groups were formed by chemical vapor deposition of silanes, at elevated temperature. Carboxyl (COOH) terminated groups were prepared by further modification of NH(2) groups with succide anhydride and positively charged NH(2) groups by adsorption of poly-L: -lysine hydrobromide. Hydroxyl (OH) terminated glass was used as control. Surface modification was verified by contact angle measurements, atomic force microscopy and X-ray photoelectron spectroscopy. A parallel plate flow chamber was used to evaluate bacterial adhesion at various shear rates. Adhesion was found to be depended on the monolayer's terminal functionality. It was higher on the CH(3) followed by the positively charged NH(2), the non-charged NH(2) groups, the COOH and minimal on the OH-terminated glass. The increase in the material surface free energy significantly reduced the adhesion of a hydrophilic bacterial strain, and this is in accordance with the predictions of the thermodynamic theory. However, the increase in the shear rate restricted the predictability of the theory and revealed macromolecular interactions between bacteria and NH(2)- and COOH-terminated surfaces.

Application of the mixture design to optimise the formulation of active consortia to decolorize azo-dye methyl red

With the aid of analysis software (Minitab 14.0), the formulation of pure culture in Mineral Salts Medium (MSM) can be optimized for several responses and the best formulation can be obtained. The influence of the different mixtures of three strains in the pure culture in MSM on the flavor components in decolorization of Methyl Red (with initial total cell density fixed at OD600 = 1 and in addition of 750 ppm of dye) was studied using equilateral triangle diagram and mixture experimental design to assess color and COD removal during species evolution. The regression model on microorganism composition and main metabolites was established. The results suggested that the highest predictable specific decolorization rate and Chemical Oxygen Demand (COD) were 77.97 and 93.77%. Based on these, the response values that satisfied all expectations were optimized, and the optimal composition of the mixed consortium for the dedolorization and COD removal were (Sphingomonas paucimobilis 45.20%, Bacillus sp 61.94% and Staphylococcus epidermidis 80.00%) and (Sphingomonas paucimobilis 77.03%, Bacillus sp 86.42% and Staphylococcus epidermidis 71.74%) respectively. Very high regression coefficient between the variables and the responses: decolorization and COD removal were respectively R(2)=0.96 and 0.81 indicated excellent evaluation of experimental data by polynomial regression model.

[Comparison of three methods detection of slime production by Staphylococcus aureus and Staphylococcus epidermidis]

In this article, slime production of Staphylococcus aureus and Staphylococcus epidermidis strains from infective skin lesions was evaluated by three different methods: Congo red agar method (CRA), Christensen tube method (CT) and spectrophotometric method (SC). All strains by CT method interpreted as negative (dark-claret or red colonies of the surface). 12 (37.5%) strains of S. aureus, 16 (50.0%) strains of S. epidermidis produced slime as shown by CT method, 6 (18.7%) strains of S. aureus, 8 (25,0%) strains of S. epidermidis by SC method. They also found a correlation of slime production by CT and SC method (p > 0.05).

Mobile genetic element-encoded cytolysin connects virulence to methicillin resistance in MRSA

Bacterial virulence and antibiotic resistance have a significant influence on disease severity and treatment options during bacterial infections. Frequently, the underlying genetic determinants are encoded on mobile genetic elements (MGEs). In the leading human pathogen Staphylococcus aureus, MGEs that contain antibiotic resistance genes commonly do not contain genes for virulence determinants. The phenol-soluble modulins (PSMs) are staphylococcal cytolytic toxins with a crucial role in immune evasion. While all known PSMs are core genome-encoded, we here describe a previously unidentified psm gene, psm-mec, within the staphylococcal methicillin resistance-encoding MGE SCCmec. PSM-mec was strongly expressed in many strains and showed the physico-chemical, pro-inflammatory, and cytolytic characteristics typical of PSMs. Notably, in an S. aureus strain with low production of core genome-encoded PSMs, expression of PSM-mec had a significant impact on immune evasion and disease. In addition to providing high-level resistance to methicillin, acquisition of SCCmec elements encoding PSM-mec by horizontal gene transfer may therefore contribute to staphylococcal virulence by substituting for the lack of expression of core genome-encoded PSMs. Thus, our study reveals a previously unknown role of methicillin resistance clusters in staphylococcal pathogenesis and shows that important virulence and antibiotic resistance determinants may be combined in staphylococcal MGEs.

The extreme danger associated with Staphylococcus aureus infections is due to the combination of frequent antibiotic resistance, which prevents efficient treatment, with extraordinary virulence, which determines the severity of disease. S. aureus is known to exchange antibiotic resistance and virulence determinants between different strains, thereby spreading the capacity to cause serious infections in the S. aureus population. The genetic information for these determinants is usually found on so-called mobile genetic elements. It has been noted that such exchangeable elements carry genes for either virulence or antibiotic resistance, but not both. Here, we identified and characterized a potent toxin, whose gene is located within an element that encodes resistance to the important antibiotic methicillin. The toxin had strong capacity to kill human white and red blood cells and significantly affected the capacity of MRSA to cause disease. Our study shows that acquisition of methicillin resistance may be combined with gaining possession of potent toxins by a single event of genetic exchange, which likely represents an important feature accelerating the evolution of MRSA virulence.

Teicoplanin in gram-positive infection: microbiological aspects

The widespread use of indwelling catheters and successful antibiotic treatment of Gram-negative infections has led to an increase of Gram-positive infections in severely neutropenic patients; Staphylococcus epidermidis is predominant in these infections. The problems associated with the use of vancomycin in treating such infections can be overcome by the glycopeptide antibiotic teicoplanin. It is as effective as vancomycin, but does not cause "red man" syndrome, is uncommonly nephrotoxic, can be given as a rapid bolus once daily, and routine serum monitoring is not required. Other approaches to reducing catheter-related infections include improved training of personnel in catheter insertion and the development of new materials and methods in cannula production.

Biofilm formation by ica-positive and ica-negative strains of Staphylococcus epidermidis in vitro

Staphylococcus epidermidis is a clinically important opportunistic pathogen that forms biofilm infections on nearly all types of indwelling medical devices. The biofilm forming capability of S. epidermidis has been linked to the presence of the ica operon in the genome, and the amount of biofilm formation measured by the crystal violet (CV) adherence assay. Six S. epidermidis strains were characterized for their ica status using PCR, and their biofilm forming ability over 6 days, using the CV assay and a flow cell system. Ica-negative strains characterized as 'negative for biofilm formation' based on the CV assay were demonstrated to form strongly attached biofilms after 6 days. However, the biofilms were not as extensive as the ica-positive strains. It was concluded that ica is not required for biofilm formation, nor is the 24-h CV assay generalizable for predicting the 6-day biofilm-forming ability for all S. epidermidis strains.

In vitro biocompatibility and bacterial adhesion of physico-chemically modified Ti6Al4V surface by means of UV irradiation

UV irradiation leads to a "spontaneous" wettability increase of the Ti6Al4V surface while preserving bulk properties of the alloy that are crucial for its performance as an orthopedic and dental implant. We hypothesized that UV treatment of Ti6Al4V may impair bacterial adhesion without compromising the good response of human bone-forming cells to this alloy. The in vitro biocompatibility of the Ti6Al4V surface, before and after UV irradiation, was analyzed by using human cells related to the osteoblastic phenotype. The adhesion processes of bacterial strains related to clinical orthopedic infections, i.e., Staphylococcus aureus and Staphylococcus epidermidis, were studied theoretically and in vitro, under dynamic and static conditions as well as in the presence or absence of shear forces. While human cell adhesion was not altered by UV irradiation of Ti6Al4V alloy, this treatment reduced not only initial bacterial adhesion rates but also the number of bacteria retained on the surface after the passage of two air-liquid interfaces on the previously adhered bacteria. This study proposes the use of UV treatment prior to implantation protocols as an easy, economic and effective way of reducing bacterial adhesion on the Ti6Al4V surface without compromising its excellent biocompatibility.

Tricarboxylic acid cycle-dependent regulation of Staphylococcus epidermidis polysaccharide intercellular adhesin synthesis

Staphylococcus epidermidis is a major nosocomial pathogen primarily infecting immunocompromised individuals or those with implanted biomaterials (e.g., catheters). Biomaterial-associated infections often involve the formation of a biofilm on the surface of the medical device. In S. epidermidis, polysaccharide intercellular adhesin (PIA) is an important mediator of biofilm formation and pathogenesis. Synthesis of PIA is regulated by at least three DNA binding proteins (IcaR, SarA, and sigma(B)) and several environmental and nutritional conditions. Previously, we observed the environmental conditions that increased PIA synthesis decreased tricarboxylic acid (TCA) cycle activity. In this study, S. epidermidis TCA cycle mutants were constructed, and the function of central metabolism in PIA biosynthesis was examined. TCA cycle inactivation altered the metabolic status of S. epidermidis, resulting in a massive derepression of PIA biosynthetic genes and a redirection of carbon from growth into PIA biosynthesis. These data demonstrate that the bacterial metabolic status is a critical regulatory determinant of PIA synthesis. In addition, these data lead us to propose that the TCA cycle acts as a signal transduction pathway to translate external environmental cues into intracellular metabolic signals that modulate the activity of transcriptional regulators.

[Induction of PBP2' by antibiotics and disinfectants in MRSE]

OBJECTIVE

Methicilllin-resitant Staphylococcus aureus (MRSA) is still the most important bacterium for hospital infection control, and is known to exhibit beta-lactam resistance. Moreover, the increase in PBP2'-producing methicillin-resistant coagulase-negaive Staphylococcus (MR-CNS), especially methicillin-resistant S. epidermidis (MRSE) has been problematic. In this study, we investigated the induction of PBP2' by MPIPC, other antibiotics and disinfectants in MRSE.

MATERIALS AND METHODS

The bacterial strains used were MRSE isolated in our clinical laboratory. MRSA-LA 'Seiken' was used for the detection of PBP2'. To investigate induction of PBP2' by MPIPC in MRSE, MRSE was cultured on the medium containing MPIPC at 11 different concentrations from 0.0001 to 6 microg/ml, and PBP2' induction was investigated. Strains in which no induction was noted at a low MPIPC concentration were cultured with other antibiotic discs and discs impregnated with various disinfectants, and PBP2' was detected in colonies that grew around the disc and PBP2' induction was investigated.

RESULTS

In the culture on MPIPC-supplemented medium, PBP2' was detected in all strains at 0.01-6 microg/ml. At 0.001 and 0.0001 microg/ml, 8/10 and 4/10 were positive, respectively. Addition of another beta-lactam, particularly cephem antibiotics, induced PBP2' in some strains that were negative at 0.0001 microg/ml. In cultures with disinfectants, inhibition zones were noted, but no PBP2' was induced.

CONCLUSION

PBP2' was induced by a low beta-lactam and was not by disinfectants in MRSE.

[Polyhydroxyalkanoates microbiological synthesis from food wastes]

To reduce the production cost of polyhydroxyalkanoates (PHAs), the process feasibility and physicochemical properties of PHAs synthesized by Alcaligenes latus, Staphylococcus epidermidis and activated sludge from malt waste, soy waste, confectionary waste, ice cream waste, milk waste, sesame oil and vinegar waste were analyzed. Results showed that through two-stage fed-batch fermentation, the maximum yield of PHAs accumulated by the three kinds of microorganisms from malt waste was 70.1%, 16.0% and 43.3%, separately. A. latus adapted itself to the food wastes in PHAs synthesis and new cell growth quickly. A. latus had higher PHAs yield and productivity under nitrogen limited condition. Micro-aerobically, S. epidermidis separated from sesame oil could produce polyhydroxybutyrate (PHB) with molecular weight of over 1 x 10(6). From soy waste, activated sludge accumulated polyhydroxybutyrate-co-hydroxyvaluate (PHBV) copolymer which had hydroxyvaleryl content (HV%) of 21%. Most food wastes are suitable for synthesizing PHAs with different physicochemical properties. The composition and properties of PHAs are influenced by the character of microorganism, the selection of substrates and optimization of ferment conditions.

Evaluation of the medicinal potentials of the methanol extracts of the leaves and stems of Halleria lucida

The medicinal potentials of the methanol extracts of the leaves and stems of Halleria lucida (Scrophulariaceae) were evaluated by assessing their antibacterial and antioxidant properties in vitro using standard procedures. The antioxidant activities of methanol extract of the leaves as determined by the ABTS, DPPH, proanthocyanidins and total flavonoids were higher than that of the stem. On the other hand, the total phenols, the flavonoids and the FRAP contents of the stem were higher than that of the leaves. The extracts however showed poor activity against both Gram-positive and Gram-negative bacteria. The methanol extract of the stem showed activities against Bacillus cereus and Staphylococcus epidermidis at MIC of 1.0 mg/ml. The methanol extract of the leaves did not show activity against any of the organisms used in this study. This study has to some extent validated the medicinal potential of the leaves and stems of H. lucida.

RecA mediated spontaneous deletions of the icaADBC operon of clinical Staphylococcus epidermidis isolates: a new mechanism of phenotypic variations

Phenotypic variation in biofilm formation is common in clinical isolates of S. epidermidis. In the current study, nearly 5% of all clinical isolates analysed showed phenotypic variation in biofilm forming ability and electrophoretic mobility (EM). This is the first report of S. epidermidis strains irreversibly switching from biofilm-positive to biofilm-negative phenotype by spontaneous deletion of icaADBC genes which represents a new, possibly common mechanism of phenotypic variation.

Receptor-interacting protein-2 deficiency delays macrophage migration and increases intracellular infection during peritoneal dialysis-associated peritonitis

BACKGROUND

Early upregulation of receptor-interacting protein-2 (RIP2) expression during peritoneal dialysis (PD)-associated peritonitis correlates with a favorable clinical outcome, while failure to upregulate RIP2 correlates with a protracted course. We noticed that patients who do not upregulate RIP2 during PD-associated peritonitis have more peritoneal macrophages during the early phase of infection.

METHODS

To study the mechanism behind this observation, we examined the role of RIP2 in the immune response to bacterial challenge in a mouse model of acute peritonitis. We injected RIP2(+/+) and RIP2(-/-) mice intraperitoneally with a Staphylococcus epidermidis cell free-preparation, and peritoneal cells were isolated 3, 6 and 24 h after challenge.

RESULTS

Surprisingly, RIP2(-/-) mice had a comparable influx of inflammatory leukocytes, but had a significantly higher number of peritoneal macrophages at 3 h, indicating delayed emigration of these cells. No significant differences were seen at later times suggesting that migration was delayed but not inhibited. In addition, RIP2(-/-) macrophages were more permissive to intracellular infection by Staphylococcus aureus, indicating that, in the absence of RIP2, resident peritoneal macrophages could become reservoirs of bacteria.

CONCLUSION

These findings provide a mechanism for the observation that upregulation of RIP2 expression is required for rapid resolution of peritonitis, by decreasing intracellular infection and by regulating the migration of antigen-presenting cells in the early stages of an inflammatory response.

The staphylococcal respiratory response regulator SrrAB induces ica gene transcription and polysaccharide intercellular adhesin expression, protecting Staphylococcus aureus from neutrophil killing under anaerobic growth conditions

In anaerobic environments, Staphylococcus aureus increases the transcription of the intercellular adhesin (ica) cluster, leading to increased polysaccharide intercellular adhesin (PIA) production. The regulatory mechanisms involved in this phenotypic change are mostly unknown. Here we show that the staphylococcal respiratory response regulator, SrrAB, significantly increases icaA transcription under anaerobic growth in S. aureus. Phosphorylated SrrA preferentially bound to a 100 bp DNA sequence located upstream of ica, and dot blot assays revealed little or no PIA expression in S. aureus srrAB deletion-replacement mutants of strains Sa113 and SH1000, grown anaerobically. The biological relevance of SrrAB for S. aureus was assessed in a phagocytosis assay employing human neutrophils. Sixty-eight per cent of PIA producing wild-type cells, but only 19% of srrAB mutant cells survived under anaerobic conditions, suggesting that PIA protected S. aureus against non-oxidative killing mechanisms of the neutrophils. No protection was observed when S. aureus or S. epidermidis strains, producing PIA also under aerobic conditions, were subjected to phagocytosis under aerobic conditions. These results demonstrate that SrrAB is a major activator of ica expression and PIA production in anaerobic environments, where it contributes to the protection of S. aureus against non-oxidative defence mechanisms.

Mechanical, tribological, and biocompatibility properties of ZrN-Ag nanocomposite films

Nanocomposite films of ZrN-Ag were produced by reactive unbalanced magnetron sputtering, and their structural, chemical, mechanical, tribological, haemocompatibility, and antibacterial properties were studied as a function of film composition. The films formed a dense and homogeneous microstructure whereby nanocrystals of Ag are distributed evenly throughout the ZrN matrix. For small additions of silver, the hardness was found to increase, whereas the elastic modulus was found to decrease drastically. In the process of optimizing the deposition conditions, three kinds of coatings were prepared on 316 L surgical steel and tested by accelerated electrochemical polarization tests in order to detect the influence of Ag and the value of the bias potential on the corrosion performance of the system. Films produced under the optimum deposition conditions were, subsequently, deposited on medical grade Ti-Al-V and worn against ball-bearing steel using a ball-on-disk tribotester in bovine serum and were found to have superior tribological properties compared with single-phase ZrN coatings. The haemocompatibility of the films was assessed by investigating the adsorption of human serum albumin and fibrinogen on samples with different phase compositions. Quantification of the protein adsorption was carried out using spectroscopic ellipsometry, which confirmed the haemocompatibility of the films. Antibiotic activity of the films was quantified by incubating the films in bacterial cultures, namely, Staphylococcus epidermis, Staphylococcus aureus, and Escherichia coli. Films with a silver content > 10% exhibited superior antibacterial activity compared with the uncoated samples.

Susceptibility of Staphylococcus epidermidis planktonic cells and biofilms to the lytic action of staphylococcus bacteriophage K

AIMS

To evaluate differences in biofilm or planktonic bacteria susceptibility to be killed by the polyvalent antistaphylococcus bacteriophage K.

METHODS AND RESULTS

In this study, the ability of phage K to infect and kill several clinical isolates of Staphylococcus epidermidis was tested. Strains were grown in suspension or as biofilms to compare the susceptibility of both phenotypes to the phage lytic action. Most strains (10/11) were susceptible to phage K, and phage K was also effective in reducing biofilm biomass after 24 h of challenging. Biofilm cells were killed at a lower rate than the log-phase planktonic bacteria but at similar rate as stationary phase planktonic bacteria.

CONCLUSIONS

Staphylococcus epidermidis biofilms and stationary growth phase planktonic bacteria are more resistant to phage K lysis than the exponential phase planktonic bacteria. SIGNIFICANCE OF STUDY: This study shows the differences in Staph. epidermidis susceptibility to be killed by bacteriophage K, when grown in biofilm or planktonic phenotypes.

Role of autolysin-mediated DNA release in biofilm formation of Staphylococcus epidermidis

Staphylococcus epidermidis has become a serious nosocomial pathogen frequently causing infections associated with implanted foreign materials. Biofilm formation is considered a major factor determining S. epidermidis pathogenicity in such device-associated infections. Here, evidence is presented that extracellular DNA is important for the initial phase of biofilm development by S. epidermidis on polystyrene or glass surfaces under static or hydrodynamic conditions. Comparative PCR amplification from S. epidermidis chromosomal and extracellular DNA indicated that the extracellular DNA is similar to chromosomal DNA. Experiments involving the S. epidermidis wild-type and an isogenic atlE mutant indicated that most of the extracellular DNA in S. epidermidis cultures and biofilms is generated through activity of the autolysin AtlE. The presented results suggest that extracellular DNA is generated in S. epidermidis populations through AtlE-mediated lysis of a subpopulation of the bacteria, and that the extracellular DNA promotes biofilm formation of the remaining population.

Mode of antibacterial action of a signal peptide, Pep27 from Streptococcus pneumoniae

The aim of this study was to assess the in vitro antimicrobial activity of Pep27 and its mode of action. The results indicated Pep27 exhibited antibacterial activities against pathogenic Gram-positive and Gram-negative bacteria without hemolytic effect on human erythrocytes, but it did not exhibit antifungal activity. To understand the mode of action of Pep27, the cellular distribution of the peptide was investigated. Flow cytometry analysis exhibited Pep27 penetrated the bacterial membrane by an energy-independent pathway without any damage to the membrane when examined using liposome and membrane probe. After penetration into the bacterial cells, Pep27 was not affected by macromolecular synthesis, but activated protein phosphatase activity in dose ranges of 10-15 microM and time range of 5-10 min in case of Staphylococcus epidermidis and Pseudomonas aeruginosa, respectively. These results demonstrated the antibacterial activities of Pep27 are fundamentally attributable to a physiological change by activated phosphatase activity.

[Diagnostic value of persistent characteristics of staphylococci during their carriage]

Comparative assessment of information value of significant persistent characteristics of staphylococci in state of carriage was made, and the usefulness of these characteristics for creating diagnostic models was defined. One hundred and fifty strains of Staphylococcus aureus and S. epidermidis isolated from healthy persons with subsequent differentiation of carriage types were used in the study. It has been established that strains isolated from resident carriers more often have more markedly expressed factors of persistence. Ranking the factors of persistence of staphylococci according to their information value during carriage allowed to identifythe leading sign among them--anti-carnosine activity. Using factor analysis, obtained signs were united in the single complex defining bacterial carriage, which allows to build a mathematical model permitting to diagnose staphylococcal carriage with 95% probability.

Microbiological assay for ceftazidime injection

A simple, sensitive, and specific biodiffusion assay for the antibacterial ceftazidime was developed using a strain of Staphylococcus epidermidis (ATCC 12228) as the test organism. Ceftazidime was measured in powder for injection at concentrations ranging from 100 to 400 microg/mL. The calibration graph for ceftazidime was linear (r2 = 1), and the method validation showed that it was precise (relative standard deviation = 0.415) and accurate. The results obtained by biodiffusion assay were statistically calculated by linear parallel model and by means of regression analysis and were verified using analysis of variance. It was concluded that the microbiological assay is satisfactory for in vitro quantification of the antibacterial activity of ceftazidime in pharmaceuticals.

Actividad y permeabilidad de linezolid y vancomicina en biocapas de Staphylococcus epidermidis

INTRODUCTION

The activity and capacity for penetration of linezolid and vancomycin were comparatively evaluated against Staphylococcus epidermidis biofilms.

METHODS

The activity of linezolid versus vancomycin was assessed against 24-hour S. epidermidis biofilms developed on silicon catheters. Penetration of the two antimicrobial agents was measured in biofilms developed on polycarbonate membrane filters. Penetration and activity were comparatively tested using S. epidermidis, slime-producing and non-slime-producing strains.

RESULTS

The activity of linezolid against S. epidermidis biofilms was significantly greater than that of vancomycin for both strains. Neither antimicrobial completely eradicated bacterial survival in 24-hour biofilms. Linezolid penetration in biofilms was greater than that of vancomycin for both S. epidermidis strains.

CONCLUSIONS

Linezolid showed higher in vitro activity than vancomycin against S. epidermidis biofilms on silicone catheters. This effect may be due to the capability of linezolid to cross the bacterial biofilm.

Raman spectroscopic discrimination of cell response to chemical and physical inactivation

Raman spectroscopy was applied to study Escherichia coli and Staphylococcus epidermidis cells that were inactivated by different chemicals and stress conditions including starvation and high temperature. E. coli cells exposed to starvation conditions over several days lost viability at the same rate that spectral bands assigned to DNA and RNA bases decreased in intensity. Band intensities correlate with standard plate counts with R(2) = 0.99 and R(2) = 0.97, respectively. Principal components analysis and discriminant analysis multivariate statistical techniques were used to evaluate the spectral data collected. Significant changes were observed in the spectra of treated cells in comparison with their respective controls (samples without treatment). As a result, there was a significant differentiation between viable and non-viable cells (treated and non-treated cells) in the first and second principal component plots for all the treatments. Discriminant analysis was used along with PCA to estimate a classification rate based on viability status of the cells. Non-viable cells were differentiated from viable cells with classification rates that ranged between 60 and 90% for specific treatments (i.e., EDTA-treated cells versus control cells). The classification rate obtained considering all the treatments (non-viable cells) and controls (viable cells) at the same time for each of the species studied was 86%. The classification rate based on species differentiation when all the spectra (viable and non-viable) were used was 87%. These results suggest that Raman spectroscopy is a powerful tool that can be used to evaluate viability and to study metabolic changes in microorganisms. It is a robust method for bacterial identification even when high spectral variations are introduced.

Activity of staphylococcal bacteriocins against Staphylococcus aureus and Streptococcus agalactiae involved in bovine mastitis

The inhibitory activity of seven bacteriocins produced by Staphylococcus aureus (aureocins A70, A53, and 215FN) and Staphylococcus epidermidis (Pep5, epidermin, epilancin K7 and epicidin 280) was tested against strains of both S. aureus (165 strains) and Streptococcus agalactiae (74 strains) isolated from udders of cows suffering from bovine mastitis. Most strains of the two species were inhibited by epidermin (>85%), aureocin A53 (>67%) and by a combination of aureocins A70 and A53 (>91%), co-expressed in the genetic background of strain A70, the native producer of aureocin A70. Synergy between aureocins A70 and A53 was also demonstrated, which broadened the spectrum of strains inhibited. The remaining staphylococcins inhibited either none of, or a lower percentage (<48%) of, the mastitis-causing pathogens tested. Our results therefore show that the use of epidermin and/or a combination of aureocins A53 and A70 may represent a new non-antibiotic alternative for successfully inhibiting both mastitic staphylococci and streptococci.

Ultrastructural analysis of slime positive & slime negative Staphylococcus epidermidis isolates in infectious keratitis

BACKGROUND & OBJECTIVE

Slime is a major determinant of Staphylococcus epidermidis adherence. The established methods of laboratory detection of slime production by this organism i.e., Christensen's tube method and congo red agar plate method, can both yield inconclusive and/or intermediate results. We, therefore tried to find out electronmicroscopically the localization of slime in relation to the bacterial cell wall and look for the effect, if any of the slime location on the staphylococcal adherence as well as on the quantum of slime production.

METHODS

A total of 132 coagulase negative staphylococci from cases of infectious keratitis were identified as S. epidermidis following the recommended protocol. Slime was detected both by Christensen's tube method and congo red agar plate method. Antibiotic sensitivity testing was performed by standardized disc diffusion method. Adherence of the organisms to artificial surfaces was determined by a quantitative method and transmission electron microscopy was carried out by the conventional techniques.

RESULTS

Of the total 132 isolates, 57 (43.2%) were slime positive and 75 (56.8%) were slime negative. Twenty seven (47.4%) of the 57 slime producing organisms were multi drug resistant as compared to only 12 (16%) of 75 nonslime-producing organisms (P<0.001). A majority i.e., 45 (78.9%) of 57 adherent organisms were slime producers as against 12 (16%) of 75 nonadherent organisms. Electron microscopic study revealed a thick viscid layer of slime anchoring to the bacterial cell wall, especially in adherent organisms and those yielding positive slime test. Some of the organisms showed loose nonadherent slime and those were mostly nonadherent to artificial surfaces.

INTERPRETATION & CONCLUSION

Slime and multi drug resistance were the important virulence factors of S. epidermidis in bacterial keratitis. It was the adherent slime (i.e., slime in intimate association with the bacterial cell wall as shown by electron microscopy) only, which was responsible for resistance to multiple antibiotics and for the adhesion phenomenon observed in the quantitative slime test.

SdrF, a Staphylococcus epidermidis Surface Protein, Binds Type I Collagen

Staphylococcus epidermidis is the leading cause of device-related infections. These infections require an initial colonization step in which S. epidermidis adheres to the implanted material. This process is usually mediated by specific bacterial surface proteins and host factors coating the foreign device. Some of these surface proteins belong to the serine-aspartate repeat (Sdr) family, which includes adhesins from Staphyloccus aureus and S. epidermidis. Using a heterologous expression system in Lactococcus lactis to overcome possible staphylococcal adherence redundancy we observed that one of these Sdr proteins, SdrF, mediates binding to type I collagen when present on the lactococcal cell surface. We used lactococcal recombinant strains, a protein-protein interaction assay and Western ligand blot analysis to demonstrate that this process occurs via the B domain of SdrF and both the alpha1 and alpha2 chains of type I collagen. It was also found that a single B domain repeat of S. epidermidis 9491 retains the capacity to bind to type I collagen. We demonstrated that the putative ligand binding N-terminal A domain does not bind to collagen which suggests that SdrF might be a multiligand adhesin. Antibodies directed against the B domain significantly reduce in vitro adherence of S. epidermidis to immobilized collagen.