The Experts below are selected from a list of 27012 Experts worldwide ranked by ideXlab platform

Johanna Finkgremmels - One of the best experts on this subject based on the ideXlab platform.

  • biofilm formation and genotyping of staphylococcus aureus bovine mastitis isolates evidence for lack of Penicillin Resistance in agr type ii strains
    Veterinary Microbiology, 2009
    Co-Authors: M B Melchior, M H J Van Osch, R M Graat, E Van Duijkeren, D J Mevius, M Nielen, Wim Gaastra, Johanna Finkgremmels
    Abstract:

    The increasing evidence for a role of biofilm formation in bovine mastitis caused by Staphylococcus aureus led to further investigations on biofilm formation by S. aureus isolates from mastitis in two growth media (TSBg and bovine milk serum). The ability of 99 S. aureus strains that were recently isolated or obtained from a culture collection (historical strains) to form biofilm, in both growth media as well as the correlation of biofilm formation with the presence of the ica-, bap-, and IS257 genes are described. These genes have been correlated with biofilm formation by human S. aureus isolates. All strains were also genotyped with respect to their Agr-type and -subtype, and for the presence of the antibiotic Resistance genes blaZ and smr by PCR. The prevalence of the Agr-types and the investigated genes and their correlation with biofilm formation were statistically evaluated. The Agr-type of a strain had a marked effect on the biofilm formation, by that strain, however in contrast to human isolates no significant effect of ica- and IS257 genes on biofilm formation was observed. The bap gene was not found in any of the investigated strains. The presence of biofilm related genes showed a high correlation with the Agr-type of the strains. The data give evidence for a very strong correlation of Agr-type I strains and Penicillin-Resistance in the bovine S. aureus mastitis strains; none of the Agr-type II strains was found to harbor Penicillin-Resistance genes. These data indicate that the most prevalent Agr-types in S. aureus bovine mastitis, Agr-type I and II, can be regarded as different subspecies, with different abilities for the formation of biofilm in bovine milk serum. The very high correlation between Agr-type II and Penicillin-susceptibility strongly suggests that these strains are not able to accommodate blaZ genes.

Regine Hakenbeck - One of the best experts on this subject based on the ideXlab platform.

  • streptococcus pneumoniae r6 interspecies transformation genetic analysis of Penicillin Resistance determinants and genome wide recombination events
    Molecular Microbiology, 2012
    Co-Authors: Julia Sauerbier, Patrick Maurer, M Rieger, Regine Hakenbeck
    Abstract:

    Summary Interspecies gene transfer has been implicated as the major driving force for the evolution of Penicillin Resistance in Streptococcus pneumoniae. Genomic alterations of S. pneumoniae R6 introduced during four successive transformations with DNA of the high-level Penicillin-resistant Streptococcus mitis B6 with beta-lactam selection have now been determined and the contribution of genes to high Resistance levels was analysed genetically. Essential for high level Resistance to Penicillins of the transformant CCCB was the combination of murMB6 and the 3′ region of pbp2bB6. Sequences of both genes were detected in clinical isolates of S. pneumoniae, confirming the participation of S. mitis in the global gene pool of beta-lactam Resistance determinants. The S. mitis PBP1b gene which contains an authentic stop codon within the transpeptidase domain is now shown to contribute only marginal to Resistance, but it is possible that the presence of its transglycosylase domain is important in the context of cognate PBPs. The genome sequence of CCCB revealed 36 recombination events, including deletion and acquisition of genes and repeat elements. A total of 78 genes were affected representing 67 kb or 3.3% of the genome, documenting extensive alterations scattered throughout the genome.

  • Mechanisms of Penicillin Resistance in Streptococcus pneumoniae: Targets, Gene Transfer and Mutations
    Antibiotic Discovery and Development, 2011
    Co-Authors: Regine Hakenbeck, Dalia Denapaite, Patrick Maurer
    Abstract:

    Penicillin Resistance in Streptococcus pneumoniae has been recognized in the bacterial population 40 years ago and has increased dramatically worldwide ever since. It is based on alterations of the Penicillin target enzymes, the Penicillin binding proteins (PBPs). In clinical isolates, horizontal gene transfer involving closely related commensal species mediates the acquisition of highly altered PBP genes, resulting in the evolution of complex mosaic structures. The identification of PBP mutations in resistant laboratory mutants has helped to reveal amino acids responsible for the decreased affinity of the target proteins, in addition to high resolution structures of PBPs from resistant clinical isolates. Moreover, non-PBP genes have been discovered that contribute to Resistance.

  • Relatedness between Streptococcus pneumoniae and viridans streptococci: transfer of Penicillin Resistance determinants and immunological similarities of Penicillin-binding proteins.
    Fems Microbiology Letters, 1991
    Co-Authors: Lynda Chalkley, Cordelia Schuster, Elsa Potgieter, Regine Hakenbeck
    Abstract:

    The occurrence of highly variable Penicillin-binding proteins (PBPs) in Penicillin-resistant Streptococcus pneumoniae suggested that transfer of homologous genes from related species may be involved in Resistance development. Antiserum and monoclonal antibodies raised against PBPs 1a and 2b from the susceptible S. pneumoniae R6 strain were used to identify related PBPs in 41 S. mitis, S. sanguis I and S. sanguis II strains mostly isolated in South Africa with MIC values ranging from < 0.15 to 16 mg/ml. Furthermore, the possibility of genetic exchange was examined with 30 Penicillin-resistant strains of this collection (MIC ≥ 0.06 mg/ml) as donors using S. pneumoniae R6 as recipient in transformation experiments. The majority of S. mitis and S. sanguis II strains but none of the S. sanguis I strains could transform Penicillin Resistance genes into S. pneumoniae R6. All positive donor strains and all susceptible isolates of S. mitis and S. sanguis II strains contained PBPs which cross-reacted with the anti-PBP 1a and/or anti-PBP 2b antibodies. On the other hand, only five of the 14 S. sanguis I strains contained a PBP that reacted with one of the antibodies. This strongly suggested the presence of genes homologous to the pneumococcal PBP 1a and 2b genes in viridans streptococci and documents that Penicillin Resistance determinants can be transformed from viridans streptococci into the pneumococcus.

  • Penicillin-binding proteins in Streptococcus pneumoniae: alterations during development of intrinsic Penicillin Resistance.
    Journal of Chemotherapy, 1991
    Co-Authors: Regine Hakenbeck, T. Briese, G. Laible, C. Martin, C. Schuster
    Abstract:

    Four out of the five high molecular weight Penicillin-binding proteins (PBPs) of Streptococcus pneumoniae are involved in the development of intrinsic Penicillin Resistance. In β-lactam resistant laboratory mutants, point mutations in the PBP 2x-genes were identified that result in low Penicillin-affinity mutant proteins

Larry M. Baddour - One of the best experts on this subject based on the ideXlab platform.

  • The Impact of Penicillin Resistance on Short-Term Mortality in Hospitalized Adults with Pneumococcal Pneumonia: A Systematic Review and Meta-Analysis
    Clinical Infectious Diseases, 2006
    Co-Authors: Imad M. Tleyjeh, Haytham M. Tlaygeh, Rana Hejal, Victor M. Montori, Larry M. Baddour
    Abstract:

    Background. The clinical impact of Penicillin Resistance on the outcome of pneumococcal pneumonia has remained controversial. We performed a meta-analysis of prospective cohort studies to examine the association between Penicillin Resistance and short-term all-cause mortality for pneumococcal pneumonia. Methods. We retrieved studies published in any language by a comprehensive search of the Medline, Current Contents, and Embase databases for all appropriate articles published up to January 2005. We also manually reviewed bibliographies of retrieved articles, recent national treatment guidelines, and review articles. We included prospective cohort studies that involved adult subjects, and we examined the association between Penicillin Resistance and short-term mortality for pneumococcal pneumonia. Two reviewers independently extracted data on crude and adjusted risk estimates of all-cause mortality for pneumococcal infections with different levels of Penicillin Resistance and assessed the methodological quality of selected studies. We also contacted authors to obtain additional information. We performed meta-analyses using a random-effect model. Results. Of 1152 articles identified in the search, 10 studies that involved 3430 patients (most of whom were hospitalized) were included. The mortality rate was 19.4% in the Penicillin-nonsusceptible Streptococcus pneumoniae group and 15.7% in the Penicillin-susceptible S. pneumoniae group. The combined relative risks of all-cause mortality for the Penicillin-nonsusceptible, -intermediate, and -resistant S. pneumoniae groups, compared with the Penicillin-susceptible S. pneumoniae group, were 1.31 (95% confidence interval [CI], 1.08-1.59), 1.34 (95% CI, 1.13-1.60), and 1.29 (95% CI, 1.01-1.66), respectively. The combined adjusted relative risks of mortality for Penicillin-nonsusceptible versus Penicillin-susceptible S. pneumoniae group was 1.29 (95% CI, 1.04-1.59) for the 6 studies that adjusted for age, comorbidities, and severity of illness. There was minimal between-study heterogeneity in these analyses. Conclusion. Penicillin Resistance is associated with a higher mortality rate than is Penicillin susceptibility in hospitalized patients with pneumococcal pneumonia. Additional efforts are needed to understand the mechanisms of this association.

  • No impact of Penicillin Resistance on mortality. Authors' reply
    Clinical Infectious Diseases, 2006
    Co-Authors: Keith P. Klugman, Imad M. Tleyjeh, Haytham M. Tlaygeh, Rana Hejal, Victor M. Montori, Larry M. Baddour
    Abstract:

    TO THE EDITOR-Tleyjeh et al. [1] argue that the association of Penicillin Resistance with short-term mortality in pneumococcal pneumonia is controversial, and theyoffer us a meta-analysis, presumably to shed light on this controversy. Unfortunately, their analysis fails. Implicit in their analysis of the clinical relevance of Resistance should be the understanding that if all other confounders are controlled, the measure of the clinical relevance of Resistance is a difference in outcome between concordant and discordant therapy. This was not found. The increased relative risk of mortality when treatment was concordant or discordant was identical (relative risk, 1.6) in their analysis, as shown in the authors' table 4 (Penicillin-nonsusceptible Streptococcus pneumoniae group) [1]. Although the authors acknowledge this failure in the text, there is no such acknowledgement in the title or abstract of the meta-analysis. We are left with the wellrecognized confounders of disease severity and comorbidity as the reason for the association of Penicillin Resistance with mortality, given that there are no data to support increased virulence of resistant strains. This meta-analysis unfortunately, contributes to the confusion in the field. Readers are likely to accept the conclusion that Penicillin Resistance is associated with higher mortality than is Penicillin susceptibility; however, Penicillin Resistance is unproven in the article to have any association with the failure of Penicillin.

  • Stabilization of Penicillin Resistance among Streptococcus pneumoniae isolated in Eastern Tennessee
    International Journal of Antimicrobial Agents, 2002
    Co-Authors: Larry M. Baddour, Mark E. Cole
    Abstract:

    Penicillin Resistance among Eastern Tennessee isolates of Streptococcus pneumoniae has been increasing since the early 1990s. To maintain active surveillance of the prevalence of Penicillin Resistance among pneumococci isolated at our institution, antibiotic susceptibility testing was performed for 95 consecutive isolates and results were compared with those of strains examined 2 years earlier. The prevalence of Penicillin Resistance among local pneumococcal isolates may have stabilized in recent years.

  • Short communication Stabilization of Penicillin Resistance among Streptococcus pneumoniae isolated in Eastern Tennessee
    2002
    Co-Authors: Larry M. Baddour, Mark E. Cole
    Abstract:

    Penicillin Resistance among Eastern Tennessee isolates of Streptococcus pneumoniae has been increasing since the early 1990s. To maintain active surveillance of the prevalence of Penicillin Resistance among pneumococci isolated at our institution, antibiotic susceptibility testing was performed for 95 consecutive isolates and results were compared with those of strains examined 2 years earlier. The prevalence of Penicillin Resistance among local pneumococcal isolates may have stabilized in recent years. # 2002 Elsevier Science B.V. and International Society of Chemotherapy. All rights reserved.

M B Melchior - One of the best experts on this subject based on the ideXlab platform.

  • biofilm formation and genotyping of staphylococcus aureus bovine mastitis isolates evidence for lack of Penicillin Resistance in agr type ii strains
    Veterinary Microbiology, 2009
    Co-Authors: M B Melchior, M H J Van Osch, R M Graat, E Van Duijkeren, D J Mevius, M Nielen, Wim Gaastra, Johanna Finkgremmels
    Abstract:

    The increasing evidence for a role of biofilm formation in bovine mastitis caused by Staphylococcus aureus led to further investigations on biofilm formation by S. aureus isolates from mastitis in two growth media (TSBg and bovine milk serum). The ability of 99 S. aureus strains that were recently isolated or obtained from a culture collection (historical strains) to form biofilm, in both growth media as well as the correlation of biofilm formation with the presence of the ica-, bap-, and IS257 genes are described. These genes have been correlated with biofilm formation by human S. aureus isolates. All strains were also genotyped with respect to their Agr-type and -subtype, and for the presence of the antibiotic Resistance genes blaZ and smr by PCR. The prevalence of the Agr-types and the investigated genes and their correlation with biofilm formation were statistically evaluated. The Agr-type of a strain had a marked effect on the biofilm formation, by that strain, however in contrast to human isolates no significant effect of ica- and IS257 genes on biofilm formation was observed. The bap gene was not found in any of the investigated strains. The presence of biofilm related genes showed a high correlation with the Agr-type of the strains. The data give evidence for a very strong correlation of Agr-type I strains and Penicillin-Resistance in the bovine S. aureus mastitis strains; none of the Agr-type II strains was found to harbor Penicillin-Resistance genes. These data indicate that the most prevalent Agr-types in S. aureus bovine mastitis, Agr-type I and II, can be regarded as different subspecies, with different abilities for the formation of biofilm in bovine milk serum. The very high correlation between Agr-type II and Penicillin-susceptibility strongly suggests that these strains are not able to accommodate blaZ genes.

Jose Campos - One of the best experts on this subject based on the ideXlab platform.

  • trends in antimicrobial Resistance in 1 968 invasive streptococcus pneumoniae strains isolated in spanish hospitals 2001 to 2003 decreasing Penicillin Resistance in children s isolates
    Journal of Clinical Microbiology, 2004
    Co-Authors: Jesus Oteo, Fernando Baquero, Edurne Lazaro, Francisco J De Abajo, Jose Campos
    Abstract:

    To address the public health problem of antibiotic Resistance, the European Union (EU) founded the European Antimicrobial Resistance Surveillance System. A network of 40 hospitals that serve approximately 30% of the Spanish population (about 12 million) participated. Each laboratory reported data on antimicrobial susceptibility testing using standard laboratory procedures that were evaluated by an external quality control program. The antibiotic consumption data were obtained from the National Health System. We compared the antibiotic susceptibility of Spanish isolates of invasive Streptococcus pneumoniae (2001 to 2003) with antibiotic consumption. Invasive S. pneumoniae was isolated from 1,968 patients, 20% of whom were children at or below the age of 14 years. Of non-Penicillin-susceptible strains (35.6%; 95% confidence interval, 34 to 37.2), 26.4% were considered intermediate and 9.2% were considered resistant. Between 2001 and 2003, Penicillin Resistance decreased from 39.5 to 33% overall and from 60.4 to 41.2% in children at or below the age of 14 years (P = 0.002). Resistance to erythromycin was at 26.6%, and coResistance with Penicillin was at 19.1%. Of total isolates, the ciprofloxacin MIC was >2 μg/ml for 2.1%, with numbers increasing from 0.4% (2001) to 3.9% (2003). Total antibiotic use decreased from 21.66 to 19.71 defined daily doses/1,000 inhabitants/day between 1998 and 2002. While consumption of broad-spectrum Penicillins, cephalosporins, and erythromycin declined, use of amoxicillin-clavulanate and quinolones increased by 17.5 and 27%, respectively. The frequency of antibiotic Resistance in invasive S. pneumoniae in Spain was among the highest in the EU. However, a significant decrease in Penicillin Resistance was observed in children. This decrease coincided with the introduction of a heptavalent conjugate pneumoccocal vaccine (June 2001) and with a global reduction in antibiotic consumption levels.