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Robson C, Tan B, Stuart R, Nicholls S, Rogers BA, Sandaradura I. A systematic review of optimal pharmacokinetic/pharmacodynamic parameters for beta-lactam therapy in infective endocarditis. J Antimicrob Chemother 2023; 78:599-612. [PMID: 36691839 DOI: 10.1093/jac/dkad005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Accepted: 01/02/2023] [Indexed: 01/25/2023] Open
Abstract
BACKGROUND Beta-lactam antibiotics are the mainstay of therapy for most bacterial causes of infective endocarditis (IE). Traditionally considered as agents with a broad therapeutic index, there is increasing recognition that standard doses may be subtherapeutic or toxic in critically ill patients. Optimizing therapy for efficacy requires a defined pharmacokinetic (PK)/pharmacodynamic (PD) target associated with clinical and microbiological cure. OBJECTIVES To elucidate the factors that influence beta-lactam PK and PD variability in IE and to examine optimal PK/PD target parameters for therapy. METHODS The review was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Clinical and laboratory in vivo animal or human studies examining PK and/or PD of beta-lactam antibiotics in IE were eligible. Ovid MEDLINE, Embase and Cochrane Central Registry were searched using defined terms. The Office of Health Assessment and Translation (OHAT) tool was used for assessing risk of bias. RESULTS From 2677 abstracts, 62 articles were selected for review and synthesis, comprising: 45 animal studies investigating the broad categories of beta-lactam diffusion into vegetations, PK/PD determinants of outcome, mode of antibiotic delivery and synergistic impact of agents; and 17 human studies totalling 347 participants. Findings supported the importance of time-dependent killing for beta-lactams but heterogeneous data limited the determination of an optimal PK/PD target for IE treatment. CONCLUSION Beta-lactam PK and PD in endocarditis are variable and specific to the particular antibiotic-organism combination. Time-dependent killing is important, consistent with non-endocarditis studies, but there is little agreement on optimal drug exposure. Clinical studies examining PK/PD targets in endocarditis are required to further inform drug selection and dosing.
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Affiliation(s)
- Christopher Robson
- Monash Infectious Diseases, Monash Health, Clayton, VIC, Australia.,Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton, VIC, Australia
| | - Bryan Tan
- Monash Infectious Diseases, Monash Health, Clayton, VIC, Australia
| | - Rhonda Stuart
- Monash Infectious Diseases, Monash Health, Clayton, VIC, Australia.,Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton, VIC, Australia.,South Eastern Public Health Unit, Monash Health, Clayton, VIC, Australia
| | - Stephen Nicholls
- Monash Heart, Monash Health, Clayton, VIC, Australia.,Victorian Heart Institute, Monash University, Clayton, VIC, Australia
| | - Benjamin A Rogers
- Monash Infectious Diseases, Monash Health, Clayton, VIC, Australia.,Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton, VIC, Australia
| | - Indy Sandaradura
- Centre for Infectious Diseases and Microbiology, Westmead Hospital, Sydney, Australia.,School of Medicine, University of Sydney, Sydney, Australia
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Salcedo-Sora JE, Kell DB. A Quantitative Survey of Bacterial Persistence in the Presence of Antibiotics: Towards Antipersister Antimicrobial Discovery. Antibiotics (Basel) 2020; 9:E508. [PMID: 32823501 PMCID: PMC7460088 DOI: 10.3390/antibiotics9080508] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 08/08/2020] [Accepted: 08/11/2020] [Indexed: 12/17/2022] Open
Abstract
Background: Bacterial persistence to antibiotics relates to the phenotypic ability to survive lethal concentrations of otherwise bactericidal antibiotics. The quantitative nature of the time-kill assay, which is the sector's standard for the study of antibiotic bacterial persistence, is an invaluable asset for global, unbiased, and cross-species analyses. Methods: We compiled the results of antibiotic persistence from antibiotic-sensitive bacteria during planktonic growth. The data were extracted from a sample of 187 publications over the last 50 years. The antibiotics used in this compilation were also compared in terms of structural similarity to fluorescent molecules known to accumulate in Escherichia coli. Results: We reviewed in detail data from 54 antibiotics and 36 bacterial species. Persistence varies widely as a function of the type of antibiotic (membrane-active antibiotics admit the fewest), the nature of the growth phase and medium (persistence is less common in exponential phase and rich media), and the Gram staining of the target organism (persistence is more common in Gram positives). Some antibiotics bear strong structural similarity to fluorophores known to be taken up by E. coli, potentially allowing competitive assays. Some antibiotics also, paradoxically, seem to allow more persisters at higher antibiotic concentrations. Conclusions: We consolidated an actionable knowledge base to support a rational development of antipersister antimicrobials. Persistence is seen as a step on the pathway to antimicrobial resistance, and we found no organisms that failed to exhibit it. Novel antibiotics need to have antipersister activity. Discovery strategies should include persister-specific approaches that could find antibiotics that preferably target the membrane structure and permeability of slow-growing cells.
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Affiliation(s)
- Jesus Enrique Salcedo-Sora
- Department of Biochemistry and Systems Biology, Institute of Systems, Molecular and Integrative Biology, Biosciences Building, University of Liverpool, Crown Street, Liverpool L69 7ZB, UK;
| | - Douglas B. Kell
- Department of Biochemistry and Systems Biology, Institute of Systems, Molecular and Integrative Biology, Biosciences Building, University of Liverpool, Crown Street, Liverpool L69 7ZB, UK;
- Novo Nordisk Foundation Centre for Biosustainability, Technical University of Denmark, Building 220, Kemitorvet, 2800 Kgs. Lyngby, Denmark
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Paradoxical Antibiotic Effect of Ampicillin: Use of a Population Pharmacokinetic Model to Evaluate a Clinical Correlate of the Eagle Effect in Infants With Bacteremia. Pediatr Infect Dis J 2020; 39:725-729. [PMID: 32235247 PMCID: PMC8628496 DOI: 10.1097/inf.0000000000002663] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BACKGROUND High doses of ampicillin are often used to achieve therapeutic drug concentrations in infants. A paradoxical antibiotic effect, often called the Eagle effect, occurs when increasing concentrations of antibiotic above a threshold results in decreased efficacy. It is unknown if infants treated with ampicillin are at risk for this paradoxical effect. METHODS We identified infants <28 days of age with Escherichia coli, Enterococcus or Streptococcus agalactiae (group B streptococcus) bloodstream infections from 1997 to 2012 and previously included in an ampicillin pharmacokinetic (PK) modeling study. We compared the odds of death for ampicillin dose, estimated time above the minimum inhibitory concentration (T > MIC) and PK parameters using separate logistic regression models. Adjusted logistic regression and Poisson models were used to calculate the odds of prolonged bacteremia ≥3 days and the duration of bacteremia, respectively, for dose, T > MIC and multiple PK parameters. RESULTS Among 1272 infants meeting inclusion criteria, odds of death 7 or 30 days after the positive blood culture were not consistent with a paradoxical effect across any of the dosing regimens or PK parameters evaluated. The odds of prolonged bacteremia was lowest at the lowest dose category and the lowest daily dose category but not associated with the area-under-the-concentration time curve from 0 to 24 hours, or the maximum or minimum concentrations at steady state. T > MIC of ≥50% of the dosing interval was associated with decreased duration of bacteremia and odds of prolonged bacteremia. CONCLUSIONS It is unlikely that a paradoxical antibiotic effect will have a clinical correlate when ampicillin is used for neonatal bacteremia. A T > MIC ≥50% decreased both duration of bacteremia and odds of prolonged bacteremia.
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Prasetyoputri A, Jarrad AM, Cooper MA, Blaskovich MA. The Eagle Effect and Antibiotic-Induced Persistence: Two Sides of the Same Coin? Trends Microbiol 2019; 27:339-354. [DOI: 10.1016/j.tim.2018.10.007] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Revised: 09/21/2018] [Accepted: 10/18/2018] [Indexed: 12/21/2022]
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Jarrad AM, Blaskovich MAT, Prasetyoputri A, Karoli T, Hansford KA, Cooper MA. Detection and Investigation of Eagle Effect Resistance to Vancomycin in Clostridium difficile With an ATP-Bioluminescence Assay. Front Microbiol 2018; 9:1420. [PMID: 30013531 PMCID: PMC6036128 DOI: 10.3389/fmicb.2018.01420] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Accepted: 06/11/2018] [Indexed: 11/24/2022] Open
Abstract
Vancomycin was bactericidal against Clostridium difficile at eightfold the minimum inhibitory concentration (MIC) using a traditional minimum bactericidal concentration (MBC) assay. However, at higher concentrations up to 64 × MIC, vancomycin displayed a paradoxical “more-drug-kills-less” Eagle effect against C. difficile. To overcome challenges associated with performing the labor-intensive agar-based MBC method under anaerobic growth conditions, we investigated an alternative more convenient ATP-bioluminescence assay to assess the Eagle effect in C. difficile. The commercial BacTiter-GloTM assay is a homogenous method to determine bacterial viability based on quantification of bacterial ATP as a marker for metabolic activity. The ATP-bioluminescence assay was advantageous over the traditional MBC-type assay in detecting the Eagle effect because it reduced assay time and was simple to perform; measurement of viability could be performed in less than 10 min outside of the anaerobic chamber. Using this method, we found C. difficile survived clinically relevant, high concentrations of vancomycin (up to 2048 μg/mL). In contrast, C. difficile did not survive high concentrations of metronidazole or fidaxomicin. The Eagle effect was also detected for telavancin, but not for teicoplanin, dalbavancin, oritavancin, or ramoplanin. All four pathogenic strains of C. difficile tested consistently displayed Eagle effect resistance to vancomycin, but not metronidazole or fidaxomicin. These results suggest that Eagle effect resistance to vancomycin in C. difficile could be more prevalent than previously appreciated, with potential clinical implications. The ATP-Bioluminescence assay can thus be used as an alternative to the agar-based MBC assay to characterize the Eagle effect against a variety of antibiotics, at a wide-range of concentrations, with much greater throughput. This may facilitate improved understanding of Eagle effect resistance and promote further research to understand potential clinical relevance.
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Affiliation(s)
- Angie M Jarrad
- Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD, Australia
| | - Mark A T Blaskovich
- Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD, Australia
| | - Anggia Prasetyoputri
- Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD, Australia
| | - Tomislav Karoli
- Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD, Australia
| | - Karl A Hansford
- Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD, Australia
| | - Matthew A Cooper
- Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD, Australia
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6
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A model of isoniazid treatment of tuberculosis. J Theor Biol 2014; 363:367-73. [PMID: 25093828 DOI: 10.1016/j.jtbi.2014.07.024] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Revised: 07/23/2014] [Accepted: 07/25/2014] [Indexed: 10/24/2022]
Abstract
A mathematical model is presented of the growth and death of bacilli in a granuloma. The granuloma is treated with isoniazid (INH), a drug that inhibits the synthesis of mycolic acids (MA). Since MA is an essential component of cell walls, the organisms fail to reach maturity if deficient in MA. Cell wall turnover is a well-known feature of bacteria, at the exterior surface material sloughs off to foil attacks by hosts or other organisms, simultaneously synthesizing products for new cell wall assembly. Thus cell wall thickness is maintained in a dynamic equilibrium (Doyle et al., 1988). Presumably cell death is a result of loss in cell wall due to autolysis in combination with stinted replenishing. The mathematical model presented here uses differential equations to predict the effects of intracellular INH on cell wall thickness and cell viability. This analysis purposely distinguishes intracellular INH concentration from the concentration in the plasma. The concentration in the plasma depends only on the dosing. The intracellular INH concentration, however, depends on diffusion through the cell walls of the bacteria. This paper addresses the complex interactions between intracellular INH, cell wall thickness, and the rate of cell wall synthesis.
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Tong Z, Zhang Y, Ling J, Ma J, Huang L, Zhang L. An in vitro study on the effects of nisin on the antibacterial activities of 18 antibiotics against Enterococcus faecalis. PLoS One 2014; 9:e89209. [PMID: 24586598 PMCID: PMC3930635 DOI: 10.1371/journal.pone.0089209] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2013] [Accepted: 01/16/2014] [Indexed: 01/06/2023] Open
Abstract
Enterococcus faecalis rank among the leading causes of nosocomial infections worldwide and possesses both intrinsic and acquired resistance to a variety of antibiotics. Development of new antibiotics is limited, and pathogens continually generate new antibiotic resistance. Many researchers aim to identify strategies to effectively kill this drug-resistant pathogen. Here, we evaluated the effect of the antimicrobial peptide nisin on the antibacterial activities of 18 antibiotics against E. faecalis. The MIC and MBC results showed that the antibacterial activities of 18 antibiotics against E. faecalis OG1RF, ATCC 29212, and strain E were significantly improved in the presence of 200 U/ml nisin. Statistically significant differences were observed between the results with and without 200 U/ml nisin at the same concentrations of penicillin or chloramphenicol (p<0.05). The checkerboard assay showed that the combination of nisin and penicillin or chloramphenicol had a synergetic effect against the three tested E. faecalis strains. The transmission electron microscope images showed that E. faecalis was not obviously destroyed by penicillin or chloramphenicol alone but was severely disrupted by either antibiotic in combination with nisin. Furthermore, assessing biofilms by a confocal laser scanning microscope showed that penicillin, ciprofloxacin, and chloramphenicol all showed stronger antibiofilm actions in combination with nisin than when these antibiotics were administered alone. Therefore, nisin can significantly improve the antibacterial and antibiofilm activities of many antibiotics, and certain antibiotics in combination with nisin have considerable potential for use as inhibitors of this drug-resistant pathogen.
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Affiliation(s)
- Zhongchun Tong
- Department of Operative Dentistry and Endodontics, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, Guangdong, China
- Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, Guangdong, China
| | - Yuejiao Zhang
- Department of Operative Dentistry and Endodontics, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, Guangdong, China
| | - Junqi Ling
- Department of Operative Dentistry and Endodontics, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, Guangdong, China
- Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, Guangdong, China
- * E-mail:
| | - Jinglei Ma
- Department of Operative Dentistry and Endodontics, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, Guangdong, China
| | - Lijia Huang
- Department of Operative Dentistry and Endodontics, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, Guangdong, China
| | - Luodan Zhang
- Department of Operative Dentistry and Endodontics, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, Guangdong, China
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Gomes DLR, Peixoto RS, Barbosa EAB, Napoleão F, Sabbadini PS, Dos Santos KRN, Mattos-Guaraldi AL, Hirata R. SubMICs of penicillin and erythromycin enhance biofilm formation and hydrophobicity of Corynebacterium diphtheriae strains. J Med Microbiol 2013; 62:754-760. [PMID: 23449875 DOI: 10.1099/jmm.0.052373-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Subinhibitory concentrations (subMICs) of antibiotics may alter bacterial surface properties and change microbial physiology. This study aimed to investigate the effect of a subMIC (⅛ MIC) of penicillin (PEN) and erythromycin (ERY) on bacterial morphology, haemagglutinating activity, cell-surface hydrophobicity (CSH) and biofilm formation on glass and polystyrene surfaces, as well as the distribution of cell-surface acidic anionic residues of Corynebacterium diphtheriae strains (HC01 tox(-) strain; CDC-E8392 and 241 tox(+) strains). All micro-organisms tested were susceptible to PEN and ERY. Growth in the presence of PEN induced bacterial filamentation, whereas subMIC of ERY caused cell-size reduction of strains 241 and CDC-E8392. Adherence to human erythrocytes was reduced after growth in the presence of ERY, while CSH was increased by a subMIC of both antibiotics in bacterial adherence to n-hexadecane assays. Conversely, antibiotic inhibition of biofilm formation was not observed. All strains enhanced biofilm formation on glass after treatment with ERY, while only strain 241 increased glass adherence after cultivation in the presence of PEN. Biofilm production on polystyrene surfaces was improved by ⅛ MIC of ERY. After growth in the presence of both antimicrobial agents, strains 241 and CDC-E8392 exhibited anionic surface charges with focal distribution. In conclusion, subMICs of PEN and ERY modified bacterial surface properties and enhanced not only biofilm formation but also cell-surface hydrophobicity. Antibiotic-induced biofilm formation may contribute to the inconsistent success of antimicrobial therapy for C. diphtheriae infections.
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Affiliation(s)
- D L R Gomes
- Faculty of Pharmacy, Federal Institute of Education, Science and Technology of Rio de Janeiro, IFRJ, Rio de Janeiro RJ, Brazil
- Laboratory of Diphtheria and Corynebacteria of Medical Relevance, Faculty of Medical Sciences, Rio de Janeiro State University, UERJ, Rio de Janeiro RJ, Brazil
| | - R S Peixoto
- Department of Medical Microbiology, Institute of Microbiology, Rio de Janeiro Federal University, UFRJ, Rio de Janeiro RJ, Brazil
- Laboratory of Diphtheria and Corynebacteria of Medical Relevance, Faculty of Medical Sciences, Rio de Janeiro State University, UERJ, Rio de Janeiro RJ, Brazil
| | - E A B Barbosa
- Faculty of Pharmacy, Federal Institute of Education, Science and Technology of Rio de Janeiro, IFRJ, Rio de Janeiro RJ, Brazil
| | - F Napoleão
- Laboratory of Diphtheria and Corynebacteria of Medical Relevance, Faculty of Medical Sciences, Rio de Janeiro State University, UERJ, Rio de Janeiro RJ, Brazil
| | - P S Sabbadini
- Laboratory of Diphtheria and Corynebacteria of Medical Relevance, Faculty of Medical Sciences, Rio de Janeiro State University, UERJ, Rio de Janeiro RJ, Brazil
| | - K R N Dos Santos
- Department of Medical Microbiology, Institute of Microbiology, Rio de Janeiro Federal University, UFRJ, Rio de Janeiro RJ, Brazil
| | - A L Mattos-Guaraldi
- Laboratory of Diphtheria and Corynebacteria of Medical Relevance, Faculty of Medical Sciences, Rio de Janeiro State University, UERJ, Rio de Janeiro RJ, Brazil
| | - R Hirata
- Laboratory of Diphtheria and Corynebacteria of Medical Relevance, Faculty of Medical Sciences, Rio de Janeiro State University, UERJ, Rio de Janeiro RJ, Brazil
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Abstract
We report a pediatric case of negative blood culture pulmonary valve endocarditis caused by a nontoxinogenic Corynebacterium diphtheriae biotype gravis and review the literature on this disease.
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10
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Hirata R, Pereira GA, Filardy AA, Gomes DLR, Damasco PV, Rosa ACP, Nagao PE, Pimenta FP, Mattos-Guaraldi AL. Potential pathogenic role of aggregative-adhering Corynebacterium diphtheriae of different clonal groups in endocarditis. Braz J Med Biol Res 2009; 41:986-91. [PMID: 19099151 DOI: 10.1590/s0100-879x2008001100007] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Accepted: 10/30/2008] [Indexed: 11/22/2022] Open
Abstract
Invasive diseases caused by Corynebacterium diphtheriae have been described increasingly. Several reports indicate the destructive feature of endocarditis attributable to nontoxigenic strains. However, few reports have dealt with the pathogenicity of invasive strains. The present investigation demonstrates a phenotypic trait that may be used to identify potentially invasive strains. The study also draws attention to clinical and microbiological aspects observed in 5 cases of endocarditis due to C. diphtheriae that occurred outside Europe. Four cases occurred in female school-age children (7-14 years) treated at different hospitals in Rio de Janeiro, Brazil. All patients developed other complications including septicemia, renal failure and/or arthritis. Surgical treatment was performed on 2 patients for valve replacement. Lethality was observed in 40% of the cases. Microorganisms isolated from 5 blood samples and identified as C. diphtheriae subsp mitis (N = 4) and C. diphtheriae subsp gravis (N = 1) displayed an aggregative adherence pattern to HEp-2 cells and identical one-dimensional SDS-PAGE protein profiles. Aggregative-adhering invasive strains of C. diphtheriae showed 5 distinct RAPD profiles. Despite the clonal diversity, all 5 C. diphtheriae invasive isolates seemed to display special bacterial adhesive properties that may favor blood-barrier disruption and systemic dissemination of bacteria. In conclusion, blood isolates from patients with endocarditis exhibited a unique adhering pattern, suggesting a pathogenic role of aggregative-adhering C. diphtheriae of different clones in endocarditis. Accordingly, the aggregative-adherence pattern may be used as an indication of some invasive potential of C. diphtheriae strains.
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Affiliation(s)
- R Hirata
- Departamento de Microbiologia, Imunologia e Parasitologia, Faculdade de Ciências Médicas, Universidade do Estado do Rio de Janeiro
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A model of the complex response of Staphylococcus aureus to methicillin. J Theor Biol 2008; 257:438-45. [PMID: 19135063 DOI: 10.1016/j.jtbi.2008.12.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2008] [Revised: 11/24/2008] [Accepted: 12/02/2008] [Indexed: 11/23/2022]
Abstract
It is widely accepted that beta-lactam antimicrobials cause cell death through a mechanism that interferes with cell wall synthesis. Later studies have also revealed that beta-lactams modify the autolysis function (the natural process of self-exfoliation of the cell wall) of cells. The dynamic equilibrium between growth and autolysis is perturbed by the presence of the antimicrobial. Studies with Staphylococcus aureus to determine the minimum inhibitory concentration (MIC) have revealed complex responses to methicillin exposure. The organism exhibits four qualitatively different responses: homogeneous sensitivity, homogeneous resistance, heterogeneous resistance and the so-called 'Eagle-effect'. A mathematical model is presented that links antimicrobial action on the molecular level with the overall response of the cell population to antimicrobial exposure. The cell population is modeled as a probability density function F(x,t) that depends on cell wall thickness x and time t. The function F(x,t) is the solution to a Fokker-Planck equation. The fixed point solutions are perturbed by the antimicrobial load and the advection of F(x,t) depends on the rates of cell wall synthesis, autolysis and the antimicrobial concentration. Solutions of the Fokker-Planck model are presented for all four qualitative responses of S. aureus to methicillin exposure.
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