Science
This page includes some of the issues in which MB Consult is involved and able to place in the public domain.
1) Can methods of isolation bias the very organisms we are looking for, a review of the Campylobacter literature suggests that this may be the case.
It is not only isolation methods that are important, in a letter to The Veterinary Record, December 8th, 2007 concerning reporting of ESBLs in companion animals, comment is made regarding the importance of providing detailed methodology when reporting antimicrobial resistance, without such information it is somewhat difficult to determine the significance of reported data.
2) Risk analysis is very much in fashion yet to be meaningful it must be based on data, here are two risk assessments presented at ICAAC, 2003 and then as a full refereed paper in Journal of Food Protection in 2004, in which MB Consult has been involved.
3) A look at Regulatory Guidelines in Animal Health and ProductionOverview of the European Regulatory Microbiology Guidelines for Veterinary Medicines.
Additives for use in animal nutrition are regulated under Regulation (EC) No.1831/2003. The scope of this paper addresses the specific microbiological issues relevant to a microbial feed additive, containing a Bacillus spp. and uses as an example a product with the trade name, Calsporin. This review uses Calsporin as an example of the type of data required by the European regulatory authorities (EFSA).
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Microbiological ADIs are a concept that pose a lot of challenge to the pharmaceutical industry and this has never been more evident than the implementation of the microbiological ADI guideline. Since 2005 sponsors and regulatory authorities have struggled to address the issues. A recent paper published in the Journal of Applied Microbiology in 2007 reviewed the progress to date in Europe and highlighted some salient issues. See SILLEY, P. (2007), Impact of antimicrobial residues on gut communities: are the new regulations effective? Journal of Applied Microbiology 102, 1220-1226. This paper can be downloaded free of charge from http://www.blackwell-synergy.com/toc/jam/102/5
4) Antimicrobial Breakpoints.
The whole area of breakpoints can be somewhat confusing; this has been exacerbated in recent times as new terminology has been introduced to describe epidemiological/microbiological breakpoints which are clearly different to the clinical breakpoint. In an attempt to clarify the issues Veterinary Microbiology has published correspondence from Bywater, Simjee & Silley explaining the differences in terminology. See Veterinary Microbiology 118, 158-159 for the full explanation. Additionally the attached pdf file is a poster presented by Silley, Bywater & Simjee at the 2006 EAVPT Meeting in Turin, also addressing this issue. This poster won the best presentation in the Regulatory Sciences section of the Turin Meeting. This debate continues following publication of the 2005 MARAN surveillance report in which resistance has been reported as a function of epidemiological rather than clinical breakpoints. This resulted in publication in the Journal of Antimicrobial Chemotherapy of correspondence from Simjee et al concerning potential confusion regarding the term 'resistance' in epidemiological surveillance. To read the full publication please see, Journal of Antimicrobial Chemotherapy 61, 228-229.
5) Companion Animals.
a) Skin and Soft Tissue Disease
"Recent advances in antimicrobial therapy of skin disease in companion animals" is a paper that was presented at a Symposium in Lisbon in September, 2006, it focuses on the currently available fluoroquinolones used in companion animal therapy.
Pradofloxacin is a fluoroquinolone antimicrobial developed solely for use in veterinary medicine. In order to evaluate its potential for use against anaerobes from cats and dogs, the comparative activity relative to other fluoroquinolones used in companion animals was determined against 141 anaerobic strains isolated in the period 2000 to 2002. The data from this study has been published in Journal of Antimicrobial Chemotherapy, by Silley et al (2007)and provides the first comparative MIC data for veterinary fluoroquinolones against anaerobes isolated from dogs and cats. It reveals significant anti-anaerobe activity of pradofloxacin and suggests that this compound may have important utility in veterinary medicine as single-drug therapy for infections caused by mixed aerobic/anaerobic infections and in this context could also be used to treat bacteria associated with dental infections.
See:
SILLEY, P., STEPHAN, B., GREIFE, H.A. & PRIDMORE, A. (2007)
Comparative activity of pradofloxacin against anaerobic bacteria isolated from dogs and cats, Journal of Antimicrobial Chemotherapy 60, 999-1003.
STEPHAN, B., GREIFE, H.A., PRIDMORE, A. & SILLEY, P. (2008)
Activity of pradofloxacin against Porphyromonas and Prevotella spp. Implicated in periodontal disease in dogs: susceptibility test data from a European multicenter study. Antimicrobial Agents and Chemotherapy 52, 2149-2155.
SILLEY, P., STEPHAN, B., GREIFE, H.A. & PRIDMORE, A. (2012)
Bactericidal properties of pradofloxacin against veterinary pathogens. Veterinary Microbiology in press http://dx.doi.org/10.1016/j.vetmic.2011.11.027
b) Periodontal Disease
Periodontal disease is a chronic, multi-factorial disease of the tissues supporting the teeth and the significance of microorganisms in the development of all types of periodontal disease is indisputable. It is microbial density that is considered critical for the development of gingivitis and some types of chronic periodontitis whilst the type of microorganisms may be of greater importance in the initiation of aggressive periodontitis. Indeed, it is now well accepted within the dental research community that periodontal disease results not just from simple accumulation of volume of dental plaque but that the development of the complex plaque leads to growth and dominance of specific pathological organisms. This thinking has arisen from studies of human disease and indeed much of the published data concerning etiology of periodontitis comes from the human arena, where the primary periodontal pathogen is considered to be P. gingivalis.
Periodontitis in companion animals is an almost identical disease to that in humans in terms of disease course and clinical presentation. It has been estimated that approximately 80% of dogs and cats demonstrate some degree of periodontal disease by 4 years of age. It is a serious condition that threatens all dogs and is among the most common disorders seen in veterinary medicine. The accelerated disease progression observed in companion animals compared to humans may be due to a relative lack of routine dental care. Companion animal periodontitis is a serious infection that can have medical consequences such as anorexia and weight loss, chronic pain, sore or loose teeth, swollen gums, tooth decay, breakage or loss of teeth and breakage of the maxillary or mandibular bone. If left untreated, periodontal bacteria may spread to other sites in the body via bacteraemia and lead to renal, coronary or hepatic diseases. As virtually all cases of periodontal disease are bacterial disorders they can be prevented or effectively treated by controlling pathogenic microbes residing in subgingival and supragingival plaque. In humans and dogs the dental practitioner has relied heavily upon mechanical debridement in combating periodontal infections. There is evidence, however, that additional strategies including use of antimicrobials are necessary to effectively combat periodontal infection especially in the case of sites with probing depths exceeding 5 mm. For periodontal therapy to be effective it must as a minimum be able to target and effectively control microorganisms capable of destroying periodontal connective tissue. It is well established that the microbial flora associated with periodontitis in humans and dogs is complex and in this context it has been established for a number of years that the absence of the black pigmented anaerobic indicator bacteria such as P. gingivalis and P. intermedia was a better predictor of no further loss of attachment than the presence of these species was for further disease progression. On this basis it has been concluded that antimicrobial therapy can be of great use in the treatment of periodontal disease.
Pradofloxacin is a third generation fluoroquinolone and like moxifloxacin has enhanced activity against Gram-positive bacteria relative to first and second generation compounds and good activity against anaerobes. It has been exclusively developed for use in veterinary medicine although has not yet received regulatory approval, it is distinguished from enrofloxacin, the first veterinary fluoroquinolone, by two structural elements: a bicyclic amine, S,S-pyrrolidino-piperidine, replacing the ethyl-piperazine moiety located at position C-7 of enrofloxacin, and a cyano group which is attached to the C-atom at position 8. The increased potency of pradofloxacin is mainly attributed to the S,S-pyrrolidino-piperidine moiety at C-7, but the cyano group at C-8 extends activity to first and second step FQ-resistant strains. Early data showed its potential for use against anaerobes. In a paper published in Antimicrobial Agents and Chemotherapy (2008) we report susceptibility data from a European multi-centre study against strains isolated from cases of periodontal disease in dogs.
See:
STEPHAN, B., GREIFE, H.A., PRIDMORE, A. & SILLEY, P. (2008)
Activity of pradofloxacin against Porphyromonas and Prevotella spp. Implicated in periodontal disease in dogs: susceptibility test data from a European multicenter study. Antimicrobial Agents and Chemotherapy 52, 2149-2155.
6) Mutant prevention Concentration (MPC).
Prevention of clonal expansion of mutant populations is fundamental to reducing the impact of resistance development. Drlica & Malik (2003) made the obvious but important point that a successful strategy to restrict mutant selection is to ensure that drug concentrations are high enough to prevent the growth of mutants already present in a bacterial population. This comment was made in the context of developing thinking relating to the mutant prevention concentration (MPC) and the mutant selection window. The MPC has been defined as the drug concentration at which no mutant is recovered when more than 1010 cells are applied to an agar plate (Drlica & Malik, 2003). Zhao & Drlica (2001) argued for a general strategy restricting the selection of antibiotic resistant fluoroquinolone mutants and presented the case for the "mutant selection window".
It was Baquero & Negri (1997) that forwarded the idea that there was a dangerous range of drug concentrations in which mutants were most frequently selected; this is now considered to be the range between the minimum inhibitory concentration (MIC) and the MPC. Placing antimicrobial concentrations inside the window will selectively enrich resistant mutant subpopulations, whereas placing concentrations above the window is expected to restrict selective enrichment. Drlica (2003) further argued that as window dimensions are characteristic of each pathogen-antimicrobial combination, they can be linked with antimicrobial pharmacokinetics to rank compounds and dosing regimens in terms of their propensity to enrich mutant fractions of bacterial populations.
There has been significant interest and much debate in recent years in the MPC and the mutant selection window concept but all MPC data so far described has related to aerobic organisms. It is much more difficult to generate MPC data for anaerobes but in a recent publication one of the groups with which I work has published the first MPC data for an anaerobe. For more information see the paper entitled, "Mutant Prevention Concentration of Pradofloxacin against Porphyromonas gingivalis" published in Veterinary Microbiology (2007) 121, 194-195 by Stephan, Greife, Pridmore and Silley.
7) Antimicrobial Resistance.
This is an extremely complex area that continues to attract much media attention. The relative contribution of veterinary and human clinical treatment to the selection of antimicrobial resistance in zoonotic pathogens remains controversial. In a recent review Wassenaar & Silley have considered bacterial pathogens that differ in host specificity and they have considered their resistance profiles: pathogens that only occur in the human host, pathogens that are specific to particular food-producing animals, and pathogens that occur in both host types. Compared to those pathogens restricted to a single animal host, pathogens found in both human and animal hosts appear to have higher incidences of resistance. However, the most urgent and severe resistance problems occur with pathogens exclusively infecting man. Differences exist in the available genetic repertoire of a bacterial species and these are reflected in the observed resistance patterns; it is important to note that different bacterial species do not automatically result in similarly resistant populations when they undergo comparable selection in different host species. Thus within a bacterial species, prevalence of resistance can differ between populations isolated from different hosts. For some species, fluctuations in dominant subpopulations, for instance particular serotypes, can be the most important factor determining resistance. The frequently expressed opinion that veterinary use of antimicrobials is at the heart of many resistance problems may be an oversimplification of the complex forces at play.
To access the full review please see
WASSENAAR, T.M. & SILLEY, P. (2008).
Antimicrobial resistance in zoonotic bacteria: lessons learned from host-specific pathogens. Animal Health Research Reviews 9, 177-186.
As interest in antimicrobial resistance in bacteria of animal origin, including food-producing animals, pet and companion animals, fish and other aquatic animals as well as wild animals, continues to gain attention there are an increasing number of published papers that include antimicrobial susceptibility testing data. An analysis of recently published articles has revealed a number of frequently occurring shortcomings, which may have an impact either directly on the quality of the results obtained or on the conclusions drawn, Peter Silley is one of a group of authors that have written an editorial that has been published in Veterinary Microbiology and Journal of Antimicrobial Chemotherapy, intended to highlight the major pitfalls and provide guidance for authors, and reviewers on the correct performance of antimicrobial susceptibility testing as well as the presentation of the obtained results and the proper comparison of data from different studies.
For further details see
SCHWARZ, S., SILLEY, P., SIMJEE, S., WOODFORD, N. VAN DUIJKEREN, E., JOHNSON, A.P. & GAASTRA, W. (2010)
Assessing the antimicrobial susceptibility of bacteria obtained from animals. Veterinary Microbiology 141, 1-4.
SCHWARZ, S., SILLEY, P., SIMJEE, S., WOODFORD, N. VAN DUIJKEREN, E., JOHNSON, A.P. & GAASTRA, W. (2010)
Assessing the antimicrobial susceptibility of bacteria obtained from animals. Journal of Antimicrobial Chemotherapy 65, 601-604.
Additionally Peter Silley was the lead author in an important paper considering antimicrobial surveillance systems in Denmark (DANMAP), The Netherlands (MARAN), Spain (VAV) and Sweden (SVARM) as well as the European Antimicrobial Susceptibility Surveillance in Animals (EASSA). Data from these surveillance systems was reviewed with particular consideration for extended-spectrum cephalosporins, fluoroquinolones and macrolides against food-borne and commensal bacteria. The paper identified that the greatest challenge arises from the lack of agreement between surveillance programmes on what is meant by resistance through the use of different interpretive criteria. Indeed, it was shown that the extent of the differences depends on the antibacterial compound being investigated, the methodology and the interpretive criteria used. This emphasises a need to agree a definition for resistance and for epidemiological cut-off values and to consider harmonising the antimicrobials used in surveillance. This analysis of the data highlights the usefulness of using both epidemiological cut-off values and clinical resistance breakpoints for the purpose of detection of decreased susceptibility and development of clinical resistance, respectively. It is concluded that harmonisation in resistance monitoring programmes is needed since there is potential for data to be appropriately used within risk analysis, providing the opportunity to implement appropriate risk management steps as a response to the public health issues arising from changes in antibiotic resistance in food-borne pathogens and commensal organisms.
The full paper can be accessed by referring to
SILLEY, P., DE JONG, A., SIMJEE, S. & THOMAS, V. (2011)
Harmonisation of resistance monitoring programmes in veterinary medicine: an urgent need in the EU? International Journal of Antimicrobial Agents 37, 504-512.
In another important publication focusing on fluoroquinolones the authors made the point that the potential for transmission of antibiotic-resistant enteric zoonotic bacteria from animals to humans has been a public health concern for several decades. Bacteria carrying antibiotic resistance genes found in the intestinal tract of food animals can contaminate carcasses and may lead to food-borne disease in humans that may not respond to antibiotic treatment. It is consequently important to monitor changes in antimicrobial susceptibility of zoonotic and commensal organism; in this context there are a number of veterinary monitoring programmes that collect bacteria in food-producing animals at slaughter and determine their susceptibility against antibiotics relevant for human medicine. The data generated are part of the risk analysis for potential food-borne transmission of resistance. There has been much debate about the use of fluoroquinolones in veterinary medicine and so this review will consider the fluoroquinolone data from two surveys and compare them to national surveillance programmes. At the outset it must be pointed out that there is, however, a lack of agreement between several programmes on what is meant by the term fluoroquinolone resistance through use of different definitions of resistance and different resistance breakpoints. An additional aim of this paper is to clarify some of those definitions. Despite the debate about the contribution of antibiotic use in veterinary medicine to the overall resistance development in human pathogens the data suggests that clinical resistance to fluoroquinolones in E. coli and non-typhoidal Salmonella is generally uncommon, except for a few countries. Ongoing surveillance will continue to monitor the situation and identify whether this situation changes within the respective animal populations. For the benefit of both the epidemiologist and the clinician it would be strongly advantageous that national monitoring surveys report both percentages of clinical resistance and decreased susceptibility.
This full paper can be accessed by going to
DE JONG, A., STEPHAN, B. & SILLEY, P. (2012)
Fluoroquinolone resistance of Escherichia coli and Salmonella from healthy livestock and poultry in the EU. Journal of Applied Microbiology 112, 239-245.
8) Animal Models.
There is little direct literature detailing exhaustive bacteriological studies comparing human donor faecal flora, human flora associated mouse models and conventional rodent faecal flora. Whilst there is a premise that the implanted donor faecal flora from humans is established in the rodent model the evidence is incomplete and indeed for groups such as Bifidobacterium spp. it is lacking. The reviewed bacteriology studies are generally lacking in detail with the exception of one study from which the data has mostly been overlooked when cited by other workers. Whilst there are studies which suggest that the human flora associated rodent (HFA) model is more relevant to man than studies with conventional rodents the hypothesis remains to be proven. In a recent review it has been concluded that the established microbial flora in the HFA-rodent model is different to that of donor human faecal flora and this clearly raises the question as to whether this matters, after all a model is a model and as such models can be useful even should they fail to be a true representation of, in this case, the gastro-intestinal tract. What matters is that there is a proper understanding of the limitations of the model as we attempt to unravel the significance of the components of the gastro-intestinal flora in health and disease; examples of why such an analysis is important are provided with regard to obesity and nutritional studies. The data does unsurprisingly suggest that diet is an extremely influential variable when interpreting HFA- and conventional rodent data. The microbiology data from direct bacteriology and indirect enzyme studies shows that the established microbial flora in the HFA-rodent model is different to that of donor human faecal flora. The significance of this conclusion remains to be established.
The definitive version is available at www.blackwell-synergy.com
9) Science Communication.
Currently responsible for the Science Communication Work Package of the EC funded Network of Excellence, MED-VET-NET addressing zoonotic disease in Europe. Funded for 5 years to the value of 14.4 million Euros, fourteen research institutes (veterinary and public health) in ten European countries involved in the network. Responsible for Society for Applied Microbiology becoming a partner in the Network of Excellence, the first learned society to be so involved.
For more information see www.medvetnet.org
10) Principal Research Interests.
Anaerobic microbiology, gastro-intestinal microbiology, antimicrobial chemotherapy, antimicrobial resistance and public health. Pharmacokinetic / Pharmacodynamic analysis using Monte Carlo simulation.
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