Campylobacter and fluoroquinolones: a bias data set?

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.

Low-Level Risk Assessment for Tylosin Use in Poultry and Swine on the Treatment of Human Food-borne Disease

Risk Assessment of Macrolide Use in Fed Cattle on the Treatment of Human Food-borne Illness

The full paper, Public Health Consequences of Macrolide Use in Food Animals: a Deterministic Risk Assessment.

Overview of the European Regulatory Microbiology Guidelines for Veterinary Medicines

Regulatory Guidelines Overview - Europe

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).

Microbial Feed Additives - Calsporin

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.

Antimicrobial Breakpoints - An Area for Clarification

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.

Recent advances in antimicrobial therapy of skin disease in companion animals

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

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, 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 Veterinary Microbiology 2010.

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 attached PDF file presents the text of the submitted paper which has been published by Peter Silley as, SILLEY, P. (2009). Human flora-associated rodents - does the data support the assumptions. Microbial Biotechnology 2, 6-14.

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.

Med-Vet-Net: The First Year of a Network Integrating the Research Activities of European Public Health and Veterinary Institutes

For more information see www.medvetnet.org