Detection of antibacterial-like activity on a silica surface: fluoroquinolones and their environmental metabolites

Background, scope, and aims

Antibacterial fluoroquinolones (FQs) are third-generation antibiotics that are commonly used as therapeutic treatments of respiratory and urinary tract infections. They are used far less in intensively farmed animal production systems, though their use may be permitted in the veterinary treatments of flocks or in medicated feeds. When used, only a fraction of ingested parent FQ actually reaches the in vivo target site of infection, while the remainder is excreted as the parent FQ and its metabolized products. In many species?? metabolism, enrofloxacin (EF) is converted into ciprofloxacin (CF) while both FQs are classified as parent FQs in human treatments. It is therefore likely that both FQs and their metabolic products will contribute to a common pool of metabolites in biological wastes. Wastes from intensive farming practices are either directly applied to agricultural land without treatment or may be temporarily stored prior to disposal. However, human waste is treated in sewage treatment plants (STPs) where it is converted into biosolids. In the storage or treatment process of STPs, FQs and their in vivo metabolites are further converted into other environmental metabolites (FQEMs) by ex vivo physicochemical processes that act and interact to produce complex mixtures of FQEMs, some of which have antibacterial-like activities. Biosolids are then often applied to agricultural land as a fertilizer amendment where FQs and FQEMs can be further converted into additional FQEMs by soil processes. It is therefore likely that FQ-contaminated biowaste-treated soils will contain complex mixtures of FQEMs, some of which may have antibacterial-like activities that may be expressed on bacteria endemic to the receiving agricultural soil environment. Concern has arisen in the scientific and in the general community that repeated use of FQ-contaminated biowaste as fertilizer amendments of nutrient-impoverished agricultural land may create a selective environment in which FQ-resistant bacteria might grow. The likelihood of this happening will depend, to some extent, on whether bioactive FQEMs are first synthesized from the parent FQs by the action and interaction of in vivo and ex vivo processes producing bioactive FQEMs in biowastes and biosolids. The postulated creation of a selective environment will also depend, in part, on whether such bioactive FQEMs are biologically available to bacteria, which may, in turn, be influenced by soil type, amendment regime, and the persistence of the bioactive FQEMs. Additionally, soil bacteria and soil processes may be affected in different ways or extents by bioactive FQEMs that could possibly act additively or synergistically at ecological targets in these non-target bacteria. This is an important consideration, since, while parent FQs have well-defined ecological targets (DNA gyrase and topoisomerase IV) and modes of bactericidal action, the FQEMs and their possible modes of action on the many different species of soil bacteria is less well studied. It is therefore understandable that there is a lack of conclusive evidence directly attributing biosolid usage to any increase in FQ-resistant bacteria detected in biowaste-amended agricultural soil. However, a lack of evidence may simply imply that a causal relationship between biosolid usage programs and any detection of low levels of FQ-resistant bacteria in soils has yet to be established, rather than an assumption of no relationship whatsoever. Based on results presented in this paper, the precautionary principle should be applied in the usage of FQ-contaminated biosolids as fertilizer amendments of agricultural land. The aim of this research was to test whether any bioactive FQEMs of EF could be synthesized by aerobic fermentation processes using Mycobacterium gilvum (American Tissue Culture Collection) and a mixed culture of microorganisms derived from an agricultural soil. High-performance thin-layer chromatography (HPTLC) and bioautography were tested as screening techniques in the detection and analysis of bioactive FQEMs.

Materials and methods

FQEMs derived from M. gilvum and mixed (soil) culture aerobic ferments were fractionated using preparative HPTLC. A standard strain of Escherichia coli was then used as the reporter organism in a bioautography assay in the detection of bioactive-FQEMs on a mid-section of the HPTLC plate. Plate sections were reassembled, and a photograph was taken under low-intensity ultraviolet (UV) light to reveal regions that contained analytes that had UV chromophores and antibacterial-like activities.

Results and discussion

Many fractionated FQEMs displayed antibacterial-like activity while bound to silica gel HPTLC plates. These results also provide evidence that sufficient quantities of biologically active FQEMs were biologically available from a silica gel surface to prevent the adherent growth of E. coli. Six to seven FQEMs derived from EF using aerobic fermentation processes had antibacterial-like activities, while two FQEMs were also detectable using UV light. Furthermore, similar banding patterns of antibacterial-like activity were observed in both the monoculture (M. gilvum) and mixed culture bioautography assays, indicating that similar processes operated in both aerobic fermentations, either producing similar biologically active FQEMs or biologically active FQEMs that had similar physicochemical properties in both ferments. The simplest explanation for these findings is that the tested agricultural soil also contained mycobacteria that metabolized EF in a similar way to the purchased standard monoculture M. gilvum. Additionally, the marked contrast between the bioautography results and the UV results indicated that the presence of UV chromophores is not a prerequisite for the detection of antibacterial-like activity.

Conclusions

A reliance on spectrophotometric techniques in the detection of bioactive FQEMs in the environment may underestimate component antibacterial-like activity and, possibly, total antibacterial-like activity expressed by EF and its FQEMs. The described bioautography method provides a screening technique with which antibacterial-like activities derived from EF and possibly other FQs can be detected directly on silica gel HPTLC plates.

Recommendations

It is recommended that both bioassay and instrumental analytical techniques be used in any measurement of hazard and risk relating to antibacterial-like activities in the environment that are derived from fluoroquinolone antibiotics and their environmental metabolites.     

Suitability of short or long conservation contracts under ecological and socio-economic uncertainty

Acquisition of land rights has become a primary tool used to protect terrestrial biodiversity. Fixed length contracts are often used when trying to secure conservation benefits on private land in agri-environment schemes and payment for environmental services schemes, but the duration of the conservation contracts used in different programmes varies. To date, very little research has been undertaken to determine the situations in which contracts of differing lengths are optimal or when conservation agencies or groups should use a portfolio of different contract lengths rather than relying on a single type. Using stochastic dynamic programming and related heuristic methods, we investigate how the choice between short or long conservation contracts is affected by uncertainty regarding the future availability of sites and their ecological condition. We also examine the benefits offered by using a portfolio of different contract lengths. Conservation agencies must pay private landowners a premium to secure longer agreements and because of this, shorter contracts are advantageous if sites are likely to remain available for conservation in the future. Long contracts are preferred when future site availability becomes more unlikely. In contrast to uncertainty over site availability, uncertainty over future ecological conditions has little effect on contract selection and only markedly influences the choice between short and long contracts when there is heterogeneity across sites in expected conservation outcomes and future availability of sites is also uncertain. Finally, when future site availability is unlikely, the use of a portfolio of short and long contracts would offer greater conservation gains than using either type in isolation, even though this option is not yet one that is commonly found in conservation practice.     

THE IMPORTANCE OF INSTITUTIONAL STRUCTURE IN CONTROLLING AGRICULTURAL RUNOFF1

Abstract: Agricultural runoff, such as dissolved mineral salts and selenium, creates pronounced downstream impacts to agricultural producers and to wildlife. The ability to manage these problems efficiently depends critically on the institutional pricing structure of irrigation water delivery agencies. An important characteristic of irrigation water delivery is whether irrigators pay per unit of water received or make one payment regardless of the quantity of water received. In this study we compare the effectiveness of agricultural runoff reduction policies in two regions that employ these different water pricing structures. We find that reduction policy is more effective and can be achieved at a lower cost when water is priced on a per unit basis and that growers have greater incentive to act on their own to reduce runoff problems. Operating under a per unit pricing system encourages water conservation and runoff reduction, which creates public benefits that are not achieved under the single-payment, fixed allotment method of irrigation water delivery.     

Sexual chases in sand martins (Riparia riparia): cues for males to increase their reproductive success

Summary During the pre-laying and laying stages of the breeding cycle, female sand martins are guarded by their mates and chased by other males seeking promiscuous copulations. Because females become exceptionally heavy when they are most likely to be fertile, their increased mass was thought to present cues during flight to males seeking promiscuous copulations. Heavy female sand martins released from the hand were selectively chased in sexual chases (Figs. 1, 2). Breeding females were heaviest during laying and pre-laying (Fig. 3), exceeding any masses normally achieved by breeding males (Fig. 3). A sample of naturally heavy females and birds whose mass had been experimentally increased to that of laying and prelaying females took longer to reach ascending flight, as determined by analysis of video recordings, than a sample of lighter birds (Table 1). It was concluded that this and other flight cues may be detected by males so that they may achieve extra-pair copulations and hence increase their reproductive success.     

Incorporating evolutionary processes into population viability models

We examined how ecological and evolutionary (eco‐evo) processes in population dynamics could be better integrated into population viability analysis (PVA). Complementary advances in computation and population genomics can be combined into an eco‐evo PVA to offer powerful new approaches to understand the influence of evolutionary processes on population persistence. We developed the mechanistic basis of an eco‐evo PVA using individual‐based models with individual‐level genotype tracking and dynamic genotype–phenotype mapping to model emergent population‐level effects, such as local adaptation and genetic rescue. We then outline how genomics can allow or improve parameter estimation for PVA models by providing genotypic information at large numbers of loci for neutral and functional genome regions. As climate change and other threatening processes increase in rate and scale, eco‐evo PVAs will become essential research tools to evaluate the effects of adaptive potential, evolutionary rescue, and locally adapted traits on persistence.     

Echolocation call design and limits on prey size: a case study using the aerial-hawking bat Nyctalus leisleri

The echolocation calls used by Nyctalus leisleri during search phase in open air space are between 9 and 14 ms long, with the peak energy between 24 and 28 kHz. The pulses are shallowly frequency-modulated with or without an initial steep frequency-modulated component. The diet consists primarily of small flies (Diptera), including many chironomids (wingspan 9–12 mm) and yellow dung flies (Scatophaga; wingspan 24 mm), but also of some larger insects such as dung beetles (Coleoptera; Scarabaeoidea), caddis-flies (Trichoptera) and moths (Lepidoptera). The echo target strength of some prey items was measured. Contrary to models based on standard targets such as spheres or disks, the echo strength of real insects was found to be virtually independent of the emitted frequency within the 20–100 kHz frequency range. A model was used to calculate probable detection distances of the prey by the bat. Using narrow-band calls of 13.7 ± 2.7 ms duration, a bat would detect the two smallest size classes of insect at greatest range using calls of 20 kHz. The results may therefore explain why many species of large and medium sized aerial-hawking bats use low-frequency calls and still eat mostly relatively small insects. The data and model challenges the assumption that small prey are unavailable to bats using low-frequency calls.     

An input-output balance study for PCBs in humans

Polychlorinated biphenyl (PCB) input-output balance studies were performed on five male volunteers, aged between 24 and 30, for periods of 8-14 days in 1998. Dietary exposure was quantified by the duplicate meals method and varied between 220 and 460 ng of sigmaPCB (sum of 20 congeners) per day for each of the five individuals over the study period. Dietary intake was dominated by congeners 118, 138, 153 and 180. Average faecal outputs for the five volunteers were 50-290 ng of sigmaPCB (sum of 20 congeners) per day for each of the five individuals over the same period and was dominated by the same four congeners. Whilst the total PCB fluxes were therefore into the body (i.e., accumulation), important differences were noted for different individual congeners. PCBs 44, 47, 49, 52, 60, 66, 101, 105, 110, 118, 149, 151 and 183 all showed net absorption for all five volunteers. Some congeners showed a net absorption in some of the individuals but net excretion in others, as seen by other workers. These congeners (PCBs 138, 153, 180, 187 and 194) are all higher chlorinated congeners and lack meta-para-vicinal hydrogen atoms. There were differences in the net absorption/excretion between individuals, which appeared to be a function of body fat index (BFI). The volunteers with the lowest BFIs showed net excretion for the greatest number of congeners, whilst the individual with the highest BFI was a net absorber of all the congeners studied. The problems in determining and interpreting absorption efficiency values for use in quantitative exposure assessments are discussed. Various factors that influence net absorption of PCBs and other persistent organic pollutants are identified. These include compound properties (including susceptibility to metabolism), the individual's fat status and balance, exposure history and diet.     

Fluldized-Bed Combustion

The Fourth International Conference on Fluidized Bed Combustion (FBC) was held at The MITRE Corporation in McLean, VA, December 9 to 11, 1975. With attendees from Great Britain, West Germany, Japan, Canada, and Sweden, the conference apparently fulfilled its international scope and intent.

The objectives of the conference were to review the current state of technology in FBC, to promote technical information exchange on FBC and related areas, and to generate a useful technical information base for further FBC development. Throughout the conference, the goal of commercialization was repeatedly emphasized.

Sponsored by the U.S. Energy Research and Development Administration (ERDA) and coordinated by MITRE, this meeting was the most comprehensive event in the seven year series of conferences on this subject according to attendees. ERDA, the government’s lead agency in FBC technology development, is the principal sponsor and coordinator of the National Fluidized Bed Combustion Program with the goal of advancing the commercialization time frame for FBC. Prior conferences in this series were hosted by the Environmental Protection Agency (EPA) at about two year intervals at Hueston Woods, Ohio. The last EPA conference was held in October 1972.     

Educational hazards? The politics of disaster risk education in Rio de Janeiro

Disaster education outcomes are highly dependent on the political context of that education. Based on a rich, in‐depth case study of the creation of community monitors in a landslide and flood‐prone city in southeast Brazil, this paper demonstrates how developmental and political environments add much additional nuance to existing theories of behaviourist and transformative education for disaster preparedness and mitigation. Beyond identifying the benefits of education, it argues that disaster risk reduction outcomes are reliant on governance frameworks that alter over time. The study reveals the political complexity associated with programme implementation and cites the perspectives of a number of participants. Disaster education is shown to be the necessary yet underappreciated twin of the militarised and technical approaches that dominate disaster response in Brazil. Understated, however, is education's situatedness: how it can become an arena of conflict between government and civil actors over matters of state and society in increasingly hazardous urbanisation settings in Latin America.