Progress of research on the toxicology of antibiotic pollution in aquatic organisms

Antibiotics are widely used to improve human and animal health and treat infections. Antibiotics are often used in livestock farms and fisheries to prevent diseases and promote growth. Recently, there has been increasing interest in the presence of antibiotics in aquatic environments. Low levels of antibiotic components are frequently detected in surface water, seawater, groundwater, and even drinking water. Antibiotics are consistently and continually discharged into the natural environment as parent molecules or metabolites, which are usually soluble and bioactive, and this results in a pseudo and persistent pollution. The effects of environmental antibiotic toxicity on non-target organisms, especially aquatic organisms, have become an increasing concern. Although antibiotics have been detected worldwide, their ecological and developmental effects have been poorly investigated, particularly in non-target organisms. This review describes the toxicity and underlying mechanism of antibiotic contamination in aquatic organisms, including the effects on vertebrate development. A considerable number of antibiotic effects on aquatic organisms have been investigated using acute toxicity assays, but only very little is known about the long-term effects. Aquatic photosynthetic autotrophs, such as Pseudokirchneriella subcapitata, Anabaena flos-aquae, and Lemna minor, were previously used for antibiotic toxicity tests because of low cost, simple operation, and high sensitivity. Certain antibiotics show a different degree of potency in algal toxicity tests on the basis of different test algae. Antibiotics inhibit protein synthesis, chloroplast development, and photosynthesis, ultimately leading to growth inhibition; some organisms exhibit growth stimulation at certain antibiotic concentrations. Daphnia magna and other aquatic invertebrates have also been used for checking the toxicity priority of antibiotics. When investigating the acute effect of antibiotics (e.g., growth inhibition), concentrations in standard laboratory organisms are usually about two or three orders of magnitude higher than the maximal concentrations in the aquatic environment, resulting in the underestimation of antibiotic hazards. Vertebrate organisms show a promising potential for chronic toxicity and potentially subtle effects of antibiotics, particularly on biochemical processes and molecular targets. The adverse developmental effects of macrolides, tetracyclines, sulfonamides, quinolones, and other antibiotic groups have been evaluated in aquatic vertebrates such as Danio rerio and Xenopus tropicalis. In acute toxicity tests, low levels of antibiotics have systematic teratogenic effects on fish. The effects of antibiotics on oxidative stress enzymes and cytochrome P450 have been investigated. Cytotoxicity, neurotoxicity, and genotoxicity have been observed for certain antibiotic amounts. However, there are no firm conclusions regarding the chronic toxicity of antibiotics at environmentally relevant levels because of the lack of long-term exposure studies. Herein, future perspectives and challenges of antibiotic toxicology were discussed. Researchers should pay more attention to the following points: chronic toxicity and potentially subtle effects of environmentally relevant antibiotics on vertebrates; effects of toxicity on biochemical processes and mode of action; combined toxicity of antibiotics and other antibiotics, metabolites, and heavy metals; and environmental factors such as temperature and pH.     

Antibiotic adjuvants – A strategy to unlock bacterial resistance to antibiotics

Resistance to available antibiotics in pathogenic bacteria is currently a global challenge since the number of strains that are resistant to multiple types of antibiotics has increased dramatically each year and has spread worldwide. To unlock this problem, the use of an ‘antibiotic adjuvant’ in combination with an antibiotic is now being exploited. This approach enables us to prolong the lifespan of these life-saving drugs. This digests review provides an overview of the main types of antibiotic adjuvants, the basis of their operation and the remaining issues to be tackled in this field. Particular emphasis is placed on those compounds that are already in clinical development, namely β-lactamase inhibitors.     

Use of antibiotics for the prevention of postoperative suppurative complications in planned surgery

Two methods for antibiotic prophylaxis in scheduled surgical treatment were studied comparatively. In the main group antibiotic prophylaxis with respect to 621 operations was started simultaneously with premedication, the duration of the course being defined by the operation type. With respect to 252 pure operations antibiotics were not used in 69.8 per cent of the cases or used for 2-3 days in 27.8 per cent of the cases. With respect to 253 conditionally pure operations shorter courses of antibiotic prophylaxis, i.e. for 2-3 days were used in 50.2 per cent of the cases. In the control group the antibiotics were used after operations in mean therapeutic doses, the duration of the course being defined by the clinical findings. The number of purulent complications in the main group decreased, while the amounts of the antibiotics used were much lower.     

我院专项治理前后抗菌药物使用情况分析

目的:通过分析抗菌药物临床应用专项治理前后住院患者抗菌药的使用情况,以促进合理用药。方法:随机抽取我院2010年1至2011年12月病例1680份,抽取甲状腺/乳腺/疝气/闭合性骨折I类切口手术病历100份,分析治理前后抗菌药物使用率、使用强度、病原送检率、DDDs、DUI及I类切口抗菌药物应用情况。结果:治理前住院患者抗菌药物使用率、使用强度分别为68.50%、49.8DDD;治理后分别为56.2%、37.8DDD,显著降低(P<0.05)。治理前有四种抗菌药物DUI>1,依次为头孢哌酮/舒巴坦钠>头孢噻吩钠=头孢唑啉>头孢呋辛;治理后有两种抗菌药物DUI>1,依次为磺苄西林>头孢哌酮/舒巴坦钠;治理后I类切口手术患者预防使用抗菌药物比例略为下降,疗程符合率、用药合理率明显上升(P<0.05)。结论:我院住院患者抗菌药使用情况基本达到《抗菌药物临床应用专项工作方案》要求。但在某些方面,如I类切口使用率、疗程、用药选择上需要持续改进,应加强对I类切口的监管力度,以确保用药的经济、有效、合理。     

Status of pathogens,antibiotic resistance genes and antibiotic residues in wastewater treatment systems

Pathogens are becoming nearly untreatable due to the rise in gaining new resistance against standard antibiotics. Coexistence of microbial pathogens, antibiotics and antibiotic resistant genes (ARGs) in wastewater treatment plants (WWTP) provide favourable conditions for the development of new antibiotic resistant bacteria (ARB); facilitate horizontal gene transfer among pathogens and may also serve as a hotspot for the spread of ARB and genes into the environment. In this study, the current status of wastewater treatment systems in the removal of pathogens, ARGs, and antibiotic residues are discussed. WWTP are efficient in removing pathogens and antibiotic residues to a greater extend during secondary and tertiary treatment processes. Recent studies, however, have shown high variations in the presence of pathogens including ARB as well as antibiotic resistance genes (ARG) in the final effluent. Prolonged sludge retention time (SRT) and hydraulic retention time (HRT) during secondary treatment will facilitate antibiotic removal by adsorption and biodegradation. However, the above conditions can also lead to the enhancement of antibiotic resistance process in microbes. Therefore, optimum conditions for the operation of conventional WWTP for the efficient removal of antibiotics are yet to be established. The removal of antibiotic residues can be accelerated by combining conventional activated sludge (CAS) process with an additional treatment technology involving dosing with ozone. The advanced biological treatment method using membrane bioreactors (MBR) in combination with coagulation reportedly has the best ARG removal efficiency, and removes both ARB and extracellular ARGs. While studies have predicted the fate for ARGs in wastewater treatment plants, the mechanisms of ARGs acquisition remains to be conclusively established. Thus, strategies to investigate the underlying mechanism of acquisition of ARGs within the WWTP are also provided in this review.     

The role of antibiotics and antibiotic resistance in nature

Investigations of antibiotic resistance from an environmental prospective shed new light on a problem that was traditionally confined to a subset of clinically relevant antibiotic‐resistant bacterial pathogens. It is clear that the environmental microbiota, even in apparently antibiotic‐free environments, possess an enormous number and diversity of antibiotic resistance genes, some of which are very similar to the genes circulating in pathogenic microbiota. It is difficult to explain the role of antibiotics and antibiotic resistance in natural environments from an anthropocentric point of view, which is focused on clinical aspects such as the efficiency of antibiotics in clearing infections and pathogens that are resistant to antibiotic treatment. A broader overview of the role of antibiotics and antibiotic resistance in nature from the evolutionary and ecological prospective suggests that antibiotics have evolved as another way of intra‐ and inter‐domain communication in various ecosystems. This signalling by non‐clinical concentrations of antibiotics in the environment results in adaptive phenotypic and genotypic responses of microbiota and other members of the community. Understanding the complex picture of evolution and ecology of antibiotics and antibiotic resistance may help to understand the processes leading to the emergence and dissemination of antibiotic resistance and also help to control it, at least in relation to the newer antibiotics now entering clinical practice.     

Rational use of antibiotics is the basis of their effectiveness and safety]

Many-year studies on the use of antibiotics in the general medical practice are summarized in the paper. The present trends in further improvement of the rational use of antibiotics are presented. It is shown that the present rational and safe antibiotic therapy is determined by 3 main factors: (1) choice of the drug with due regard for its pharmacological properties and spectrum, (2) isolation, identification and determination of the bacterial flora sensitivity to the antibiotic, (3) revealing or prevention of high sensitivity of the patients to the antibiotics chosen.     

Stronger together? Perspectives on phage-antibiotic synergy in clinical applications of phage therapy

Increasingly, clinical infections are becoming recalcitrant or completely resistant to antibiotics treatment and multidrug resistance is rising alarmingly. Patients suffering from infections that used to be treated successfully by antibiotic regimens are running out of the treatment options. Bacteriophage (phage) therapy, long practiced in parts of Eastern Europe and the states of the former Soviet Union, is now being reevaluated as a treatment option complementary to and synergistic with antibiotic treatments. We discuss some current studies that have addressed synergistic killing activity between phages and antibiotics, the issues of treatment order and antibiotic class, and point to considerations that will have to be addressed by future studies. Overall, co-treatments with phages and antibiotics promise to extend the utility of antibiotics in current use. Nevertheless, a lot of work, both basic and clinical, remains to be done before such co-treatments become routine options in the hospital setting.     

Phenotypes selected during chronic lung infection in cystic fibrosis patients: implications for the treatment of Pseudomonas aeruginosa biofilm infections

During chronic lung infection of patients with cystic fibrosis, Pseudomonas aeruginosa can survive for long periods of time under the challenging selective pressure imposed by the immune system and antibiotic treatment as a result of its biofilm mode of growth and adaptive evolution mediated by genetic variation. Mucoidy, hypermutability and acquirement of mutational antibiotic resistance are important adaptive phenotypes that are selected during chronic P.?aeruginosa infection. This review dicsusses the role played by these phenotypes for the tolerance of biofilms to antibiotics and show that mucoidy and hypermutability change the architecture of in vitro formed biofilms and lead to increase tolerance to antibiotics. Production of high levels of beta-lactamase impairs penetration of beta-lactam antibiotics due to inactivation of the antibiotic. In conclusion, these data underline the importance of biofilm prevention strategies by early aggressive antibiotic prophylaxis or therapy before phenotypic diversification during chronic lung infection of patients with cystic fibrosis.     

Crossroads of Antibiotic Resistance and Biosynthesis

The biosynthesis of antibiotics and self-protection mechanisms employed by antibiotic producers are an integral part of the growing antibiotic resistance threat. The origins of clinically relevant antibiotic resistance genes found in human pathogens have been traced to ancient microbial producers of antibiotics in natural environments. Widespread and frequent antibiotic use amplifies environmental pools of antibiotic resistance genes and increases the likelihood for the selection of a resistance event in human pathogens. This perspective will provide an overview of the origins of antibiotic resistance to highlight the crossroads of antibiotic biosynthesis and producer self-protection that result in clinically relevant resistance mechanisms. Some case studies of synergistic antibiotic combinations, adjuvants, and hybrid antibiotics will also be presented to show how native antibiotic producers manage the emergence of antibiotic resistance.     

环境抗生素污染的微生物修复进展

近年来随着抗生素在畜牧业、水产养殖业以及医疗行业的广泛应用,大量抗生素通过排泄物进入环境,导致我国大面积水体及土壤环境中抗生素残留量急剧增高。环境中不同种类的抗生素的残留导致微生物种群结构失衡,对生态环境及人类造成极大危害。因此,解决抗生素残留问题是21世纪新型环境污染物领域的一个重要课题。已有研究显示,一些微生物能够以抗生素为碳源生存,可用于降解环境中残留抗生素,但人们对微生物降解抗生素的降解机制了解较少。文中概括了近十年来抗生素降解菌株和菌群对抗生素的去除情况,以及应用微生物菌群处理抗生素残留的技术方法,同时对未来利用微生物修复法减少环境中抗生素残留进行了展望。     

What are the missing pieces needed to stop antibiotic resistance?

As recognized by several international agencies, antibiotic resistance is nowadays one of the most relevant problems for human health. While this problem was alleviated with the introduction of new antibiotics into the market in the golden age of antimicrobial discovery, nowadays few antibiotics are in the pipeline. Under these circumstances, a deep understanding on the mechanisms of emergence, evolution and transmission of antibiotic resistance, as well as on the consequences for the bacterial physiology of acquiring resistance is needed to implement novel strategies, beyond the development of new antibiotics or the restriction in the use of current ones, to more efficiently treat infections. There are still several aspects in the field of antibiotic resistance that are not fully understood. In the current article, we make a non-exhaustive critical review of some of them that we consider of special relevance, in the aim of presenting a snapshot of the studies that still need to be done to tackle antibiotic resistance.     

Why and how antibiotics are used in swine production

In summary, published research data clearly show that the use of antibiotics during all phases of growth benefits the rate and efficiency of body weight gain, reduces mortality and morbidity, reduces subclinical disease, and improves health in pigs. Also, antibiotics at breeding and during lactation benefits reproductive and lactational performance in sows. The economic benefits are several-fold greater than the cost of the antibiotic when a cost-effective antibiotic is used for this purpose. Monitoring and surveillance of microbial resistance in animals and humans has continued, with no animal-to-human infection path being clearly delineated. Although the incidence of antibiotic resistance in the human population remains high, there is no clear evidence that the levels or patterns have changed. The high levels of antimicrobial resistance in humans likely result from antibiotics prescribed directly to humans, because well over half of the antibiotics produced in the United States is used in human medicine. Whether antibiotic usage in swine, poultry, and other food-producing animals contributes to antibiotic resistance in the human population will continue to be debated. Even though antibiotics have been fed for nearly 50 years to literally billions of animals, there is still no convincing evidence of unfavorable health effects in humans that can be directly linked to the feeding of subtherapeutic levels of antibiotics to swine or other animals. Hopefully, policy decisions in the future regarding the use of antimicrobials in animals will be based on science and sound risk assessment, and not on emotionalism.     

Do we need new antibiotics? The search for new targets and new compounds

Resistance to antibiotics and other antimicrobial compounds continues to increase. There are several possibilities for protection against pathogenic microorganisms, for instance, preparation of new vaccines against resistant bacterial strains, use of specific bacteriophages, and searching for new antibiotics. The antibiotic search includes: (1) looking for new antibiotics from nontraditional or less traditional sources, (2) sequencing microbial genomes with the aim of finding genes specifying biosynthesis of antibiotics, (3) analyzing DNA from the environment (metagenomics), (4) reexamining forgotten natural compounds and products of their transformations, and (5) investigating new antibiotic targets in pathogenic bacteria.     

Estimation of the Use of Antibiotics in the Small Ruminant Industry in the Netherlands in 2011 and 2012

The aim of this study was to estimate the quantity of antibiotics and classes of antibiotics used in the small ruminant industry in the Netherlands in 2011 and 2012. Twelve large veterinary practices, located throughout the Netherlands were selected for this study. All small ruminant farms associated with these practices that had complete records on the quantity of antibiotics prescribed were included. The veterinary practices provided data on all antibiotics prescribed, and the estimated animal used daily dose of antibiotics per year (AUDD/Y) was calculated for each farm. The median AUDD/Y in small ruminant farms was zero in both years (mean 0.60 in 2011, and 0.62 in 2012). The largest quantity of antibiotic use was observed in the professional goat industry (herds of ≥32 goats) with a median AUDD/Y of 1.22 in 2011 and 0.73 in 2012. In the professional sheep industry (flocks of ≥32 sheep), the median AUDD/Y was 0 in 2011 and 0.10 in 2012. In the small scale industry (flocks or herds of <32 sheep or goats), the median AUDD/Y never exceeded 0. The most frequently prescribed antibiotics in the small scale industry and professional sheep farms belonged to the penicillin class. In professional goat farms, antibiotics of the aminoglycoside class were most frequently prescribed. This study provides the first assessment on the quantity of antibiotic use in the small ruminant industry. Given a comparable attitude towards antibiotic use, these results might be valid for small ruminant populations in other north-western European countries as well. The antibiotic use in the small ruminant industry appeared to be low, and is expected to play a minor role in the development of antibiotic resistance. Nevertheless, several major zoonotic bacterial pathogens are associated with the small ruminant industry, and it remains important that antibiotics are used in a prudent way.     

Combined Antibiotic Therapy

The indications for combined antibiotic therapy are reviewed, and two major indications are discussed at length: the prevention of development of antibiotic resistance and the possibility of achieving antibiotic synergism.Since micro-organisms vary in their behaviour in the presence of different antibiotic combinations, careful evaluation of clinical response and close laboratory control are necessary.Antibiotics are divided into four groups and their possible combinations are described. It is emphasized that bactericidal antibiotics, e.g. penicillin and streptomycin, which act only on multiplying bacteria, may be antagonized by some bacteriostatic antibiotics, e.g. tetracycline. Clinical observations appear to confirm the usefulness of this division of the antibiotics.     

Identifi cation of antibiotics that are effective 2 in eliminatingAgrobacterium tumefaciens

An assay was performed to identify the antibiotics that are most effective againstAgrobacterium tumefaciens strains EHA101 and LBA4404, and to determine if these antibiotics inhibited tobacco callus and shoot formation. We tested ten antibiotics: cefotaxime, carbenecillin, erythromycin, spectinomycin, polymixin B, chloramphenicol, methicillin, Augmentin 500, Augmentin 250, and moxalactam. The effectiveness of each antibiotic against the two strains was determined by measuring the zones of inhibition of bacterial growth in a disk-diffusion assay. The five antibiotics that generated the largest zones of inhibition for each strain were assayed to determine their effects on callus formation. Cefotaxime was the most active antibiotic tested against strain LBA4404, and moxalactam was the most effective antibiotic against EHA101. Both cefotaxime and moxalactam had little or no effect on callus development.     

PYOGENIC INFECTIONS IN ORTHOPEDIC SURGERY—Prevention and Management

A problem that confronts surgeons in clinical practice is that a patient may acquire new infections while in the hospital. When such infections occur they are predominantly staphylococcal and these bacteria are often, but not always resistant to penicillin, streptomycin and the tetracycline antibiotics. They are often but neither completely nor uniformly sensitive to the newer or less frequently used antimicrobial agents.The extension of antibiotic usage from proven situations to “routine” prophylaxis has been a widespread practice. There are many reasons to discourage and to reexamine the validity and purpose, as well as the safety of this practice. We now have sufficient background and experience to revert from widespread and indiscriminate use to a practice of discriminate prophylactic therapy.In general, soft tissue lacerations and clean wounds do not require operation under an “antibiotic umbrella.” Similarly, elective orthopedic surgical procedures of soft tissues such as muscle biopsy, tenorrhaphy and muscle and tendon transplants as well as plastic surgical procedures can be safely performed without antibiotic therapy if technique is good and operation not prolonged. Operations of major magnitude on the motor-skeletal system, such as open fractures, internal fixation of fractures with bone grafts, and major operations of joints are indication for antibiotic therapy for impending infection postoperatively for five days. Reliance is mainly on antistaphylococcal drugs to which hospital organisms are predominantly sensitive. The two remaining indications for antibiotic therapy against impending infection are: (1) major crush injury—for example, to the thigh—and (2) the need for a patient with a healing fracture to have other surgical procedures such as tooth extraction or excision of an infected area which might predispose to transient bacteremia and embolic infection in bone or joint.     

Effect of antibiotics in the environment on microbial populations

Antibiotics act as an ecological factor in the environment that could potentially affect microbial communities. The effects include phylogenetic structure alteration, resistance expansion, and ecological function disturbance in the micro-ecosystem. Numerous studies have detected changes of microbial community structure upon addition of antibiotics in soil and water environment. However, the causal relationship between antibiotic input and resistance expansion is still under debate, with evidence either supporting or declining the contribution of antibiotics on alteration of antibiotic resistance. Effects of antibiotics on ecological functions have also been discovered, including nitrogen transformation, methanogenesis, and sulfate reduction. In the latter part, this review discusses in detail on factors that influence antibiotic effects on microbial communities in soil and aquatic environment, including concentration of antibiotics, exposure time, added substrates, as well as combined effects of multiple antibiotics. In all, recent research progress offer an outline of effects of antibiotics in the natural environment. However, questions raised in this review need further investigation in order to provide a comprehensive risk assessment on the consequence of anthropogenic antibiotic input.