beta-Lactam resistance and beta-lactamases in bacteria of animal origin

beta-Lactams are among the most clinically important antimicrobials in both human and veterinary medicine. Bacterial resistance to beta-lactams has been increasingly observed in bacteria, including those of animal origin. The mechanisms of beta-lactam resistance include inaccessibility of the drugs to their target, target alterations and/or inactivation of the drugs by beta-lactamases. The latter contributes predominantly to beta-lactam resistance in Gram-negative bacteria. A variety of beta-lactamases have been identified in bacteria derived from food-producing and companion animals and may further serve as a reservoir for beta-lactamase-producing bacteria in humans. While this review mainly describes beta-lactamases from animal-derived Escherichia coli and Salmonella spp., beta-lactamases from animal-derived Campylobacter spp., Enterococcus spp., Staphylococcus spp. and other pathogens are also discussed. Of particular concern are the increasingly-isolated plasmid-encoded AmpC-type CMY and extended-spectrum CTX-M beta-lactamases, which mediate acquired resistance to extended-spectrum beta-lactams. The genes encoding these enzymes often coexist with other antimicrobial resistance determinants and can also be associated with transposons/integrons, increasing the potential enrichment of multidrug resistant bacteria by multiple antimicrobial agents as well as dissemination of the resistance determinants among bacterial species. Characterization of beta-lactam-resistant animal-derived bacteria warrants further investigation of the type and distribution of beta-lactamases in bacteria of animal origin and their potential impact on human medicine.     

曲靖地区仔猪腹泻细菌性病原的分离鉴定与耐药性分析

为了解曲靖地区仔猪出现腹泻的细菌性病因,对5个养殖场148份出现仔猪腹泻症状的样品进行细菌分离培养及耐药性分析,结果显示,检出致病性大肠杆菌(E.coli)114份,阳性率为77.03%;沙门氏菌(Salmonella)26份,阳性率为17.57%,混合感染率为17.57%.致病性大肠杆菌和沙门氏菌对多种抗生素产生了耐药性,其中114株致病性大肠杆菌中97株呈多重耐药性,占总菌数的85.09%,26株沙门氏菌中20株呈多重耐药性,占总菌数的76.92%.结果表明,致病性大肠杆菌是导致当地哺乳仔猪腹泻的主要细菌性病原,部分仔猪继发感染沙门氏菌,两种细菌对多种抗生素产生了耐药性,多重耐药现象较严重.     

腹泻仔猪肠道致病性大肠埃希氏菌和沙门氏菌的分离鉴定与耐药性研究

为探明仔猪细菌性腹泻肠道致病性大肠埃希氏菌和沙门氏菌流行的血清型、耐药表型及耐药基因型,本试验采集了贵州省5个地（州）市7个规模化养猪场的128份腹泻仔猪肠道样本,并对采集的样本进行了大肠埃希氏菌和沙门氏菌分离与鉴定,通过动物试验鉴定菌株的致病性,利用血清学方法鉴定其血清型,并通过药敏纸片法对主要致病菌进行耐药性研究,采用PCR技术检测各致病菌株耐药相关基因,分析细菌耐药表型和耐药基因型相关性。结果显示,本研究共分离鉴定到78株致病性大肠埃希氏菌与21株沙门氏菌,致病性大肠埃希氏菌血清型以O138、O87为主,沙门氏菌血清型以鼠伤寒沙门氏菌、肠炎沙门氏菌居多;药敏试验结果表明,本试验分离到的78株致病性大肠埃希氏菌对β-内酰胺类药物耐药率达80%以上,对其他种类的抗菌药耐药率均超过40%,分离鉴定的21株沙门氏菌对氨基糖苷类药物耐药率达50%以上,对其他种类的抗菌药耐药率均达20%以上;本试验分离鉴定的致病性大肠埃希氏菌共检出12种耐药相关基因,沙门氏菌共检出10种耐药相关基因,两种细菌耐药基因型与耐药表型符合率均达60%以上,且均为多重耐药。本研究为仔猪腹泻的综合防控提供了理论依据。     

Isolation,Identification and Drug Resistance Analysis of Interstinal Pathogenic Escherichia coli and Salmonella Isolated from Diarrhea Piglets

In order to find out the serotype, resistant phenotype and genotype of Escherichia coli (E. coli) and Salmonella in piglets, this study collected 128 samples of diarrhea piglets from seven large-scale pig farms in five cities in Guizhou province, and the E. coli and Salmonella were isolated and identified. The pathogenicity of the strain was identified by animal test. The drug resistance of the main pathogen was tested by drug susceptibility paper. The resistance gene of each pathogen was detected by PCR. The drug resistance and genotype correlation of the bacterial were analyzed. The results showed that 78 strains of pathogenic E. coli and 21 strains of Salmonella were isolated and identified in this study. The serotypes of pathogenic E. coli were predominantly O138 and O87. Salmonella Typhimurium and Salmonella Enteritidis were predominant serotypes. The susceptibility test showed that the resistant strains of 78 strains of E. coli were more than 80% resistant to β-lactams and more than 40% for other antibacterials. The resistance rate of 21 strains of Salmonella to aminoglycosides was more than 50% and more than 20% to other types of antibacterials; 12 and 10 kinds of drug resistance-related genes of E. coli and Salmonella were detected, respectively; The coincidence rate of resistant genotype and phenotype of two kinds of bacteria were above 60%, and both were multiple drug resistance. This study provided a theoretical basis for comprehensive prevention and control of piglets diarrhea.     

The multiple antibiotic resistance (mar) locus and its significance

Chromosomally encoded systems involved in low level resistance of bacteria to different classes of antibiotics (mainly beta-lactams, chloramphenicol, quinolones and tetracycline), disinfectants and in resistance to organic solvents have been the focus of considerable interest in recent years. The multiple antibiotic resistance (mar) locus of Escherichia coli and Salmonella is perhaps the best described system involved in this type of resistance which is induced by MarA, the activator protein encoded by the marRAB locus. The mar -locus is reported to mediate resistance primarily by up-regulating efflux of some antibiotics, disinfectants and organic solvents via the AcrAB-TolC efflux pump and down regulating influx through Outer Membrane Protein F (OmpF). Whilst the level of antibiotic resistance conferred by marRAB is only low level, there are increasing data to suggest that marRAB and related systems are important in clinical antibiotic resistance, possibly as a 'stepping stone' to higher levels of resistance. Other related systems include up-regulation of RobA, SoxS and AcrAB which give rise to a similar resistance phenotype to that conferred by up-regulation of MarA. The aim of this paper is to review the function and significance of the mar -locus and related systems with a particular focus on its implications in veterinary medicine.     

Prevalence and characteristics of quinolone resistance in Escherichia coli in veal calves

Quinolone resistance is studied and reported increasingly in isolates from humans, food-producing animals and companion animals. Resistance can be caused by chromosomal mutations in topoisomerase genes, plasmid-mediated resistance genes, and active transport through efflux pumps. Cross sectional data on quinolone resistance mechanisms in non-pathogenic bacteria from healthy veal calves is limited. The purpose of this study was to determine the prevalence and characteristics of quinolone resistance mechanisms in Escherichia coli isolates from veal calves, after more than 20 years of quinolone usage in veal calves. MIC values were determined for all isolates collected as part of a national surveillance program on antimicrobial resistance in commensal bacteria in food-producing animals in The Netherlands. From the strains collected from veal calves in 2007 (n=175) all isolates with ciprofloxacin MIC ≥ 0.125 mg/L (n=25) were selected for this study, and screened for the presence of known quinolone resistance determinants. In this selection only chromosomal mutations in the topoisomerase type II and IV genes were detected. The number of mutations found per isolate correlated with an increasing ciprofloxacin MIC. No plasmid-mediated quinolone resistance genes were found. The contribution of efflux pumps varied from no contribution to a 16-fold increase in susceptibility. No correlation was found with the presence of resistance genes of other antimicrobial classes, even though all quinolone non-wild type isolates were resistant to 3 or more classes of antibiotics other than quinolones. Over twenty years of quinolone usage in veal calves in The Netherlands did not result in a widespread occurrence of plasmid-mediated quinolone resistance, limiting the transmission of quinolone resistance to clonal distribution.     

大肠埃希菌多重耐药性的形成机制

细菌耐药(尤其多重耐药)现象的出现,给我国养殖业带来巨大的经济损失,大肠埃希菌耐药性可分为原发性和获得性.大肠埃希菌外排泵功能增强、膜通透性下降均可以导致多重耐药的产生,而质粒、整合子/基因盒系统等可移动的遗传因子在多重耐药性的传播上有着重要作用.此外,细菌生物被膜的形成使细菌对多种抗菌药物产生强大的抵抗力.文章从上述几个方面阐述大肠埃希菌产生多重耐药的形成机制,并提出相应的防控对策.     

In vitro inhibition of Salmonella organisms isolated from reptiles by an inactivated culture of microcin-producing Escherichia coli

OBJECTIVE: To determine whether an inactivated culture of a microcin-producing avian Escherichia coli was capable of killing Salmonella isolates from reptiles in an in vitro test system. SAMPLE POPULATION: 57 Salmonella isolate from reptiles. PROCEDURE: A wild-type avian E. coli electrotransformed with a plasmid coding for the production of microcin 24 was tested in an in vitro microassay system for its ability to kill 57 Salmonella spp isolated from reptiles. The reptile population included snakes, iguana, frilled lizards, turtles, other lizards, and unspecified reptiles. RESULTS: 44 of the Salmonella isolates were inhibited strongly, compared with the in vitro assay controls; 12 had weak inhibition, and 1 was not inhibited by the microcin-producing E. coli. Thirteen of the 57 isolates had resistance to at least 1 antibiotic, primarily streptomycin. There were 9 O serogroups identified in the 57 isolates, with serogroup H being the most prevalent (18 to 57). CONCLUSION AND CLINICAL RELEVANCE: Antibiotics are not recommended to eliminate Salmonella organisms from reptiles because of the development of antibiotic resistance. Further studies are necessary to determine whether the use of microcin-producing bacteria will be effective in controlling Salmonella infections in companion reptiles.     

Plasmid-mediated quinolone resistance gene detected in Escherichia coli from cattle

Fluoroquinolones resistance in bacteria can be due to chromosomal and plasmid-mediated mechanisms. Of growing concern is the acquisition of genes encoding quinolone resistance in combination with other resistance mechanisms such as extended-spectrum beta-lactamases. In this study we describe the identification of an isolate of Escherichia coli from cattle which carried qnrS1 in combination with a blaCTX-M gene, although they were not co-localised on the same plasmid. In addition, using a DNA array it was possible to identify several other antimicrobial resistance genes in this isolate. This is the first report of a qnr gene in E. coli from cattle in the UK and highlights the need for surveillance of these emerging resistance mechanisms.     

细菌排出泵、TolC家族和生物薄膜的作用机制研究进展

在多种重要病原体中存在抗生素排出泵,它与其它抗性一起构成了细菌显著的耐药性,其识别的底物非常广泛.G-菌中还存在与排出泵不同的另一种以蛋白质构成的排出系统,通过底物特异性内膜蛋白和外膜蛋白TolC家族的可逆性互作,也可以直接将包括小分子药物和大分子蛋白毒素等的多种分子从胞浆经周质区运到体外.粘附在内置医疗装置或组织中的细菌因其形成生物薄膜结构和以蛋白质、多糖为主的水性基质包裹的菌体也可以产生长期感染以及对抗生素的持久抗性,这种抗性与经典的质粒、转座子或突变产生的抗性不同.本文对细菌TolC家族和生物薄膜引起的抗性机制进行了综述.     

Resistance to various antibiotics of Salmonella and Escherichia coli isolated from registrable farm feeds

Resistance to 20 antibiotics of 128 Salmonella and 97 Escherichia coli isolates from various registrable farm feeds was determined. A high frequency of comparatively low levels of resistance was found in both the Salmonella and E. coli isolates. This, together with an elevated frequency of multiple resistance, indicates that problems related to an effective transfer in bacterial populations of resistance to certain antibiotics are a distinct possibility. The addition of antibiotics, such as penicillin and tetracyclines, to animal feeds can create conditions for rapid selection amongst bacteria resistant to antibiotics. The numbers of resistant bacteria in the animal environment may be increased and may lead to the development of veterinary and human health problems from the possible transfer of antimicrobial resistance from animal pathogens to human pathogens or spreading in the human population of animal pathogens resistant to antibiotics. There is a need for caution in the use of antibiotics, particularly in animal feeds. Extended survey of, and epidemiological research on, farm feeds, manufacturing mills and animal production units are emphasized.     

猪源乳酸杆菌的分离鉴定及生物学特性分析

乳酸杆菌制剂可以替代抗生素,用于预防和治疗细菌性腹泻。为获取可作为微生态制剂的候选菌株,从健康仔猪肠道分离到5株乳酸杆菌,经抑菌试验、生长曲线测定、耐酸、耐胆盐、耐胰酶试验等,筛选到1株对大肠杆菌、沙门氏菌、金黄色葡萄球菌等致病菌有较好的抑制作用,对低pH值、高胆盐、胰酶均有一定耐受能力的乳酸杆菌,命名为LY7。经PCR鉴定,该菌株为约氏乳杆菌。     

The resistance to anti-microbial agents of bacteria isolated from pathological conditions of birds in Victoria, 1978 to 1983

The resistance to anti-microbial agents of bacteria isolated from pathological conditions of birds in Victoria, 1978 to 1983, was determined for isolates of Escherichia coli, Salmonella species, Staphylococcus aureus, Pasteurella multocida, P. anatipestifer, Yersinia pseudotuberculosis and Haemophilus paragallinarum. The isolates of E. coli had a high prevalence of resistance to tetracycline and sulphonamides, and a lower prevalence of resistance to furazolidone and sulphamethoxazole-trimethoprim. The isolates of Salmonella spp commonly had resistance to tetracycline, sulphonamides, furazolidone and sulphamethoxazole-trimethoprim. Almost half the isolates of S. aureus showed resistance to lincomysin and many showed resistance to penicillin. Resistance to tetracycline was found in isolates of P. multocida, P. anatepestifer and Y. pseudotuberculosis. Some isolates of H. paragallinarum showed resistance to sulphonamides, streptomycin and sulphamethoxazole-trimethoprim.     

载铜蒙脱石体外杀菌效果及其机理

选用断奶仔猪肠道中的大肠杆菌K88和猪霍乱沙门菌作为指示菌。杀菌性能的测定采用最低抑菌浓度（MIC）和最小杀菌浓度（MBC）,并绘制杀菌曲线。原子吸收光谱仪测定Cu2＋在肉汤和生理盐水中的释放量;透射电镜观察细菌细胞壁的变化;全自动生化分析仪测定细菌胞内酶的活性;通过K＋电极测定K＋释放量;采用SP-2型溶氧仪测定菌体悬浮液中的溶氧量。结果显示,载铜蒙脱石对E.coli K88的MIC为64mg/L,MBC为256mg/mL;对S.choleraesuis的MIC为128mg/L,MBC为512mg/L。而蒙脱石未显抗菌活性。透射电镜下观察细菌与载铜蒙脱石作用后形态发生了变化,细菌细胞膜受损,内容物外漏;细菌胞内酶活性结果显示,胞内酶的大量外漏,与对照组相比,均差异极显著（P〈0.01）;大量自由的K＋从细菌细胞内释放出来;呼吸代谢结果显示,载铜蒙脱石抑制了细菌呼吸代谢的三羧酸循环途径。结果表明,载铜蒙脱石具有强大的杀菌作用。     

黄芪提取物对常见致病菌的体内外抑菌活性测定

为了研究黄芪提取物对金黄色葡萄球菌、大肠杆菌和沙门氏菌等致病菌的抑菌活性,采用试管二倍稀释法,测定黄芪提取物对金黄色葡萄球菌、大肠杆菌和沙门氏菌的体外抑菌活性;采用相同浓度致病菌灌胃小鼠后,分别用黄芪提取物灌胃治疗,测定小鼠十二指肠、空肠、回肠和盲肠中肠道菌群数量,以确定黄芪提取物的体内抑菌活性.结果表明,无论是在体外还是在体内,黄芪提取物对金黄色葡萄球菌、大肠杆菌和沙门氏菌均具有抑制作用,对大肠杆菌的抑制作用最强,对沙门氏菌的抑制作用最弱;且通过灌注黄芪提取物,显著降低了各种致病菌致病后小鼠的死亡率.通过研究可以得出,黄芪提取物对常见的金黄色葡萄球菌、大肠杆菌和沙门氏菌等致病菌具有较明显的体内外抑菌作用.     

Increase of bacterial resistance in human medicine by resistance genes of bacteria from meat supplying animals

Two different groups of bacteria carrying genes encoding for resistance to antibiotics may be transmitted from animals to humans via food products: a.) obligate infectious agents (enteric pathogens, e.g. Salmonella enterica spp., Campylobacter spp., EHEC) and b) facultative pathogenic species (e.g. E. coli, enterococci). Thus far, it is unknown whether genes encoding for resistance to antibiotics from these bacteria may be transferred to bacteria in normal flora of the host. The transfers of genes encoding for resistance to vancomycin from animal sources to the mucosa of humans has been suggested. Thus, there is a threat that these plasmid-encoded resistance genes may also be transferred to other gram-positive organisms present in the human flora. Vancomycin is the antibiotic in reserve for treatment of infections caused by oxacillin (methicillin) resistant strains of S. aureus and by strains of pneumococcus resistant to penicillin.     

Research Progress on Bacterial Resistance

Antibiotic resistance of bacteria is a major problem in the clinical treatment of infectious diseases,and it has received the extensive attention.Bacteria producing inactivated enzyme or passivated enzyme is a mainly way to acquire resistance.Besides,the mechanisms of cell wall permeability barrier,efflux pump and target changes are existed,these mechanisms interact to the level of the bacterial antibiotic resistance.With the clinical application of new antibiotic,the new resistant mechanisms emerge and the antibiotic-resistant bacteria are widespread.The study of bacterial resistance mechanisms has instructional meaning for antibiotic-resistant bacteria control and new drug development.We elaborated the bacterial resistance from the origin of the resistance,mechanisms,characteristics and test method in this article.     

Human health hazards associated with the administration of antimicrobials to slaughter animals. Part II. An assessment of the risks of resistant bacteria in pigs and pork

Risks for the consumer regarding the acquisition of resistant bacteria and/or resistance genes via the consumption of pork are discussed. In general, Salmonella spp. and Escherichia coli that originate from animals do not easily transfer their resistance genes to the resident intestinal flora of humans. The prevalence of resistant E. coli in humans seems more associated with being a vegetarian (odds ratio (OR) 1.89) than with the consumption of meat and meat products. Other risk factors are treatment with antimicrobials (OR 2-5), becoming hospitalized (OR 5.93), or working in a health setting (OR 4.38). In the Netherlands, annually an estimated 45,000 people (0-150,000) become a carrier of resistant E. coli and/or resistance genes that ori ginate from pigs, while an estimated 345,000 persons (175,000-600,000) become a carrier of resistant E. coli and/or resistance genes that originate from hospitals, e.g. other patients. Any problems with resistant Salmonella spp. that stem from pigs are, in fact, an integral part of the total problem of food-borne salmonellosis. Sometimes there are outbreaks of a specific multi-resistant clone of S. typhimurium that causes problems in both farm animals and humans. The probability that in the next 30 years there is no or maximally one outbreak of a specific clone that originates from pig herds is estimated at about 75%. Antimicrobials used as a growth promoter can have a measurable influence on the prevalence of resistant bacteria. The likely chain of events regarding avoparcin and the selection and dissemination of resistance against vancomycin in the enterococci gives the impression that the impact of the use of antimicrobials in animals on the prevalence of resistance in humans is largely determined by whether resistance genes are, or become, located on a self-transferable transposon. Furthermore, consumer health risks of antimicrobials used in slaughter pigs are mainly determined by the selection and dissemination of bacterial resistance and much less by the toxicological properties of any residues in pork. It is also concluded that most of the problems with resistant bacteria in humans are associated with the medical use of antimicrobials, and that the impact of particularly the veterinary use of antimicrobials is limited. However, the impact of antimicrobials used as a feed additive appears to be much greater than that of antimicrobials used for strictly veterinary purposes. The use of antimicrobials as a feed additive should therefore be seriously reconsidered.     

氟苯尼考耐药性研究进展

氟苯尼考由于其广谱、高效的特性而广泛使用于兽医临床.然而,最近几年氟苯尼考在不少菌群中出现的耐药性问题已引起了人们的普遍关注.本文综述了国外近几年对氟苯尼考在大肠杆菌、沙门氏菌和葡萄球菌属耐药性方面的研究进展.     

大肠埃希菌多重耐药调节子研究进展

大肠埃希菌多重抗生素耐药主要是由多重耐药调节基因和外输泵共同作用产生的。大肠埃希菌多重耐药调节子是广泛存在于肠杆菌科细菌染色体上的抗生素多重耐药调节中心,是大肠埃希菌耐药的主要组成部分。为解决多重抗生素耐药问题,很多专家和学者对大肠埃希菌多重耐药调节子和外输泵的耐药机制进行了深入的研究,研究开发多重抗生素耐药基因消除剂和外输泵抑制剂,或增加外输泵抑制基因的表达,将成为从根本上解决多重抗生素耐药问题的最好方法。文章对大肠埃希菌AcrAB、AcrAB-Tolc,Mar和膜孔蛋白Ompf、Ompc等多重抗生素耐药调节子的组成、功能及其影响因素进行了综述。