鱼塘生态体系中大肠埃希菌和沙门菌的耐药性研究

为了解鱼塘生态体系大肠埃希菌和沙门菌的耐药情况,从广东省佛山某鱼塘随机采集草鱼及生活圈的水土样品中(包括鱼肠内容物、鱼塘底泥、鱼塘水)分离出47株大肠埃希菌和23株沙门菌.采用纸片扩散法(Kirby-bauer,KB)对分离菌株进行了15种抗生素的敏感性试验,结果显示100%的菌株均耐1种及1种以上的抗生素多表现出对氨...     

Antibiotic resistance among indicator bacteria isolated from healthy pigs in New Zealand

AIM: To determine the resistance to antibiotics among the indictor bacteria, Escherichia coli and Enterococcus spp, isolated from the faeces of healthy pigs on three conventional pig farms and one organic farm in the North Island of New Zealand. METHODS: Faecal samples, collected at intervals between March and October 2001, were plated onto MacConkey agar and Slanetz-Bartley agar and examined after 1-3 days incubation for colonies resembling E. coli and Enterococcus spp, respectively. Typical colonies were subcultured for further identification and storage. The isolates were tested for antibiotic resistance, using disc diffusion, to ampicillin, gentamicin, streptomycin, and tetracycline. Escherichia coli isolates were also tested for resistance to ciprofloxacin, cotrimoxazole and neomycin. Enterococcus spp isolates were also tested for resistance to vancomycin, erythromycin and virginiamycin. RESULTS: A total of 296 E. coli and 273 Enterococcus spp isolates were obtained from the three conventional farms, and 79 E. coli and 80 Enterococcus spp isolates were obtained from the organic farm. All the E. coli isolates from both the conventional and organic pig farms were susceptible to ciprofloxacin, and all the Enterococcus spp isolates were susceptible to ampicillin, gentamicin and vancomycin. Isolates of E. coli from conventional pig farms were resistant to gentamicin (0.7%), neomycin (0.7%), ampicillin (2.7%), cotrimoxazole (11%), streptomycin (25%) and tetracycline (60%). Enterococcus spp isolates from the same farms were resistant to erythromycin (68%), tetracycline (66%), streptomycin (54%) and virginiamycin (49%). By contrast, for the organic pig farm 相似文献   

Quantitative resistance level (MIC) of Escherichia coli isolated from calves and pigs suffering from enteritis: national resistance monitoring by the BVL

National Resistance Monitoring of the Federal Office of Consumer Protection and Food Safety (BVL), which was put into service in 2001, has made it possible to implement a valid and representative database on the basis of which the resistance situation, development and spread in animal pathogens can be evaluated. Escherichia coil (E. coli) strains originating from calves and pigs suffering from enteritis were first included in the investigations in the 2004/2005 study. A total of 258 bovine and 492 porcine E. coli strains were tested using the broth microdilution method to determine the in vitro susceptibility (minimum inhibitory concentration) to 23 (fattening pigs) and 28 (calves, piglets, weaners) different antimicrobial substances. Considerable prevalences of resistance were found for some antimicrobials. The strains originating from both animal species displayed high prevalences of resistance for tetracycline, trimethoprim, trimethoprim/sulfamethoxazole, doxycycline and ampicillin. Reduced susceptibility was detected particularly in the E. coli strains from calves. The data reveal that the resistance level of E. coli strains isolated from cases of enteric disease in calves and pigs is altogether higher than has so far been reported in pathogens causing different diseases and in other food-producing animal species. Based on the results presented, it is possible to assess the current resistance situation for E. coli strains in calves and pigs in Germany. This in turn helps to deduce the necessary management measures that can be taken in order to minimise resistance to antibiotics. Furthermore, the data help to decide on adequate therapy of E. coli infections of the intestinal tract in calves and pigs and encourage the responsible use of antibiotics in the interests of animal health and consumer protection.     

Antimicrobial resistance of Salmonella isolated from finishing swine and the environment of 60 Alberta swine farms

The study objective was to describe and evaluate antimicrobial resistance profiles in Salmonella isolated from Alberta swine finishing farms. Salmonella isolates (n = 322) were obtained from 192 fecal and 84 environmental samples of the 60 Salmonella-positive swine finishing farms. Isolates were classified susceptible, intermediate or resistant based on NCCLS guidelines. More than half of the isolates (53.4%) were susceptible to all of the 18 antimicrobials in the testing panel. No resistance was observed to amikacin, amoxicillin/clavulanic acid, cefoxitin, ceftiofur, ceftriaxone, cephalothin, ciprofloxacin, imipenem or nalidixic acid. Less than 1% of isolates were resistant to apramycin, gentamicin and trimethoprim/sulfamethoxazole. Higher frequencies of resistance were observed for chloramphenicol (4.7%), ampicillin (7.8%), kanamycin (11.8%), sulfamethoxazole (21.1%), streptomycin (25.5%) and tetracycline (38.8%). Eleven Salmonella serovars had isolates with resistance to > or =3 antimicrobials. The most frequently resistant serovar was Salmonella Derby, with 27 (38.0%) isolates resistant to > or =3 antimicrobials, including resistance to five and six antimicrobials. An absence of resistance to cephalosporins and fluoroquniolones and a low proportion of isolates resistant to amikacin, amoxicillin/clavulanic acid, apramycin, gentamicin and trimethoprim/sulfamethoxazole are encouraging findings from public health and animal health perspectives. Frequent resistance observed for ampicillin, kanamycin, sulfamethoxazole, streptomycin and tetracycline, antimicrobials commonly used in veterinary medicine for decades, indicates an urgent need to utilize these antimicrobials more prudently if their benefits are to be preserved.     

Comparison of antimicrobial resistance in generic Escherichia coli and Salmonella spp. cultured from identical fecal samples in finishing swine

The objectives of this study were to investigate the associations between antimicrobial resistance patterns in generic Escherichia coli and Salmonella spp. isolates recovered from identical pen pooled fecal samples, and to evaluate potential clustering of multiple isolates of these organisms within identical fecal samples. Up to 5 generic E. coli (n = 922 isolates) and Salmonella spp. (n = 922 isolates) isolates were obtained from each of 188 pen pooled fecal samples that had been collected from 45 finishing swine farms in Alberta in 2000, and tested for susceptibility to 15 antimicrobials. No isolates of either organism were resistant to 3rd generation cephalosporins or fluoroquinolones, which in Canada are considered antimicrobials of very high importance to human health. Approximately twice as many generic E. coli isolates as Salmonella spp. isolates were resistant to at least 1 antimicrobial. In addition, E. coli isolates showed more multidrug-resistance patterns. No significant association was observed between the resistance phenotypes of Salmonella spp. and E. coli at the fecal sample level. More clustering at the sample level was observed for proportions of antimicrobial resistance (AMR) in Salmonella spp. isolates than E. coli indicating that in future studies it might be sufficient to test fewer than 5 Salmonella spp. isolates per sample.     

屠宰前鸡、猪源大肠杆菌耐药性调查

本试验旨在了解屠宰前鸡、猪源食品动物体内大肠杆菌耐药情况,分析潜在的食品安全问题。从广州市畜禽交易市场随机采集待屠宰鸡和猪的粪便样品,分离鉴定大肠杆菌,并采用琼脂稀释法检测大肠杆菌对15种抗菌药物的敏感性。结果显示,从658份猪源样品和133份鸡源样品中共分离鉴定出731株大肠杆菌,其中猪源606株,鸡源125株。药敏试验结果显示,731株大肠杆菌均表现出不同程度的耐药,耐药谱广且多重耐药现象严重。对复方新诺明和四环素的耐药率为90.0%以上,仅对头孢西丁、黏菌素和阿米卡星较敏感(耐药率均低于3%)。鸡源大肠杆菌对头孢噻肟、头孢曲松、新霉素、阿米卡星、萘啶酸和环丙沙星的耐药率显著高于猪源大肠杆菌(P＜0.05)。鸡源大肠杆菌中3耐及3耐以上的菌株占97.60%,猪源大肠杆菌占94.72%。结果表明,屠宰前畜禽体内大肠杆菌对临床常用抗菌药物的耐药性非常严重,以多重耐药为主,且耐药谱丰富多样。提示屠宰前畜禽携带的耐药菌对食品安全和人类健康存在较大的安全隐患。     

鸡源大肠杆菌和沙门氏菌的分离鉴定及耐药分析

为探究甘肃省民勤县某饲养场肉仔鸡腹泻的病原及复方中草药制剂和抗生素分别对分离病原的抑菌效果,对7日龄病死肉鸡进行解剖，通过采集死亡肉仔鸡肝脏、脾脏、心脏进行病原菌分离培养、形态观察、16S rDNA分子鉴定，最终鉴定该病死肉仔鸡为大肠杆菌与沙门氏菌混合感染。抑菌结果显示，复方中草药对分离得到的大肠杆菌、鸡白痢沙门氏菌、鸡副伤寒沙门氏菌均有良好的抑菌效果。10种抗生素药敏试验结果显示，此三株菌同时对氨苄西林、环丙沙星、四环素、恩诺沙星四种药物耐药；鸡大肠杆菌对庆大霉素、阿米卡星敏感，鸡白痢沙门氏菌对链霉素、氟苯尼考、头孢噻肟敏感，鸡副伤寒沙门氏菌对头孢曲松、链霉素、头孢噻肟敏感。上述研究结果为肉仔鸡大肠杆菌与沙门氏菌混合感染的分离鉴定以及科学指导用药提供参考。     

The current antimicrobial resistance situation in Swiss veterinary medicine]

Antimicrobial susceptibility data (n = 1501) and bacterial isolates (n = 258) of important bacterial pathogens from animals were collected in collaboration with eight Swiss laboratories from May 1999 to February 2000. Using these data, the antimicrobial resistance situation could be assessed for the following bacterial species: Escherichia coli, Salmonella, Haemophilus parasuis, Actinobacillus pleuropneumoniae, Pasteurella multocida, Mannheimia haemolytica, Bordetella bronchiseptica, Campylobacter jejuni, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus intermedius, Streptococci, and enterococci. Differences in the distribution of resistance between animal species could be evidenced in E. coli and salmonella. Some resistance frequency data were compared with those obtained in 1980. A significant increase of resistance frequency was observed for several antibiotics. This includes in particular an increase of ampicillin, gentamicin, and cotrimoxazole resistance in E. coli. A similar increase was observed in salmonella for ampicillin, streptomycin, sulfonamides, and nalidixic acid. Staphylococci from dogs (S. intermedius and S. aureus) also presented a clear increase of resistance for penicillin, neomycin, sulfonamides, cotrimoxazole, and erythromycin. Finally, a comparison with data from abroad shows that the antibiotic resistance situation in Switzerland is relatively favorable.     

新疆地区奶牛子宫内膜炎病原菌的分离鉴定及其对抗菌药的敏感性试验

通过细菌形态学和细菌生化特性,分离和鉴定了新疆地区患子宫内膜炎的21头奶牛子宫分泌物中的病原菌分别为蜡样芽孢杆菌(24.5%)、非溶血性链球菌(18.4%)、大肠杆菌(14.3%)、溶血性链球菌(10.2%)、表皮葡萄球菌(10.2%)、金黄色葡萄球菌(10.2%)、胎儿弯曲菌(10.2%)和不动杆菌等.其中革兰氏阳性菌检出率较高(73.5%).子宫内膜炎病原菌以单一菌株感染为主(47.6%).采用Kirby-Barer法测定了鉴定菌株对13种抗微生物药的体外药物敏感性.链球菌、大肠杆菌和葡萄球菌对氨苄西林不敏感,而对卡那霉素和庆大霉素敏感性较高;大肠杆菌对青霉素和氨苄西林全部耐药(100%),对四环素和多西环素耐药率较高(均为83.3%);溶血性链球菌对青霉素和四环素全部耐药,对链霉素耐药率为80%;相对而言,表皮葡萄球菌和金黄色葡萄球菌的耐药率较低;氟喹诺酮类对各种分离菌株比较敏感.     

Uterine microbiology and antimicrobial susceptibility in isolated bacteria from mares with fertility problems

Uterine microbiology and antimicrobial susceptibility was investigated in 239 mares with fertility problems in a prospective study in Sweden. Uterine swab samples were collected with double guarded swabs and transported overnight before being cultured. The Minimum Inhibitory Concentrations (MIC) was determined for a panel of antimicrobials. From 152 of the 239 mares at least one bacterial species was isolated, most frequently E. coli (104 isolates), beta-haemolytic streptococci (31) and fungi (16). beta-haemolytic streptococci were more frequently (p < 0.01) associated with clinical endometritis than with repeat breeding. The opposite was true for E. coli (p < 0.01). Among beta-haemolytic streptococcal isolates some resistance was noted for 4 of 11 tested antibiotics, however, all isolates were susceptible to the widely used penicillin G. Among E. coli isolates enrofloxacin was the only of the 10 tested antibiotics for which no resistance was noted. Resistance was most commonly noted to cephalothin (39% of the isolates), streptomycin (22%), trimethoprim/sulphamethoxazole (15%) and ampicillin (11%). In conclusion, we show that both E.coli and beta-haemolytic streptococci are frequently associated with fertility problems in mares and that antimicrobial resistance is a common feature of E. coli but also recognised for beta-haemolytic streptococcal uterine isolates.     

2019年湖南省部分地区鸡、鸭、猪源大肠杆菌耐药性调查

旨在调查2019年湖南省部分地区不同来源的大肠杆菌对抗生素的耐药水平,为养殖合理用药提供参考。从4个市畜禽养殖场采集猪、鸡和鸭粪便285份,使用麦康凯琼脂培养基和伊红美蓝培养基对大肠杆菌筛选,利用基质辅助激光解析电离飞行时间质谱进行鉴定,采用微量肉汤稀释法检测16种抗生素对大肠杆菌的最小抑菌浓度(MIC)。共分离出203株大肠杆菌(鸡源146株、鸭源20株和猪源37株),对四环素和氨苄西林耐药率最高,分别达到89.2%和84.7%;对头孢他啶、奥格门丁、黏菌素耐药率较低,分别为2.5%、2.0%和0.5%;所有菌株均对美罗培南敏感。抗3种及以上抗生素的菌株数目占比为87.7%,而仅5.42%的菌株对所有检测的抗生素敏感。另外,来源于减抗示范养殖场的大肠杆菌对大部分抗生素的耐药率,与来源于非减抗养殖场大肠杆菌相比未见显著差异。上述结果表明,湖南省动物源大肠杆菌的耐药水平仍处在较高水平,重视兽药使用管理并持续开展对大肠杆菌的耐药性监测十分必要。     

Identification, antimicrobial resistance profiles, and virulence of members from the family Enterobacteriaceae from the feces of yellow-headed blackbirds (Xanthocephalus xanthocephalus) in North Dakota

Public pressure to reduce or eliminate antimicrobials as ingredients of feed for poultry and other agricultural animals is mounting, primarily due to the fear of multidrug-resistant bacteria in clinical infections in both animals and humans. Exploration of the occurrence of antibiotic resistance in the gut flora of wildlife avian flocks that presumptively do not receive antimicrobials will determine the rate of resistance in a na?ve population. Fecal samples collected from a healthy population of the yellow-headed blackbirds (YHB) (Xanthocephalus xanthocephalus) in North Dakota were cultured to determine what genera and species of gram-negative facultative anaerobic bacteria these wild birds carry in their intestinal flora and to evaluate the antimicrobial susceptibility profiles. Isolates of Escherichia coli were further characterized for the presence of putative virulence factors and for pathogenic potential using the chicken embryo lethality assay (ELA). The ELA was performed in chicken embryos with challenges at both 12 days and 16 days of incubation to determine whether the 16-day-old embryos were better able to fight the infection and subsequent disease and also to determine whether the ELA could distinguish between primary and secondary avian Escherichia coli pathogens. After screening 33 isolates from the 21 fecal samples, only two E. coli isolates were identified. The predominant genus and species of bacterium identified was Pantoea agglomerans. Collectively, 12 of the 33 isolates (36%) exhibited no resistance to any antimicrobial tested. However, several multidrug-resistant isolates of varying genera were identified. Among the antimicrobial resistances observed, the most common was to ampicillin (60%), followed by cephalothin (33%). Neither E. coli isolate belonged to serogroups that are notorious for causing major outbreaks of colibacillosis in poultry, and only one E. coli isolate retained resistance to any antibiotics; nevertheless, the ELA results indicate that at least one of these E. coli may be a primary pathogen of chickens. This study demonstrates that antibiotic resistance occurs in the gut flora of natural populations of YHB despite the absence of antibiotic pressure. In addition, these results indicate that YHB will harbor E. coli isolates that are potentially pathogenic in poultry. However, these E. coli isolates are not a significant reservoir for multiple antibiotic resistances nor are they widespread in the population of YHB surveyed in North Dakota.     

In vitro antibiotic resistance profiles of Ornithobacterium rhinotracheale strains from Minnesota turkeys during 1996-2002

Antimicrobial resistance in nearly all human and animal pathogens is on the increase. In poultry, Ornithobacterium rhinotracheale has been identified as a newly emerging respiratory bacterial pathogen that has caused significant economic losses to the poultry industry. In this study, we examined in vitro antibiotic resistance profiles of 125 isolates of O. rhinotracheale isolated from turkeys in Minnesota during 1996-2002. A majority of isolates was sensitive to clindamycin, erythromycin, spectinomycin, and ampicillin. Resistance against sulfachloropyridiazine decreased from 1996 to 2002, but an increase in resistance was seen against gentamicin, ampicillin, trimethoprim sulfa, and tetracycline. The annual trend slopes for these antibiotics were 7.36%, 3.02%, 2.43%, and 1.95%, respectively. The resistance against penicillin remained constant from year to year with a trend slope of only 0.54% per year. These results emphasize the need for continued monitoring of O. rhinotracheale isolates for antibiotic resistance and establishment of baseline resistance pattern data for this organism. These data can then be used to design and evaluate local epidemiological interventions.     

Antimicrobial resistance of Actinobacillus pleuropneumoniae isolated from swine

The aim of this retrospective study was to evaluate the antimicrobial resistance rates and the trend in resistance of Actinobacillus pleuropneumoniae isolated from pigs in Italy from 1994 to 2009. A total of 992 A. pleuropneumoniae isolates were tested for their susceptibility to a panel of antimicrobial agents in a disk diffusion method. Resistance to 7 drugs (amoxicillin, amoxicillin/clavulanic acid, ampicillin, cefquinome, cotrimoxazole, penicillin G and tilmicosin) showed a significant increasing trend over the time, while for 2 drugs (gentamycin and marbofloxacin) a significant decrease was observed. Resistance to the remaining 14 antimicrobial agents tested did not change significantly over the study period. Most of the isolates retained high susceptibility to antimicrobials usually effective against A. pleuropneumoniae such as amphenicols, fluoroquinolones and ceftiofur. However, high rates of resistance were observed for potentiated sulfa drugs, tetracyclines and penicillins which are currently recommended antimicrobials for pig pleuropneumonia therapy. Our results suggest the importance of continued monitoring of A. pleuropneumoniae clinical isolates in order to choose the most appropriate treatment of infections and to control the increase of resistance to currently used antimicrobials.     

河南省部分地区猪群大肠杆菌分离菌的耐药性比较分析

为掌握河南省猪源大肠杆菌的耐药情况,于2013年至2018年对河南省郑州、开封、焦作、许昌四个地区部分规模化养猪场分离出的856株大肠杆菌,采用CLSI推荐的微量肉汤稀释法,调查其对8类13种代表性抗菌药物的耐药性。结果表明,856株大肠杆菌对氧氟沙星、黏菌素、庆大霉素、头孢噻呋和阿莫西林/棒酸等5种药物的耐药率在35.0%以下,分别为32.2%、31.1%、25.5%、15.5%和30.0%;对恩诺沙星、四环素、多西环素、大观霉素、氟苯尼考、磺胺异恶唑、复方新诺明和氨苄西林等8种药物的耐药率范围为45.0%～95.0%,其中对四环素、多西环素和磺胺异恶唑等3种药物的耐药率高达90.0%以上;多重耐药集中于耐5、6和7类抗生素,耐3类及以上药物的菌株占90.0%。本研究结果表明河南省部分养殖场猪源大肠杆菌耐药形势严峻,应加强对其监测和控制。     

Antimicrobial susceptibility of hazard analysis critical control point Escherichia coli isolates from federally inspected beef processing plants in Alberta, Saskatchewan, and Ontario

A survey to estimate the prevalence of antimicrobial resistance in Escherichia coli was conducted in 7 Canadian federally inspected processing plants during 2001. Escherichia coli isolates were recovered during routine hazard analysis critical control point sampling from beef carcasses and trim and subsequently tested for their antimicrobial susceptibility by using susceptibility panels. Of the 2653 isolates analyzed, 68% were sensitive to all 18 antimicrobials tested. For 14 of the 18 antimicrobials evaluated, the percentage of resistant isolates was < or = 1. Twenty-five percent of the isolates were resistant to tetracycline, 9% to sulfamethoxazole, 7% to streptomycin, and 3% to ampicillin. Multiple resistance was found in 12% of the isolates, with 7% showing resistance to 2 antimicrobials, 2% to 3 antimicrobials, 2% to 4 antimicrobials, and 1% to 5 or more antimicrobials. Forty-five different antimicrobial resistance patterns were observed. The reasons for the development of the antimicrobial resistance were not investigated in this study. This study was useful as a pilot to help to develop a national antimicrobial resistance surveillance program in Canada. This study indicates that laboratory standardization is possible for consistent results across the country and that the indicator organism, E. coli, is fairly easy to obtain for surveillance but Salmonella are not, due to their low prevalence in beef.     

Effects of bovine lactoferrin hydrolysate on the in vitro antimicrobial susceptibility of Escherichia coli strains isolated from baby pigs

OBJECTIVE: To determine the antibacterial activity of bovine lactoferrin hydrolysate (bLf-lysate) alone or in combination with other antimicrobials against antimicrobial-resistant Escherichia coli strains isolated from baby pigs. SAMPLE POPULATION: 3 clinical strains of E coli were isolated from baby pigs with severe diarrhea and designated as strains 9061, 9062, and 9065. PROCEDURE: The broth microdilution checkerboard and fractional inhibitory (or bactericidal) concentration index were used to evaluate the antibacterial effect elicited by bLf-lysate in combination with kanamycin, gentamicin, cephalothin, cefamandole, penicillin G, ampicillin, tetracycline, erythromycin, or rifampicin against the 3 strains of E coli. RESULTS: The 3 strains of E coli were susceptible to gentamicin and rifampicin but highly resistant to most of the other antimicrobials tested, except for strain 9061 that was also susceptible to cephalothin but intermediately inhibited by kanamycin and cefamandole. Synergistic growth-inhibitory activity was observed between bLf-lysate and gentamicin against 1 strain of E coli (strain 9062); synergistic bactericidal activity was found between bLf-lysate and rifampicin against all 3 strains of E coli. Moreover, partial synergy was observed between bLf-lysate and kanamycin, gentamicin, cephalothin, or cefamandole against the strains of E coli, but this partial synergistic activity was mostly seen against only 1 of the strains. Little interaction between bLf-lysate and tetracycline, ampicillin, penicillin G, or erythromycin was observed against the clinical strains of E coli. CONCLUSIONS AND CLINICAL RELEVANCE: A combination of bLf-lysate and certain antimicrobials may prove clinically effective against antimicrobial-resistant strains of E coli.     

Antimicrobial resistance of fecal Escherichia coli isolated from grow-finish pigs in 20 herds in Alberta and Saskatchewan.

Escherichia coli (n = 1439), isolated from the feces of apparently healthy grow-finish pigs in 20 herds in Alberta and Saskatchewan, were tested for susceptibility to 16 antimicrobials. All isolates were susceptible to amikacin, ceftriaxone, and ciprofloxacin and less than 1% was resistant to amoxicillin-clavulanic acid, cefoxitin, ceftiofur, gentamicin, and nalidixic acid. Resistance was most common to tetracycline (66.8%), sulfamethoxazole (46.0%) and streptomycin (33.4%). Twenty-one percent of the isolates were susceptible to all drugs, while 57% were resistant to 2 or more antimicrobials. Unconditional associations between resistances provided insight into the potential for co-selection. Every resistance-outcome was associated with at least 2 other drug-resistances. These associations illustrate the propensity for resistance phenotypes to occur together and the importance of considering co-selection in antimicrobial use decisions. A 2nd analysis explored the associations between resistance phenotypes in E. coli and Salmonella spp. from the same herd. Only 2 resistances in Salmonella were associated with herd-level E. coli resistance, indicating that E. coli is a poor sentinel for Salmonella AMR within herds. Herd-level management, including antimicrobial use, could affect antimicrobial resistance. The intra-class correlation between isolates within herds ranged from 0.1 to 0.46, which confirmed resistance clustered within herds. This suggests herd-level interventions might mitigate antimicrobial resistance. Overall, these results reflect the on-farm selection pressure for resistance and the potential food-safety risk from near-market animals. These data provide a baseline for comparisons with future on-farm monitoring of antimicrobial resistance in E. coli.     

A survey of the fecal bacteria of bison (Bison bison) for potential pathogens and antimicrobial susceptibility of bison-origin E. coli

An observational study determined the normal fecal bacterial flora of clinically healthy bison, detected the presence of common potential zoonotic pathogens, and determined the antimicrobial susceptibility of isolated E. coli strains. Ninety-six fecal samples from 10 captive herds were cultured for aerobic, anaerobic, facultative, and microaerophillic bacteria. Nineteen major genera of gram-positive and 8 genera of gram-negative bacteria were identified. Salmonella spp. were not detected but some of the isolated bacteria are potential gastrointestinal pathogens. Minimum inhibitory concentrations (MIC) of 24 antimicrobials were determined for the E. coli isolated. Nearly all were susceptible to 23 of the 24 antimicrobials but there was a reduced susceptibility to sulphonamide. There were fewer resistant strains than were reported in recent studies of generic E. coli from cattle living in the same area.     

Comparative analysis of antibiotic resistance characteristics of Gram-negative bacteria isolated from laying hens and eggs in conventional and organic keeping systems in Bavaria, Germany

By investigating the prevalence and resistance characteristics of Gram-negative bacteria from organic and conventional kept laying hens against 31 (Campylobacter: 29) different antibiotics using the microdilution method, we determined to what extent different keeping systems influence bacterial resistance patterns. For this purpose, samples from 10 organic and 10 conventional flocks in Bavaria (Germany) were investigated four times between January 2004 and April 2005. Altogether, 799 cloacal swabs and 800 eggs (contents and shells) were examined. The bacterial investigation performed with standardized cultural methods showed prevalence for all bacteria groups in about the same order of magnitude in the two different keeping systems: Salmonella spp. 3.5% (organic ([org])) versus 1.8% (conventional ([con])); Campylobacter spp. 34.8%(org) versus 29.0%(con) and E. coli 64.4%(org) versus 69.0%(con). Coliforms (Citrobacter, Enterobacter, Pantoea) were only isolated in single cases. In eggs, generally less bacteria were detected, predominantly Escherichia; Salmonella and Campylobacter were only scarcely isolated. Salmonella enterica ssp. enterica serovar Typhimurium (n=10) were resistant to up to nine, S. of the serogroup B (n=4) up to six antibiotics. All tested Salmonella (n=23) proved to be resistant to spectinomycin. Escherichia coli (n=257(org) and 276(con)) from organic layers showed significant lower resistance rates and higher rates of susceptible isolates to nine agents, namely amoxicillin/clavulanic acid, ampicillin, cefaclor, cefoxitin, cefuroxime, doxycycline, mezlocillin, neomycin and piperacillin. In contrast, only two antibiotics turned out to be more effective in conventional isolates (gentamicin and tobramycin). In the case of Campylobacter jejuni (n=118(org) and 99(con)), statistically significantly better rates were observed for isolates from organic flocks concerning imipenem and amoxicillin/clavulanic acid, whereas fosfomycin was more potent in strains from conventional flocks. Results of this study indicate that both resistance rates and mean minimum inhibitory concentrations of bacteria isolated from organic keeping systems have lower values than those from conventional ones, particularly recognizable for E. coli. Thus, organic livestock farming with its restrictions and additional requirements contributes to further effectiveness of antibiotics.