牛肉源大肠杆菌的耐药性检测及相关耐药基因分布

为了解牛肉源大肠杆菌的耐药性并检测其相关耐药基因分布,本研究选取了117株牛肉源大肠杆菌,经药敏纸片法对11种抗菌药物进行了药敏检测,并根据耐药表型利用普通和(或)多重PCR技术对耐四环素菌中tet(A)、tet(B)和tet(C)基因,耐氨苄西林菌中blaTEM1、blaPSE1和blaOXA1基因,耐链霉素菌中strA-strB、aadA1基因,耐磺胺类药菌中sul1、sul2和sul3基因进行了调查分析。结果显示,117株大肠杆菌对四环素、氨苄西林、链霉素和磺胺异恶唑的耐药率较高,分别为89%、42%、38%和22%。tet(A)基因是所有四环素耐药基因中最为流行的一种基因(55%);在检测的3个β-内酰胺类药物耐药基因中,最流行的为blaTEM1基因(73%);链霉素的耐药性主要由strA-strB基因(38%)编码;sul2基因在耐磺胺异恶唑菌中的检出率最高(77%)。结果表明本次分离的牛肉源大肠杆菌耐药非常严重,进一步肯定了肉牛业生产中抗菌药的使用对大肠杆菌耐药性的产生和发展所发挥的重要作用,提示食品动物养殖应严格控制饲料中抗菌药的滥用。     

Antimicrobial resistance pattern of Salmonella serotypes isolated from food items and personnel in Addis Ababa, Ethiopia

Antimicrobial susceptibility test of 98 isolates of Salmonella was assayed from September 2003 to February 2004 using the guidelines of the National Committee for Clinical Laboratory Standards (NCCLS).The result revealed that 32.7% of Salmonella isolates were resistant to one or more of the 24 antimicrobials tested. Generally resistance for 13 different antimicrobial drugs was recognized. The most common resistance was to streptomycin (24/32, 75%), ampicillin (19/32, 59.4%), tetracycline (15/32, 46.9%), spectinomycin (13/32, 40.6%) and sulfisoxazole (13/32, 40.6%). All the three Salmonella Kentucky isolates showed resistance to at least 8 antimicrobials. Out of the 12 Salmonella Braenderup isolates, 10 (83.3%) showed multidrug resistance to ampicillin, spectinomycin, streptomycin, sulfisoxazole, sulfamethoxazole/trimethoprim, amoxicillin/clavulanic acid and trimethoprim. Among the 8 S. Hadar isolates 7 (86.5%) showed antimicrobial resistance. All the 6 S. Dublin isolates were resistant to carbadox (100%). All the 6 S. Haifa isolates were resistant for at least ampicillin, streptomycin and tetracycline. Up to ten different antimicrobial resistances pattern was observed. Multiple antimicrobial drug resistance was observed in 23 Salmonella isolates (23.5%). The level of antimicrobial resistance was significantly higher for isolates from chicken carcass (18/29, 62.1%) and pork isolates (5/22, 22.7%) (p = 0.003). The findings of the present study ascertain that significant proportion Salmonella isolates have developed resistance for routinely prescribed antimicrobial drugs and poses considerable health hazards to the consumers unless prudent control measures are instituted.     

Re-emergence of multi-drug resistant <Emphasis Type="Italic">Salmonella enterica</Emphasis> serovar Stanley from cattle

During 2009, Salmonella enterica subspecies enterica serovar Stanley isolates were recovered from cattle diagnostic specimens in southern Japan, and the isolates were examined to characterize the genetic determinants involved in this new pathogenicity that associated with mortality in cattle. All the isolates were multi-drug resistance exhibited resistance to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, oxytetracycline, and kanamycin (ACSSuT-Km) encoded by bla _TEM, catA, aadA1, sul1, tet(A), and aphA1 genes, respectively. Class 1 integrons of 1.5-kb size were detected in all MDR isolates. The isolates harboured easily transferable plasmids of ca. 210-kb with the potential of transmitting resistance phenotype and genotype detected in the donor isolates. XbaI-digested PFGE patterns generated two related clusters implicated in the dissemination of multi-drug resistance amongst Salmonella Stanley isolates. An emergence of multi-drug resistant Salmonella Stanley amongst food-producing animals, including cattle is a threat to human health, as resistant isolates may be transmitted to humans through the food chain.     

High level of multidrug-resistant Escherichia coli in young dairy calves in southern Vietnam

This study investigated the occurrence of antimicrobial-resistant Escherichia coli in dairy calves in southern Vietnam. Fecal samples were taken directly from the rectum of 84 calves from 41 smallholder dairy farms, when newborn and at 14 days of age for isolation of E. coli. Escherichia coli strains were isolated from 144 of the 168 fecal samples tested. Of the 144 E. coli isolates, 40% were found to be susceptible to all 12 antimicrobial drugs tested and 53% of the E. coli isolates were resistant to at least three antimicrobials. Calves were colonized with antimicrobial-resistant E. coli already on the day of birth. Resistance to tetracycline was most common, followed by resistance to sulfamethoxazole, ampicillin, trimethoprim, and ciprofloxacin. Four isolates carried a gene encoding for extended-spectrum cephalosporinases (ESC), and these genes belonged to bla_CTX-M group 1 (2 isolates), bla_CTX-M group 9 (1 isolate), and bla_CMY-2 (1 isolate). Thirty-three isolates had a plasmid-mediated quinolone resistance (PMQR) phenotype, and 30 of these carried the qnrS gene. These results are of importance for management routines of dairy cattle to prevent the spread of antimicrobial resistance.

     

Detection and Molecular Characterization of Salmonella enterica Serovar Eppendorf Circulating in Chicken Farms in Tunisia

Salmonella enterica subsp. enterica serovar Eppendorf, with antigenic formula 1,4,12,[27]:d:1,5, is an infrequent serovar. However, 14% (20 of 142) of the isolates recovered during June–July 2012 in chicken farms in Tunisia belonged to S. Eppendorf. These isolates were analysed for resistance and virulence profiles. None of them were susceptible to all antimicrobials tested, while 70%, 60%, 50%, 50%, 20% and 5% were resistant to sulphonamides (sul1, sul2 and sul3), streptomycin (aadA1‐like), trimethoprim (dfrA1‐like), nalidixic acid (GyrA Asp₈₇→Asn and not identified), gentamicin (not identified) and ampicillin (bla_TEM‐1‐like). About 30% of the isolates showed decreased susceptibility to ciprofloxacin and carried the qnrB gene; 65% of the isolates were multidrug resistant and contained class 1 integrons with sul1 or sul3 in the 3′ conserved segment. The orgA, ssaQ, mgtC, siiD and sopB virulence genes located on SPI1 to SPI5 and the fimbrial bcfC gene were present in all isolates; the sopE1 and sodC1 carried by prophages were variably detected; however, the prophage gipA gene and the spvC gene of serovar‐specific virulence plasmids were absent. Altogether, ten resistance and three virulence profiles were identified. Typing of the isolates with XbaI‐ and BlnI‐PFGE supports a close relationship, although they appear to be evolving under selective pressure probably caused by antimicrobial use in chicken husbandry. As far as we know, this is the first study investigating the molecular bases of antimicrobial drug resistance, the virulence gene content and the PFGE profiles of S. Eppendorf. The epidemiological surveillance of this serovar would be necessary to evaluate its possible impact on human health, particularly in Tunisia and other African countries where it was already reported.     

Antimicrobial resistance in Salmonella enterica serovars Enteritidis and Typhimurium isolated from animals in Korea: comparison of phenotypic and genotypic resistance characterization

Fourteen and 22 each of Salmonella Enteritidis and Salmonella Typhimurium (S. Typhimurium) were isolated from animals from 1983 to 1999 in Korea and tested for their antibiotic resistance patterns, phage types and resistance gene patterns. S. Typhimurium isolates were highly resistant to streptomycin, sulfisoxazole and tetracycline, 95, 95 and 86%, respectively. The incidence of multiple antibiotic resistance (resistant to more than two drugs tested) of S. Typhimurium isolates was extremely high (100%) comparing to S. Enteritidis isolates (21%). Two of the five ACSSuT (ampicillin, chloramphenicol, streptomycin, sulfisoxazole and tetracycline) resistant type S. Typhimurium isolates were phage type definitive type 104 (DT104).For the detection of resistance related genes in S. Enteritidis and S. Typhimurium isolates, particularly ACSSuT type S. Typhimurium, antibiotic resistance genes, cmlA/tetR, bla(PSE-1) and bla(TEM), and genus Salmonella specific gene, sipB/C, were amplified using four pairs of primers in a hot-start multiplex polymerase chain reaction (PCR). Two Korean isolates of S. Typhimurium DT104 showed bla(TEM) amplicons instead of bla(PSE-1) for the ampicillin resistance and they were susceptible to florfenicol. The multiplex PCR used in this study was useful in characterization of multiple drug resistant Salmonella isolates, especially ACSSuT type S. Typhimurium, and identification of beta-lactamase gene distribution among Salmonella isolates.     

Occurrence and characterization of resistance to extended-spectrum cephalosporins mediated by β-lactamase CMY-2 in Salmonella isolated from food-producing animals in Canada

Resistance of Salmonella to extended-spectrum cephalosporins (ESCs) is being reported with increasing frequency. In humans, infections with Salmonella resistant to ESCs threaten the efficacy of ceftriaxone, the drug of choice for treating salmonellosis in children. To determine the occurrence of resistance to ESCs, we examined 8426 strains isolated from food-producing animals in Canada in 1994–99 for reduced susceptibility or resistance to ceftriaxone. Of the 8 such strains identified (7 from turkeys and 1 from cattle), 5 had reduced susceptibility, and 3 were resistant; 2 were isolated in 1995, 1 was isolated in each of 1996 and 1997, and 4 were isolated in 1999. Isoelectric focusing showed that all 8 isolates produced a β-lactamase with a pI ≥ 9. The strains were resistant to cefoxitin and not inhibited by clavulanic acid. Primers specific for the Citrobacter freundii bla_AmpC gene produced the expected product in the polymerase chain reaction. DNA sequencing showed that all isolates possessed the bla_CMY-2 gene. Plasmid DNA from all 8 isolates transformed Escherichia coli DH10B, whereas only 1 isolate transferred bla_CMY-2 conjugally. All transformants and the transconjugant were resistant to ampicillin, cefoxitin, ceftiofur, cephalothin, streptomycin, sulfisoxazole, and tetracycline. Southern blots of plasmids from the isolates, the transformants, and the transconjugant showed that bla_CMY-2 was located on similar-sized plasmids (60 or 90 MDa) in the transformants and the transconjugant. In the S. Typhimurium DT104 and S. Ohio isolates, the flo_St gene was found on the same plasmid. Class 1 integrons with the aadB gene cassette were detected in the S. Bredeney isolates but not in their transformants or the transconjugant. Pulsed-field gel electrophoresis and plasmid profiles indicated that both clonal dispersion and horizontal transfer of bla_CMY-2 may have caused dissemination of the resistance determinant.     

Association between antimicrobial treatment and resistance of pathogenic Escherichia coli isolated from diseased swine in Kagoshima Prefecture,Japan

Pathogenic Escherichia coli is an important cause of diarrhea, edema disease, and septicemia in swine. In Japan, the volume of antimicrobial drugs used for animals is highest in swine, but information about the prevalence of antimicrobial-resistant bacteria is confined to apparently healthy animals. In the present study, we determined the O serogroups, virulence factors, and antimicrobial resistance of 360 E. coli isolates from swine that died of disease in Kagoshima Prefecture, Japan, between 1999 and 2017. The isolates of the predominant serogroups O139, OSB9, O149, O8, and O116 possessed virulence factor genes typically found in diarrheagenic E. coli. We further found five strains of third-generation cephalosporin-resistant E. coli that each produced an extended-spectrum β-lactamase encoded by bla_CTX-M-14, bla_CTX-M-15, bla_CTX-M-24, bla_CTX-M-61, or bla_SHV-12. In 218 swine with a clear history of antimicrobial drug use, we further analyzed associations between the use of antimicrobials for the treatment of diseased swine and the isolation of resistant E. coli. We found significant associations between antimicrobial use and selection of resistance to the same class of antimicrobials, such as the use of ceftiofur and resistance to cefotaxime, cefazolin, or ampicillin, the use of aminoglycosides and resistance to streptomycin, and the use of phenicols and resistance to chloramphenicol. A significant association between antimicrobial use and the resistance of E. coli isolates to structurally unrelated antimicrobials, such as the use of ceftiofur and resistance to chloramphenicol, was also observed.     

Multidrug‐Resistant Outbreak‐Associated Salmonella Strains in Irrigation Water from the Metropolitan Region,Chile

Salmonella enterica (S. enterica) is the main cause of foodborne diseases in the Chilean population. With the aim of characterizing the presence of S. enterica in bodies of water, samples from 40 sources were obtained, including rivers and irrigation canals used by agricultural farms in the most populated regions of Chile. As result, 35 S. enterica isolates belonging to several serotypes were detected, with the highest frequency represented by Typhimurium and Enteritidis. All strains showed phenotypic antimicrobial resistance, and most of them were multiresistant to critically important antimicrobials. In addition, the pulse‐field gel electrophoresis analysis using XbaI and BlnI endonucleases showed that seven Salmonella isolates belonging to serotypes Typhimurium, Enteritidis and Infantis had identical pulsotypes to outbreak‐associated clinical isolates detected in the Chilean population, suggesting a public health risk of water pollution in this region. Among sampling sites, the higher detection rates were observed in rural than urban and peri‐urban areas, suggesting that the animal husbandry might contribute for environmental dispersion of this pathogen. Future efforts should address the characterization of cause‐and‐effect relationship between water contamination and foodborne disease, including the implementation of surveillance programmes to tackle potential risks for both human and animal populations.     

Genetic Characterization of Antibiotic Resistance in Enteropathogenic Escherichia coli Carrying Extended‐Spectrum β‐Lactamases Recovered from Diarrhoeic Rabbits

A total of 52 Escherichia coli strains isolated from diarrhoeic rabbits were investigated for their enteropathogenic E. coli (EPEC) pathotype by PCR amplification of eae and bfp virulence genes. A total of 22 EPEC isolates were identified, serotyped and studied for antibiotic resistance and screened for the detection of extended‐spectrum β‐lactamases (ESBLs). The EPEC isolates belonged to three serogroups (O26, O92 and O103). The most common serogroup (O103:K‐:H2) was observed among 17 EPEC strains, the O92:K‐serogroup in three isolates (the antibiotic sensitive ones) and the remaining O26:K‐serogroup in two isolates (the ESBLs isolates). Resistances to ampicillin and tetracycline were the most frequent and detected followed by resistance to nalidixic acid, streptomycin, trimethoprim–sulphamethoxazole, cefoxitin, gentamicin and ciprofloxacin. All the isolates were sensitive for amikacin, ceftazidime, aztreonam, imipenem, chloramphenicol, tobramycin and amoxicillin + clavulanic acid. Two isolates recovered from two adult animals showed an intermediate susceptibility to cefotaxime, and a positive screening test for ESBL was demonstrated in both. The bla_TEM gene was demonstrated in the majority of ampicillin‐resistant isolates. The aac(3)‐II or aac(3)‐IV genes were detected in the four gentamicin‐resistant isolates. In addition, the aadA gene was detected in 60% of streptomycin‐resistant isolates. The tet(A) or tet(B) genes were identified in all tetracycline‐resistant isolates. A total of nine EPEC isolates showed the phenotype SXT‐resistant, and the sul1 and/or sul2 and/or sul3 genes were detected in all of them. Our findings showed that the molecular detection by the eae and bfp genes by PCR followed by serotyping is useful for monitoring trends in EPEC infections of rabbits allowing the identification of their possible reservoirs. The detection of genes involved in the resistance to antibiotics of different families in a relatively high proportion of faecal E. coli isolates of rabbits is of great interest and could be considered a serious public health problem.     

食品动物源产CTX-M-14大肠杆菌传播分子机制的演变

从保存的2002-2009年分离的食品动物源大肠杆菌中,挑选16株bla_CTX-M-14阳性菌,用PCR方法检测超广谱β-内酰胺酶(ESBLs)编码基因、PMQR耐药基因及其他重要抗生素耐药基因(rmtB和floR);通过脉冲场凝胶电泳(PFGE)及种族进化关系分析16株细菌的亲缘关系;通过接合转移试验、复制子分型和bla_CTX-M-14上下游插入元件的检测,分析产CTX-M-14大肠杆菌的传播分子机制。PCR检测结果表明,16株食品动物源产CTX-M-14大肠杆菌大多属于系统发育组A组,其次为B1和D组,没有B2组;PFGE分型结果表明,同一时间内不同动物间存在产CTX-M-14共生型大肠杆菌克隆的扩散传播,但养殖场内CTX-M-14主要是随质粒或其他元件进行水平传播;质粒复制子分型结果表明,携带bla_CTX-M-14的质粒属于IncK(3/14)、 IncF(5/14)、 IncHI2(1/14)、IncFIB 和 IncF(1/14)、IncHI1和IncN(2/14)、 IncI1(2/14)等,且随着时间推移,复制子的种类呈增多趋势。2002-2007年的菌株bla_CTX-M基因的上下游均检测到ISEcp1和IS903;但2009年菌株除了部分在上下游都可以检测到ISEcp1和IS903外,还有的只检测到上游的ISEcp1或下游的IS903;2002-2009年的菌均未检测到ISCR1。16株产CTX-M-14大肠杆菌除了携带其他ESBLs编码基因,如bla_CTX-M79和bla_TEM-135外,还携带其他重要抗生素耐药基因,如oqxA、floR、aac(6')-1b-cr及rmtB,而且2002-2009年大肠杆菌携带耐药基因的种类和数量逐年增多;接合转移试验发现,2002-2005年的菌株,bla_CTX-M-14往往发生单独转移,而2009年分离菌bla_CTX-M-14往往和floR或rmtB位于同一质粒上发生共同转移。这说明养殖场使用氨基糖苷类或氟苯尼考等任何一种抗生素,都可以筛选出产CTX-M-14大肠杆菌并促进其扩散,所以动物养殖过程中要慎用这些抗生素。     

Serotype identification and antimicrobial resistance profiles of <Emphasis Type="Italic">Salmonella</Emphasis> spp. isolated from chicken carcasses

In this study, 32 Salmonella strains isolated from 400 chicken carcasses were serotyped, and antibiotic resistance profiles were detected against 12 selected antimicrobial agents using disc diffusion method. Thirty-two isolates were identified as follows; 22 (68.7%) Salmonella Enteritidis, five (15.6%) Salmonella Virchow, three (9.3%) Salmonella Typhimurium and two (6.2%) Salmonella Hadar. In all Salmonella isolates, antibiotic resistance were detected. Out of 32 Salmonella strains, 22 (68.75%) displayed multi-drug resistance. Thirty-two (100.0%) of the isolates were found to be resistant to penicillin G, 20 (62.5%) to nalidixic acid, four (12.5%) to cephalothin, two (6.2%) to streptomycin and two (6.2%) to tetracycline. Fifteen (68.1%) Salmonella Enteritidis, one (33.3%) Salmonella Typhimurium, two (100.0%) Salmonella Hadar and two (40.0%) Salmonella Virchow were shown to be resistant to nalidixic acid. Cephalothin resistance was detected in 9.0%, 33.3%, and 20.0% for Salmonella Enteritidis, Salmonella Typhimurium and Salmonella Virchow, respectively. The results indicate that Salmonella recovered from chicken carcasses were resistant to multiple antimicrobials and that resistance among these isolates varies by serotype. Also, this emerged as a significant public health problem.     

动物源性沙门氏菌的耐药性分析及氟苯尼考类耐药基因的鉴定

为了解动物沙门氏菌的流行情况和药物敏感性及氟苯尼考耐药株的耐药基因分布,本试验对临床上疑似患沙门氏菌病的病料进行病原分离和细菌的多重PCR鉴定;采用K-B法测定分离株对23种抗菌药物的敏感性;选择氟苯尼考耐药菌株扩增floR、fexA、fexB、cfr和pexA基因。结果显示,共鉴定出61株沙门氏菌,其中肠炎沙门氏菌10株,鸡白痢沙门氏菌12株,鼠伤寒沙门氏菌39株。所有菌株对青霉素、红霉素、万古霉素耐药,90.16%对6种及6种以上抗菌药耐药。floR基因广泛存在于鼠伤寒沙门氏菌氟苯尼考耐药菌株中(8/12,66.67%),未发现其他耐药基因。研究结果表明鼠伤寒沙门氏菌是鹅源分离株中的优势血清型;floR基因主要介导沙门氏菌对氟苯尼考耐药性,但可能还存在其他机制。     

Characterization of Salmonella isolates from beef cattle, broiler chickens and human sources on Prince Edward Island

Non-typhoid Salmonella serovars remain a potential threat to human health, and beef cattle and broiler chickens are possible sources of these organisms on Prince Edward Island (PEI). In this study, the ceca of beef cattle belonging to fasted and non-fasted groups, and broiler chickens were examined for Salmonella at the time of slaughter. The characteristics of the isolates, including antimicrobial resistance patterns and virulence genes, were studied along with the isolates obtained from cases of human salmonellosis on PEI during the study period (1996–97). The prevalence of Salmonella in beef cattle was 4.6% (11/240). The rate was significantly higher in fasted cattle (7.46%), than in non-fasted cattle (0.94%). The prevalence rate in chickens was 32.5% (39/120). In beef cattle, Salmonella typhimurium phage type (PT) or definitive type (DT) 104 which was resistant to ampicillin, chloramphenicol, streptomycin, sulfisoxazole and tetracycline, was the most predominant type (64%). In chickens, S. heidelberg, with resistance to gentamicin, streptomycin and sulfisoxazole, predominated. Of 26 isolates from humans, the most common serovar was S. typhimurium, including a multidrug-resistant strain of DT104. Examination by PCR revealed presence of the virulence gene invA in all serovars, and the spvC gene in all S. typhimurium isolates, of both beef cattle and human origin. Among the other serovars the latter gene was found in 7 human isolates, but in none of the chicken or beef isolates. All but 3 of the spvC-positive isolates possessed a 90 kilobasepair (kbp) plasmid suggesting that the 3 isolates had the spvC gene on their chromosome. These findings were confirmed by plasmid DNA isolation using 3 different protocols and by sequence analysis of the spvC-PCR product.     

Antimicrobial resistance of Escherichia coli isolates from canine urinary tract infections

This study determined the antimicrobial resistance profiles of Escherichia coli isolates from dogs with a presumptive diagnosis of urinary tract infection (UTI). Urine samples from 201 dogs with UTI diagnosed through clinical examination and urinalysis were processed for isolation of Escherichia coli. Colonies from pure cultures were identified by biochemical reactions (n=114) and were tested for susceptibility to 18 antimicrobials. The two most frequent antimicrobials showing resistance in Urinary E. coli isolates were oxytetracycline and ampicillin. Among the resistant isolates, 17 resistance patterns were observed, with 12 patterns involving multidrug resistance (MDR). Of the 69 tetracycline-resistant E. coli isolates, tet(B) was the predominant resistance determinant and was detected in 50.9% of the isolates, whereas the remaining 25.5% isolates carried the tet(A) determinant. Most ampicillin and/or amoxicillin-resistant E. coli isolates carried bla_TEM-1 genes. Class 1 integrons were prevalent (28.9%) and contained previously described gene cassettes that are implicated primarily in resistance to aminoglycosides and trimethoprim (dfrA1, dfrA17-aadA5). Of the 44 quinolone-resistant E. coli isolates, 38 were resistant to nalidixic acid, and 6 were resistant to nalidixic acid, ciprofloxacin and enrofloxacin. Chromosomal point mutations were found in the GyrA (Ser83Leu) and ParC (Ser80Ile) genes. Furthermore, the aminoglycoside resistance gene aacC2, the chloramphenicol resistant gene cmlA and the florfenicol resistant gene floR were also identified. This study revealed an alarming rate of antimicrobial resistance among E. coli isolates from dogs with UTIs.     

Study on Molecular Characterization of Class Ⅰ Integron and Integron-associated Antimicrobial Resistance in Escherichia coli from Beef Cattle

To investigate the prevalence and molecular characterization of class Ⅰ integron in Escherichia coli isolated from beef cattle, and analyze the relationship between integron and antimicrobial resistance, susceptibilities to 11 antimicrobials were conducted on 92 isolates, the presence and characterization of class Ⅰ integrons and inserted gene cassettes were performed using PCR combined with sequencing analysis. The results showed that 29 isolates had been detected positive for class Ⅰ integron integrase gene (intⅠ1) among 92 isolates, and aadA1 and dfrA17＋aadA5 were the most prevalent gene cassette arrays detected. The resistance rates of 92 isolates to ampicillin, streptomycin, sulfisoxazole and tetracycline were all more than 45.0%. As revealed by analyzing the association between resistance phenotypes and class Ⅰ integron, isolates that contained the class Ⅰ integron were significantly highly resistant to ampicillin, chloramphenicol, streptomycin, sulfisoxazole and sulfamethoxazole-trimethoprim (P<0.05), but not to quinolones and amoxicillin/clavulanic acid. The conclusion was that E.coli isolated from beef cattle were seriously resistant to antimicrobials,and integron/cassettes widely existed. The presence of integrons and the association of antimicrobial resistance determinants with transferable elements might play a crucial role in the dissemination of antibiotic resistance among E.coli. Data reported here clearly emphasized the need for a stricter application of antimicrobials restriction policies in feedlot setting.     

广州市农贸市场猪肉源伦敦沙门菌的流行情况及耐药性分析

本研究旨在探究广州市2016年5—10月农贸市场猪肉源伦敦沙门菌的流行和耐药情况。从广州市农贸市场采集样品198份,分离得到28株猪肉源伦敦沙门菌,用K-B法测定其对18种抗菌药物的耐药性,用PCR方法鉴定其所携带的耐药基因。结果表明,市场猪肉样品中沙门菌的阳性率为74.2%（147/198）,伦敦沙门菌的分离率为19%（28/147）,其对磺胺异唑、四环素的耐药率分别为78.6%和75.0%;其次为链霉素、复方新诺明、氨苄西林、庆大霉素、氯霉素和氟苯尼考,耐药率依次为71.4%、67.9%、67.9%、67.9%、46.4%和42.8%;对萘啶酸（3.6%）和多黏菌素B （3.6%）耐药水平较低。有71.4%（20/28）的菌株对3种及3种以上抗菌药物耐药。氨基糖苷类耐药基因检出率为100%,aadA2（7.1%）、strA（37.9%）、aadB（100%）;酰胺醇类耐药基因检出率为42.6%,cat1b（39.3%）、floR（39.3%）;磺胺类耐药基因检出率为67.9%,sul1（60.7%）、sul2（60.7%）;四环素类耐药基因的检出率为78.6%,均同时携带tetA和tetB;β内酰胺类耐药基因bla_TEM检出率为10.7%;喹诺酮耐药基因qnrA、oqxAB和aac（6’）-lb-cr检出率为3.6%、10.7%和7.1%;黏菌素耐药基因mcr-1检出率为3.6%。伦敦沙门菌在广州农贸市场猪肉中是主要流行血清型之一,其对传统抗菌药物磺胺异唑、四环素、链霉素、复方新诺明、氨苄西林等耐药性严重,携带多种耐药基因,且具有多种多重耐药表型。这提示人们需要对市场沙门菌进行常态化检测与监测,加强对抗生素使用的监管,确保公共卫生和食品安全。     

Analysis of Salmonella enterica serotype Enteritidis isolated from human and chickens by repetitive sequence-PCR fingerprinting, antibiotic resistance and plasmid profiles

A total of 22 Salmonella enterica serotype Enteritidis (S. Enteritidis) strains isolated from human and chicken were subjected to DNA fingerprinting by repetitive sequence PCR using ERIC and BOX primers, antibiotic resistance and plasmid patterns. Both ERIC and BOX PCR amplification data revealed a highly genetic homogeneity between isolates from human and chicken except one isolate, which originated from chicken and showed a different DNA band pattern from others. Eleven of 22 S. Enteritidis isolates (50%) were resistant to more than one antibiotics and characterized by 5 resistance patterns. The most common pattern was penicillin resistant (63.6%). Only one isolate from chicken showed a multiple drug resistance patterns to 4 antibiotics. All 22 S. Enteritidis isolates harbored more than two plasmids with eight different plasmid profiles including two to six plasmids with approximate molecular size ranging from 1.9 to 21 kb. A band of 15 kb size was detected in all isolates tested, however, the band sizes smaller than 15 kb were found only in isolates from chicken.     

Phenotypic and genotypic antimicrobial resistance patterns of Escherichia coli isolated from dairy cows with mastitis

Pulsed field gel electrophoresis (PFGE) patterns, susceptibility to 26 antimicrobial agents used in veterinary and human medicine, and prevalence of antimicrobial resistance genes of Escherichia coli isolated from cows with mastitis were evaluated. Among 135 E. coli isolates, PFGE analysis revealed 85 different genetic patterns. All E. coli were resistant to two or more antimicrobials in different combinations. Most E. coli were resistant to antimicrobials used in veterinary medicine including ampicillin (98.4%, >or=32 microg/ml) and many E. coli were resistant to streptomycin (40.3%, >or=64 microg/ml), sulfisoxazole (34.1%, >or=512 microg/ml), and tetracycline (24.8%, >or=16 microg/ml). Most E. coli were resistant to antimicrobials used in human medicine including aztreonam (97.7%, >or=32 microg/ml) and cefaclor (89.9%, >or=32 microg/ml). Some E. coli were resistant to nitrofurantoin (38%, >or=128 microg/ml), cefuroxime (22.5%, >or=32 microg/ml), fosfomycin (17.8%, >or=256 microg/ml). All E. coli were susceptible to ciprofloxacin and cinoxacin. Almost 97% (123 of 127) of ampicillin-resistant isolates carried ampC. Eleven of 52 (21.2%) streptomycin-resistant isolates carried strA, strB and aadA together and 29 streptomycin-resistant isolates (55.8%) carried aadA alone. Among 44 sulfisoxazole-resistant E. coli, 1 isolate (2.3%) carried both sulI and sulII, 12 (27.3%) carried sulI and 10 (22.7%) isolates carried sulII. Among 32 tetracycline-resistant isolates, 14 (43.8%) carried both tetA and tetC and 14 (43.8%) carried tetC. Results of this study demonstrated that E. coli from cows with mastitis were genotypically different, multidrug resistant and carried multiple resistance genes. These bacteria can be a reservoir for antimicrobial resistance genes and can play a role in the dissemination of antimicrobial resistance genes to other pathogenic and commensal bacteria in the dairy farm environment.     

Resistance phenotypes and genotypes among multiple-antimicrobial-resistant Salmonella enterica subspecies enterica serovar Choleraesuis strains isolated between 2008 and 2012 from slaughter pigs in Okinawa Prefecture,Japan

A total of 349 Salmonella enterica subspecies enterica serovar Choleraesuis (S. Choleraesuis) strains, which were isolated between 2008 and 2012 from 349 pigs at two slaughterhouses in Okinawa Prefecture, Japan, were investigated for antimicrobial susceptibility and the presence of antimicrobial resistance genes. All isolates were resistant to at least four antimicrobial agents. The antimicrobial agents for which isolates showed a high incidence of resistance were as follows: ampicillin (100%) and streptomycin (100%), followed by gentamicin (99.7%), oxytetracycline (99.7%), sulfamethoxazole/trimethoprim (99.4%), nalidixic acid (40.1%) and oxolinic acid (40.1%). All isolates were sensitive to cefuroxime, ceftiofur, colistin, fosfomycin, enrofloxacin, orbifloxacin and danofloxacin. The predominant resistance phenotypes and genotypes were: resistance to ampicillin, streptomycin, gentamicin, oxytetracycline and sulfamethoxazole/trimethoprim (58.5%, 204/349) and blaTEM-strA-strB-aadA1-aadA2-aacC2-tet (B)-sul1-sul2-dhfrXII-dhfrXIII (36.1%, 126/349). The quinolone resistance-determining regions (QRDRs) of gyrA, gyrB, parC and parE of the quinolone-resistant isolates (n=12) showed amino acid substitutions of Ser-83→Phe or Asp-87→Tyr in GyrA and Ser-107→Ala in ParC. To our knowledge, this is the first report on the molecular characterization of antimicrobial resistance among S. Choleraesuis strains in Japan.