Isolation and characterization of Shiga toxin-producing Escherichia coli (STEC) in retail edible beef by-products

The prevalence of Shiga toxin-producing Escherichia coli (STEC) was investigated in 350 edible beef intestinal samples, including omasum (n=110), abomasum (n=120), and large intestines (n=120), collected from traditional beef markets in Seoul, Korea. A total of 23 STEC strains were isolated from 15 samples (four strains from three omasa, 10 from five abomasa, and nine from seven large intestines). The O serotypes and toxin gene types of all STEC isolates were identified, and antimicrobial resistance was assessed using the disk diffusion method. The isolation rates of STEC from edible beef intestines were 2.8% in omasum, 4.2% in abomasums, and 5.9% in large intestines. All STEC isolates harbored either stx1, or both stx1 and stx2 genes simultaneously. Among the 23 isolates, 13 strains were identified as 11 different O serogroups, and 10 strains were untypable. However, enterohemorrhagic Esherichia coli O157, O26, and O111 strains were not isolated. The highest resistance rate observed was against tetracycline (39%), followed by streptomycin (35%) and ampicillin (22%). Of the 23 isolates, 12 isolates (52%) were resistant to at least one antibiotic, nine (39%) isolates were resistant to two or more antibiotics, and one isolate from an abmasum carried resistance against nine antibiotics, including beta-lactam/beta-lactamase inhibitor in combination and cephalosporins. This study shows that edible beef by-products, which are often consumed as raw food in many countries, including Korea, can be potential vehicles for transmission of antimicrobial-resistant pathogenic E. coli to humans.     

Prevalence, structure and expression of urease genes in Shiga toxin-producing Escherichia coli from humans and the environment

A component of the ure gene cluster in E. coli, ureC, encodes a subunit of urease. We have investigated the distribution of ureC in 202 Shiga toxin-producing E. coli (STEC) strains from Austria belonging to 61 different serotypes. These strains were of human (n=150), animal (n=38), and food (n=14) origin. ureC was present in all 72 E. coli O157:H7 and O157:NM (non-motile) strains, as well as in all 29 strains of serotypes O26:H11/NM, O111:H8/NM and O145:NM. In contrast, none of eight sorbitol-fermenting E. coli O157:NM were ureC-positive. ureC occurred significantly more frequently among STEC that carry eae (113 of 132; 85.6%) than among eae-negative STEC strains (four of 70; 5.7%; p<0.0001). However, only 4 (2%) of the 202 strains (3.4% of ureC positive strains) expressed urease activity. There was no significant association (p=0.56) between urease expression and the source of the isolates (humans vs. animals). Nucleotide sequence analysis of PCR amplicons derived from all seven genes of the ure cluster in STEC of 10 different serotypes demonstrated a high degree of homology (>or=99%), indicating a recent acquisition of not necessarily expressed ure genes.     

Human infections with non-O157 Shiga toxin-producing Escherichia coli, Switzerland, 2000-2009

We characterized 97 non-O157 Shiga toxin (stx)-producing Escherichia coli strains isolated from human patients during 2000-2009 from the national reference laboratory in Switzerland. These strains belonged to 40 O:H serotypes; 4 serotypes (O26:H11/H-, O103:H2, O121:H19, and O145:H28/H-) accounted for 46.4% of the strains. Nonbloody diarrhea was reported by 23.2% of the patients, bloody diarrhea by 56.8%. Hemolytic uremic syndrome developed in 40.0% of patients; serotype O26:H11/H- was most often associated with this syndrome. Forty-five (46.4%) strains carried stx2 genes only, 36 strains (37.1%) carried stx1, and 16 (16.5%) strains carried stx1 and stx2. Genes encoding enterohemolysin and intimin were detected in 75.3% and 70.1% of the strains, respectively. Resistance to ≥1 antimicrobial agent was present in 25 isolates. High genetic diversity within strains indicates that non-O157 stx-producing E. coli infections in Switzerland most often occurred as single cases.     

Antimicrobial drug resistance in Escherichia coli from humans and food animals, United States, 1950-2002

We conducted a retrospective study of Escherichia coli isolates recovered from human and food animal samples during 1950-2002 to assess historical changes in antimicrobial drug resistance. A total of 1,729 E. coli isolates (983 from humans, 323 from cattle, 138 from chickens, and 285 from pigs) were tested for susceptibility to 15 antimicrobial drugs. A significant upward trend in resistance was observed for ampicillin (p<0.001), sulfonamide (p<0.001), and tetracycline (p<0.001). Animal strains showed increased resistance to 11/15 antimicrobial agents, including ampicillin (p<0.001), sulfonamide (p<0.01), and gentamicin (p<0.001). Multidrug resistance (≥3 antimicrobial drug classes) in E. coli increased from 7.2% during the 1950s to 63.6% during the 2000s. The most frequent co-resistant phenotype observed was to tetracycline and streptomycin (29.7%), followed by tetracycline and sulfonamide (29.0%). These data describe the evolution of resistance after introduction of new antimicrobial agents into clinical medicine and help explain the range of resistance in modern E. coli isolates.     

食品中大肠埃希菌的耐药性与质粒图谱研究

目的　研究深圳市食品中污染的大肠埃希菌的耐药性 ,并分析其与细菌所携带的质粒之间的关系。方法　按国家食品卫生标准方法分离食品中的大肠埃希菌 ,K -B法测定细菌对 19种抗生素的耐药性 ,碱裂解法提取细菌质粒。结果　食品中污染的大肠埃希菌对四环素 (6 8% )、磺胺 (5 0 % )、复方新诺明 (5 0 % )、氨苄西林 (4 4% )、萘啶酸 (36 % )、链霉素 (34% )和庆大霉素 (32 % )等耐受性较强 ,而头孢菌素类抗生素特别是 3代头孢以及抗菌活性与 3代头孢相当的非典型 β -内酰胺类抗生素如头孢美唑和氨曲南较为敏感。 94 %的试验菌株对 1种以上抗生素耐药 ,74 %对 2种或 2种以上抗生素耐药 ,4 4%的菌株对 5种以上抗生素耐药 ,最多的达 14种抗生素。但细菌耐药性与其所携带的质粒的数量和大小并无直接联系。结论　深圳市食品中污染的大肠埃希菌普遍耐药 ,且与细菌所携带的质粒之间无直接关系     

Prevalence and characterization of Escherichia coli O26 and O111 in retail minced beef in Ireland

Verocytotoxigenic Escherichia coli (VTEC) O157 are recognized as bacterial pathogens with significant public health impact. However, other serogroups, including O26, O111, O103, and O145, have the potential to cause the same spectrum of illness. In this study, 800 minced (ground) beef samples covering a large geographical region in Ireland were collected and tested for Escherichia coli (E. coli) O26 and E. coli O111 by conventional microbiological protocols. Two minced beef samples (0.25%) tested positive for E. coli O26, indicating fecal contamination. None of these isolates possessed verocytotoxin-encoding genes, (vt1/vt2 also known as stx1/stx2), the hemolysinencoding gene (hlyA), or the E. coli attachment-effacement (eae) gene, as determined by polymerase chain reaction (PCR). None of the beef samples analyzed contained E. coli O111. Although the E. coli O26 isolates were nonvirulent, the presence of these isolates in raw minced beef is an indication of fecal contamination and therefore potentially of public health significance.     

Comparison of Escherichia coli Isolates from humans, food, and farm and companion animals for presence of Shiga toxin-producing E. coli virulence markers

The objective of this study was to characterize Escherichia coli isolates from dairy cows/feedlots, calves, mastitis, pigs, dogs, parrot, iguana, human disease, and food products for prevalence of Shiga toxin-producing E. coli (STEC) virulence markers. The rationale of the study was that, isolates of the same serotypes that were obtained from different sources and possessed the same marker profiles, could be cross-species transmissible. Multiplex polymerase chain reaction (PCR) was used to detect presence of genes encoding Shiga toxin 1 and 2 (stx1 and stx2), H7 flagella (flicC), enterohemolysin (hly) and intimin (eaeA) in E. coli isolates (n = 400). Shiga toxin-producing isolates were tested for production of Shiga toxins (Stx1 and Stx2 and enterohemolysin. Of the E. coli O157:H7/H- strains, 150 of 164 (mostly human, cattle, and food) isolates were stx+. Sixty-five percent of O157 STEC produced both Stx1 and Stx2; 32% and 0.7% produced Stx2 or Stx1, respectively. Ninety-eight percent of O157 STEC had sequences for genes encoding intimin and enterohemolysin. Five of 20 E. coli O111, 4 of 14 O128 and 4 of 10 O26 were stx+ . Five of 6 stx+ O26 and O111 produced Stx1, however, stx+ O128 were Stx-negative. Acid resistance (93.3%) and tellurite resistance (87.3%) were common attributes of O157 STEC, whereas, non-O157 stx+ strains exhibited 38.5% and 30.8% of the respective resistances. stx-positive isolates were mostly associated with humans and cattle, whereas, all isolates from mastitis (n = 105), and pigs, dogs, parrot and iguanas (n = 48) were stx-negative. Multiplex PCR was an effective tool for characterizing STEC pathogenic profiles and distinguished STEC O157:H7 from other STEC. Isolates from cattle and human disease shared similar toxigenic profiles, whereas isolates from other disease sources had few characteristics in common with the former isolates. These data suggest interspecies transmissibility of certain serotypes, in particular, STEC O157:H7, between humans and cattle.     

Molecular characterization and antibiotic resistance profiling of Salmonella isolated from retail Turkey meat products

Contaminated poultry meat has been identified as one of the principal foodborne sources of Salmonella. Molecular characterization of Salmonella is important in addressing methods to control this pathogen. Seventy-four retail turkey meat samples were collected from various stores in Fargo, North Dakota in the fall of 2003. Salmonella was recovered from 30 samples using the standard conventional culture method (FSIS, USDA). Isolated Salmonella were characterized by serotyping, pulsed-field gel electrophoresis (PFGE) analysis, plasmid analysis, and antibiotic resistance profiling. Five serotypes were identified among the isolates: Newport (n = 12), Hadar (n = 8), Heidelberg (n = 7), 4,12:nonmotile (n = 2), and Reading (n = 1). XbaI PFGE analysis revealed 13 PFGE types and succeeded in grouping the isolates according to their serotypes. Plasmid profiling identified 5 plasmid types (with 1 or 2 plasmids) among eleven isolates that harbored plasmids. Seventeen isolates were resistant to antibiotics. The Heidelberg serotype showed resistance to multiple antibiotics: 1 isolate had resistance to gentamicin, sulfamethoxazole, and streptomycin, and 6 isolates had resistance to tetracycline, gentamycin, sulfamethoxazole, kanamycin, and streptomycin. The Hadar serotype isolates were resistant to 2 or 3 antibiotics: tetracycline and streptomycin (1 isolate); tetracycline and kanamycin (1 isolate); and tetracycline, kanamycin, and streptomycin (6 isolates). The 4,12:nonmotile serotype isolates showed resistance to tetracycline only. The Newport and the Reading serotypes were susceptible to all 16 of the antimicrobials tested.     

深圳市健康人群肠道大肠埃希菌耐药性调查

目的：研究深圳市健康人群肠道大肠埃希菌耐药性.方法：按《预防医学微生物学及检验技术》的方法分离健康人肠道大肠埃希菌,K-B法测定细菌对15种抗生素的耐药性.结果：健康人大肠埃希菌对四环素（63.33%）萘啶酸（49.33%）磺胺甲基异[口恶]唑（40.67%）氨苄西林（38.67%）复方新诺明（35.33%）较耐受,对头孢菌素类及头孢美唑和氨曲南很敏感.121株（80.67%）对1种以上抗生素耐药,对两种以上抗生素耐药的菌株为87株（58%）,36株（24%）对5种以上抗生素耐药,有2株对9种抗生素耐药.结论：深圳市健康人群肠道大肠埃希菌耐药性较严重,应严格控制抗生素使用并继续做好耐药性监测工作.     

Antibiotic resistance of retail food and human Campylobacter isolates on the island of Ireland from 2001-2002

The antimicrobial resistance profiles of Campylobacter isolates recovered from a range of retail food samples (n=374) and humans (n=314) to eight antimicrobial compounds were investigated. High levels of resistance in food C. jejuni isolates were observed for ceftiofur (58%), ampicillin (25%) and nalidixic acid (17%) with lower levels observed for streptomycin (7.9%) and chloramphenicol (8.3%). A total of 80% of human C. jejuni isolates were resistant to ceftiofur, while 17% showed resistance to ampicillin and nalidixic acid, 8.6% to streptomycin and 4.1% to chloramphenicol. Resistance to clinically relevant antimicrobials such as erythromycin, ciprofloxacin and tetracycline was 6.7, 12, and 15% respectively for all food isolates and was similar to corresponding resistance prevalences observed for human isolates, where 6.4, 12 and 13% respectively were found to be resistant. Comparisons of C. jejuni isolates in each location showed a high degree of similarity although some regional variations did exist. Comparison of total C. jejuni and C. coli populations showed minor differences, with C. jejuni isolates more resistant to ampicillin and ceftiofur. Multidrug resistance patterns showed some profiles common to human and clinical isolates.     

2011-2019年33株人源非O157产志贺毒素大肠埃希菌耐药表型及耐药相关基因分析

目的了解人源非O157产志贺毒素大肠埃希菌(STEC)抗生素耐药表型及耐药基因携带状况。方法33株非O157 STEC菌株来自2011-2019年7个省份,包括青海、黑龙江(各1例),广西、山东(各2例),广东(4例),河南(11例),上海(12例),均分离自感染性腹泻患者粪便标本。采用改良微量肉汤法对非O157 STEC进行19种抗生素最小抑菌浓度(MIC)检测;通过全基因组测序进行O∶H血清分型、多位点序列分型(MLST)及耐药相关基因预测。结果33株非O157 STEC分为19种O∶H血清型、17种MLST序列型;10株菌对1种或以上抗生素耐药,5株为多重耐药菌株,对四环素耐药率最高(30.3%,10株),并检出阿奇霉素耐药菌株(12.1%,4株),但所有菌株均对碳青霉烯类药物敏感;共检出22种耐药基因,全部菌株均携带blaEC基因,并检出超广谱β-内酰胺酶(ESBL)基因型blaCTX-M-15(3.0%,1株),首次检出fosA7基因。结论中国7省份33株人源非O157 STEC中存在多重耐药和阿奇霉素耐药菌株,且携带多种耐药基因型,但均对碳青霉烯类药物敏感。     

Continuous surveillance of Shiga toxin-producing Escherichia coli infections by pulsed-field gel electrophoresis shows that most infections are sporadic

The purpose of this study was to evaluate the value of real-time molecular typing of Shiga toxin (Verocytotoxin)-producing Escherichia coli (STEC) infections in order to detect possible outbreaks of infections. All laboratory confirmed STEC infections in Denmark from 2003 to mid 2005 were routinely characterized by serotyping, virulence genes characterization, and subtyping by pulsed-field gel electrophoresis (PFGE) using the PulseNet protocol for STEC O157. The study included 312 STEC isolates representing 50 different O groups and 75 O:H-serotypes, and 68% of the isolates belonged to the eight most common O-groups: O157 (26%), O103 (13%), O146 (8%), O26 (8%), O117 (4%), O145 (3%), O128 (3%), and O111 (2%). The remaining O-groups constituted less than 2% each, and 8.1% of the isolates were O-rough. The eae gene was found in 60% of all isolates, and detection of the two main Shiga toxin genes showed that 40% had stx1 only, 31% had stx2 only, and 29% had both stx1 and stx2. A high diversity was seen within all O groups, and for most of the rare O groups, the number of PFGE profiles equaled the number of isolates. However, one outbreak of E. coli O157 was detected by the routine PFGE typing. The value of "real-time' PFGE typing of the infrequent serotypes is limited if the full scheme for O-grouping or O:H-serotyping is used routinely for all STEC isolates. Possible outbreaks can then be detected by the increased number of isolates within a particular serotype. PFGE typing would then be valuable in subsequent steps of the outbreak investigation. However, routine PFGE typing of the three to five most common O groups will enable early recognition of possible outbreaks.     

Detection by multiplex real-time polymerase chain reaction assays and isolation of Shiga toxin-producing Escherichia coli serogroups O26, O45, O103, O111, O121, and O145 in ground beef

Six Shiga toxin-producing Escherichia coli (STEC) serogroups, which include O26, O45, O103, O111, O121, and O145, are responsible for the majority of non-O157 STEC infections in the United States, representing a growing public health concern. Cattle and other ruminants are reservoirs for these pathogens; thus, food of bovine origin may be a vehicle for infection with non-O157 STEC. Methods for detection of these pathogens in animal reservoirs and in food are needed to determine their prevalence and to develop intervention strategies. This study describes a method for detection of non-O157 STEC in ground beef, consisting of enrichment in modified tryptic soy broth at 42°C, followed by real-time multiplex polymerase chain reaction (PCR) assays targeting stx(1), stx(2), and genes in the O-antigen gene clusters of the six serogroups, [corrected] and then immunomagnetic separation (IMS) followed by plating onto Rainbow? Agar O157 and PCR assays for confirmation of isolates. All ground beef samples artificially inoculated with 1-2 and 10-20 CFU/25?g of ground beef consistently gave positive results for all of the target genes, including the internal amplification control using the multiplex real-time PCR assays after enrichment in modified tryptic soy broth for a total of 24?h (6?h at 37°C and 18?h at 42°C). The detection limit of the real-time multiplex PCR assays was ～50 CFU per PCR. IMS for O26, O103, O111, and O145 was performed with commercially available magnetic beads, and the IMS beads for O45 and O121 were prepared using polyclonal antiserum against these serogroups. A large percentage of the presumptive colonies of each serogroup picked from Rainbow Agar O157 were confirmed as the respective serogroups; however, the percent recovery of STEC O111 was somewhat lower than that of the other serogroups. This work provides a method for detection and isolation in ground beef and potentially other foods of non-O157 STEC of major public health concern.     

Antimicrobial resistance and class 1 integrons in pathogenic Escherichia coli from dairy farms

The goal of this study was to assess the prevalence of antimicrobial resistance and class 1 integrons, including integron-associated genes, in 24 Escherichia coli isolates from dairy farms. Escherichia coli isolates (n = 14) from dairy cows with mastitis (ECDM), Shiga toxin-producing (STEC) O157:H7 from cull dairy cow fecal samples (n = 9) and bulk tank milk (n = 1) were evaluated for sensitivity to 19 antimicrobial agents used commonly in human and/or veterinary medicine. Multiplex PCR was used to determine presence of genes associated with class 1 integrons (intI1, qacEDelta1, and sulI1). Class 1 integrons were found only in eight of 10 isolates (one STEC O157:H7 and seven ECDM) that demonstrated antimicrobial resistance, and seven of these were resistant to two or more antimicrobial agents. Eight of 10 STEC O157:H7 and six of 14 ECDM were susceptible to all commonly used antibiotics. Five ECDM demonstrated multiple resistances to four or more antibiotics. Most of the 24 isolates examined exhibited resistance against sulfamethoxazole, followed by streptomycin and tetracycline. STEC O157:H7 strains had less prevalence of antibiotic resistance and integron carriage than ECDM. The multiplex PCR method developed for detection of intI1, qacEDelta1, and sulI1 can be used routinely for monitoring presence of these genes. Class 1 integrons were found in eight of 10 E. coli strains that demonstrated antimicrobial resistance; seven of these were resistant to two or more antibiotics. It appears that integrons played a role in the incidence of antimicrobial resistance of the strains used in this study.     

35株引起食物中毒的副溶血性弧菌病原学特征分析

目的了解广东省部分地区近年发生的副溶血性弧菌食物中毒菌株血清分型、毒力基因及耐药状况,为预防和控制由副溶血性弧菌引起的食物中毒提供科学依据。方法对35株由湛江、东莞、中山、惠州市疾病预防控制中心从食物中毒病例中分离获得的副溶血性弧菌进行血清分型;采用PCR检测副溶血性弧菌的耐热直接溶血素基因（tdh）和耐热直接相关溶血素基因（trh）;采用K-B纸片扩散法进行药敏试验。结果 35株从食物中毒病例中分离到的副溶血性弧菌菌株分属6个血清群,分别为O1、O2、O3、O4、O8及O10群,分别占20.0%、2.9%、62.9%、8.6%、2.9%、2.9%,其中O3：K6血清型共检出18株,占51.4%（18/35）。tdh携带率为88.6%（31/35）,trh携带率为8.6%（3/35）。35株副溶血性弧菌对链霉素、氨苄西林和阿米卡星的耐药率分别为100.0%、80.0%（28/35）和74.3%（26/35）,而对四环素、环丙沙星、复方新诺明、磺胺复合物S3、氯霉素、头孢曲松的敏感性均达80%以上（82.9%～94.3%）。结论在广东省部分地区引起食物中毒的副溶血性弧菌血清型主要是O3群,其中又以O3：K6为主,主要携带tdh基因,对大多数抗生素敏感。     

Antimicrobial susceptibility and mechanism of resistance to antibiotics for Escherichia coli O157 and verotoxin-producing E. coli isolated in northern Kyushu and Yamaguchi area

The purpose of this study was to investigate the biochemical characteristics and antimicrobial susceptibility of Escherichia (E.) coli O157 and verotoxin-producing E. coli isolates from the Northern Kyushu Island and Yamaguchi area of Japan. A total of 54 isolates- 50 E. coli O157, 3 verotoxin-producing E. coli O26 and 1 verotoxin-producing E. coli O111 - were used in this study. Regarding H antigen, H7 type in E. coli O157 accounted for 98% (49/50), and residual 1 strain of E. coli O157 was untypable H type. Two of 3 E. coli O26 isolates were H11 type, residual 1 strain of E. coli O26 was untypable H type, and E. coli O111 isolate was non-motile strain. All 54 isolates were susceptible to cephems, fosfomycin, kanamycin, amikacin and co-trimoxazole. Tetracycline-resistant isolates existed in 13 of all 54 isolates, 5 of those 13 isolates had tetA, and the other 7 isolates had tetB. Eight amoxicillin-resistant isolates had TEM-1 beta-lactamase. Four of the 5 isolates that had tetA also had TEM-1 beta-lactamase. Nalidixic acid and 6 fluoroquinolone used had no insensitive or resistant isolates. Kanamycin-resistant isolates, fosfomycin- and nalidixic acid-insensitive isolates have been reported, so we must notice the antibiogram of such strains. It is important that the surveillance of antimicrobial susceptibility of enterohemorragic E. coli should be continued after this.     

Validation of a method for simultaneous isolation of Shiga toxin-producing Escherichia coli O26, O103, O111, and O145 from minced beef by an international ring-trial

An isolation method described by Possé et al. (FEMS Microbiol Lett 2008;282:124-131) was satisfactorily validated in an international ring-trial using artificially contaminated minced beef samples. Until now, no validated method existed for the simultaneous isolation of Shiga toxin-producing Escherichia coli serogroups O26, O103, O111, and O145 in food. Twelve laboratories from five European countries participated and received 16 inoculated beef samples contaminated with cold-stressed cells of the four serogroups O26, O103, O111, and O145 in two levels (approximately 30 and 300 CFU 25?g?1) in duplicate. In addition, they received four non-inoculated samples. The isolation protocol comprised a selective enrichment step, a selective isolation step on a non-O157 agar plate differentiating the serogroups by color, followed by confirmation by plating on confirmation agar media and agglutination. All laboratories were able to isolate the inoculated serogroups from the samples, both for the high and the low inoculation level. Results did not differ whether in-house-prepared or ready-to-use non-O157 agar plates were used, demonstrating that by following the instructions laboratories managed to perform the complete protocol with success.     

Characterization of Salmonella Typhimurium of animal origin obtained from the National Antimicrobial Resistance Monitoring System

Salmonella Typhimurium remains one of the most common causes of salmonellosis in animals and humans in the United States. The emergence of multi-drug resistant Salmonella reduces the therapeutic options in cases of invasive infections, and has been shown to be associated with an increased burden of illness. In this study, 588 S. Typhimurium (including var. Copenhagen) isolates obtained from either animal diagnostic specimens (n = 199) or food animals after slaughter/processing (n = 389) were examined for antimicrobial susceptibility, presence of class-1 integrons, and characterized using pulsed-field gel electrophoresis and phage typing. Seventy-six percent (448/588) of isolates were resistant to at least one antimicrobial. Salmonella isolates displayed resistance most often to streptomycin (63%), tetracycline (61%), ampicillin (61%), and to a lesser extent, chloramphenicol (36%), ceftiofur (15%), gentamicin (9%), and nalidixic acid (4%), with more resistance observed among diagnostic isolates. Salmonella recovered from turkeys (n = 38) exhibited the highest rates of resistance, with 92% of isolates resistant to least one antimicrobial, and 58% resistant to > or =10 antimicrobials. Class 1 integrons were present in 51% of all isolates. Five integron associated resistance genes (aadA, aadB, pse-1, oxa-2 and dhfr) were identified. A total of 311 PFGE patterns were generated using XbaI, indicating a genetically diverse population. The largest PFGE cluster contained 146 isolates, including DT104 isolates obtained from all seven animal species. Results demonstrated a varied spectrum of antimicrobial resistance, including several multidrug resistant clonal groups, among S. Typhimurium and S. Typhimurium var. Copenhagen isolates recovered from both diagnostic and slaughter/processing samples.     

Antimicrobial susceptibility of Shiga toxin-producing Escherichia coli isolated from organic dairy farms, conventional dairy farms, and county fairs in Minnesota

This study compared the antimicrobial susceptibility of Shiga toxin-producing Escherichia coli (STEC) isolates from organic dairy farms, conventional dairy farms, and Minnesota county fairs. A total of 83 STEC isolates (43 O157 and 40 non-O157 STEC) were tested for antimicrobial susceptibility as determined by the automated broth microdilution method. Resistance to tetracycline was identified in 19 (23%) isolates and to sulphadimethoxine in 40 (48%) isolates. Half of the STEC isolates were resistant to at least one antimicrobial agent. Resistance to at least one antimicrobial agent was observed in 18 (62%) isolates from conventional farms and in 11 (48%) isolates from organic farms. Resistance to at least one antimicrobial agent was more frequent in isolates from calves (77%) than from cows (39%). Multidrug resistant patterns were more common in non-O157 STEC than O157 STEC. This study provides data to document the degree of STEC antimicrobial resistance from dairy cattle sources in Minnesota. The use of antimicrobial agents on farms, and other environmental influences, may affect resistance patterns in isolates from cattle sources. Systematic surveillance of STEC from cattle could potentially detect emergence of antimicrobial resistance that may be spread to humans through the food chain.     

158例新生儿败血症病原菌种类及其耐药性

目的了解引起新生儿败血症的病原菌种类及其耐药情况,为临床治疗提供依据。方法对某院2007年1月—2010年12月收治的158例新生儿败血症患儿血培养阳性菌及其药敏试验结果进行分析。结果 158例新生儿败血症患儿血培养居前3位的细菌分别为凝固酶阴性葡萄球菌（77株,48.73%）、金黄色葡萄球菌（44株,27.84%）、大肠埃希菌（19株,12.03%）。金黄色葡萄球菌和凝固酶阴性葡萄球菌对青霉素、红霉素的耐药率较高,对万古霉素、替考拉宁无耐药株;大肠埃希菌对环丙沙星、头孢噻肟、复方磺胺甲口恶唑的耐药率较高,对四环素、头孢哌酮∕舒巴坦的耐药率较低,对亚胺培南、美罗培南无耐药株。结论葡萄球菌属与大肠埃希菌是引起新生儿败血症的主要病原体,应重视其耐药性检测,合理选择抗菌药物进行目标性治疗。