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.     

Antimicrobial resistance pattern of Salmonella serotypes isolated from apparently healthy slaughtered camels (Camelus dromedarius) in eastern Ethiopia

A total of 714 samples consisting of faeces, mesenteric lymph nodes, liver, spleen, abdominal and diaphragmatic muscles (each 119) were collected from November 2001 to April 2002 from apparently healthy slaughtered camels (Camelus dromedarius) in eastern Ethiopia. One hundred sixteen (16.2%) Salmonella strains belonging to 16 different serovars were isolated. All Salmonella strains isolated were examined for antimicrobial resistance to 17 selected antimicrobials. The minimum inhibitory concentration (MIC) values were determined by the microdilution broth test. Fifty-two (44.8%) of the Salmonella isolates were resistant to one or more antimicrobials. Thirty-nine of the 52 (75%) resistant Salmonella serovars exhibited multiple resistance to up to eight different antimicrobials. Among the serovars tested, S. Typhimurium, S. Heidelberg, S. Braenderup and S. Hadar displayed multiple resistance mainly to streptomycin (35.3%), spectinomycin (28.4%), sulfamethoxazole (25.0%), ampicillin (24.1%), trimethoprim (22.4%), trimethoprim/sulfamethoxazole (18.9%), tetracycline (12.9%) and colistin (11.2%). All Salmonella strains tested were susceptible to ciprofloxacin, nalidixic acid, gentamicin, kanamycin and neomycin. The present study showed the importance of camels as a potential source of single and multiple resistant Salmonella strains to different antimicrobials that are also used in the public health sector for the treatment of different bacterial diseases in Ethiopia.     

Analysis of Antimicrobial Resistance and Detection of ESBLs Genes of Pathogenic Salmonella Isolates from Dairy Cows in Inner Mongolia

The aim of the present study was to investigate the characteristics of antimicrobial resistance and prevalence of ESBLs genes of Salmonella isolates from dairy cows in Inner Mongolia.Micro-dilution broth method recommended by CLSI was used to determine the MICs of 22 antimicrobial agents commonly employed in veterinary clinic against the 38 Salmonella isolates.PCR analysis was carried out to detect the presence of 8 ESBLs genes mostly observed in animal origin Salmonella in the isolates with resistance to at least one β-lactam antibiotics, and the features of multi-resistance of the isolates were also analyzed.The results showed that most Salmonella isolates were resistant to trimethoprim(97.4%), sulfamethoxazole(94.7%), and to most of the β-lactam, aminoglycosides, chloramphenicol and tetracycline antibiotics with the resistance rate ranging from 40% to 80%, however, all of the isolates were sensitive to fluoroquinolone drugs.76.3%(n＝29) of the isolates were simultaneously resistant to 6 categories antibiotics and the multi-resistance rate was 94.7%. 85.7%(n＝30) of the β-lactam antibiotics resistant isolates were ESBLs genes positive.Of the six genotype of ESBLs genes found in this study, CTX-M (40.0%) was the mostly encountered ESBLs gene, however, the SHV and PSE types gene were absent in the isolates.A total of fifteen genotypes of the ESBLs genes and nine ESBLs genes combinations were observed in this study, and 16 isolates (45.7%) simultaneously contained two or more than two ESBLs genes.It was indicated that the current situation of the resistance of the Salmonella isolates from dairy cows in Inner Mongolia to the commonly used antimicrobial agents in veterinary clinic was serious, and the prevalence pattern of the ESBLs genes in the isolates was complex, suggesting that the irrational employment of the antibiotic in the treatment of animal infectious diseases was the crucial reason causing the antimicrobial resistance of the isolates.     

内蒙古地区奶牛源致病性沙门氏菌耐药性分析及ESBLs基因检测

为研究内蒙古地区奶牛源致病性沙门氏菌的耐药特性及ESBLs基因流行特征,试验采用微量肉汤稀释法测定了22种兽医临床常用抗菌药物对临床分离沙门氏菌的最低抑菌浓度(MICs),并对其多重耐药特性进行了分析;采用PCR法对具有β-内酰胺类药物耐药表型的菌株进行了8种动物源沙门氏菌常见ESBLs基因的检测。结果显示,内蒙古地区奶牛源致病性沙门氏菌对甲氧苄啶(97.4%)及磺胺甲基噁唑(94.7%)的耐药率最高,对多数β-内酰胺类、氨基糖甙类、氯霉素类及四环素类药物的耐药性也较为严重(耐药率为40%~80%),所有菌株对氟喹诺酮类药物均敏感;菌株的多重耐药率为94.7%,有29株菌(76.3%)同时对6类抗菌药物具有耐药性;35株对β-内酰胺类药物耐药的菌株中,有30株(85.7%)为ESBLs基因阳性,共检出6种ESBLs基因,其中CTX-M型基因检出率最高(40.0%),未检出SHV和PSE型基因;共发现15种ESBLs基因型,9种ESBLs基因型组合,有16株菌(45.7%)同时携带两种或两种以上ESBLs基因。结果表明,内蒙古地区奶牛源致病性沙门氏菌对兽医临床常用抗菌药物的耐药性较为严重,且ESBLs基因的流行模式较为复杂,提示兽医临床抗菌药物不合理使用可能是造成该地区奶牛源沙门氏菌耐药性产生的原因。     

In vitro antibacterial susceptibility of Arcobacter butzleri isolated from different sources

The objective of this study was to determine the antibiotic susceptibility of Arcobacter spp. isolated from various sources. Seventy Arcobacter spp. isolates were tested for their susceptibility to 13 antimicrobial agents. Antimicrobial susceptibility testing was performed by using the agar disc diffusion method on Mueller-Hinton agar supplemented with 5% defibrinated sheep blood. The antibiotics tested included enrofloxacin, erythromycin, streptomycin, gentamycin, rifampin, tetracycline, ampicillin, trimethoprim/sulfamethoxazole, nalidixic acid, danofloxacin, amoxycillin-clavulonic acid, cefuroxime-sodium, neomycine. Although all the arcobacters tested were susceptible to gentamycin, resistance to three or more antibacterial agents (especially, trimethoprim/sulfamethoxazole, cefuroxime-sodium and rifampin) was observed. A. butzleri isolates were found to be resistant to amoxycillin+clavulonic acid, nalidixic acid and ampicillin, at the rate of 20%, 44.28% and 78.57% respectively. In conclusion, gentamycin, streptomycin and tetracycline may be suitable antibiotics for the treatment or control of disease caused by Arcobacter spp. in veterinary and human medicine.     

Antimicrobial resistance in generic fecal Escherichia coli from 29 beef farms in Ontario

The occurrence of antimicrobial resistance in generic Escherichia coli can serve as an indicator of the pool of resistance genes potentially available for transfer to pathogenic organisms. This study was conducted on 29 volunteer beef farms in Ontario to describe the prevalence and patterns of antimicrobial resistance in E. coli, and to describe changes in the prevalence of resistance during the feedlot stage of production. From the pooled fecal samples on 28 of the 29 farms, 31% of isolates from feedlots (n = 993) and 12% of isolates from cow-calf farms (n = 807) were resistant to one or more of 16 antimicrobials tested. No isolates were resistant to ceftriaxone, ciprofloxacin, gentamicin, or nalidixic acid, and < 1% of the pooled isolates were resistant to ceftiofur. Two percent of both feedlot and cow-calf isolates were resistant to > or = 5 antimicrobials. Cow-calf farms were at significantly lower risk than feedlots for having E. coli isolates that were resistant to streptomycin, sulfamethoxazole, and tetracycline. On average, the prevalence of sulfamethoxazole resistant E. coli isolates was significantly higher in calves than in cows. No resistance was observed to ceftriaxone or ciprofloxacin among isolates (n = 1265) obtained from individually sampled feedlot animals on 2 farms. Less than 1% of these isolates were resistant to gentamicin, nalidixic acid, and ceftiofur. From the individually sampled feedlot animals, resistance to streptomycin (on 1 farm), sulfamethoxazole, and tetracycline increased significantly from arrival to mid-point during the feeding period, and these levels persisted until market-readiness.     

Clinical herd health, farm management and antimicrobial resistance in Campylobacter coli on finishing pig farms in Switzerland

The world-wide increase of antimicrobial resistance in micro-organisms complicates medical treatment of infected humans. We did a risk-factor analysis for the prevalence of antimicrobial resistant Campylobacter coli on 64 Swiss pig finishing farms. Between May and November 2001, 20 faecal samples per farm were collected from the floor of pens holding finishing pigs shortly before slaughter. Samples were pooled and cultured for Campylobacter species. Isolated Campylobacter strains were tested for resistance against selected antimicrobials. Additionally, information on herd health and management aspects was available from another study. Because data quality on the history of antimicrobial use on the farms was poor, only non-antimicrobial risk factors could be analysed. Statistical analyses were performed for resistance against ciprofloxacin, erythromycin, streptomycin, tetracycline, and for multiple resistance, which was defined as resistance to three or more antimicrobials. Risk factors for these outcomes – corrected for dependency of samples at herd level – were analysed in five generalised estimation-equation models. Prevalence of antimicrobial resistance among Campylobacter isolates was ciprofloxacin 26.1%, erythromycin 19.2%, streptomycin 78.0%, tetracycline 9.4%, and multiple resistance 6.5%. Important risk factors contributing to the prevalence of resistant strains were shortened tails, lameness, skin lesions, feed without whey, and ad libitum feeding. Multiple resistance was more likely in farms which only partially used an all-in-all-out system (OR = 37), or a continuous-flow system (OR = 3) compared to a strict all-in-all-out animal-flow. Presence of lameness (OR = 25), ill-thrift (OR = 15), and scratches at the shoulder (OR = 5) in the herd also increased the odds for multiple resistance. This study showed that on finishing farms which maintained a good herd health status and optimal farm management, the prevalence of antimicrobial resistance was also more favourable.     

部分鸡场大肠杆菌对抗菌药物的耐药性

从江西、辽宁、广东3个省的鸡场分离到204株大肠杆菌，按NCCLs推荐的纸片扩散法测定了其对24种抗菌药物的敏感性。结果表明，分离菌对四环素的耐药性最高，为92．2％．余下依次为二氟沙星、萘啶酸、磺胺、复方新诺明、氨苄西林、阿莫西林、恩诺沙星、沙拉沙星、洛美沙星、链霉素、达氟沙星、培氟沙星、环丙沙星、诺氟沙星、氧氟沙星、氯霉素、庆大霉素、卡那霉素、头孢噻吩、奥格门丁(阿莫西林和克拉维酸钾)、阿米卡星、氟苯尼考．头孢曲松无1例耐药。     

Prevalence of Salmonella spp. on Canadian pig farms using liquid or dry-feeding

The objective of this study was to determine whether the shedding and antibody titre to Salmonella was lower for pig herds provided liquid-feed compared to those on traditional dry rations. Twenty liquid-feeding farms and 61 dry-feeding farms were selected. The amount of antibodies to Salmonella in sera from 15 finisher pigs on each of 80 Ontario swine farms was analyzed by means of enzyme-linked immunosorbent assay (ELISA). In addition, the presence of Salmonella on the 20 liquid-feeding farms and 21 of the dry-feeding farms was assessed by culture of 15 fecal samples taken directly from finisher pigs and five pooled pen-fecal samples at each farm.

A cut-off of OD% 10 was used. The Salmonella sero-prevalence differed between the two groups of farms. At least one pig tested sero-positive on 98% of the dry-feeding farms and 84% of the liquid-feeding farms (P < 0.05). A multi-variable mixed linear regression model with the farm as a random variable and farm factors as the fixed effects was fitted. Crude optical density (OD) of the individual pig was considered as the continuous dependent variable. Dry-feeding and antimicrobial daily usage was associated with crude OD (P < 0.05). In addition, crude OD increased with increasing herd size (P < 0.05).

Salmonella was isolated from 25 out of 420 fecal samples (6%) from dry-feeding farms compared to three out of 400 samples (0.8%) from liquid-feeding farms. Eight of the dry-feeding farms (38%) tested positive compared to only three of the liquid-feeding farms (15%). Salmonella was also recovered from the pen environment on five dry-feeding farms but were not isolated from the facilities using liquid-feeding. Salmonella Typhimurium was isolated from four farms in the dry-feed group and on one farm with liquid-feeding. The one S. Typhimurium isolate from the liquid-feeding farm exhibited no antimicrobial resistance, but those from dry-feeding farms were resistant to four or more antimicrobial agents. The results of the logistic regression, with farm as a random effect showed that dry-feeding [OR = 2.7 (1.1–15.1)] and continuous flow system [OR = 2.3 (1.2–12.7)] increased risk of finding Salmonella in the individual pig.

These findings indicate that liquid-feeding and all-in all-out management of the grower–finisher barns can reduce the Salmonella prevalence.     

Herd-level risk factors for Salmonella enterica subsp. enterica in U.S. market pigs

Midwest U.S. herds (n = 63) were studied to identify risk factors for harboring Salmonella enterica among slaughter-weight pigs. Samples collected on farms (feces) and at slaughter (distal colonic content, cecal content and ileocolic lymph nodes) were cultured using conventional means. Approximately 15 pigs were studied per herd, for a total of 3754 samples. The proportion of pigs positive in one or more samples was calculated for each herd. Herd characteristics were described by a combination of interview and written survey. Logistic regression was used to detect relationships between the detection of Salmonella and potential herd-level risk factors. The mean individual pig prevalence was 5% for feces, 4% for distal colonic content, 15% for ileocolic lymph nodes, and 17% for cecal contents. One or more Salmonella isolates were detected in at least one sample type in every herd. The five most common serovars were S. Agona, S. Derby, S. Schwarzengrund, S. Typhimurium and S. Senftenberg, with 25 additional serovars detected. Salmonella prevalence estimates were positively correlated among all samples except distal colonic content and ileocolic lymph nodes. Pigs with culture positive fecal samples were at increased odds of being detected positive for each of the slaughter-collected samples examined, namely distal colonic content (OR = 30.5), ileocolic lymph nodes (OR = 12.9) and cecal content (OR = 23.2). Herds with positive fecal sample(s) had increased odds of having positive cecal content (OR > 1.5), distal colonic content (OR = 15.3) and ileocolic lymph nodes (OR = 12.7). Pigs from herds with at least some bowl drinkers had eight-fold higher odds of testing Salmonella positive than did pigs from herds with only nipple drinkers. Pigs from herds with only dry feeders had five-fold higher odds of testing Salmonella positive when compared with pigs from herds with combinations of wet/dry style feeders. Interventions at these two points should be considered when designing growing pig facilities to reduce Salmonella shedding.     

Risk factors for intramammary infections and relationship with somatic-cell counts in Italian dairy goats

Routine examination of milk was performed on five herds of lactating goats in northern Italy as part of a milk quality-monitoring program in the year 2000. As part of the study, aseptic samples of foremilk were collected monthly from both half udders during the entire lactation for 305 goats, resulting in a total of 4571 samples. The samples were tested with cytological and bacteriological analyses to evaluate the relationship between mammary infections and somatic-cell count (SCC; Fossomatic (TM) method). Prevalence of intramammary infection (IMI) was 40.2% (n = 1837) of all udder-half samples examined. The most-prevalent mastitis agents were coagulase-negative Staphylococci (CNS), 80% (n = 1474 udder-half samples); within this group, Staphylococcus epidermidis was the most-prevalent species (38%). Other prevalence were Staphylococcus aureus 6% (n = 112 udder-half samples) and environmental pathogens 14% of infected udder-half samples (n = 251) with a diverse mixture of species, none of which had a frequency of >4%. Enterococcus faecalis was the most-frequently isolated among this group. Neither Salmonella spp. nor Listeria monocytogenes were detected. The risk (sample level) of infection differed across herds, parities, and stage of lactation according to results from logistic multiple regression. Infection was more common among goats in third and fourth parities and during the later stages of lactation. Of the 2734 samples from uninfected udder halves, the mean log₂ SCC was 3.9 cell/ml; of the 1837 bacteriological positive samples, the mean log₂ SCC was 5.6 cell/ml. According to results from a linear mixed model, concentrations of somatic cells tended to increase with increasing age and days in milk and with the presence of bacteria. Infection with S. aureus was associated with the highest SCS.     

重庆部分羊场沙门氏菌的分离鉴定、耐药表型分析及耐药基因检测

本研究旨在初步了解重庆市羊源沙门氏菌的耐药性及耐药基因流行情况。在5个山羊养殖场采集185份山羊粪便样品，经选择性增菌和PCR鉴定分离沙门氏菌，确定了其血清型，测定了分离菌对28种抗菌药物的敏感性，并检测了喹诺酮耐药决定区（QRDR）的耐药突变位点和质粒介导的喹诺酮耐药（PMQR）、超广谱β-内酰胺酶（ESBL）基因。共分离到羊源沙门氏菌11株，其中10株为德尔卑沙门氏菌。分离的菌株对氨苄西林、头孢唑啉、头孢氨苄、头孢噻肟、四环素和培氟沙星耐药严重；9株菌表现为多重耐药，对3~7类药物耐药。所有菌株均存在QRDR耐药突变且携带bla_TEM基因；7株菌携带1~5种PMQR基因。本研究分离的羊源沙门氏菌对常用抗菌药物整体耐药较为严重，且广泛存在耐药突变和携带耐药基因。     

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.     

Antimicrobial resistance of fecal Salmonella spp. isolated from all phases of pig production in 20 herds in Alberta and Saskatchewan

Salmonella spp. (n = 468), isolated from the feces of sows, nursery, and grow-finish pigs in 20 farrow-to-finish herds in Alberta and Saskatchewan, were tested for susceptibility to 16 antimicrobials. No resistance was identified to amikacin, amoxicillin-clavulanic acid, ceftiofur, ceftriaxone, ciprofloxacin or nalidixic acid, and less than 1% of the isolates were resistant to cefoxitin and gentamicin. Isolates were most commonly resistant to tetracycline (35%) and sulfamethoxazole (27%). Overall, 59% of the Salmonella were susceptible to all 16 drugs (pansusceptible). Isolates from sows were more likely to be pansusceptible than isolates from nursery or grow-finish pigs. Resistance to 2 or more drugs occurred in 29% of the isolates and was significantly more likely to occur in Salmonella from nursery pigs than from sows. The odds of resistance to 4 of the drugs, streptomycin, ampicillin, kanamycin and cephalothin, were significantly higher in isolates from nursery pigs than grow-finish pigs, while the odds of resistance to 2 drugs, tetracycline and streptomycin, were higher in Salmonella from nursery pigs than from sows. More age-specific risk factor studies are needed to investigate these differences between production phases.     

广东省零售市场鸡肉中肯塔基沙门菌的流行情况及耐药性分析

本研究旨在了解广东省零售市场鸡肉中肯塔基沙门菌的流行情况、耐药水平与耐药基因携带情况。对2016年从广东省五个地级市采集的鸡肉样品进行沙门菌分离鉴定、血清型鉴定、药敏试验、耐药基因的检测和分子分型。结果显示，245份鸡肉样品中沙门菌阳性率为62.04%（152/245），共鉴定出19种血清型，其中主要血清型有阿贡纳（Salmonella Agona，29/152，19.08%）、科瓦利斯（S.Corvallis，25/152，16.45%）以及肯塔基（S.Kentucky，20/152，13.16%）。肯塔基沙门菌药敏试验结果显示对磺胺异噁唑（100%）、萘啶酸（90%）、四环素（75%）、氨苄西林（65%）、头孢他啶（55%）、环丙沙星（55%）的耐药率较高，有85%（17/20）的菌株对3种及3种以上的抗菌药物耐药。对喹诺酮耐药基因的检测结果显示，95%（19/20）的菌株具有gyrA突变（Ser83Phe、Asp87Asn、Asp87Gly），其中有57.89%（11/19）的菌株发生gyrA双突变（Ser83Phe与Asp87Asr、Ser83Phe与Asp87Gly），5.26%（1/19）发生gyrA三突变（Ser83Phe、Asp87Asn、Asp87Gly）；100%（20/20）的菌株具有parC突变（Tyr62Ser、Ser85Ile）。45%（9/20）分离株携带质粒介导的喹诺酮抗性（PMQR）基因（aac（6'）-Ib-cr、qnrB、qnrS、oqxAB），最常见的是aac（6'）-Ib-cr耐药基因。β-内酰胺类耐药基因bla_TEM-1、bla_OXA-1和bla_CTX-M-55的检出率分别为25%、10%和5%。PFGE图谱的聚类分析结果显示，肯塔基沙门菌之间具有不同的亲缘关系与遗传多样性，部分菌株具有高度同源性。肯塔基沙门菌在广东省零售市场鸡肉中是主要的流行血清型之一。其对传统药物磺胺异噁唑、萘啶酸、四环素和氨苄西林耐药较严重，对环丙沙星以及头孢他啶耐药尤其严重，具有多种多重耐药表型。肯塔基沙门菌其喹诺酮耐药决定区突变率高。分子分型揭示了菌株间跨地区传播的可能，为肯塔基沙门菌溯源提供一定的依据。     

International disease surveillance. International disease monitoring, October to December 2004

To assess whether the rates of antimicrobial susceptibility in bacteria isolated from the urine of dogs with urinary tract infections are similar to those of bacteria isolated from bitches with pyometra, the antimicrobial resistance of Escherichia coli isolated from the two groups were determined and compared. The samples were collected in Sweden between April 2002 and March 2003, and potential changes over time were assessed by comparing the results with corresponding data from 1991 to 1993. Among 80 isolates of E coli from cases of pyometra, the proportions that were resistant to the antimicrobials used in canine practice were generally low (ampicillin 10 per cent, enrofloxacin 4 per cent, gentamicin 0 per cent, streptomycin 5 per cent, sulfamethoxazole 8 per cent, tetracycline 4 per cent and trimethoprim 2 per cent) and similar to the proportions reported previously. Significantly lower proportions of resistance were recorded among the pyometra isolates than among 92 isolates from urine samples submitted by animal hospitals to ampicillin (P=0.04), streptomycin (P=0.002) and tetracycline (P=0.03), but there were no differences between the pyometra isolates and 113 isolates from urine samples submitted by animal clinics.     

Antimicrobial susceptibility of Haemophilus parasuis and Histophilus somni from pigs and cattle in Denmark

A total of 52 Haemophilus parasuis and 80 Histophilus somni isolates were tested for antimicrobial susceptibility by MIC-determinations. None of the isolates were resistant to ampicillin, ceftiofur, ciprofloxacin, erythromycin, florphenicol, penicillin, spectinomycin, tetracycline, tiamulin, or tilmicosin. Two H. parasuis isolates were resistant to trimethoprim + sulfamethoxazole. Six H. parasuis isolates had reduced susceptibility (0.06-0.5 microg/ml) to ciprofloxacin and 10 reduced susceptibility to TMP + sulfamethoxazole (1-2 microg/ml). This study showed that Danish isolates of H. parasuis and H. somni in general are fully susceptible to antimicrobial agents currently used for treatment of infections with these pathogens.     

Antimicrobial susceptibility of Salmonella isolates recovered from calves with diarrhoea in Australia

OBJECTIVE To identify the common serotypes and antimicrobial resistance patterns of Salmonella spp. associated with diarrhoea in Australian dairy calves under the age of 6 weeks. DESIGN Cross-sectional study. METHODS Faecal samples were collected from outbreaks of diarrhoea in dairy and dairy beef calves less than 6 weeks old. Samples were screened for Salmonella using standard enrichment culture techniques. The antimicrobial susceptibility to 12 commonly used veterinary and human antimicrobials was assessed using the Kirby-Bauer disk diffusion method and the susceptibility profiles of dairy and dairy beef properties were compared using Fisher's exact test. RESULTS Salmonella ser. Dublin, S. ser. Typhimurium and S. ser. Bovismorbificans were the three most common salmonella serotypes isolated. The majority of properties had one serotype. Most of the Salmonella isolates were not resistant to any of the antimicrobials tested. No resistance was seen to amikacin and nalidixic acid, and only one isolate was resistant to ceftiofur or amoxicillin-clavulanic acid. The most common antimicrobial resistance was to streptomycin, ampicillin or combination sulfonamides. Multi-drug resistance was detected in S. ser. Anatum, S. ser. Bovismorbificans, S. ser. Muenster, S. ser. Newport and S. ser. Typhimurium. Isolates from dairy beef properties were more likely to be resistant to ampicillin, kanamycin, neomycin, sulfamethoxazole/trimethoprim and tetracycline (P < 0.05) and were more likely to exhibit multi-drug resistance. CONCLUSION The prevalence of antimicrobial resistance in Salmonella isolates from dairy calves in Australia is low compared with that reported overseas. From a human health perspective, resistance to antimicrobials used in the treatment of human salmonellosis was infrequent.     

Prevalence of resistance to 11 antimicrobials among Campylobacter coill isolated from pigs on 80 grower-finisher farms in Ontario.

We carried out a cross-sectional study to investigate antimicrobial resistance patterns of Campylobacter coli isolated from Ontario grower-finisher pigs. From January to June 2004, 1200 samples were collected from 80 farms by obtaining a constant number (15) of fecal samples per farm. Susceptibility of the isolates to 11 antimicrobial drugs was determined by the agar-dilution technique. The overall prevalence of resistance to 1 or more antimicrobials among the isolates was 99.2%. High levels of resistance were observed for azithromycin, clindamycin, erythromycin, streptomycin, and tetracycline: 91.7%, 82.5%, 81.4%, 70.7%, and 63.7%, respectively. For sulfamethoxazole, ampicillin, and nalidixic acid, resistance was observed in 40.3%, 26.6%, and 22.7% of the isolates, respectively. Although at very low levels, resistance was observed for ciprofloxacin (a fluoroquinolone), chloramphenicol, and gentamicin: in 2.4%, 1.7%, and 0.2%, respectively. Many of the isolates (29.7%) were resistant to 5 antimicrobials, the most common being azithromycin, clindamycin, erythromycin, streptomycin, and tetracycline. Isolates from the same farm showed at least 5 patterns of resistance. Results from this study indicate high levels of resistance to the antimicrobial drugs most commonly used in the Canadian swine industry (macrolides, lincosamides, and tetracyclines) among C. coli isolated from grower-finisher pigs in Ontario. Macrolides and fluoroquinolones are the drugs most commonly used to treat severe human campylobacteriosis. Fortunately, at present, there is little resistance to fluoroquinolones among C. coli from pigs in Ontario.     

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.