scholarly journals Association between the blaCTX-M-14-harboring Escherichia coli Isolated from Weasels and Domestic Animals Reared on a University Campus

Antibiotics ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 432
Author(s):  
Montira Yossapol ◽  
Miku Yamamoto ◽  
Michiyo Sugiyama ◽  
Justice Opare Odoi ◽  
Tsutomu Omatsu ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Antimicrobial Resistance ◽  
Animal Health ◽  
Domestic Animals ◽  
Group Method ◽  
University Campus ◽  
E Coli ◽  
Pair Group ◽  
Generation Sequencing ◽  
M 14

Antimicrobial-resistant (AMR) bacteria affect human and animal health worldwide. Here, CTX-M-14-producing Escherichia coli isolates were isolated from Siberian weasels (Mustela sibirica) that were captured on a veterinary campus. To clarify the source of bacteria in the weasels, we examined the domestic animals reared in seven facilities on the campus. Extended-spectrum β-lactamase (ESBL)-producing E. coli were isolated on deoxycholate hydrogen sulfide lactose agar, containing cephalexin (50 μg/mL) or cefotaxime (2 μg/mL), and were characterized with antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE), replicon typing, and β-lactamase typing analyses. Next-generation sequencing of the ESBL-encoding plasmids was also performed. CTX-M-14 producers isolated from both domestic animals and weasels were classified into six clusters with seven PFGE profiles. The PFGE and antimicrobial resistance profiles were characterized by the animal facility. All CTX-M-14 plasmids belonged to the IncI1 type with a similar size (98.9–99.3 kb), except for one plasmid that was 105.5 kb in length. The unweighted pair group method with arithmetic mean (UPGMA) revealed that the CTX-M-14 plasmid in the weasel isolates might have the same origin as the CTX-M-14 plasmid in the domestic animals. Our findings shed further light on the association of antimicrobial resistance between wild and domestic animals.

scholarly journals Antimicrobial Resistance Profiles and Characterization of Escherichia coli Strains from Cases of Neonatal Diarrhea in Spanish Pig Farms

2020 ◽  
Vol 7 (2) ◽  
pp. 48
Author(s):  
Anna Vidal ◽  
Laia Aguirre ◽  
Chiara Seminati ◽  
Montse Tello ◽  
Noelia Redondo ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Antimicrobial Resistance ◽  
Animal Health ◽  
Phenotypic Analysis ◽  
Low Frequencies ◽  
Neonatal Diarrhea ◽  
E Coli ◽  
Pig Farms ◽  
Diagnostic Approaches ◽  
Low Prevalence

Escherichia coli is considered one of the most common agents associated with neonatal diarrhea in piglets. The aim of this work was to characterize the pathogenic and antimicrobial resistance (AMR) profiles of 122 E. coli strains isolated from pigs suffering diarrhea (n = 94) and pigs without diarrhea (n = 28) of 24 farms in Spain. Virulence factors, toxins and AMR (ESBL and colistin) genes and AMR phenotypes of E. coli isolates were analyzed. Low prevalence of pathogenic E. coli strains (26%) was found in both groups. However, ETEC and VTEC strains were more frequently isolated from diarrheic piglets. Irrespectively of diarrhea occurrence, 97.5% of the strains showed a multidrug-resistance (MDR) profile to aminopenicillins, sulfonamides and tetracyclines. It was found that 22% of E. coli was CTX-M+, with CTX-M-14 being the principal allelic variant. Remarkably, 81.5% of CTX-M+ strains were isolated from diarrheic animals and presented an extended MDR profile to aminopenicillins, quinolones and aminoglycosides. Finally, low frequencies of colistin resistance genes mcr-1 (4/122) and mcr-4 (1/122) were found. MDR E. coli strains are circulating in pig farms of Spain, representing a serious threat to animal and public health. More appropriate diagnostic approaches (genetic and AMR phenotypic analysis) should be implemented in animal health to optimize antibiotic treatments.

scholarly journals Broiler Farms and Carcasses Are an Important Reservoir of Multi-Drug Resistant Escherichia coli in Ecuador

2020 ◽  
Vol 7 ◽  
Author(s):  
David Ortega-Paredes ◽  
Sofía de Janon ◽  
Fernando Villavicencio ◽  
Katherine Jaramillo Ruales ◽  
Kenny De La Torre ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Antimicrobial Resistance ◽  
Animal Health ◽  
Poultry Meat ◽  
Meat Production ◽  
Drug Resistant ◽  
Food Component ◽  
Production Chain ◽  
Animal Food ◽  
E Coli

Antimicrobial resistance (AMR) is a major health threat for public and animal health in the twenty-first century. In Ecuador, antibiotics have been used by the poultry industry for decades resulting in the presence of multi-drug resistant (MDR) bacteria in the poultry meat production chain, with the consequent risk for public health. This study evaluated the prevalence of ESBL/AmpC and mcr genes in third-generation cephalosporin-resistant Escherichia coli (3GC-R E. coli) isolated from broiler farms (animal component), broiler carcasses (food component), and human enteritis (human component) in Quito-Ecuador. Samples were collected weekly from November 2017 to November 2018. For the animal, food, and human components, 133, 335, and 302 samples were analyzed, respectively. Profiles of antimicrobial resistance were analyzed by an automated microdilution system. Resistance genes were studied by PCR and Sanger sequencing. From all samples, 122 (91.7%), 258 (77%), and 146 (48.3%) samples were positive for 3GC-R E. coli in the animal, food, and human components, respectively. Most of the isolates (472/526, 89.7%) presented MDR phenotypes. The ESBL blaCTX-M-55, blaCTX-M-3, blaCTX-M-15, blaCTX-M-65, blaCTX-M-27, and blaCTX-M-14 were the most prevalent ESBL genes while blaCMY-2 was the only AmpC detected gene. The mcr-1 gene was found in 20 (16.4%), 26 (10.1%), and 3 (2.1%) of isolates from animal, food, and human components, respectively. The implication of poultry products in the prevalence of ESBL/AmpC and mcr genes in 3GC-R must be considered in the surveillance of antimicrobial resistance.

scholarly journals mcr-1 Identified in Fecal Escherichia coli and Avian Pathogenic E. coli (APEC) From Brazil

2021 ◽  
Vol 12 ◽  
Author(s):  
Nicolle Lima Barbieri ◽  
Ramon Loureiro Pimenta ◽  
Dayanne Araujo de Melo ◽  
Lisa K. Nolan ◽  
Miliane Moreira Soares de Souza ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Antimicrobial Resistance ◽  
Animal Health ◽  
Animal Husbandry ◽  
Pulse Field ◽  
Pfge Analysis ◽  
E Coli ◽  
Gene Screening ◽  
Plasmid Replicon ◽  
Antimicrobial Resistance Genes

Colisitin-associated resistance in bacteria of food producing animals has gained significant attention with the mcr gene being linked with resistance. Recently, newer variants of mcr have emerged with more than nine variants currently recognized. Reports of mcr associated resistance in Escherichia coli of poultry appear to be relatively limited, but its prevalence requires assessment since poultry is one of the most important and cheapest sources of the world’s protein and the emergence of resistance could limit our ability to treat disease outbreaks. Here, 107 E. coli isolates from production poultry were screened for the presence of mcr 1–9. The isolates were collected between April 2015 and June 2016 from broiler chickens and free-range layer hens in Rio de Janeiro, Brazil. All isolates were recovered from the trachea and cloaca of healthy birds and an additional two isolates were recovered from sick birds diagnosed with colibacillosis. All isolates were screened for the presence of mcr-1 to 9 using PCR and Sanger sequencing for confirmation of positive genes. Additionally, pulse field gel electrophoresis (PFGE) analysis, avian fecal E. coli (APEC) virulence associated gene screening, plasmid replicon typing and antimicrobial resistance phenotype and resistance gene screening, were also carried out to further characterize these isolates. The mcr-1 gene was detected in 62 (57.9%) isolates (61 healthy and 1 APEC) and the mcr-5 gene was detected in 3 (2.8%) isolates; mcr-2, mcr-3, mcr-4, mcr-6, mcr-7, mcr-8, and mcr-9 were not detected in any isolate. In addition, mcr 1 and 5 positive isolates were phenotypically resistant to colistin using the agar dilution assay (> 8ug/ml). PFGE analysis found that most of the isolates screened had unique fingerprints suggesting that the emergence of colistin resistance was not the result of clonal dissemination. Plasmid replicon types IncI2, FIB, and B/O were found in 38, 36, and 34% of the mcr positive isolates and were the most prevalent replicon types detected; tetA and tetB (32 and 26%, respectively) were the most prevalent antimicrobial resistance genes detected and iutA, was the most prevalent APEC virulence associated gene, detected in 50% of the isolates. Approximately 32% of the isolates examined could be classified as APEC-like, based on the presence of 3 or more genes of APEC virulence associated path panel (iroN, ompT, hlyF, iss, iutA). This study has identified a high prevalence of mcr-1 in poultry isolates in Brazil, suggesting that animal husbandry practices could result in a potential source of resistance to the human food chain in countries where application of colistin in animal health is practiced. Emergence of the mcr gene and associated colisitin resistance in production poultry warrants continued monitoring from the animal health and human health perspective.

scholarly journals Diverse commensal E. coli clones and plasmids disseminate antimicrobial resistance genes in domestic animals and children in a semi-rural community in Ecuador

2019 ◽  
Author(s):  
Liseth Salinas ◽  
Paúl Cárdenas ◽  
Timothy J. Johnson ◽  
Karla Vasco ◽  
Jay Graham ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Antimicrobial Resistance ◽  
Rural Community ◽  
Resistance Genes ◽  
Domestic Animals ◽  
Drug Resistant ◽  
Phenotypic Resistance ◽  
E Coli ◽  
Antimicrobial Resistance Genes ◽  
Resistance Patterns

ABSTRACTThe increased prevalence of antimicrobial resistance (AMR) among Enterobacteriaceae has had major clinical and economic impacts in human medicine. Many of the multi-drug resistant (MDR) Enterobacteriaceae found in humans are community-acquired and linked to food animals (i.e. livestock raised for meat and dairy products). In this study, we examined whether numerically dominant, commensal Escherichia coli strains from humans (n=63 isolates) and domestic animals (n=174 isolates) in the same community and with matching phenotypic AMR patterns, were clonally related or shared the same plasmids. We identified 25 multi-drug resistant isolates (i.e. resistant to 3 or more antimicrobial classes) that shared identical phenotypic resistance patterns. We then investigated the diversity of E. coli clones, AMR genes and plasmids carrying the AMR genes using conjugation, replicon typing and whole genome sequencing. None of the MDR E. coli isolates (from children and domestic animals) analyzed were clonal. While the majority of isolates shared the same antimicrobial resistance genes and replicons, DNA sequencing indicated that these genes and replicons were found on different plasmid structures. Our findings suggest that nonclonal resistance gene dissemination is common in this community and that diverse plasmids carrying AMR genes presents a significant challenge for understanding the movement of AMR in a community.IMPORTANCEEven though Escherichia coli strains may share nearly identical AMR profiles, AMR genes, and overlap in space and time, the diversity of clones and plasmids challenges to research that aims to identify sources of AMR. Horizontal gene transfer appears to play a much larger role than clonal expansion in the spread of AMR in the community.

scholarly journals Prevalence and antimicrobial resistance profiles of Escherichia coli isolated from free-range pigs

2017 ◽  
Vol 11 (08) ◽  
pp. 652-655
Author(s):  
Hongna Zhang ◽  
Xiaonan Zhao ◽  
Xuepeng Wang ◽  
Weishan Chang
Keyword(s):  
Escherichia Coli ◽  
Antimicrobial Resistance ◽  
Eastern China ◽  
Resistance Rate ◽  
E Coli ◽  
Free Range ◽  
Resistant Genes ◽  
Potential Reservoir ◽  
Free Ranging ◽  
M 14

Introduction: Numerous studies about antimicrobial resistant Escherichia coli (E. coli) of animal origins have been conducted around the world, most of them focus on bacteria from animals raised in intensive breeding farms, but systematic studies on antimicrobial resistance in E. coli of free range animals are still lacking. Methodology: This study aimed to investigate the prevalence and antimicrobial resistance profiles of E. coli from free-range pigs in Laiwu mountainous areas, eastern China. Results: Among 123 fecal samples, 123 non-duplicate E. coli were obtained with an isolation rate of 100.0％ (123/123). These E. coli showed the highest resistance rate to tetracycline (77/123, 62.6％), but all were sensitive to amoxicillin/clavulanic acid. Thirty-eight E. coli (38/123, 30.9％) showed multidrug resistance (MDR). Among 123 E. coli isolates, only 39 carried antimicrobial resistant genes detected in this study. Of these 39 isolates, blaTEM-1, blaCTX-M-14, blaCTX-M-15, qnrB, qnrD, qnrS1, floR and cfr genes were detected in 13, 9, 4, 7, 10, 7, 20, and 7 isolates, respectively. blaTEM-1 and blaCTX-M-14 genes were concomitantly detected in 6 isolates, and blaTEM, qnrB, qnrS and qnrD genes were concomitantly detected in 7 isolates. Conclusions: Free-ranging pigs may be regarded as a potential reservoir for antibiotic resistant genes.

scholarly journals Antimicrobial Resistance Genes and Diversity of Clones among Faecal ESBL-Producing Escherichia coli Isolated from Healthy and Sick Dogs Living in Portugal

Antibiotics ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 1013
Author(s):  
Isabel Carvalho ◽  
Rita Cunha ◽  
Carla Martins ◽  
Sandra Martínez-Álvarez ◽  
Nadia Safia Chenouf ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Antimicrobial Resistance ◽  
Genetic Characteristics ◽  
E Coli ◽  
Faecal Samples ◽  
Antimicrobial Resistance Genes ◽  
Healthy Dogs ◽  
Positive Isolate ◽  
Sequence Types ◽  
M 14

The purpose of this study was to analyse the prevalence and genetic characteristics of ESBL and acquired-AmpC (qAmpC)-producing Escherichia coli isolates from healthy and sick dogs in Portugal. Three hundred and sixty-one faecal samples from sick and healthy dogs were seeded on MacConkey agar supplemented with cefotaxime (2 µg/mL) for cefotaxime-resistant (CTXR) E. coli recovery. Antimicrobial susceptibility testing for 15 antibiotics was performed and the ESBL-phenotype of the E. coli isolates was screened. Detection of antimicrobial resistance and virulence genes, and molecular typing of the isolates (phylogroups, multilocus-sequence-typing, and specific-ST131) were performed by PCR (and sequencing when required). CTXRE. coli isolates were obtained in 51/361 faecal samples analysed (14.1%), originating from 36/234 sick dogs and 15/127 healthy dogs. Forty-seven ESBL-producing E. coli isolates were recovered from 32 sick (13.7%) and 15 healthy animals (11.8%). Different variants of blaCTX-M genes were detected among 45/47 ESBL-producers: blaCTX-M-15 (n = 26), blaCTX-M-1 (n = 10), blaCTX-M-32 (n = 3), blaCTX-M-55 (n = 3), blaCTX-M-14 (n = 2), and blaCTX-M-variant (n = 1); one ESBL-positive isolate co-produced CTX-M-15 and CMY-2 enzymes. Moreover, two additional CTXR ESBL-negative E. coli isolates were CMY-2-producers (qAmpC). Ten different sequence types were identified (ST/phylogenetic-group/β-lactamase): ST131/B2/CTX-M-15, ST617/A/CTX-M-55, ST3078/B1/CTX-M-32, ST542/A/CTX-M-14, ST57/D/CTX-M-1, ST12/B2/CTX-M-15, ST6448/B1/CTX-M-15 + CMY-2, ST5766/A/CTX-M-32, ST115/D/CMY-2 and a new-ST/D/CMY-2. Five variants of CTX-M enzymes (CTX-M-15 and CTX-M-1 predominant) and eight different clonal complexes were detected from canine ESBL-producing E. coli isolates. Although at a lower rate, CMY-2 β-lactamase was also found. Dogs remain frequent carriers of ESBL and/or qAmpC-producing E. coli with a potential zoonotic role.

Non-O157 Verotoxin-Producing Escherichia coli: A Problem, Paradox, and Paradigm

2003 ◽  
Vol 228 (4) ◽  
pp. 333-344 ◽  
Author(s):  
Karl A. Bettelheim
Keyword(s):  
Escherichia Coli ◽  
Animal Health ◽  
Domestic Animals ◽  
Emerging Pathogens ◽  
E Coli ◽  
The Impact ◽  
Identification And Characterization

The problems associated with identification and characterization of non-O157 verotoxin-producing Escherichia coli (VTEC) are discussed. The paradox of VTEC is that most reports of human illnesses are associated with serotypes such as O157:H7, O111:H– (nonmotile), O26:H11, and O113:H21, which are rarely found in domestic animals. However, those VTEC serotypes commonly found in domestic animals, especially ruminants, rarely cause human illnesses. When they cause human illnesses, the symptoms are similar to those caused by the serotypes E. coli O157:H7, O111:H–, O26:H11, and O113:H21. The impact of VTEC on human and animal health is also addressed. The VTEC and their toxicity are considered as a paradigm for emerging pathogens. The question on how such pathogens could arise from a basic commensal population is also addressed.

Coinfection with Human Norovirus and Escherichia coli O25:H4 Harboring Two Chromosomal blaCTX-M-14 Genes in a Foodborne Norovirus Outbreak in Shizuoka Prefecture, Japan

2020 ◽  
Vol 83 (9) ◽  
pp. 1584-1591
Author(s):  
HIROMI NAGAOKA ◽  
SHINICHIRO HIRAI ◽  
HIROTAKA MORINUSHI ◽  
SHIRO MIZUMOTO ◽  
KANA SUZUKI ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Antimicrobial Resistance ◽  
Resistance Genes ◽  
Human Norovirus ◽  
E Coli ◽  
Hospital Acquired Infections ◽  
Antimicrobial Resistance Genes ◽  
Hospital Acquired ◽  
Healthy Persons ◽  
M 14

ABSTRACT Hospital-acquired infections caused by extended-spectrum β-lactamase (ESBL)–producing Escherichia coli are a global problem. Healthy people can carry ESBL-producing E. coli in the intestines; thus, E. coli from healthy people can potentially cause hospital-acquired infections. Therefore, the transmission routes of ESBL-producing E. coli from healthy persons should be determined. A foodborne outbreak of human norovirus (HuNoV) GII occurred at a restaurant in Shizuoka, Japan, in 2018. E. coli O25:H4 was isolated from some of the HuNoV-infected customers. Pulsed-field gel electrophoresis showed that these E. coli O25:H4 strains originated from one clone. Because the only epidemiological link among the customers was eating food from this restaurant, the customers were concurrently infected with E. coli O25:H4 and HuNoV GII via the restaurant food. Whole genome analysis revealed that the E. coli O25:H4 strains possessed genes for regulating intracellular iron and expressing the flagellum and flagella. Extraintestinal pathogenic E. coli often express these genes on the chromosome. Additionally, the E. coli O25:H4 strains had plasmids harboring nine antimicrobial resistance genes. These strains harbored ESBL-encoding blaCTX-M-14 genes on two loci of the chromosome and had higher ESBL activity. Multilocus sequence typing and fimH subtyping revealed that the E. coli O25:H4 strains from the outbreak belonged to the subclonal group, ST131-fimH30R, which has been driving ESBL epidemics in Japan. Because the E. coli O25:H4 strains isolated in the outbreak belonged to a subclonal group spreading in Japan, foods contaminated with ESBL-producing E. coli might contribute to spreading these strains among healthy persons. The isolated E. coli O25:H4 strains produced ESBL and contained plasmids with multiple antimicrobial resistance genes, which may make it difficult to select antimicrobials for treating extraintestinal infections caused by these strains. HIGHLIGHTS

scholarly journals Molecular characterization of extended-spectrum β-lactamase-producing Escherichia coli isolates from chickens in Henan Province, China

2009 ◽  
Vol 58 (11) ◽  
pp. 1449-1453 ◽  
Author(s):  
Li Yuan ◽  
Jian-Hua Liu ◽  
Gong-Zheng Hu ◽  
Yu-Shan Pan ◽  
Zhi-Ming Liu ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Molecular Characterization ◽  
Antimicrobial Agents ◽  
Animal Health ◽  
Henan Province ◽  
E Coli ◽  
Nucleotide Base ◽  
Extended Spectrum ◽  
M 14

Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli has spread rapidly worldwide and poses a serious threat to human and animal health. This study collected 51 non-replicate E. coli isolates from 14 different chicken farms in Henan Province in China from December 2007 to August 2008. The prevalence of ESBL-producing E. coli, molecular characterization of the ESBL-related bla genes, including bla TEM, bla SHV and bla CTX-M, and the susceptibilities of these bacteria to various antimicrobial agents were determined. Thirty-one of the 51 isolates were positive for an ESBL phenotype and 29 of these isolates carried one or more bla genes. Twenty-two isolates harboured bla TEM genes and 15 isolates carried bla CTX-M genes (one CTX-M-14, three CTX-M-24 and 11 CTX-M-65). One isolate carried bla TEM -57; the remaining bla TEM isolates carried bla TEM-1 with one silent nucleotide base variation (T18C). We believe that this is the first study to report TEM-57 in E. coli isolates. All isolates harbouring bla CTX-M-24 and bla CTX-M-14 and five of the bla CTX-M-65 isolates also harboured the bla TEM-1 gene. To our knowledge, this study is the first to describe detection of CTX-M-65-producing E. coli isolated from chickens. None of the isolates contained the bla SHV gene. Conjugation experiments demonstrated that bla CTX-M and bla TEM genes could be transferred to E. coli DH5α. The results indicate that ESBL frequency has reached an alarming level in chicken isolates in China, with TEM-1 and CTX-M-65 enzymes being the two predominant β-lactamases detected.

scholarly journals Effects of In-Feed Chlortetracycline Prophylaxis in Beef Cattle on Animal Health and Antimicrobial-Resistant Escherichia coli

2016 ◽  
Vol 82 (24) ◽  
pp. 7197-7204 ◽  
Author(s):  
Getahun E. Agga ◽  
John W. Schmidt ◽  
Terrance M. Arthur
Keyword(s):  
Escherichia Coli ◽  
Antimicrobial Resistance ◽  
Human Health ◽  
Bacterial Infections ◽  
Animal Health ◽  
Agricultural Practices ◽  
Control Group ◽  
Content Type ◽  
E Coli ◽  
The Impact

ABSTRACTConcerns have been raised that in-feed chlortetracycline (CTC) may increase antimicrobial resistance (AMR), specifically tetracycline-resistant (TETr)Escherichia coliand third-generation cephalosporin-resistant (3GCr)E. coli. We evaluated the impact of a 5-day in-feed CTC prophylaxis on animal health, TETrE. coli, and 3GCrE. coli. A control group of cattle (n= 150) received no CTC, while a CTC group (n= 150) received in-feed CTC (10 mg/lb of body weight/day) from the 5th to the 9th day after feedlot arrival. Over 25% (38/150) of the animals in the control group developed illnesses requiring therapeutic treatment with antimicrobials critically important to human medicine. Only two animals (1.3%) in the CTC group required such treatments. Fecal swab and pen surface occurrences of genericE. coli(isolated on media that did not contain antimicrobials of interest and were not isolated based on any specific resistance), TETrE. coli, and 3GCrE. coliwere determined on five sampling occasions: arrival at the feedlot, 5 days posttreatment (5 dpt), 27 dpt, 75 dpt, and 117 dpt. On 5 dpt, TETrE. coliconcentrations were higher for the CTC group than the control group (P< 0.01). On 27 dpt, 75 dpt, and 117 dpt, TETrE. coliconcentrations did not differ between groups. 3GCrE. colioccurrences did not differ between control and CTC groups on any sampling occasion. For both groups, generic, TETr, and 3GCrE. colioccurrences were highest on 75 dpt and 117 dpt, suggesting that factors other than in-feed CTC contributed more significantly to antimicrobial-resistantE. colioccurrence.IMPORTANCEThe occurrence of human bacterial infections resistant to antimicrobial therapy has been increasing. It has been postulated that antimicrobial resistance was inevitable, but the life span of the antimicrobial era has been prematurely compromised due to the misuse of antimicrobials in clinical and agricultural practices. Direct evidence relating the use of antimicrobials in livestock production to diminished human health outcomes due to antimicrobial resistance is lacking, and the U.S. Food and Drug Administration has taken an approach to maximize therapeutic efficacy and minimize the selection of resistant microorganisms through judicious use of antimicrobials. This study demonstrated that prophylactic in-feed treatment of chlortetracycline administered for 5 days to calves entering feedlots is judicious, as this therapy reduced animal morbidity, reduced the use of antimicrobials more critical to human health, and had no long-term impact on the occurrence of antimicrobial-resistantE. coli.

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