Avian pathogenic Escherichia coli (APEC) and uropathogenic Escherichia coli (UPEC): characterization and comparison

Introduction: Avian pathogenic E. coli (APEC) and uropathogenic E. coli (UPEC) are responsible for avian colibacillosis and human urinary tract infections, respectively. There are genetic similarities between the APEC and UPEC pathotypes, suggesting the APEC strains could be a potential reservoir of virulence and antimicrobial-resistance genes for the UPEC strains. This study aimed to characterize and compare APEC and UPEC strains regarding the phylogroup classification, pathogenicity and antimicrobial susceptibility. Methodology: A total of 238 APEC and 184 UPEC strains were selected and characterized. The strains were assayed for antimicrobial susceptibility and classified into phylogenetic groups using a multiplex-PCR protocol. In addition, the APEC strains had previously been classified according to their in vivo pathogenicity. Results: The results showed that both pathotypes had variation in their susceptibility to most of the antimicrobial agents evaluated, with few strains classified as multidrug resistant. The highest resistance rate for both pathotypes was to amoxicillin. Classifying the APEC and UPEC strains into phylogenetic groups determined that the most frequently frequencies were for groups D and B2, respectively. These results reflect the pathogenic potential of these strains, as all the UPEC strains were isolated from unhealthy patients, and most of the APEC strains were previously classified as pathogenic. Conclusions: The results indicate that distribution into phylogenetic groups provided, in part, similar classification to those of in vivo pathogenicity index, as it was possible to adequately differentiate most of the pathogenic and commensal or low-pathogenicity bacteria. However, no relationship could be found between the specific antimicrobial agents and pathogenicity or phylogenetic group for either pathotype.

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Antimicrobial susceptibility and pathogenicity of Escherichia coli strains of environmental origin

Ciência Rural ◽

10.1590/0103-8478cr20141020 ◽

2015 ◽

Vol 45 (7) ◽

pp. 1249-1255 ◽

Cited By ~ 5

Author(s):

Daiane Carvalho ◽

Fabrine Finkler ◽

Tiela Trapp Grassotti ◽

Hiran Castagnino Kunert Filho ◽

Francisco Esmaile de Sales Lima ◽

...

Keyword(s):

Escherichia Coli ◽

Antimicrobial Susceptibility ◽

Disc Diffusion ◽

Diffusion Test ◽

Pathogenic Potential ◽

Highly Pathogenic ◽

E Coli ◽

Intermediate Degree

The study aimed to evaluate the antimicrobial susceptibility of 109 samples of Escherichia coli (E. coli) of environmental origin and to characterize these isolates according to the degree of pathogenicity in vivo, verifying a possible relationship between this variable and susceptibility to the active principles tested. The isolates were subjected to disc diffusion test to 14 antibiotics. From 16.5% to 90% of the samples were sensitive; 1 - 28.5% showed intermediate degree of susceptibility and between 9 to 78% of E. coli analyzed were resistant. The highest resistance percentages were seen in the class of quinolones and tetracyclines (>75%), and for sensitivity in the class of amphenicols (68.8%). By inoculating 1- day - old chicks, the isolates were classified as highly pathogenic (2.7%), intermediate (10.1%), low (42.2%) and apathogenic (45%). It was observed a wide variation in the susceptibility profile of isolates in relation to antimicrobials. It was also found that most of the samples had pathogenic potential (55%), thus being considered as APEC (avian pathogenic E. coli). No relationship between pathogenicity and antimicrobial susceptibility (P≤0.05) was observed.

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Phylogenetic groups and antimicrobial susceptibility patterns of uropathogenic Escherichia coli clinical isolates from patients at Mulago National Referral Hospital, Kampala, Uganda

F1000Research ◽

10.12688/f1000research.20930.1 ◽

2019 ◽

Vol 8 ◽

pp. 1828 ◽

Cited By ~ 1

Author(s):

Paul Katongole ◽

Daniel Bulwadda Kisawuzi ◽

Henry Kyobe Bbosa ◽

David Patrick Kateete ◽

Christine Florence Najjuka

Keyword(s):

Escherichia Coli ◽

Antimicrobial Susceptibility ◽

Phylogenetic Group ◽

Diffusion Method ◽

Clinical Microbiology Laboratory ◽

Phylogenetic Groups ◽

E Coli ◽

Pcr Method ◽

Tract Infections ◽

Susceptibility Patterns

Introduction: Uropathogenic Escherichia coli (UPEC) remains the most common cause of urinary tract infections (UTIs). They account for over 80-90% of all community-acquired and 30-50% of all hospital-acquired UTIs. E. coli strains have been found to belong to evolutionary origins known as phylogenetic groups. In 2013, Clermont classified E. coli strains into eight phylogenetic groups using the quadruplex PCR method. The aim of this study was to identify the phylogenetic groups of UPEC strains in Uganda using Clermont’s quadruplex PCR method and to assess their antibiotic susceptibility patterns in Uganda. Methods: In this cross-sectional study, 140 stored uropathogenic E. coli isolates from the Clinical Microbiology Laboratory, Department of Medical Microbiology, College of Health Sciences Makerere University were subjected to phylogenetic typing by a quadruplex PCR method. Antimicrobial susceptibility testing was performed by disk diffusion method according to Clinical & Laboratory Standards Institute (CLSI) guidelines. Phenotypic detection of extended-spectrum beta-lactamase, AmpC and carbapenemases was done according to CLSI guidelines and Laboratory SOPs. Results: Phylogenetic group B2 (40%) was the most predominant, followed by A (6.23%), clade I and II (5%), D and E (each 2.14%), B1 (1.43%) and F and C (each 0.71%). The most common resistant antibiotic was trimethoprim-sulphamethoxazole (90.71%) and the least was imipenem (1.43%). In total, 73.57% of isolates were multi-drug resistant (MDR). Antibiotic resistance was mainly detected in phylogenetic group B2 (54%). Conclusions: Our findings showed the high prevalence of MDR E. coli isolates, with the dominance of phylogenetic group B2. About 9% of E. coli isolates belonged to the newly described phylogroups C, E, F, and clade I and II.

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Characterization of multidrug-resistant Escherichia coli isolated from extraintestinal clinical infections in animals

Journal of Medical Microbiology ◽

10.1099/jmm.0.018002-0 ◽

2010 ◽

Vol 59 (5) ◽

pp. 592-598 ◽

Cited By ~ 19

Author(s):

Justine S. Gibson ◽

Rowland N. Cobbold ◽

Darren J. Trott

Keyword(s):

Escherichia Coli ◽

Antimicrobial Susceptibility ◽

Animal Species ◽

Antimicrobial Agents ◽

Multidrug Resistant ◽

Phylogenetic Group ◽

Phylogenetic Groups ◽

Diagnostic Laboratory ◽

E Coli

Multidrug-resistant (MDR) Escherichia coli causes extraintestinal infections in both humans and animals. This study aimed to determine whether MDR E. coli isolates cultured from extraintestinal infections in several animal species were clonal and crossed host-species boundaries, as suggested by initial characterization of a subset of canine and human isolates, or whether they represented a diverse group of host-specific strains. Isolates were obtained either from The University of Queensland Veterinary Diagnostic Laboratory or from an independent diagnostic laboratory between October 1999 and December 2007. Ninety-six MDR E. coli isolates cultured from extraintestinal clinical infections in 55 animals comprising dogs (n=45), cats (n=5), horses (n=4) and a koala (n=1) were analysed by phylogenetic grouping, antimicrobial susceptibility testing and PFGE. The isolates were cultured from the urinary tract (n=61), reproductive tract (n=11), wounds (n=11), surgical site infections (n=4) and other sites (n=9). Isolates from the same E. coli phylogenetic group with 100 % PFGE similarity and the same antimicrobial susceptibility pattern were considered to be repeat clones and excluded from further analysis. Three of the four E. coli phylogenetic groups (A, n=19; B1, n=8; and D, n=49) were represented. Analysis of PFGE similarity identified clusters of related phylogenetic group A isolates [clonal group (CG) 1] and group D isolates (CG2 and CG3), with the remainder of the isolates demonstrating diversity. The majority of CG2 isolates contained a plasmid-borne AmpC β-lactamase, imparting resistance to cefoxitin and third-generation cephalosporins, and were obtained between 2000 and 2003. CG3 isolates were sensitive to these antimicrobial agents and appeared to replace CG2 isolates as the dominant clones from 2003 to 2007. Apart from several canine and feline isolates that demonstrated clonality, PFGE profiles tended to be divergent across species. Whilst MDR E. coli isolates from extraintestinal infections in different animal species are diverse, some dominant CGs may persist over several years.

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Population structure and uropathogenic potential of extended-spectrum cephalosporin-resistant Escherichia coli from retail chicken meat

BMC Microbiology ◽

10.1186/s12866-021-02160-y ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

May Linn Buberg ◽

Solveig Sølverød Mo ◽

Camilla Sekse ◽

Marianne Sunde ◽

Yngvild Wasteson ◽

...

Keyword(s):

Escherichia Coli ◽

Antimicrobial Resistance ◽

Monitoring Program ◽

Chicken Meat ◽

Pathogenic Potential ◽

E Coli ◽

Extended Spectrum ◽

Antimicrobial Resistance Genes ◽

Tract Infections ◽

Retail Chicken Meat

Abstract Background Food-producing animals and their products are considered a source for human acquisition of antimicrobial resistant (AMR) bacteria, and poultry are suggested to be a reservoir for Escherichia coli resistant to extended-spectrum cephalosporins (ESC), a group of antimicrobials used to treat community-onset urinary tract infections in humans. However, the zoonotic potential of ESC-resistant E. coli from poultry and their role as extraintestinal pathogens, including uropathogens, have been debated. The aim of this study was to characterize ESC-resistant E. coli isolated from domestically produced retail chicken meat regarding their population genetic structure, the presence of virulence-associated geno- and phenotypes as well as their carriage of antimicrobial resistance genes, in order to evaluate their uropathogenic potential. Results A collection of 141 ESC-resistant E. coli isolates from retail chicken in the Norwegian monitoring program for antimicrobial resistance in bacteria from food, feed and animals (NORM-VET) in 2012, 2014 and 2016 (n = 141) were whole genome sequenced and analyzed. The 141 isolates, all containing the beta-lactamase encoding gene blaCMY-2, were genetically diverse, grouping into 19 different sequence types (STs), and temporal variations in the distribution of STs were observed. Generally, a limited number of virulence-associated genes were identified in the isolates. Eighteen isolates were selected for further analysis of uropathogen-associated virulence traits including expression of type 1 fimbriae, motility, ability to form biofilm, serum resistance, adhesion- and invasion of eukaryotic cells and colicin production. These isolates demonstrated a high diversity in virulence-associated phenotypes suggesting that the uropathogenicity of ESC-resistant E. coli from chicken meat is correspondingly highly variable. For some isolates, there was a discrepancy between the presence of virulence-associated genes and corresponding expected phenotype, suggesting that mutations or regulatory mechanisms could influence their pathogenic potential. Conclusion Our results indicate that the ESC-resistant E. coli from chicken meat have a low uropathogenic potential to humans, which is important knowledge for improvement of future risk assessments of AMR in the food chains.

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Antimicrobial Resistance Genes and Diversity of Clones among ESBL- and Acquired AmpC-Producing Escherichia coli Isolated from Fecal Samples of Healthy and Sick Cats in Portugal

Antibiotics ◽

10.3390/antibiotics10030262 ◽

2021 ◽

Vol 10 (3) ◽

pp. 262

Author(s):

Isabel Carvalho ◽

Nadia Safia Chenouf ◽

Rita Cunha ◽

Carla Martins ◽

Paulo Pimenta ◽

...

Keyword(s):

Escherichia Coli ◽

Public Health Problem ◽

Phylogenetic Groups ◽

Disk Diffusion Test ◽

Extended Spectrum Beta Lactamase ◽

E Coli ◽

Specific Pcr ◽

Flight Mass Spectrometry ◽

Antimicrobial Resistance Genes ◽

Esbl Producers

The aim of the study was to analyze the mechanisms of resistance in extended-spectrum beta-lactamase (ESBL)- and acquired AmpC (qAmpC)-producing Escherichia coli isolates from healthy and sick cats in Portugal. A total of 141 rectal swabs recovered from 98 sick and 43 healthy cats were processed for cefotaxime-resistant (CTXR) E. coli recovery (in MacConkey agar supplemented with 2 µg/mL cefotaxime). The matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) method was used for E. coli identification and antimicrobial susceptibility was performed by a disk diffusion test. The presence of resistance/virulence genes was tested by PCR sequencing. The phylogenetic typing and multilocus sequence typing (MLST) were determined by specific PCR sequencing. CTXRE. coli isolates were detected in seven sick and six healthy cats (7.1% and 13.9%, respectively). Based on the synergy tests, 11 of 13 CTXRE. coli isolates (one/sample) were ESBL-producers (ESBL total rate: 7.8%) carrying the following ESBL genes: blaCTX-M-1 (n = 3), blaCTX-M-15 (n = 3), blaCTX-M-55 (n = 2), blaCTX-M-27 (n = 2) and blaCTX-M-9 (n = 1). Six different sequence types were identified among ESBL-producers (sequence type/associated ESBLs): ST847/CTX-M-9, CTX-M-27, CTX-M-1; ST10/CTX-M-15, CTX-M-27; ST6448/CTX-M-15, CTX-M-55; ST429/CTX-M-15; ST101/CTX-M-1 and ST40/CTX-M-1. Three of the CTXR isolates were CMY-2-producers (qAmpC rate: 2.1%); two of them were ESBL-positive and one ESBL-negative. These isolates were typed as ST429 and ST6448 and were obtained in healthy or sick cats. The phylogenetic groups A/B1/D/clade 1 were detected among ESBL- and qAmpC-producing isolates. Cats are carriers of qAmpC (CMY-2)- and ESBL-producing E. coli isolates (mostly of variants of CTX-M group 1) of diverse clonal lineages, which might represent a public health problem due to the proximity of cats with humans regarding a One Health perspective.

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Three-Year Trend in Escherichia coli Antimicrobial Resistance among Children’s Urine Cultures in an Italian Metropolitan Area

Children ◽

10.3390/children8070597 ◽

2021 ◽

Vol 8 (7) ◽

pp. 597

Author(s):

Luca Pierantoni ◽

Laura Andreozzi ◽

Simone Ambretti ◽

Arianna Dondi ◽

Carlotta Biagi ◽

...

Keyword(s):

Escherichia Coli ◽

Metropolitan Area ◽

Bacterial Infections ◽

Asymptomatic Bacteriuria ◽

Multidrug Resistant ◽

Resistance Rate ◽

First Line ◽

E Coli ◽

First Line Therapy ◽

Tract Infections

Urinary tract infections (UTIs) are among the most common bacterial infections in children, and Escherichia coli is the main pathogen responsible. Several guidelines, including the recently updated Italian guidelines, recommend amoxicillin-clavulanic acid (AMC) as a first-line antibiotic therapy in children with febrile UTIs. Given the current increasing rates of antibiotic resistance worldwide, this study aimed to investigate the three-year trend in the resistance rate of E. coli isolated from pediatric urine cultures (UCs) in a metropolitan area of northern Italy. We conducted a retrospective review of E. coli-positive, non-repetitive UCs collected in children aged from 1 month to 14 years, regardless of a diagnosis of UTI, catheter colonization, urine contamination, or asymptomatic bacteriuria. During the study period, the rate of resistance to AMC significantly increased from 17.6% to 40.2% (p < 0.001). Ciprofloxacin doubled its resistance rate from 9.1% to 16.3% (p = 0.007). The prevalence of multidrug-resistant E. coli rose from 3.9% to 9.2% (p = 0.015). The rate of resistance to other considered antibiotics remained stable, as did the prevalence of extended spectrum beta-lactamases and extensively resistant E. coli among isolates. These findings call into question the use of AMC as a first-line therapy for pediatric UTIs in our population, despite the indications of recent Italian guidelines.

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Biological Cost of Single and Multiple Norfloxacin Resistance Mutations in Escherichia coli Implicated in Urinary Tract Infections

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.49.6.2343-2351.2005 ◽

2005 ◽

Vol 49 (6) ◽

pp. 2343-2351 ◽

Cited By ~ 91

Author(s):

Patricia Komp Lindgren ◽

Linda L. Marcusson ◽

Dorthe Sandvang ◽

Niels Frimodt-Møller ◽

Diarmaid Hughes

Keyword(s):

Escherichia Coli ◽

Urinary Tract ◽

Infection Model ◽

Resistance Mutations ◽

Topoisomerase Iv ◽

E Coli ◽

Tract Infections ◽

Subsequent Selection

ABSTRACT Resistance to fluoroquinolones in urinary tract infection (UTIs) caused by Escherichia coli is associated with multiple mutations, typically those that alter DNA gyrase and DNA topoisomerase IV and those that regulate AcrAB-TolC-mediated efflux. We asked whether a fitness cost is associated with the accumulation of these multiple mutations. Mutants of the susceptible E. coli UTI isolate Nu14 were selected through three to five successive steps with norfloxacin. Each selection was performed with the MIC of the selected strain. After each selection the MIC was measured; and the regions of gyrA, gyrB, parC, and parE, previously associated with resistance mutations, and all of marOR and acrR were sequenced. The first selection step yielded mutations in gyrA, gyrB, and marOR. Subsequent selection steps yielded mutations in gyrA, parE, and marOR but not in gyrB, parC, or acrR. Resistance-associated mutations were identified in almost all isolates after selection steps 1 and 2 but in less than 50% of isolates after subsequent selection steps. Selected strains were competed in vitro, in urine, and in a mouse UTI infection model against the starting strain, Nu14. First-step mutations were not associated with significant fitness costs. However, the accumulation of three or more resistance-associated mutations was usually associated with a large reduction in biological fitness, both in vitro and in vivo. Interestingly, in some lineages a partial restoration of fitness was associated with the accumulation of additional mutations in late selection steps. We suggest that the relative biological costs of multiple mutations may influence the evolution of E. coli strains that develop resistance to fluoroquinolones.

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Frequency and antimicrobial susceptibility pattern of hospital isolates of Escherichia coli and Klebsiella pneumoniae in urine samples

Acta Medica Saliniana ◽

10.5457/ams.v49i0.527 ◽

2019 ◽

Vol 49 ◽

Author(s):

Ivana Jukić ◽

Danijel Topić ◽

El-Jesah Đulić ◽

Amela Dedeić- Ljubović

Keyword(s):

Escherichia Coli ◽

Antimicrobial Susceptibility ◽

Public Health Problem ◽

Urine Samples ◽

Distribution Analysis ◽

Susceptibility Pattern ◽

E Coli ◽

Antimicrobial Susceptibility Pattern ◽

Urinary Infections ◽

Tract Infections

Objectives/Aim: Urinary tract infections (UTI) are a serious public health problem and caused by many pathogens, most often by Escherichia coli and Klebsiella pneumoniae.Aim of this study was to show the frequency and antimicrobial susceptibility pattern of E. coli and K. pneumoniae in hospital isolates, following the GLASS methodology.Methods: This is a retrospective study that was conducted in the Laboratory for Urinary Infections OU Clinical Microbiology CCUS in the period from January till December 2018.A total of 13760 urine samples were processed, using standard laboratory methods, in which significant bacteriuria was detected in 3218 (23.4%) of specimens.Results: Out of the total number of positive samples, E. coli was isolated in 1166 (36.2%) and K. pneumoniae at 341 (10.6%) patients. The presence of E. coli and K. pneumoniae isolates is dominant in females (1103/73.2%) and age group 60 and older (812/54.7%). Out of the total E. coli isolates, the ESBL strain was presented with 79 (6.8%) and K. pneumoniae with 145 (42.5%). The proportion of carbapenemase (CPE) produced by K. pneumoniae isolates was 8 (2.4%). The ESBL strain distribution analysis on clinics showed the highest prevalence of both isolates at the Clinic for Nephrology: K. pneumoniae 26/17,9%; E. coli: 12/15.4%. Isolated E. coli showed the highest resistance to ampicillin 673/1166 (57,7%), trimethoprim-sulfamethoxazole 454/1166 (38.9%) and ciprofloxacin 253/970 (26.1%), while K. pneumoniae to ciprofloxacin and trimethoprim-sulfamethoxazole with 151/285 (53.0%) and 164/341 (48.1%), respectively.Conclusions: Our study has shown that the most common cause of urinary infections in hospital settings are E. coli and K. pneumoniae. Data analysis showed that the presence of ESBL isolates was significantly higher in K. pneumoniae than E. coli. CPE isolates of K. pneumoniae were also detected.

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Detection of virulence genes and antimicrobial resistance profiles of Escherichia coli isolates from raw milk and artisanal cheese in Southern Brazil

Semina Ciências Agrárias ◽

10.5433/1679-0359.2019v40n1p163 ◽

2019 ◽

Vol 40 (1) ◽

pp. 163 ◽

Cited By ~ 3

Author(s):

Leandro Parussolo ◽

Ricardo Antônio Pilegi Sfaciotte ◽

Karine Andrezza Dalmina ◽

Fernanda Danielle Melo ◽

Ubirajara Maciel Costa ◽

...

Keyword(s):

Public Health ◽

Escherichia Coli ◽

Antimicrobial Susceptibility ◽

Virulence Genes ◽

Antimicrobial Agents ◽

Raw Milk ◽

Diffusion Method ◽

Public Health Issue ◽

Southern Brazil ◽

E Coli

The serrano artisanal cheese is a typical product from South region of Brazil, which is produced by skilled cheesemakers using raw milk. The contamination of this food by Escherichia coli has a great impact on public health, since it could threat the consumers’ health. The study evaluated the presence of virulence genes, antimicrobial susceptibility profiles and bofilm-production ability of Escherichia coli isolates obtained from raw milk and artisanal cheese produced in Southern Brazil. A total of 117 isolates of E. coli were characterized by multiplex PCR to detect the following virulence genes: eae for enteropatogenic E. coli (EPEC), lt and st for enterotoxigenic E. coli (ETEC), stx for shiga toxin-producing E. coli (STEC), stx and eae for enterohemorrhagic E. coli (EHEC), ipaH for enteroinvasive E. coli (EIEC) and aggR for enteroaggregative E. coli (EAEC). In addition, antimicrobial susceptibility profile to 22 antimicrobial agents was also performed by disk diffusion method, and we searched for extended-spectrum beta-lactamases (ESBL) and/or carbapenemase- producing isolates. Isolates that were positive for ESBL and carbapenemase were further investigated for the presence of the genes: blaTEM, blaSHV, blaOXA, blaCTX-M, for ESBL and blaOXA-48 for carbapenemase. Further, isolates had their ability to form biofilms investigated by the red Congo agar method. Virulence genes of E. coli were identified in 21.37% of the tested isolates, which were classified as EPEC (the most prevalent pathotype) and ETEC or EAEC. Ten (8.55%) of the total studied E. coli isolates revealed a multidrug-resistant profile, since they were resistant to three or more antimicrobial classes; whereas four isolates (3.42%) were classified as ESBL-producers and showed the presence of blaTEM gene. None of the isolates exhibited carbapenemase activity nor did they carry carbapenemase genes. From the total of E. coli isolates, 79 (67.52%) were considered potential biofilm producers. These results address a serious public health issue, since artisanal cheeses pose a risk to consumers’ health, since may be sources of dissemination of diarrheogenic E. coli, that can cause from subclinical to severe and fatal infections in children and adults, and also emphasize the need to improve adaptations/adjustments in the manufacturing processes of these products.

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Evaluation of Immunocompetent Urinary Tract Infected Balb/C Mouse Model For the Study of Antibiotic Resistance Development Using Escherichia Coli CFT073 Infection

Antibiotics ◽

10.3390/antibiotics8040170 ◽

2019 ◽

Vol 8 (4) ◽

pp. 170 ◽

Cited By ~ 1

Author(s):

Ashok Chockalingam ◽

Sharron Stewart ◽

Lin Xu ◽

Adarsh Gandhi ◽

Murali K. Matta ◽

...

Keyword(s):

Escherichia Coli ◽

Antibiotic Resistance ◽

Urinary Tract ◽

Bladder Tissue ◽

Resistance Development ◽

Once Daily ◽

E Coli ◽

Low Levels ◽

Tract Infections

Urinary tract infections (UTI) are common worldwide and are becoming increasingly difficult to treat because of the development of antibiotic resistance. Immunocompetent murine models of human UTI have been used to study pathogenesis and treatment but not for investigating resistance development after treatment with antibiotics. In this study, intravesical inoculation of uropathogenic Escherichia coli CFT073 in immunocompetent Balb/c mice was used as a model of human UTI. The value of the model in investigating antibiotic exposure on in vivo emergence of antibiotic resistance was examined. Experimentally infected mice were treated with 20 or 200 mg/kg ampicillin, 5 or 50 mg/kg ciprofloxacin, or 100 or 1000 mg/kg of fosfomycin. Ampicillin and ciprofloxacin were given twice daily at 8 h intervals, and fosfomycin was given once daily. Antibiotic treatment began 24 h after bacterial inoculation and ended after 72 h following the initial treatment. Although minimum inhibitory concentrations (MIC) for the experimental strain of E. coli were exceeded at peak concentrations in tissues and consistently in urine, low levels of bacteria persisted in tissues in all experiments. E. coli from bladder tissue, kidney, and urine grew on plates containing 1× MIC of antibiotic, but none grew at 3× MIC. This model is not suitable for studying emergent resistance but might serve to examine bacterial persistence.

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