scholarly journals Characterisation of AmpC Hyper-Producing Escherichia coli from Humans and Dairy Farms Collected in Parallel in the Same Geographical Region

2019 ◽  
Author(s):  
Maryam Alzayn ◽  
Jacqueline Findlay ◽  
Hannah Schubert ◽  
Oliver Mounsey ◽  
Virginia C. Gould ◽  
...  
Keyword(s):  
Risk Factors ◽  
Phylogenetic Analysis ◽  
Human Population ◽  
Dairy Farms ◽  
Generation Cephalosporin ◽  
Adaptive Mutations ◽  
E Coli ◽  
Increased Risk ◽  
Amoxicillin Clavulanate ◽  
Cephalosporin Resistance

AbstractObjectivesTo characterise putative AmpC hyper-producing 3rd generation cephalosporin-resistant E. coli from dairy farms and their phylogenetic relationships as well as to identify risk factors for their presence; to assess evidence for their zoonotic transmission into the local human populationMethodsProteomics was used to explain differences in antimicrobial susceptibility. Whole genome sequencing allowed phylogenetic analysis. Multilevel, multivariable logistic regression modelling was used to identify risk factors.ResultsIncreased use of amoxicillin-clavulanate was associated with an increased risk of finding AmpC hyper-producers on farms. Expansion of cephalosporin resistance in AmpC hyper-producers was seen in farm isolates with marR mutations (conferring cefoperazone resistance) or when AmpC was mutated (conferring 4th generation cephalosporin and cefoperazone resistance). Phylogenetic analysis confirmed the dominance of ST88 amongst farm AmpC hyper-producers but there was no evidence for acquisition of farm isolates by members of the local human population.ConclusionsIn this two-year surveillance study of 53 dairy farms, AmpC hyper-production was the cause of cefotaxime resistance in 46.2% of E. coli. There was evidence of recent farm-to-farm transmission and of adaptive mutations to expand resistance. Whilst there was no evidence of isolates entering the local human population, efforts to reduce 3rd generation cephalosporin resistance on dairy farms must address the high prevalence of AmpC hyper-producers. The finding that amoxicillin-clavulanate use was associated with increased risk of finding AmpC hyper-producers is important because this is not currently categorised as a highest-priority critically important antimicrobial and so is not currently targeted for specific usage restrictions in the UK.

scholarly journals Characterization of AmpC-hyperproducing Escherichia coli from humans and dairy farms collected in parallel in the same geographical region

2020 ◽  
Vol 75 (9) ◽  
pp. 2471-2479 ◽  
Author(s):  
Maryam Alzayn ◽  
Jacqueline Findlay ◽  
Hannah Schubert ◽  
Oliver Mounsey ◽  
Virginia C Gould ◽  
...  
Keyword(s):  
Risk Factors ◽  
Phylogenetic Analysis ◽  
Human Population ◽  
Dairy Farms ◽  
Generation Cephalosporin ◽  
Third Generation ◽  
E Coli ◽  
Increased Risk ◽  
Amoxicillin Clavulanate ◽  
Cephalosporin Resistance

Abstract Objectives To characterize putative AmpC-hyperproducing third-generation cephalosporin-resistant E. coli from dairy farms and their phylogenetic relationships; to identify risk factors for their presence; and to assess evidence for their zoonotic transmission into the local human population. Methods Proteomics was used to explain differences in antimicrobial susceptibility. WGS allowed phylogenetic analysis. Multilevel, multivariable logistic regression modelling was used to identify risk factors. Results Increased use of amoxicillin/clavulanate was associated with an increased risk of finding AmpC hyperproducers on farms. Expansion of cephalosporin resistance in AmpC hyperproducers was seen in farm isolates with marR mutations (conferring cefoperazone resistance) or when AmpC was mutated (conferring fourth-generation cephalosporin and cefoperazone resistance). Phylogenetic analysis confirmed the dominance of ST88 amongst farm AmpC hyperproducers but there was no evidence for acquisition of farm isolates by members of the local human population. Conclusions Clear evidence was found for recent farm-to-farm transmission of AmpC-hyperproducing E. coli and of adaptive mutations to expand resistance. Whilst there was no evidence of isolates entering the local human population, efforts to reduce third-generation cephalosporin resistance on dairy farms must address the high prevalence of AmpC hyperproducers. The finding that amoxicillin/clavulanate use was associated with an increased risk of finding AmpC hyperproducers is important because this is not currently categorized as a highest-priority critically important antimicrobial and so is not currently targeted for specific usage restrictions in the UK.

scholarly journals Fluoroquinolone-Resistant Escherichia coli Originating on Dairy Farms are an Infrequent Cause of Bacteriuria in Humans Living in the Same Geographical Region

2021 ◽  
Author(s):  
Oliver Mounsey ◽  
Hannah Schubert ◽  
Jacqueline Findlay ◽  
Katy Morley ◽  
Emma F. Puddy ◽  
...  
Keyword(s):  
Risk Factors ◽  
Escherichia Coli ◽  
Positive Association ◽  
Dairy Farms ◽  
Generation Cephalosporin ◽  
Geographical Region ◽  
E Coli ◽  
Dry Cow Therapy ◽  
On Farm ◽  
South West England

SynopsisBackgroundOur primary aim was to test whether cattle-associated fluoroquinolone-resistant (FQ-R) Escherichia coli found on dairy farms were a significant cause of bacteriuria in humans living in the same 50 x 50 km geographical region located in South West England. Another aim was to identify risk factors for the presence of FQ-R E. coli on dairy farms.MethodsFQ-R E. coli were isolated during 2017-18 from 42 dairy farms and from community urine samples. Forty-two cattle and 489 human urinary isolates were subjected to WGS, allowing phylogenetic comparisons. Risk factors were identified using a Bayesian regularisation approach.ResultsOf 489 FQ-R human isolates, 255 were also 3rd generation cephalosporin-resistant (3GC-R), with strong genetic linkage between aac(6’)Ib-cr and blaCTX-M-15. We identified possible farm-to-human sharing for pairs of ST744 and ST162 isolates, but core genome SNP distances (71 and 63, respectively) were smaller in pairs of ST744 and ST162 isolates from different farms (7 and 3 SNPs, respectively). Total farm fluoroquinolone use showed a positive association with the odds of isolating FQ-R E. coli while total dry cow therapy use showed a negative association.ConclusionsThis work suggests that FQ-R E. coli found on dairy farms have a limited impact on community bacteriuria within the local human population, however, this appears greater than observed for 3GC-R E. coli when studied in parallel. Reducing fluoroquinolone use may reduce the on-farm prevalence of FQ-R E. coli, and this reduction may be greater when dry cow therapy is targeted to the ecology of resistant E. coli on the farm.

scholarly journals Risk Factors for Infection or Colonization with CTX-M Extended-Spectrum-β-Lactamase-Positive Escherichia coli

2012 ◽  
Vol 56 (11) ◽  
pp. 5575-5580 ◽  
Author(s):  
Jennifer H. Han ◽  
Kei Kasahara ◽  
Paul H. Edelstein ◽  
Warren B. Bilker ◽  
Ebbing Lautenbach
Keyword(s):  
Risk Factors ◽  
Escherichia Coli ◽  
Control Strategies ◽  
Content Type ◽  
E Coli ◽  
Extended Spectrum ◽  
Increased Risk ◽  
Urinary Culture ◽  
Multivariable Analyses ◽  
And Control

ABSTRACTThere has been a significant increase in the prevalence ofEnterobacteriaceaethat produce CTX-M-type extended-spectrum β-lactamases. The objective of this study was to evaluate risk factors for infection or colonization with CTX-M-positiveEscherichia coli. A case-control study was conducted within a university system from 1 January 2007 to 31 December 2008. All patients with clinical cultures withE. colidemonstrating resistance to extended-spectrum cephalosporins were included. Case patients were designated as those with cultures positive for CTX-M-positiveE. coli, and control patients were designated as those with non-CTX-M-producingE. coli. Multivariable logistic regression analyses were performed to evaluate risk factors for CTX-M-positive isolates. A total of 83 (56.8%) of a total of 146 patients had cultures with CTX-M-positiveE. coli. On multivariable analyses, there was a significant association between infection or colonization with CTX-M-type β-lactamase-positiveE. coliand receipt of piperacillin-tazobactam in the 30 days prior to the culture date (odds ratio [OR], 7.36; 95% confidence interval [CI], 1.61 to 33.8;P= 0.01) and a urinary culture source (OR, 0.36; 95% CI, 0.17 to 0.77;P= 0.008). The rates of resistance to fluoroquinolones were significantly higher in isolates from case patients than in isolates from control patients (90.4 and 50.8%, respectively;P< 0.001). We found that nonurinary sources of clinical cultures and the recent use of piperacillin-tazobactam conferred an increased risk of colonization or infection with CTX-M-positiveE. coli. Future studies will need to focus on outcomes associated with infections due to CTX-M-positiveE. coli, as well as infection control strategies to limit the spread of these increasingly common organisms.

Risk factors for multidrug-resistant Escherichia coli rectal colonization of dogs on admission to a veterinary hospital

2010 ◽  
Vol 139 (2) ◽  
pp. 197-205 ◽  
Author(s):  
J. S. GIBSON ◽  
J. M. MORTON ◽  
R. N. COBBOLD ◽  
L. J. FILIPPICH ◽  
D. J. TROTT
Keyword(s):  
Risk Factors ◽  
Antimicrobial Agents ◽  
Imaging Techniques ◽  
Multivariable Analysis ◽  
Multidrug Resistant ◽  
E Coli ◽  
Increased Risk ◽  
Potential Risk Factors ◽  
Control Procedures ◽  
Rectal Colonization

SUMMARYThis study aimed to identify risk factors for intestinal colonization with multidrug-resistant (MDR) E. coli in dogs on admission to a veterinary teaching hospital. Exposures to potential risk factors, including prior treatments, hospitalizations and interventions during the 42 days prior to admission were assessed for 82 case admissions and 82 time-matched controls in a retrospective prevalence-based case-control study of 20 months duration. On multivariable analyses, risk of MDR E. coli colonization on admission was increased with prior hospitalization for 4–7 days and >7 days relative to shorter periods, and in dogs that had prior diagnostic imaging techniques. Univariable analyses indicated that risk was increased following prior treatment with several antimicrobial agents. However, on multivariable analysis, administration of fluoroquinolones was associated with increased risk but risk did not appear to increase following administration of other antimicrobials. These results can inform management of canine patients and infection control procedures to mitigate the risk of clinical disease due to MDR bacteria in hospitalized dogs.

scholarly journals Role of Ceftiofur in Selection and Dissemination of blaCMY-2-Mediated Cephalosporin Resistance in Salmonella enterica and Commensal Escherichia coli Isolates from Cattle

2009 ◽  
Vol 75 (11) ◽  
pp. 3648-3655 ◽  
Author(s):  
Joshua B. Daniels ◽  
Douglas R. Call ◽  
Dale Hancock ◽  
William M. Sischo ◽  
Katherine Baker ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
The United States ◽  
Generation Cephalosporin ◽  
Plasmid Transfer ◽  
Third Generation ◽  
Antimicrobial Drugs ◽  
E Coli ◽  
History Of ◽  
Cephalosporin Resistance

ABSTRACT Third-generation cephalosporin resistance of Salmonella and commensal Escherichia coli isolates from cattle in the United States is predominantly conferred by the cephamycinase CMY-2, which inactivates β-lactam antimicrobial drugs used to treat a wide variety of infections, including pediatric salmonellosis. The emergence and dissemination of bla CMY-2 --bearing plasmids followed and may in part be the result of selection pressure imposed by the widespread utilization of ceftiofur, a third-generation veterinary cephalosporin. This study assessed the potential effects of ceftiofur on bla CMY-2 transfer and dissemination by (i) an in vivo experimental study in which calves were inoculated with competent bla CMY-2-bearing plasmid donors and susceptible recipients and then subjected to ceftiofur selection and (ii) an observational study to determine whether ceftiofur use in dairy herds is associated with the occurrence and frequency of cephalosporin resistance in Salmonella and commensal E. coli. The first study revealed bla CMY-2 plasmid transfer in both ceftiofur-treated and untreated calves but detected no enhancement of plasmid transfer associated with ceftiofur treatment. The second study detected no association (P = 0.22) between ceftiofur use and either the occurrence of ceftiofur-resistant salmonellosis or the frequency of cephalosporin resistance in commensal E. coli. However, herds with a history of salmonellosis (including both ceftiofur-resistant and ceftiofur-susceptible Salmonella isolates) used more ceftiofur than herds with no history of salmonellosis (P = 0.03) These findings fail to support a major role for ceftiofur use in the maintenance and dissemination of bla CMY-2-bearing plasmid mediated cephalosporin resistance in commensal E. coli and in pathogenic Salmonella in these dairy cattle populations.

scholarly journals Prevalence and Risk Factors for ESBL/AmpC-E. coli in Pre-Weaned Dairy Calves on Dairy Farms in Germany

2021 ◽  
Vol 9 (10) ◽  
pp. 2135
Author(s):  
Laura Patricia Weber ◽  
Sylvia Dreyer ◽  
Maike Heppelmann ◽  
Katharina Schaufler ◽  
Timo Homeier-Bachmann ◽  
...  
Keyword(s):  
Risk Factors ◽  
Animal Health ◽  
Significant Risk ◽  
Dairy Farms ◽  
Positive Sample ◽  
Dairy Calves ◽  
Federal States ◽  
E Coli ◽  
German Federal States ◽  
Waste Milk

The objectives of this study were to ascertain the fecal ESBL/AmpC-E. coli prevalence and to detect risk factors for their occurrence in young pre-weaned calves and their dams on large dairy farms in Germany. From 2018–2019 we investigated 2816 individual fecal samples from pre-weaned dairy calves and their dams, representing seventy-two farms (mean = 667 milking cows) from eight German federal states. To assess possible risk factors associated with ESBL/AmpC-E. coli prevalence in calves and dams, a questionnaire was performed, collecting management data. We observed an ESBL/AmpC-E. coli prevalence of 63.5% (95% CI: 57.4–69.5) among the sampled calves and 18.0% (95% CI: 12.5–23.5) among the dams. On all farms, at least one positive sample was obtained. To date, this is the highest ESBL/AmpC-E. coli prevalence observed in dairy herds in Europe. Feeding with waste milk was identified as a significant risk factor for a high prevalence of ESBL/AmpC-E. coli in calves. Many calves at large dairies in Germany are fed with waste milk due to the large amounts generated as a result of antibiotic dry-off routines and mastitis treatment with antibiotics. Other notable risk factors for high ESBL/AmpC-E. coli in calves were the general fitness/health of dams and calves, and the quality of farm hygiene. Taken together, these findings suggest that new or improved approaches to animal health management, for example, antibiotic dry cow management (selective dry cow therapy) and mastitis treatment (high self-recovery), as well as farm hygiene, should be researched and implemented.

scholarly journals OmpF Downregulation Mediated by Sigma E or OmpR Activation Confers Cefalexin Resistance in Escherichia coli in the Absence of Acquired β-Lactamases.

2021 ◽  
Author(s):  
Maryam Alzayn ◽  
Punyawee Dulyayangkul ◽  
Naphat Satapoomin ◽  
Kate J Heesom ◽  
Matthew B Avison
Keyword(s):  
Escherichia Coli ◽  
Generation Cephalosporin ◽  
Loss Of Function ◽  
E Coli ◽  
Large Numbers ◽  
Regulatory Mutations ◽  
Cephalosporin Resistance ◽  
Human Infections ◽  
Sigma E ◽  
Group 1

Cefalexin is a widely used 1st generation cephalosporin, and resistance in Escherichia coli is caused by Extended-Spectrum (e.g. CTX-M) and AmpC β-lactamase production and therefore frequently coincides with 3rd generation cephalosporin resistance. However, we have recently identified large numbers of E. coli isolates from human infections, and from cattle, where cefalexin resistance is not β-lactamase mediated. Here we show, by studying laboratory selected mutants, clinical isolates, and isolates from cattle, that OmpF porin disruption or downregulation is a major cause of cefalexin resistance in E. coli. Importantly, we identify multiple regulatory mutations that cause OmpF downregulation. In addition to mutation of ompR, already known to downregulate OmpF and OmpC porin production, we find that rseA mutation, which strongly activates the Sigma E regulon, greatly increasing DegP production, which degrades OmpF, OmpC and OmpA porins. Furthermore, we reveal that mutations affecting lipopolysaccharide structure, exemplified by the loss of GmhB, essential for lipopolysaccharide heptosylation, also modestly activate DegP production, resulting in OmpF degradation. Remarkably, given the critical importance attached to such systems for normal E. coli physiology, we find evidence for DegP-mediated OmpF downregulation, gmhB and rseA loss of function mutation in E. coli isolates derived from human infections. Finally, we show that these regulatory mutations enhance the ability of group 1 CTX-M β-lactamase to confer reduced carbapenem susceptibility, particularly those mutations that cause OmpC in addition to OmpF downregulation.

scholarly journals The Importance of Perioperative Prophylaxis with Cefuroxime or Ceftriaxone in the Surgical Site Infections Prevention after Cranial and Spinal Neurosurgical Procedures

PRILOZI ◽  
2017 ◽  
Vol 38 (2) ◽  
pp. 85-97
Author(s):  
Aleksandra Dimovska-Gavrilovska ◽  
Aleksandar Chaparoski ◽  
Andreja Gavrilovski ◽  
Zvonko Milenkovikj
Keyword(s):  
Risk Factors ◽  
Antibiotic Prophylaxis ◽  
Infection Rate ◽  
Surgical Site Infections ◽  
Generation Cephalosporin ◽  
Secondary Outcome ◽  
Neurosurgical Procedures ◽  
Postoperative Infections ◽  
Perioperative Prophylaxis ◽  
Increased Risk

Abstract Introduction Surgical site infections pose a significant problem in the treatment of neurosurgical procedures, regardless of the application of perioperative prophylaxis with systemic antibiotics. The infection rate in these procedures ranges from less than 1% to above 15%. Different antibiotics and administration regimes have been used in the perioperative prophylaxis so far, and there are numerous comparative studies regarding their efficiency, however, it is generally indicated that the choice thereof should be based on information and local specifics connected to the most probable bacterial causers, which would possibly contaminate the surgical site and cause infection, and moreover, the mandatory compliance with the principles of providing adequate concentration of the drug at the time of the anticipated contamination. Objective Comparing the protective effect of two perioperative prophylactic antibiotic regimes using cefuroxime (second generation cephalosporin) and ceftriaxone (third generation cephalosporin) in the prevention of postoperative surgical site infections after elective and urgent cranial and spinal neurosurgical procedures at the University Clinic for Neurosurgery in Skopje in the period of the first three months of 2016. Design of the study Prospective randomized comparative study. Outcome measures Establishing the clinical outcome represented as prevalence of superficial and deep incision and organ/space postoperative surgical site infections. Material and method We analyzed prospectively 40 patients who received parenteral antibiotic prophylaxis with two antibiotic regimes one hour before the routine neurosurgical cranial and spinal surgical procedures; the patients were randomized in two groups, according to the order of admission and participation in the study, alternately, non-selectively, those persons who fulfilled inclusion criteria were placed in one of the two programmed regimes with cefuroxime in the first, and cefotaxime in the second compared group. All relevant demographic and perioperative patient data were analyzed for both comparative groups, especially the factors known to cause disposition (predisposition) to infections. The prevalence of postoperative infections was evaluated as the primary outcome in both comparative groups, while the secondary outcome was the postoperative infection rate after cranial and spinal neurosurgical procedures at the Neurosurgical clinic in Skopje (having in consideration that so far no data have been published in this context), as well as the prevalence of the risk factors for occurrence of postoperative infections, pre-surgically in patients undergoing neurosurgical interventions locally in the Republic of Macedonia. Results A total of three cases of postoperative infections were registered, two of which classified as superficial incisional, while one case organ/space infection – meningitis (elective intervention) without etiological confirmation. Both comparative groups were statistically similar, without any statistically significant differences in the basic demographic and perioperative characteristics, especially in relation to the incidence of the factors, which, regardless of the antibiotic prophylaxis, show predisposition to postoperative infections. All three cases with infections were registered in the group of persons who received prophylaxis with ceftriaxone preoperatively, with isolated etiological S. aureus agent (elective intervention) in one of them, and methicillin resistant staphylococcus aureus (MRSA) in another (urgent intervention) with superficial incisional SSI. There was no case of SSI in the group of patients who received cefuroxime before surgery. Conclusion Administration of parenteral antibiotics before surgery reduces the incidence of postoperative infections after neurosurgical procedures, especially in cases with increased risk factors for SSI, such as ACA score of ≥ 2/3, the duration of the surgical intervention ≥ 4 hours, contaminated wound and comorbidities. Perioperative antibiotic prophylaxis should be directed to better coverage of the S.aureus arrays.

scholarly journals Molecular Epidemiology of Escherichia coli Producing CTX-M and pAmpC β-Lactamases from Dairy Farms Identifies a Dominant Plasmid Encoding CTX-M-32 but No Evidence for Transmission to Humans in the Same Geographical Region

2020 ◽  
Vol 87 (1) ◽  
Author(s):  
Jacqueline Findlay ◽  
Oliver Mounsey ◽  
Winnie W. Y. Lee ◽  
Nerissa Newbold ◽  
Katy Morley ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Geographical Location ◽  
Dairy Farms ◽  
Generation Cephalosporin ◽  
Sequencing Analysis ◽  
Third Generation ◽  
Content Type ◽  
E Coli ◽  
Animal Populations ◽  
Close Relatives

ABSTRACT Third-generation cephalosporin resistance (3GC-R) in Escherichia coli is a rising problem in human and farmed-animal populations. We conducted whole-genome sequencing analysis of 138 representative 3GC-R isolates previously collected from dairy farms in southwest England and confirmed by PCR to carry acquired 3GC-R genes. This analysis identified blaCTX-M (131 isolates encoding CTX-M-1, -14, -15, -and 32 and the novel variant CTX-M-214), blaCMY-2 (6 isolates), and blaDHA-1 (1 isolate). A highly conserved plasmid was identified in 73 isolates, representing 27 E. coli sequence types. This novel ∼220-kb IncHI2 plasmid carrying blaCTX-M-32 was sequenced to closure and designated pMOO-32. It was found experimentally to be stable in cattle and human transconjugant E. coli even in the absence of selective pressure and was found by multiplex PCR to be present on 26 study farms representing a remarkable range of transmission over 1,500 square kilometers. However, the plasmid was not found among human urinary E. coli isolates we recently characterized from people living in the same geographical location, collected in parallel with farm sampling. There were close relatives of two blaCTX-M plasmids circulating among eight human and two cattle isolates, and a closely related blaCMY-2 plasmid was found in one cattle and one human isolate. However, phylogenetic evidence of recent sharing of 3GC-R strains between farms and humans in the same region was not found. IMPORTANCE Third-generation cephalosporins (3GCs) are critically important antibacterials, and 3GC resistance (3GC-R) threatens human health, particularly in the context of opportunistic pathogens such as Escherichia coli. There is some evidence for zoonotic transmission of 3GC-R E. coli through food, but little work has been done examining possible transmission via interaction of people with the local near-farm environment. We characterized acquired 3GC-R E. coli found on dairy farms in a geographically restricted region of the United Kingdom and compared these with E. coli from people living in the same region, collected in parallel. While there is strong evidence for recent farm-to-farm transmission of 3GC-R strains and plasmids—including one epidemic plasmid that has a remarkable capacity to be transmitted—there was no evidence that 3GC-R E. coli found on study farms had a significant impact on circulating 3GC-R E. coli strains or plasmids in the local human population.

scholarly journals Sequential Combined Effect of Phages and Antibiotics on the Inactivation of Escherichia coli

2018 ◽  
Vol 6 (4) ◽  
pp. 125 ◽  
Author(s):  
Ana Lopes ◽  
Carla Pereira ◽  
Adelaide Almeida
Keyword(s):  
Escherichia Coli ◽  
Bacterial Resistance ◽  
Combined Treatment ◽  
Rapid Evolution ◽  
Generation Cephalosporin ◽  
Resistant Bacteria ◽  
Antibiotic Concentration ◽  
E Coli ◽  
Cephalosporin Resistance ◽  
Community Environments

The emergence of antibiotic resistance in bacteria is a global concern. The use of bacteriophages (or phages) alone or combined with antibiotics is consolidating itself as an alternative approach to inactivate antibiotic-resistant bacteria. However, phage-resistant mutants have been considered as a major threat when phage treatment is employed. Escherichia coli is one of the main responsible pathogens for moderate and serious infections in hospital and community environments, being involved in the rapid evolution of fluoroquinolones and third-generation cephalosporin resistance. The aim of this study was to evaluate the effect of combined treatments of phages and antibiotics in the inactivation of E. coli. For this, ciprofloxacin at lethal and sublethal concentrations was added at different times (0, 6, 12 and 18 h) and was tested in combination with the phage ELY-1 to inactivate E. coli. The efficacy of the combined treatment varied with the antibiotic concentration and with the time of antibiotic addition. The combined treatment prevented bacterial regrowth when the antibiotic was used at minimum inhibitory concentration (MIC) and added after 6 h of phage addition, causing less bacterial resistance than phage and antibiotic applied alone (4.0 × 10-7 for the combined treatment, 3.9 × 10-6 and 3.4 × 10-5 for the antibiotics and the phages alone, respectively). Combined treatment with phage and antibiotic can be effective in reducing the bacterial density and it can also prevent the emergence of resistant variants. However, the antibiotic concentration and the time of antibiotic application are essential factors that need to be considered in the combined treatment.

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