Prevalence and molecular characterization of multi-resistant Escherichia coli isolates from clinical bovine mastitis in China

Different antibiotics are used to treat mastitis in dairy cows that is caused by Escherichia coli (E. coli). Antimicrobial resistance in food-producing animals in China has been monitored since 2000. Surveillance data have shown that the prevalence of multiresistant E. coli in animals has increased significantly. This study aimed to investigate the occurrence and molecular characteristics of resistance determinants in E. coli strains (n = 105) obtained from lactating cows with clinical bovine mastitis (CBM) in China. A total of 220 cows with clinical mastitis, which has swollen mammary udder with reduced and red or gangrenous milk, were selected from 5000 cows. The results showed 94.3% of the isolates were recognized as multidrug resistant. The isolates (30.5%) were positive for the class I integrase gene along with seven gene cassettes that were accountable for resistance to trimethoprim resistance (dfrA17, dfr2d and dfrA1), aminoglycosides resistance (aadA1 and aadA5) and chloramphenicol resistance (catB3 and catB2), respectively. The blaTEM gene was present in all the isolates, and these carried the blaCTX gene. A double mutation in gyrA (i.e., Ser83Leu and Asp87Asn) was observed in all fluoroquinolone-resistant isolates. In total, nine fluoroquinolone-resistant E. coli isolates were identified with five different types of mutations in parC. In four (44.4%) isolates, Ser458Ala was present in parE, and in all nine (9/9) fluoroquinolone-resistant isolates, Pro385Ala was present in gyrB. Meanwhile, fluoroquinolone was observed as highly resistant, especially in isolates with gyrA and parC mutations. In summary, the findings of this research recognize the fluoroquinolone resistance mechanism and disclose integron prevalence and ESBLs in E. coli isolates from lactating cattle with CBM.

When the solution becomes the problem: a review on antimicrobial resistance in dairy cattle

Antibiotics' action, once a 'magic bullet', is now hindered by widespread microbial resistance, creating a global antimicrobial resistance (AMR) crisis. A primary driver of AMR is the selective pressure from antimicrobial use. Between 2000 and 2015, antibiotic consumption increased by 65%, reaching 34.8 billion tons, 73% of which was used in animals. In the dairy cattle sector, antibiotics are crucial for treating diseases like mastitis, posing risks to humans, animals and potentially leading to environmental contamination. To address AMR, strategies like selective dry cow therapy, alternative treatments (nanoparticles, phages) and waste management innovations are emerging. However, most solutions are in development, emphasizing the urgent need for further research to tackle AMR in dairy farms.

Extended-Spectrum Beta-Lactamase-Producing Escherichia coli and Other Antimicrobial-Resistant Gram-Negative Pathogens Isolated from Bovine Mastitis: A One Health Perspective

Antimicrobial resistance (AMR) poses an imminent threat to global public health, driven in part by the widespread use of antimicrobials in both humans and animals. Within the dairy cattle industry, Gram-negative coliforms such as Escherichia coli and Klebsiella pneumoniae stand out as major causative agents of clinical mastitis. These same bacterial species are frequently associated with severe infections in humans, including bloodstream and urinary tract infections, and contribute significantly to the alarming surge in antimicrobial-resistant bacterial infections worldwide. Additionally, mastitis-causing coliforms often carry AMR genes akin to those found in hospital-acquired strains, notably the extended-spectrum beta-lactamase genes. This raises concerns regarding the potential transmission of resistant bacteria and AMR from mastitis cases in dairy cattle to humans. In this narrative review, we explore the distinctive characteristics of antimicrobial-resistant E. coli and Klebsiella spp. strains implicated in clinical mastitis and human infections. We focus on the molecular mechanisms underlying AMR in these bacterial populations and critically evaluate the potential for interspecies transmission. Despite some degree of similarity observed in sequence types and mobile genetic elements between strains found in humans and cows, the existing literature does not provide conclusive evidence to assert that coliforms responsible for mastitis in cows pose a direct threat to human health. Finally, we also scrutinize the existing literature, identifying gaps and limitations, and propose avenues for future research to address these pressing challenges comprehensively.

Multidrug-resistant Shiga toxin-producing Escherichia coli and hybrid pathogenic strains of bovine origin

Antimicrobial-resistant Escherichia coli strains have been circulating in various sectors and can be cross-transferred between them. Among pathogenic E. coli strains, Shiga toxin-producing E. coli (STEC) and hybrid pathogenic E. coli (HyPEC) emerged as responsible for outbreaks worldwide. As bovine are reservoir of STEC strains, these pathogens primarily spread to food products, exposing humans to risk. Therefore, this study aimed to characterize antimicrobial-resistant and potentially pathogenic E. coli strains from fecal samples of dairy cattle. In this regard, most E. coli strains (phylogenetic groups A, B1, B2, and E) were resistant to β-lactams and non-β-lactams and were classified as multidrug-resistant (MDR). Antimicrobial resistance genes (ARGs) related to multidrug resistance profiles were detected. Furthermore, mutations in fluoroquinolone and colistin resistance determinants were also identified, highlighting the deleterious mutation His152Gln in PmrB that may have contributed to the high level (> 64 mg/L) of colistin resistance. Virulence genes of diarrheagenic and extraintestinal pathogenic E. coli (ExPEC) pathotypes were shared among strains and even within the same strain, evidencing the presence of HyPEC (i.e., ExPEC/STEC), which were assigned as unusual B2-ST126-H3 and B1-ST3695-H31. These findings provide phenotypic and molecular data of MDR, ARGs-producing, and potentially pathogenic E. coli strains in dairy cattle, contributing to the monitoring of antimicrobial resistance and pathogens in healthy animals and alerting to potential bovine-associated zoonotic infections.

Molecular epidemiology and pathogenomics of extended-spectrum beta-lactamase producing- Escherichia coli and - Klebsiella pneumoniae isolates from bulk tank milk in Tennessee, USA

Introduction

The rise in extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in dairy cattle farms poses a risk to human health as they can spread to humans through the food chain, including raw milk. This study was designed to determine the status, antimicrobial resistance, and pathogenic potential of ESBL-producing -E. coli and -Klebsiella spp. isolates from bulk tank milk (BTM).

Methods

Thirty-three BTM samples were collected from 17 dairy farms and screened for ESBL-E. coli and -Klebsiella spp. on CHROMagar ESBL plates. All isolates were confirmed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and subjected to antimicrobial susceptibility testing and whole genome sequencing (WGS).

Results

Ten presumptive ESBL-producing bacteria, eight E. coli, and two K. pneumoniae were isolated. The prevalence of ESBL-E. coli and -K. pneumoniae in BTM was 21.2% and 6.1%, respectively. ESBL-E. coli were detected in 41.2% of the study farms. Seven of the ESBL-E. coli isolates were multidrug resistant (MDR). The two ESBL-producing K. pneumoniae isolates were resistant to ceftriaxone. Seven ESBL-E. coli strains carry the blaCTX-M gene, and five of them co-harbored blaTEM-1. ESBL-E. coli co-harbored blaCTX-M with other resistance genes, including qnrB19, tet(A), aadA1, aph(3'')-Ib, aph(6)-Id), floR, sul2, and chromosomal mutations (gyrA, gyrB, parC, parE, and pmrB). Most E. coli resistance genes were associated with mobile genetic elements, mainly plasmids. Six sequence types (STs) of E. coli were detected. All ESBL-E. coli were predicted to be pathogenic to humans. Four STs (three ST10 and ST69) were high-risk clones of E. coli. Up to 40 virulence markers were detected in all E. coli isolates. One of the K. pneumoniae was ST867; the other was novel strain. K. pneumoniae isolates carried three types of beta-lactamase genes (blaCTX-M, blaTEM-1 and blaSHV). The novel K. pneumoniae ST also carried a novel IncFII(K) plasmid ST.

Conclusion

Detection of high-risk clones of MDR ESBL-E. coli and ESBL-K. pneumoniae in BTM indicates that raw milk could be a reservoir of potentially zoonotic ESBL-E. coli and -K. pneumoniae.

Characterization of mammary pathogenic Escherichia coli reveals the diversity of Escherichia coli isolates associated with bovine clinical mastitis in Brazil

Mammary pathogenic Escherichia coli (MPEC) is one of the most common pathogens associated with clinical mastitis. We analyzed isolates obtained from milk samples of cows with clinical mastitis, collected from 10 farms in Brazil, to verify molecular and phenotypic characteristics. A total of 192 (4.5%) mammary pathogenic E. coli isolates were obtained from 4,275 milk samples analyzed, but we tested 161. We assigned most of these isolates to E. coli phylogroups B1 (52.8%) and A (36.6%), although phylogroups B2, C, D, E, and unknown also occurred. All isolates were assessed for the presence of several genes encoding virulence factors, such as adhesins (sfaDE, papC, afaBC III, ecpA, fimH, papA, and iha), toxins (hlyA, cnf1, sat, vat, and cdt), siderophores (iroN, irp2, iucD, ireA, and sitA), an invasion protein (ibeA), and serum resistance proteins (traT, KpsMTII, and ompT), and isolates from phylogroups B1, B2, and E showed up to 8 genes. Two isolates harbored the locus of enterocyte effacement (escN⁺) and lack the bundle-forming pilus (bfpB^-) operon, which corresponds to a molecular profile of a subgroup of diarrheagenic E. coli (aEPEC), thus being classified as hybrid MPEC/aEPEC isolates. These isolates displayed a localized adherence-like pattern of adherence in HeLa cells and were able to promote F-actin polymerization underneath adherent bacteria. Based on the pulsed-field gel electrophoresis analyses, considerable genetic variability was observed. A low index of antimicrobial resistance was observed and 2 extended-spectrum β-lactamase-producing E. coli were identified, both harboring bla_CTX-M15 gene, and were classified as ST10 and ST993 using multilocus sequence typing. A total of 148 (91.2%) isolates were weak biofilm producers or formed no biofilm. Because raw milk is still frequently consumed in Brazil, the occurrence of virulence factor-encoding genes from extraintestinal or diarrheagenic E. coli added to the presence of extended-spectrum β-lactamase-producing isolates can turn this veterinary medicine problem into a public health concern.

Invited review: Antimicrobial resistance in bovine mastitis pathogens: A review of genetic determinants and prevalence of resistance in European countries

Antimicrobial resistance is an urgent and growing problem worldwide, both for human and animal health. In the animal health sector actions have been taken as concerns grow regarding the development and spread of antimicrobial resistance. Mastitis is the most common infection in dairy cattle. We aimed to summarize the genetic determinants found in staphylococci, streptococci, and Enterobacteriaceae isolated from mastitic milk samples and provide a comparison of percentage resistance to a variety of antimicrobials in European countries.

Molecular Characterization and Antimicrobial Resistance of Pathogenic Escherichia coli Strains in Children from Wolaita Sodo, Southern Ethiopia

Introduction

Pathogenic Escherichia coli strains cause diarrheal infection in children due to their virulence factors. A nonanalytical observational study followed by a purposive sampling technique was conducted from October 2017 to June 2018, to determine the antimicrobial susceptibility patterns and molecularly detect pathogenic Escherichia coli strains in under-five children at Wolaita Sodo town using molecular and the Kirby-Bauer disc diffusion method.

Result

In the current investigation, out of 110 stool samples, Escherichia coli was isolated in 68 (61.8%) (95% CI: 52.1–70.9%). Out of 68 Escherichia coli isolates, 61.9% of Escherichia coli isolates were resistant, 9.4% were intermediately resistant, and 28.7% were susceptible. Among the antimicrobial agents, 91.2% of Escherichia coli isolates were highly sensitive to ciprofloxacin followed by norfloxacin (86.8%). Virulence genes were detected in 55.9% (38/68) (95% CI 52.1%–70.9%) of isolates. The following genes were detected: stx1 (6 (8.8%)), stx2 (4 (5.9%)), eaeA (5 (7.4%)), eaat (14 (20.5%)), and St (4 (5.9%)). Out of 68 Escherichia coli isolates, 43 (63.2%) isolates had shown multidrug resistance patterns. Furthermore, 11.8% of Escherichia coli isolates had shown resistance to eight different drugs. The multidrug resistance index value of Diarrheagenic Escherichia coli pathotypes was greater than or equal to 0.4, which indicates the high risk of resistance.

Conclusion

This study demonstrated important pathogenic Escherichia coli strains and multidrug resistance in isolates containing virulence genes. Wise use of antimicrobials and improving the hygienic practices amongst parents of children reduce its occurrence. Therefore, appropriate usage of antimicrobial agents should also be highly practiced in hospitals.

Antimicrobial Resistance in Escherichia coli Isolates from Healthy Food Animals in South Korea, 2010-2020

Antimicrobial-resistant bacteria in food animals pose a major public health threat worldwide. In this study, we aimed to assess the antimicrobial resistance profiles and resistance trends of commensal Escherichia coli isolated from the feces of healthy cattle, pigs, and chickens in South Korea during 2010 and 2020. A total of 7237 E. coli isolates (2733 cattle, 2542 pig, and 1962 chicken isolates) were tested for susceptibility towards 12 antimicrobials. About 48%, 90%, and 97% of cattle, pig, and chicken isolates, respectively, were resistant to one or more antimicrobial agents. Cattle isolates presented low resistance (<15%) to most of the tested antimicrobials. In contrast, chicken and pig isolates demonstrated a relatively high (>45%) resistance rate to ampicillin, chloramphenicol, streptomycin, and tetracycline. We observed high ciprofloxacin and nalidixic acid resistance rates in chicken (76.1% and 88.6%, respectively), isolates in pig (12.7% and 26.7%, respectively) and cattle (2.7% and 8.2%, respectively) isolates. Notably, a very small proportion of isolates (<5%) from cattle, chickens, and pigs demonstrated resistance to amoxicillin/clavulanic acid, cefoxitin, and colistin. We identified ceftiofur resistance in a small proportion of chicken (8.8%), pig (3.7%), and cattle (0.7%) isolates. We noted an increasing but fluctuating trend of ampicillin, amoxicillin/clavulanic acid, ceftiofur, cefoxitin, chloramphenicol, ciprofloxacin, and streptomycin resistance in pig isolates. Similarly, the ampicillin, ceftiofur, and chloramphenicol resistance rates were increased but fluctuated through time in chicken isolates. Overall, 56% of the isolates showed multidrug-resistant (MDR). The proportion of MDR isolates was low in cattle (17.1%); however, this proportion was high in chickens (87.1%) and pigs (73.7%). Most of the resistance patterns included streptomycin and tetracycline in pigs and cattle, and ciprofloxacin and nalidixic acid in chickens. In conclusion, this study showed high resistance of commensal E. coli isolated from major food animals in Korea to commonly used antimicrobials including critically important antimicrobials. These bacteria could not only be a resistance reservoir but also could have potential to spread this resistance through gene transfer to pathogenic bacteria. Thus, the high prevalence of antimicrobial resistance in food animals highlights the urgent need for measures to restrict and ensure the prudent use of antimicrobials in Korea.

Characterisation of AmpC / ESBL genes in some pathogen gram-negatives isolated from clinical cases of livestock and companion animals

This study was aimed to search and characterize the AmpC and/or ESBL genes of Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa isolated from clinical cases of local livestock and companion animals between 2017 and 2019. A total of eight ceftiofur-resistant E. coli (n= 7) and ceftiofur-resistant K. pneumoniae (n= 1) and seven P. aeruginosa were isolated from different cases in local animals. By combination disc method, six E. coli isolates and one K. pneumoniae isolate were found to be ESBL producers. By combination of the disc method and double disc synergy test, no P. aeruginosa isolates were found as ESBL producers. In the agar disc diffusion test (ADDT) performed with cefoxitin and cefoxitin-boronic, only one E. coli was determined as AmpC producer. In ESBL-producing isolates, only the CTX-M class gene was detected by polymerase chain reaction (PCR) and subsequent sequence analysis revealed CTX-M-3 and CTX-M-15 variants. An AmpC positive E. coli isolate was found to carry plasmidic ampC gene in cmy-2 variant from CIT family. It was observed that P. aeruginosa isolates did not carry the plasmidic ampC gene. After the chromosomal ampC gene of one P. aeruginosa was amplified by PCR and sequenced, R79Q and T105A mutations in the chromosomal ampC gene was revealed. This showed that overproduction of the ampC enzyme is involved in the resistance to β-lactams in P. aeruginosa isolates in the study.

Virulence and enterotoxin gene profile of methicillin-resistant Staphylococcus aureus isolates from bovine mastitis

Bovine mastitis is a major infectious disease affecting dairy animals resulting in enormous economic losses, prolonged antibiotic treatment, reduced milk yield and death of livestock. Emergence of Methicillin-resistant Staphylococcus aureus (MRSA) among bovine mastitis is matter of concern for animal health and dairy industry. The present study was conducted to detect the distribution of virulence and enterotoxin genes among MRSA isolates from bovine mastitis. Out of 500 milk samples, 126 isolates were identified as Staphylococcus and from these only 56 were S. aureus. S.aureus were resistant to cefoxitin (75%), ceftazidime (75%), amoxicillin (71.4%), cefodaxime (67.8%), cefepime (66.1%), oxacillin (64.3%), norfloxacin (60.7%) and gentamicin (58.9%). Only 42 isolates were identified as MRSA strains among staphylococci isolates. MRSA were harbouring virulence genes; mecA (100%), coa (100%) and nuc (100%). The other virulence factors such as hlg (80.9%, 34/42), pvl (47.6%, 20/42) and spa (92.8%, 39/42) were also reported. Molecular characterisation of enterotoxin genes revealed that out of 42 tested isolates 11 were found negative (26%) for any enterotoxin gene whereas 7 (16.6%), 6 (14.3%), 18 (42.8%), 1 (2.3%), 26 (61.9%),27(64.2%),3 (7.1%) were found positive for sea, seb, sec, sed, seg, sei, and seq enterotoxin respectively.

Virulence determinants and antimicrobial resistance of E. coli isolated from bovine clinical mastitis in some selected dairy farms of Bangladesh

E. coli is one of the major significant pathogens causing mastitis, the most complex and costly diseases in the dairy industry worldwide. Present study was undertaken to isolate, detect the virulence factors, phylogroup, antimicrobial susceptibility and antimicrobial resistance genes in E. coli from cows with clinical mastitis. A total of 68 milk samples comprising 53 from clinical mastitis and 15 from apparently healthy cattle were collected from four different established dairy farms in Bangladesh. E. coli was isolated from the milk samples and identified by PCR targeting malB gene and sequencing of 16S rRNA gene. E. coli isolates were screened by PCR for the detection of major virulence genes (stx, eae and cdt) of diarrheagenic E. coli followed by phylogenetic grouping. Antimicrobial susceptibility of the E. coli isolates was determined by disk diffusion test and E. coli showing resistance was further screened for the presence of antimicrobial resistance genes. E. coli was isolated from 35.8% of the mastitis milk samples but none from the apparently healthy cattle milk. All the E. coli isolates were negative for stx, eae and cdt genes and belonged to the phylogenetic groups A and B1 which comprising of commensal E. coli. Antibiotic sensitivity testing revealed 84.2% (16/19) of the isolates as multidrug resistant. Highest resistance was observed against amoxicillin (94.5%) followed by ampicillin (89.5%) and tetracycline (89.5%). E. coli were found resistant against all the classes of antimicrobials used at the farm level. Tetracycline resistance gene (tetA) was detected in 100% of the tetracycline resistant E. coli and blaTEM-1 was present in 38.9% of the E. coli isolates. Findings of this study indicate a potential threat of developing antimicrobial resistance in commensal E. coli and their association with clinical mastitis. Occurrence of multidrug resistant E. coli might be responsible for the failure of antibiotic therapies in clinical mastitis as well as pose potential threat of transmitting and development of antibiotic resistance in human.

Molecular characteristics of Escherichia coli from bulk tank milk in Korea

Background

Escherichia coli, which causes subclinical or clinical mastitis in cattle, is responsible for transmitting antimicrobial resistance via human consumption of raw milk or raw milk products.

Objectives

The objective of this study was to investigate the molecular characteristics of 183 E. coli from bulk tank milk of five different dairy factories in Korea.

Methods

The molecular characteristics of E. coli such as serogroup, virulence, antimicrobial resistance, and integron genes were detected using polymerase chain reaction and antimicrobial susceptibility were tested using the disk diffusion test.

Results

In the distribution of phylogenetic groups, group D was the most prevalent (59.6%) and followed by group B1 (25.1%). The most predominant serogroup was O173 (15.3%), and a total of 46 different serotypes were detected. The virulence gene found most often was fimH (73.2%), and stx1, fimH, incC, fyuA, and iutA genes were significantly higher in isolates of phylogenetic group B1 compared to phylogenetic groups A, B2, and D (p < 0.05). Among 64 E. coli isolates that showed resistance to at least one antimicrobial, the highest resistance rate was observed for tetracyclines (37.5%). All 18 integron-positive E. coli carried the integron class I (int1) gene, and three different gene cassette arrangements, dfrA12+aadA2 (2 isolates), aac(6′)-Ib3+aac(6′)-Ib-cr+aadA4 (2 isolates), and dfrA17+aadA5 (1 isolate) were detected.

Conclusions

These data suggest that the E. coli from bulk tank milk can be an indicator for dissemination of antimicrobial resistance and virulence factors via cross-contamination.

Prevalence, Antimicrobial Susceptibility, and Molecular Characterization of Escherichia coli Isolated From Raw Milk in Dairy Herds in Northern China

Escherichia coli is a common bacterium in the intestines of animals, and it is also the major important cause of toxic mastitis, which is an acute or peracute disease that causes a higher incidence of death and culling of cattle. The purpose of this study was to investigate E. coli strains isolated from the raw milk of dairy cattle in Northern China, and the antibacterial susceptibility of these strains and essential virulence genes. From May to September 2015, 195 raw milk samples were collected from 195 dairy farms located in Northern China. Among the samples, 67 (34.4%) samples were positive for E. coli. About 67 E. coli strains were isolated from these 67 samples. The prevalence of Shiga toxin-producing E. coli (STEC), enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC), and enteroinvasive E. coli (EIEC) were 9, 6, 4.5, and 1.5%, respectively. Among the virulence genes detected, stx1 was the most prevalent (6/67, 9%) gene, followed by eae (3/67, 4.5%), and estB (2/67, 3%). Moreover, the strains exhibited different resistance levels to ampicillin (46.3%), amoxicillin-clavulanic acid (16.4%), trimethoprim-sulfamethoxazole (13.4%), tetracycline (13.4%), cefoxitin (11.9%), chloramphenicol (7.5%), kanamycin (7.5%), streptomycin (6.0%), tobramycin (4.5%), azithromycin (4.5%), and ciprofloxacin (1.5%). All of the E. coli isolates were susceptible to gentamicin. The prevalence of β-lactamase-encoding genes was 34.3% in 67 E. coli isolates and 45% in 40 β-lactam-resistance E. coli isolates. The overall prevalence of bla SHV, bla TEM, bla CMY, and bla CTX-M genes were 1.5, 20.9, 10.4, and 1.5%, respectively. Nine non-pathogenic E. coli isolates also carried β-lactamase resistance genes, which may transfer to other pathogenic E. coli and pose a threat to the farm's mastitis management projects. Our results showed that most of E. coli were multidrug resistant and possessed multiple virulence genes, which may have a huge potential hazard with public health, and antibiotic resistance of E. coli was prevalent in dairy herds in Northern China, and ampicillin should be used cautiously for mastitis caused by E. coli in Northern China.

Comparative analysis of genetic characterization of β-lactam-resistant Escherichia coli from bulk tank milk in Korea

BACKGROUND

This study was conducted to analyze the genetic characteristics of 41 β-lactam-resistant Escherichia coli isolates, which are one of the common causes of environmental mastitis, isolated from the bulk tank milk of 290 dairy farms in five factories operated by three dairy companies in Korea.

RESULTS

Analysis of the phenotypic and genotypic characteristics of β-lactam-resistant E. coli isolates revealed differences between factories even within the same company. Isolates from factory A1 and C1 showed high resistance to cephalothin (76.9 and 100%, respectively), which is a first-generation cephalosporins, whereas resistance to tetracycline was showed by only the isolates from factories B1 (60.0%), C2 (66.7%), and C3 (100%). Although all the 41 β-lactam-resistant E. coli isolates were positive for blaOXA-1, blaTEM-1 was highly prevalent in isolates from factories C2 (100%) and C3 (100%). Among 17 isolates resistant to both β-lactams and aminoglycosides, the most common multilocus sequence type was ST399 (13isolates, 76.5%). Furthermore, 2 (11.8%) and 12 (70.6%) isolates belonged to the phylogenetic groups B2 and D, respectively, which are invasive strains that cause intestinal infections, respectively. The predominant serogroup was O15 (70.6%), which is a globally distributed extraintestinal pathogen. Interestingly, one isolate from factory A1 belonged to O157 and carried six virulence genes, simultaneously.

CONCLUSIONS

Although E. coli isolates were isolated from bulk tank milk, and not the clinical mastitis samples, the presence of the phylogenetic groups B2 and D, and the serogroups O15 and O157, which harbor antimicrobial resistance genes and virulence factors, can pose a threat to public health.

Comparative occurrence and antibiogram of extended-spectrum β-lactamase-producing Escherichia coli among post-weaned calves and lactating cows from smallholder dairy farms in a parallel animal husbandry area

Background and Aim:

Inappropriate overuse of antimicrobials might be associated with the spreading of antimicrobial-resistant bacteria in animal-based food products. Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli have been recognized as an emerging global problem in a One Health approach. This study aimed to assess the occurrence and antimicrobial-susceptible profiles of ESBL-producing E. coli among post-weaned calves and lactating cows in a parallel animal husbandry area.

Materials and Methods:

Seventy-two pool fecal samples were collected from 36 smallholder dairy farms registered in Ban Hong Dairy Cooperatives, Lamphun Province, Thailand. Pre-enriched fecal samples were cultured in MacConkey agar supplemented with cefotaxime. The potential E. coli isolates were identified by not only biochemical tests but also polymerase chain reaction assay of the 16S rRNA gene. ESBL production was confirmed by the combination disk test. Antimicrobial susceptibility testing was performed by the Kirby–Bauer disk diffusion method.

Results:

The occurrence of ESBL-producing E. coli at the farm level was 80.56%. The different phenotypic antibiogram of ESBL-producing E. coli was observed among post-weaned calf and lactating cow specimens. The most frequent resistance patterns of ESBL-producing isolates from both groups were amoxicillin-ceftiofur-cephalexin-cephalothin-cloxacillin-streptomycin-oxytetracycline-sulfamethoxazole/trimethoprim. For the median zone diameter, enrofloxacin-resistant isolates with narrow zone diameter values from lactating cow specimens were particularly more than post-weaned calf specimens (p<0.05).

Conclusion:

These findings revealed the dynamic changes in ESBL-producing E. coli from calves and lactating cows in Lamphun Province, posing the inevitability to prevent bacterial transmission and optimize antimicrobial therapy in dairy farming.

Review on the occurrence of the mcr-1 gene causing colistin resistance in cow's milk and dairy products

Both livestock farmers and the clinic use significant amount of antibiotics worldwide, in many cases the same kind. Antibiotic resistance is not a new phenomenon, however, it is a matter of concern that resistance genes (mcr - Mobilized Colistin Resistance - genes) that render last-resort drugs (Colistin) ineffective, have already evolved. Nowadays, there is a significant consumption of milk and dairy products, which, if not treated properly, can contain bacteria (mainly Gram-negative bacteria). We collected articles and reviews in which Gram-negative bacteria carrying the mcr-1 gene have been detected in milk, dairy products, or cattle. Reports have shown that although the incidence is still low, unfortunately the gene has been detected in some dairy products on almost every continent. In the interest of our health, the use of colistin in livestock farming must be banned as soon as possible, and new treatments should be applied so that we can continue to have a chance in fighting multidrug-resistant bacteria in human medicine.

Detection of multi-drug resistance and AmpC β-lactamase/extended-spectrum β-lactamase genes in bacterial isolates of loggerhead sea turtles (Caretta caretta) from the Mediterranean Sea

Sea turtles are useful sentinels to monitor the dissemination of antimicrobial resistance (AMR) in the marine coastal ecosystems. Forty Gram negative bacteria were isolated from wounds of 52 injured Caretta caretta, living in the Mediterranean Sea. Bacteria were identified using 16S rRNA gene sequencing and tested for susceptibility to 15 antibiotics. In addition, NGS amplicon sequencing was performed to detect the presence of AmpC β-lactamase genes (bla_AmpC) and extended-spectrum β-lactamase (ESBL) genes (bla_CTX-M,bla_SHV,bla_TEM). Seventy-five percent of the isolates (30/40 isolates) exhibited multidrug resistance (MDR) phenotypes and 32.5% (13/40 isolates) were confirmed to be positive for at least one gene. The variants of ESBLs genes were bla_CTX-M-3,bla_TEM-236 and bla_SHV-12. Variants of the bla_AmpCβ-lactamase gene i.e., bla_ACT-24, bla_ACT-2, bla_ACT-17, bla_DHA-4 and bla_CMY-37, were also detected. In addition, 4 isolates were found simultaneously harboring CTX and AmpC genes while 2 strains harbored 3 genes (bla_{ACT-2+TEM-236+SHV-12}, and bla_{CTX-M-3+ACT-24+TEM-236}).

Molecular Characterization of Multidrug-Resistant Escherichia coli Isolated from Milk of Dairy Cows with Clinical Mastitis in Algeria

The objective of this study was to investigate the occurrence of multidrug-resistant Escherichia coli in cows with clinical mastitis in 42 different dairy farms located in the Bordj Bou Arreridj region of Algeria. Milk samples were cultured on Columbia blood agar, and isolates were then identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry. In total, 200 samples were screened and 52 E. coli strains confirmed as causative agents were obtained. The antimicrobial susceptibility testing was performed by disk diffusion method. Antibiotic resistance genes, including those conferring resistance to extended-spectrum β-lactamases (i.e., blaTEM, blaSHV, and blaCTX-M), tetracyclines (tetA, tetB, tetC, and tetJ), aminoglycosides [aph(3'), aac(3'), aac(6'), ant, aad, and armA], and quinolones (qnrA and qnrB) were amplified by standard PCR and sequenced when positive. Transferability of resistance genes has been investigated by conjugation experiments and multilocus sequence typing. The most frequently observed resistance was to amoxicillin (86.5%), followed by tetracycline (75%), amoxicillin-clavulanic acid (59.6%), trimethoprim-sulfamethoxazole (36.5%), doxycycline (13.5%), and ciprofloxacin (13.5%). Multidrug resistance was observed in 38.4% of isolates. Genotypic characterization showed that tetA (44.2%) and blaTEM-1 (30.7%) genes were the most prevalent. Screening for plasmid-mediated quinolone resistance genes demonstrated that seven isolates (13.5%) expressed qnrB and one isolate (1.9%) harbored qnrA. In addition, aminoglycoside resistance determinants including aadA1 and aac(3)-Id were detected in seven and two isolates, respectively. Moreover, blaTEM, tetA, tetB, qnrB, and aadA1 were successfully transferred horizontally to transconjugant strains. The multilocus sequence typing revealed the presence of three different sequence types (ST162, ST371, and ST 949).

Monitoring and Characteristics of Major Mastitis Pathogens from Bulk Tank Milk in Korea

Simple Summary

The monitoring of milk quality and the presence of major mastitis pathogens is an important part of milk quality assurance program. Bulk tank milk has been used in many countries to identify multiple milk quality problems and mastitis pathogens that might exist in a dairy herd. This study aimed to compare the presence of mastitis pathogens and the antimicrobial resistance of the isolates from bulk tank milk by dairy companies. The results showed that the prevalence of mastitis pathogens and the antimicrobial resistance of the isolates were significantly different among factories, and support the development of strong monitoring and prevention programs in dairy operations.

Abstract

In many countries, bulk tank milk (BTM) has been used for examining milk and analyzed as an important part of milk quality assurance programs. The objectives of this study were to investigate milk quality and the presence of major mastitis pathogens in BTM, and to compare the characteristics of BTM by dairy factory or company. A total of 1588 batches of BTM samples were collected from 396 dairy farms of seven dairy factories owned by four companies in Korea. The means of individual bacterial counts (IBC) and somatic cell count (SCC) were 3.7 × 10⁴ cells/mL and 1.1 × 10⁵ cells/mL, respectively, and no significant differences among dairy factories were observed. The most common pathogen was Staphylococcus spp. (60.1%), followed by E. faecalis (53.8%), E. coli (37.6%) and Streptococcus spp. (22.5%). Enterococcus spp. showed the highest resistance to tetracyclines (51.1% to 73.9%) and macrolides (46.5%). S. aureus and coagulase-negative staphylococci (CNS) showed the highest resistance to penicillin (28.4% and 40.2%, respectively), and three (3.2%) S. aureus and seven (3.3%) CNS were also methicillin-resistant. These data show the diverse prevalence and characteristics of major mastitis pathogens among factories, and support the development of strong monitoring and prevention programs of mastitis pathogens by commercial dairy operations.

Antimicrobial resistance modulation of MDR E. coli by antibiotic coated ZnO nanoparticles

We evaluated three types of total six preparations against multidrug resistant E. coli i) three antibiotic coated ZnO nanoparticles (gentamicin coated nanoparticle-GNp; chloramphenicol coated nanoparticles-CNp; and both gentamicin & chloramphenicol coated nanoparticle-GCNp), ii) ZnO nanoparticle alone-Np, and iii) two antibiotics used in single (Gentamicin-G; and Chloramphenicol-C). A total of n = 200 sub-clinically positive mastitic milk samples of bovine origin were processed for isolation of MDR E. coli using microbiological and clinical laboratory & standard institute's protocols. ZnO Nps were prepared from zinc acetate dihydrate (Zn (CH₃COO)₂. 2H₂O), polyethylene glycol (C_2nH_4n+2O_n+1), and urea (CH₄N₂O) by standard chemical protocol. Nps were characterized by XRD and STEM analyses while coating of antibiotics on Nps was confirmed by UV-Visible spectrophotometric analysis. Analysis of variance and student t-test were applied at 5% probability using SPSS version 22 statistical software for inferences on obtained data. There was significantly (p < 0.05) lowest minimum inhibitory concentrations (MICs) and highest zone of inhibitions (ZOIs) in case of GCNp (10.42 ± 4.51 μg/mL & 22.00 ± 1.00 mm) followed by GNp (20.79 ± 8.95 μg/mL & 20.00 ± 1.00 mm) and then CNp (25.96 ± 8.95 μg/mL & 12.33 ± 0.57 mm). Percentage increase in ZOI were expressed as 135.8, 78.43, and 312.76% by GCNp when compared with that of G, C, and Np, respectively. GNp and CNp coated preparations exhibited 114.36 and 275.73% increase in ZOI than to that of G and C, respectively. Similar trend was found in percentage reduction of MICs of preparations. Highest filamentation, indicator of bacterial damage, of E. coli was noted at MIC of GCNp followed by GNp and CNp. The study concluded antibiotic coated ZnO nanoparticles significant candidates modulating antibiotic resistance in MDR E. coli.

Antimicrobial resistance genes in bacteria from animal-based foods

Antimicrobial resistance is a worldwide public health threat. Farm animals are important sources of bacteria containing antimicrobial resistance genes (ARGs). Although the use of antimicrobials in aquaculture and livestock has been reduced in several countries, these compounds are still routinely applied in animal production, and contribute to ARGs emergence and spread among bacteria. ARGs are transmitted to humans mainly through the consumption of products of animal origin (PAO). Bacteria can present intrinsic resistance, and once antimicrobials are administered, this resistance may be selected and multiply. The exchange of genetic material is another mechanism used by bacteria to acquire resistance. Some of the main ARGs found in bacteria present in PAO are the bla, mcr-1, cfr and tet genes, which are directly associated to antibiotic resistance in the human clinic.

Antimicrobial susceptibility of nine udder pathogens recovered from bovine clinical mastitis milk in Europe 2015-2016: VetPath results

VetPath is an ongoing pan-European antimicrobial susceptibility monitoring programme collecting pathogens from diseased cattle, pigs and poultry not recently treated with antibiotics. Non-duplicate isolates (n = 1244) were obtained from cows with acute clinical mastitis in eight countries during 2015-2016 for centrally antimicrobial susceptibility testing according CLSI standards. Among Escherichia coli (n = 225), resistance was high to ampicillin and tetracycline, moderate to kanamycin and low to amoxicillin/clavulanic acid and cefazolin. The MIC_50/90 of danofloxacin, enrofloxacin and marbofloxacin were 0.03 and 0.06 μg/mL. For Klebsiella spp. (n = 70), similar results were noted, except for ampicillin and kanamycin. We detected 3.7 % (11/295) Enterobacteriaceae isolates carrying an ESBL/AmpC gene. Staphylococcus aureus (n = 247) and coagulase-negative staphylococci (CoNS; n = 189) isolates were susceptible to most antimicrobials tested except to penicillin (25.1 and 29.1 % resistance). Two S. aureus and thirteen CoNS isolates harboured mecA gene. Streptococcus uberis isolates (n = 208) were susceptible to β-lactam antibiotics (87.1-94.7 % susceptibility), 23.9 % were resistant to erythromycin and 37.5 % to tetracycline. Resistance to pirlimycin was moderate. For Streptococcus dysgalactiae (n = 132) the latter figures were 10.6 and 43.2 %; pirlimycin resistance was low. MIC values for Streptococcus agalactiae, Trueperella pyogenes and Corynebacterium spp. were generally low. This current VetPath study shows that mastitis pathogens were susceptible to most antimicrobials with exceptions of staphylococci against penicillin and streptococci against erythromycin or tetracycline. For most antimicrobials, the percentage resistance and MIC_50/90 values among the major pathogens were comparable to that of the preceeding VetPath surveys. This work highlights the high need to set additional clinical breakpoints for antimicrobials frequently used to treat mastitis.

Molecular Detection of Multidrug Resistant Staphylococcus aureus Isolated from Bovine Mastitis Milk in Bangladesh

The current study was conducted to isolate and identify multidrug-resistant Staphylococcus aureus (MDR-SA) from mastitis milk samples and to determine their antimicrobial susceptibility pattern. A total of 48 bovine mastitis (BM) milk samples were collected from different parts of the Rangpur division, Bangladesh. After the collection of milk samples, mastitis was confirmed using the California mastitis test. Isolation and identification of Staphylococcus aureus were performed using conventional cultural and biochemical tests as well as using molecular methods of PCR. Nucleotide sequence analysis of the 23S rRNA gene of Staphylococcus aureus was determined. The antibiogram of the isolated bacteria was conducted using the disc diffusion method. Phylogenetic analysis of 23S rRNA was done using MEGA 7, ClustalW multiple sequence alignment, and NCBI-BLAST tools, where the sequence of the isolate showed 98% to 99% identity. Antibiogram test using 15 antimicrobial agents showed that all of the Staphylococcus aureus isolates were classified as multidrug-resistant (MDR). It was found that the isolates were resistant to tetracycline, novobiocin, methicillin, vancomycin, and cephradine, and the isolates were sensitive to ciprofloxacin, azithromycin, norfloxacin, levofloxacin, gentamicin, and amoxicillin. The detection of MDR-SA in mastitis milk is alarming and represents a great public health concern. The findings of the present study help identify Staphylococcus aureus at the molecular level using 23S rRNA gene sequencing and will help select the appropriate and effective antimicrobial agent to control BM in the northern part of Bangladesh.

Extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in cattle production - a threat around the world

Food producing animal is a global challenge in terms of antimicrobial resistance spread. Extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae are relevant opportunistic pathogens that may spread in many ecological niches of the One Health approach as human, animal and environment due to intestinal selection of antimicrobial resistant commensals in food production animals. Cattle production is a relevant ecological niche for selection of commensal bacteria with antimicrobial resistance from microbiota. Enterobacteriaceae show importance in terms of circulation of resistant-bacteria and antimicrobial resistance genes via food chain creating a resistance reservoir, setting up a threat for colonization of humans and consequent health risk. ESBL-producing Enterobacteriaceae are a threat in terms of human health responsible for life threatening outbreaks and silent enteric colonization of community populations namely the elder population. Food associated colonization is a risk difficult to handle and control. In a time of globalization of food trading, population intestinal colonization is a mirror of food production and in that sense this work aims to make a picture of ESBL-producing Enterobacteriaceae in animal production for food over the world in order to make some light in this reality of selection of resistant threats in food producing animal.

Antimicrobial Activity of Lactic Acid Bacteria Starters against Acid Tolerant, Antibiotic Resistant, and Potentially Virulent E. coli Isolated from a Fermented Sorghum-Millet Beverage

Bacterial contamination of fermented foods is a serious global food safety challenge that requires effective control strategies. This study characterized presumptive E. coli isolated from Obushera, a traditional fermented cereal beverage from Uganda. Thereafter, the antimicrobial effect of lactic acid bacteria (LAB) previously isolated from Obushera, against the E. coli, was examined. The presumptive E. coli was incubated in brain heart infusion broth (pH = 3.6) at 25°C for 48 h. The most acid-stable strains were clustered using (GTG)5 rep-PCR fingerprinting and identified using 16S rRNA sequencing. E. coli was screened for Shiga toxins (Stx 1 and Stx 2) and Intimin (eae) virulence genes as well as antibiotic resistance. The spot-on-the-lawn method was used to evaluate antimicrobial activity. Eighteen isolates were acid stable and are identified as E. coli, Shigella, and Lysinibacillus. The Stx 2 gene and antibiotic resistance were detected in some E. coli isolates. The LAB were antagonistic against the E. coli. Lactic acid bacteria from traditional fermented foods can be applied in food processing to inhibit pathogens. Obushera lactic acid bacteria could be used to improve the safety of fermented foods.

Antimicrobial resistance and genetic characterization of coagulase-negative staphylococci from bovine mastitis milk samples in Korea

Coagulase-negative staphylococci (CNS) are one of the most common bovine mastitis pathogens found worldwide. In this study, we investigated the prevalence and distribution of CNS species in mastitis milk samples and further characterized the methicillin-resistant (MR) CNS. A total of 311 CNS were isolated from 3,692 quarter milk samples from 1,373 dairy cattle at 81 farms between 2013 and 2017. Further evaluation of the CNS isolates revealed 14 CNS species among the samples and 3 predominant species-namely, Staphylococcus chromogenes, Staphylococcus simulans, and Staphylococcus epidermidis. Resistance was higher in S. epidermidis than in other CNS species except for resistance against oxacillin in Staphylococcus sciuri. Resistance to β-lactams was the most common in all CNS species (8.4% in ampicillin, 21.2% in oxacillin, and 13.5% in penicillin). Conversely, only minimal resistance to cephalothin, ceftiofur, and pirlimycin/novobiocin was found. Twenty-one isolates from 4 species were mecA-carrying MRCNS strains, including 18 S. epidermidis and 1 each of S. sciuri, Staphylococcus equorum, and Staphylococcus hominis. The majority of the mecA-carrying MRCNS isolates were produced in the biofilm. Furthermore, multidrug-resistant sequence type 179 isolate produced the strongest biofilm. Seven genotypes were detected in the 18 MR S. epidermidis strains, the most predominant of which persisted on a farm for 2 yr. Our findings for the antimicrobial susceptibility profiles and genotypic characterization of the MRCNS isolates could provide valuable information for controlling the spread of resistance and the selection of appropriate antimicrobial therapies for mastitis in the future. Further, strategic antibiotic use for mastitis treatment and hygienic management practices aimed at the prevention of the growth of resistant bacteria are urgently needed on dairy farms.

Phenotypic antimicrobial susceptibility of environmental bacteria from mastitic milk of pastured dairy cows of S. Miguel (Azores)

The aim of this study was to evaluate the phenotypic (in vitro) antimicrobial susceptibility of milk pathogens isolated from subclinical and clinical mastitis in outdoor dairy herds of S. Miguel, Azores. Between January and March 2018, a total of 144 isolates was obtained from dairy cows with mastitis. Escherichia coli (38.9%; n = 56), Streptococcus uberis (20.1%; n = 29), and coagulase-negative staphylococci (17.4%; n = 25) were the major milk pathogens isolated. An in vitro average susceptibility of 52.0% was observed for 13 different antimicrobials (n = 725). According to an analysis of the mean for proportions, the proportions of bacterial isolates presenting in vitro susceptibility to danofloxacin (75.3%; P < 0.001) and to trimethoprim-sulfamethoxazole (25.0%; P < 0.05) were outside of the upper (65.8%) and lower (25.6%) decision lines, respectively. This profile was related to mainly with E. coli and Strep. uberis isolates. Multidrug resistance was observed in 2.1% isolates, namely, in two Strep. uberis strains from the same farm and one Enterococcus sp. strain. In conclusion, varying degrees of in vitro susceptibility of milk pathogens to the tested antimicrobials were observed, suggesting that these environmental bacteria probably play an important role in the spread of antimicrobial resistances in pastures. The use of fluoroquinolones to treat mastitis of dairy cows should be carefully evaluated in order to maintain their suitability for human medicine.

Analysis of milk-derived isolates of E. coli indicating drug resistance in central Ethiopia

Mastitis is one of the most important diseases in dairy cows throughout the world and is responsible for significant economic losses to the dairy industry. This study was performed to characterize the genetic basis of drug resistance in Escherichia coli isolated from cases of clinical and sub-clinical bovine mastitis. A total of 224 California mastitis test (CMT)-positive milk samples were collected from December 2015 to April 2016 to characterize the phenotypic and genetic basis of antimicrobial resistance in E. coli isolated from raw milk from dairy farms found in Burayu, Sebeta, and Holeta areas of Ethiopia. The prevalence of E. coli was 7.1% (16) and both phenotypic and molecular techniques were used to identify E. coli antimicrobial susceptibility trait. The most commonly observed phenotypic resistance was against ampicillin (68.7%), sulphamethazole-trimethoprim (50%), and streptomycin (25%). Multidrug resistance phenotypes were found in 11 of 16 (68.7%) of E. coli isolates. Tetracycline (tet (A)) and chloramphenicol (cml (A)) genes were the most predominant encoding resistance genes identified (50%) each, followed by gentamycin resistance encoding gene (aac (3)-IV) (37.5%). Overall, 11 (68.7%) of the isolates had multidrug resistance genes responsible to two or more classes of antibiotics. The most common pattern detected was cml (A) and tet (A) together 37.5% followed by aac (3)-IV and tet (A) 25%. The current study indicated that raw milk could be regarded as critical source of antibiotic-resistant pathogenic E. coli.

Prevalence, identification of virulence factors, O-serogroups and antibiotic resistance properties of Shiga-toxin producing Escherichia coli strains isolated from raw milk and traditional dairy products

Background

Shiga-toxigenic Escherichia coli strains are one of the most important foodborne bacteria with an emergence of antibiotic resistance. Foodborne STEC strains are mainly associated with presence of certain virulence factors and O-seogroups. The present investigation was done to study the distribution of virulence factors, O-serogroups and antibiotic resistance properties of Shiga-toxigenic Escherichia coli isolated from milk and dairy products.

Methods

Six-hundred samples were randomly collected and immediately transferred to laboratory. All samples were cultured and E. coli strains were isolated. STEC strains were identified based on the presence of putative virulence factors and subtypes. STEC isolates were subjected to multiplex PCR and disk diffusion methods.

Results

One-hundred and eighty-one out of 600 samples (30.16%) harbored E. coli. Prevalence of STEC strains was 10.66%. O157 (43.75%) and O26 (37.50%) were the most frequently identified serogroups. Aac(3)-IV (100%), CITM (96.87%) and tetA (76.56%) were the most commonly detected antibiotic resistance genes. STEC strains had the highest prevalence of resistance against ampicillin (100%), gentamicin (100%) and tetracycline (96.87%).

Conclusions

Kashk and dough were negative for presence of E. coli strains. High prevalence of resistant-O157 strains and simultaneous presence of multiple virulence factors pose an important public health problem regarding the consumption of raw milk and dairy products.

Characteristics of quinolone-resistant Escherichia coli isolated from bovine mastitis in China

Escherichia coli is the leading causative agent of bovine mastitis worldwide. Quinolone-resistant E. coli is becoming a potential threat to veterinary and public health. The aim of this study was to investigate the characteristics of quinolone-resistant E. coli isolated from bovine mastitis cases in China. Antimicrobial susceptibility of the isolates against 15 antimicrobial agents was determined by disc diffusion method. Phylogenetic grouping was detected by PCR. Extended-spectrum β-lactamase-producing isolates were determined by double-disc synergy test. In addition, the plasmid-mediated quinolone resistance (PMQR) and β-lactamase-encoding genes, as well as mutations of quinolone resistance-determining regions in GyrA, GyrB, ParC, and ParE, were measured by PCR and DNA sequencing. Overall, 75 (22.9%) out of 328 E. coli isolates were confirmed as ciprofloxacin-resistant from 2,954 mastitic milk samples. Phylogenetic group analysis showed that the majority of these strains belonged to phylogenetic group A (57.3%) and group B1 (24.0%). All the resistant isolates were identified as multidrug resistant, showing high resistance to cephalosporins and non-β-lactams. Forty-nine (65.3%) of the quinolone-resistant isolates were positive for PMQR genes; aac-(6')-Ib-cr was the most common PMQR determinant detected in 33 (44.0%) isolates. Eighteen (24.0%), 4 (5.3%), 3 (4.0%), and 1 (1.3%) of the quinolone-resistant isolates were harboring oqxA/B, qepA4, qnrS, and qnrB2, respectively. Additionally, 55 (73.3%) of the quinolone-resistant E. coli isolates were found to be extended-spectrum β-lactamase producers. The preponderant β-lactamase-encoding gene, bla_TEM, was detected in 44 (58.7%) isolates; bla_CTX-M, bla_CMY, and bla_SHV were found in 35 (46.7%), 22 (29.3%), and 2 (2.7%) isolates, respectively. Moreover, the most frequently identified substitutions were S83L/D87N or S83L in GyrA, detected in all of the quinolone-resistant isolates. Meanwhile, 74 (98.7%), 33 (44.0%), and 6 (8.0%) of the isolates were carrying substitutions S80I in ParC, S458A in ParE, and S492N in GyrB, respectively. All 58 (77.3%) isolates with a high level of ciprofloxacin resistance (>32 µg/mL) carried single or double mutations in GyrA combined with single mutation in ParC. To the best of our knowledge, this is the first report on the high occurrence of PMQR determinants and quinolone-determining resistant regions mutations in quinolone-resistant E. coli isolated from bovine mastitis in China.