Fluoroquinolone-resistant and extended-spectrum β-lactamase-producing Escherichia coli from the milk of cows with clinical mastitis in Southern Taiwan

Background/Purpose Escherichia coli is a common pathogen to cause clinical and subclinical mastitis in cows. A total of 57 E. coli isolates from raw milk from cows were characterized genetically and biochemically. Methods Extended-spectrum β-lactamase (ESBL) genes, the mechanism for fluoroquinolone resistance, and variations in virulence genes and genomes of these E. coli isolates were investigated by the antimicrobial susceptibility test , simplex and multiplex polymerase chain reaction (PCR), and pulsed-field gel electrophoresis (PFGE). Results All E. coli isolates were resistant to cloxacillin (100%) and to a lesser extent (50%) to tetracycline , neomycin , gentamycin , ampicillin , ceftriaxone , cefotaxime (CTX), and ceftazidime (CAZ). Nearly 70% of the isolates were resistant to at least two antimicrobials and 28.1% carried AmpA and AmpC genes simultaneously. The predominant bla gene was bla TEM , followed by bla CMY , bla CTX , bla SHV , and bla DHA. Among the six (10.5%) ESBL-producing E. coli carrying bla CTX-M15 , bla CTX-M55 , or bla CTX-M14 , two isolates 31 of ST410 in the ST23 complex and 58 of ST167 in the ST10 complex were also resistant to ciprofloxacin , enrofloxacin , and levofloxacin , with mutations at codon 83 from serine to leucine and codon 87 from aspartic acid to asparagine in GyrA and at codon 80 from serine to isoleucine in ParC. These isolates were genetically diverse in pulsotype analysis, lacked toxin genes of human pathogenic E. coli and carried mostly the prevalent virulence genes fimH , papGII , and α-hemolysin . Conclusion Lacking virulence genes examined, genetic diverse E. coli isolates are unrelated to human pathogenic E. coli . Enhancing sanitation in milk processing and transportation is needed to eliminate multidrug-resistant (MDR), fluoroquinolone-resistant, and ESBL-producing E. coli isolates.