The AmpC enzyme normally is expressed constitutively in Escherichia coli, and its overproduction confers resistance to cefoxitin. A newly reported AmpC, the extended-spectrum AmpC (ESAC), is related to resistance to cefepime, a fourth-generation cephalosporin. This enzyme presents more flexibility in the active site due to insertions, replacements, and deletions on AA sequences. Many isolates producing ESAC were reported in human clinical isolates, but E. coli ESAC producers were reported in animals only in France. The animal E. coli strains can produce this enzyme and possibly disseminate it to human and production environments. In our study, 3 strains of E. coli from milk and feces bovine samples, collected in Rio de Janeiro, Brazil, were suspected to produce ESAC. After excluding other mechanisms of resistance, the gene was sequenced to verify ESAC characteristics. These strains presented replacement of AA in omega and R2 loops, suggesting ESAC production. This is the first report to study ESAC E. coli in dairy farms in Brazil.

AmpC酶通常在大肠杆菌中组成性表达，并且其过量生产赋予对头孢西丁的抗性。最新报道的AmpC，即广谱AmpC（ESAC），与对第四代头孢菌素头孢吡肟的耐药性有关。由于AA序列上的插入，替换和缺失，该酶在活性位点表现出更大的灵活性。在人类临床分离株中报告了许多产生ESAC的分离株，但仅在法国报道了在动物中报道了大肠杆菌ESAC的生产者。动物大肠杆菌菌株可以产生这种酶，并可能将其传播给人类和生产环境。在我们的研究中，有3株大肠杆菌怀疑从巴西里约热内卢收集的牛奶和粪便牛样品中的牛样品产生了ESAC。在排除其他抗性机制后，对该基因进行测序以验证ESAC特性。这些菌株在ω和R2环中呈现出AA置换，表明产生了ESAC。这是在巴西奶牛场研究ESAC大肠杆菌的第一份报告。