Antibiotic Resistance Monitoring & Reference Laboratory, Health Protection Agency Microbiology Services, Colindale, London NW9 5EQ, UK.
J Antimicrob Chemother. 2012 Jun;67(6):1354-8. doi: 10.1093/jac/dks079. Epub 2012 Mar 22.
Ceftaroline + avibactam (NXL104) is a novel inhibitor combination active against Enterobacteriaceae with class A and C β-lactamases. We investigated its risk of mutational resistance.
Single- and multi-step mutants were sought and characterized from Enterobacteriaceae with extended-spectrum β-lactamases (ESBLs), AmpC β-lactamases and KPC β-lactamases.
Overgrowth occurred on agar with low MIC multiples of ceftaroline + avibactam, but frequencies for single-step mutants were <10(-9). Most mutants were unstable, with only three remaining resistant on subculture. For one, from an CTX-M-15-positive Escherichia coli, the ceftaroline + avibactam MIC was raised, but the organism had reduced resistance to ceftaroline and lost resistance to other oxyimino-cephalosporins, with this profile retained when the mutant bla(CTX-M-15) was cloned into E. coli DH5α. Sequencing identified a Lys237Gln substitution in the CTX-M-15 variant. The other two stable single-step mutants were from an AmpC-derepressed Enterobacter cloacae strain; these had unaltered or slightly reduced resistance to other β-lactams. Both had amino acids 213-226 deleted from the Ω loop of AmpC. Further stable mutants were obtained from AmpC-inducible and -derepressed E. cloacae in multi-step selection, and these variously had reduced expression of OmpC and OmpF, and/or Asn366His/Ile substitutions in AmpC.
Stable resistant mutants were difficult to select. Those from AmpC-derepressed E. cloacae had porin loss or AmpC changes, including Ω loop deletions. A Lys237Gln substitution in CTX-M-15 conferred resistance, but largely abolished ESBL activity.
头孢他啶+阿维巴坦（NXL104）是一种新型抑制剂组合，对具有 A 类和 C 类β-内酰胺酶的肠杆菌科具有活性。我们研究了它产生突变耐药性的风险。
从具有扩展谱β-内酰胺酶（ESBLs）、AmpC β-内酰胺酶和 KPC β-内酰胺酶的肠杆菌科中寻找并表征单步和多步突变体。
在琼脂上出现了低 MIC 倍数的头孢他啶+阿维巴坦的过度生长，但单步突变体的频率<10(-9)。大多数突变体不稳定，只有三个在传代培养中仍然具有抗性。对于一个来自 CTX-M-15 阳性大肠杆菌的突变体，头孢他啶+阿维巴坦的 MIC 升高，但该菌对头孢他啶的耐药性降低，对其他氧肟头孢菌素的耐药性丧失，当突变 bla(CTX-M-15) 被克隆到大肠杆菌 DH5α 中时，保留了这种表型。测序确定 CTX-M-15 变体中的 Lys237Gln 取代。另外两个稳定的单步突变体来自一个 AmpC 去阻遏的阴沟肠杆菌株；这些突变体对其他β-内酰胺类药物的耐药性不变或略有降低。两个突变体的 AmpC 的Ω环都缺失了 213-226 个氨基酸。在多步选择中，从 AmpC 诱导和去阻遏的阴沟肠杆菌中进一步获得了稳定的突变体，这些突变体的 OmpC 和 OmpF 的表达减少，或 AmpC 中的 Asn366His/Ile 取代。
稳定的耐药突变体难以选择。那些来自 AmpC 去阻遏的阴沟肠杆菌的突变体失去了孔蛋白或 AmpC 发生了变化，包括Ω环缺失。CTX-M-15 中的 Lys237Gln 取代赋予了耐药性，但大大削弱了 ESBL 活性。
