Prof Benjamin M Pulimood Laboratories for Infection, Immunity & Inflammation, Medicine Unit I & Infectious Diseases, Christian Medical College, Vellore, India.
Indian J Med Res. 2012 Mar;135(3):359-64.
BACKGROUND & OBJECTIVES: AmpC β-lactamases which are often plasmid mediated hydrolyze all β-lactam antibiotics except cefepime and carbapenems. We evaluated the presence of AmpC β-lactamases among Enterobacteriaceae strains recovered prospectively from patients at five Indian tertiary care centres.
The study included 909 consecutive Gram-negative isolates recovered from clinically significant specimens during June 2007 - May 2008 as part of an ICMR-ESBL study. Among the study isolates, 312 were found to be cefoxitin resistant by disc diffusion test (DDT). Minimum inhibitory concentration (MIC) determination by E test was done against amikacin, levofloxacin, impinem, meropenem, ertapenem, tigecycline and piperacillin-tazobactam. Combined DDT using phenyl boronic acid as inhibitor with cefoxitin was used for phenotypic confirmation of AmpC phenotype. The common Amp C genotypes ACC, FOX, MOX, DHA, CIT and EBC were detected by multiplex PCR.
Plasmid mediated Amp C phenotype was confirmed in 114 of the 312 (36.5%) cefoxitin resistant isolates with 255 (81.7%) showing multidrug resistance. Susceptibility to tigecycline was highest (99%) followed by imipenem, meropenem (97%), ertapenem (89%), amikacin (85%), and piperacillin-tazobactam (74.6%). Levofloxacin resistance was 82 per cent. ESBL co carriage was observed among 92 per cent of Amp C producers. Among 114 Amp C producers, 48 could be assigned a genotype, this included CIT- FOX (n = 25), EBC (n = 10), FOX (n = 4), CIT (n = 3), EBC-ACC (n = 2) and one each of DHA, EBC-DHA, FOX -DHA and FOX-EBC-DHA.
INTERPRETATION & CONCLUSIONS: Overall, AmpC phenotypes were found in 12.5 per cent isolates, multidrug resistance and ESBL co-carriage among them was high suggesting plasmid mediated spread. The study results have implications in rational antimicrobial therapy and continued surveillance of mechanisms of resistance among nosocomial pathogens.
AmpC β-内酰胺酶通常由质粒介导，可水解除头孢吡肟和碳青霉烯类以外的所有β-内酰胺类抗生素。我们评估了印度 5 家三级护理中心前瞻性采集的肠杆菌科菌株中 AmpC β-内酰胺酶的存在情况。
该研究纳入了 2007 年 6 月至 2008 年 5 月间临床标本中分离的 909 株连续的革兰氏阴性菌，作为 ICMR-ESBL 研究的一部分。在研究分离株中，312 株经纸片扩散试验（DDT）证实对头孢西丁耐药。通过 E 试验测定阿米卡星、左氧氟沙星、亚胺培南、美罗培南、厄他培南、替加环素和哌拉西林他唑巴坦的最低抑菌浓度（MIC）。使用苯硼酸作为抑制剂与头孢西丁联合使用，对 AmpC 表型进行表型确证。采用多重 PCR 检测常见的 Amp C 基因型 ACC、FOX、MOX、DHA、CIT 和 EBC。
在 312 株头孢西丁耐药的分离株中，有 114 株（36.5%）证实为质粒介导的 Amp C 表型，其中 255 株（81.7%）表现出多重耐药。替加环素的敏感性最高（99%），其次是亚胺培南、美罗培南（97%）、厄他培南（89%）、阿米卡星（85%）和哌拉西林他唑巴坦（74.6%）。左氧氟沙星耐药率为 82%。在 Amp C 产生菌中，ESBL 共携带率为 92%。在 114 株 Amp C 产生菌中，48 株可被分配基因型，其中包括 CIT-FOX（n=25）、EBC（n=10）、FOX（n=4）、CIT（n=3）、EBC-ACC（n=2）和 1 株 DHA、EBC-DHA、FOX-DHA 和 FOX-EBC-DHA。
总体而言，在 12.5%的分离株中发现了 Amp C 表型，其中多重耐药和 ESBL 共携带率较高，提示质粒介导的传播。研究结果提示在医院获得性病原体的合理抗菌治疗和持续监测耐药机制方面具有重要意义。
