Bonfiglio G, Laksai Y, Franchino L, Amicosante G, Nicoletti G
Instituto di Microbiologia, Università di Catania, Italy.
J Antimicrob Chemother. 1998 Dec;42(6):697-702. doi: 10.1093/jac/42.6.697.
The mechanisms of resistance to beta-lactam antibiotics in 325 isolates of Pseudomonas aeruginosa were examined. These isolates were selected because of their resistance to meropenem and imipenem (breakpoint, >4 mg/L), carbenicillin (>128 mg/L), ceftazidime (>8 mg/L), piperacillin and ticarcillin/clavulanate (>64 mg/L). The most frequent mechanism of resistance was beta-lactamase-independent, so called 'intrinsic resistance', which was found in 183 isolates and was probably due to impermeability and/or efflux mechanisms. beta-Lactamase-mediated resistance was demonstrated in 111 strains (11.1%). Derepression of Ambler Class C chromosomal beta-lactamase was detected in 64 isolates, most of which were resistant to ceftazidime and piperacillin but susceptible to meropenem, whereas secondary plasmid-encoded beta-lactamases were found in 34 isolates, all of them resistant to carboxypenicillins and ureidopenicillins and susceptible to carbapenems. Twelve strains showed more than one plasmid-encoded beta-lactamase plus derepression of chromosomal Class C enzyme. Resistance to carbapenems was independent of resistance to other beta-lactam antibiotics, indicating a different mechanism of resistance, probably due to the loss of the D2 porin. In total, 32 strains were resistant to carbapenems: 24 only to imipenem and eight to both imipenem and meropenem.
对325株铜绿假单胞菌对β-内酰胺类抗生素的耐药机制进行了研究。选择这些菌株是因为它们对美罗培南和亚胺培南耐药（折点，>4mg/L）、对羧苄西林耐药（>128mg/L）、对头孢他啶耐药（>8mg/L）、对哌拉西林和替卡西林/克拉维酸耐药（>64mg/L）。最常见的耐药机制是不依赖β-内酰胺酶的，即所谓的“固有耐药性”，在183株菌株中发现，可能是由于通透性降低和/或外排机制。111株菌株（11.1%）表现出β-内酰胺酶介导的耐药性。在64株菌株中检测到安布勒C类染色体β-内酰胺酶的去阻遏，其中大多数对头孢他啶和哌拉西林耐药但对美罗培南敏感，而在34株菌株中发现了继发性质粒编码的β-内酰胺酶，所有这些菌株对羧基青霉素和脲基青霉素耐药但对碳青霉烯类敏感。12株菌株表现出不止一种质粒编码的β-内酰胺酶加上染色体C类酶的去阻遏。对碳青霉烯类的耐药性与对其他β-内酰胺类抗生素的耐药性无关，表明存在不同的耐药机制，可能是由于D2孔蛋白的缺失。总共有32株菌株对碳青霉烯类耐药：24株仅对亚胺培南耐药，8株对亚胺培南和美罗培南均耐药。
