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Carbapenems have been the most successful beta-lactam antibiotics in evading bacterial resistance. Nevertheless, acquired carbapenemases are increasingly reported, mostly in Pseudomonas and Acinetobacter isolates but occasionally also in Enterobacteriaceae. They include beta-lactamases of classes B (IMP and VIM), D (OXA-23 to -27) and A (IMI, KPC, NMC and SME). Major outbreaks of producers have occurred in a few centers and, in the US, there has been progressive erosion of carbapenem activity against Acinetobacter species, maybe due to carbapenemases. Acquired carbapenemases are still sufficiently rare not to have placed widespread constraints on chemotherapy, but there is reasonable concern that they will become a greater problem in the future. This is a good argument for continued caution with carbapenem use, and for extending this prudence to the oral and long half-life carbapenems shortly to become available. Most carbapenemase producers are broadly resistant to beta-lactams, and many are also resistant to fluoroquinolones and aminoglycosides. Clinicians facing infections caused by carbapenemase producers consequently are forced to use 'unusual' antibiotics such as polymyxins, isepamicin, minocycline and sulbactam (Pfizer Inc), which has inherent activity against A baumannii. Carbapenemase inhibitors might be developed in the future, despite difficulties in choosing the range of enzymes to target and obtaining broad-spectrum inhibition. For now, the best pharmaceutical strategy seems to lie in the development of novel antimicrobial classes with anti-Gram-negative activity, rather than in overcoming carbapenemases directly.
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PMID:The impact of carbapenemases on antimicrobial development and therapy. 1202 49

Carbapenem-hydrolyzing beta-lactamases of several Ambler molecular classes have been reported as the source of acquired beta-lactam antibiotic resistance in Gram negative bacteria. The metallo-enzymes of Ambler class B are the most prevalent enzymes in this case. These clavulanic-acid resistant enzymes have a large spectrum of hydrolysis including penicillins, cephalosporins (third and fourth generations), carbapenems but not monobactams. They are responsible for acquired resistance in several Gram negative species of clinical relevance in human medicine. IMP-1 was the first reported as acquired in Japan, mostly from Serratia marcescens and Pseudomonas aeruginosa isolates, and has been detected in Europe recently. Several variants of IMP-1 (IMP-2 to -9) have been characterized, possessing 85 to 99% amino acid identity, mostly from P. aeruginosa isolates. In addition, VIM-1 to -3 beta-lactamases have also been described, first in Europe (Italy, France, and Greece) and now in Korea. The VIM series shares 30% amino acid identity with the IMP-series. Most of these class B enzymes have genes that are integron- and plasmid-located. Finally, a few Ambler class A (SME-1, NMC-A, IMI-1, KPC-1) and class D (OXA-23 to -27) beta-lactamases involved in carbapenem hydrolysis have been reported also from rare isolates of Gram-negative rods. This review underlines the worldwide spread of carbapenem-hydrolyzing beta-lactamases as representing an important threat for efficacy of antibiotics in the near future.
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PMID:Acquired carbapenem-hydrolyzing beta-lactamases and their genetic support. 1202 55

Carbapenemases may be defined as beta-lactamases that significantly hydrolyze at least imipenem or/and meropenem. Carbapenemases involved in acquired resistance are of Ambler molecular classes A, B, and D. Class A, clavulanic acid-inhibited carbapenemases are rare. They are either chromosomally encoded (NMC-A, Sme-1 to Sme-3, IMI-1) in Enterobacter cloacae and Serratia marcescens, or plasmid encoded, such as KPC-1 in Klebsiella pneumoniae and GES-2 in Pseudomonas aeruginosa, the latter being a point-mutant of the clavulanic acid-inhibited extended-spectrum beta-lactamase GES-1. The class B enzymes are the most clinically significant carbapenemases. They are metalloenzymes of the IMP or VIM series. They have been reported worldwide but mostly from South East Asia and Europe. Metalloenzymes, whose genes are plasmid and integron located, hydrolyze virtually all beta-lactams except aztreonam. Finally, the class D carbapenemases are increasingly reported in Acinetobacter baumannii but compromise imipenem and meropenem susceptibility only marginally. The sources of the acquired carbapenemase genes remain unknown, as does the relative importance of the spread of epidemic strains as opposed to the spread of plasmid- or integron-borne genes. Because most of these carbapenemases confer only reduced susceptibility to carbapenems in Enterobacteriaceae, they may remain underestimated as a consequence of the lack of their detection.
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PMID:Emerging carbapenemases in Gram-negative aerobes. 1208 99

Ertapenem is a carbapenem that shares the activity of imipenem and meropenem against most species, but is less active against non-fermenters. Activity is retained against most strains with AmpC and extended-spectrum beta-lactamases, although resistance can arise if these enzymes are combined with extreme impermeability. Resistance can also be caused by IMP, VIM, KPC and NMC carbapenemases, but again, co-requires impermeability. Although the spread of carbapenemases in the future is a concern, they are currently very rare. Given as a 1 g intravenous (iv) infusion once daily, ertapenem has a plasma half-life of approximately 4 h in healthy volunteers, and a Cmax of 155 mg/L and 13 mg/L for total and free drug, respectively. Excretion is largely renal, divided equally between native drug and an open-ring derivative. Trials show equivalence to piperacillin/tazobactam or ceftriaxone in (a) intra-abdominal infections, (b) community-acquired pneumonia, (c) acute pelvic infections, (d) skin and skin structure infections and (e) complicated urinary tract infections. The USA licence grants all these five indications; the EU licence grants the first three. Further potential uses include home iv therapy, directed therapy against Enterobacteriaceae with AmpC or extended-spectrum cephalosporinases, and tentatively, surgical prophylaxis. Widening the usage of carbapenems raises public health concerns, somewhat allayed by the continued rarity of carbapenemases after 17 years of imipenem use, and by the fact that carbapenemases occur mostly in non-fermenters outside the spectrum of ertapenem, and co-require impermeability to confer resistance in Enterobacteriaceae. Nevertheless, if ertapenem is to be used widely, its effects on the resistance ecology need to be monitored carefully.
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PMID:Properties and potential of ertapenem. 1291 43

Doripenem (S-4661), a new parenteral carbapenem, was tested against over 250 clinical isolates, mutants, and transconjugants of Enterobacteriaceae and Acinetobacter spp., selected or derived for their beta-lactamase expression characteristics. Imipenem, meropenem, and ertapenem were tested as comparators, along with cephalosporins and piperacillin-tazobactam, by using National Committee for Clinical Laboratory Standards agar dilution methodology. Doripenem MICs were from 0.03 to 0.25 microg/ml for Klebsiella isolates, irrespective of the presence of extended-spectrum beta-lactamases (ESBLs) or plasmid-mediated AmpC or hyperproduced K1 beta-lactamase. Similarly, MICs of doripenem for both AmpC-inducible and -derepressed Enterobacter isolates were 0.06 to 0.5 microg/ml. ESBL production did not raise the MICs of doripenem for Escherichia coli transconjugants, and studies with known expression mutants confirmed that neither inducible nor depressed AmpC beta-lactamase expression was protective in Enterobacter cloacae, Citrobacter freundii, Serratia marcescens, or Morganella morganii. In all of these respects, doripenem resembled meropenem and imipenem, whereas the MICs of ertapenem were raised (but still < or =1 microg/ml) for many ESBL-producing klebsiellas and AmpC-derepressed E. cloacae and C. freundii strains. Resistance to all carbapenems, including doripenem (MICs of mostly 16 to 64 microg/ml, compared with 0.25 to 1 microg/ml for typical strains), was seen in Acinetobacter isolates with metallo-beta-lactamases or OXA-carbapenemases. Isolates of Klebsiella and Serratia spp. with IMP, KPC, and SME beta-lactamases also were resistant to doripenem (MICs, 8 to >64 microg/ml) and to other carbapenems, although the continued apparent susceptibility (MICs, < or =0.5 microg/ml) of E. coli derivatives with cloned IMP-1 and NMC-A beta-lactamases suggested that carbapenem resistance might require other factors besides the enzymes.
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PMID:Comparative activities of doripenem versus isolates, mutants, and transconjugants of Enterobacteriaceae and Acinetobacter spp. with characterized beta-lactamases. 1504 35

Resistance to beta-lactam antibiotics continues to increase, mostly due to the presence of various beta-lakta mases. As a result of the ability of the plasmids to acquire additional resistance determinants, many of the beta-lactamase producing pathogens became multidrug resistant. The most important beta-lactamases which compomise the use of beta-lactams nowdays are extended-spectrum beta-lactamases, inhibitor-resistant TEM and SHV beta-lactamases and carbapenemases. Carbapenemases are beta-lactamases which hydrolyse carbapenems. They belong to molecular classes A, B, and D. Class A comprises carbapenemases sensitive to inhibition by clavulanic acid. Most of them are chromosomaly encoded, but some of them are plasmid-mediated such as KPC-1 in Klebsiella pneumoniae and GES-2 in Pseudomonas aeruginosa. The class B carbapenemases are metallo-beta-lactamases of the IMP or VIM group. The class D carbapenemases are the most frequent in Acinetobacter baumannii but confer resistance to carbapenems only if other resistance mechanisms such as porin alterations, are present. Inhibitor resistant beta-lactamases are one of the most important causes of resistance to beta-lactam-inhibitor combinations. The resistance to these formulations can be also due to hyperproduction of TEM-1 beta-lactamase, modifications of the outer membrane proteins or production of OXA-type enzymes. IRT enzymes are derived from parenthal TEM-1 or TEM-2 beta-lactamases by point mutations in the beta-lactamase gene. The frequent use of beta-lactamase inhibitors in hospitals and general practice pose a selection pressure which favours spread of such strains in hospitals and community.
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PMID:[Beta-lactamases and their role in resistance. PART 2: beta-lactamases in 21st century]. 1614 68

The acquired resistance against the wide-spectrum and highly stable beta-lactams including third-generation cephalosporins (3GC) and carbapenems is constinuously increasing and widespead with the discovery of various plasmid-encoded, or genes cassette or integrons coding for a novel beta-lactamase, always a major mechanism of resistance. To explain resistance against 3GC, with the continuing story with TEM and SHV mutated enzymes, several types of ESBL (class A) emerge the CTX-M type, at least CTX-M-40, but also other non predominant types intitled BES, GES, PLA, PER, VEB. The wider resistance including 3GC, cephamycins and beta-lactamase inhibitor is correlated to synthesis of transferable cephalosporinases (class C) usually located in the chromosome but mobilized from Enterobacter spp., Citrobacter freundii, Hafnia alvei, Morganella morganii, Aeromonas caviae. Such genes encoded the following types: ACC-1, ACT-1, CFE-1, CMY group, DHA-1, FOX group, MIR-1, MOX-1. Finally the resistance against carbapemens e.g. imipenem originally restricted to Pseudomonas aeruginosa, then to Acinetobacter baumannii and finally to enterobacteria is related to production of novel enzymes (classes B, D and A) denominated IMP, VIM SME, GIM, OXA, KPC. A striking exemple of evolution towards more and more resistance is given by Salmonella, even from animal origins, a great threat fo public health. So far it appears necessary to perform molecular approaches to identify such enzymatic production. Finally because the absence of real new drugs, the discovery of some progenitors of the gene beta-lactamase, a strict control of beta-lactam antibiotics must be provide not only in medecine or veterinary field but also in agriculture, including aquaculture for example.
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PMID:[Beta-lactamases of Gram negative bacteria: never-ending clockwork!]. 1642 Sep 89

Ertapenem is a carbapenem that shares the activity of imipenem and meropenem against most species, but is less active against non-fermenters. The activity is retained against most strains with AmpC and extended-spectrum beta-lactamases, although the resistance can arise if these enzymes are combined with extreme impermeability. The resistance can also be caused by IMP, VIM, KPC and NMC carbapenemases, but again, co-requires impermeability. Although the spread of carbapenemases in the future is a concern, they are currently very rare. Given as a 1 g intravenous (i.v.) infusion once daily, ertapenem has a plasma half-life of -4 h in healthy volunteers, and a Cn,a, of 155 mg/l and 13 mg/l for total and free drug, respectively. Excretion is largely renal, divided equally between native drug and an open-ring derivative. The trials showed equivalence to piperacillin/tazobactam or ceftriaxone in (a) abdominal infections, (b) community-acquired pneumonia, (c) acute pelvic infections, (d) skin and skin structure infections and (e) complicated urinary tract infections. The USA licence grants all these five indications; the ED licence grants the first three. Further potential uses include home i.v. therapy, target therapy against Enterobacteriaceae with AmpC or extended-spectrum cephalosporinases, and tentatively, surgical prophylaxis. Widening the usage of carbapenems raises public health concerns, somewhat allayed by the continued rarity of carbapenemases after 17 years of imipenem use, and by the fact that carbapenemases occur mostly in non-fermenters outside the spectrum of ertapenem, and co-require impermeability to confer resistance in Enterobacteriaceae. Nevertheless, if ertapenem is to be used widely, its effects on the microbial resistance ecology need to be monitored carefully.
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PMID:[Ertapenem and other antibacterials]. 1687 90

Carbapenemases are beta-lactamases with versatile hydrolytic capacities. They have the ability to hydrolyze penicillins, cephalosporins, monobactams, and carbapenems. Bacteria producing these beta-lactamases may cause serious infections in which the carbapenemase activity renders many beta-lactams ineffective. Carbapenemases are members of the molecular class A, B, and D beta-lactamases. Class A and D enzymes have a serine-based hydrolytic mechanism, while class B enzymes are metallo-beta-lactamases that contain zinc in the active site. The class A carbapenemase group includes members of the SME, IMI, NMC, GES, and KPC families. Of these, the KPC carbapenemases are the most prevalent, found mostly on plasmids in Klebsiella pneumoniae. The class D carbapenemases consist of OXA-type beta-lactamases frequently detected in Acinetobacter baumannii. The metallo-beta-lactamases belong to the IMP, VIM, SPM, GIM, and SIM families and have been detected primarily in Pseudomonas aeruginosa; however, there are increasing numbers of reports worldwide of this group of beta-lactamases in the Enterobacteriaceae. This review updates the characteristics, epidemiology, and detection of the carbapenemases found in pathogenic bacteria.
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PMID:Carbapenemases: the versatile beta-lactamases. 1763 Mar 34

Carbapenemases are beta-lactamases that hydrolyze most beta-lactams including carbapenems. Carbapenemases are classified in four molecular classes; those belonging to class A are the chromosomally-encoded and clavulanic acid-inhibited IMI, NMC-A and SME, identified in Enterobacter cloacae and Serratia marcescens; the plasmid-encoded KPC enzymes identified in Enterobacteriaceae (and rarely in Pseudomonas aeruginosa); and the GES-type enzymes identified in Enterobacteriaceae and P. aeruginosa. The class B enzymes are the most clinically-significant carbapenemases; they are metallo-beta-lactamases, mostly of the IMP and the VIM series. They have been reported worldwide and their genes are plasmid- and integron-located, hydrolyzing all beta-lactams with the exception of aztreonam. One single plasmid-mediated AmpC beta-lactamase, CMY-10, identified in an Enterobacter aerogenes isolate, has been shown to be a cephaslosporinase with some carbapenemase properties. Finally, the class D carbapenemases are being increasingly reported, mostly in Acinetobacter baumannii, and they compromise the efficacy of imipenem and meropenem significantly.
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PMID:Carbapenemases: molecular diversity and clinical consequences. 1792 73


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