Activity Of Carbapenems Research Articles

First Class A Carbapenemase Isolated from Enterobacteriaceae in Argentina

Although many β-lactamases have been described as conferring resistance to β-lactam antibiotics, including extended-spectrum cephalosporins, production of acquired carbapenemases remains infrequent in Enterobacteriaceae. According to the National Survey for Antibiotic Resistance in Argentina (SIR Program) during 2000, carbapenem resistance was reported in only one enterobacterial isolate (out of 6,126 tested), identified as Enterobacter cloacae (1 of 128 strains). From 4,964 enterobacterial strains isolated during 2001, no carbapenem-resistant isolates were reported. Acquired carbapenemase ocurrence is already rare, although some belonging to molecular classes A, B and D have been described. Sme-1 to Sme-3, NMC-A, IMI-1, and KPC-1 to KPC-3 are, to date, the only known class A carbapenemases (1, 4, 5) (T. Hong, E.S. Moland, B. Abdalhamid et al., K. Young, P. Tierno, Jr., L. Tysall et al., Abstr. 43rd Intersci. Conf. Antimicrob. Agents Chemother., abstr. C1-665, 2003; K. Young, P. Tierno, Jr., L. Tysall et al., Abstr. 43rd Intersci. Conf. Antimicrob. Agents Chemother., abstr. C2-50, 2003). All but KPC enzymes have greater activity against imipenem than meropenem, conferring resistance to penicillins, cephalosporins, and aztreonam; oxymino-cephalosporins are weak substrates (8). They are well inhibited by clavulanate and tazobactam. E. cloacae D was isolated from blood cultures of a leukemic patient at the Hospital Israelita, Buenos Aires, Argentina, during 2000. Susceptibility tests were performed according to the recommendations of the National Committee for Clinical Laboratory Standards. The strain was resistant to imipenem and had intermediate resistance to meropenem (32 and 8 μg/ml, respectively), but was susceptible to ceftriaxone (0.125 μg/ml), ceftazidime (0.5 μg/ml), and cefepime (0.06 μg/ml). Clavulanate improved the activity of carbapenems by a factor of 4. Trimethroprim-sulfamethoxazole, aminoglycosides, polymyxin, and quinolone susceptibilities were conserved. Double-disk diffusion tests were performed with EDTA and amoxicillin-clavulanate disks placed near carbapenem disks. The β-lactamase was inhibited by the latter, suggesting the presence of a serine β-lactamase. The crude extract displayed two active bands after isoelectric focusing at apparent pIs of 5.4 (characterized as TEM-1) and 6.9 that were active on 500-μg/ml ampicillin; the latter was also active on 1,000-μg/ml imipenem, according to the iodometric overlay system (7). A 2,058-bp fragment was amplified by PCR with specific primers for nmcA (NMC1, 5′-GCATTGATATACCTTTAGCAGAGA-3′; and NMC4, 5′-CGGTGATAAAATCACACTGAGCATA-3′) (3), with genomic DNA as a template. No positive reaction could be obtained on plasmid DNA preparations. The amplicon was cloned at SmaI site of a pK19 vector (kanamycin resistance) (6) and introduced by transformation in competent Escherichia coli Top10 cells (Invitrogen). Transformants were selected on Luria-Bertani agar plates containing isopropyl-β-d-thiogalactopyranoside (IPTG; 1 mM), 5-bromo--4-chloro-3-indolyl-β-d-galactopyranoside (X-Gal; 40 μg/ml),and kanamycin (30 μg/ml). The sequence of this fragment showed the presence of two genes and an intercistronic region (the putative binding site for NMC-R) identical to nmcA and its regulator, nmcR ({type:entrez-nucleotide,attrs:{text:AJ536087,term_id:33112004,term_text:AJ536087}}AJ536087). Transformant TKC-1, expressing these genes, was also moderately resistant to carbapenems (MICs of 16 and 4 μg/ml for imipenem and meropenem, respectively). No inducibility could be detected by double-disk tests with ampicillin-sulbactam, despite the fact that some induction could be detected in the original strain. Inhibition of the enzyme was observed when both inhibitors were used in the same test with the transformant. We describe herein the detection of one imipenem-resistant E. cloacae isolate due to the production of a class A carbapenemase, NMC-A, corresponding to the first detection of this class of enzymes in South America. It is interesting to point out that, except for plasmid KPCs, the other class A carbapenemases have been chromosomally encoded in microorganisms in which there is a functional regulatory system ending in AmpC-AmpR, reinforcing the general concept that some (or all) of the regulatory system components play a role in the expression of these enzymes reported before (2).

Results from the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Programme: report of the 2001 data from 15 United States medical centres

The Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Programme is an international surveillance network of more than 100 medical centres where meropenem is the primary therapeutic carbapenem. Institutions have been monitored since 1997 (1999 in United States (US)) using National Committee for Clinical Laboratory Standards (NCCLS) reference susceptibility methods to monitor in vitro activity of meropenem and selected other broad-spectrum antimicrobial agents. In 2001, a total of 2874 strains were processed from the 15 US medical centres. Molecular methods were associated with MIC methods as needed for defining epidemic spread of resistant strains. The meropenem MIC 90 values were 0.03 mg/l for Citrobacter spp., Escherichia coli and Klebsiella spp.; 0.06 mg/l for Proteus mirabilis and Serratia spp. and 0.12 mg/l for Enterobacter spp. This potency was 8–16-fold greater than that of imipenem and the meropenem spectrum of activity versus the Enterobacteriaceae was the broadest of all tested antimicrobial agents. Only piperacillin/tazobactam (MIC 9, 64 mg/l) and tobramycin (MIC 90, 4 mg/l) were active against more than 90.0% of Pseudomonas aeruginosa at the NCCLS susceptible breakpoint, and the carbapenems were the most active compounds against Acinetobacter spp. However, Acinetobacter spp. isolates were resistant to all of the antimicrobial agents tested and the molecular typing results suggested that they were epidemiologically related. Only ciprofloxacin and ceftazidime had significantly reduced activity against oxacillin-susceptible staphylococci (87.9–92.6% susceptible. These 2001 US MYSTIC Programme results demonstrated no significant decline in carbapenem activity or susceptibility rates compared with the previously monitored years (1999–2000). Most apparent were the decreasing susceptibility rates for ciprofloxacin and ceftazidime against staphylococci. Continued surveillance in these institutions appears warranted as sites of high potential emerging resistance risk.

Pharmacology Review: Newer Antibiotics: Imipenem/cilastatin and Meropenem

The carbapenem antibiotics imipenem/cilastatin and meropenem offer therapeutic options for unusual and highly antibiotic-resistant organisms encountered in the neonatal intensive care unit. The agents have a very broad spectrum of antibiotic activity, favorable safety profiles, and good drug penetration into all body sites, making them a reasonable choice for term and preterm infants who have difficult-to-treat infections. Although a moderate amount of pharmacokinetic data support the safe use of carbapenem antibiotics in neonates, the broad-spectrum activity of the agents dictates that their use be limited to the treatment of highly resistant, nosocomially acquired bacteria and mixed aerobic and anaerobic infections. Carbapenems are beta-lactam antibiotics that have broad-spectrum aerobic and anaerobic activity. Like other beta-lactam antibiotics, they exert an antibacterial effect by binding penicillin-binding proteins, thereby disrupting bacterial cell wall synthesis. Because imipenem is rapidly degraded by renal proximal tubule dipeptidases, it is marketed in combination with the dipeptidase inhibitor cilastatin. Meropenem is stable to renal dipeptidases and requires no cilastatin. In adults and older children, imipenem and meropenem have been used extensively for treatment of a wide variety of infections, most notably intra-abdominal, gynecologic, lower respiratory tract, and urinary tract. These clinical uses, particularly in mixed and highly resistant infections, reflect the broad-spectrum activity of carbapenems against important clinical pathogens. Imipenem and meropenem have excellent in vitro activity against streptococci (including S pyogenes , S agalactiae , and viridans group streptococci), enterococci, pneumococci, and methicillin-susceptible (but not methicillin-resistant) staphylococci. These drugs also are active against almost all enteric gram-negative rods (GNRs) (eg, Escherichia coli, Klebsiella, Enterobacter, Serratia, Citrobacter, Proteus sp) and most nonenteric GNRs (eg, Pseudomonas, Acinetobacter sp). A notable exception is Stenotrophomonas maltophilia . Anaerobes, including Bacteroides fragilis and clostridia, are very susceptible to carbapenem antibiotics. Although in vitro susceptibility data suggest that imipenem offers superior gram-positive activity and …

Validation of HPLC and UV spectrophotometric methods for the determination of meropenem in pharmaceutical dosage form

A high-performance liquid chromatographic method and a UV spectrophotometric method for the quantitative determination of meropenem, a highly active carbapenem antibiotic, in powder for injection were developed in present work. The parameters linearity, precision, accuracy, specificity, robustness, limit of detection and limit of quantitation were studied according to International Conference on Harmonization guidelines. Chromatography was carried out by reversed-phase technique on an RP-18 column with a mobile phase composed of 30 mM monobasic phosphate buffer and acetonitrile (90:10; v/v), adjusted to pH 3.0 with orthophosphoric acid. The UV spectrophotometric method was performed at 298 nm. The samples were prepared in water and the stability of meropenem in aqueous solution at 4 and 25 °C was studied. The results were satisfactory with good stability after 24 h at 4 °C. Statistical analysis by Student's t-test showed no significant difference between the results obtained by the two methods. The proposed methods are highly sensitive, precise and accurate and can be used for the reliable quantitation of meropenem in pharmaceutical dosage form.

Effect of siliconized latex urinary catheters on the activity of carbapenems against Pseudomonas aeruginosa strains with defined mutations in ampC, oprD, and genes coding for efflux systems

The decreased activity of carbapenems against Pseudomonas aeruginosa in the presence of eluates from siliconized latex urinary catheters is related to the loss of OprD and the expression of a new outer membrane protein (OMP). To understand this phenomenon, the activity of carbapenems and quinolones against P. aeruginosa strains, some producing AmpC β-lactamase (BL), OprD, MexA–MexB–OprM and MexE–MexF–OprN, were determined in Mueller–Hinton broth (MH) and in MH-containing eluates. OMP profiles and BL activities were also studied. Resistance to imipenem in P. aeruginosa grown in eluate is due to both the loss of OprD and expression of BL. For meropenem this phenomenon is related to both the loss of OprD and the integrity of MexA–MexB–OprM.

Zinc eluted from siliconized latex urinary catheters decreases OprD expression, causing carbapenem resistance in Pseudomonas aeruginosa.

The activities of carbapenems against Pseudomonas aeruginosa decreased in the presence of siliconized latex urinary catheters (SLUCs). This effect was associated with the loss of OprD. The zinc that eluted from SLUCs is responsible for this phenomenon. We have found that zinc exerts a negative effect on the expression of OprD, the porin responsible for carbapenem entry into P. aeruginosa.

Relationship between beta-lactamase production, outer membrane protein and penicillin-binding protein profiles on the activity of carbapenems against clinical isolates of Acinetobacter baumannii

Twenty blood isolates of Acinetobacter baumannii were studied, representing eight pulsed-field gel electrophoresis patterns and all different antimicrobial susceptibility patterns observed during 1995-97 at the University Hospital Virgen Macarena, Seville, Spain. The MIC(90)s (mg/L) of imipenem and meropenem decreased from 16 to 0.5 and from 8 to 4, respectively, in the presence of BRL 42715 (BRL) but not clavulanic acid. Hydrolysing activity (nmol/min/mg) of bacterial supernatants against cefaloridine ranged from 8.8 to 552.3 for A. baumannii type I (imipenem MICs < or = 2), which expressed only a beta-lactamase of pI > or = 9, and from 12.3 to 1543.5 for A. baumannii type II (imipenem MICs > or = 4), which expressed a beta-lactamase of pI > or = 9 and two others of pI 6.3 and 7. The hydrolysing activities of A. baumannii type II against imipenem, meropenem and oxacillin were higher than those observed for A. baumannii type I. Ten outer membrane protein (OMP) profiles (A. baumannii types I and II) were visualized on 10% SDS-PAGE gels with 6 M urea, whereas only five OMP profiles (A. baumannii types I and II) were differentiated in 12% SDS-PAGE gels. Five A. baumannii with OMP profile type B, characterized by the absence of a 22.5 kDa OMP, were resistant to meropenem and/or imipenem. Twelve penicillin-binding protein (PBP) patterns were observed. PBP patterns of A. baumannii type II were characterized by the absence of a 73.2 kDa band (PBP 2). We concluded that production of beta-lactamases of pI 6.3 and 7.0 and reduced expression of PBP 2 are the most frequently observed mechanisms of resistance to carbapenems. In some isolates, loss of a 22.5 kDa OMP is also related to resistance to carbapenems.

Preface.

Efficient monitoring for the emergence of resistance to various antimicrobial agents has, in the face of global trends in resistance, recently assumed great importance. Many programmes have been developed to survey resistance, each varying in scope or emphasis as well as commitment to long-term monitoring. A programme that specifically addresses pathogens from populations of the most severely ill patients is the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC). This programme was started in 1997 to monitor carbapenem activity in vitro in centres using carbapenems because their prevalent strains were resistant to other β-lactams and drug classes. Meropenem is a broad-spectrum carbapenem and differs microbiologically from imipenem by having a greater potency in vitro against many Gram-negative pathogens and a slightly lower potency against some Gram-positive pathogens. Meropenem has improved stability to renal-based enzymatic metabolism, and does not require the addition of an enzyme inhibitor such as cilastatin. Material in this publication is based on the many abstracts and oral presentations delivered at recent national and international meetings including: the International Congress of Infectious Disease in Buenos Aires, Argentina (April, 2000); the European Congress of Chemotherapy in Madrid, Spain (May, 2000); and the European Congress of Clinical Microbiology and Infectious Disease in Stockholm, Sweden (May, 2000). All of the authors are active participants in the MYSTIC programme and bring to it experience in the design of surveillance studies and the detection of resistance mechanisms. Professor Jones discusses the most useful ways of storing and presenting susceptibility data to preserve the long-term value of all results. He argues for the publication of expanded study details and the limited use of MIC90 values or susceptibility rates. Dr Turner has coordinated the MYSTIC programme, and he summarizes here the similarities and differences in the results seen to date between the Americas, Europe and centres in Asia and the Middle East. The Americas have been one of the most recently monitored regions. Professors Pfaller and Jones give baseline data for the USA (10 sites), Mexico and Brazil. Professor Goossen's article focuses on the results of MYSTIC in the European centres. Doctor Masterton presents a comprehensive overview of various surveillance studies and assesses their value and characteristics for the continued optimal management of infected patients.

Nosocomial Outbreak of Cross-Infection due to Multiple-Antibiotic-Resistant Klebsiella pneumoniae: Characterization of the Strain and Antibiotic Susceptibility Studies

A multiple-antibiotic-resistant (MAR) strain of Klebsiella pneumoniae was introduced into a pediatric ward and subsequently colonized neonates of two wards with several cases of systemic infection. This strain produced an extended-spectrum β-lactamase and was resistant to cefotaxime, ceftazidime, and, among others, all aminoglycosides including amikacin. The majority of representative isolates examined with macrorestriction analysis of genomic DNA (pulsed-field gel electrophoresis) were identical. The strain was susceptible to the innate antibacterial systems operative in fresh defibrinated blood from two adults. Combined human blood/antimicrobial drug assays documented the in vitro bactericidal activity of carbapenems (meropenem was slightly more effective than imipenem), fluoroquinolones (ciprofloxacin and trovafloxacin), and polymyxin B against this MAR strain of K. pneumoniae.

Roles of beta-lactamases and porins in activities of carbapenems and cephalosporins against Klebsiella pneumoniae.

Two clinical isolates of extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae were noted to be less susceptible than expected to imipenem. Both were missing outer membrane proteins that serve as channels for antibiotic entry. The role of beta-lactamase in resistance was investigated by eliminating the original ESBL and introducing plasmids encoding various ESBLs and AmpC beta-lactamase types, by studying the effect of an increased inoculum, and by evaluating interactions with beta-lactamase inhibitors. The contribution of porin deficiency was investigated by restoring a functional ompK36 gene on a plasmid. Plasmids encoding AmpC-type beta-lactamases provided resistance to imipenem (up to 64 microg/ml) and meropenem (up to 16 microg/ml) in strains deficient in porins. Carbapenem resistance showed little inoculum effect, was not affected by clavulanate but was blocked by BRL 42715, and was diminished if OmpK36 porin was restored. Plasmids encoding TEM- and SHV-type ESBLs conferred resistance to cefepime and cefpirome, as well as to earlier oxyimino-beta-lactams. This resistance was magnified with an increased inoculum, was blocked by clavulanate, and was also lowered by OmpK36 porin restoration. In addition, SHV-2 beta-lactamase had a small effect on carbapenem resistance (imipenem MIC, 4 microg/ml, increasing to 16 microg/ml with a higher inoculum) when porins were absent. In K. pneumoniae porin loss can thus augment resistance provided either by TEM- or SHV-type ESBLs or by plasmid-mediated AmpC enzymes to include the latest oxyimino-beta-lactams and carbapenems.

Antibiotic sensitization using biphenyl tetrazoles as potent inhibitors of Bacteroides fragilis metallo-beta-lactamase.

High level resistance to carbapenem antibiotics in gram negative bacteria such as Bacteroides fragilis is caused, in part, by expression of a wide-spectrum metallo-beta-lactamase that hydrolyzes the drug to an inactive form. Co-administration of metallo-beta-lactamase inhibitors to resistant bacteria is expected to restore the antibacterial activity of carbapenems. Biphenyl tetrazoles (BPTs) are a structural class of potent competitive inhibitors of metallo-beta-lactamase identified through screening and predicted using molecular modeling of the enzyme structure. The X-ray crystal structure of the enzyme bound to the BPT L-159,061 shows that the tetrazole moiety of the inhibitor interacts directly with one of the two zinc atoms in the active site, replacing a metal-bound water molecule. Inhibition of metallo-beta-lactamase by BPTs in vitro correlates well with antibiotic sensitization of resistant B. fragilis. BPT inhibitors can sensitize a resistant B. fragilis clinical isolate expressing metallo-beta-lactamase to the antibiotics imipenem or penicillin G but not to rifampicin.

Survey of the sensitivities of clinical isolates to antibacterial agents (annual report)

Research groups were formed in 21 institutions nationwide to investigate carbapenem resistance. The activities of various antibacterial agents, principally carbapenems were tested against clinical isolates collected from these institutions. The broth microdilution method was used to determine the minimum inhibitory concentrations (MIC) of 17 antibacterial agents for 1,282 strains of 11 bacterial species isolated at all institutions between October and December 1995. The results were as follows: 1. Carbapenems exhibited strong antibacterial activities against MSSA and Streptococcus pneumoniae. Their activities against Enterococcus faecalis were comparable to that of ABPC. Carbapenems showed low activities against MRSA. 2. OFLX exhibited the greatest antibacterial activity against Haemophilus influenzae, followed by MEPM. The antibacterial activities of the other carbapenems were comparable to those of FMOX and CTM. 3. The carbapenems showed high activities against Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, and Bacteroides fragilis group. Their activities were greater than that exhibited by other beta-lactam antibacterial agents. The carbapenems also exhibited greater antibacterial activities against Serratia marcescens than the other beta-lactam antibacterial agents, but some resistant strains were detected. 4. The antibacterial activities of carbapenems against Pseudomonas aeruginosa were comparable to those of CAZ, AZT, AMK.

Evaluation of the Antimicrobial Activity of Carbapenem and Cephem Antibiotics Against Pseudomonas aeruginosa Isolated from Hospitalized Patients

Pseudomonas aeruginosa is an opportunistic pathogen that infects compromised hosts. It is therefore important to clarify the bactericidal activity of antimicrobial agents against this bacterium. We evaluated the antimicrobial potency of several antibiotics againstP. aeruginosa by measuring the MIC and the minimum bactericidal concentration (MBC). Imipenem, panipenem meropenem, ceftazidime, cefpirome, cefepime, and cefozopran were the antibiotics evaluated. The 40 strains ofP. aeruginosa used in this analysis were isolated from the sputum of 40 patients. The MIC was determined by the microbroth dilution method. Afterwards, we determined the MBC, which is the lowest concentration of antibiotic at which all bacteria in the diluted culture are killed. The MIC and MBC of meropenem was determined to be 2 to 8 times lower and 2 to 4 times lower, respectively, than those of other carbapenem antibiotics tested. The MIC and MBC of cefozopran were determined to be 2 to 16 times lower and 4 to 16 times lower, respectively, than those of other cephem antibiotics tested. Meropenem and cefozopran show the greatest bactericidal activity againstP. aeruginosa among the, carbapenem and cephem antibiotics tested. Meropenem would be one of the best selections for treatment of pyocyanic infections in immunocompromised patients, because it also provides a postantibiotic effect againstP. aeruginosa.

Outer membrane permeability and effect of basic amino acids on antipseudomonal activity of carbapenems

Outer membrane permeability and effect of basic amino acids on antipseudomonal activity of carbapenems

Potential Factors Influencing Carbapenem Activity Against Bacteroides fragilis Group Isolates

Journal Article Potential Factors Influencing Carbapenem Activity Against Bacteroides fragilis Group Isolates Get access Joseph P. Iaconis, Joseph P. Iaconis From Microbiology Development, Pharmaceutical Research and Development, Zeneca Pharmaceuticals Croup, Wilmington, Delaware Reprints or correspondence: Dr. Joseph P. Iaconis, Microbiology Development, Pharmaceutical Research and Development, Zeneca Pharmaceuticals Group, Wilmington, Delaware 19897. Search for other works by this author on: Oxford Academic PubMed Google Scholar Harriette L. Nadler, Harriette L. Nadler From Microbiology Development, Pharmaceutical Research and Development, Zeneca Pharmaceuticals Croup, Wilmington, Delaware Search for other works by this author on: Oxford Academic PubMed Google Scholar Waheed Sheikh Waheed Sheikh From Microbiology Development, Pharmaceutical Research and Development, Zeneca Pharmaceuticals Croup, Wilmington, Delaware Search for other works by this author on: Oxford Academic PubMed Google Scholar Clinical Infectious Diseases, Volume 20, Issue Supplement_2, June 1995, Pages S361–S363, https://doi.org/10.1093/clinids/20.Supplement_2.S361 Published: 01 June 1995

In vitro activity of BMS-181139, a new carbapenem with potent antipseudomonal activity

The in vitro activities of the carbapenem BMS-181139 were determined in comparison with those of imipenem, meropenem, ciprofloxacin, ceftriaxone, and vancomycin. BMS-181139 was the most active against species of Pseudomonas and related genera Alteromonas and Burkholderia, with MICs for 147 of 149 isolates of < 4 micrograms/ml. Of 22 imipenem-resistant (MIC > 8 micrograms/ml) P. aeruginosa strains, only 1 required an MIC of BMS-181139 of > 4 micrograms/ml, compared with 14 requiring the same meropenem MIC. BMS-181139 was the most active carbapenem against the majority of other gram-negative species except members of the tribe Proteeae, against which meropenem was more active. Although imipenem was more active against gram-positive species, BMS-18139 MICs at which 90% of strain tested were inhibited were < 1 microgram/ml for these species. BMS-181139 was generally active against isolates resistant to ciprofloxacin or broad-spectrum cephalosporins, including those containing plasmid-encoded beta-lactamases or high levels of chromosome-encoded beta-lactamases, as well as anaerobes except Clostridium difficile. Inoculum effects were noted for all three carbapenems against Klebsiella pneumoniae, Enterobacter cloacae, and Serratia marcescens but not Escherichia coli, Pseudomonas aeruginosa, or Staphylococcus aureus. BMS-181139's inoculum effect tended to be more marked. BMS-181139 exhibited bactericidal activity at the MIC for some strains and up to four to eight times the MIC for others. The postantibiotic effect of BMS-181139 was equal to or less than that of imipenem and, like meropenem, exhibited intraspecies variability. BMS-181139 was 30-fold more stable than imipenem and 7-fold more stable than meropenem to hydrolysis by hog kidney dehydropeptidase.

Transient carbapenem resistance induced by salicylate in Pseudomonas aeruginosa associated with suppression of outer membrane protein D2 synthesis

Pseudomonas aeruginosa PAO1 showed increased phenotypic resistance to imipenem, panipenem, and biapenem specifically in the presence of salicylate. The antipseudomonal activity of carbapenems was reduced in proportion to the concentration of salicylate. This resistance was transient and nonheritable. The synthesis of the outer membrane protein D2 (OprD or OprD2) in P. aeruginosa PAO1 was inhibited by 4 to 32 mM salicylate in the bacterial growth medium, whereas no changes in any other outer membrane proteins were observed. These results indicate that salicylate suppresses the synthesis of OprD and therefore reduces the antipseudomonal activity of carbapenems. Under these conditions, one carbapenem--meropenem--is still active against P. aeruginosa, which indicates that meropenem can pass through the outer membrane via both the D2 channel and another undefined route(s).

Activity of the carbapenem panipenem and role of the OprD (D2) protein in its diffusion through the Pseudomonas aeruginosa outer membrane

Evidence of permeation of panipenem through the OprD (D2) channel of Pseudomonas aeruginosa outer membrane was shown by using OprD protein-producing and -nonproducing strains which contained plasmid pHN4, which codes for L-1 beta-lactamase of Xanthomonas maltophilia. Permeation by panipenem was determined by measuring hydrolysis of the carbapenem by beta-lactamase in the periplasmic space. Permeation by panipenem was also determined by counting uptake of [14C]panipenem into P. aeruginosa PAO1 and its OprD protein-deficient mutant, and this permeation of PAO1 was inhibited by L-lysine. These results indicate that panipenem, as well as imipenem, uses the OprD channel, which functions as a specific channel for diffusion of basic amino acids. Panipenem and imipenem showed stronger activities against PAO1 and clinical isolates in human serum than in Mueller-Hinton broth, which contains more amino acids than human serum does. The activities of the carbapenems were reduced by addition of L-lysine to human serum. Similar results were obtained with mouse serum and ascitic fluid. In contrast, such a change in the activities of carbapenems was not observed with an OprD protein-deficient mutant, suggesting that the main reason for the strong activities of carbapenems in biological fluids is a decrease in competition between the antibiotics and basic amino acids for permeation through the OprD channel. Panipenem and imipenem showed much stronger therapeutic efficacies against experimental infections with P. aeruginosa in mice than did the reference antibiotics. Their in vivo activities were more consistent with their MICs in biological fluids than with those in Mueller-Hinton broth.

Chemistry of O-Silylated Ketene Acetals: A Stereoselective Synthesis of Optically Active Carbapenem Antibiotics, (+)-Thienamycin and (+)-PS-5.

A stereoselective synthesis of the chiral thienamycin intermediate (16) involving a diastereoselective Michael addition and a silicon-induced Pummerer-type reaction is described. In a similar way, the key intermediate for(+)-PS-5 was also prepared from 4-(phenylsulfinylmethyl)butanamide (21).

Susceptibility of naturally occurring carbapenem antibiotics to renal dehydropeptidase-I. An easy assay using a plate technique based on a novel chromogenic beta-lactamase substrate.

A general screening procedure is described which allows the rapid determination of the susceptibility of naturally occurring carbapenem antibiotics to renal dehydropeptidase-I at the broth level. The procedure is based on the incubation of carbapenem-containing solutions with dehydropeptidase-I and the subsequent assay of residual beta-lactamase-inhibiting/inactivating activity of carbapenems by means of a plate technique using the chromogenic beta-lactamase substrate PADAC.