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In vitro activity and beta-lactamase stability of a new carbapenem, SM-7338.

SM-7338, a new carbapenem, inhibited most members of the family Enterobacteriaceae at MICs of 0.015 to 0.25 microgram/ml, including Klebsiella oxytoca, Citrobacter freundii, Enterobacter cloacae, and Proteus vulgaris isolates resistant to cefotaxime, ceftazidime, piperacillin, and gentamicin. It was two- to eightfold more active than imipenem, but it inhibited Pseudomonas aeruginosa at 1 to 8 micrograms/ml, which was comparable to the activity of imipenem. Haemophilus, Neisseria, and Branhamella species were inhibited by less than or equal to 0.25 microgram/ml, which was superior to the activity of imipenem. SM-7338 inhibited Staphylococcus aureus and coagulase-negative staphylococci at 0.25 microgram/ml, but for methicillin-resistant isolates MICs were 4 to 16 micrograms/ml. Group A, B, and C streptococci and Streptococcus pneumoniae were inhibited by less than or equal to 0.03 microgram/ml. Bacteroides species, including clindamycin-resistant isolates, were inhibited by 0.25 microgram/ml. There was no major inoculum size effect, and the MBCs were within a dilution of the MICs. SM-7338 was more active than imipenem at an acid pH under anaerobic conditions. Plasmid beta-lactamases of TEM-1, TEM-2, TEM-3, TEM-5, SHV-1, SHV-2, PSE-1, PSE-2, PSE-3, OXA-2, OXA-3, OXA-4, OXA-5, and OXA-7; Staphylococcus aureus enzymes; and the chromosomal beta-lactamases P-99 and K-1; Morganella species; and Proteus vulgaris did not hydrolyze SM-7338. The repeated transfer of organisms increased the MICs of SM-7338, as it did the MICs of imipenem.

Anti-Bacterial Agents↗

Comparative in vitro activity of SM7338, a new carbapenem antimicrobial agent.

The comparative in vitro activity of SM7338 was tested against 670 routine clinical isolates and 130 cefoperazone-resistant isolates of bacteria by agar dilution methods. SM7338 was at least as active as imipenem against gram-negative organisms but was slightly less active against gram-positive organisms. SM7338 was particularly active against members of the family Enterobacteriaceae, with MICs for 90% of strains of less than or equal to 0.125 micrograms/ml for all species tested. Differences in activity between SM7338 and imipenem were particularly striking against Proteus vulgaris, Proteus mirabilis, and Morganella morganii, against which MICs of SM7338 and imipenem for 90% of strains were 0.125 and 4 micrograms/ml, respectively. The presence of unique plasmid-mediated beta-lactamases in Pseudomonas aeruginosa PU21 transconjugants did not affect activity substantially, except in the case of OXA-2 (eightfold-increased MIC) and OXA-3 (fourfold-increased MIC). SM7338 was also active against a laboratory-derived strain of P. aeruginosa which hyperproduced chromosomal beta-lactamase, inhibiting both the wild type and the mutant at a concentration of 1.0 micrograms/ml.

Anti-Bacterial Agents↗

Outer membrane protein D2 catalyzes facilitated diffusion of carbapenems and penems through the outer membrane of Pseudomonas aeruginosa.

The outer membrane of imipenem-resistant mutants of Pseudomonas aeruginosa with decreased permeability to imipenem was shown by Western (immuno-) blotting to contain protein D1 and to lack protein D2. Protein D2 was purified and was shown to allow the permeation of imipenem at a rate higher than expected from its molecular weight. Spontaneous imipenem-resistant mutants of P. aeruginosa PAO1 appeared at a frequency of 10(-8) in the laboratory and did not synthesize protein D2. Experiments performed with intact cells carrying plasmid pHN4 containing the gene for L-1 beta-lactamase from Pseudomonas maltophilia showed that this channel could also be used by SM-7338, Sch 33755, and Sch 33440 but apparently not by Sch 34343 or Sch 29482.

Anti-Bacterial Agents↗

Affinities of SM-7338 for penicillin-binding proteins and its release from these proteins in Staphylococcus aureus.

SM-7338, a carbapenem antibiotic, had high affinities for penicillin-binding proteins (PBPs) 1, 2, and 4 of Staphylococcus aureus but not for PBP 3 when a competition assay with [14C]benzylpenicillin was used. However, binding of [14C]SM-7338 was saturated for PBP 3 at a concentration of 1 microgram/ml. These results were due to the rapid release of SM-7338 from PBP 3-SM-7338 complexes with a half-life of 2 min.

Bacterial Proteins↗

Carbapenem resistance in a clinical isolate of Citrobacter freundii.

Carbapenem resistance was studied in two sets of Citrobacter freundii strains: (i) strain CFr950, resistant to imipenem (MIC, 16 microg/ml) and isolated in vivo during imipenem therapy, and strain CFr950-Rev, the spontaneous, imipenem-susceptible revertant of CFr950 selected in vitro, and (ii) strains CFr801 and CFr802, two imipenem-resistant mutants selected in vitro from the susceptible clinical isolate CFr800. In all strains, whether they were imipenem-susceptible or -resistant strains, production of the cephalosporinase was derepressed and their Km values for cephaloridine were in the range of 128 to 199 microM. No carbapenemase activity was detected in vitro. The role of cephalosporinase overproduction in the resistance was demonstrated after introduction of the ampD gene which decreased the level of production of cephalosporinase at least 250-fold and resulted in an 8- to 64-fold decrease in the MICs of the carbapenems. The role of reduced permeability in the resistance was suggested by the absence, in CFr950 and CFr802, of two outer membrane proteins (the 42- and 40-kDa putative porins whose levels were considerably decreased in CFr801) and the reappearance of the 42-kDa protein in imipenem-susceptible strain CFr950-Rev. This role was confirmed after introduction of the ompF gene of Escherichia coli into the CFr strains, which resulted in 8- to 16-fold decreases in the MICs of carbapenems for CFr802 and CFr950. We infer from these results that the association of reduced, porin-mediated permeability with high-level cephalosporinase production, observed previously in other gram-negative bacteria, may also confer carbapenem resistance on C. freundii.

Anti-Bacterial Agents↗

Brain abscess caused by Streptococcus pyogenes in a previously healthy child.

Responsible for many childhood diseases, group A Streptococcus (GAS) is a rare cause of central nervous system infections. We report the case of a previously healthy boy with brain abscesses caused by M/emm type 12 GAS and review the case in the context of the published literature and recent epidemiological data.

Anti-Bacterial Agents↗

Host range variability in the transfer of antibiotic resistance determinants from Pseudomonas aeruginosa strains.

Twelve multiply drug-resistant strains of Pseudomonas aeruginosa, isolated in Frankfurt University Clinics during the year 1998, transferred determinants of antibiotic resistance with remarkable variability in the host range of transferred plasmids. As a new phenomenon, two of them transferred resistance genes to both groups of recipients, i.e. to Enterobacteriaceae as well as to a strain of P. aeruginosa. Six strains had more restrictive activity and transferred resistance determinants to Enterobacteriaceae only, while four additional strains demonstrated transferability only to P. aeruginosa. Two isolates transferred imipenem resistance and one cefepime resistance. Differences in selection pressure occurring during therapy of individual patients seems to be one of the possible factors influencing the spectrum of antibiotic resistance genes present in P. aeruginosa and their transfer to susceptible strains.

Drug Resistance, Multiple↗

Nosocomial infections due to multidrug-resistant Pseudomonas aeruginosa: epidemiology and treatment options.

Pseudomonas aeruginosa is one of the leading gram-negative organisms associated with nosocomial infections. The increasing frequency of multi-drug-resistant Pseudomonas aeruginosa (MDRPA) strains is concerning as efficacious antimicrobial options are severely limited. By searching MEDLINE from January 1966-February 2005 and relevant journals for abstracts, we reviewed the frequency, risk factors, and patient outcomes of MDRPA nosocomial infections in critically ill patients, determined the available antimicrobial therapies, and then provided recommendations for clinicians. The definition of MDRPA was established as isolates intermediate or resistant to at least three drugs in the following classes: beta-lactams, carbapenems, aminoglycosides, and fluoroquinolones. Reported rates of MDRPA varied from 0.6-32% according to geographic location and type of surveillance study. Risk factors for MDRPA infection included prolonged hospitalization, exposure to antimicrobial therapy, and immunocompromised states such as human immunodeficiency virus infection. Emergence of MDRPA isolates during therapy was reported in 27-72% of patients with initially susceptible P. aeruginosa isolates. Patients with severe MDRPA infections should be treated with combination therapy, consisting of an antipseudomonal beta-lactam with an aminoglycoside or fluoroquinolone rather than aminoglycoside and fluoroquinolone combinations, to provide adequate therapy and improve patient outcomes. Synergy has been observed when resistant antipseudomonal drugs were combined in vitro against MDRPA with successful clinical application reported in two centers. Colistin with adjunctive therapy, such as a beta-lactam or rifampin, may be a useful agent in MDRPA when antimicrobial options are limited, but patients should be monitored closely for toxicities associated with this agent. Standardization of terminology for MDRPA isolates is needed for consistency and comparability of surveillance and institutional reports. Clinical studies are needed to identify risk factors for MDRPA development and to determine the economic impact of these infections, as well as to determine the most efficacious antimicrobial regimens and duration of therapy to maximize outcomes in the treatment of MDRPA infections.

Anti-Bacterial Agents↗

Infective endocarditis developing as uremia.

A 49-year-old man presented with fever and uremic symptoms such as general malaise, leg edema and decreased urine output. He was diagnosed as having infective endocarditis (IE) accompanied by renal failure. Although he had been receiving hemodialysis for a long time, renal function dramatically improved after heart valve replacement. This case suggests that uremia can develop as an initial manifestation of IE and removal of an infected heart valve can improve renal function despite persistent renal failure. From the perspective of recovery of renal function, early surgery should be considered in patients with renal failure following IE.

Anuria↗

Q fever with clinical features resembling systemic lupus erythematosus.

A 23-year-old woman with prolonged fever, rash, and pericarditis associated with high titers of antinuclear, anti-Sm, and anti-RNP antibodies was suspected of having systemic lupus erythematosus (SLE). However, we also considered infectious diseases, particularly Q fever, as the C-reactive protein level was elevated and the patient reported contact with zoo animals around two weeks before the onset. The condition responded rapidly to administration of minocycline; symptoms resolved without using steroids. Thereafter, no recurrence of the illness was observed. Titer of Coxiella burnetii antibody was high and the illness was accordingly diagnosed as acute Q fever rather than SLE.

Adult↗

[A case in which the subject was affected by Listeia meningoencephalitis during administration of infliximab for steroid-dependent adult onset Still's disease].

The subject was a 22-year-old woman who developed high fever and arthralgias and eruptions in the extremities around June 2005. She sought medical advice at a nearby dermatology clinic, where hepatic dysfunction was noted on blood testing. The patient was thus hospitalized the next day. Although CRP levels were significantly high, no sign of infection was observed and bone marrow cell differentiation was normal. Adult onset Still's disease was diagnosed based on the observation of persistent high fever >39 degrees C, eruptions, increased leukocytes, pharyngeal pain, splenomegaly, hepatic dysfunction, negative autoantibody results from blood testing, and high serum ferritin levels. Administration of prednisolone 30 mg/day was initiated, but proved ineffective. Steroid pulse therapy was conducted, and the subject was transferred to our medical facility for continued treatment. Attempts were made to control the disease using combined steroid and cyclosporine administration; but exacerbation of high serum ferritin levels and hepatic dysfunctions were observed, so a second course of steroid pulse therapy was conducted. Symptoms improved temporarily, but steroid levels were difficult to reduce. Cyclosporine was therefore replaced by methotrexate, and administration of infliximab was initiated. In the course of treatment, administration of a sulfamethoxazole/trimethoprim combination was initiated, but was discontinued due to suspicion of drug-induced hepatic injury. A second administration of infliximab was conducted in late August, and rapid improvements in clinical symptoms and abnormal test values was observed. However, high fever and headache developed suddenly in early September. Based on the results of spinal fluid testing, blood and spinal fluid cultures and MRI of the head, Listeria meningoencephalitis was diagnosed. Diplopia and impaired consciousness occurred during the disease course, and formation of a brain abscess was observed on imaging. However, symptoms were controlled by long-term combination administration of ampicillin and gentamicin. Administration of infliximab was discontinued for treatment of adult onset Still's disease, and steroid levels were reduced following double-membrane filtration plasma exchange. On follow-up, no relapse of symptoms or abnormalities in blood test values were observed, so the subject was discharged from our medical facility in December 2005. In treatment for rheumatic diseases, a dramatic improvement in treatment results for pathologies displaying tolerance against conventional treatments has been acquired with the development of biological drugs. However, opportunistic infections represent a serious problem, and appropriate preventative measures are required. The present report describes a case in which the subject was affected by Listeria meningoencephalitis during administration of infliximab for steroid-dependent adult Still's disease. Since listeriosis is one of the complications, along with tuberculosis, that warrants precautionary measures, this case is reported and discussed.

Adult↗

Comparison of two carbapenems, SM-7338 and imipenem: affinities for penicillin-binding proteins and morphological changes.

We investigated the binding affinities of SM-7338 for penicillin-binding proteins (PBPs) and the morphological changes induced by it compared with those of imipenem. Both SM-7338 and imipenem had the highest binding affinities for PBP-2 of Escherichia coli, which were in good agreement with the primary morphological response of spherical cell formation. SM-7338 also showed high affinities for PBP-1A, -1Bs, and -3, and imipenem showed high affinities for PBP-1A and -1Bs but not for PBP-3. At 4-fold MIC, SM-7338 induced a indeterminate form, whereas imipenem did not. This may be due to the higher affinity of SM-7338 for PBP-3 compared to that of imipenem. Against Pseudomonas aeruginosa, SM-7338 had very high affinities for PBP-2 and -3, and imipenem had higher affinities for PBP-2 and -1A. SM-7338 induced this organism to filamentous cells at a concentration lower than its MIC, bulge cells at 2-fold MIC, and spherical cells at 4-fold MIC, while imipenem principally induced round cell formation at each concentration. These morphological differences in P. aeruginosa may be due to the differences in binding profiles to PBPs. We also studied the affinities for PBPs using radioactive SM-7338. The data obtained supported these results.

Bacterial Proteins↗

A novel carbapenem antibiotic, SM-7338 structure-activity relationships.

A series of new carbapenem compounds, which have a pyrrolidin-3'-ylthio group substituted with various aminocarbonyl group at C-5' position as C-2 side chain, have been prepared. The antibacterial activity and the stability to renal dehydropeptidase-I of these compounds were investigated, and the structure-activity relationships were discussed. In this series, SM-7338; (1R,5S,6S)-2-[(3S,5S)-5-dimethylaminocarbonylpyrrolidin-3-ylthi o]-6-[(R)-1-hydroxyethyl]-1-methylcarbapen-2-em-3-carboxylic acid (5a) was the most interesting compound.

Bacteria↗