Multisite reproducibility of results obtained by the broth microdilution method for susceptibility testing of Mycobacterium abscessus, Mycobacterium chelonae, and Mycobacterium fortuitum.
(9/848)
A multicenter study was conducted to assess the interlaboratory reproducibility of broth microdilution testing of the more common rapidly growing pathogenic mycobacteria. Ten isolates (four Mycobacterium fortuitum group, three Mycobacterium abscessus, and three Mycobacterium chelonae isolates) were tested against amikacin, cefoxitin, ciprofloxacin, clarithromycin, doxycycline, imipenem, sulfamethoxazole, and tobramycin (M. chelonae only) in four laboratories. At each site, isolates were tested three times on each of three separate days (nine testing events per isolate) with a common lot of microdilution trays. Agreement among MICs (i.e., mode +/- 1 twofold dilution) varied considerably for the different drug-isolate combinations and overall was best for cefoxitin (91.7 and 97.2% for one isolate each and 100% for all others), followed by doxycycline, amikacin, and ciprofloxacin. Agreement based on the interpretive category, using currently suggested breakpoints, also varied and overall was best for doxycycline (97.2% for one isolate and 100% for the rest), followed by ciprofloxacin and clarithromycin. Reproducibility among MICs and agreement by interpretive category was most variable for imipenem. Based on results reported from the individual sites, it appears that inexperience contributed significantly to the wide range of MICs of several drugs, especially clarithromycin, ciprofloxacin, and sulfamethoxazole. New interpretive guidelines are presented for the testing of M. fortuitum against clarithromycin; M. abscessus and M. chelonae against the aminoglycosides; and all three species against cefoxitin, doxycycline, and imipenem. (+info)
Relationship between morphological changes and endotoxin release induced by carbapenems in Pseudomonas aeruginosa.
(10/848)
The relationship between morphological changes and endotoxin release induced in vitro by carbapenems in a clinical isolate of Pseudomonas aeruginosa was examined. The time-course and magnitude of endotoxin release induced varied among imipenem, panipenem, meropenem and biapenem and related to the morphological changes caused by these agents which variously affected cell shape, cell-wall disintegration and cell lysis. The amount of endotoxin released by carbapenem-treated cells correlated with both the cell-wall morphology and bacterial shape immediately before lysis. Meropenem and biapenem caused markedly increased endotoxin release during cell lysis and cell-wall disintegration, whereas imipenem and panipenem caused much less release of endotoxin. (+info)
Kinetic properties and metal content of the metallo-beta-lactamase CcrA harboring selective amino acid substitutions.
(11/848)
The crystal structure of the metallo-beta-lactamase CcrA3 indicates that the active site of this enzyme contains a binuclear zinc center. To aid in assessing the involvement of specific residues in beta-lactam hydrolysis and susceptibility to inhibitors, individual substitutions of selected amino acids were generated. Substitution of the zinc-ligating residue Cys181 with Ser (C181S) resulted in a significant reduction in hydrolytic activity; kcat values decreased 2-4 orders of magnitude for all substrates. Replacement of His99 with Asn (H99N) significantly reduced the hydrolytic activity for penicillin and imipenem. Replacement of Asp103 with Asn (D103N) showed reduced hydrolytic activity for cephaloridine and imipenem. Deletion of amino acids 46-51 dramatically reduced both the hydrolytic activity and affinity for all beta-lactams. The metal binding capacity of each mutant enzyme was examined using nondenaturing electrospray ionization mass spectrometry. Two zinc ions were observed for the wild-type enzyme and most of the mutant enzymes. However, for the H99N, C181S, and D103N enzymes, three different zinc content patterns were observed. These enzymes contained two zinc molecules, one zinc molecule, and a mixture of one or two zinc molecules/enzyme molecule, respectively. Two enzymes with substitutions of Cys104 or Cys104 and Cys155 were also composed of mixed enzyme populations. (+info)
Markedly different rates and resistance profiles exhibited by seven commonly used and newer beta-lactams on the selection of resistant variants of Enterobacter cloacae.
(12/848)
Seven beta-lactam antibiotics (cefepime, cefoperazone, ceftazidime, ceftriaxone, cefamandole, imipenem and meropenem) were tested for their potential to select resistance in standard and clinical strains of Enterobacter cloacae (n = 9). The strains were subcultured daily with the test antibiotics at doubling concentrations starting at 0.125 x MIC. Development of resistance throughout the passages was detected by a disc diffusion test. Ceftazidime, ceftriaxone and cefamandole selected resistance at a faster rate than cefoperazone, cefepime and meropenem. Imipenem did not select resistance in the nine strains tested and was the only antibiotic that eradicated all the strains during selection. The resistance patterns of strains selected by meropenem, cefepime and the other cephalosporins were markedly different, although cross-resistance to the early generation cephalosporins was common. The resistance phenotypes of most strains remained stable upon serial passages in antibiotic-free medium. The findings of this study highlight the importance of the choice of antibiotic for therapy not only on the basis of its antibacterial activity, but also on its potential to select resistance to itself and other antibiotics. (+info)
Biochemical characteristics of a carbapenemase from an Acinetobacter baumannii isolate collected in Buenos Aires, Argentina.
(13/848)
Three carbapenem-resistant Acinetobacter baumannii isolates were collected at a hospital in Buenos Aires, Argentina. Isoelectric focusing revealed multiple beta-lactamases, with two of the isolates showing identical profiles. A pI 6.9 carbapenemase with a molecular weight of 30 kDa was purified from one of these two isolates. The enzyme was predominantly a penicillinase, with its highest Vmax for oxacillin but highest Vmax/Km for benzylpenicillin. First-generation cephalosporins and imipenem were weaker substrates than penicillins, and oxyimino-aminothiazolyl cephalosporins were essentially stable. Meropenem-hydrolysing activity was not detected, despite resistance. The carbapenemase was inhibited by clavulanic acid and tazobactam, but not by EDTA. These kinetics place the enzyme into functional group 2; as an oxacillinase it could be placed in sub-group 2d or, as a zinc-independent carbapenemase, in sub-group 2f. (+info)
In-vitro susceptibilities of species of the Bacteroides fragilis group to newer beta-lactam agents.
(14/848)
The in-vitro activities of imipenem and four beta-lactam-beta-lactamase inhibitor combinations were tested against 816 strains of the Bacteroides fragilis group, and compared with other anti-anaerobic agents. None of the strains was resistant to metronidazole, and only one was resistant to chloramphenicol. Mezlocillin and piperacillin were moderately active, while clindamycin was the least active. Rates of resistance varied between various species. The new beta-lactam agents tested showed excellent activity; piperacillin-tazobactam and imipenem were the most active. The emergence of strains that are resistant to these agents, observed in this study, suggests there is a need to perform periodic antimicrobial susceptibility tests. (+info)
In-vitro antimicrobial activity of a carbapenem, MK-0826 (L-749,345) and provisional interpretive criteria for disc tests.
(15/848)
The in-vitro activity of MK-0826, a new oral carbapenem, was compared with that of imipenem by broth microdilution susceptibility tests against 545 bacterial isolates. MK-0826 had significantly greater activity against Enterobacteriaceae and poorer activity against Pseudomonas aeruginosa and many gram-positive species. MK-0826 disc diffusion tests were also performed according to the NCCLS procedure and tentative interpretive criteria were determined for possible susceptible MIC breakpoints of < or = 4.0 and < or = 2.0 mg/L. (+info)
In vitro antibacterial activity of LJC 11,036, an active metabolite of L-084, a new oral carbapenem antibiotic with potent antipneumococcal activity.
(16/848)
LJC 11,036 is the active metabolite of L-084, a novel oral carbapenem that exhibits potent broad-spectrum activity. Antibacterial activities of LJC 11,036 against clinical isolates from respiratory infections, such as Streptococcus pneumoniae (n = 52), Streptococcus pyogenes (n = 19), Haemophilus influenzae (n = 50), Klebsiella pneumoniae (n = 53), and Moraxella catarrhalis (n = 53), and from urinary-tract infections, such as Escherichia coli (n = 53) (MICs at which 90% of the isolates were inhibited [MIC(90)s], 0.1, +info)