Segundo estudio multicéntrico de la sensibilidad in vitro a piperacilina-tazobactam / Second multicenter study of the in vitro susceptibility to piperacillin-tazobactam

Se estudia la actividad de piperacilina-tazobactam, en el año 1999, sobre 1349 cepas recogidas en un estudio multicéntrico español en el cual participaron diez hospitales. Se incluyeron 897 gramnegativos de los siguientes géneros: Escherichia coli (169), Klebsiella spp. (112), Pseudomonas spp. (122), Enterobacter spp. (92), Serratia spp. (44), Citrobacter spp. (37), Proteus spp. (114), Morganella spp. (49), Acinetobacter spp. (47), Stenotrophomonas spp. (47) Haemophilus spp. (45) y Moraxella spp. (19). Los grampositivos incluyeron S. aureus (116), S. pneumoniae (92) y Enterococcus spp. (114). También se determinó la actividad frente a diversos anaerobios: Bacteroides spp. (88), Clostridium spp. (25), Prevotella spp. (5), Fusobacterium spp. (3) y Peptosteptococcus spp. (9). La asociación piperacilina-tazobactam mantiene su actividad con respecto al estudio previo frente a los microorganismos aislados. (AU)

[Second multicenter study of the in vitro susceptibility to piperacillin-tazobactam]. / Segundo estudio multicéntrico de la sensibilidad in vitro a piperacilina-tazobactam.

A study was conducted in 1999 on the activity of piperacillin-tazobactam on 1349 strains collected in a Spanish multicenter study involving 10 hospitals. A total of 897 Gram-negative bacteria of the following genuses were collected: Escherichia coli (169), Klebsiella spp. (112), Pseudomonas spp. (122), Enterobacter spp. (92), Serratia spp. (44), Citrobacter spp. (37), Proteus spp. (114), Morganella spp. (49), Acinetobacter spp. (47), Stenotrophomonas spp. (47), Haemophilus spp. (45), Moraxella spp. (19). The Gram-positive bacteria included Staphylococcus aureus (116), Streptococcus pneumoniae (92), and Enterococcus spp. (114). Piperacillin-tazobactam activity against different anaerobic bacteria was also determined: Bacteroides spp. (88), Clostridium spp. (25), Prevotella spp. (5), Fusobacterium spp. (3) and Peptosteptococcus spp. (9). The piperacillin-tazobactam combination was found to maintain its activity against the isolated microorganisms with regard to the previous study.

Fluorescent whole-cell hybridization with 16S rRNA-targeted oligonucleotide probes to identify Brucella spp. by flow cytometry.

A whole-cell hybridization assay with fluorescent oligonucleotide probes derived from the 16S rRNA sequence of Brucella abortus in combination with flow cytometry has been developed. With the three fluorescent probes selected, a positive signal was observed with all the representative strains of the species and biovars of Brucella and with a total of nine different Brucella clinical isolates. Using the B9 probe in the hybridization assay, it was possible to discriminate between Brucella suis biovars 2, 3, 4, and 5 and almost all the other Brucella spp. On the basis of differences in fluorescence intensities, no discrimination was established between Brucella spp. and other phylogenetically related microorganisms. No positive fluorescence signals were detected with any of the bacteria showing serological cross-reactions with Brucella spp. and with a total of 17 clinical isolates not belonging to the genus Brucella. These results suggest that the 16S rRNA whole-cell hybridization technique could be a valuable diagnostic tool for the detection and identification of Brucella spp.

Multicenter Spanish study of ciprofloxacin susceptibility in gram-negative bacteria. The Spanish Study Group on Quinolone Resistance.

The susceptibility of 2,426 gram-negative bacteria obtained from 18 Spanish hospitals to ciprofloxacin was evaluated. Among different medical centers, susceptibility to ciprofloxacin ranged from 83 to 100% for Enterobacteriaceae, from 35 to 100% for Pseudomonas aeruginosa, from 0 to 100% for Xanthomonas maltophilia, Acinetobacter spp. and other gram-negative non-fermenting bacilli, and from 33 to 100% for Campylobacter spp. All clinical isolates of Haemophilus influenzae, Moraxella catarrhalis and Neisseria gonorrhoeae were susceptible to ciprofloxacin.

Susceptibilities of Brucella melitensis isolates to clinafloxacin and four other new fluoroquinolones.

The susceptibilities of 120 clinical isolates of Brucella melitensis and 3 reference strains of the same species to six fluoroquinolones (clinafloxacin, PD 117596, PD 131628, PD 138312, PD 140248, and ciprofloxacin) were examined by agar dilution MIC methodology. Clinafloxacin was the most active compound tested (MIC at which 50% of strains tested were inhibited [MIC50] and MIC90 of 0.06 micrograms/ml). Its level of activity was slightly higher than that of PD 117596 (MIC50 and MIC90 of 0.12 micrograms/ml). PD 131628 and ciprofloxacin were less active than clinafloxacin, with MIC50s ranging from 0.12 to 0.25 micrograms/ml and MIC90s of between 0.25 and 0.5 micrograms/ml for the two compounds. The activity levels of PD 138312 and PD 140248, with MIC50s ranging from 1 to 2 micrograms/ml and MIC90s of 4 to 8 micrograms/ml, were lower than those of the other fluoroquinolones tested.

In-vitro activity of four new fluoroquinolones.

The in-vitro activities of four new fluoroquinolones, E-4749, E-4874, E-4884 and E-4904, were compared with that of ciprofloxacin and sparfloxacin against 1106 clinical isolates. Against majority of Enterobacteriaceae, general antibacterial activities of E-4749 (MIC90s 0.06-1 mg/L), E-4874 (MIC90s, 0.03-0.25 mg/L) and E-4884 (MIC90s 0.01-0.5 mg/L) were comparable or slightly lower than those of ciproloxacin (MIC90s 0.01-0.25 mg/L) and sparfloxacin (MIC90s 0.01-1 mg/L). The activity of E-4904 (MIC90s 0.06-2 mg/L) was lower than those of its analogues. Most of the Escherichia coli which were resistant to ciprofloxacin (MIC > or = 2 mg/L) and Serratia spp., were resistant to the new fluoroquinolones. beta-Lactamase producing strains of Moraxella catarrhalis were very susceptible to these compounds (MICs < or = 0.008 mg/L). Most of Pseudomonas aeruginosa, non-aeruginosa Pseudomonas spp., Xanthomonas maltophilia, and Acinetobacter spp. were resistant to the new quinolones (MIC90s 8- > 16 mg/L). On the contrary, these new antimicrobials were active against the majority of the Aeromonas spp. (MIC90s < or = 0.5 mg/L). E-4749, E-4874, E-4884 and E-4904 remained active (MIC90s < or = 0.25 mg/L) against Staphylococcus aureus strains susceptible to methicillin. However, its activity was two- to eight-fold lower than that of ciprofloxacin (MIC90 0.03 mg/L) and sparfloxacin (MIC90 0.06 mg/L). Against S. aureus resistant to methicillin or ciprofloxacin, activity of these new compounds and comparators agents, was very low (MIC90s 2- > 16 mg/L). Most of the strains of Enterococcus faecalis were resistant (MIC90s > 16 mg/L). The activity of E-4874, E-4904 and sparfloxacin (MIC90 1 mg/L for each one) was higher than that of the rest of the agents tested. E-4874 (MIC90 0.25 mg/L) was four-fold more active than the other antibacterials tested (MIC90 2 mg/L) against Listeria monocytogenes. No new quinolone was active against Bacteroides fragilis (MIC90s 4-16 mg/L), Bacteroides thetaiotaomicron (MIC90s 8- > 16 mg/L), and other B. fragilis group (MIC90s 16- > 16 mg/L). Ciprofloxacin (MIC90s > 16 mg/L), and sparfloxacin (MIC90s 8-16 mg/L) also were inactive. E-4874 (MIC90 4 mg/L) was the most active quinolone tested against B.fragilis.

In vitro activities of new macrolides and rifapentine against Brucella spp.

We have tested the in vitro activities of streptomycin, rifampin, tetracyclines, trimethoprim-sulfamethoxazole, erythromycin, four new macrolides (roxithromycin, azithromycin, clarithromycin, and dirithromycin), and rifapentine against 62 strains of Brucella spp. Azithromycin and clarithromycin were, respectively, eight- and twofold more active than erythromycins (MIC for 90% of strains = 2, 8, and 16 micrograms/ml, respectively). The activity of rifapentine was similar to that of rifampin (MIC for 90% of strains = 1 microgram/ml).

Meropenem: in-vitro activity and kinetics of activity against organisms of the Bacteroides fragilis group.

Meropenem was compared with imipenem and nine other antimicrobial agents, against 101 strains of the Bacteroides fragilis group. Meropenem was active against all strains tested, and its activity was similar to, and in many cases better than, that of imipenem. The activity of meropenem was similar to that of metronidazole, and greater than that of the other antimicrobial agents tested. The bactericidal activity of meropenem against B. fragilis was impressive, since the MBC to MIC ratios were no greater than two. The bactericidal activity was confirmed by time-killing curve assays with two strains which showed that meropenem was rapidly bactericidal and reduced the initial inoculum significantly during the first 4-6 h. The postantibiotic effect of meropenem (2-4 h) and a sub-inhibitory concentration of 1/4 x MIC suggested that meropenem interferes with the normal growth of B. fragilis, even when administered concentrations fall below the MIC. MICs of meropenem were affected minimally by the pH of the medium or by an increase in inoculum size. Meropenem continued to have good activity against a B. fragilis strain that had been induced for the production of cephalosporinase. The in-vitro data presented in this paper indicate that meropenem is a promising antimicrobial agent which may be useful in the treatment of problematic mixed infections.

Lack of effective bactericidal activity of new quinolones against Brucella spp.

The in vitro activities of six fluoroquinolones against 43 Brucella spp. were compared by testing three different inocula at two medium pH values. The influence of the test conditions was moderate. The activities of all quinolones were lower at pH 5 and with a high inoculum size. Results indicate the lack of effective bactericidal activity of quinolones against most strains of Brucella spp., particularly B. abortus.

In vitro activities of irloxacin and E-3846, two new quinolones.

Irloxacin and E-3846 are two new fluorinated quinolones. We evaluated the activities of these antimicrobial agents, ciprofloxacin, ofloxacin, enoxacin, pefloxacin, norfloxacin, and nalidixic acid against 1,161 bacterial strains. Ciprofloxacin was the most active quinolone. Irloxacin did not show great activity. The activity of E-3846 against gram-negative bacteria was similar to those of ofloxacin and pefloxacin, and E-3846 was the most active quinolone against gram-positive bacteria and anaerobes.

Kinetics of antimicrobial activity of amoxicillin/clavulanic acid and metronidazole against beta-lactamase-producing Bacteroides fragilis group.

Bacteroides fragilis group are the most common anaerobic bacteria isolated in clinical specimens. The use of a beta-lactam with a beta-lactamase inhibitor should result in a marked increase in the group's sensitivity to the beta-lactams. Since the activity (MIC) shown by the amoxicillin + clavulanic acid combination against Bacteroides fragilis group is good, other parameters of in vitro activity have been studied. This study was also done with metronidazole. The minimum inhibitory concentration (MIC) was determined in 26 strains of Bacteroides fragilis group (14 B. fragilis; 5 B. thetaiotaomicron; 4 B. vulgatus; 3 B. distasonis). Likewise, the minimum bactericidal concentration (MBC), the killing curve, the sub-MIC and post-antibiotic effect were determined. The MIC ranged between 0.5 and 32 mg/l. The MBC was two- to four-fold the MIC for amoxicillin/clavulanic acid, and one- to two-fold the MIC for metronidazole for most strains. The killing curve showed a continuous decrease, sloping most sharply between 0-2 hours and 6-8 hours. Amoxicillin + clavulanic acid showed a post-antibiotic effect between 2 and 4 hours. The inhibitory minimum antibiotic concentration was one-half the MIC for most strains.

Kinetics of Antimicrobial Activity of Amoxicillin/Clavulanic Acid and Metronidazole against ß-Lactamase-Producing Bacteroides fragilis Group.

Bacteroides fragilis group are the most common anaerobic bacteria isolated in clinical specimens. The use of a beta-lactam with a ß-lactamase inhibitor should result in a marked increase in the group's sensitivity to the ß-lactams. Since the activity (MIC) shown by the amoxicillin + clavulanic acid combination against Bacteroides fragilis group is good, other parameters of in vitro activity have been studied. This study was also done with metronidazole. The minimum inhibitory concentration (MIC) was determined in 26 strains of Bacteroides fragilis group (14 B. fragilis; 5 B. thetaiotaomicron; 4 B. vulgatus; 3 B. distasonis). Likewise, the minimum bactericidal concentration (MBC), the killing curve, the sub-MIC and post-antibiotic effect were determined. The MIC ranged between 0.5 and 32 mg/l. The MBC was two- to four-fold the MIC for amoxicillin/clavulanic acid, and one- to two-fold the MIC for metronidazole for most strains. The killing curve showed a continuous decrease, sloping most sharply between 0-2 hours and 6-8 hours. Amoxicillin + clavulanic acid showed a post-antibiotic effect between 2 and 4 hours. The inhibitory minimum antibiotic concentration was one-half the MIC for most strains.

The in-vitro activity of SQ 82,291, a new monobactam, in comparison with aztreonam.

The in-vitro activity of a new monobactam antibiotic, SQ 82,291, was compared with that of aztreonam against 529 strains of aerobic and facultatively anaerobic bacteria. SQ 82,291, which is absorbed orally when administered as an ester, has shown good activity against different bacteria of the family Enterobacteriaceae and Haemophilus influenzae. The susceptibility of SQ 82,291 is lower than that to aztreonam in the species that were sensitive and SQ 82,291 showed no activity at all against staphylococci and strict anaerobes (like aztreonam); unlike aztreonam SQ 82,291 was not effective against Pseudomonas aeruginosa.