Providencia Joyanes

Evaluation of the VITEK 2 System for the Identification and Susceptibility Testing of Three Species of Nonfermenting Gram-Negative Rods Frequently Isolated from Clinical Samples

ABSTRACT VITEK 2 is a new automatic system for the identification and susceptibility testing of the most clinically important bacteria. In the present study 198 clinical isolates, including Pseudomonas aeruginosa (n = 146), Acinetobacter baumannii (n = 25), andStenotrophomonas maltophilia (n = 27) were evaluated. Reference susceptibility testing of cefepime, cefotaxime, ceftazidime, ciprofloxacin, gentamicin, imipenem, meropenem, piperacillin, tobramycin, levofloxacin (only for P. aeruginosa), co-trimoxazole (only for S. maltophilia), and ampicillin-sulbactam and tetracycline (only for A. baumannii) was performed by microdilution (NCCLS guidelines). The VITEK 2 system correctly identified 91.6, 100, and 76% of P. aeruginosa, S. maltophilia, and A. baumannii isolates, respectively, within 3 h. The respective percentages of essential agreement (to within 1 twofold dilution) for P. aeruginosa and A. baumannii were 89.0 and 88.0% (cefepime), 91.1 and 100% (cefotaxime), 95.2 and 96.0% (ceftazidime), 98.6 and 100% (ciprofloxacin), 88.4 and 100% (gentamicin), 87.0 and 92.0% (imipenem), 85.0 and 88.0% (meropenem), 84.2 and 96.0% (piperacillin), and 97.3 and 80% (tobramycin). The essential agreement for levofloxacin against P. aeruginosa was 86.3%. The percentages of essential agreement for ampicillin-sulbactam and tetracycline against A. baumannii were 88.0 and 100%, respectively. Very major errors for P. aeruginosa (resistant by the reference method, susceptible with the VITEK 2 system [resistant to susceptible]) were noted for cefepime (0.7%), cefotaxime (0.7%), gentamicin (0.7%), imipenem (1.4%), levofloxacin (2.7%), and piperacillin (2.7%) and, for one strain of A. baumannii, for imipenem. Major errors (susceptible to resistant) were noted only forP. aeruginosa and cefepime (2.0%), ceftazidime (0.7%), and piperacillin (3.4%). Minor errors ranged from 0.0% for piperacillin to 22.6% for cefotaxime against P. aeruginosa and from 0.0% for piperacillin and ciprofloxacin to 20.0% for cefepime against A. baumannii. The VITEK 2 system provided co-trimoxazole MICs only for S. maltophilia; no very major or major errors were obtained for co-trimoxazole against this species. It is concluded that the VITEK 2 system allows the rapid identification of S. maltophilia and most P. aeruginosa andA. baumannii isolates. The VITEK 2 system can perform reliable susceptibility testing of many of the antimicrobial agents used against P. aeruginosa andA. baumannii. It would be desirable if new versions of the VITEK 2 software were able to determine MICs and the corresponding clinical categories of agents active against S. maltophilia.

Energy-Dependent Accumulation of Norfloxacin and Porin Expression in Clinical Isolates of Klebsiella pneumoniae and Relationship to Extended-Spectrum β-Lactamase Production

ABSTRACT The relationships between porin deficiency, active efflux of fluoroquinolones, and extended-spectrum β-lactamase (ESBL) production were determined for 53 clinical isolates of Klebsiella pneumoniae. Thirty-two ESBL-positive strains (including 22 strains expressing porins and 10 strains lacking porins) and 21 ESBL-negative strains were evaluated. Active efflux of norfloxacin was defined as a ≥50% increase in the accumulation of norfloxacin in the presence of carbonyl cyanide m-chlorophenylhydrazone (CCCP) in comparison with the corresponding basal value in the absence of CCCP. The quinolone resistance-determining regions of both gyrA and parC from 13 strains, representing all isolates with different porin profiles and with or without active efflux, were determined. Porin loss was significantly more common among ESBL-positive strains (10 of 32 [31.2%]) than among ESBL-negative strains (0 of 2 [0%]) (P < 0.01). Active efflux was observed in 7 of 10 (70%) strains lacking porins and in 4 of 43 (9.3%) strains producing porins (P < 0.001). The 11 strains showing active efflux corresponded to 3 of 21 (14.3%) ESBL-negative strains and 8 of 32 (25.5%) ESBL-positive strains (P > 0.05). Basal values of norfloxacin accumulation were higher in strains lacking active efflux than in those that had this mechanism (P < 0.05). In the absence of topoisomerase changes, the contribution of either porin loss or active efflux to fluoroquinolone resistance in K. pneumoniae was negligible. It is concluded that among K. pneumoniae strains of clinical origin, porin loss was observed only in those producing ESBL, and that a significant number of porin-deficient strains also expressed active efflux of norfloxacin. In terms of fluoroquinolone resistance, both mechanisms are significant only in the presence of topoisomerase modifications.

In Vitro Adherence of Enterococcus faecalis and Enterococcus faecium to Urinary Catheters

Abstract The in vitro adherence of ten strains of Enterococcus faecalis and ten strains of Enterococcus faecium to siliconized latex urinary catheters and to silicone elastomer was evaluated. Bacterial suspensions (2.5×105 cfu/ml) in tryptic soy broth containing 0.5 cm segments from each type of catheter were incubated at 37 °C. At specified intervals, the segments were washed to remove nonadherent bacteria and sonicated for 1 min, and colony-forming units were quantified. Bacterial adherence occurred rapidly, reaching maximal peaks after 24 h of incubation. Enterococcus faecium adherence to both biomaterials was significantly lower than that of Enterococcus faecalis. No differences were observed between the two elastomers. Bacterial adherence was not related to bacterial surface hydrophobicity, hemolysin or gelatinase production.

Activities of Gemifloxacin and Five Other Antimicrobial Agents against Listeria monocytogenes and Coryneform Bacteria Isolated from Clinical Samples

ABSTRACT The in vitro activities of gemifloxacin, ciprofloxacin, ampicillin, doxycycline, gentamicin, and vancomycin were evaluated against 15Listeria monocytogenes strains and 205 coryneform bacteria isolated from clinical samples. The percentages of strains inhibited by gemifloxacin at 0.5 μg/ml were 100% (L. monocytogenes), 93.3% (Brevibacterium spp.), 90% (Corynebacterium minutissimum), 42.5% (Corynebacterium amycolatum), 20% (Corynebacterium striatum), 12.5% (Corynebacterium jeikeium), and 10% (Corynebacterium urealyticum). One hundred percent of the L. monocytogenes strains were inhibited by 0.25 μg of gemifloxacin per ml, whereas 0% of the strains were inhibited by 0.25 μg of ciprofloxacin per ml. Vancomycin at 2 μg/ml inhibited all strains. Doxycycline and gentamicin at 4 μg/ml inhibited 94 and 49% of the strains, respectively, while ampicillin at 0.5, 2, and 8 μg/ml inhibited 24, 61, and 66% of the strains, respectively. It is concluded that gemifloxacin shows good in vitro activity againstL. monocytogenes and coryneform bacteria exceptC. jeikeium and C. urealyticum.

Intracellular penetration and activity of gemifloxacin in human polymorphonuclear leukocytes.

ABSTRACT The intracellular penetration and activity of gemifloxacin in human polymorphonuclear leukocytes (PMN) were evaluated. Gemifloxacin reached intracellular concentrations eight times higher than extracellular concentrations. The uptake was rapid, reversible, and nonsaturable and was affected by environmental temperature, cell viability, and membrane stimuli. At therapeutic extracellular concentrations, gemifloxacin showed intracellular activity against Staphylococcus aureus.

Differences between two new quinolones (gemifloxacin and trovafloxacin) and ciprofloxacin in their concentration-dependent killing of Streptococcus pneumoniae.

Background: Ciprofloxacin resistance influences the in vitro effect of new quinolones on Streptococcus pneumoniae.Methods: The early (over 3 h) in vitro bactericidal activity of gemifloxacin, trovafloxacin and ciprofloxacin was explored by time-kill tests against two ciprofloxacin-susceptible (MIC = 0.5 and 1 µg/ml) and two ciprofloxacin-resistant (MIC = 16 µg/ml) S. pneumoniae strains. Results: At subinhibitory concentrations (0.5 × MIC) and inhibitory concentrations (1 × MIC), only gemifloxacin exhibited significant bactericidal activity with, respectively, approximately 85 and approximately 95% decrease in the initial inoculum of the two ciprofloxacin-resistant strains. At concentrations similar to peak serum concentrations (1.5, 3 and 2.5 µg/ml for gemifloxacin, trovafloxacin and ciprofloxacin, respectively) after standard doses, only gemifloxacin exhibited an approximately 99.9% (3 log10) reduction in the initial inoculum for the four strains tested, regardless of their susceptibility to ciprofloxacin. No bactericidal activity was exhibited for the other two quinolones against the ciprofloxacin-resistant strains. Conclusions: Gemifloxacin offers high early bactericidal activity at concentrations similar to peak and trough levels, theoretically preventing regrowth over the dosing interval, and thus dealing with the problem of ciprofloxacin resistance in S. pneumoniae.

Actividad de cuatro fluoroquinolonas frente a cepas de Pseudomonas aeruginosa con diferente patrón de sensibilidad a ceftazidima e imipenem

Fundamento Evaluar la actividad de cuatro fluoroquinolonas (ciprofloxacino, clinafloxacino, norfloxacino y pefloxacino) frente cepas clinicas de Pseudomas aeruginosa con diferentes patrones de sensibilidad a ceftazidima e imipenem Material y metodos Se estudiaron 156 cepas de P. aeruginosa aisladas en el Hospital Universitario Virgen Macarena de Sevilla en los anos 1998 y 1999. La actividad in vitro de cuatro fluoroquinolonas se determino mediante microdilucion en caldo Mueller Hinton suplementado con cationes siguiendo las recomendaciones del NCCLS Resultados Para el total de cepas evaluadas, los valores de concentracion minima inhibitoria (CMI)90 de clinafloxacino (4 mg/l) fueron significativamente inferiores a los de ciprofloxacino (64 mg/l). Para las 76 cepas resistentes a ciprofloxacino, las CMI90 de clinafloxacino y ciprofloxacino fueron de 16 y > 128 mg/l respectivamente. Clinafloxacino fue mas activa que ciprofloxacino, norfloxacino y pefloxacino, con independencia del patron de sensibilidad o resistencia a ceftazidima e imipenem Conclusion Clinafloxacino fue mas activa in vitro que ciprofloxacino frente a P. aeruginosa