Colonization by high-level aminoglycoside-resistant enterococci in intensive care unit patients: epidemiology and clinical relevance.

A cohort study was performed to investigate the risk factors for colonization with high-level aminoglycoside-resistant enterococci (HLARE) in intensive care unit (ICU) patients. Colonization was investigated by performing surveillance samples during ICU stay. Clonal relatedness of the isolates was assessed by pulsed-field gel electrophoresis. Eighty-six patients with an ICU stay of >48 h were included; two were colonized with HLARE at admission, and 24 (28.5%) acquired HLARE during their stay in the ICU. HLARE were initially isolated from rectal swabs alone. Thirty-five percent of Enterococcus faecalis and 57% of E. faecium showed high-level resistance to gentamicin or streptomycin. Most isolates were clonally unrelated. Using multi-variate analysis, the only variable associated with HLARE colonization was previous antimicrobial use. Five patients had HLARE isolated from clinical samples, three of them with infection; in all of these, colonization with the same clone had been detected previously by surveillance samples. We conclude that most infections due to HLARE in the ICU are preceded by previous colonization, and that antimicrobial use is the main risk factor for colonization.

[The activity of four fluoroquinolones against strains of Pseudomonas aeruginosa with a different sensitivity pattern to ceftazidime and imipenem]. / Actividad de cuatro fluoroquinolonas frente a cepas de Pseudomonas aeruginosa con diferente patrón de sensibilidad a ceftazidima e imipenem.

OBJECTIVES: To evaluate the activity of four fluorquinolones (ciprofloxacin, clinafloxacin, norfloxacin and perfloxacin) against clinical strains of Pseudomonas aeruginosa with different sensitivity patterns to ceftazidime and imipenem. MATERIAL AND METHODS: 156 strains of isolated P. aeruginosa were studied at the Virgin Macarena University Hospital in Seville during 1998 and 1999. The in vitro activity of four fluorquinolones was determined by microdilution in Mueller Hinton bouillon, supplemented with cations, following the NCCLS guidelines. RESULTS: For all the strains evaluated, the minimum inhibitory concentration values (MIC90) of the clinafloxacin (4 mg/l) were significantly less than those for ciprofloxacin (64 mg/l). In the 76 strains resistant to ciprofloxacin, the clinafloxacin and ciprofloxacin MCI90 were 16 and >128 mg/l respectively. Clinafloxacin was more active than ciprofloxacin, norfloxacin and pefloxacin, independent to the sensitivity pattern or the resistance to ceptazidime and imipenem. CONCLUSION: Clinafloxacin was more active in vitro than ciprofloxacin against P. aeruginosa.

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.

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), and Stenotrophomonas 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 for P. 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 and A. baumannii isolates. The VITEK 2 system can perform reliable susceptibility testing of many of the antimicrobial agents used against P. aeruginosa and A. 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.

Activities of gemifloxacin and five other antimicrobial agents against Listeria monocytogenes and coryneform bacteria isolated from clinical samples.

The in vitro activities of gemifloxacin, ciprofloxacin, ampicillin, doxycycline, gentamicin, and vancomycin were evaluated against 15 Listeria monocytogenes strains and 205 coryneform bacteria isolated from clinical samples. The percentages of strains inhibited by gemifloxacin at 0.5 microg/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 microg of gemifloxacin per ml, whereas 0% of the strains were inhibited by 0.25 microg of ciprofloxacin per ml. Vancomycin at 2 microg/ml inhibited all strains. Doxycycline and gentamicin at 4 microg/ml inhibited 94 and 49% of the strains, respectively, while ampicillin at 0.5, 2, and 8 microg/ml inhibited 24, 61, and 66% of the strains, respectively. It is concluded that gemifloxacin shows good in vitro activity against L. monocytogenes and coryneform bacteria except C. jeikeium and C. urealyticum.

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 microg/ml) and two ciprofloxacin-resistant (MIC = 16 microg/ml) S. pneumoniae strains. RESULTS: At subinhibitory concentrations (0.5 x MIC) and inhibitory concentrations (1 x 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 microg/ml for gemifloxacin, trovafloxacin and ciprofloxacin, respectively) after standard doses, only gemifloxacin exhibited an approximately 99.9% (3 log(10)) 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.

Intracellular penetration and activity of gemifloxacin in human polymorphonuclear leukocytes.

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.

In vitro adherence of Enterococcus faecalis and Enterococcus faecium to urinary catheters.

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 (2.5x10(5) cfu/ml) in tryptic soy broth containing 0.5 cm segments from each type of catheter were incubated at 37 degrees 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.

[The activity of eight fluoroquinolones versus biolayers of Escherichia coli and Pseudomonas aeruginosa in siliconized latex urinary catheters]. / Actividad de ocho fluoroquinolonas frente a biocapas de Escherichia coli y Pseudomonas aeruginosa sobre sondas urinarias de látex siliconizado.

OBJECTIVE: To evaluate the in vitro activity of eight fluoroquinolones against Escherichia coli and Pseudomonas aeruginosa biofilms on siliconized latex urinary catheters. MATERIAL AND METHODS: The MICs and MBCs of norfloxacin, ciprofloxacin, ofloxacin, levofloxacin, clinafloxacin, sparfloxacin, trovafloxacin, and moxifloxacin for two strains of E. coli (CBR-3 and CBR-4) and two strains of P. aeruginosa (HUS-3 and PBR-2) were determined according to the NCCLS guidelines. The susceptibility of bacteria attached to siliconized latex catheters to fluoroquinolones was also evaluated. Catheter segments containing 6 or 24 hours old biofilms were used as inocula for the studies of antimicrobial activity against bacterial biofilms. RESULTS: MICs of ciprofloxacin for planktonic and attached bacteria were equal. MICs values for the others fluoroquinolones increased two or more times when bacterial biofilms were used as inocula, except for ofloxacin and E. coli CBR-4, trovafloxacin and E. coli CBR-3, and levofloxacin and trovafloxacin and P. aeruginosa PBR-4; in these cases the MIC values for planktonic and attached bacteria were similar. When bacteria attached to siliconized latex were used as inocula, MBCs values increased 8-> 4,096-fold for all the fluoroquinolones evaluated. CONCLUSIONS: E. coli and P. aeruginosa biofilms on siliconized latex were more resistant to the bactericidal activity of fluoroquinolones than planktonic bacteria.

The association of false-positive rapid plasma reagin results and HIV infection.

BACKGROUND AND OBJECTIVES: To study the relationship between a false positive rapid plasma reagin (RPR) result (FP), syphilis, and HIV infection in our patients. METHODS: A prospective study of the incidence of FP tests and syphilis in the general population and its relationship to HIV infection over a period of 6 months. RESULTS: 8.76% of the population were HIV positive. False positives were found in 15% and 1.2% of the HIV infected and noninfected patients, respectively; the attributable risk for HIV was 14.97. Syphilis was found in 5% and 0.9% of the positive and negative HIV patients, respectively; the attributable risk for HIV was 5.4. CONCLUSIONS: The incidence of false positive RPR results in the HIV-infected population is significantly higher than that of the non-HIV-infected patients.

[Opsonin requirements for phagocytosis of Enterococcus spp. by human polymorphonuclear leukocytes]. / Requerimientos opsónicos en la fagocitosis de Enterococcus spp. por los leucocitos polimorfonucleares humanos.

BACKGROUND: Interaction of Enterococcus spp. and host defense mechanisms is not well known. Opsonic requirements of Enterococcus faecalis and Enterococcus faecium to be phagocyted by human polymorphonuclear leukocytes (PMN) were evaluated. METHODS: Twenty strains (10 E. faecalis and 10 E. faecium) were studied. Phagocytosis was determined by a radiometric assay. Bacterial cells were labelled with 3H-adenine and opsonized with: a) 10% of human pool sera (HPS); b) 10% of decomplemented HPS, and c) albumin and fibronectin. RESULTS: Phagocytosis of Enterococcus spp. by PMN in the presence of HPS was significantly higher than that in the absence of opsonins. The phagocytosis of E. faecium was higher than that of E. faecalis. A strain-dependent effect of complement in the phagocytosis of Enterococcus spp. was observed. Neither albumin nor fibronectin showed an opsonic activity on Enterococcus spp. CONCLUSIONS: A great heterogeneity in the opsonic requirements of Enterococcus spp. was observed. Serum opsonins show a critical role in the phagocytosis of E. faecalis and E. faecium by PMN, this effect being more relevant with E. faecium. A strain-dependent opsonic activity of complement was observed.

[Usefulness of the disk diffusion method for evaluating the sensitivity of Neisseria meningitidis to penicillin and cefotaxime]. / Utilidad del método de difusión con disco para evaluar la sensibilidad de Neisseria meningitidis a penicilina y cefotaxima.

BACKGROUND: Routine susceptibility testing of Neisseria meningitidis to penicillin and other beta lactams is recommended after the isolation of N. meningitidis of moderately resistant to penicillin (MRP). We have evaluated the disk-diffusion method to determine susceptibility of N. meningitidis to penicillin (using disks of either penicillin or oxacillin) and to cefotaxime. METHODS: Fifty-four strains of N. meningitidis isolated from clinical samples were studied. MICs of penicillin and cefotaxime were determined by microdilution. Disks of 2 U of penicillin, 1 microgram of oxacillin and 30 micrograms of cefotaxime and two culture media, Mueller-Hinton agar (MHA) and MHA supplemented with 5% sheep blood (MHS) were used in the disk-diffusion assay. RESULTS: For disk of 2 U of penicillin assayed in MHA, 86.4% of the susceptible strains and 20% of MRP strains were considered susceptible when a breakpoint of 28 mm was considered. None of the MRP strains was considered susceptible when using MHS, but only 38.6% of susceptible strains appeared as such on this medium. When a 1 microgram oxacillin disk was used all MRP strains presented an inhibition zone < or = 10 mm on both MHA and MHS, but 54.4 and 4.5% of susceptible strains presented an inhibition zone > or = 11 mm on MHA and MHS, respectively. All strains were susceptible to cefotaxime, showing inhibition zones around a 30 micrograms disk on MHA and MHS of > or = 35 mm and > or = 25 mm, respectively. CONCLUSION: Disk diffusion with cefotaxime (30 micrograms) allows to determine susceptibility of N. meningitidis to this antimicrobial agent. Discs of penicillin (2 U) and oxacillin (1 microgram) are not useful for screening of MRP N. meningitidis.

Comparison of broth microdilution and E-test for susceptibility testing of Neisseria meningitidis.

The susceptibilities of 54 clinical isolates of Neisseria meningitidis to penicillin, cefotaxime, ceftriaxone, cefepime, imipenem, ciprofloxacin, chloramphenicol, and rifampin were determined by the microdilution method in both cation-adjusted Mueller-Hinton broth (CAMHB) and Haemophilus test medium (HTM). Poor growth was observed in 16.6 and 9% of the strains in CAMHB and HTM, respectively. As a result, the growth of the 54 N. meningitidis strains was evaluated in three other commercially available batches of CAMHB and in one in-house batch of HTM. Poor growth was observed for 9.3 to 16.6% of the strains in all four batches. More important, three of the CAMHB batches failed to support growth for 3.7 to 33.3% of the strains; 3.7% of the strains did not grow in the in-house-prepared HTM. Ten (18.7%) strains were relatively resistant to penicillin (RRP; MIC, > 0.125 mu g/ml) in CAMHB and 13 (24%) strains were RRP in HTM. The percentages of agreement obtained by using CAMHB as the reference ranged from 78% for cefepime to 100% for ceftriaxone. Seven minor errors were observed for penicillin; five of them were for strains susceptible to penicillin in CAMHB and RRP in HTM. All strains were susceptible to the other antimicrobial agents evaluated. The growth of N. meningitidis was also evaluated in four batches of Mueller-Hinton agar (MHA). In two of them, 3.7 and 44.4% of the strains did not grow, and considering all four batches, 5.5 to 11.1% grew poorly. All strains grew adequately in MHA supplemented with blood (MHA-b). The activities of penicillin and cefotaxime were also evaluated by the E-test in MHA and MHA-b. The proportion of RRP strains were 24% in MHA and 59% in MHA-b. For penicillin, the percentages of agreement of the E-test with the microdilution method in CAMHB (reference) were 64.8 and 70.3% in MHA and MHA-b, respectively. For cefotaxime, the agreement was 98.1%. Minor errors for the penicillin MIC were detected for 38% of the strains tested. Further studies are needed to define adequate culture media for reference methods to evaluate the susceptibility of N. meningitidis to antimicrobial agents.

[False sensitivity of Enterococcus faecium to amoxicillin-clavulanic acid with the MicroScan system]. / Falsa sensibilidad de Enterococcus faecium a amoxicilina-ácido clavulánico con el sistema MicroScan.

BACKGROUND: We have observed by using MicroScan automatic system discrepancies in susceptibility results of Enterococcus faecium strains to ampicillin and amoxicillin/clavulanic acid. METHODS AND RESULTS: Seventy-six strains of E. faecium were studied with MicroScan; 98.7% of them were inhibited by 16 mg/l of amoxycillin-clavulanic acid versus 60.5% inhibited by the same concentration of ampicillin. We have evaluated the susceptibility to ampicillin, amoxicillin and amoxicillin-clavulanic acid of 7 strains of E. faecium by both MicroScan and standard microdilution assay. MIC values of ampicillin were similar by both methods but MIC values of amoxicillin/clavulanic acid obtained by MicroScan (< or = 4/2 mg/l in 6 strains) were considerably lower than those obtained by standard microdilution (> or = 16/8 in 6 strains). This phenomenon was not dependent of betalactamase production or bacterial inocula. CONCLUSIONS: When using MicroScan, E. faecium strains resistant to ampicillin (betalactamase non producers) must be also considered resistant to amoxicillin/clavulanic acid without considering the values obtained by this system.