Filtration of dialysate using an on-line dialysate filter.

UNLABELLED: Increased concerns about pyrogenic contamination of dialysate have led to the development of an on-line dialysate filtration system. Bacteriological testing of the system was performed (n = 6) by introducing bicarbonate concentrate contaminated with E. coli 026:B 6 (3 x 10(9) cfu/ml) into a dialysis machine equipped with a two-stage polysulfone filtration system. The bacterial concentration of the dialysate entering the filtration system was maintained above 10(6) cfu/ml and endotoxin levels ranged from 30-300 ng/ml during the 3-hour test period. Bacterial and endotoxin levels on the input side of the first-stage filter reached minimum concentrations of 5.4 x 10(9) cfu/ml and 30,000 ng/ml respectively. All output samples of filtered dialysate showed no bacterial growth and endotoxin levels were below the sensitivity (0.003 ng/ml) of the LAL assay. A dialysis machine (QD = 500), equipped with a single stage filtration system, was used for 18 months of clinical testing. In order to evaluate the system's reliability with regard to membrane failures and reduced dialysate flow, filter membrane integrity was verified weekly using a pressure holding test and dialysate flow was measured under routine clinical conditions. No membrane failures occurred, and dialysate flow was maintained at 511 +/- 17 ml/min (n = 70) during the test period. IN CONCLUSION: dialysate filtration is an effective and practical method for prevention of pyrogenic reactions due to high levels of bacteria and endotoxins.

In-vitro susceptibility of staphylococci to fleroxacin in comparison with six other quinolones.

Susceptibilities of methicillin-resistant Staphylococcus aureus (MRSA, n = 32), methicillin-sensitive S. aureus (MSSA, n = 32), and S. epidermidis (SE, n = 24) were determined to fleroxacin, amifloxacin, ciprofloxacin, difloxacin, enoxacin, norfloxacin, and ofloxacin. All organisms were isolated from the blood of patients with infective endocarditis. MRSA and MSSA MIC90s were less than 1.0 mg/l of fleroxacin, ciprofloxacin, difloxacin, and ofloxacin while amifloxacin and norfloxacin produced MIC90s of less than 2.0 mg/l and enoxacin MIC90s of less than 4.0 mg/l. For S. epidermidis MIC90s were less than 1.0 mg/l of all quinolones except amifloxacin whose MIC90 was less than 2.0 mg/l. Two strains from each staphylococcal group were used in time-kill trials performed with all seven quinolones. Within 8 h, all quinolones colony counts were decreased by one log. At 24 h, most quinolones decreased MRSA, MSSA, and SE colony counts by two to four logs; however, exceptions were found with (1) difloxacin, enoxacin, and norfloxacin against MRSA, (2) ciprofloxacin and enoxacin against MSSA, and (3) ciprofloxacin against SE in which all colony counts increased one to three logs in 24 h. When quinolone time-kill trials did not show a decrease in colony counts at 24 h, the MIC's for the 24 h growth showed a four- to 250-fold increase when compared with pre-trial MICs. No selection or emergence of resistant organisms was found with fleroxacin, amifloxacin or ofloxacin.

Inhibition of Legionella pneumophila multiplication within human macrophages by fleroxacin.

The susceptibility of Legionella pneumophila to a new quinolone, fleroxacin, was studied in both an extra- and an intracellular system. The activity of fleroxacin was compared with that of erythromycin, cefoxitin, and rifampicin. In the extracellular system, erythromycin inhibited while cefoxitin killed the organism. Extracellularly, fleroxacin performed similarly to cefoxitin. Rifampicin was initially bactericidal for L. pneumophila but resistant bacteria emerged at 48 h. The Horwitz monocyte model was used for studies of intracellular antimicrobial activity. At ten times the MIC, cefoxitin did not inhibit intracellular L. pneumophila. Fleroxacin was as active as erythromycin and rifampicin in inhibiting intracellular L. pneumophila. No intracellular, rifampicin-resistant L. pneumophila emerged. Addition of rifampicin to cefoxotin, erythromycin or fleroxacin provided neither synergy nor antagonism.

In-vitro susceptibility of gram-positive cocci to LY146032 teicoplanin, sodium fusidate, vancomycin, and rifampicin.

LY146032, a new antimicrobial agent with activity against Gram-positive cocci, was tested against methicillin-susceptible and methicillin-resistant Staphylococcus aureus, methicillin-susceptible and methicillin-resistant Staph. epidermidis, Staph. saprophyticus, and Streptococcus faecalis. MIC90s in cation-supplemented Mueller Hinton broth by the microdilution broth method were less than 1.0 mg/l for all organisms tested. Increasing or decreasing the inoculum size did not appreciably effect the MIC50 or MIC90 for any organism group nor did decreasing the incubation temperature. The addition of sodium chloride to the test system did not appreciably effect the susceptibility of methicillin-resistant Staph. aureus to LY146032. All organisms were 4 to 32 times more susceptible to LY146032 than to vancomycin. The Staph. aureus had LY146032 susceptibility patterns which were similar to those of teicoplanin and sodium fusidate. LY146032 was 4-16 times more active than teicoplanin against Staph. saprophyticus and Staph. epidermidis while teicoplanin was 8-16 times more active than LY146032 against Str. faecalis.

The effect of heat upon the interaction between aminoglycosides and semi-synthetic penicillins in human serum: a consideration for HIV infectious serum.

We conducted 2 experiments to study the effect of heat on the interaction between aminoglycosides and semi-synthetic penicillins in human serum. In one experiment, human serum spiked with either gentamicin or tobramycin at a concentration of 4.7 mg/l plus carbenicillin, ticarcillin, piperacillin, mezlocillin, or azlocillin at concentrations of either 50 mg/l or 150 mg/l was subjected to a 30-min, 56 degrees C waterbath incubation. In the second experiment, randomly selected sera from patients receiving either gentamicin or tobramycin were also heat-treated. Two methods, the Abbott TDx and the Syva Emit, were used for each aminoglycoside assay. The difference between pre- and post-heat treatment aminoglycoside concentration was less than 10% in approximately 92% of the patient sera and in 93% of the spiked sera containing an aminoglycoside plus a semi-synthetic penicillin at 50 mg/l. For sera spiked with an aminoglycoside plus a semi-synthetic penicillin at 150 mg/l, post-heat treatment concentrations were 5-19% lower than pre-heat treatment concentrations. In most instances, heat treatment of sera does not alter aminoglycoside concentrations to any clinically significant degree.

In vitro susceptibility of gram-positive cocci to paldimycin.

Paldimycin (U-70138F) is a new antimicrobial agent with activity against gram-positive cocci. Clinical isolates of staphylococci and streptococci were tested. MICs were higher in Mueller-Hinton broth than in nutrient broth. Change in pH had minimal effect on the MICs in either broth. When inoculum size was varied, an inoculum effect was observed. The gram-positive cocci tested were generally more susceptible to paldimycin than to vancomycin.

Lack of bacterial aerosols associated with heat and moisture exchangers.

Contaminated condensate might serve as a source for cross infection. Heat and moisture exchangers (HME) are devices that humidify inspired gases, which pass through a hygroscopic felt pad surrounded by a cellulose sponge housed in a plastic case. In our study, we used a Servo 150 HME in place of a cascade humidifier in mechanical ventilator circuits. We performed 2 studies to evaluate the microbiologic safety of the HME. First, 42 HMEs used by patients for 24 h were tested in the laboratory for contamination. To simulate patient/air exchange, the HMEs were connected to the Andersen Sampler (flow at 35 L/min x 20 min). Although the inner felt pad of the HMEs was contaminated in 74% of the units (31 of 42), only 4.8% (2 of 42) generated 1 to 2 bacteria/702 L of air. In a second study, HMEs contaminated with either Staphylococcus aureus or Pseudomonas aeruginosa (at 10(3), 10(5), or 10(8) organisms/ml) were connected to an Andersen Air Sampler to simulate a ventilator circuit. Bacterial aerosols were not generated, with the exception of 2 to 4 bacteria recovered after contamination with 10(8) bacteria. The HME can provide humidification for mechanically ventilated patients with little risk of generating respirable bacterial aerosols.

Serum and crevicular fluid concentrations after a single oral dose of metronidazole.

Previous studies have shown that metronidazole is an effective chemotherapeutic agent in the treatment of certain types of periodontal disease. The purpose of this study was to assess, over 18 hours, the concentration of the drug in serum and gingival crevicular fluid after a single oral dose. Six female volunteers with gingivitis created by cessation of brushing for 2 weeks, took 250 mg of metronidazole orally. Micropipettes were used to collect 20 microliters of serum and 4 to 5 microliters of gingival fluid hourly for 8 hours, and at the 12th and 18th hours. Samples were assayed with a high pressure liquid chromatograph. Mean drug levels in serum closely matched those reported by Stephen et al. (Br Dent J 7: 313, 1966) with polography. Mean serum drug levels peaked at 6.09 micrograms/ml at the 2nd hour, and mean gingival crevicular fluid drug levels peaked at 3.62 micrograms/ml at the 2nd and 7th hours. The drug was detectable in both fluids for up to 18 hours. Mean serum concentrations remained greater than mean gingival fluid concentrations at all time intervals, though the differences were not significant (P less than 0.05) as determined by a Hoteling's T2 test. Using reported minimal inhibitory concentration values of metronidazole for various periodontopathogens, it was concluded that a single oral dose of metronidazole will deliver potentially inhibitory levels of the drug to the periodontium in serum and in gingival crevicular fluid.

Comparison of enzyme-multiplied immunoassay technique with fluorescence polarization immunoassay for determination of gentamicin and tobramycin levels in serum.

We assayed serum gentamicin and tobramycin specimens by the enzyme multiplied immunoassay technique (Syva EMIT) and the fluorescence polarization immunoassay (Abbott TDx). When interassay and intraassay control samples were evaluated, both methods gave an overall coefficient of variation of less than +/- 10%. Using patient serum samples, we obtained excellent correlation with both methods in the assay of gentamicin (correlation coefficient, 0.985) and tobramycin (correlation coefficient, 0.982).

Comparison of fluorescence polarization immunoassay and bioassay of vancomycin.

Human serum samples were analyzed for vancomycin concentrations by two different methods: the fluorescence polarization immunoassay and the disk plate bioassay. Each assay method offered acceptable precision. The correlation between both assay methods was excellent (correlation coefficient = 0.985). Excluding technical time, the bioassay was the least expensive method to perform but was more labor intensive than the fluorescence polarization immunoassay.

In vitro susceptibilities of 393 recent clinical isolates to WIN 49375, cefotaxime, tobramycin, and piperacillin.

The in vitro susceptibilities of 393 recent clinical isolates to WIN 49375, a new quinolone derivative, were determined and concurrently tested with cefotaxime, tobramycin, and piperacillin. In general, members of the family Enterobacteriaceae were not as susceptible to tobramycin and piperacillin as they were to WIN 49375. Methicillin-resistant and -susceptible Staphylococcus aureus were equally susceptible to WIN 49375.

In vitro susceptibility patterns of methicillin-resistant and-susceptible Staphylococcus auerues strains in a population of parenteral drug abusers from 1972 to 1981.

Since 1980, infections caused by methicillin-resistant (MR) Staphylococcus aureus have been epidemic among Detroit-area parenteral drug abusers. Because of the increasing importance of this pathogen, in vitro susceptibilities were compared for 39 isolates of MR S. aureus from 1980 to 1981, and for 56 strains of methicillin-susceptible (MS) S. aureus from 1972 to 1981, recovered from drug abusers with community-acquired infections. Agar dilution studies were performed at 35 degrees C, and minimal inhibitory concentrations were determined after incubation for 18 and 48 h. MR S. aureus exhibited cross-resistance to other beta-lactam antibiotics which frequently required 48 h for expression. MR S. aureus isolates were also resistant to tetracycline, clindamycin, tobramycin, and amikacin. All MR S. aureus isolates investigated synthesized an aminoglycoside 4'-nucleotidyltransferase. Emergence of resistance to cefotaxime, tetracycline, and clindamycin was noted among current MS S. aureus isolates. Vancomycin, fusidic acid, trimethoprim/sulfamethoxazole, and rifampin were the most active agents against MR S. aureus and were equally effective against MS S. aureus.

Community-acquired methicillin-resistant Staphylococcus aureus infections: a new source for nosocomial outbreaks.

Over a 19-month period, 165 patients with 183 infections caused by community-acquired, methicillin-resistant Staphylococcus aureus were seen at Henry Ford Hospital in Detroit, Michigan. The proportion of community-acquired staphylococcal infections resistant to methicillin rose from 3 % in March 1980 to 38% in September 1981. Drug abuse, serious underlying illness, previous antimicrobial therapy, and previous hospitalization were all associated with the development of this infection. Concurrent with the community epidemic was a nosocomial epidemic of methicillin-resistant S. aureus infection, which accounted for 30.6% of all nosocomial staphylococcal infections in January 1981. Control measures that included isolation, discharge precautions for carriers, and eradication of employee carriage were effective in preventing nosocomial transmission. The prevalence of methicillin-resistant S. aureus carriage among employees was 0.7%. Methicillin-resistant S. aureus may originate in the community as well as in the hospital, and presents a threat to patients in both settings.

Failure of probenecid to alter the pharmacokinetics of ceforanide.

This investigation evaluated the effect of probenecid on ceforanide concentrations in eight healthy volunteers. Each volunteer was given 1 or 2 g of ceforanide either alone or with 1 g of probenecid. Concentrations of ceforanide in plasma, urine, and saliva were then measured. Probenecid did not alter the plasma concentrations of ceforanide, nor did it affect the urinary excretion of this agent. Ceforanide was not secreted into saliva in any detectable amount either when administered alone or with probenecid. It is not clear why probenecid has a negligible effect on ceforanide concentrations in plasma. It may be that tubular secretion plays less of a role in the excretion of ceforanide than expected, or that the physical properties of ceforanide prevent probenecid from affecting its excretion.

The effect of inoculum, culture medium and antimicrobial combinations on the in-vitro susceptibilities of Legionella pneumophila.

The in-vitro susceptibility of 14 strains of Legionella pneumophila to 17 anti-microbial agents were determined. The most active antibiotics were cefoxitin, erythromycin and doxycycline while the least active were cephalothin, cefamandole and cefazolin. Subculturing, type of medium and duration of incubation did not alter the effect of the antimicrobial agents. A change in the inoculum size, from 10(4) to 10(6) cfu, increased MICs two- to sixfold. Erythromycin was not synergistic with gentamicin, tobramycin or amikacin.

Effect of clavulanic acid on minimal inhibitory concentrations of 16 antimicrobial agents tested against Legionella pneumophila.

A total of 15 Legionella pneumophilia isolated were tested against 16 antimicrobial agents used singly and in combination with clavulanic acid. When combined with clavulanic acid, 4 of the 16 antimicrobial agents produced no enhanced effect. However, the minimal inhibitory concentrations of 12 of the antimicrobial agents were reduced by one-half to one-third when in combination with clavulanic acid. These reductions reflected only a one-dilution decrease, however, in the original minimal inhibitory concentrations. Thus, clavulanic acid combinations appear to be only nominally effective beta-lactamase inhibitors against L. pneumophilia.

Antimicrobial susceptibility of Legionella pneumophila Serogroups I--IV.

Strains of Legionella pneumophila from 10 geographic areas were evaluated for their in vitro susceptibility to 14 antimicrobial agents. Included in this study were clinical and environmental isolates as well as strains from all 4 known serogroups. The minimal inhibitory concentration was established by agar dilution with a Steers replicator. The inhibitory index was then calculated considering the mean peak serum level for the associated antibiotic. Rifampicin, cefoxitin, chloramphenicol, ticarcillin, and parenteral erythromycin had the highest inhibitory indices. The only difference among serogroups was the increased susceptibility among serogroup II isolates to the penicillins and the increased susceptibility of serogroups III and IV to sulfamethoxazole-trimethoprim. Though there have been recent reports of the inadequacy of oral erythromycin in clinical cases of Legionnaires' disease, there was no erythromycin resistance noted among the 14 isolates tested.