In-vitro activity of imipenem, in comparison with cefuroxime and ciprofloxacin, against coagulase-negative staphylococci in broth and peritoneal dialysis fluid

The activity of cefuroxime, ciprofloxacin and imipenem against 50 coagulase-negative staphylococci (CNS) strains isolated from patients with peritonitis while on continuous ambulatory peritoneal dialysis (CAPD) was examined. Strains were cultured in both used peritoneal dialysis fluid (PUD) and broth (ISB) in an atmosphere of air with 5% CO2. MICs of cefuroxime, ciprofloxacin and imipenem differed significantly between the two media for 40%, 26% and 42% of strains, respectively. In three-quarters of these cases the MICs were higher in PUD compared to ISB. The ability of each antibiotic to kill six strains of CNS adherent to silicone rubber was also examined. Once again, differences in killing were noted between the two media. At least two-thirds of the strains remained viable in the presence of concentrations of antibiotic equal to the MBC of each antibiotic and at least one-third survived antibiotic concentrations equivalent to those attained during treatment. Assessment of activity in PUD may provide a more realistic test for antibiotics to be used in the treatment of CAPD peritonitis.

Variation in the expression of cell envelope proteins of coagulase-negative staphylococci cultured under iron-restricted conditions in human peritoneal dialysate

Strains of coagulase-negative staphylococci (CNS), including Staphylococcus epidermidis, S. hominis, S. warnerii, S. simulans, S. capitis, S. haemolyticus and S. saprophyticus, were isolated from patients with continuous-ambulatory-peritoneal-dialysis-related peritonitis. The cell wall and cytoplasmic membrane protein profiles of CNS strains cultured in either nutrient broth (NB) or pooled human peritoneal dialysate (HPD) were compared. Some interspecies variation in both the wall and membrane protein profiles was noted. However, the cell wall protein profiles of HPD-grown CNS strains differed markedly from those cultured in NB. Growth in HPD resulted in a marked reduction in the total number of cell-wall-associated proteins but up to three antigenically related proteins in the 40-56 kDa range, depending on the species, predominated. Growth in HPD also resulted in the induction of two iron-repressible cytoplasmic membrane proteins (IRMPs) of 32 and 36 kDa in S. epidermidis. Other CNS strains only appeared to express a single IRMP, which varied in molecular mass from 32 to 36 kDa. Whilst the IRMP in these CNS strains showed considerable antigenic homology with the 32 kDa IRMP, the S. warneri IRMP showed cross-reactivity with both the 32 and 36 kDa IRMPs of S. epidermidis. Immunoblotting experiments revealed that whilst the CNS cell wall proteins were poorly immunogenic, the IRMPs were the immunodominant CNS protein antigens, reacting strongly with antibodies present in HPD. This finding provides evidence to suggest that the IRMPs are expressed in vivo during infection.

Relationship between cefpirome clearance, serum creatinine, weight and age in patients treated for infection

Cefpirome serum concentrations were measured by microbiological assay in 30 patients after five to nine days of treatment with 1 or 2 g bd for moderate to severe infection of presumed bacterial origin. Patients with serum creatinine (SCr) greater than 220 mumol/L were excluded. The age of patients ranged from 34-86 years. Creatinine clearance (Clcr) was calculated from age, sex, weight and SCr. The range of SCr was 63-220 mumol/L and the range of Clcr was 18-169 mL/min. The correlation coefficient with cefpirome clearance was 0.464 for SCr and 0.747 for Clcr. More than half of the patients with Clcr less than 50 mL/min had SCr within the normal range of 70-150 mumol/L. Mean cefpirome clearance in patients with Clcr 18-50 mL/min was 42.7 mL/min, which is very similar to the figure of 43.5 mL/min reported in a single dose volunteer study in patients with renal failure. Mean cefpirome clearance in patients with Clcr greater than 80 mL/min was 107.6 mL/min. In conclusion, these data on cefpirome clearance obtained after multiple dose treatment of patients with presumed bacterial infection are consistent with data previously obtained from single dose volunteer studies and support the currently recommended dose regimens. Clinicians should take account of age, weight and sex when estimating renal function from SCr.

Effects of carbon dioxide and sub-lethal levels of antibiotics on adherence of coagulase-negative staphylococci to polystyrene and silicone rubber

Fifty coagulase-negative staphylococci (CNS) strains were investigated for adherence to both silicone rubber and polystyrene using a microtitre tray system. Culture in an atmosphere containing a physiological level of carbon dioxide (5% CO2) profoundly affected adherent growth to both surfaces. Most strains adhered less well in this atmosphere compared to in air alone, with mean reductions in adherence of 84% and 86% to silicone rubber and polystyrene respectively. Occasional strains adhered better in 5% CO2. The effects of antibiotic concentrations equivalent to 1/4 MIC of cefuroxime, ciprofloxacin, vancomycin and teicoplanin on the adherence of 10 CNS strains were also studied. Vancomycin and teicoplanin frequently increased adherence to silicone rubber and polystyrene compared to controls. The effects of antibiotics on adherence were not only strain dependent but also sometimes atmosphere or surface specific. Antibiotic-induced changes in adherence did not appear to correlate with changes in strain protein profiles or surface hydrophobicities.

Peritonitis complicating continuous ambulatory peritoneal dialysis in Nottingham 1983-1988

During the period 1983-1988 the incidence of peritonitis in patients undergoing continuous ambulatory peritoneal dialysis (CAPD) in Nottingham fell from 2.0 to 1.2 episodes/patient/year. Cefuroxime, given intraperitoneally for 10 days, as recommended in published guidelines, failed to cure 35% of episodes of peritonitis, although only 7% of the pathogens responsible for these episodes were resistant in vitro. Cefuroxime is probably no longer appropriate as first line treatment of CAPD peritonitis.

Influence of carbon dioxide on growth and antibiotic susceptibility of coagulase-negative staphylococci cultured in human peritoneal dialysate

Used peritoneal dialysis fluid was collected from patients undergoing continuous ambulatory peritoneal dialysis, and its pH and composition were assessed after incubation in either air or air with 5% CO2. Precipitation of calcium, magnesium, phosphate, and proteins occurred in the dialysis fluid incubated in air at 37 degrees C and was associated with a mean pH increase of 1.23 U. Incubation of dialysis fluid in air with 5% CO2 prevented precipitation and maintained pCO2 and pH levels at those found physiologically. Coagulase-negative staphylococcal strains isolated from patients with peritonitis tended to grow less well in dialysis fluid incubated in air than in dialysis fluid incubated in the carbon dioxide-enriched atmosphere. MICs of cefuroxime, ciprofloxacin, and vancomycin for seven strains of coagulase-negative staphylococci in dialysis fluid were markedly affected by atmosphere type (16 of 21 MICs). Of these 16 atmosphere-dependent MICs, 14 were at least fourfold higher in air than in air with 5% CO2.

Influence of carbon dioxide on the surface characteristics and adherence potential of coagulase-negative staphylococci

Coagulase-negative staphylococci obtained from patients with continuous ambulatory peritoneal dialysis-related peritonitis were cultured in nutrient broth in an atmosphere of air containing 5% carbon dioxide (reflecting the CO2 tension found in freshly used dialysate). Significant differences were observed between the surface chemistries of cells grown in the two atmospheres, as determined by X-ray photoelectron spectroscopy and changes in the cell wall protein profile. The growth atmosphere also influenced the adherence potential toward polystyrene and silicone in a proportion of strains examined. Thus, gaseous conditions can profoundly influence the nature of the staphylococcal surface, and this should be considered in any in vitro study of in vivo behavior.

Toxoplasmosis and systemic lupus erythematosus

The toxoplasma serological status of 50 patients with systemic lupus erythematosus (SLE) was compared with that of 50 healthy controls; high titres of toxoplasma antibody were significantly more common in the patients with SLE. These titres did not correlate with any of the routinely measured indices in SLE nor with the patients' prior treatment. A case history is used to illustrate the difficulty in diagnosing toxoplasmosis in the presence of SLE.

Laboratory studies on coagulase-negative staphylococci from CAPD-associated peritonitis

This study compared the static and kinetic activities, in both broth and used-dialysate, of selected antibiotics against 23 strains of coagulase-negative staphylococci causing peritonitis in patients on continuous ambulatory peritoneal dialysis (CAPD). Vancomycin was shown to be effective against all isolates with similar rates of kill to flucloxacillin and cefuroxime, although a few strains were found to be resistant to cefuroxime. Gentamicin was rapidly bactericidal for sensitive strains which accounted for 60% of the strains tested. Fusidic acid was associated with significant resistance and lack of bactericidal activity in the kinetic studies. Emergence of resistance occurred with rifampicin. The combinations clavulanic acid/amoxycillin and sulbactam/ampicillin generally showed good static activity. In addition a broad range of biotypes and phage types were demonstrated among these organisms with biotype SII (Staphylococcus epidermidis) predominating. There was no correlation between biotype and antibiogram.