The activity of piperacillin/tazobactam against clinical isolates collected in 20 UK centres and the design of a disc test for susceptibility testing.

The in-vitro activities of piperacillin plus tazobactam at ratios of 4:1, 8:1 and 16:1 were determined against 952 non-copy clinical aerobic bacterial isolates collected from 20 UK centres. Tazobactam enhanced the activity of piperacillin against Enterobacteriaceae, Staphylococcus aureus, Haemophilus influenzae and Moraxella catarrhalis. No enhancement was noted for Pseudomonas aeruginosa, other Pseudomonas spp., streptococci and enterococci. For 95.6% of strains MICs were either the same or only one two-fold dilution different with all the three ratios of tazobactam, and for most of the remaining strains the piperacillin MIC was lowest with the highest proportion of the tazobactam (4:1). The percentage of strains which remained resistant was also lowest with the 4:1 ratio. Regression analysis of MICs versus inhibition zone size with a variety of disc strengths tested on DST agar indicated that for Enterobacteriaceae, and H. influenzae 30 +4 micrograms, and 5 +1 microgram piperacillin/tazobactam discs gave the most reliable results. However, for S. aureus no disc gave good discrimination. Zone sizes obtained on DST and Iso-Sensitest agar were similar, with 96.1% of 1450 paired tests showing agreement to within 3 mm.

The activity of cefpirome and ten other antibacterial agents against 2858 clinical isolates collected from 20 centres.

Two thousand eight hundred and fifty-eight aerobic clinical isolates of Enterobacteriaceae, Pseudomonas species, staphylococci, streptococci and Haemophilus species were collected in 19 geographically separated centres in the UK and one in Ireland. The identity of each isolate was confirmed at Southmead Hospital and the MIC of cefpirome, cefotaxime, ceftazidime, cefuroxime, cephradine, amoxycillin, piperacillin, imipenem, gentamicin, ciprofloxacin and trimethoprim was determined by an agar dilution method. Against species of Enterobacteriaceae not associated with producing an inducible cephalosporinase, cefpirome had a similar degree of activity to cefotaxime and was more active than ceftazidime and earlier cephalosporins. Against species with a high prevalence of inducible beta-lactamase production, cefpirome was superior to other cephalosporins; imipenem was also active against these isolates. Cefpirome was active against Pseudomonas aeruginosa, methicillin-sensitive staphylococci, non-enterococcal streptococci and Haemophilus spp. When the isolates were exposed to 0.1 mg/L of imipenem in agar plus the test agent, cefpirome had superior activity compared with the other cephalosporins tested for the Enterobacteriaceae, except Proteus vulgaris and Proteus penneri. 8.7% of Enterobacter spp., 7% of Citrobacter spp. and 6.7% of Morganella morganii had susceptibilities to beta-lactams suggesting constitutive hyperproduction of chromosomal cephalosporinase; cefpirome, unlike the other cephalosporins tested, was active against these isolates, although to a lesser degree than against the wild-type inducible isolates. No isolates were thought to produce an extended-spectrum beta-lactamase.

Audit of turn-around times in a microbiology laboratory.

To determine the turn-around time in a microbiology laboratory a survey form was designed to collect data on the origin and type of specimen and the dates and times when (i) the sample was taken; (ii) the specimen was received in the laboratory; (iii) the report was signed by the microbiologist; (iv) the report was sorted by the laboratory clerical staff; and (v) the final report was received on the ward. The cumulative time from sampling to a result arriving on the ward was 51.5 (SD 28.6) hours. The survey is a simple method of determining turn-around time and high-lighted minor deficiencies in the service which were easily rectified.

In-vitro activity of cefpodoxime against 1834 isolates from domiciliary infections at 20 UK centres.

A total of 1834 non-copy, general practice or outpatient isolates were collected by 20 hospital laboratories within the British Isles, and identified and tested for susceptibility to nine antimicrobial agents available by oral administration at one centre. Against Enterobacteriaceae cefpodoxime was the most active beta-lactam agent tested, the MIC90s being: for Escherichia coli 1.0 mg/l, for Proteus mirabilis 1.0 mg/l, for Citrobacter spp. 2.0 mg/l, and for Enterobacter spp., Serratia spp., Morganella spp. and Klebsiella spp. 16-64 mg/l. Cefpodoxime also showed a certain amount of activity against staphylococci and high activity against streptococci, the MIC90s being for Staphylococcus aureus 2 mg/l, for coagulase negative staphylococci 8 mg/l, for Streptococcus pyogenes 0.015 mg/l, for Str. pneumoniae 0.06 mg/l and for Str. agalactiae 0.5 mg/l.

In vitro antimicrobial susceptibility of Listeria monocytogenes isolated in the UK and other Listeria species.

The MICs and MBCs of 21 antimicrobial agents were determined for 103 strains of Listeria monocytogenes isolated in the UK and 27 strains of other Listeria species. Ampicillin, penicillin, azlocillin, imipenem, gentamicin, netilmicin, amikacin, erythromycin, rifampicin, trimethoprim, clindamycin and vancomycin had good activity, while cephalothin, chloramphenicol, ciprofloxacin and ofloxacin were less active, and cefuroxime, enoxacin, norfloxacin and fosfomycin were the least active. Tetracycline had good activity against many strains, but the MIC was high for some. Unlike the other Listeria species tested, Listeria ivanovii was susceptible to fosfomycin. Inoculum size and media employed were shown to affect the MBC, tryptose phosphate broth yielding higher MBCs than Mueller-Hinton or Isosensitest broths.

Resistance of bacterial pathogens to four aminoglycosides and six other antibacterials and prevalence of aminoglycoside modifying enzymes, in 20 UK centres.

A total of 5116 non-fastidious bacterial strains isolated from either blood or urine culture were collected from 20 geographically distributed centres within the UK. Upon receipt the strains were identified and the minimum inhibitory concentrations of ten antimicrobial agents in hospital usage were determined for each of the strains. All laboratories submitted a similar range of bacterial species and in species normally considered as sensitive the overall rates of resistance to the different antibiotics tested were: amikacin 2.4%, gentamicin 3.7%, netilmicin 2.6%, tobramycin 3.4%, ampicillin 41.7%, cefadroxil 11.6%, cefotaxime 1.4% [corrected], cefuroxime 4.3%, ciprofloxacin 0.6% and trimethoprim 13.0%. For those strains resistant to one or more aminoglycosides the mechanisms of resistance responsible were determined from the aminoglycoside-resistance patterns of the strains to 16 different aminoglycoside antibiotics. The predominant mechanisms of resistance found were APH(2") + AAC(6') production in staphylococci. AAC(2') production in Providencia spp., and AAC(3) production in the other Gram-negative genera.

Activity in vitro of CGP 31608, a new penem antibacterial agent.

The in-vitro activity of CGP 31608 (hereinafter termed CGP), a new penem, was tested by an agar dilution technique in comparison with imipenem, Sch 34343, cefotaxime, ceftazidime, aztreonam, ampicillin, gentamicin and ciprofloxacin. 480 clinical isolated were tested, some of which were selected because of their multiple resistance. CGP showed consistent activity against a wide range of species, having MIC90 values of 2-8 mg/l for almost all Enterobacteriaceae, Pseudomonas spp., Haemophilus spp., Corynebacterium spp. and Bacteroides spp. It was the most active agent tested against staphylococci having an MIC90 of 0.25 mg/l, showing no reduction in activity against methicillin-resistant strains. Lesser activity was observed against some streptococci, Proteus spp. and clostridia. Tests carried out in broth demonstrated that CGP activity was constant over a pH range of 6-8 and was unaffected by the presence of 50% serum or 50% urine. The rate of killing of CGP, gentamicin, cefotaxime and ciprofloxacin was investigated in broth against log and stationary-phase cultures of Staphylococcus aureus and Escherichia coli. The most rapid rate of kill was seen with ciprofloxacin, while CGP exhibited a more rapid bactericidal effect than cefotaxime against Staph. aureus. The stability of CGP was studied at two concentrations in serum, broth and phosphate buffer at 4 degrees C, room temperature and 37 degrees C. In serum the half-life was 112 h at 4 degrees C, 35 h at room temperature and 11.4 h at 37 degrees C. Protein binding tested at concentrations of 5-100 mg/l was 2-6.3%.

Comparative in-vitro activity of Sch 34343, a new penem antibiotic.

Using an agar dilution technique we examined the in-vitro activity of Sch 34343 against 485 clinical bacterial isolates. Ampicillin, mezlocillin, cefuroxime, cefotaxime, cefotetan, ceftazidime, ceftriaxone, imipenem (N-formimidoyl thienamycin) and gentamicin were used for comparison. Sch 34343 exhibited activity against all species tested, excepting Pseudomonas aeruginosa and Pseudomonas species. Unlike many newer beta-lactams, Sch 34343 was highly active against Gram-positive species. It was consistently active against the Enterobacteriaceae, with MIC50 and MIC90 being usually closely similar, as were results with two inoculum sizes (104 and 106 cfu). This, together with its activity against strains resistant to many other beta-lactam agents, suggested high stability to beta-lactamases. Sch 34343 was the most active compound tested against Bacteroides fragilis. In tests of combined bacteriostatic action with gentamicin no synergy was seen. It had bactericidal action in broth culture, against sensitive strains of E. coli, Klebsiella pneumoniae, Staphylococcus aureus and Streptococcus faecalis. It showed good stability in aqueous solution and serum at low temperatures at pH values in the physiological range, and was moderately stable at 37 degrees C. Binding in human plasma was 72%. We concluded that Sch 34343 is a highly promising agent with a broad spectrum of activity making it potentially suitable as monotherapy for patients with infection of undetermined bacterial aetiology, particularly if Bact. fragilis is a possible pathogen.

The human pharmacokinetics of cefotaxime and its metabolites and the role of renal tubular secretion on their elimination.

The pharmacokinetics of cefotaxime were investigated in human volunteers given constant intravenous infusions, intravenous bolus, and intramuscular doses of the drug. After intravenous dosing, the plasma levels of cefotaxime declined in a biphasic manner with a terminal half-life varying between 0.92 and 1.65 hr. Moreover, the pharmacokinetics were linear up to at least a 2.0 g dose for volume of distribution based on area (23.3-31.3 l), plasma clearance (249-2.88 ml/min), and renal clearance (151-177 ml/min). Renal tubular secretion of intact cefotaxime and each of its metabolites was demonstrated by its interaction with probenecid, although the ratio of drug to metabolites ultimately excreted in urine after probenecid was similar to that seen normally (54 +/- 6, 19 +/- 4, 6.5 +/- 0.7 and 5.5 +/- 0.7% for cefotaxime, DACM, M2, and M3, respectively, when calculated as a percentage of the dose). The observed half-lives of DACM, M2, and M3 were 2.3 +/- 0.4, 2.2 +/- 0.1 and 2.2 hr, respectively. However, when the true half-life of DACM was calculated (0.83 +/- 0.23 hr) it was not only significantly shorter than that observed but also shorter than that for intact cefotaxime. The plasma clearance of DACM (744 +/- 226 ml/min) was much higher than that of cefotaxime while the volume of distribution was of a similar order (56 +/- 24 l). When administered intramuscularly, there was good absorption of cefotaxime from the site of injection (92-94%) giving maximum plasma levels of the drug of between 30 and 35 mg/l at approximately 40 min after dosing. Thereafter, the plasma levels of cefotaxime declined in a monophasic manner with a half-life (1.0-1.2 hr) similar to that of the terminal half-life seen after intravenous administration. Lidocaine had no significant effect on either its absorption or elimination kinetics.

The in vitro antibacterial activity of ceftriaxone in comparison with nine other antibiotics.

The results of a large three centre co-ordinated study into the in vitro susceptibility of bacterial clinical pathogens showed no significant evidence of regional variation within the U.K. towards the 10 antibiotics examined. The newer cephalosporins were highly potent and superior to other antibiotics against the Enterobacteriaceae, with ceftriaxone and cefotaxime the most potent. Against Pseudomonas aeruginosa, gentamicin was the most active, followed by ceftazidime, piperacillin and ceftriaxone; cefotetan was the least active. Staphylococcus aureus and Staphylococcus albus were most susceptible to cefuroxime and gentamicin, though most were also susceptible to ceftriaxone, cefotaxime and cefoxitin. Streptococcus (Groups A and B), Streptococcus pneumoniae and Neisseria spp. were susceptible to most agents other than gentamicin, but ceftriaxone and cefotaxime were overall the most potent. Ceftriaxone was the most active agent against Haemophilus influenzae. The newer agents were variable and relatively poor against anaerobes and only amoxycillin and piperacillin were significantly active against Streptococcus faecalis. The overall resistance level to the third generation cephalosporins was low.

The activity of enoxacin against clinical bacterial isolates in comparison with that of five other agents, and factors affecting that activity.

The activity of enoxacin against 362 clinical bacterial isolates in comparison with norfloxacin, nalidixic acid, ampicillin, latamoxef (moxalactam) and gentamicin was tested by an agar dilution method. Typical MICs for enterobacteria lay between 0.12 and 1.0 mg/l. Enterobacter spp. and Serratia spp. tended to be more resistant. Enoxacin was also active against Pseudomonas aeruginosa (mean MIC 0.5 mg/l) and highly active against fastidious Gram-negative aerobes. Typical MICs for Staphylococcus aureus were 1-2 mg/l while streptococci were more resistant (16-32 mg/l). Enoxacin had no useful activity against Bacteroides fragilis and Clostridium perfringens. Enoxacin was generally more active at pH 8 than pH 6, and in broth than in urine. It was bactericidal in its action. Daily serial passage from growth in broth containing enoxacin caused decreased sensitivity which was limited to four- to 16-fold greater than the original MIC. Enoxacin was about half as active as norfloxacin against enterobacteria, equally active against staphylococci, and some two to four times less active against streptococci.

In-vitro studies with ciprofloxacin, a new 4-quinolone compound.

Ciprofloxacin is a new antibacterial agent of the 4-quinolone group. With an agar dilution technique we compared its activity on 365 clinical isolates with those of norfloxacin, nalidixic acid, ampicillin, mezlocillin, cefadroxil, cefuroxime, ceftazidime, ceftriazone , cefotaxime, latamoxef (moxalactam), and gentamicin. Ciprofloxacin was overall the most active agent tested against aerobic Gram-negative species, with the MIC90 values for all species being below 1 mg/l (excepting Providencia stuartii with 4 mg/l), and the large majority being below 0.12 mg/l. Many of the strains were selected on the basis of resistance to beta-lactam agents or gentamicin, and ciprofloxacin was also active against these. There was little difference in the activity of ciprofloxacin at inocula of 10(4) or 10(6) cfu. Strains with higher MIC's of the related agents norfloxacin and nalidixic acid were less susceptible to ciprofloxacin . Ciprofloxacin was less active against Gram-positive species (typical MIC90 values were 0.5 or 1 mg/l) and obligate anaerobes (4 mg/l for Bacteroides fragilis). The activity of ciprofloxacin in broth dilution tests was little affected by pH over the range 6.0-8.0, or by human serum or tissue fluid; its activity was reduced by the presence of urine. Binding to human serum protein was 20-28%. Ciprofloxacin was rapidly bacterial in broth at concentrations near to its MICs. By exposure to subinhibitory concentrations of ciprofloxacin it was possible to increase its MIC for bacteria in daily subcultures. The final MIC values after ten days were often about 16-fold greater than those observed initially.

Assay of netilmicin in serum by substrate labelled fluoroimmunoassay.

A substrate-labelled fluoroimmunoassay (SLFIA) for gentamicin was used to assay netilmicin by substituting serum calibrators containing netilmicin. The assay proved highly reproducible and the results obtained showed a good correlation with the results of EMIT and microbiological assays.