Development of a novel assay method for colistin sulphomethate.

Increased use of colistin therapy for infections caused by Pseudomonas aeruginosa has indicated a need for a more robust microbiological assay technique. This report describes a quick and simple microbiological assay for quantifying levels of colistin sulphomethate in serum and urine samples from cystic fibrosis patients. The technique uses no specialised or costly equipment and is suitable for use in all routine diagnostic microbiology laboratories.

Resolution of antibiotic mixtures in serum samples by high-voltage electrophoresis.

The use of high-voltage electrophoresis and bioautography for the separation mixtures of antibiotics received in clinical serum samples is described. The electrophoretic characteristics of 39 antibiotics are given as is the accuracy of the method for quantitating three antibiotics. In screening 189 consecutive serum samples submitted for routine antibiotic assay, undisclosed antibiotics were revealed by the technique in 35.

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.

Resistance to third-generation cephalosporins in Barbados.

Resistance to third-generation, or extended-spectrum, cephalosporins caused by induction of class I beta-lactamases has been reported rarely from developing countries. Seven isolates of cephalosporin-resistant Gram-negative rods were recovered recently from urine, burns and ulcers in the Queen Elizabeth Hospital, Barbados. The isolates were identified as Acinetobacter calcoaceticus (2), Citrobacter freundii (1), Enterobacter cloacae (1), Morganella morganii (1), Providencia stuartii (1) and Proteus sp. (1). Induction of beta-lactamase by cefoxitin was demonstrated, and minimal inhibitory concentrations (MIC) were determined by agar dilution. beta-lactamases were demonstrated by isoelectric focusing; the presence of chromosomal beta-lactamases was confirmed in at least three of the resistant isolates. The only antibiotics which were uniformly active against these resistant strains were imipenem and ciprofloxacin. These data confirm the existence of resistance to the third-generation cephalosporins in Barbados, and emphasise the necessity for continuous surveillance of resistance patterns in the Caribbean region.

Complete duplication of bladder and urethra: a case report.

A case of complete duplication of the bladder and urethra in a girl is reported, demonstrating outlet obstruction in the bladder on the left side. Associated anomalies and pertinent literature are reviewed.

A problem encountered using staphylococcus/streptococcus supplement.

A problem was encountered while using a commercial staphylococcus/streptococcus selective supplement in blood agar culture medium. A number of strains of Staphylococcus aureus failed to grow, although they grew well on non-selective media. The phenomenon was shown to be a result of a pH change caused by incubation in a carbon dioxide-enriched atmosphere, potentiating the activity of the nalidixic acid component. It is recommended that media containing this supplement are not incubated in CO2 enriched atmospheres.

Gas exchange and water relations of Fraxinus americana affected by flurprimidol.

Effects of flurprimidol on plant water relations and leaf gas exchange were investigated in one-year-old white ash (Fraxinus americana L.) seedlings subjected to soil water deficits. Flurprimidol (20 mg kg(-1) of soil equivalent) was applied to the soil surface of pot-grown seedlings after shoot growth was completed. Two months after flurprimidol application, water was withheld from one-half of the seedlings. Leaf water relations and gas exchange parameters were measured 5, 7, 10, 14, 18 and 22 days after withholding water. Under both irrigated and nonirrigated conditions, flurprimidol treatment resulted in reduced net CO(2) assimilation rate and transpirational water loss of seedlings as a result of decreased stomatal conductance. Consequently, flurprimidol-treated seedlings had higher leaf water potential and relative water content than untreated seedlings. Nonirrigated flurprimidol-treated seedlings also had greater turgor and sap osmolality and lower osmotic potential at full turgor than seedlings in the other treatments, indicating that flurprimidol increased osmotic adjustment. Under water-stress conditions, water use efficiency was lower and gas exchange efficiency was higher in flurprimidol-treated seedlings than in untreated seedlings, suggesting that flurprimidol treatment enhances survival of plants subjected to soil water deficits.

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.

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%.

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.

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 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.

In-vitro synergy testing of nine antimicrobial combinations against Listeria monocytogenes.

In-vitro antimicrobial synergy against Listeria monocytogenes was assessed using nine combinations in chequerboard (bacteriostatic) tests and time-kill (bactericidal) studies. Ampicillin/gentamicin and trimethoprim/sulphamethoxazole were the most synergistic combinations in bacteristatic tests, whereas gentamicin with ampicillin, trimethoprim or vancomycin and trimethoprim/sulphamethoxazole were the most synergistic in bactericidal tests. Gentamicin-containing combinations were most effective at killing L. monocytogenes and those containing rifampicin least effective.

The antibacterial efficacy of levofloxacin and ciprofloxacin against Pseudomonas aeruginosa assessed by combining antibiotic exposure and bacterial susceptibility.

Ciprofloxacin has a four-fold greater in-vitro activity than levofloxacin against Pseudomonas aeruginosa, but levofloxacin has a four-fold higher area under the serum concentration-time curve (AUC) for an equivalent dose. It has been proposed that the AUC/MIC ratio is a general predictor of antibacterial efficacy for quinolones. Using an in-vitro kill curve technique, performed in quadruplicate, with nine antibiotic concentrations and three strains of P. aeruginosa with varying quinolone susceptibility, we constructed sigmoidal dose-response curves for AUC(0-6.5)/MIC and area under the bacterial kill curve (AUBKC) or AUC(0-24)/MIC and log change in viable count at 24 h (delta24). For levofloxacin the log AUC(0-6.5)/MIC ratio to produce 50% of the maximal effect was 0.74 +/- 0.13 (r2 = 0.9435) for levofloxacin and 0.82 +/- 0.06 (r2 = 0.7935) for ciprofloxacin. The log AUC(0-24)/MIC ratio to produce 50% maximal effect was 1.58 +/- 0.13 (r2 = 0.7788) for levofloxacin and 1.37 +/- 0.12 (r2 = 0.7207) for ciprofloxacin. An AUC(0-24)/MIC ratio of 125 produced 85.4% of the maximal response with levofloxacin and 81.5% with ciprofloxacin. These data suggest that levofloxacin and ciprofloxacin have equivalent activity against P. aeruginosa at equivalent AUC/MIC ratios.

Bay 12-8039, a new 8-methoxy-quinolone: comparative in-vitro activity with nine other antimicrobials against anaerobic bacteria.

The in-vitro activity of a new 8-methoxy-quinolone, Bay 12-8039, was assessed against 218 anaerobic bacteria. Ninety-eight per cent of strains belonging to the Bacteroides fragilis group (n = 65) were inhibited by < or = 2 mg/L of Bay 12-8039 whereas 97%, 94%, 94% and 100%, respectively, of Gram-negative bacilli (n = 93), non-sporing Gram-positive bacilli (n = 36), endospore-forming Gram-positive bacilli (n = 34) and Gram-positive cocci (n = 45) were also inhibited by < or = 2 mg/L. Eighty-three per cent of all anaerobes tested were inhibited by < or = 1 mg/L Bay 12-8039 and 99.5% by < or = 4 mg/L. When compared with ciprofloxacin, clinafloxacin, ofloxacin and trovafloxacin, Bay 12-8039 was more active than ciprofloxacin and ofloxacin, equipotent to trovafloxacin but not as active as clinafloxacin.

In vitro activities of Y-688, a new 7-substituted fluoroquinolone, against anaerobic bacteria.

The in vitro activities of Y-688, a new 7-substituted fluoroquinolone derivative, against 317 nonduplicate anaerobic isolates were determined. Eighty-five percent of the Bacteroides fragilis group (n = 89) were inhibited by < or = 2 mg of Y-688 per liter, while 78, 100, 89, and 98% of gram-negative bacilli (n = 135), gram-positive cocci (n = 59), and non-spore-forming (n = 58) and spore-forming (n = 51) gram-positive bacilli, respectively, were inhibited by < or = 1 mg of Y-688 per liter.

Bactericidal or bacteristatic effects of two sulphonamide plus trimethoprim preparations in human urine.

Rrine collections were made by ten volunteers taking cotrimoxazole and a sulphamoxole/trimethoprim combination on a cross-over basis. The latter was given in approximately half the dose of cotrimoxazole. Following collection of urine and its sterile filtration, the trimethoprim and sulphonamide concentrations were estimated. The urines were then inoculated with various species of Enterobacteriaceae whose minimum inhibitory concentrations had been previously determined. The viable counts in these urines were followed for 24 hours and from these the times to kill 90% of bacteria were calculated. These were very reproducible for any one experiment but showed no correlation with drug concentration, source of the urine or organism sensitivity, except for one organism which had high resistance to both sulphonamide and trimethoprim. When the organism was sensitive to at least trimethoprim a slow bactericidal effect was generally seen with either combination. We concluded that in this type of experiment the higher dosed combination showed no advantage contrary to a previous report, but in agreement with another. This brings into question the current dosage regime of cotrimoxazole when used to treat urinary tract infections in that its higher dosage over certain other sulphonamide/trimethoprim combinations appears to confer no advantage in our experiments.

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.

Bactericidal activity, post antibiotic effect and modified controlled effective regrowth time of meropenem at high concentrations.

The effect of increasing meropenem concentrations up to 250 mg/L, as might occur if 3 g was given as a single daily intravenous dose, was investigated in terms of bactericidal activity, post antibiotic effect (PAE) and modified controlled effective regrowth time (mCERT). Increasing the meropenem concentration above 50 mg/L did not result in increased bacterial killing, while concentrations over 75 mg/L did not result in longer PAE or mCERT.

Evaluation of Innofluor fluorescence polarization immunoassay kits for the determination of serum concentrations of gentamicin, tobramycin, amikacin and vancomycin.lesassays@ukneqasaa.win-uk.net.

The Innofluor fluorescence polarization immunoassay (FPIA) kits for gentamicin, tobramycin, amikacin and vancomycin were evaluated on an Abbott TDX analyser. Intra-assay reproducibility was excellent with a coefficient of variation of <3% for all analytes. The coefficient of variation for inter-assay reproducibility was usually <5%. Assay linearity was good and standard curve stability was seen with kits of the same batch for at least 32 days. Using clinical samples, the results obtained with the Innofluor FPIA reagents correlated well with those obtained using Abbott FPIA reagents, but Innofluor gentamicin and amikacin results were slightly higher than Abbott results (P < 0.001). Results of UK NEQAS returns showed acceptable accuracy for the Innofluor kits, but mean Innofluor gentamicin returns were 4% higher (P = 0.001) and mean vancomycin returns were 5% lower (P = 0.001) than overall mean returns. Innofluor and Abbott vancomycin assay reagents showed similar cross-reactivity to degraded vancomycin.