An assessment of the risks associated with the use of antibiotic resistance genes in genetically modified plants: report of the Working Party of the British Society for Antimicrobial Chemotherapy

Development of genetically modified (GM) plants is contentious, in part because bacterial antibiotic resistance (AR) genes are used in their construction and often become part of the plant genome. This arouses concern that cultivation of GM plants might provide a reservoir of AR genes that could power the evolution of new drug-resistant bacteria. We have considered bacterial DNA transfer systems (conjugation, transduction and transformation) and mechanisms of recombination (homologous recombination, transposition, site-specific recombination and DNA repair) that together might productively transfer AR genes from GM plants to bacterial cells, but are unable to identify a credible scenario whereby new drug-resistant bacteria would be created. However, we cannot entirely rule out the possibility of rare transfer events that involve novel mechanisms. Hence, we also considered if occasional transfers of AR genes (bla(TEM), aph(3'), aadA) from GM plants into bacteria would pose a threat to public health. These AR genes are common in many bacteria and each is found on mobile genetic elements that have moved extensively between DNA molecules and bacterial cells. This gene mobility has already severely compromised clinical use of antibiotics to which resistance is conferred. Accordingly, the argument that occasional transfer of these particular resistance genes from GM plants to bacteria would pose an unacceptable risk to human or animal health has little substance. We conclude that the risk of transfer of AR genes from GM plants to bacteria is remote, and that the hazard arising from any such gene transfer is, at worst, slight.

Self-medication of antibacterials without prescription (also called 'over-the-counter' use). A report of a Working Party of the British Society for Antimicrobial Chemotherapy

The availability of antimicrobial agents for self-medication may increase and could include antibacterial agents for oral or topical use. Wholesale deregulation of antibacterials would be undesirable and likely to encourage misuse of classes of agents currently important in the management of serious infections. Changed regulation from Prescription-Only Medicine (POM) to Pharmacy (P) medicine of selected agents with indications for short-term use in specific minor infections and illness is likely to have advantages to the user. However, safeguards to their use would need to be included in the Patient Information Leaflet (PIL). Agents and indications for self-medication are discussed. Any alteration in licensed status from POM to P will require careful risk-benefit assessment, including the likely impact on bacterial resistance. Safety issues also include concerns relating to age of the user, pregnancy, underlying disease and the potential for drug interactions. The importance of appropriate information with the PIL is emphasized, as is the role of the pharmacist, while ways of improving adverse event notification and monitoring are discussed. The paucity of good denominator-controlled data on the prevalence of in-vitro resistance is highlighted, and recommendations for improving the situation are made. There are currently no levels of resistance accepted by regulatory bodies on which to base a licensing decision, be it for granting a product licence, renewal of a licence or a change in licensed status from POM to P. Due consideration should be given to: the validation of user-defined indications in comparison with those medically defined; the enhancement of pharmacy advice in the purchase of such agents; improved safety monitoring; the establishment of systematic surveillance of susceptibility data.

Comparative pharmacodynamics of meropenem using an in-vitro model to simulate once, twice and three times daily dosing in humans

An in-vitro pharmacokinetic model was used to study the antibacterial activity of meropenem. Strains of Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus were exposed to meropenem concentrations likely to be produced in an adult by rapid iv infusion of 3 g once a day (q24h regimen), 1.5 g twice a day (ql2h regimen) or 1 g three times a day (q8h regimen). Each of these three dosing regimens produced a rapid reduction in viable bacterial count over the first 16 h after dosing. There were no differences in the pattern of reduction in viable count with the q24h, q12h or q8h regimens with any of the three bacterial strains tested over the first 16 h. However, reduction in viable counts was poorer at 24 h with the q24h than q12h or q8h regimens. A simulation lasting 48 h of the q24h dosing regimen indicated a reduction in bacterial count below the limit of detection from the model with E. coli but not with P. aeruginosa or S. aureus. The time for which the meropenem concentration was higher than the MIC for the bacteria correlated best with the reduction in viable bacterial count at 24 h. The AUC for the bacterial time-kill curve, which may be a better measure of antibacterial efficacy, was not related to the length of time for which the concentration was above the MIC or the peak concentration/MIC ratio. The antibacterial effect of the conventional q8h dosing simulation was indistinguishable from that given by the q12h simulation, and both the q8h and q12h regimens offered minor advantages over a q24h regimen. Dosing of meropenem 12 hourly or 24 hourly in humans should be investigated.

Comparison of the modified Stokes' method of susceptibility testing with results obtained using MIC methods and British Society of Antimicrobial Chemotherapy breakpoints

The majority of clinical microbiology laboratories in the UK use comparative disc diffusion methods based on the Stokes' method to determine antibiotic susceptibility. The technical validity of the results obtained from the modified Stokes' method of disc testing and how they relate to MIC data are not known. We studied susceptibility testing using a modified Stokes' disc diffusion method for a wide range of clinical isolates against which MICs had been determined by collaborators not involved with the disc testing evaluation. Results indicated that for 1301 organism-antibiotic combinations the number of major errors (where resistant strains were reported as sensitive) was 21/468 (4.4%) and the number of minor errors (where sensitive strains were reported as resistant) was 14/713 (1.9%) using ciprofloxacin breakpoints of 0.5 and 2 mg/L. There was good correlation between the disc susceptibility test and the MIC for 119 isolates of Enterobacteriaceae tested with the exception of Serratia spp. Excluding Serratia spp. the number of major errors for Enterobacteriaceae was 1/200 (0.5%). Data revealed 2/25 (8%) major errors for Pseudomonas aeruginosa and 1/45 (2.2%) for Acinetobacter spp. Haemophilus influenzae showed a number of unexpected categorization errors. The modified Stokes' method performed accurately for Staphylococcus aureus and coagulase-negative staphylococci when tested for susceptibility to gentamicin, erythromycin, teicoplanin and vancomycin. No major errors were reported for Streptococcus pneumoniae and beta-haemolytic streptococci. Problems occurred with the detection of antibiotic resistance in Enterococcus spp. Major errors were seen for ampicillin (2/12 strains), teicoplanin (5/6 strains) and vancomycin (5/13 strains) using a 30 microg disc but only 1/13 strains using a 5 microg disc. Overall, from our data, the modified Stokes' disc diffusion antibiotic susceptibility test showed an unacceptable number of major errors but an acceptable number of minor errors.

Susceptibility testing of Klebsiella spp.--an international collaborative study in quality assessment

In order to compare the prevalence of antibiotic resistance in different geographical areas, it is necessary to ensure agreement between laboratories on the assignment of strains to 'susceptible' and 'resistant' categories. An international quality assessment was performed to investigate the performance of susceptibility testing of Klebsiella spp. Ninety-five strains of klebsiellae were selected from clinical isolates at the London Hospital Medical College (LHMC). These included strains with a diversity of susceptibility profiles to amoxycillin/clavulanate, piperacillin, ceftazidime, cefuroxime, ciprofloxacin, gentamicin and trimethoprim. The strains were sent to 13 participating laboratories in Europe and the USA and laboratories were asked to test the susceptibility of these strains to these antibiotics by their usual methods. They were also asked to provide details of the method used to test susceptibility. Several different standard recommended testing methods were used. Reporting of susceptibilities was generally accurate, but a number of anomalies were noted. Discrepancies of reporting between the LHMC and the participating laboratories was more marked for resistant strains, particularly in the detection of resistance to cefuroxime and ciprofloxacin, as well as the assignment of susceptibility and resistance to piperacillin and amoxycillin/clavulanate. Some discrepancies could be attributed to the use of different breakpoints, leading to differing assignment of susceptibility. Methodological variations including disc content, inoculum and failure to measure and interpret zone sizes consistently also led to anomalies. This quality assessment programme has helped to identify problems in susceptibility testing which should be investigated further.

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.

Three cases of meningococcal pneumonia

Three cases of pneumonia due to Neisseria meningitidis are described. In all three cases the organism was isolated only from blood cultures, but in the presence of good clinical and radiological evidence of pneumonia. The isolates belonged to three different serogroups: B type 2b, C, and Y. The cases illustrate the fact that N meningitidis can cause pneumonia and that culture of blood plays an important part in the diagnosis. Clinically there is nothing to differentiate meningococcal pneumonia from other causes of community acquired pneumonia. Predisposing factors include aspiration, immunosuppression, influenza, and adenovirus infections. When diagnosed, pneumonia due to N meningitidis should be notified and prophylaxis given as for meningitis or septicaemia.

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.

Microbiologically proven bacterial infections in AIDS

We have reviewed the incidence, type and site of microbiologically proven bacterial infection occurring in 52 patients with the acquired immunodeficiency syndrome (AIDS) who presented to Southmead Hospital, Bristol between 1990 and 1994. A total of 30 (58%) patients had significant bacterial isolates. The majority of infections were community acquired. Overall, more infections were caused by Gram-negative organisms but Gram-positive organisms predominated in bacteraemia. Mycobacterium avium intracellulare (MAI) caused infection in the largest number of patients, followed by Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas sp, and Campylobacter sp. When individual episodes of infection were considered, after MAI, Haemophilus influenzae, Streptococcus pneumoniae and Pseudomonas sp were the organisms most frequently isolated; often these same organisms caused recurrent chest infection. Bacterial infections in AIDS patients are common and although they generally respond well to antimicrobial chemotherapy there is a high recurrence rate, particularly in the respiratory tract, which is the commonest site of infection.

The pharmacokinetics of intravenous ciprofloxacin 400 mg 12 hourly in patients with severe sepsis: the effect of renal function and intra-abdominal disease

Serum concentrations of ciprofloxacin were reviewed in 22 patients given ciprofloxacin 400 mg intravenously 12 hourly for severe infection. No dosage modifications were made in patients with renal impairment. Patients who had either bowel or liver pathology in addition to renal failure had significantly higher serum concentrations than all other patients. Dosage reduction of ciprofloxacin in patients with severe sepsis and impaired renal function is not required unless they have co-existent intra-abdominal disease.

A comparison of the penetration of cefuroxime and cephamandole into bone, fat and haematoma fluid in patients undergoing total hip replacement

Twelve patients undergoing total hip anthroplasty received, at the induction of anaesthesia, cephamandole (1 g) and cefuroxime (1.5 g); further doses of cephamandole (1 g) and cefuroxime (750 mg) were given at 8 and 16 h after the operation. Routine total hip arthroplasty was performed and at timed intervals during operation samples of bone, fat and blood were collected for assay for HPLC analysis. Samples of the haematoma fluid that formed around the operation site and further blood samples were also collected at 7 and 15 h after the operation. Although considerable variation was observed in the bone and fat concentrations of both agents, the cefuroxime levels were substantially higher than those of cephamandole, with mean values for bone of cefuroxime 36.0 mg/L (95% CI 29.0-43.0 mg/L) and cephamandole 18.3 mg/L (95% CI 14.2-22.4 mg/L) and for fat of cefuroxime 15.0 mg/L (95% CI 11.1-18.9 mg/L) and cephamandole 11.2 mg/L (95% CI 7.2-15.2 mg/L). When corrected for blood concentrations the penetration of both agents was similar (bone, 43.6% cefuroxime and 37.8% cephamandole; fat, 16.0% cefuroxime and 19.2% cephamandole). Cefuroxime concentrations in haematoma drain fluid were higher than those of cephamandole 6-8 h after the operation (17.8 versus 8.3 mg/L) but lower at 14-16 h (7.7 versus 9.6 mg/L). We conclude that there are no significant differences between the bone, fat or haematoma penetration of cefuroxime and cephamandole and that any differences in the absolute levels of the two agents are due to differences in the total drug administered rather than their ability to penetrate into these sites. Time-kill curves for cefuroxime and cephamandole against five clinical isolates of Staphylococcus aureus failed to identify any significant differences between the rates of kill for the two agents at the concentrations seen in bone, fat or haematoma fluid. For both prophylaxis regimens antibiotic concentrations exceeded the MICs for potential pathogens for the duration of the operation and also in the haematoma which surrounds the operation site for up to 24 h after the operation.

The pharmacokinetics and protein-binding of fusidic acid in patients with severe renal failure requiring either haemodialysis or continuous ambulatory peritoneal dialysis

Fusidic acid is metabolized and excreted by the liver. It is generally assumed that renal impairment has no effect on serum concentrations. However, there are few data on the pharmacokinetics of fusidic acid in patients with chronic renal failure, particularly in those requiring dialysis. Seven patients with chronic renal failure on haemodialysis were given 500 mg sodium fusidate orally every 8 h for the 48 h between dialysis. Seven patients on continuous ambulatory peritoneal dialysis (CAPD) were given the same dosage regimen for seven doses. Fusidic acid concentrations were measured by HPLC. Accumulation was seen, and in 12 of the 14 patients steady-state pharmacokinetics had not been achieved by the third day. In haemodialysis patients, mean (range) Cmax values for the first dose were 13.0 (2.0-25.5) mg/L and for the sixth dose were 40.5 (10.1-69.9) mg/L. Serum concentrations were not reduced by haemodialysis. In CAPD patients mean Cmax values for the first dose were 16.0 (4.8-33.8) mg/L and for the seventh dose were 33.9 (23.4-61.9) mg/L. Fusidic acid concentrations of 1.0-2.3 mg/L were detected in peritoneal dialysis fluid in six of the seven CAPD patients. In both patient groups there was a tendency towards increased T(1/2) with repeated dosing. Protein-binding of fusidic acid in patient serum samples was 87.6-94.6%.

Control of varicella-zoster infection on renal and other specialist units

The introduction of chickenpox onto our renal unit recently raised several issues surrounding the management of patient and staff contracts. This paper describes the action taken and makes various recommendations for future management of similar cases. Guidelines are proposed for the management of patients and staff as well as the role of the infection control team in handling a chickenpox problem. Future developments, including the use of VZ vaccine for patient and staff, are also discussed.

The pharmacokinetics of once-daily oral 400 mg ofloxacin in patients with peritonitis complicating continuous ambulatory peritoneal dialysis

Seven patients with end-stage renal disease requiring support by continuous ambulatory peritoneal dialysis received once-daily 400 mg oral ofloxacin for 7 days for the treatment of bacterial peritonitis. Serum and peritoneal dialysis fluid (PDF) were collected for assay throughout the course of the study and for 5 days thereafter. Ofloxacin, desmethyl ofloxacin and ofloxacin-N-oxide accumulated over the course of therapy and could still be detected in serum and PDF 5 days after the end of therapy. The mean elimination half-life of ofloxacin in serum was 32 +/- 7 h, desmethyl ofloxacin 45 +/- 26 h and for ofloxacin-N-oxide 44 +/- 15 h. The total mean recovery of ofloxacin and its metabolites from the PDF was 15.4%. This regimen results in serum and PDF concentrations likely to be effective for the treatment of infection for at least 10 days.

Therapeutic monitoring, the concentration-effect relationship and impact on the clinical efficacy of antibiotic agents

Therapeutic monitoring is now technically feasible for a wide variety of antibiotic agents and data are accumulating on the relationship of blood levels and clinical efficacy. For each antibiotic a therapeutic range and dosage regimen can be based theoretically on its known pharmacokinetics, pharmacodynamics in vitro, and also use in animal and human treatment studies. Antibiotics can be characterised into types by their mechanism of kill, as either concentration-dependent (for which achieving a large post-dose concentration to MIC ratio appears important) or concentration-independent/time-dependent (where efficacy is related to maintain the overall concentration above the MIC). Hopefully, concentration-controlled trials will be performed when new antibiotics are introduced, to determine a therapeutic range which correlates with clinical efficacy, and so enable monitoring to lead to a more rational approach to antibiotic administration.

Health care resource utilization and antimicrobial use in elderly patients with community-acquired lower respiratory tract infection who develop Clostridium difficile-associated diarrhoea

We conducted a prospective observational study on the medical management and health service resource utilization associated with the hospital care of patients with community-acquired lower respiratory tract infection. Between January 1994 and June 1995, 28 such patients developed Clostridium difficile-associated diarrhoea; these 28 patients were matched with 56 age-matched patients, who were used as a control group in a comparative study. Progress during the first week after admission was similar as measured by fever days and pathology or radiology use. The use of iv cephalosporins (g/day) during the first week was greater in the group who developed C. difficile-associated diarrhoea than in controls. The length of hospital stay was 36.4 +/- 21.6 days in patients with C. difficile-associated diarrhoea compared with 19.8 +/- 13.3 days in controls. Cases also required more pathological and radiological tests and greater use of antimicrobials and other drugs; however, if pathology and radiology use was calculated per day of patient stay there was no difference between the two groups. When antimicrobial use was compared, controlling for the time taken until found to be C. difficile toxin positive, patients with C. difficile infection received more iv cefuroxime as well as more total cephalosporins, beta-lactams and macrolides measured in g/day. Interestingly, in this study we could not show an increased mortality associated with C. difficile diarrhoea despite obvious evidence of morbidity. The development of C. difficile-associated diarrhoea substantially increases health care resource utilization for individual patients who are admitted to hospital with lower respiratory tract infection.

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.

Salt tolerance of EMRSA-16 and its effect on the sensitivity of screening cultures

The salt (NaCl) tolerance of methicillin-resistant Staphylococcus aureus (EMRSA)-16 was compared with 18 other MRSA isolates by an agar incorporation technique. The NaCl minimum inhibitory concentration (MIC) of EMRSA-16 was 7% which compared with an MIC50 of 7%, MIC90 of 10%, range (5.5-10.5%) for the other isolates. Study of the growth kinetics in broth containing NaCl at concentrations up to 10% indicated complete inhibition of growth by 7 and 10% NaCl and partial inhibition by 5%. Addition of EMRSA-16 at inocula of < or = 1 cfu/mL into salt broths revealed lower than expected EMRSA recovery from broths containing 5, 7.5 and 10% NaCl. Two and a half per cent NaCl broths were not inhibitory. Selective broth containing 2.5% NaCl should be considered for use when screening for EMRSA-16.

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.

Trends in-original research published from the United Kingdom in the antimicrobial chemotherapy literature, 1980-1994

There is a feeling that the contribution of researchers from the United Kingdom in the antimicrobial chemotherapy area is in decline, and we, therefore, reviewed publications in the Journal of Antimicrobial Chemotherapy (JAC) and Antimicrobial Agents and Chemotherapy (AAC) in 4 of the last 14 years. In absolute numbers the total number of UK first author publications in these two journals were 103, 78, 107 and 82 in 1980, 1985, 1990 and 1994 respectively. The percentage of first author papers from the UK in JAC was 35%, 21%, 24%, 23% and in AAC was 5.7%, 4.9%, 5.1% and 4.7% for the years 1980, 1985, 1990 and 1994 respectively. Within the UK there has been a relative decline in the number of publications produced by NHS hospital departments and an increase in those produced by universities. Ten institutions (four universities, two pharmaceutical companies and four NHS departments) produced almost half of the UK publications. There is no room for complacency about the state of British antimicrobial research and the relative decline in the NHS hospital sector's contribution, the largest contributor numerically, even before the full impact of the ongoing NHS reforms, is cause for concern.

The elution and binding characteristics of rifampicin for three commercially available protein-sealed vascular grafts

Rifampicin was absorbed onto gelatin-sealed (Gelsoft and Unigraft) or collagen-sealed (Hemashield) vascular grafts by soaking for 15 min in a 1000 mg/L solution. Bound drug was then eluted from the grafts by incubation in phosphate buffered saline (PBS) at 37 degrees C and at timed intervals the concentration of rifampicin remaining in the grafts was determined. Although all three grafts contained high concentrations of rifampicin immediately after absorption of drug, rifampicin concentrations rapidly fell during elution with PBS to approximately 1.25 mg/kg of graft after 5 h incubation in PBS, indicating that most of the rifampicin absorbed to the grafts was only loosely bound. However, once this loosely bound fraction had been removed there was a much slower elution of the remaining rifampicin from the grafts, suggesting a second and much more tightly bound fraction. The tightly bound fraction eluted with an apparent half-life of 47-76 h, depending on the graft, and extrapolation back to time zero from this phase suggests that only a very small amount of the rifampicin is tightly bound to the graft after initial soaking (0.6-1.3 mg/kg).

The quality of clinical serum teicoplanin assays: an experimental European EQA distribution

Two sets of six samples of human serum spiked with predetermined concentrations of teicoplanin were circulated, 6 months apart, to 22 European laboratories for the purposes of external quality assessment (EQA). The laboratories returned assay results using either bioassay, high-performance liquid chromatography (HPLC) or fluorescence polarization immunoassay (FPIA). FPIA was the most popular method and performance was generally satisfactory. Some laboratories using HPLC or microbiological assay performed satisfactorily but others did not. Only seven laboratories (32%) showed consistently satisfactory performance. There appears to be a need for continuing EQA of clinical teicoplanin assays.

Pharmacokinetics of once-a-day netilmicin (6 mg/kg) in neonates

The pharmacokinetics of once a day netilmicin (6 mg/kg) was studied in 21 neonates. The babies were divided into three groups according to gestational age: group I aged > 36 weeks; group II between 34-36 weeks and group III < 34 weeks. Serum concentrations were variable between patients and the concentration 24 h after the first dose ranged from 0.8 to 3.8 mg/L with only two babies having concentrations of < 1 mg/L while seven had concentrations of > 2 mg/L. There were also large patient-to-patient variations in serum half-life, volume of distribution, area under the curve and relative plasma clearance such that these parameters could not be correlated to gestational age or weight. Absolute plasma clearance was correlated with both gestational age and weight. There was evidence of accumulation between the first and second dose for all three patient groups and for patients of gestational age < 34 weeks (group III) these observations were statistically significant. A netilmicin dosage of 4.5 mg/kg once a day may be more suitable for all neonates supported by assay of serum concentrations.

A new time-kill method of assessing the relative efficacy of antimicrobial agents alone and in combination developed using a representative beta-lactam, aminoglycoside and fluoroquinolone

A time-kill curve employing nine sampling times over 6 h was used to provide data which were then used to develop a theoretical (best-fit) curve. From the theoretical curve parameters describing the rate of kill (alpha), time from addition of antibiotic to initiation of killing (d) and a function of the degree of killing observed (Ym/Yo) were defined. The area-under-the-curve (AUC) was calculated from the theoretical curve. The variability of each parameter was assessed using a theoretical curve to fit the data from experiments done on three occasions and in triplicate. In terms of the parameters alpha, d, Ym/Yo and AUC, no synergy was demonstrated with combinations of piperacillin/tazobactam plus ciprofloxacin or gentamicin when compared with single antibiotics. The AUC represents the best summary parameter of a time-kill curve but should be supported by other parameters describing the best-fit curve.

The in-vitro activity of trovafloxacin and nine other antimicrobials against 413 anaerobic bacteria

The in-vitro activity of trovafloxacin and nine other antimicrobials was determined for 413 non copy anaerobic clinical isolates. Trovafloxacin was the most active quinolone tested with an MIC90 of 0.5 mg/L against Gram-positive cocci (n = 75); MIC90 of 4 mg/L against Gram-positive bacilli (n = 151); MIC90 of 0.5 mg/L for Gram-negative cocci (n = 12) and MIC90 of 1 mg/L for Gram-negative bacilli (n = 175). Overall the MIC90 of trovafloxacin was 1 mg/L which was equivalent to co-amoxiclav and one dilution higher than that of imipenem. The other seven comparators, including clindamycin and metronidazole, had higher MIC90 values than trovafloxacin. Trovafloxacin is likely to have clinically useful activity against anaerobes from human infection.

The effects of swaddling versus standard positioning on neuromuscular development in very low birth weight infants

A randomized control design was used to compare the effect of swaddling to standard positioning on neuromuscular development in very low birth weight (VLBW) infants (< 1,250 gm). The outcome of neuromuscular development was measured at 34 weeks postconceptional age using the Morgan Neonatal Neurobehavioral Exam (MNNE). The sample included 50 infants who met criteria for birth weight, age and who were classified as appropriate for gestational age. Exclusion criteria were also used. The infants were randomly assigned to the experimental group or the comparison group. Data analysis included descriptive and inferential statistical techniques. The results demonstrated that swaddled infants had higher total scores on the MNNE as compared to infants with standard positioning. Swaddling appears to be a positioning technique that can enhance neuromuscular development of the very low birth weight infant.

Bacterial resistance to cephalosporins as a function of outer membrane permeability and access to their target

Resistance of Gram-negative bacteria to cephalosporins, as with other beta-lactam antibiotics, is a function of a combination of outer-membrane permeability, affinity and stability to beta-lactamases, and their activity against target sites (penicillin-binding proteins). Permeation through the outer-membrane is largely governed by the presence and properties of porins, which are water-filled channels facilitating the movement of hydrophilic molecules across the membrane. The properties of porins vary considerably between wild-type bacterial species, and their numbers (and hence the ability of a bacterial cell to exclude the antibiotic) may be reduced in strains with acquired resistance. In the case of cephalosporins, ability to cross the outer-membrane is related to physico-chemical properties such as molecular size, hydrophobicity and the number and charge of ionised groups. Thus, for example, dianionic compounds have in general lower permeability rates than dipolar cephalosporins. These relationships are discussed in detail. The phenotypically expressed susceptibility of a particular bacterial strain to a cephalosporin is brought about by a dynamic combination of permeation, the ability of the agent to resist degradation or binding to the beta-lactamases in the periplasmic space which act upon the relatively low concentration of cephalosporin present there, and target affinity. The interplay of these factors is discussed.

Do blood cultures need continuous monitoring so that clinical action can be taken outside normal working hours?

Many automated blood culture reading systems monitor bacterial growth 24 hours a day but it is unclear if reacting to prompts indicating bacterial growth outside normal laboratory hours is of clinical benefit. An analysis of 50 blood cultures from 43 patients which had organisms seen on Gram films and had triggered positive out-of-hours showed that examination of the Gram film altered management of seven patients and the results of culture or sensitivity testing altered that of a further four. However, after review, it was felt the clinical outcome would not have been influenced by earlier intervention in any of these patients. We therefore consider that an out-of-hours service for dealing with positive blood cultures is not justified in our hospital. This conclusion may not apply universally, especially in hospitals where potential pathogens show less predictable antimicrobial sensitivity patterns.

Typing of Listeria monocytogenes by random amplified polymorphic DNA (RAPD) analysis

The aim of the study was to determine the effectiveness of random amplified polymorphic DNA analysis in typing Listeria monocytogenes from human infections. Twenty-five L. monocytogenes serogroup 1/2 and 70 serogroup 4 including 14 serovar 4b(x) were typed by RAPD-PCR analysis. Six primers were used to type each L. monocytogenes isolate and the DNA amplification performed with supertaq DNA polymerase in a Hybaid Thermal Reactor. Each bacterial strain was analysed separately with all primers and the profiles were judged by eye and designated to a group by comparison to other strains. Bands were classified as major or minor. Based on analysis of major band patterns, the 25 serogroup 1/2 isolates gave rise to 12 different groups. The groups only contained serovar 1/2a or 1/2b with a single exception. Using minor bands all isolates could be distinguished. All the serogroup 4 isolates gave the same major band patterns. The 14 serovar 4b(x) isolates which were epidemiologically related gave identical profiles with the exception of one isolate. Of the remaining strains, 41 produced individual patterns on minor band analysis. RAPD analysis with multiple primers is low cost, discriminatory and is most ideally suited to testing small (< 50) numbers of strains. We have shown that serogroup 1/2 L. monocytogenes strains are a more diverse group than serovar 4b strains and RAPD-PCR will provide a technique of considerable value in typing L. monocytogenes in the future.

An audit of ciprofloxacin use in a district general hospital

An audit of ciprofloxacin use at Southmead Hospital, Bristol was carried out for forty patients treated in early 1992 employing a modified Delphi technique with six assessors. Most patients assessed (20/40, 50%) had urinary tract infections (UTIs), 5/40 (12.5%) had chest infections, 4/40 (10%) had bacterial gastroenteritis and 3/40 (7.5%) had either bacteraemia or infection following an orthopaedic procedure. A likely bacterial pathogen was isolated from 32/40 (80%) of patients; 14/32 (44%) had Pseudomonas aeruginosa infections and from the remainder Enterobacteriaceae including Salmonella spp. (non-typhoid) were cultured. Oral therapy with ciprofloxacin was used in 37 (93%) of the 40 patients, and the three others received iv treatment. In 21/35 (60%) of patients where an assessment was made by majority scoring, a quinolone was felt to be clinically justified. A quinolone was least likely to be thought justified if the patient had a chest infection. The assessors had few concerns about the effectiveness or toxicity of ciprofloxacin but for 41% (14/34) of patients, where there was a majority opinion, a cheaper alternative was felt to be available; most of these patients had hospital-acquired UTIs caused by Enterobacteriaceae. The duration of therapy was felt to be too long in 35% (10/29) of patients, mainly because of prolonged treatment of UTIs. In some cases of P. aeruginosa infection the assessors would have used higher doses than those prescribed. Ciprofloxacin was the quinolone of choice in 24/32 (75%) of assessable cases. Norfloxacin was chosen to treat UTI due to multi-resistant Enterobacteriaceae in 6.2% (2/32) cases.(ABSTRACT TRUNCATED AT 250 WORDS)

The pharmacokinetics of meropenem in surgical patients with moderate or severe infections

The pharmacokinetics of meropenem were studied in a group of 11 surgical patients (four male, seven female; mean age 63 years; mean weight 72 kg) all of whom had moderate or severe infection and who received a mean dose of 14.5 mg/kg +/- 2.7 meropenem 8-hourly iv for a minimum of 4 days. Venous blood samples were collected at timed intervals after the first dose on day 1 and the second dose on the fourth or fifth day of therapy. Serum meropenem concentrations were assayed by HPLC and fitted to a two compartment pharmacokinetic model. The mean pharmacokinetic parameters (+/- standard deviation) on day 1 were T1/2 84.6 +/- 24.1 min, Vdss 0.22 +/- 0.06 L/kg, AUC 6028 +/- 1983.2 mg.min/L, Cltot 188 +/- 67 mL/min and MRT 89.1 +/- 67.8 min. On the fourth or fifth days of therapy the values were T1/2 79.9 +/- 18.2 min, Vdss 0.17 +/- 0.8 L/kg, AUC 6000.7 +/- 2417 mg.min/L, Cltot 190 +/- 60 mL/min and MRT 67.8 +/- 30.4 min. Although the T1/2, Vdss and MRT decreased from day 1 to day 4 or 5 these changes were not statistically significant (Student's t-test, P > 0.05). Total clearance of meropenem was linearly related to creatinine clearance or patient age on the first day of therapy. Although the T1/2 and MRT were longer and the Cltot lower than those reported for young healthy volunteers, they were similar to those found in elderly volunteers.(ABSTRACT TRUNCATED AT 250 WORDS)