Nisin, alone and combined with peptidoglycan-modulating antibiotics: activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci.

OBJECTIVE: We have sought ways to circumvent resistance, by combining nisin with other antibiotics known to target bacterial cell wall biosynthesis. METHODS: Twenty strains each of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) were tested in vitro by standardized methods against nisin alone and combined with bacitracin, ramoplanin and chloramphenicol. RESULTS: Ramoplanin was the most potent compound, and bacitracin had the least activity. Two-way synergy was observed with nisin and ramoplanin. However, chloramphenicol was clearly antagonistic to the activity of nisin. CONCLUSIONS: Observations of synergy between nisin and ramoplanin against MRSA and VRE offer a promising approach to the concept of combining nisin with inhibitors of cell wall peptidoglycan. Further investigations are needed in order to develop this approach as a clinical possibility.

Cefaclor into the millennium.

We review the discovery and development of the cephalosporins and subsequently cefaclor. Cefaclor is active against a wide range of commonly encountered bacterial pathogens, acting by inhibiting cell wall synthesis. Its in vitro activity compares favourably with other beta-lactam antibiotics. Its pharmacokinetic properties indicate that an 8-hourly dosing schedule is appropriate. In addition a delayed release formulation allowing twice daily dosage has been developed. The efficacy of both formulations of cefaclor has been verified by many clinical trials. Cefaclor has been widely used in infections of the respiratory tract (including otitis media), urinary tract and soft tissues. The results of therapy are summarized. The low incidence of adverse events is highlighted and the beneficial influence of this on compliance is described. Finally, the pharmaco-economics of cefaclor are considered.

Efficacy and safety profile of long-term nitrofurantoin in urinary infections: 18 years' experience.

Case records from 219 female patients between 1975 and 1992 who were given long-term prophylaxis (1 year) with nitrofurantoin for the prevention of recurrent urinary infections have been reviewed. Patients' age ranged from 9 to 89 years (median 31-35 years, mode 26-30 years); most (61%) were < 40 years old. The median number of symptomatic episodes in the 12 months immediately before prophylaxis was six (mode 4, mean 6.9). 14.4% of the patients were allergic to an antibiotic, and 23.6% had an imaging abnormality. Three regimens were used: group A (43 patients), 50 mg microcrystalline nitrofurantoin, bd; group B (110 patients), 100 mg macrocrystalline nitrofurantoin (Macrodantin), od; group C (66 patients), 50 mg Macrodantin, od. There were no obvious differences in efficacy between the patient groups (173 assessable patients). The mean incidence of symptomatic episodes decreased 5.4-fold during prophylaxis. Four-fifths of the 43 breakthrough infections (mostly due to Escherichia coli), were caused by nitrofurantoin-sensitive strains. An important finding was that patients with an imaging abnormality responded as well as those with no such abnormalities. In 16% of patients, prophylaxis was not helpful, objectively or subjectively, for no obvious reasons. In most patients where prophylaxis was successful, clinical improvement was maintained for at least 6 months after the end of prophylaxis. Nausea was more common in group A (P < 0.001), as were 'all adverse events'. Of those in group A 25.6% stopped prematurely as a result of an adverse event of any type, compared with 13% of those taking Macrodantin (P < 0.01). Older patients (> 65 years) did not report more adverse events than younger patients. No adverse event was life-threatening. Faecal flora analysis showed neither overgrowth by nitrofurantoin-resistant bacteria nor elimination of sensitive coliforms. Thus, macrocrystalline nitrofurantoin 50 mg at bedtime is appropriate for use in the long-term (12 months) prophylaxis of recurrent urinary infections, in view of its efficacy and favourable safety and tolerability profile. Patients can be managed by their family doctor.

Antimicrobial activities in vitro and in vivo of transition element complexes containing gold(I) and osmium(VI).

Metal compounds have been used as antibacterial agents for centuries. The in-vitro activity of two metal containing complexes, one gold, the other osmium, was investigated using a panel of clinically isolated bacteria and Candida albicans. Twenty strains of each organism were used and MIC and MBC values determined using the agar plate dilution method. Protein binding effects on the activity of the compounds were also investigated using media supplemented with 5% human blood. In-vivo activity of the two compounds was subsequently determined in a hairless-obese mouse skin-surface activity model. Both compounds were highly active against the Gram-positive organisms and Candida albicans in vitro. The gold compound had some Gram-negative activity but the osmium complex was inactive against these organisms. Both were extensively protein bound. In the in-vivo experiment the gold compound achieved a 2-3 log reduction for all the test organisms and was at least as good as or superior to mupirocin in its eradication rate. The osmium compound was inactive.

Teicoplanin vs. vancomycin for the treatment of serious infections: a randomised trial.

A prospective, randomised study of 56 patients comparing teicoplanin with vancomycin for suspected or proven severe Grampositive infection was conducted. The majority of infections were soft tissue infections (8 teicoplanin; 16 vancomycin) and by chance a significantly higher number of Hickman catheter-related infections occurred in the vancomycin arm (4 vs. 14, P < 0.01). Teicoplanin was administered as a single daily dose of 400 mg iv or im; 5 patients received 200 mg following the initial dose of 400 mg. Vancomycin was given 1 g every 12 h. Fifty-four patients were evaluable for efficacy (26 teicoplanin, 28 vancomycin). Of these, 18 episodes in 17 patients (teicoplanin) and 19 episodes in 18 patients (vancomycin) gave an evaluable clinical response, the success rates being similar (76% teicoplanin; 68% vancomycin). Staphylococcus aureus was the most common pathogen isolated; all pathogens were susceptible to both glycopeptides with MICs < 4 mg/l. Bacteriological elimination rates were similar in both groups (71% teicoplanin; 78% vancomycin). Significantly more patients given vancomycin experienced adverse events (7 teicoplanin; 16 vancomycin; P = 0.03). This caused treatment to be discontinued in 4 cases, compared with only one receiving teicoplanin. The most common vancomycin-related events were histamine-associated reactions (15 patients), including 2 cases of Red Man Syndrome, and nephrotoxicity (5 patients). There were no histamine-mediated events and only one case of nephrotoxicity with teicoplanin. Teicoplanin and vancomycin show similar clinical and bacteriological efficacy and teicoplanin is significantly less toxic and easier to use in patients with severe infection.

Combinations of sulphonamides with diaminopyrimidines: how, when and why?

Co-trimoxazole is still widely used for indications where trimethoprim alone is equally effective. The pharmacological rationale of the combination of trimethoprim and sulphamethoxazole involves synergistic action of the two drugs. This is true only from a laboratory point of view; several considerations have led to the conclusion that the synergism between the two components is of only in vivo marginal importance in determining the clinical efficacy of co-trimoxazole. This is due to a greater tissue affinity of trimethoprim compared to that of sulphamethoxazole and, therefore, to the different tissue concentration ratios obtained in vitro and in vivo. Another claim sustaining the combination is the prevention of developing resistance to trimethoprim; however, there is no substantial clinical evidence to support this claim. It does seem likely that trimethoprim has protected against the emergence of that sulphonamide resistance. This slight benefit is outweighed by the disadvantages of the combination, mainly consisting of the occurrence of adverse events due to the sulphonamide moiety. Consequently, the incidence and severity of the adverse events seen with co-trimoxazole should be reduced by using trimethoprim alone. There are only a few cases where co-trimoxazole is better than trimethoprim: toxoplasmosis, brucellosis, nocardiosis, chancroid and pneumonia due to Pneumocystis carinii. For the other and many common infections, scientific rationale, economic and clinical reasons dictate that trimethoprim is superior to co-trimoxazole.

A comparative trial of low dose cefaclor and macrocrystalline nitrofurantoin in the prevention of recurrent urinary tract infection.

One hundred and twenty women, aged between 18 and 90 years, with a history of at least four episodes of symptomatic urinary tract infection in the preceding 12 months, were randomized in an open, prospective study to prophylactic treatment with cefaclor 250 mg at bedtime or macrocrystalline nitrofurantoin 50 mg at bedtime for 12 months. Ninety-seven (49 taking cefaclor, 48 taking macrocrystalline nitrofurantoin) were assessed for efficacy; 80% of these were symptomatically improved and remained abacteriuric during the period of prophylaxis. Symptomatic attacks while patients were taking prophylaxis occurred at least five times less often than before prophylaxis had started. Seventy percent of the patients continued in an improved condition after having stopped prophylaxis. All 120 patients were assessed for adverse events; these were twice as frequent in patients taking macrocrystalline nitrofurantoin (20% vs. 10%), but only 11 patients (three taking cefaclor, eight taking macrocrystalline nitrofurantoin) withdrew from the study. Due to the small numbers of patients experiencing adverse events, these differences are not statistically significant. No significant changes in haematological or biochemical parameters were found during or after the end of the 12-month course. The 22 patients assessable for efficacy who had a non-obstructive radiological abnormality responded as well to prophylaxis as those with no detectable abnormality. Long-term, low-dose prophylaxis with a suitable antimicrobial agent is highly effective management for patients with recurrent urinary tract infections, and can appropriately be provided by the family doctor. Prophylaxis given for 1 year gives better results than when given for 6 months.

Consensus viewpoint on management of urinary infections.

Twenty-four general practitioners completed a questionnaire on behalf of their partners in the practices before attending the symposium. The main points that emerged were that trimethoprim was the most popular antibiotic for treatment of acute urinary infection and that the most common duration of treatment was 5 to 7 days. A panel discussion, with audience participation, covered duration of treatment, antibiotic resistance, specimen collection, management of different patient groups and availability of information concerning resistance patterns. Nineteen of the original 24 general practitioners returned the post-meeting questionnaire, and stated that, as a result of what they had heard at the symposium, they were contemplating changing the way in which they managed urinary infections. Information concerning bacteriuria in pregnancy and changing patterns of bacterial resistance to antibiotics were of particular interest.

Limitations of and indications for the use of co-trimoxazole.

Co-trimoxazole is still widely used for indications where trimethoprim alone is equally effective. Microbiological and pharmacokinetic considerations reveal that trimethoprim alone provides adequate anti-microbial activity for treatment of conditions for which co-trimoxazole is often given. Synergy may be shown in vitro, but in clinical practice is an unusual occurrence. There is no evidence from clinical studies that the sulphonamide moiety fo co-trimoxazole prevents the development of resistance to trimethoprim. The adverse event profile of co-trimoxazole is a summation of that of sulphonamide and of trimethoprim. Thus, using trimethoprim alone should reduce both the incidence and potential severity of adverse events seen when co-trimoxazole is used. Clinical trials have shown trimethoprim to be as effective as co-trimoxazole in many of the common bacterial infections of the urinary and respiratory tracts. However, there are a few specific varieties of infection for which co-trimoxazole can be shown to be superior to trimethoprim: these include toxoplasmosis, brucellosis, nocardiosis, chancroid and pneumonia caused by Pneumocystis carinii. For many common infections, scientific, rational, economic and clinical reasons dictate that trimethoprim is preferable to co-trimoxazole.

The challenge of methicillin-resistant Staphylococcus aureus.

Staphylococcus aureus strains resistant both to methicillin and aminoglycosides emerged during the late 1970s. These have become endemic in hospitals all over the world. Outbreaks of infection and colonization may cause severe clinical and managerial problems, as therapeutic options are limited and it may be difficult to clear the carrier state. The genetics and biochemistry of these organisms are well studied, but additional antibiotics active against these strains are needed. The most urgent requirement is for rational and effective policies for control of their spread.

Reassessment of the rationale for the combinations of sulphonamides with diaminopyrimidines.

Trimethoprim is the best known inhibitor of bacterial dihydrofolate reductase. Initially, this was always combined with sulphamethoxazole. It was later combined with other sulphonamides (eg. sulphamoxole, sulphadiazine or sulfametopyrazine), but the sulphonamide moiety as a contributor to clinical efficacy was increasingly questioned. Thus, in 1979 (in UK) trimethoprim alone was introduced. Justification for the combination was based on: (a) synergy occurs in vitro (b) bactericidal activity, while the two components are bacteriostatic (c) the emergence of resistance was claimed to be lower. However, these claims were not substantiated by studying the microbiological and pharmacokinetic properties of trimethoprim and the sulphonamides, but most importantly by the results of clinical trials. These show that in most indications, trimethoprim alone is as good, cheaper and causes considerably fewer adverse events than use with a sulphonamide. For urinary infections most agree that monotherapy is best. In respiratory infections diaminopyrimidines have relatively poor activity against important pathogens, eg pneumococci and especially Moraxella catarrhalis. It could be argued in these case that the addition of a sulphonamide may increase therapeutic efficacy. This can only be resolved by large clinical trials. In brucellosis and gonorrhoea, where sulphonamides are more microbiologically active than diaminopyrimidines, it is likely that combination with another antibiotic is needed. However, too much reliance must not be placed on extrapolating from trimethoprim to other diaminopyrimidines; conclusions should be drawn from work using the other compounds.

Effect of alkalinisation and increased fluid intake on bacterial phagocytosis and killing in urine.

The effect of alkalinisation and increased fluid intake on bacterial phagocytosis and killing in urine was studied. Phagocytosis of Escherichia coli and Staphylococcus saprophyticus by polymorphonuclear neutrophils (PMN) took place in only one of three first voided early morning urine samples from volunteers, and no bacterial killing occurred. This was attributed to the high osmolality (690 to 720 mOsm) and low pH of the early morning urine; two samples were pH 5.8 and the third, in which phagocytosis occurred, was pH 6.4. Afternoon urine samples from the same volunteers had lower osmolality and a higher pH, with a high rate of phagocytosis (> or = 88%) and 55-69% killing. PMN remained viable (mean 94%) after exposure for 1 h to both early morning and afternoon urine. Volunteers taking 4 g sodium citrate showed a mean rise of urinary pH of 1 unit. Water loading in patients with urinary tract infections produced a bacteria to neutrophil ratio conducive to bacterial killing, bacterial counts being reduced by a mean of 2.5 logs after 1-3 h without a corresponding reduction in neutrophils. Thus, raising the pH and reducing the osmolality of urine increases the ability of neutrophils to eliminate infecting organisms.

Effect of bacterial products including endotoxin on neutrophil function in infected urine.

Experiments were performed to determine the effects of products of bacterial growth (including endotoxin) on phagocytosis and intracellular killing by polymorphonuclear leucocytes (PMNL) in urine. Bacteriologically filtered supernates of two strains of Escherichia coli grown in urine were added in varying amounts to mixtures of PMNL and E. coli, also in urine. Phagocytosis of the two strains was reduced from > 90% in controls to 66% and 48%, respectively, in the presence of undiluted culture filtrate (containing endotoxin 2-2.5 micrograms/ml). Intracellular killing was also decreased and was abolished by dilutions corresponding to endotoxin concentrations of 0.6 and 0.75 micrograms/ml. When PMNL exposed to these inhibitory dilutions were resuspended in fresh urine, their phagocytic ability was fully restored and 13-24% of their killing activity was regained. A minimum concentration of commercially purified E. coli endotoxin of 200 micrograms/ml was required to abolished PMNL killing, with phagocytosis uninhibited. The results strongly suggest that bacterial growth metabolites, not endotoxin, are responsible for the depression of phagocytosis and intracellular killing in infected urine. A moderate dilution of the bacterial products in urine permits good PMNL function. Extrapolating this to the clinical situation, diluting the urine by water loading (as recommended for patients with urinary infections) should ensure efficient activity of PMNL under in-vivo conditions providing urinary pH and osmolality are not adversely affected.

Enoxacin relieves symptoms of recurrent urinary infections more rapidly than cefuroxime axetil.

In patients with a history of recurrent infections, treatment with enoxacin (200 mg/12 h for 3 days) relieved symptoms of acute urinary infection significantly more rapidly than treatment with cefuroxime axetil (125 mg/12 h for 7 days). Other parameters, including clinical and bacteriological cure rates and patients' overall opinion of their treatment, did not differ significantly between the treatments.

M2 mitochondrial antibodies and urinary rough mutant bacteria in patients with primary biliary cirrhosis and in patients with recurrent bacteriuria.

Primary biliary cirrhosis (PBC) patients have a higher incidence of recurrent urinary tract infection and an increased prevalence of rough forms (mutants) of E. coli in their stool samples than other chronic liver disease patients. PBC patients exhibit autoantibody reactivity against mitochondria, the most common antigen (M2) being a family of antigens with the major components having approximate molecular weights of 74, 56, 52 and 48 kD. Cross-reactivity between M2 antigen components and corresponding antigenic bands of bacteria has been demonstrated with PBC sera. Patients with recurrent urinary tract infections, all of whom had normal liver function and were taking prophylactic antibiotic treatment, had weak anti-mitochondrial antibody (AMA) reactivity (69%), with reactivity against the 74-kD antigen alone being the most common. When antibody to the 74-kD band was eluted, it was found to cross-react with bacterial membrane fractions. In the controls, 12/77 chronic liver disease patients and 2/24 normals possessed AMA. Rough forms of bacteria were found in the urine of patients with significant bacteriuria: 39% PBC, 5.3% chronic liver disease and 41% of the recurrent urinary tract infection group. M2 antibodies may be induced by urinary organisms in 'normal' women with recurrent bacteriuria and in females with PBC.

Effect of pH and osmolality on in vitro phagocytosis and killing by neutrophils in urine.

Phagocytosis and intracellular killing of two strains of Escherichia coli and a Staphylococcus saprophyticus by polymorphonuclear neutrophils (PMN) in pooled sterile urine at three osmolalities (800, 485, and 200 mosM/kg of H2O) between pHs 5 and 8 was investigated. Urine at 800 mosM virtually abolished phagocytosis of both E. coli strains, regardless of pH, and reduced the phagocytosis of S. saprophyticus to 30%; no killing of any organisms took place at this osmolality. On the other hand, phagocytosis was a good in urine as in Hanks balanced salt solution at both 485 and 200 mosM between pHs 6 and 8. Phagocytosis of all three strains was virtually abolished at pH 5. Killing of the strains by PMN was optimal between pHs 6.5 and 7.5 in urine at 485 mosM (being at least 90% of the control values in Hanks balanced salt solution), whereas at 200 mosM killing was reduced to 50 to 70% of these values. Reduced killing of all three strains occurred at pH 8, whereas at pH 6 only S. saprophyticus was killed. Thus, the bactericidal activity of PMN in urine was more sensitive than phagocytic function to alterations in pH. The dominant modulating factor affecting PMN function in urine of 500 mosM or less was pH, but osmolality had a greater influence at 800 mosM. Thus, raising the pH of urine and reducing the osmolality may increase the ability of natural defense mechanisms to eliminate infecting organisms.

Antibacterial oxazolidinones. In vitro activity of a new analogue, E3709.

The oxazolidinone compound E3709, which contains a 4-pyridyl group, was found to be more active in vitro than other members of this series, such as DuP 721. MIC90 for staphylococci(including methicillin-resistant isolates), streptococci (including Enterococcus faecalis), Clostridia, and diphtheroids was less than 0.5 micrograms/ml. Haemophilus influenzae, Moraxella catarrhalis, and Bacteroides fragilis were less susceptible, with an MIC90 between 2 and 8 micrograms/ml. E3709 MICs of Gram-negative species ranged from 100 to greater than 1000 micrograms/ml. At a concentration of 10 micrograms/ml, E3709 was bactericidal for selected Gram-positive species. A postantibiotic effect of 3 hr was observed against staphylococci. Resistance to E3709 was not detected.