Retrograde contamination and practical handling of urine-meters: a comparison of three systems for the measurement of hourly diuresis in an experimental bladder-drainage model and in clinical use

OBJECTIVE

To compare three different urine metering systems for their ability to prevent retrograde contamination in an in vitro model of a closed urinary drainage system and for qualities important to their practical handling in a clinical setting.

PATIENTS, MATERIALS AND METHODS

Using three urine-meters (the Braun Ureofix 511, the Kendall Curity 4000 and the Unoplast Unometer 500) the in vitro model was constantly flushed with a solution of Mueller-Hinton broth diluted with saline. On the first day, the urine collecting bag was inoculated with 10(8) cells of Pseudomonas aeruginosa. The system was operated for 12 days with daily sampling of the model bladder to detect any contamination. After 12 days the experiment was stopped and sampling performed at various locations, including the urine-meter and the tubing. Nine of each type of urine-meter were tested, i.e. three in three different experiments. In the clinical study, 45 patients were randomized to each of the three urine-meters and the nurses attending them were asked to complete a questionnaire on the practical handling of the urine-meters.

RESULTS

When the urine-meters was omitted from the model system, the 'bladder' became contaminated with the test bacteria within 3 days. None of the nine Unometer 500 systems became contaminated, compared with four of each of the other two systems (P < 0.05). In clinical use, the Unometer 500 and Ureofix 511 were easier to suspend and empty than was the Curity 4000. The Unometer 500 was significantly easier to handle when the collecting bag was emptied.

CONCLUSION

Urine-meters can prevent retrograde contamination in a closed bladder-drainage model, but the degree of prevention depends upon the type of urine-meter. In daily practice, there were differences in the ease of suspension of the systems and in the emptying of the urine-meter and collecting bag.

[Vibrio vulnificus infections in Denmark during the summer of 1994]

The clinical manifestations and epidemiological data of 11 patients infected with Vibrio vulnificus found in Denmark during the unusually warm summer of 1994 are reported. All patients had been exposed to seawater prior to illness, but none had consumed seafood. Nine patients, including four with bacteraemia, developed skin manifestations of various degrees of severity. One patient died of septic shock despite surgery and treatment with relevant antibiotics. Four patients contracted the disease while fishing. High seawater temperature increases the risk of V. vulnificus infections even in temperate climates such as the Danish. Exposure to seawater, including handling of fresh seafood, during warm periods carries a risk of infection with V. vulnificus.

Detection of penicillin resistance in Streptococcus pneumoniae by diffusion tests

Four different diffusion tests used to detect penicillin resistance in Streptococcus pneumoniae were evaluated for 34 penicillin-susceptible pneumococci (MIC < 0.1 microgram/ml), 35 intermediate pencillin-resistant (MIC 0.1-1.0 microgram/ml) and 23 penicillin-resistant strains (MIC > 2 micrograms/ml). The 1 microgram oxacillin disk from AB Biodisk, the 1 microgram oxacillin Neo-Sensitabs from Rosco, the 5 micrograms penicillin Low Neo-Sensitabs and the penicillin E test were tested on Mueller-Hinton blood agar, PDM Antibiotic Sensitivity Medium II supplemented with blood, and Danish Blood Agar. MICs obtained by the agar dilution method were used as reference. The 1 microgram oxacillin AB Biodisk was able to separate all the penicillin-susceptible pneumococci correctly from those with reduced penicillin susceptibility (MIC > or = 0.1 microgram/ml), whereas use of the 1 microgram oxacillin Neo-Sensitabs resulted in high frequencies (14-29%) of intermediate penicillin-resistant strains interpreted as penicillin susceptible. The 5 micrograms penicillin Low Neo-Sensitabs proved completely useless for detecting penicillin resistance in pneumococci. High rates of agreement (82-93%) were found between the penicillin E test and the reference MIC determination method on all the tested media.

[Pleural empyema]

Despite of extensive use of antibiotics for respiratory tract infections pleural empyema is still seen as a complication to pneumonia (7-10 cases/100.000 inhabitants pr. year). Pleural empyema as a complication to pulmonary surgery is reported in 2-3% of the patients even with use of antibiotic prophylaxis. Pleural empyema is most often a serious disease of long duration. The diagnosis is obtained with microbiological and histological examination of the pleural fluid. Mixed infection occurs in over half of the cases, most often including anaerobic bacteria, but most human pathogens have been reported as etiological agents. Treatment includes drainage of pus and administration of relevant antibiotics, systemically and pleurally. Drainage can be performed via thoracocentesis, by tubes, or by resection of a part of the rib. The optimal treatment strategy is so far unknown, since good prospective comparative clinical studies are lacking.

In vitro activity of six macrolides, clindamycin and tetracycline on Streptococcus pneumoniae with different penicillin susceptibilities

A collection of 99 clinical isolates of Streptococcus pneumoniae, chosen due to their different susceptibilities to penicillin, were investigated with respect to their susceptibility to the macrolides azithromycin, clarithromycin, dirithromycin, erythromycin, roxithromycin, spiramycin, and to clindamycin and tetracycline by the agar dilution method. We found complete cross resistance among the macrolides. The pneumococci were either susceptible, MIC < or = 0.5 micrograms/ml, or resistant, MIC > or = 16 micrograms/ml, to the tested macrolides, giving a bimodal distribution. In addition, complete cross resistance was observed between clindamycin and macrolides. Pneumococci resistant to macrolides were also resistant to tetracycline, and 26% of the macrolide-susceptible strains were tetracycline resistant.

Clinical manifestations and molecular epidemiology of Vibrio vulnificus infections in Denmark

The clinical manifestations of and epidemiological data from 11 patients infected with Vibrio vulnificus admitted to Danish hospitals during the unusually warm summer of 1994 are reported. All patients contracted the disease after exposure to seawater; however, none had consumed seafood. Four patients developed bacteremia, one of whom subsequently died; nine patients, including the four with bacteremia, exhibited skin manifestations. Four patients contracted the disease while fishing; in at least one case the patient had handled eels. All Vibrio vulnificus strains were highly susceptible to 11 antimicrobial agents tested. Plasmid analysis revealed that 8 of 11 strains carried plasmids. Ribotyping using the enzyme HindIII on the 11 strains showed five different types, two of which comprised four strains each. The present study provides the first clinical and epidemiological data about a series of human Vibrio vulnificus infections from a temperate zone.

Experimental Streptococcus pneumoniae infection in mice for studying correlation of in vitro and in vivo activities of penicillin against pneumococci with various susceptibilities to penicillin

The purpose of the study was to investigate the correlation of in vitro activity with the in vivo effect and the pharmacokinetics of penicillin in the treatment of infections with pneumococci with various susceptibilities to penicillin. We used 10 pneumococcal strains for which penicillin MICs ranged from 0.016 to 8 micrograms/ml. Time-kill curve experiments were performed with all strains. We found that the effect of penicillin in vitro is concentration independent, with a maximum effect at two to four times the MIC for penicillin-susceptible as well as penicillin-resistant pneumococci. The mouse peritonitis model with an inoculum of approximately 10(6) CFU, to which mucin was added, resulted in a reproducible lethal infection with the pneumococci. The 50% effective dose was determined for each strain, and we found a highly significant correlation between the log MIC and the log 50% effective dose of penicillin against these strains (P < 0.01). Furthermore, it was shown that the most important pharmacokinetic parameter determining the effect of penicillin in vivo was the time that the concentration of penicillin in serum was greater than the MIC.

Dicloxacillin and flucloxacillin: pharmacokinetics, protein binding and serum bactericidal titers in healthy subjects after oral administration

The pharmacokinetics of dicloxacillin and flucloxacillin were studied in 12 healthy volunteers after oral administration. The participants received a single dose of either dicloxacillin (0.5 g, 0.75 g or 1.0 g) or flucloxacillin (0.75 g) in a cross-over fashion. Antibiotic concentrations were determined in serum and urine by bioassay and followed for 8 and 24 h, respectively. The three dicloxacillin dosages showed no significant differences for the serum elimination half-lives (t1/2 beta, median: 72 min). Comparing 0.75 g flucloxacillin with the same dose of dicloxacillin, no significant differences between the values of Cmax, t1/2 beta and AUC were found. Protein binding as determined by ultrafiltration in pooled serum was 94.7-96.2% for flucloxacillin and 96.4-97.2% for dicloxacillin. The serum bactericidal titers were similar for the two drugs. In conclusion, dicloxacillin and flucloxacillin showed similar pharmacokinetic behavior after 0.75 g doses in human volunteers.

Collagen with gentamicin for prophylaxis of postoperative infection. Staphylococcus aureus osteomyelitis studied in rabbits

In 34 rabbits, both tibiae were inoculated with Staphylococcus aureus. 14 legs received no treatment and served as controls. In 12 legs, the wound was treated with pure collagen and in 18 legs, collagen with gentamicin (Gentacoll) in a dose of 10 mg/kg body weight was applied to the wound before closure. Postoperatively 12 received 10 mg/kg body weight gentamicin intravenously and no local treatment. The animals were killed 7 days after inoculation and evaluated macroscopically and microbiologically for infection. 6 rabbits (12 legs) were used for pharmacokinetic studies only and they were killed after 2, 4, and 18 hours, respectively. 11/14 untreated legs developed a macroscopically acute osteomyelitis. No infection was found in the 18 legs treated with Gentacoll and 1/12 treated with gentamicin systemically had growth of the inoculated bacteria in tissue biopsies. The concentrations of gentamicin in the serum as well as locally reached peak values were well above the MIC value in all groups, with a maximum after 1-2 hours. No gentamicin could be detected after 18 hours, independently of the mode of administration.

Staphylococcus aureus endocarditis in Danish intravenous drug users: high proportion of left-sided endocarditis

In a retrospective study covering the years 1982-1989 episodes of Staphylococcus aureus endocarditis in 51 intravenous drug users were studied. Tricuspid involvement dominated (34/51), but the frequency of left-sided involvement (33.3%) was greater than in earlier reports. Involvement of both sides of the heart was not detected, but 27.8% of the left-sided endocarditis cases had multiple pulmonary infiltrates, indicating that some of them might have had a concomitant right-sided endocarditis. The 2 groups were compared: patients with left-sided endocarditis were significantly older and with a longer time of intravenous drug use. The complication rate was the same (44.1%) as was the duration of antibiotic treatment (median 42 days). In total, five patients underwent surgery, two (5.8%) due to right-sided failure and three (29.4%) because of left-sided endocarditis. The mortality of tricuspid endocarditis was low (2.9%), whereas 5 patients (29.4%) with left-sided involvement died. The patients who died were significantly older and had a shorter duration of symptoms before hospitalization.

Staphylococcus aureus bacteremia: a 14-year nationwide study in hematological patients with malignant disease or agranulocytosis

This retrospective nationwide study of 756 cases of S. aureus bacteremia in hematological patients, between 1977-1990, confirms that S. aureus bacteremia is disproportionately prevalent among, and a major cause of morbidity and mortality in, hematological patients. The case mortality rate attributable to S. aureus bacteremia (44%) was significantly higher than the rate (29%) found in patients without hematological disease. A decreasing mortality was, however, observed from the first to the last part of the study period (53 and 37% respectively). A logistic regression analysis showed that mortality was further dependent on age, the type of hematological disease and origin of infection/primary focus of infection. Analysis of clinical features confirmed that in comparison with other patients, S. aureus bacteremia in hematological patients more often was hospital-acquired, acquired without known portal of infection/primary focus of infection and much less frequently resulted in osteomyelitis or endocarditis. From phage typing and antibiotic susceptibility patterns no specific types of S. aureus were associated with hematological patients.

Effect of treatment with methicillin and gentamicin in a new experimental mouse model of foreign body infection

A new mouse model of foreign body infection has been developed. Intraperitoneal placement of a silicone catheter followed by injection of 10(8) Staphylococcus aureus organisms resulted in a reproducible, localized foreign body infection. The infection persisted as an intra-abdominal abscess surrounding the catheter for at least 30 days. Treatment with up to nine doses of methicillin or gentamicin or both was started 3 days after infection. The treatment showed a significant effect (P < 0.05), measured as reduction of bacteria on the foreign body, for all three regimens with a reduction of up to 2 log units, but no synergism was observed. The result of the treatment was poor, despite the facts that the local concentrations of methicillin were greater than the MIC for at least 72 h and that nine peak concentrations of gentamicin of > 13 micrograms/ml were obtained. The poor result of the treatment was not caused by development of antibiotic resistance or influenced by protein concentration, pH, or local presence in the pus of inhibitors of antibiotics. Both antibiotics showed good effects in time-kill studies in vitro on bacteria on catheters taken out of infected mice and catheters infected in vitro. During treatment, the proportion of intracellular bacteria increased in all treated mice to 60 to 75% compared with 20 to 30% in nontreated mice (P < 0.05). This indicates that intracellular survival of staphylococci may influence the outcome of the treatment in foreign body infections.

Infections with the unusual human pathogens Agrobacterium species and Ochrobactrum anthropi

Agrobacterium species and Ochrobactrum anthropi are generally considered innocuous in clinical settings, yet during the last decade a number of sporadic cases of human infection due to these organisms have been reported. We studied nine cases of infection (septicemia and peritonitis) caused by Agrobacterium-like microorganisms in eight patients. All patients were immunocompromised and had permanent central venous or peritoneal dialysis catheters in place. Seven patients were women, and eight infections were community acquired. Six isolates were identified as Agrobacterium species and three as O. anthropi. These two groups of strains differed in the production of beta-galactosidase and of acid from lactose, erythritol, salicin, and cellobiose. All strains were strictly aerobic, peritrichous, gram-negative bacilli that produced oxidase, urease, and acid from glucose, fructose, arabinose, xylose, mannitol, inositol, and ethanol. The in vitro adherence of isotope-labeled bacteria to silicone tubes was similar to that of staphylococci. We conclude that Agrobacterium species and O. anthropi can be pathogenic in immunocompromised patients with permanent catheters.

The antibacterial activity of a siderophore. 3. The activity of deferoxamine in vitro and its influence on the effect of antibiotics against Escherichia coli, Proteus mirabilis and coagulase-negative staphylococci

The in vitro activity of deferoxamine (DFO) both per se and in combination with the reductant ascorbic acid (AA) was determined against 10 E. coli strains, 5 P. mirabilis strains, and 10 coagulase-negative staphylococci. In terms of interaction, the influence of DFO on the activities of cephalothin and gentamicin was furthermore investigated against the same panel of strains employing a macrobroth dilution technique and killing-curve kinetics. The MICs of cephalothin and gentamicin were lowered for one half of the strains. Moreover, DFO prolonged the generation times of logarithmic growth phase considerably, especially when the reductant AA was present. The interactions between DFO or DFO+AA and subinhibitory concentrations of antibiotics were established by the application of growth constants, and resulted in synergy for 15 out of 25 strains with cephalothin and 9 out of 25 strains with gentamicin.

Attachment of staphylococci to different plastic tubes in vitro

Adherence of 18 staphylococcal strains to 13 types of uncoated plastic tubes made from 10 different plastic materials were investigated by binding of radiolabelled bacteria in phosphate-buffered saline for 2 h at 37 degrees C. The different materials could be divided into five groups based on their ability to bind staphylococci. Lowest adhesion was found for plasticised polyvinylchloride. Simple assays for the relative binding of peroxidase-labelled human IgG or fibrinogen did not predict the result of adhesion studies. Neither bacterial surface hydrophobicity measured in a two-phase partitioning assay, nor hydrophobicity of materials (wettability) as measured by their contact angles in water correlated with bacterial adhesion. Adhesion of staphylococci to certain plastic materials was greatly influenced by the method used for sterilisation of the material.

Antibiotic usage in an intensive care unit in a Danish university hospital

We report a study of antimicrobial use in patients admitted to the Intensive Care Unit (ICU) in a Danish university hospital during the course of 1 year. Of 615 patients admitted, 434 (71%) received antibiotics, 220 (36%) for infections and 222 (36%) for prophylaxis. Therapy for suspected infection accounted for 67% of the total consumption of antibiotics and prophylaxis for 33%. Ampicillin was the drug most frequently used; 43% of the patients treated for infection received this drug. One hundred and thirty-one patients (60%) were treated for suspected lower respiratory tract infection. Relevant microbiological specimens were obtained from 120 (92%) of these patients and a possible pathogen was isolated in 92 patients (77%, 92/120). Staphylococcus aureus and Streptococcus pneumoniae were each isolated in almost a quarter of the patients, and Enterobacteriaceae in 53%. However, many of the pathogens isolated were of no clinical relevance and merely reflected a state of colonization. Most treatments were given during the first few days following admission. Of 220 patients receiving antibiotics for an infection, 87% were treated on day 1, but only 34% (14 of 41) on day 11. The frequent use of laboratory investigations combined with good communication between clinicians and microbiologists probably resulted in rapid cessation of unnecessary therapy. Fifty-two per cent of the antibiotics given for prophylaxis were administered later than the first postoperative day. This study emphasizes the need for consultation between surgeons and clinical microbiologists to supervise postoperative antibiotic use.

Staphylococcus aureus meningitis. A review of 104 nationwide, consecutive cases

METHODS

Based on a nationwide registration, the clinical and bacteriologic data from 61 postoperative and 43 hematogenous cases of Staphylococcus aureus meningitis in Denmark from 1986 through 1989 were reviewed.

RESULTS

Postoperative meningitis was a foreign body infection in 89% of the cases and had a lower mortality (18% [11/61]) compared with hematogenous meningitis (56% [24/43]). Hematogenous S aureus meningitis seems to be part of an overwhelming, disseminated infection as indicated by the following: 81% of the patients had bacteremia, 21% had endocarditis, and 12% had osteomyelitis. Most patients were older, often with underlying diseases, community-acquired infections, and a clinical picture of severe meningitis. The major findings were mental status changes and a high rate (34%) of focal neurological changes. The initial leukocyte count in the cerebrospinal fluid sample was low, and the bacteria were seen in Gram's stain smears in 40% of cases only. The prognosis was related to the age of the patients and the initial antibiotic treatment. Patients treated with penicillinase-stable penicillins in combination with fusidic acid may have a better prognosis. Three (12%) of 25 surviving patients had severe sequelae.

CONCLUSIONS

Hematogenous S aureus meningitis is a severe disease with a high mortality related to age, presence of shock, and infection with strains of phage type 95.

[Daily single-dose aminoglycoside administration. Therapeutic and economic benefits]

Aminoglycosides are among the most active antimicrobial agents against Gram-negative infections, but they also share the potential for oto- and nephrotoxicity. Animal studies have shown that dosing aminoglycosides once daily is more efficient and less nephrotoxic than the conventional multiple daily dosing regimens. Pharmacokinetic and microbiological data support this finding. Clinical trials confirm that once-daily dosing is more efficient and less toxic than multiple daily dosing. The two most important risk factors for nephrotoxicity seem to be the duration of aminoglycoside treatment and high trough levels of aminoglycoside. Netilmicin and amikacin are the drugs most often used in clinical trials of once-daily dosing regimens. Recommendations for once-daily dosing of netilmicin are given.

The mouse peritonitis model: present and future use

The mouse peritonitis model was the first experimental animal model to be used in antibiotic research in 1935, where it proved the effect of Prontosil and derivative sulphonamides against Streptococcus pyogenes in vivo. Since then the mouse peritonitis model has been a natural step in testing antibiotics in vivo before moving to larger animals or humans. Only a few bacteria are naturally virulent to mice, e.g. Streptococcus pneumoniae, but the mice can be rendered susceptible to most human pathogens by inhibition of one or more parts of the natural defence of the animals. For measuring the effect of antibiotics two parameters are usually considered: bacterial counts in fluids or tissues, or death/survival of the animal. Both parameters have flaws, but death is usually used, owing to the ease of observation and quantification by calculation of the 50% effective (protective or curative) doses. With these parameters a number of significant factors of importance for antibiotic effect have been detected or proven in this model. Together with the recent insight into the correlation of pharmacokinetic behaviour between these small animals and man, it is predicted that the mouse peritonitis model will continue to be an important means of studying the effect of antibiotics in vivo.

Experimental foreign body infection in mice

A number of experimental foreign body infections have been described. We present here an easy, reproducible staphylococcal foreign body infection model in mice. The failure of treatment with methicillin and gentamicin is demonstrated, while the usefulness of antibiotic prophylaxis is documented. The usual correlations between pharmacokinetic parameters and the effect of antibiotics in vivo seem not to hold when a foreign body is present. The model may be applicable to large-scale evaluation of different antibiotic regimens.

Catheter-related Staphylococcus aureus infections

Among 3394 patients with Staphylococcus aureus bacteraemia from the years 1986-89, 88 patients were found whose intravenous catheter and blood grew organisms of the same phage type. Strains of phage type 95 were more frequent among the patients with confirmed catheter-related bacteraemia than among other bacteraemia cases. Strains with particular phage-type patterns occurring with increasing frequency in Denmark during recent years also occurred with significantly higher frequencies among the confirmed catheter-related bacteraemias. No major differences in antibiotic resistance were observed. Patients with catheter-related bacteraemia had, in spite of a higher frequency of underlying diseases, a lower mortality compared with other bacteraemia patients, and endocarditis occurred less frequently (2% vs. 6%). Among 201 S. aureus isolates from catheters in 1988 only strains of group I occurred with increased frequency. The possible role of catheters as selection pressure on the S. aureus population is discussed.

Ceftriaxone versus latamoxef in febrile neutropenic patients: empirical monotherapy in patients with solid tumours

121 patients with 132 febrile episodes were randomised to ceftriaxone or latamoxef monotherapy in order to compare antibiotic efficacy in neutropenic patients treated with cytotoxic chemotherapy for solid tumours. In 80 evaluable episodes no significant differences were observed between the two groups with respect to efficacy and fatal failure rates. Of episodes treated with ceftriaxone, 67% showed a favourable clinical response vs. 61% in the latamoxef group. The clinical response rates in episodes with documented bacterial infections were 67 and 56% in the two treatment groups. In 18% of the episodes with documented initial infections the patients died of presumably uncontrolled infection. The convenient once daily dosage schedule combined with fewer severe adverse reactions favours the use of ceftriaxone instead of latamoxef. Although a relative high degree of response was seen, empirical antibiotic monotherapy apparently does not offer a sufficient antibacterial cover in infections in this type of patient with defective host immunity.