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S Ringertz

Publications and source records attributed to S Ringertz.

At least 37 records · Page 2Linked to original sources
PubMed1991

Comparison of 30 microgram and 120 microgram gentamicin disks for the prediction of gentamicin resistance in Enterococcus faecalis.

Single strain regression analysis was performed on PDM II medium for E. faecalis with 10, 30 and 120 micrograms gentamicin disks using E. faecalis, strain ATCC 29212 as the reference. This method permits the calculation of zone diameters corresponding to different MIC values for different disk contents. The lack of discrimination between normal low-level resistant strains and high-level resistance using the 10 micrograms disk was confirmed. However, both the 30 micrograms and 120 micrograms disks seemed to provide a separation of the normal low-level gentamicin-resistant population from strains with increased resistance. Since the 30 micrograms disk is used routinely in some countries, there should be no need for an extra high content disk in these laboratories. This was confirmed when 96 clinical isolates of E. faecalis were analysed and the results of routine disk diffusion tests were compared with the MIC values. Two of the strains showed high-level gentamicin resistance (greater than 2000 mg/l) and produced no zone of inhibition. The other 94 isolates showed gentamicin MIC values between 4-16 mg/l, and 72 of the MIC results were 8 mg/l. The zone diameters for these strains ranged between 15 and 25 mm with a mean of 18.2 and a median value of 18 mm. In order to include statistical considerations of the zone size populations for setting of breakpoints, a study of gentamicin zone size distributions was performed for several bacterial species. Inhibition zone diameter values around the 30 micrograms gentamicin disk for 2079 clinical isolates of E. faecalis, 2268 S. aureus, 3201 E. coli and 547 strains of P. mirabilis from different years were plotted as histograms. Tests for agreement with a Gaussian distribution showed that the histograms were slightly peaked and skewed towards higher zone values. Parametric and non-parametric statistical tests were compared and the results showed that means and medians were very similar and that parametric fractile estimations at the lower end of the histogram populations were conservative and could be used in view of a slightly lower rate of false resistance. The 1% parametric fractile of 12 mm was selected as a suitable breakpoint for the identification of normal, low-level resistant isolates of E. faecalis using the standardized disk test of the Swedish Reference Group for Antibiotics.

Drug Resistance, Microbial↗
PubMed1991

Antibiotic disk diffusion testing revisited. Single strain regression analysis. Review article.

The standardized (NCCLS, ICS, DIN etc.) disk diffusion method is the most widespread technique for antibiotic susceptibility testing. Interpretive zone breakpoints are calculated from the regular regression line between minimum inhibitory concentrations (MIC) of bacterial isolates and the corresponding inhibition zone diameters around the disk containing the antibiotic. Studies of the regression line has revealed marked differences between different bacterial species. A newly described equation, the single strain regression analysis (SRA) equation, can be used to determine the regression line constants for individual strains. This method was applied to ciprofloxacin and S. aureus, E. faecalis, E. coli, P. mirabilis, P. aeruginosa, and P. maltophilia. The slope and intercept constants were determined for all 40 strains and showed a strong similarity within each species. A close similarity was also observed between the two Pseudomonas species and between S. aureus and E. faecalis. When the regression lines calculated by SRA for individual strains were extrapolated towards higher MIC values, the lines obtained for the more susceptible strains predicted the zones of more resistant strains within the species. The applications of SRA to several other antibiotics and bacterial species in earlier studies were reviewed. One exception to the predictive power of SRA has been detected earlier, H. influenzae and erythromycin. This led to the formulation of the standard curve regression analysis (SCA) equation which requires the use of two or more strains. Methodological aspects of SRA/SCA applications were presented. Three areas are particularly well suited for the use of SRA/SCA: 1. Calculation of interpretive zone breakpoints corresponding to recommended MIC limits in the individual laboratory. 2. Analysis of the effects of various disk contents of antibiotic on the resulting inhibition zones for various bacteria when new antibiotics are introduced. 3. Analytical tool as part of external quality control programmes.

Diffusion↗
PubMed1991

Disk diffusion method for susceptibility testing of Neisseria gonorrhoeae.

The standard medium for disk diffusion and MIC testing of Neisseria gonorrhoeae (that of the National Committee for Clinical Laboratory Standards) was tested to establish zone correlations for the MIC breakpoints currently used in Sweden. Eight gonococcal control strains representing both susceptible and resistant strains and 50 clinical isolates were tested. The standard medium did not support the growth of two control strains and three clinical isolates when the standardized inoculum was used in the disk diffusion test. The same medium with the addition of hemoglobin was introduced. This medium supported the growth of all strains. The correlations between the MICs and the zones of inhibition were calculated for penicillin, ampicillin, cefuroxime, erythromycin, tetracycline, doxycycline, ciprofloxacin, and spectinomycin. The range of MICs for the clinical isolates were broad, without bimodal distribution, for all antibiotics, except ciprofloxacin and spectinomycin. With the susceptibility distribution of MICs and zones near the current susceptible and intermediate or intermediate and resistant limits, a low reproducibility of tests and a high frequency of minor interpretive errors can be expected. A revision of MIC breakpoints seems warranted but can only be done after renewed clinical evaluation of different treatment regimens.

Ampicillin↗
PubMed1990

Antimicrobial susceptibility testing of Haemophilus influenzae. Improvement of accuracy of the disc diffusion test.

A national quality control study was performed in 1986 to investigate the standard of performance of the disc diffusion antimicrobial susceptibility testing of Haemophilus influenzae in Sweden. The accuracy of susceptibility interpretations was unacceptably low. A new standardized method for susceptibility testing of H. influenzae was then worked out, and a new method of setting interpretive zone breakpoints was introduced. The susceptibility category of the main population of clinical isolates was determined according to the MIC50 of the strains. The zone histograms of clinical isolates from five reference laboratories were used for the calculation of interpretive breakpoints. For instance, for susceptible strains the mean of the combined zone values from these laboratories +/- 2 S.D. covered the zone range of the susceptible group, and one more S.D. below covered the intermediate/indeterminate group. The new zone breakpoints would place the main population of clinical isolates in the correct susceptibility group, and even make it possible to detect strains with different degrees of reduced susceptibility in the routine test. In a follow-up quality control study in 1988 the interpretive errors for clinical isolates were eliminated for all antibiotics except doxycycline in some laboratories. Laboratory-related zone breakpoints for doxycycline calculated by the single strain regression analysis method led to correct susceptibility interpretations also in these cases.

Diffusion↗
PubMed1990

Comparison of Oxoid Signal and biphasic blood culture systems in clinical practice.

The 1-bottle Oxoid Signal blood culture system was compared with a biphasic 2-bottle system in a clinical trial. A total of 851 routine blood samples were processed in the study which was run as a multicenter study at 4 university hospitals. Microorganisms were isolated from 104 (12.2%) blood cultures by one or both methods. 75 (72%) were clinically significant isolates, 61 of them were recovered in both systems, 9 in Oxoid Signal only and 5 in the biphasic system only. 29 isolates (28%) were judged as contaminants, 6 of them were found in both systems, 18 in Oxoid Signal only and 5 in the biphasic system only. The Oxoid Signal System had many advantages although it sometimes gave false positive signals in the device. The growth of pathogens was equally good, 93% versus 88% positive cultures.

Bacteriological Techniques↗
PubMed1990

Antibiotic susceptibility of Escherichia coli isolates from inpatients with urinary tract infections in hospitals in Addis Ababa and Stockholm.

A high level of antimicrobial resistance of bacteria has been detected at the Tikur Anbessa Hospital (TAH), Addis Ababa, for many years. In contrast, at the Karolinska Hospital (KH), Stockholm, the level of resistance is low. Reported are the results of an investigation of the correlation between antibiotic usage and the antimicrobial resistance rates of Escherichia coli isolates from patients with urinary tract infections in these hospitals. At TAH the strains of E. coli isolated were considerably more resistant to all seven antibiotics tested. The level of multiresistance was 63% at TAH and 7% at KH. There were no significant differences in the total amount of antibiotics used in the two hospitals, except for antituberculosis agents. The strain biotypes and antibiograms, together with the length of patients' hospitalization before a positive urine culture was obtained, suggest that the majority of the strains from TAH were of nosocomial origin.

Cross Infection↗
PubMed1989

Septicaemia with coagulase negative staphylococci in a neonatal intensive care unit. Risk factors for infection, and antimicrobial susceptibility of the bacterial strains.

Septicaemia caused by coagulase negative staphylococci is a problem in the neonatal intensive care units (NICU). The very low birthweight (VLBW) infants are at a special high risk because of their immature host defense. In this study the potential risk factors were compared between the VLBW septicaemia patients and the VLBW infants who had not contracted septicaemia in the NICU. The factor most clearly related with septicaemia was the use of umbilical artery catheters. The strategy against neonatal septicaemia includes restriction of the use of intravascular catheters. Also enhancement of the host defense by immunoglobulin therapy is considered. The coagulase negative staphylococci were multiresistant to antibiotics. The combination of netilmicin and benzylpenicillin covered the bacteria found in septicaemia cases in the NICU, and is now the standard treatment in suspected cases. Coagulase negative staphylococci are treated with vancomycin or netilmicin.

Anti-Bacterial Agents↗
PubMed1989

Types of interpretive errors in susceptibility testing. Zone breakpoints for norfloxacin disk diffusion testing.

A total of 548 strains of the eleven most common urinary tract pathogens were investigated for possible errors in norfloxacin susceptibility tests comparing MIC determinations with disk diffusion assays. Most strains were found to be sensitive with MIC-90 values below 1.0 for the Enterobacteriaceae while the classical nalidixic acid resistant species, the gram-positive bacteria and Pseudomonas aeruginosa, were less susceptible to norfloxacin with MIC-90 above 1.0 mg/l. MIC-values close to interpretive MIC-limits were recorded for S. faecalis and S. agalactiae using the recommendations of the national Committee for Clinical Laboratory Standards (NCCLS) (susceptible, S less than or equal to 4.0) and for P. aeruginosa and S. aureus using the Swedish Reference Group for Antibiotics (SRGA) standards (S less than or equal to 1.0). Susceptibility interpretations for these species showed a lack of accuracy consistent with methodological problems of reproducibility, an error called type I. The changes in the MIC-limits required for these strains to correct the error would be S less than or equal to 4 for P. aeruginosa and S. aureus, S less than or equal to 8 for S. agalactiae and S less than or equal to 0.5 for S. faecalis. A type II error, occurring when a bacterial species shows a regression line different from the regular line, was also identified for S. saprophyticus. The use of breakpoints derived from single strains regression analysis corrected this error and also reduced the frequency of similar misinterpretations in other species. The term "species-specific MIC-limits" should be introduced along with the established concept of "species-specific interpretive zone breakpoints" to allow for the correction of type I interpretive errors. Type II errors can be corrected by using species-specific interpretive breakpoints, either issued by reference laboratories or derived by calculations from single-strain regression analysis in the individual laboratory.

Microbial Sensitivity Tests↗
PubMed1989

Species-specific interpretive breakpoints for ciprofloxacin disk diffusion susceptibility testing.

When ciprofloxacin was introduced on the Swedish market the recommended interpretive standards for disk diffusion susceptibility testing using a 10 microgram disk were: Sensitive greater than or equal to 24 mm (MIC less than or equal to 1 mg/l) and Resistant less than 18 mm (MIC greater than 4 mg/l), except for enterococci where S greater than or equal to 18 mm and R less than 14 mm were recommended. A quality control study revealed that the accuracy of the routine susceptibility testing of ciprofloxacin was low. 50% of the strains of Staphylococcus aureus and 90% of Streptococcus agalactiae strains were falsely assigned to the intermediate instead of the sensitive category, and the test missed to detect true resistance in Pseudomonas maltophilia. New species-specific breakpoints were determined by the SRA method. Separate breakpoints were required only for the pseudomonas species. Streptococcus faecalis was found to belong mainly to the intermediate group and it is suggested that these strains are not categorized as sensitive. The breakpoints that gave acceptable accuracy in routine susceptibility testing of ciprofloxacin were S greater than or equal to 20 mm, R less than 13 mm for all relevant bacteria except Pseudomonas aeruginosa for which S greater than or equal to 27 mm, R less than 18 mm is proposed, and Pseudomonas maltophilia where S greater than or equal to 30 mm, R less than 23 mm are adequate breakpoints. The 10 microgram disk gave acceptable inhibition zones for all strains with MICs within the clinically interesting MIC range.

Bacteria↗
PubMed1988

Laboratory- and species-specific interpretive breakpoints for disk diffusion tests of chloramphenicol susceptibility of Haemophilus influenzae.

A total of 601 clinical isolates of Haemophilus influenzae isolated in six different regions of Sweden were tested for chloramphenicol susceptibility by using agar dilution MIC determinations and disk diffusion tests. For seven strains MICs were 4 micrograms/ml or higher, and for one strain the MIC was 2 micrograms/ml. All eight strains produced chloramphenicol acetyltransferase. For the remaining 593 strains, MICs were less than or equal to 1 microgram/ml, and the MICs for 50% and 90% of the strains were both 0.5 microgram/ml. Disk diffusion tests carried out by using revised interpretive criteria introduced in 1984 by the Swedish Reference Group for Antibiotics correctly identified the 593 strains as susceptible and the 8 strains as resistant. Quality assessments were performed in 29 clinical microbiology laboratories. The revised criteria for chloramphenicol disk diffusion testing gave rise to false resistance results in some laboratories. The interpretive accuracy improved when the interlaboratory variation was compensated for by using adjusted breakpoints. Such revision was possible through peak correction, single-strain regression analysis, and standard curve regression analysis. Peak-corrected breakpoints improved the accuracy from an overall incidence of false-resistant isolates of 4.4% to 2.3%. Single-strain regression analysis and standard curve regression analysis provided laboratory- and species-specific breakpoints which reduced false resistance rates of 0.14% and 0%, respectively.

Chloramphenicol↗
PubMed1988

Neonatal septicemia due to group B streptococci--perinatal risk factors and outcome of subsequent pregnancies.

All cases of early onset group B streptococcal (GBS) septicemia in infants born at Karolinska Hospital 1975-1986 were reviewed. GBS-septicemia was diagnosed in 40 infants within the first five days of life. The incidence was 1.24 per 1000 births. Fifty-five percent of the infants were preterm and 48% were born more than or equal to 12 hours after rupture of membranes. Prematurity and/or prolonged rupture of membranes were present in 83% of all neonates with fatal outcome. Case fatality was 22%. Deliveries by both cesarean section (31%) and vacuum extraction (26%) were increased in the mothers when compared to an overall incidence of 14 and 12% (p less than 0.01). Twenty-four (89%) of 27 mothers had low type specific IgG antibodies against the infecting GBS-serotype. Late onset GBS-septicemia was diagnosed in only two infants during the period. Seventeen mothers went through 24 subsequent pregnancies. In 11 of those the mothers were colonized with GBS and 10 received penicillin prophylaxis during pregnancy and/or delivery. None of the infants born after prophylaxis were colonized with GBS. Two were born prematurely and all had an uneventful course; whereas one infant delivered at 26 weeks gestation of a colonized untreated mother died of GBS-septicemia. Screening of parturients at risk and selective antibiotic prophylaxis may help to prevent early onset GBS-septicemia.

Antibodies, Bacterial↗
PubMed1988

On the theory of the disk diffusion test. Evidence for a non-linear relationship between critical concentration and MIC, and its practical implications for susceptibility testing of Haemophilus influenzae.

The procedure for disk diffusion susceptibility testing has been worked out for rapidly growing non-fastidious bacteria. Using the general zone diameter breakpoints for interpretation of susceptibility, it was found that clinical isolates of H. influenzae were assigned to the wrong SIR category in fifty per cent of the strains for erythromycin, and ten per cent for doxycycline. New species- and laboratory-specific interpretive zone diameter breakpoints corresponding to the recommended MIC limits were therefore worked out. The Standard Curve regression Analysis (SCA) method used for this purpose is based on the correlation between zone size and disk content, using two reference strains with different MICs. In its original version (the Single strain Regression Analysis, SRA) only one reference strain was used. This equation was found not to be generally valid since the relationship between MIC and the critical concentration is not constant, as was originally assumed. The slope and intercept of the regression line obtained by SCA is species related, while a general regression line based on results from many different species assumes that there is the same relation between the zone size and MIC for all species. Breakpoints for erythromycin and doxycycline calculated by the SCA equation gave more accurate results in routine susceptibility testing of H. influenzae and reduced the error rate from fifty three and ten per cent to four and three per cent for the two antibiotics.

Doxycycline↗
PubMed1988

In vitro susceptibility to tetracycline and doxycycline in clinical isolates of Haemophilus influenzae.

The most common indication for the use of tetracyclines in Sweden is respiratory tract infections. Among the tetracyclines, doxycycline dominates with about 75% of the consumption. It is therefore used for routine susceptibility testing, while tetracycline is the test drug in most other countries. Six hundred strains of Haemophilus influenzae isolated from different parts of Sweden were tested for susceptibility to doxycycline and tetracycline. The results were compared with those from earlier reports on resistance rates in Sweden and other countries. The MIC50's of the strains were slightly lower for tetracycline than for doxycycline, but some strains with reduced susceptibility to tetracycline were fully susceptible to doxycycline. The level of resistance to doxycycline in H. influenzae was very low (less than 1%) and has not changed significantly over the past ten years, making doxycycline a suitable antibiotic for instance in the treatment of chronic bronchitis when H. influenzae is involved.

Adolescent↗
PubMed1987

Neonatal septicemia in Stockholm.

In a prospective study to determine the incidence and etiology of neonatal septicemia at Karolinska Hospital, Stockholm, all cases of neonatal septicemia in infants born at the hospital from 1981 to 1985 were reviewed. There were 4.0 cases of neonatal septicemia per 1,000 live births during the study period. During the five year period the incidence of septicemia tended to increase, mainly due to the increasing incidence of septicemia in infants with a birth weight below 1,500 grams. The single most common causative organism was group B streptococci with an incidence of 1.4 per 1,000 live births, Staphylococcus aureus accounting for 1.1 cases, Staphylococcus epidermidis for 0.7 cases, and gram-negative rods for only 0.4 cases per 1,000 live births. In a retrospective study of the incidence of neonatal septicemia in a non-selected patient population, all cases in the Stockholm area in 1983 were reviewed. In that year there were 17,586 live births in the area and the incidence of neonatal septicemia was 2.6 per 1,000 live births. Group B streptococci, Staphylococcus aureus, Staphylococcus epidermidis and gram-negative rods were equally common as causative agents.

Birth Weight↗
PubMed1987

The bacteriology of nosocomial infections at Tikur Anbessa Teaching Hospital, Addis Ababa.

Patients admitted to a teaching hospital in Addis Ababa were studied for nosocomial infection. Of 2506 patients, 13% developed clinical infections, with the highest rate among obstetric/gynaecologic patients (17.0%). Wound infection was the most frequent type of nosocomial infection (49%) followed by urinary tract infection (25%). Antibiotic prophylaxis was given to 43% of the patients. Gram-negative bacteria comprised 88% of all isolated strains Enterobacteriaceae; 75% of all isolates were found in over 60% of the infection, Proteus 25%, Escherichia coli 20% and Klebsiella 19%. The most widely used antibiotics were ineffective against 65 to 85% of the Gram-negative strains. Cefotaxime and gentamicin were more effective. Staphylococcus aureus isolates were also similarly resistant, against which cephalothin, lincomycin and gentamicin were the more effective ones. Over 70% of the strains were multiple resistant. The findings underscore the need for a surveillance program and infection control system to reduce the high rate of infection and to institute appropriate guidelines for the use of prophylactic and therapeutic antibiotics.

Anti-Bacterial Agents↗
PubMed1987

Increased use of erythromycin causes resistance in Haemophilus influenzae.

The use of erythromycin in Sweden has increased since 1975. An increasing prevalence of Haemophilus influenzae (H.i.) with reduced susceptibility to erythromycin has been noted in our laboratory during the years 1980 to 1985. The largest consumers of erythromycin were found to be children less than 4 years of age. Variations in resistance level of H.i. isolated from patients within this age group and variations in consumption of erythromycin were analysed for each year. The highest prevalence of resistant strains was found during spring and summer. The consumption of the antibiotic was highest during the first quarter of the year, gradually decreasing, and increasing sharply again during the fourth quarter of the year. Judging also from deviations from this pattern there seems to be an association between consumption and resistance. The different levels of resistance reported in the literature may reflect different populations of patients with different consumption of erythromycin, and different levels at different time of the year. Considering the present high level of H.i. with decreased susceptibility to erythromycin the drug is not likely to have clinical effect in H.i. infections.

Child, Preschool↗
PubMed1985

Use of the antimicrobial removal device prior to blood culture in patients on antibiotic therapy.

The efficacy of the antimicrobial removal device in facilitating isolation of bacteria from blood containing antibiotics was evaluated in a multicenter study. Blood specimens from 143 patients who had culture-proven septicemia and had been on antibiotic treatment for at least 24 hours were recultured with and without the aid of the device. Septicemia persisted in 33 of the patients and use of the device improved the isolation rates: 63% of the gram-positive bacteria and 32% of the gram-negative bacteria were isolated only with the aid of the device. Use of the device was an advantage in 10 of 13 cases where the antibiotic concentration in the bottles exceeded the MIC for the infecting microorganism but in only 5 of 19 cases where the concentration was lower than the MIC. It is concluded that the antimicrobial removal device may be useful in patients already on antibiotic treatment, but that its use is limited by the cost and the amount of work involved.

Adsorption↗