Haemophilus influenzae, Pneumococci, group A streptococci and Staphylococcus aureus: sensitivity of outpatient strains to commonly prescribed antibiotics

Antimicrobial susceptibility of bacterial isolates in south Sweden including a 13-year follow-up study of some respiratory tract pathogens

The antibiotic susceptibility of consecutive isolates of the upper respiratory tract pathogens Streptococcus pyogenes, Streptococcus pneumoniae, Haemophilus influenzae, Branhamella catarrhalis, and Staphylococcus aureus, (100 strains of each species collected each year during March through April 1985, 1988 and 1992) to penicillin V, amoxycillin, cefaclor, cefuroxime, doxycycline, erythromycin, and cotrimoxazole was investigated by MIC determination on PDM and PDM II agar. The MICs of the upper respiratory isolates from 1992 supplemented with 100 isolates each of Escherichia coli, Klebsiella spp., Enterobacter cloacae, Proteus mirabilis and Staphylococcus saprophyticus collected during 1992 were determined against the above antibiotics plus cefadroxil, cefpodoxime, roxithromycin, ciprofloxacin, ofloxacin, and BAY Y 3118. Beta-lactamase production was found in 10% of H. influenzae and 80-90% of S. aureus and B. catarrhalis in 1992. Among H. influenzae isolates, non-beta-lactamase-induced resistance to all beta-lactam antibiotics was first detected in 1988 and amounted to 3% of isolates in 1992. Decreased susceptibility of S. preumoniae to penicillin (> or = 0.12 mg/l), co-trimoxazole > or = 32 mg/l, doxycycline (> or = 2 ml/l) and erythromycin (> or = 1 mg/l) was detected in 11%, 7%, and 8%, respectively, in 1992, which is significantly higher than in previous years at the same laboratory. Decreased susceptibility of S. pyogenes to doxycycline and erythromycin was detected in 11% and 9% in 1992. The two most recently developed antibiotics, cefpodoxime and BAY Y 3118, showed high antibacterial activity. The study emphasizes the need to screen for resistance mechanisms such as beta-lactamase production and lowered penicillin affinity.

A one-year study of streptococcal infections and their complications among Ethiopian children

Post-streptococcal complications are known to be common among Ethiopian children. Little is known, however, about the epidemiology of beta-haemolytic streptococci in Ethiopia. A total of 816 children were studied during a one-year period: 24 cases of acute rheumatic fever (ARF), 44 chronic rheumatic heart disease (CRHD), 44 acute post streptococcal glomerulonephritis (APSGN), 143 tonsillitis, 55 impetigo, and 506 were apparently healthy children. Both ARF and APSGN occurred throughout the year with two peaks during the rainy and cold seasons. The female:male ratio among ARF patients was 1.4:1 and 1:1.9 among APSGN. The monthly carrier rate of beta-haemolytic streptococci group A varied from 7.5-39%, average being 17%. T type 2 was the most frequent serotype. Marked seasonal fluctuations were noted in the distribution of serogroups among apparently healthy children. Beta-haemolytic streptococci group A dominated during the hot and humid months of February-May. Strains were susceptible to commonly used antibiotics, except for tetracycline.

Outbreaks of infections with erythromycin-resistant group A streptococci in child day care centres

Erythromycin-resistant group A streptococci (ERGAS) are considered rare in Sweden. In the county of Halland (240,000 inhabitants) in southern Sweden, we had 294 isolates of ERGAS between January 1984 and June 1985. Almost all strains were of T-type 12 and only resistant to erythromycin (MIC values approximately 8 g/l). Seven child day care centres (DCC) were involved in the outbreaks and on average 49% of all children were infected in each outbreak. Employees were seldom infected (8%), but parents and siblings more often (23% and 36%). One course of phenoxymethylpenicillin succeeded in eradicating ERGAS from 75% of those infected. The ERGAS strains are now established in southern Sweden and account for about 2% of all group A streptococcal infections in the county of Halland.

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.

The regression line for erythromycin is not valid for beta-hemolytic streptococci group A

The antibacterial activity of erythromycin to 50 beta-hemolytic streptococci group A was assessed using disc diffusion and MIC techniques on solid media at pHs 6, 7 and 8 in CO2, aerobic and anaerobic atmospheres. The majority of the strains were only intermediately sensitive to erythromycin according to the disc diffusion method, whereas they were sensitive as judged by the MIC determination. This demonstrates that the regression line is invalid for the drug-bug combination of erythromycin and beta-hemolytic streptococci group A. It was also shown that the activity of erythromycin is reduced at a lower pH and in CO2 incubation.

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.

Effects of carbon dioxide upon the in vitro activity of erythromycin

The in vitro activity of erythromycin against clinical isolates of Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Streptococcus pyogenes and Haemophilus influenzae was examined by agar dilution and agar diffusion methods. The plates were incubated in air alone or in 8% CO2 and air. The minimal inhibitory concentrations (MICs) measured in air alone were lower for most of the isolates, compared to those found in 8% CO2. The greatest differences in MIC values were found for H. influenzae; the MIC 50% was 0.5 mg/l in air and 4 mg/l in 8% CO2. Sensitivity testing by the agar diffusion method (ICS) showed considerable differences between results obtained in air and in 8% CO2; the inhibition zones were generally smaller in CO2. The most marked reduction in zone sizes after incubation in 8% CO2 was seen with the H. influenzae isolates; 15 out of 43 isolates moved from the "sensitive" to "moderately sensitive" group. Sensitivity determination of aerobic bacteria for erythromycin should be performed in air alone in the routine laboratory.

Penetration of penicillins into cardiac valves and auricles of patients undergoing open-heart surgery

Prophylactic use of antibiotics in open-heart surgery for insertion of prosthetic valves is common, because of the serious consequences of postoperative staphylococcal infections, most notably prosthetic valve endocarditis. To ensure effective antibiotic cover during surgery, the penetration of cloxacillin and benzylpenicillin into the heart muscle and valves was studied intraoperatively. Both antibiotics were given intravenously (respective initial doses 2 g and 6 g) at induction of anesthesia to ten patients undergoing replacement of aortic or mitral valve, and the same doses were repeated after 4 hours. Serial serum samples and tissue samples from the right atrial auricle and the excised heart valve were analyzed for antibiotic concentrations. The mean serum concentrations of cloxacillin were 204 +/- 93 mg/l 10 min after the initial dose and less than or equal to 26 mg/l 30 min before the second dose. The corresponding values for benzylpenicillin were 323 +/- 145 and 43 +/- 24 mg/l. The cloxacillin concentrations in the auricle just before the start of extracorporeal circulation ranged from 4.5 to 80 mg/kg and (later) in the excised heart valves they were 8.5 to 45 mg/kg. The benzylpenicillin range was 16 to 153 mg/kg in auricle and 13 to 87 mg/kg in valve tissue. The authors conclude that the employed doses of the penicillins are adequate cover against the staphylococci which may be implicated in postoperative infections.

The effect of erythromycin on the nasopharyngeal pathogens in children with secretory otitis media

Seventy-five children not older than 11 years, with secretory otitis media of more than 3 months' duration were randomly divided into two groups prior to myringotomy. One group remained untreated, whereas the other received erythromycin ethylsuccinate (Abboticin) in standard dosage for the last 10 days before surgery. Nasopharyngeal cultures were taken under general anaesthesia, which ensured an uniform mode of sampling. In the erythromycin-treated group the occurrence of Streptococcus pneumoniae (3%) and Branhamella catarrhalis (0%) was significantly lower than in the control group (35% and 32%, respectively); and the frequency of cultures with no pathogen was significantly higher in the treated group. The occurrence of Haemophilus influenzae remained essentially unchanged.

Frequency and type distribution of pneumococcal strains in the Stockholm region with resistance or reduced susceptibility to antibiotics

Of 191 consecutive clinical isolates of Streptococcus pneumoniae tested for antibiotic susceptibility with the agar dilution technique 87% were fully sensitive to all of 11 antimicrobial agents examined. 90% of the strains were inhibited by 0.016 micrograms/ml of benzylpenicillin, by 0.032 micrograms/ml of ampicillin, cefuroxime, erythromycin, clindamycin or rifampicin, by 0.13 micrograms/ml of cephalothin, oxacillin or doxycycline, by 4.0 micrograms/ml of chloramphenicol and by 8.0 micrograms/ml of cotrimoxazole. 18 strains exhibited a reduced susceptibility to one (11 strains) or more (7 strains) of erythromycin, doxycycline, chloramphenicol and cotrimoxazole. One of these strains also showed a reduced susceptibility to all 5 examined beta-lactam antibiotics, as did another 4 strains. Two of these 5 strains were isolated from small children recently adopted from 2 Asian countries. Cotrimoxazole-resistant strains were significantly more often isolated from children 1 yr of age or less than from older patients. All strains were fully sensitive to clindamycin and rifampicin. The existence of pneumococcal strains with resistance or reduced susceptibility to antibiotics commonly used for treatment of pneumococcal infections is important to bear in mind and necessitates antibiotic susceptibility testing of strains isolated from patients with severe infections.

Activity of common antibiotics against Branhamella catarrhalis, Haemophilus influenzae, pneumococci, group A streptococci and Staphylococcus aureus in 1983

The activity of phenoxymethylpenicillin (PcV), ampicillin, cefaclor, cefuroxime, chloramphenicol, co trimoxazole, doxycycline and erythromycin against clinical isolates of Branhamella catarrhalis, Haemophilus influenzae, pneumococci, group A streptococci and Staphylococcus aureus in 1983 was investigated with the MIC-method (plate-dilution technique). Forty-six percent of B. catarrhalis, 2% of H. influenzae and 78% of S. aureus were beta-lactamase producing and had high MIC-values for penicillin and ampicillin. Thus MIC for 90% of all strains of B. catarrhalis was 32 mg/l and 8 mg/l for penicillin and ampicillin while MIC for 90% of non beta-lactamase producing Branhamella strains was 2 mg/l and 0.25 mg/l respectively. This indicates a high susceptibility of penicillins to the action of Branhamella beta-lactamase. Almost all strains of B. catarrhalis, pneumococci, group A streptococci and S. aureus were inhibited at low concentrations of erythromycin. However, 4 mg/l was required to inhibit 90% of H. influenzae. Co-trimoxazole and doxycycline had good activity against all B. catarrhalis and H. influenzae strains while a few pneumococci, streptococci and staphylococci had intermediate sensitivity or were resistant. Essentially all strains were sensitive to cefuroxime and chloramphenicol.

Patterns of antimicrobial therapy for pediatric patients

The pattern of antimicrobial prescribing for outpatients and inpatients in a Swedish pediatric department was evaluated in 1975 and 1982. The changes in the pattern during these 7 yr were small and, with regard to outpatients, very similar to those in the whole of Sweden. In these children phenoxymethylpenicillin (penicillin V) was the predominant antimicrobial (approximately 70%), followed by erythromycin and medium wide-spectrum penicillins (ampicillin/amoxycillin). Prescriptions for erythromycin in outpatients increased from 8 to 16%. The corresponding figures for Sweden as a whole were from 13 to 20%. This increase might partly be explained by the higher frequency of pertussis in Sweden in the last few years, but it is probably also a manifestation of an insufficiently motivated widening of the range of indications for erythromycin. A comparison between the prescribing patterns in Sweden and North America showed an obvious difference. In the USA the medium wide-spectrum penicillins are more used than penicillin V. This difference is discussed and found to be probably due to a real difference in antimicrobial policy. Penicillin V and G also dominated the inpatient prescriptions (51% in 1975 and 42% in 1982), which also differed from some North American hospitals.

Antibiotic susceptibility pattern and capsular types of Haemophilus influenzae recovered from clinical specimens in northern Norway

One hundred and nine strains of Haemophilus influenzae recovered from clinical specimens were examined for antibiotic sensitivity pattern and capsular types. All strains from blood cultures, cerebrospinal fluid and a joint aspirate were type b whereas most of the isolates were acapsular when recovered from other specimens viz. wound secretions (67%), maxillary sinus (75%), lower resp tract (86%), nasal cavity (90%). Out of the 109 strains 88 (81%) were non-typable, and 3.6% were beta-lactamase-producing, two of which were type e, one was type b and one was acapsular. Three beta-lactamase-producing strains were isolated from specimens from the respiratory tract and one from blood cultures. Beta-lactamase-producing strains including one chloramphenicol-resistant strain harboured similar plasmids, as judged by agarose gel electrophoresis. The strains showed quite a uniform sensitivity to antibacterial agents with the exception of sulphonamides to which the capsular strains, particularly type b strains, were less susceptible.