Helinä Järvinen

Resistance to Erythromycin in Group A Streptococci

BACKGROUND The use of erythromycin in Finland nearly tripled from 1979 to 1989. In 1988, we observed an unusually high frequency of resistance to erythromycin in group A streptococci in one geographic region. Because routine testing does not detect the sensitivity of these organisms to antibiotics, we initiated a national study to evaluate the extent of this resistance. METHODS We studied 272 isolates of group A streptococci obtained from blood cultures from 1988 through 1990. In 1990 we collected from six regional laboratories 3087 consecutive isolates from throat swabs and 1349 isolates from pus samples. Resistance was indicated by growth on blood agar containing 2 micrograms of erythromycin per milliliter after incubation in 5 percent carbon dioxide. We also evaluated the clinical importance of erythromycin resistance in a retrospective study of consecutive patients with pharyngitis. RESULTS The frequency of resistance to erythromycin in group A streptococci from blood cultures increased from 4 percent in 1988 to 24 percent in 1990. From January to December 1990, the frequency of resistance in isolates from throat swabs increased from 7 percent to 20 percent, and resistance in isolates from pus increased from 11 percent to 31 percent. In four communities within 50 km of each other, the frequency of erythromycin resistance ranged from 2 to 5 percent to 26 to 44 percent. Several distinct DNA restriction profiles and serotypes were found among resistant isolates from the same area, suggesting a multiclonal origin. The treatment of pharyngitis with erythromycin failed in 9 of 19 patients infected with erythromycin-resistant group A streptococci, as compared with 1 of 26 patients with erythromycin-susceptible isolates (47 percent vs. 4 percent, P = 0.008). CONCLUSIONS In Finland since 1988 there has been a rapid and substantial increase in resistance to erythromycin in group A streptococci. The extent of this resistance is particularly serious since there are only a few alternative antibiotics available for peroral treatment of group A streptococcal infections.

In vitro susceptibility of Streptococcus mutans to chlorhexidine and six other antimicrobial agents.

The susceptibility of Streptococcus mutans to chlorhexidine and to six commonly used, systemic antibacterial agents (amoxicillin, cefuroxime, penicillin, sulfamethoxazole-trimethoprim, tetracycline, and erythromycin) was studied for 424 clinical isolates from 116 children and students. The MIC of chlorhexidine for all isolates was < or = 1 micrograms/ml. No resistance to the other antimicrobial agents was detected. Although widely exposed to various antimicrobial agents, S. mutans has remained susceptible to common antimicrobial agents, most importantly to chlorhexidine.

Antimicrobial and mercury resistance in aerobic gram-negative bacilli in fecal flora among persons with and without dental amalgam fillings.

Antimicrobial resistance is more widespread than can be accounted for as being a consequence of the selection pressure caused by the use of antibiotics alone. In this study, we tested the hypothesis that a high mercury content in feces might select for mercury-resistant bacteria and thus for antimicrobial resistance linked to mercury resistance. Three subject groups with different exposures to dental amalgam fillings were compared. None of the subjects had taken antimicrobial agents during the three preceding months or longer. The group exposed to dental amalgam (n = 92) had 13 times more mercury in feces than the group that had never been exposed to amalgam (n = 43) and the group whose amalgam fillings had been removed (n = 56). No significant differences in either mercury resistance or antibiotic resistance in the fecal aerobic gram-negative flora of these subject groups were seen. The following antimicrobial resistance frequencies were detected with a replica plating method: > or = 1% resistance was seen in 40% of the subjects for ampicillin, 14% of the subjects for cefuroxime, 6% of the subjects for nalidixic acid, 14% of the subjects for trimethoprim, 19% of the subjects for sulfamethoxazole, and 25% of the subjects for tetracycline. The amount of mercury in feces derived from amalgam was not selective for any resistance factors in aerobic gram-negative bacteria, but antimicrobial resistance was widespread even among healthy subjects with no recent exposure to antibiotics.

Resistance to Mercury and Antimicrobial Agents in Streptococcus mutans Isolates from Human Subjects in Relation to Exposure to Dental Amalgam Fillings

ABSTRACT Resistance to cefuroxime, penicillin, tetracycline, and mercury is reported for 839 Streptococcus mutans isolates from 209 human study subjects. The MICs of these drugs did not differ for isolates from one dental amalgam group and two nonamalgam subsets: a group with no known exposure to amalgam and a group whose members had their amalgam fillings removed.

Effect of prophylactic antibiotics on antimicrobial resistance of viridans streptococci in the normal flora of cataract surgery patients

Purpose: To evaluate the effect of prophylactic treatment including vancomycin in the irrigating solution and topical chloramphenicol on antimicrobial resistance in viridans‐group streptococci in the normal flora of patients having cataract surgery. Setting: Department of Ophthalmology, Turku University Central Hospital and Antimicrobial Research Laboratory, National Public Health Institute, Turku, Finland. Methods: Minimal inhibitory concentrations (MICs) of 15 antimicrobials were determined for 529 viridans streptococci isolated from throat, nasopharyngeal, and conjunctival swabs of 23 patients on 4 sampling occasions: before cataract surgery and 1 day, 1 month, and 3 months after surgery. Resistance mechanisms of erythromycin‐resistant isolates were studied by the double‐disk test and polymerase chain reaction of resistance genes. Results: No statistically significant changes occurred in the proportions of isolates with elevated MICs between different sampling occasions. Resistance to vancomycin or chloramphenicol was not found. Resistance to tetracycline, erythromycin, penicillin, quinupristin–dalfopristin, clindamycin, levofloxacin, and moxifloxacin was found on different sampling occasions in 27.9% to 38.7%, 13.1% to 21.8%, 11.5% to 19.4%, 8.9% to 16.9%, 2.3% to 5.6%, 0% to 2.4%, and 0% to 2.2% of the isolates, respectively. Of the erythromycin‐resistant isolates, 80.8% had the M phenotype and mefA gene and 19.2% has the macrolide–lincosamide–streptogramin B phenotype and ermB gene. Conclusions: Development of resistance of viridans streptococci in the normal flora to vancomycin and chloramphenicol during prophylactic use with uneventful cataract surgery is unlikely; the effect on resistance patterns of other antimicrobials is minor. Routine use of prophylactic vancomycin is discouraged, however, because of the lack of scientific proof of its efficacy in preventing postoperative endophthalmitis.

Evaluation of a New Cellulose Sponge-Tipped Swab for Microbiological Sampling: a Laboratory and Clinical Investigation

ABSTRACT A new type of swab (Cellswab; Cellomeda, Turku, Finland), utilizing a highly absorbent cellulose viscose sponge material, was compared to some traditional swabs. The survival of 14 aerobic and 10 anaerobic and microaerophilic bacterial species in the Cellswab, two commercial swab transport systems (Copan, Brescia, Italy, and Orion Diagnostica, Espoo, Finland), and one Dacron swab (Technical Service Consultants Ltd. [TSC], Heywood, United Kingdom) was evaluated. Bacteria were suspended in broth, into which the swabs were dipped. The Cellswab absorbed 1.3 times more fluid and released 3.5 times more fluid upon plating than the other swabs. Aerobic bacteria were stored in dry tubes, the others in transport medium, at 4°C and room temperature (RT), for up to 14 days. Swab samples were transferred to plates at 0, 1, 2, 4, 7, and 14 days. For 10 strains the Cellswab yielded ≥10% of the original CFU for longer than all the other swabs. In the clinical study, the ability of the Cellswab to detect beta-hemolytic streptococci from throat samples (n = 995) was compared to that of the TSC Dacron swab. The swabs performed equally, both when their samples were transferred to plates immediately and after storage for 1 day at 4°C or RT. The changes in normal microbiota after storage were also similar. The Cellswab was found to perform at least as well as ordinary swabs. It was better at storing fastidious strains, and at keeping bacteria viable for long storage times; it might well be a useful replacement or complement to ordinary swabs.

Infrequent isolation of multiresistant Acinetobacter baumannii from the staff tending a colonized patient with severe burns

A patient with severe burns who was colonized by multiresistant Acinetobacter baumannii was cared for in contact isolation by staff intensively trained on hospital hygiene. Of the 1,907 postexposure cultures from the staff and 425 environmental samples, only 0.7% and 4%, respectively, yielded this microorganism. These data show that strict hygienic measures may limit staff colonization and contamination of the environment byA baumannii.

Antimicrobial resistance in Neisseria gonorrhoeae in Finland, 1976 to 1995

Background and Objectives: The worldwide increase in antimicrobial resistance in Neisseria gonorrhoeae prompted the authors to evaluate the status and course of resistance in gonococci in Finland. Goals: The minimal inhibitory concentrations (MIC) of penicillin, tetracycline, spectinomycin, ciprofloxacin, ceftriaxone, and cefixime were tested for 337 consecutive clinicalN. gonorrhoeae isolates collected in 19 Finnish microbiology laboratories in 1993. Study Design: The results were compared with data obtained in three Finnish laboratories in 1986 and contrasted with the development of the incidence of gonorrhea and the prevalence of penicillinase‐producing N. gonorrhoeae (PPNG) in Finland, 1976 to 1995. The number of strains with an elevated MIC to ciprofloxacin was assessed by questionnaire. Results: A decrease, from more than 50% in 1986 to 20% in 1993, of strains susceptible to penicillin and tetracycline was observed. The prevalence of PPNG increased from 0% (1976) to 5.7% (1995). In 1995, two strains with a ciprofloxacin MIC of ≥ 32 μg/ml were reported. No resistance to ceftriaxone or spectinomycin was detected. Conclusions: In spite of the rarity of gonorrhea and the avail‐ability of efficient antimicrobials in Finland, monitoring of the antimicrobial resistance of N. gonorrhoeae remains important.

Multiresistance in Staphylococcus spp. blood isolates in Finland with special reference to the distribution of the mecA gene among the Staphylococcus epidermidis isolates

A total of 570 Staphylococcus spp. blood isolates collected in Finland in 1991 were tested for susceptibility to oxacillin and 19 additional antimicrobial agents. The Staphylococcus epidermidis isolates were also analyzed for the presence of the mecA gene by the polymerase chain reaction (PCR). Of the 238 S. epidermidis, 137 (58%) were in vitro identified as methicillin‐resistant and 5 (2%) exhibited oxacillin MICs between 1 and 3 μg/ml. All these isolates were positive for the mecA gene in PCR as an indication of genetic resistance to methicillin, while none of the remaining 96 S. epidermidis isolates (oxacillin MICs ≥0.25 μg/ml) was positive. Multiresistance was observed in 123 (87%) of the 142 mecA‐positive S. epidermidis. Of the 332 Staphylococcus aureus isolates, only one (0.3%) was phenotypically resistant to methicillin; the strain was also resistant to three other unrelated classes of antimicrobials. True methicillin resistance of this strain was manifested by the presence of the mecA gene in PCR. Based on these results, multiresistance was still extremely rare among the S. aureus in our country, whereas among the S. epidermidis as many as half of the blood isolates in central hospitals were multiresistant.

Testing of Methicillin Resistance by in vitro Susceptibility and the Presence of the mecA Gene in Clinical Staphylococcus aureus Isolates in Finland

A total of 140 epidemiologically unrelated Staphylococcus aureus strains collected in Finland between 1983 and 1994 were sent to the reference laboratory with verified or suspected methicillin resistance. These strains and 37 S. aureus strains previously identified as methicillin-susceptible were retested using 5 different susceptibility test methods including agar screening, disc diffusion, growth around methicillin (25 micrograms) test strips and minimal inhibitory concentration (MIC) determinations by an agar dilution method and E-test. The isolates were also analyzed for the presence of the mecA gene by the polymerase chain reaction (PCR). Based on in vitro susceptibility, 69 strains were identified as methicillin-resistant and were positive for the mecA gene in PCR, while 84 strains were methicillin-susceptible and negative for this gene. Susceptibility testing gave conflicting results for 24 (14%) strains. When the tests were repeated in triplicate for each isolate, discrepant results were still achieved with 18 of the 24 strains in at least 2 different tests. Thus, based on in vitro susceptibility, these strains could not be definitely classified as resistant or susceptible to methicillin. Yet 7 of them were positive for the mecA gene as an indication of genetic resistance to methicillin. Corroborating earlier studies, these results illustrate the difficulty of detecting methicillin resistance/susceptibility based only on susceptibility testing and underscore the importance of confirming methicillin resistance in S. aureus in specialized laboratories.