Antibiotic susceptibility of pneumococci isolated in Austria over a four-year period

Antimicrobial resistance of Streptococcus pneumoniae in Southeast Austria, 1997-2008

Antibiotic resistance in Streptococcus pneumoniae has increased worldwide but varies within geographical regions. We conducted a retrospective analysis of resistance in S. pneumoniae over a 12-year period to assess local and temporal trends in antibacterial resistance. From 1997 to 2008, a total of 1814 non-duplicate S. pneumoniae isolates were identified at the Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, Austria. Antibiotic resistance was determined by the Clinical and Laboratory Standards Institute (CLSI) disk diffusion test. For penicillin, the minimum inhibitory concentration was determined by Etest. Susceptibility was defined according to CLSI interpretive criteria. For penicillin, resistance rates were consistently low at 0.2% over the 12-year study period. An increase in resistance was remarkable for erythromycin (3.5% in 1997; 14.7% in 2008), clindamycin (1.8% in 1997; 10.6% in 2008) and tetracycline (1.8% in 2000; 11.0% in 2008). For trimethoprim/sulfamethoxazole, resistance increased slightly to 9.2% in 2008. Quinolones showed a low resistance rate of 0.2% that persisted over the whole study period. In contrast to previously published national data, resistance to penicillin was observed to remain at a remarkably low and constant level. Although international surveillance programmes have set up sustainable and interlinked data networks, our results suggest that regional surveillance may still be needed as decision support for appropriate empirical antibiotic therapy in the local health setting.

Clinical relevance of macrolide-resistant Streptococcus pneumoniae for community-acquired pneumonia

Macrolides are often the first choice for empirical treatment of community-acquired pneumonia. However, macrolide resistance among Streptococcus pneumoniae has escalated at alarming rates in North America and worldwide. Macrolide resistance among pneumococci is primarily due to genetic mutations affecting the ribosomal target site (ermAM) or active drug efflux (mefE). Prior antibiotic exposure is the major risk factor for amplification and perpetuation of resistance. Clonal spread facilitates dissemination of drug-resistant strains. Data assessing the impact of macrolide resistance on clinical outcomes are spare. Many experts believe that the clinical impact is limited. Ribosomal mutations confer high-grade resistance, whereas efflux mutations can likely be overridden in vivo. Favorable pharmacokinetics and pharmacodynamics, high concentrations at sites of infections, and additional properties of macrolides may enhance their efficacy. In this article, we discuss the prevalence of macrolide resistance among S. pneumoniae, risk factors and mechanisms responsible for resistance, therapeutic strategies, and implications for the future.

Accuracy of broth microdilution and E test methods for detecting chloramphenicol acetyl transferase mediated resistance in Streptococcus pneumoniae: Geographic variations in the prevalence of resistance in The SENTRY Antimicrobial Surveillance Program (1999)

High antimicrobial resistance rates in Streptococcus pneumoniae has caused a need for alternative therapies. Chloramphenicol is currently being reconsidered as an empiric treatment for respiratory tract infections particularly in developing countries. In this study, we assessed the ability of the reference broth microdilution and Etest (AB BIODISK, Solna, Sweden) methods to detect chloramphenicol resistance among pneumococci as compared to the chloramphenicol acetyltransferase (CAT) assay. In the 1999 SENTRY Antimicrobial Surveillance Program, 1671 S. pneumoniae strains from respiratory tract infections were collected from 49 participants located in the Americas and Europe. The rates of penicillin and macrolide non-susceptibility were 15.6-41.3 and 12.4-26.8%, respectively. All chloramphenicol-resistant strains were CAT assay positive (n = 154; 9.2% of isolates) with highest resistance rates in Europe (12.7%; range among sites, 0.0-38.5%) and the United States (10.6%; range, 0.0-25.6%). Etest MICs correlated with reference results and the current breakpoint for chloramphenicol resistance (> or = 8 microg/mL) remains valid for S. pneumoniae and Haemophilus influenzae (eight strains tested). CAT-mediated resistances dominate among chloramphenicol-resistant S. pneumoniae, and marked geographic variations in susceptibility were discovered.

Genetic diversity of the tet(M) gene in tetracycline-resistant clonal lineages of Streptococcus pneumoniae

The aim of the present study was to examine the stability and evolution of tet(M)-mediated resistance to tetracyclines among members of different clonal lineages of Streptococcus pneumoniae. Thirty-two tetracycline-resistant isolates representing three national (Spanish serotype 14, Spanish serotype 15, and Polish serotype 23F) and one international (Spanish serotype 23F) multidrug-resistant epidemic clones were all found to be tet(M) positive and tet(O), tet(K), and tet(L) negative. These isolates all carried the integrase gene, int, which is associated with the Tn1545-Tn916 family of conjugative transposons. High-resolution restriction analysis of tet(M) products identified six alleles, tet(M)1 to tet(M)6: tet(M)1 to tet(M)3 and tet(M)5 in isolates of the Spanish serotype 14 clone, tet(M)4 in both the Spanish serotype 15 and 23F clones, and tet(M)6, the most divergent allele, in the Polish 23F clone. This indicates that tet(M) variation can occur at the inter- and intraclone levels in pneumococci. Two alleles of int were identified, with int1 being found in all isolates apart from members of the international Spanish 23F clone, which carried int2. Susceptibility to tetracycline, doxycycline, and minocycline was evaluated for all isolates with or without preincubation in the presence of subinhibitory concentrations of tetracyclines. Resistance to tetracyclines was found to be inducible in isolates of all clones; however, the strongest induction was observed in the Spanish serotype 15 and 23F clones carrying tet(M)4. Tetracycline was found to be the strongest inducer of resistance, and minocycline was found to be the weakest inducer of resistance.

Epidemiological studies on drug resistance in Streptococcus pneumoniae in Hungary: an update for the 1990s

The aim of this study was to give an overview about the epidemiological features of pneumococcal resistance in Hungary in the 1990s, and to assess the clinical relevance of drug resistance in Streptococcus pneumoniae primarily in upper respiratory tract infections and the role of risk factors in the acquisition of resistant strains. In Hungary, resistance in S. pneumoniae decreased slightly in recent years, but is still highly prevalent (around 40% to penicillin) compared to the prevalence in western and northern neighboring countries. The prevalent serogroup among resistant strains is 19A, as it was several years ago. In 76 case histories studies, chronic underlying diseases associated with long hospitalization, episodes of earlier hospitalization, and antibiotic therapy were found more frequently if the patient was infected with a resistant strain than with a susceptible one, indicating that these factors promote the acquisition of drug-resistant S. pneumoniae. Resistant S. pneumoniae modified the course of infection by prolonging the duration of hospitalization, making more courses of antibiotics necessary, including parenteral drugs, as well as more invasive interventions such as myringotomy and sinus puncture. These data justify the clinical relevance of resistance, particularly in the upper respiratory tract infections.

A 1-year study of antibiotic resistance among paediatric pneumococcal isolates in 1995 from four regions of France

The main object of this study was to describe the features of antibiotic resistance in pneumococci from children in four regions of France in 1995. Despite the high prevalence (40%) of pneumococci with diminished susceptibilty to penicillin (PDSP), resistance to amoxycillin (0.8%) and cefotaxime (0.4%) was rare; 16% of pneumococci were resistant to penicillin G (PRP, MIC > 1 mg/l). PDSP showed the expected resistance to macrolides (67%) and cotrimoxazole (57%) and were predominantly serotypes 23F, 14, 9 and 6. This study by the Regional Pneumococcal Observatories confirms the high prevalence and the main characteristics of antibiotic resistance among pneumococci isolated from children. Nevertheless, the resistance to all antibiotics was lower than that found in French multicentre, nationwide surveys, possibly because of differences in the mode of strain collection and geographic origin.

Prevalence of mefE, erm and tet(M) genes in Streptococcus pneumoniae strains from Central Italy

One hundred and seventy-three Streptococcus pneumoniae strains isolated from surveillance studies conducted in daycare centres were studied. The mefE, erm and tet(M) genes were detected in 16.2, 45.1 and 47.4% of isolates respectively. Agreement between PCR results and antibiotic susceptibility patterns was 100%. Macrolide resistance was due to the presence of erm in 73.6% of strains and to the presence of mefE in the remaining 26.4%. All tetracycline resistant strains carried the tet(M) gene. erm was associated with tet(M) in 98.7% of strains, whereas no isolate carrying mefE carried tet(M). A significant association was found between mefE and serogroup 6 (P < 0.0005) and between erm and tet(M) and serogroup 19 (P < 0.00001).

Decreased susceptibility of Streptococcus pneumoniae to fluoroquinolones in Canada. Canadian Bacterial Surveillance Network

BACKGROUND

Fluoroquinolones are now recommended for the treatment of respiratory tract infections due to Streptococcus pneumoniae, particularly when the isolates are resistant to beta-lactam antibiotics. Although pneumococci with reduced susceptibility to fluoroquinolones have been identified, their prevalence has not been determined in a defined population.

METHODS

We performed susceptibility testing on 7551 isolates of S. pneumoniae obtained from surveillance in Canada in 1988 and from 1993 to 1998. Pneumococci with reduced susceptibility to fluoroquinolones (defined as a minimal inhibitory concentration of ciprofloxacin of at least 4 microg per milliliter) were further characterized. We also examined antibiotic prescriptions dispensed in Canadian retail pharmacies.

RESULTS

Between 1988 and 1997, fluoroquinolone prescriptions increased from 0.8 to 5.5 per 100 persons per year. The prevalence of pneumococci with reduced susceptibility to fluoroquinolones increased from 0 percent in 1993 to 1.7 percent in 1997 and 1998 (P=0.01). Among adults, the prevalence increased from 1.5 percent in 1993 and 1994 combined to 2.9 percent in 1997 and 1998 combined. The prevalence was higher in isolates from older patients (2.6 percent among those 65 years of age or older vs. 1.0 percent among those 15 to 64 years of age, P<0.001) and among those from Ontario (1.5 percent, vs. 0.4 percent among those from the rest of Canada; P< 0.001). Fluoroquinolone use was greatest among the elderly and in Ontario. The 75 isolates (17 serotypes) of pneumococci with reduced susceptibility to fluoroquinolones were submitted by 40 laboratories in eight provinces. Reduced susceptibility to fluoroquinolones was associated with resistance to penicillin.

CONCLUSIONS

The prevalence of pneumococci with reduced susceptibility to fluoroquinolones is increasing in Canada, probably as a result of selective pressure from the increased use of fluoroquinolones.

Gradual increase in the minimum inhibitory concentration of penicillin among both susceptible and resistant Streptococcus pneumoniae isolates from Greek children during 1995-1997

A total of 140 non-replicate Streptococcus pneumoniae community isolates from Greek children collected during the period 1995-1997 were studied. Combined intermediate and high penicillin resistance rates were 23% in 1995, 29% in 1996, and 27% in 1997. The proportion of highly resistant isolates steadily increased from 2% in 1995 to 12% in 1997. There was no significant difference in penicillin resistance rates among colonizing and infecting isolates (23 and 27%, respectively). Over the study period, a clear shift towards higher penicillin MIC was observed among both the susceptible and resistant groups. Thus, penicillin resistance rates were equally high among colonizing and infecting isolates and resistance levels appeared to be gradually increasing throughout the entire S. pneumoniae population.