Relationship between antibiotic resistance in Streptococcus pneumoniae and that in Haemophilus influenzae: evidence for common selective pressure

Cotrimoxazole resistance of Streptococcus pneumoniae and commensal streptococci from Kampala, Uganda

Trimethoprim sulfamethoxazole (cotrimoxazole, CTX) is used frequently as part of standard medical care for people living with HIV/AIDS in Africa. The mechanisms of resistance to sulfonamides and trimethoprim in commensal streptococci from Uganda were determined and compared to S. pneumoniae. Commensal streptococci showing high-level resistance to cotrimoxazole were cultured and analysed for species identity and polymorphisms in the genes coding for dihydropteroate synthase (DHPS) and dihydrofolate reductase (DHFR). Seven isolates of S. pneumoniae from blood and cerebrospinal fluid (CSF) were similarly examined. There was considerable polymorphism in both DHPS and DHFR. In DHFR, the mutations E20D and I100L were present in all sequenced isolates. Other mutations such as L135F, and different substitutions in D92, were frequent. The most common DHPS variants had 2 serine residues added after amino acid 60, or arginine and proline added after amino acid 59. In addition, 3 new insertions/substitutions were found. There were no obvious differences between the mutation patterns in S. pneumoniae and commensal streptococci, suggesting that the chromosomal mutations have been spread by transformational interchanges of DNA among related organisms.

Geographical and ecological analysis of resistance, coresistance, and coupled resistance to antimicrobials in respiratory pathogenic bacteria in Spain

A multicenter susceptibility surveillance (the S.A.U.C.E. project) including 2,721 Streptococcus pneumoniae, 3,174 Streptococcus pyogenes, and 2,645 Haemophilus influenzae consecutive isolates was carried out in 25 hospitals all over Spain from November 2001 to October 2002 to evaluate the current epidemiology of resistance of the main bacteria involved in community-acquired respiratory tract infections. Susceptibility testing was performed in a single centralized laboratory by a broth microdilution method. The prevalence of resistant S. pneumoniae strains was 0.4% for cefotaxime, 4.4% for amoxicillin and amoxicillin-clavulanic acid, 25.6% for cefuroxime-axetil, 34.5% for erythromycin, clarithromycin, and azithromycin, and 36.0% for cefaclor. Phenotypes of resistance to erythromycin were MLS(B) (macrolide-lincosamide-streptogramin B) in 89.9% (gene ermB) and M (macrolide) in 9.7% of cases (gene mefA). No strain harbored both genes simultaneously. Serotypes 19, 6, 23, 14, and 3 were the most prevalent, accounting for 54.6% of the total isolates. Resistance to macrolides seems to be the most alarming point, since among penicillin-susceptible isolates it reached 15.1% compared to 55.8% among penicillin-resistant strains. Geographically, a number of regions had rates of erythromycin resistance above 40% (even higher in children). Resistance to erythromycin was also high in S. pyogenes isolates: mean regional 33.2%, beta-lactamase-producing H. influenzae were 20%, whereas 4.4% had a beta-lactamase-negative, ampicillin-resistant phenotype. We highlight the importance of different geographical frequencies of coresistance (associations of resistance to different drugs within the same species) and coupled resistance (association of resistance between different species) probably resulting from different local coselective events.

Transposon mutagenesis identifies genes which control antimicrobial drug tolerance in stationary-phaseEscherichia coli

Tolerance to antimicrobial agents is a universal phenomenon in bacteria which are no longer multiplying or whose growth rate slows. Since slowly multiplying bacteria occur in clinical infections, extended periods of antimicrobial chemotherapy are needed to eradicate these organisms and to achieve cure. In this study, the molecular basis of antibiotic tolerance was investigated using transposon mutagenesis. We screened 5000 Escherichia coli Tn10Cam mutants for reduction of kanamycin tolerance in late stationary phase and found that 4935 mutants were able to grow to late stationary phase. Reduced tolerance was observed in nine mutants which became sensitive to killing by kanamycin. The mutant KS639 was the most sensitive one to kanamycin, and its genome was disrupted in an intergenic region which lies between aldB and yiaW open reading frames. This mutant showed increased sensitivity not only to kanamycin but also to gentamicin, ciprofloxacin and rifampicin. Reduced tolerance of KS639 to kanamycin was also observed in a murine thigh infection model. P1 transduction to the wild type strains confirmed that the intergenic region was responsible for the tolerance of the bacterium to antibiotics. Using PCR-directed one-step gene replacement, we inactivated the genes aldB, yiaW and yiaV. We also deleted the intergenic region. There was no difference in kanamycin tolerance between each mutant (DeltaaldB, DeltayiaW and DeltayiaV) and the parental strain. But the mutant lacking the intergenic region showed reduced tolerance to kanamycin. These data suggest that the intergenic region between aldB and yiaW genes may be involved in tolerance to antimicrobial agents in E. coli. Furthermore, they show that it is important in murine infection during antibiotic treatment and lead to a faster kill of the mutant bacteria.

The activity of levofloxacin and other antimicrobials against clinical isolates of Streptococcus pneumoniae collected worldwide during 1999-2002

Streptococcus pneumoniae is the most important causative bacterial pathogen in respiratory infections. Globally, increasing levels of resistant strains highlight the need for continued surveillance programs to guide antibiotic choice. The current study compared susceptibility results of 4,788 strains of S. pneumoniae collected during 2001-2002 to susceptibility results from 3,884 strains collected from the same hospitals during 1999-2000. Participant centers were dispersed throughout five regions. By region, the prevalence of penicillin-resistant S. pneumoniae and percentage change from the previous 1999-2000 study was Mexico (26.0%, 12.5%), Brazil (7.9%; 5.5%), Asia (China, Hong Kong, South Korea, Thailand) (44.1%; 0.8%), Europe (France, Germany, Italy, Spain, UK) (11.1%; -0.6%) and South Africa (7.9; -1.8%). Multidrug-resistant (MDR) strains of S. pneumoniae were most frequently isolated from Asia (36.3%) compared with approximately 5% in the other four regions. Increases in the incidence of MDR isolates in Mexico (13.5%), Brazil (1.7%) and Asia (6.1%) were reported with no increases in MDR in South Africa and Europe. Levofloxacin resistance was rarely associated with MDR phenotypes. Levofloxacin maintained an MIC(90) of 1 microg/ml against the isolates collected from all five regions with no change during the study periods, despite differences in levofloxacin resistance rates between regions or nations (0%-3.2%). The prevalence of levofloxacin resistance (MIC > or =8 microg/ml) increased only slightly over the study period in Europe (0.3%-0.7%) and in Asia (3.0-3.2%), but little or no change was seen in Mexico (3.8%-0%) or Brazil or South Africa, where no levofloxacin resistant isolates were detected in either study period.

Susceptibility trends of haemophilus influenzae and Moraxella catarrhalis against orally administered antimicrobial agents: five-year report from the SENTRY Antimicrobial Surveillance Program

The assessment of orally administered antimicrobial susceptibilities of common pathogens that cause community-acquired respiratory tract infections (CARTI) has become exceedingly important due to the number of office visits for this indication. Numerous local, regional and global studies have documented the susceptibilities of Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis, the most common CARTI pathogens. SENTRY Antimicrobial Surveillance Program sites in North and Latin America, and Europe were requested to send a combined total of 100 isolates of these pathogens to the local monitor for reference broth microdilution testing (1997-2001). This study compared the susceptibility profiles of H. influenzae and M. catarrhalis isolates (13,370 strains) from the three geographic regions over a five year period. beta-lactamase mediated ampicillin resistance among H. influenzae was highest among North American isolates (27.9%) compared to Latin America and Europe (16.2 to 16.3%), although it was noted that during the five year study period, ampicillin resistance was steadily increasing in the latter two regions. Cefprozil (84.3% susceptible) and clarithromycin (81.1% susceptible) were also less active against North American H. influenzae isolates. Latin American isolates were much less susceptible to trimethoprim/sulfamethoxazole (T/S; 59.3%) compared to the other regions (75.8 to 78.6%). M. catarrhalis isolates were also significantly less susceptible to T/S in Latin America (10.5% resistance). The production of beta-lactamase enzymes among the M. catarrhalis isolates exceeded >95% in all three regions during the five year period. The fluoroquinolones (FQ) remained very active against these two respiratory pathogens with rare isolates with elevated FQ MIC results. It is apparent from this investigation that many commonly prescribed empiric treatments remain viable therapeutic options for CARTI caused by these two Gram-negative respiratory tract pathogens.

Geographic diversity and temporal trends of antimicrobial resistance in Streptococcus pneumoniae in the United States

Resistance of Streptococcus pneumoniae to antibiotics is increasing throughout the United States, with substantial variation among geographic regions. We show that patterns of geographic variation are best explained by the intensity of selection for resistance, which is reflected by differences between the proportions of resistance within individual serotypes, rather than by differences between the frequencies of particular serotypes. Using a mathematical transmission model, we analyzed temporal trends in the proportions of singly and dually resistant organisms and found that pneumococcal strains resistant to both penicillin and erythromycin are increasing faster than strains singly resistant to either. Using the model, we predict that by 1 July 2004, in the absence of a vaccine, 41% of pneumococci at the Centers for Disease Control and Prevention (CDC)'s Active Bacterial Core surveillance (ABCs) sites, taken together, will be dually resistant, with 5% resistant to penicillin only and 5% to erythromycin only.