A common clone of erythromycin-resistant Streptococcus pneumoniae in Greece and the UK

Fourteen years in resistance

Resistance trends have changed greatly over the 14 years (1997-2011) whilst I was Director of the UK Antibiotic Resistance Monitoring and Reference Laboratory (ARMRL). Meticillin-resistant Staphylococcus aureus (MRSA) first rose, then fell with improved infection control, although with the decline of one major clone beginning before these improvements. Resistant pneumococci too have declined following conjugate vaccine deployment. If the situation against Gram-positive pathogens has improved, that against Gram-negatives has worsened, with the spread of (i) quinolone- and cephalosporin-resistant Enterobacteriaceae, (ii) Acinetobacter with OXA carbapenemases, (iii) Enterobacteriaceae with biochemically diverse carbapenemases and (iv) gonococci resistant to fluoroquinolones and, latterly, cefixime. Laboratory, clinical and commercial aspects have also changed. Susceptibility testing is more standardised, with pharmacodynamic breakpoints. Treatments regimens are more driven by guidelines. The industry has fewer big profitable companies and more small companies without sales income. There is good and bad here. The quality of routine susceptibility testing has improved, but its speed has not. Pharmacodynamics adds science, but over-optimism has led to poor dose selection in several trials. Guidelines discourage poor therapy but concentrate selection onto a diminishing range of antibiotics, threatening their utility. Small companies are more nimble, but less resilient. Last, more than anything, the world has changed, with the rise of India and China, which account for 33% of the world's population and increasingly provide sophisticated health care, but also have huge resistance problems. These shifts present huge challenges for the future of chemotherapy and for the edifice of modern medicine that depends upon it.

Distribution of serotypes, genotypes, and resistance determinants among macrolide-resistant Streptococcus pneumoniae isolates

Macrolide resistance in Streptococcus pneumoniae has emerged as an important clinical problem worldwide over the past decade. The aim of this study was to analyze the phenotypes (serotype and antibiotic susceptibility), genotypes (multilocus sequence type [MLST] and antibiotic resistance gene/transposon profiles) among the 31% (102/328) of invasive isolates from children in New South Wales, Australia, in 2005 that were resistant to erythromycin. Three serotypes--19F (47 isolates [46%]), 14 (27 isolates [26%]), and 6B (12 isolates [12%])--accounted for 86 (84%) of these 102 isolates. Seventy four (73%) isolates had the macrolide-lincosamide-streptogramin B (MLS(B)) resistance phenotype and carried Tn916 transposons (most commonly Tn6002); of these, 73 (99%) contained the erythromycin ribosomal methylase gene [erm(B)], 34 (47%) also carried the macrolide efflux gene [mef(E)], and 41 (55%) belonged to serotype 19F. Of 28 (27%) isolates with the M phenotype, 22 (79%) carried mef(A), including 16 (57%) belonging to serotype 14, and only six (19%) carried Tn916 transposons. Most (84%) isolates which contained mef also contained one of the msr(A) homologues, mel or msr(D); 38 of 40 (95%) isolates with mef(E) (on mega) carried mel, and of 28 (39%) isolates with mef(A), 10 (39%) carried mel and another 11(39%) carried msr(D), on Tn1207.1. Two predominant macrolide-resistant S. pneumoniae clonal clusters (CCs) were identified in this population. CC-271 contained 44% of isolates, most of which belonged to serotype 19F, had the MLS(B) phenotype, were multidrug resistant, and carried transposons of the Tn916 family; CC-15 contained 23% of isolates, most of which were serotype 14, had the M phenotype, and carried mef(A) on Tn1207.1. Erythromycin resistance among S. pneumoniae isolates in New South Wales is mainly due to the dissemination of multidrug-resistant S. pneumoniae strains or horizontal spread of the Tn916 family of transposons.

Characterization of invasive isolates of Streptococcus pneumoniae among Taiwanese children

Accurate molecular surveillance is important in monitoring the dynamics of Streptococcus pneumoniae. A prospective study was conducted to collect invasive isolates of S. pneumoniae from children for genetic analysis from January 2004 to December 2006 in Taiwan. PCRs were performed to detect the zmpC and zmpD genes, both encoding a metalloprotease virulence factor in pneumococci, among these invasive isolates. During the study period, 68 invasive isolates of S. pneumoniae were obtained for analysis. Serotype 14 was the most common type isolated from children with invasive disease and was significantly associated with pneumonia (OR 3.1; 95% CI] 1.1-8.8; p 0.035). Serotype 23F was significantly associated with bacteraemia (OR 7.5; 95% CI 1.8-31.3; p 0.006). The seven-valent conjugate vaccine covered 83.8% of invasive isolates, but non-vaccine serotypes were more frequently isolated from patients with underlying diseases than from patients without underlying diseases (p 0.007 by Fisher's exact test). Clonal complexes related to international clones Spain23F ST81, Spain6B ST95, England14 ST9, Taiwan19F ST236, Taiwan23F ST242 and Colombia23F ST338 accounted for 52.9% of invasive isolates. Dissemination of the penicillin-resistant clones ST876, ST46, ST76 and ST2889, which were first identified in Taiwan, was also found; 1.5% of these invasive isolates carried the zmpC gene, and 47.1% of these invasive isolates carried the zmpD gene. In conclusion, the spread of certain international clones and some domestic antibiotic-resistant clones resulted in invasive diseases among Taiwanese children.

Prevalence and macrolide resistance phenotypes and genotypes among clinical isolates of Streptococcus pneumoniae collected in Sofia, Bulgaria from 2001 to 2005

A total of 328 clinical isolates of Streptococcus pneumoniae were analyzed to determine the rate of macrolide and penicillin resistance as well as macrolide resistance phenotypes and genotypes. Erythromycin resistance was found in 81 pneumococcal isolates (24.7%) and 10.7% of isolates were clindamycin resistant. The prevalence of penicillin G-intermediate (minimum inhibitory concentrations, MICs, 0.125 to 1 microg/ml) and penicillin-resistant (MICs, >or=2 microg/ml) S. pneumoniae isolates was 25.6% and 13.7%, respectively. The rate of ceftriaxone-intermediate and ceftriaxone-resistant strains was 2.7% and 1.2%, respectively. Among erythromycin-resistant S. pneumoniae isolates, strains harboring mef(A) genes (n=42; 51.8%) were found to be predominant over strains with erm(B) genes (n=34; 42.0%). One (1.2%) isolate carried both erm(B) and mef(A), while 4 (4.9%) isolates carried L4 protein mutations. By using the erythromycin, clindamycin and rokitamycin triple-disk test, 42 strains were assigned to the M phenotype of macrolide resistance, 31 isolates were assigned to the partially inducible (iMcLS) phenotype, 4 were assigned to the constitutive (cMLS) phenotype. Four strains with L4 gene showed a rare phenotype with the triple-disk test. Serotyping of S. pneumoniae isolates suggested that serotype (or serogroup) 14, 6 and 19 were predominant (81.5%) among erythromycin-resistant strains. Among mef(A) positive isolates serotype 14 was predominant, among erm(B) positive isolates serogroups 6 and 19 were the most prevalent.

Rapid Spread in Norway of an Erythromycin-Resistant Pneumococcal Clone, Despite Low Usage of Macrolides

During the last 4 years, Norway has experienced an increase in macrolide resistance among systemic isolates of Streptococcus pneumoniae. The Norwegian reference laboratory for pneumococci received the isolates from over 85% of the Norwegian cases of systemic pneumococcal disease in the period studied. To study the details of the increased macrolide resistance, all macrolide-resistant systemic pneumococcal isolates (410 isolates) collected in the period from 1995 to 2005 were characterized phenotypically, and a representative selection of 68 strains was also studied genotypically. The serogroups most frequently associated with macrolide resistance in the studied period were 14, 6, 23, 19, and 9. The resistance M-type was expressed in 85% of the resistant isolates. Of the 68 isolates analyzed by multilocus sequence typing, 19 different sequence types (STs) were represented, including several of the international resistant clones. All but one of the clones appeared at a low frequency; mainly as isolated cases. The increase in macrolide resistance seen from 2001 to 2005 proved to be caused by ST-9, defined as the England(14)-9 clone by the Pneumococcal Molecular Epidemiology Network. All ST-9 isolates tested, carried the mef(A) gene and expressed the resistance M-type. This clone first appeared in the Oslo region in 1993, but was by 2005 isolated from all over the country. Children were overrepresented among the cases caused by this clone; however, people aged 20-29, possibly involving the parent generation, were also represented at an increased frequency. The England(14)-9 clone has been able to spread successfully in the Norwegian population despite a relatively low consumption of macrolides.

Clonal spread of mef-positive macrolide-resistant Streptococcus pneumoniae isolates causing invasive disease in adults in Germany

Isolates (3,845) obtained from German adults with invasive pneumococcal disease between 1992 and 2004 were investigated. Of these, 430 isolates (11.2%) were erythromycin A nonsusceptible. Macrolide resistance genotypes and multilocus sequence types were determined. Among the isolates, 35.6% were erm(B) positive and 63.5% were mef positive. Over the study period, the frequency of resistance rose significantly from 2.2 to 17.0% (P < 0.001). A serotype 14, sequence type 9 clone was the most widespread.

Increase of the M phenotype among erythromycin-resistant Streptococcus pneumoniae isolates from Spain related to the serotype 14 variant of the Spain9V-3 clone

Between 1998 and 2003 the rate of erythromycin resistance among pneumococci in Spain was 34.4%. Although the MLS(B) phenotype was prevalent (94.7%), the rate of the M phenotype increased from 3.3% to 8.9% (P < 0.01). Clonal dissemination of mef(E)-carrying strains of serotype 14 variant of the Spain(9V)-3 clone was the major contributor to this increase.

Molecular epidemiology of macrolide-resistant isolates of Streptococcus pneumoniae collected from blood and respiratory specimens in Norway

Norway has a low prevalence of antimicrobial resistance, including macrolide-resistant Streptococcus pneumoniae (MRSP). In a nationwide surveillance program, a total of 2,200 S. pneumoniae isolates were collected from blood cultures and respiratory tract specimens. Macrolide resistance was detected in 2.7%. M-type macrolide resistance was found in 60% of resistant isolates, and these were mainly mef(A)-positive, serotype-14 invasive isolates. The erm(B)-encoded macrolide-lincosamide-streptogramin B (MLS(B)) type dominated among the noninvasive isolates. One strain had an A2058G mutation in the 23S rRNA gene. Coresistance to other antibiotics was seen in 96% of the MLS(B)-type isolates, whereas 92% of the M-type isolates were susceptible to other commonly used antimicrobial agents. Serotypes 14, 6B, and 19F accounted for 84% of the macrolide-resistant isolates, with serotype 14 alone accounting for 67% of the invasive isolates. A total of 29 different sequence types (STs) were detected by multilocus sequence typing. Twelve STs were previously reported international resistant clones, and 75% of the macrolide-resistant isolates had STs identical or closely related to these clones. Eleven isolates displayed 10 novel STs, and 7/11 of these "Norwegian strains" coexpressed MLS(B) and tetracycline resistance, indicating the presence of Tn1545. The invasive serotype-14 isolates were all classified as ST9 or single-locus variants of this clone. ST9 is a mef-positive M-type clone, commonly known as England(14)-9, reported from several European countries. These observations suggest that the import of major international MRSP clones and the local spread of Tn1545 are the major mechanisms involved in the evolution and dissemination of MRSP in Norway.

Efflux-mediated antimicrobial resistance

Antibiotic resistance continues to plague antimicrobial chemotherapy of infectious disease. And while true biocide resistance is as yet unrealized, in vitro and in vivo episodes of reduced biocide susceptibility are common and the history of antibiotic resistance should not be ignored in the development and use of biocidal agents. Efflux mechanisms of resistance, both drug specific and multidrug, are important determinants of intrinsic and/or acquired resistance to these antimicrobials, with some accommodating both antibiotics and biocides. This latter raises the spectre (as yet generally unrealized) of biocide selection of multiple antibiotic-resistant organisms. Multidrug efflux mechanisms are broadly conserved in bacteria, are almost invariably chromosome-encoded and their expression in many instances results from mutations in regulatory genes. In contrast, drug-specific efflux mechanisms are generally encoded by plasmids and/or other mobile genetic elements (transposons, integrons) that carry additional resistance genes, and so their ready acquisition is compounded by their association with multidrug resistance. While there is some support for the latter efflux systems arising from efflux determinants of self-protection in antibiotic-producing Streptomyces spp. and, thus, intended as drug exporters, increasingly, chromosomal multidrug efflux determinants, at least in Gram-negative bacteria, appear not to be intended as drug exporters but as exporters with, perhaps, a variety of other roles in bacterial cells. Still, given the clinical significance of multidrug (and drug-specific) exporters, efflux must be considered in formulating strategies/approaches to treating drug-resistant infections, both in the development of new agents, for example, less impacted by efflux and in targeting efflux directly with efflux inhibitors.

Molecular epidemiology of macrolide-resistant Streptococcus pneumoniae isolates in Europe

In many European countries, the level of pneumococcal resistance to macrolides has now passed the level of resistance to penicillin G. A total of 82 erythromycin A-resistant isolates of Streptococcus pneumoniae were collected by 11 laboratories in seven European countries. All of the isolates were tested for antimicrobial susceptibility, analyzed for clonal relatedness by multilocus sequence typing, and characterized for macrolide resistance genotypes. The prevalence of the macrolide resistance genotypes varied substantially between countries. In France (87.5% of all strains), Spain (77.3%), Switzerland (80%), and Poland (100%), strains were predominantly erm(B) positive, whereas higher levels of mef(A)-positive strains were reported from Greece (100%) and Germany (33.3%). Macrolide resistance was caused by the oligoclonal spread of some multilocus sequence types, but significant differences in clonal distribution were noted between France and Spain, countries from which high levels of macrolide resistance have been reported. Overall, sequence type 81 (Spain23F-1 clone) was by far the most widespread. The mainly erm(B)-positive serotype 14 clone (sequence type 143), first reported in Poland in the mid-1990s, is now widespread in France.

Distribution of subclasses mefA and mefE of the mefA gene among clinical isolates of macrolide-resistant (M-phenotype) Streptococcus pneumoniae, viridans group streptococci, and Streptococcus pyogenes

The distribution of subclasses mefA and mefE of the mefA gene among 116 M-phenotype streptococci was as follows: pneumococci (38 strains had mefE and 4 mefA), viridans streptococci (49 mefE and 1 mefA), and Streptococcus pyogenes (24 mefA). Spain(9V)-3-14 and England(14)-9 clones of serotype 14 were dominant among pneumococci.

Erythromycin resistance in invasive serotype 14 pneumococci is highly related to clonal type

Sixty-seven serotype 14 pneumococci, isolated from invasive disease in Scotland during the first 6 months of 2003, were characterized. Serotype 14 pneumococci accounted for 18.2 % of the total number of cases. Serotyping, multilocus sequence typing and antibiotic susceptibility testing revealed 10 different sequence types (STs), predominantly ST 9 and ST 124; most ST 9 pneumococci were erythromycin-resistant whilst those of ST 124 were not.