Distribution of resistance genes tet(M), aph3'-III, catpC194 and the integrase gene of Tn1545 in clinical Streptococcus pneumoniae harbouring erm(B) and mef(A) genes in Spain

International tempo-spatial study of antibiotic resistance genes across the Rhine river using newly developed multiplex qPCR assays

The aim of this study was to capture and explain changes in antibiotic resistance gene (ARG) presence and concentration internationally across the Rhine river. Intl1 concentrations and national antibiotic usage were investigated as proxies to predict anthropogenic ARG pollution. Newly-developed multiplex qPCR assays were employed to investigate ARG profiles across 8 locations (L1-L8) in three countries (Switzerland, Germany, the Netherlands) and to detect potential regional causes for variation. Two of these locations were further monitored, over the duration of one month. A total of 13 ARGs, Intl1 and 16S rRNA were quantified. ARG presence and concentrations initially increased from L1(Diepoldsau) to L3(Darmstadt). A continuous increase could not be observed at subsequent locations, with the large river volume likely being a major contributing factor for stability. ARG presence and concentrations fluctuated widely across different locations. L2(Basel) and L3 were the two most polluted locations, coinciding with these locations being well-developed pharmaceutical production locations. We draw attention to the characteristic, clearly distinct ARG profiles, with gene presence being consistent and gene concentrations varying significantly less over time than across different locations. Five genes were Rhine-typical (ermB, ermF, Intl1, sul1 and tetM). Intl1 and sul1 were the genes with highest and second-highest concentration, respectively. Aph(III)a and bla_OXA were permanently introduced downstream of L1, indicating no source of these genes prior to L1. We highlight that correlations between Intl1 and ARG concentrations (R² = 0.72) were driven by correlations to sul1 and disappeared when excluding sul1 from the analysis (R² = 0.05). Intl1 therefore seems to be a good proxy for sul1 concentrations but not necessarily for overall (anthropogenic) ARG pollution. Aminoglycoside usage per country correlated with concentrations of aph(III)a and several unrelated antibiotic resistance genes (bla_OXA,ermB, ermF and tetM). This correlation can be explained by co-resistance caused by mobile genetic elements (MGEs), such as Tn1545.

Multiplex gene transfer by genetic transformation between isolated S. pneumoniae cells confined in microfluidic droplets

Gene exchange via genetic transformation makes major contributions to antibiotic resistance of the human pathogen, Streptococcus pneumoniae (pneumococcus). The transfers begin when a pneumococcal cell, in a transient specialized physiological state called competence, attacks and lyses another cell, takes up fragments of the liberated DNA, and integrates divergent genes into its genome. Recently, it has been demonstrated that the pneumococcal cells can be enclosed in femtoliter-scale droplets for study of the transformation mechanism, offering the ability to characterize individual cell-cell interactions and overcome the limitations of current methods involving bulk mixed cultures. To determine the relevance and reliability of this new method for study of bacterial genetic transformation, we compared recombination events occurring in 44 recombinants recovered after competence-mediated gene exchange between pairs of cells confined in femtoliter-scale droplets vs. those occurring in exchanges in parallel bulk culture mixtures. The pattern of recombination events in both contexts exhibited the hallmarks of the macro-recombination exchanges previously observed within the more complex natural contexts of biofilms and long-term evolution in the human host.

Neonatal colonization of group B Streptococcus in China: Prevalence, antimicrobial resistance, serotypes, and molecular characterization

BACKGROUND

Group B Streptococcus (GBS) remains a leading cause of neonatal mortality and morbidity. This study aimed to determine the prevalence, antimicrobial susceptibility, serotypes, and molecular characterization of GBS colonized in neonates.

METHODS

A cross-sectional study was conducted using a multistage sampling method. Swabs for GBS identification were taken from infants' ear, oral cavity, and umbilicus immediately after birth. All GBS isolates were tested for antimicrobial susceptibility, resistance genes, serotyping, multilocus sequence typing, and virulence genes.

RESULTS

Of the 1,814 neonates, 1.3% tested positive for GBS, with 66.7% tested as multidrug resistant. All GBS isolates were susceptible to penicillin, but rates of resistance to tetracycline and erythromycin were high (70.8%), with the predominant resistance genes being tetM and ermB. The predominant serotype was III, followed by Ia and Ib, and the most common genotypes were sequence type (ST) 19, ST10, and ST485. Notably, we found that ST19 and ST17 isolates were associated with serotype III, resistant to tetracycline, erythromycin, and clindamycin, and carrying ermB, tetM, and rib; ST10 and ST12 isolates were associated with serotype Ib, resistant to erythromycin and clindamycin, and carrying ermB and alphaC; and ST485 isolates were associated with serotype Ia and carrying mefA/E, tetM, and epsilon.

CONCLUSIONS

These findings indicate a high prevalence of multidrug-resistant GBS and specific phenotype-genotype combinations for GBS clones.

Phenotypic and molecular characterization of Streptococcus pneumoniae in pre-conjugate vaccine era: A Chinese hospital-based retrospective study

BACKGROUND

Streptococcus pneumoniae (S. pneumoniae) is an important pathogen in causing global morbidity and mortality among children. This study aimed to determine phenotypic and molecular characteristics of S. pneumoniae causing infections in children under five years in China.

METHODS

A hospital-based retrospective study was conducted. All 537 S. pneumoniae isolates were tested for antimicrobial susceptibility by E-test method, molecular characteristics including resistance genes, virulence genes and serotypes by multiplex polymerase chain reaction (PCR) method, and sequence types (STs) by sequencing seven housekeeping genes. Minimum spanning tree and correspondence analysis were used to reveal the potential relationship between serotypes and STs.

RESULTS

Most of S. pneumoniae isolates were resistant to erythromycin (93.9%) and tetracycline (86.4%), with the predominant resistance genes being erm(B) (92.6%) and tet(M) (95.5%). The prevalent serotypes were 19F, 6B, 19A, 23F and 14, the coverage rate of PCV13 was high in 85.8%, and the predominant STs were ST271, ST320, ST3173, ST81 and ST876. A significant correlation existed between STs and serotypes, with ST271/19F and ST320/19A as the most prevalent clones. Notably, ST271/19F and ST320/19A isolates were associated with resistance to specific antibiotics and carrying of mef(A/E), rlrA and sipA genes.

CONCLUSIONS

Our findings suggest the introduction of PCV13 vaccine to Chinese children, and underscore the value of monitoring multiple characteristics to detect new epidemiologic trends and provide implications for the formulation of multivalent pneumococcal vaccines.

Evidence for clonal expansion after antibiotic selection pressure: pneumococcal multilocus sequence types before and after mass azithromycin treatments

BACKGROUND

A clinical trial of mass azithromycin distributions for trachoma created a convenient experiment to test the hypothesis that antibiotic use selects for clonal expansion of preexisting resistant bacterial strains.

METHODS

Twelve communities in Ethiopia received mass azithromycin distributions every 3 months for 1 year. A random sample of 10 children aged 0-9 years from each community was monitored by means of nasopharyngeal swab sampling before mass azithromycin distribution and after 4 mass treatments. Swab specimens were tested for Streptococcus pneumoniae, and isolates underwent multilocus sequence typing.

RESULTS

Of 82 pneumococcal isolates identified before treatment, 4 (5%) exhibited azithromycin resistance, representing 3 different sequence types (STs): 177, 6449, and 6494. The proportion of isolates that were classified as one of these 3 STs and were resistant to azithromycin increased after 4 mass azithromycin treatments (14 of 96 isolates [15%]; P = .04). Using a classification index, we found evidence for a relationship between ST and macrolide resistance after mass treatments (P < .0001). The diversity of STs-as calculated by the unbiased Simpson index-decreased significantly after mass azithromycin treatment (P = .045).

CONCLUSIONS

Resistant clones present before mass azithromycin treatments increased in frequency after treatment, consistent with the theory that antibiotic selection pressure results in clonal expansion of existing resistant strains.

Tn916-like genetic elements: a diverse group of modular mobile elements conferring antibiotic resistance

Antibiotic-resistant Gram-positive bacteria are responsible for morbidity and mortality in healthcare environments. Enterococcus faecium, Enterococcus faecalis, Staphylococcus aureus and Streptococcus pneumoniae can all exhibit clinically relevant multidrug resistance phenotypes due to acquired resistance genes on mobile genetic elements. It is possible that clinically relevant multidrug-resistant Clostridium difficile strains will appear in the future, as the organism is adept at acquiring mobile genetic elements (plasmids and transposons). Conjugative transposons of the Tn916/Tn1545 family, which carry major antibiotic resistance determinants, are transmissible between these different bacteria by a conjugative mechanism during which the elements are excised by a staggered cut from donor cells, converted to a circular form, transferred by cell-cell contact and inserted into recipient cells by a site-specific recombinase. The ability of these conjugative transposons to acquire additional, clinically relevant antibiotic resistance genes importantly contributes to the emergence of multidrug resistance.

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.

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.

In vitro activity of cefditoren and other antimicrobial agents against 288 Streptococcus pneumoniae and 220 Haemophilus influenzae clinical strains isolated in Zaragoza, Spain

In vitro cefditoren antimicrobial activity was tested against 288 Streptococcus pneumoniae and 220 Haemophilus influenzae clinical strains isolated in our hospital from January 2005 to May 2006 by agar dilution and broth microdilution method, respectively. MICs were also determined for 13 and 10 comparison drugs, respectively. The pneumococci tested comprised 113 (39.2%) penicillin susceptible, 91 (31.6%) penicillin intermediate, and 84 (29.2%) penicillin resistant. Cefditoren was the most active drug on the basis of the MICs (MIC(90)=0.5 microg/mL), followed by ceftriaxone and levofloxacin (MIC(90)=1 microg/mL). Cefditoren MICs ranged from 0.25 to 1 microg/mL for ceftriaxone-resistant isolates, with a modal MIC of 0.5 microg/mL and an MIC(90) of 1.0 microg/mL. No S. pneumoniae isolates evaluated in this study showed MICs to cefditoren higher than 1 microg/mL (MIC range, <or=0.015 to 1 microg/mL). Against penicillin-resistant pneumococci, the rank order of intrinsic activity (MIC(90), microg/mL) was cefditoren (0.5)<ceftriaxone (2.0)=cefotaxime (2.0)<amoxicillin/clavulanate (8.0)=amoxicillin (8.0)=cefuroxime (8.0). Among the 220 strains of H. influenzae, 42 (19.09%) produced a beta-lactamase (Hi beta+) and 3 (1.1%) were beta-lactamase (Hi beta-) negative but have reduced susceptibility to ampicillin (BLNAR). The most active drugs on the basis of MICs were cefditoren and levofloxacin, showing MIC(50) and MIC(90) values of 0.015/0.06 microg/mL. Cefditoren at concentration of 0.06 microg/mL inhibited all 3 BLNAR (ampicillin MICs >4 microg/mL). Against H. influenzae (Hi beta+), the rank order of intrinsic activity (MIC(90), microg/mL) was cefditoren (0.03) < cefixime (0.06)<ceftriaxone (0.12)=cefotaxime (0.12)<cefuroxime (1.0)<amoxicillin/clavulanate (2.0)<ampicillin (>8.0).

erm(B)-carrying elements in tetracycline-resistant pneumococci and correspondence between Tn1545 and Tn6003

This study investigated the genetic organization of erm(B)-carrying transposons of Streptococcus pneumoniae and their distribution in tetracycline-resistant clinical isolates. By comparatively analyzing reference pneumococci carrying erm(B)/tet(M) transposon Tn1545, Tn6003, Tn6002, or Tn3872, we demonstrated a substantial correspondence between Tn1545 and Tn6003, which have the same resistance gene combination [tet(M) (tetracycline), erm(B) (erythromycin), and aphA-3 (kanamycin)]; share the macrolide-aminoglycoside-streptothricin element, containing a second erm(B); and only differ by a ca. 1.2-kb insertion (containing a putative IS1239 insertion sequence) detected in Tn1545 from S. pneumoniae reference strain BM4200. These results enabled elucidation of the structure of Tn1545, the first erm(B)-carrying transposon described in S. pneumoniae. A collection of 83 erythromycin- and tetracycline-resistant clinical pneumococci, representative of recent Italian isolates carrying erm(B) as the sole erythromycin resistance gene, was used to investigate the distribution of the different transposons. All 83 organisms were positive for tet(M) and bore an erm(B)/tet(M) transposon that could be characterized by using a specific set of primer pairs; Tn3872 was detected in 18 isolates, Tn6002 in 59 isolates, and Tn6003 in 6 (the sole kanamycin-resistant) isolates. The genetic organization of transposon Tn1545, with its specific insertion, was not detected in any of the isolates tested. The erm(B)-carrying elements of tetracycline-resistant pneumococci substantially corresponded to those [bearing a silent tet(M) gene] recently detected in tetracycline-susceptible pneumococci. Overall, in erm(B)-positive pneumococci, Tn6003 was the least common erm(B)-carrying Tn916-related element and Tn6002 the most common.

Molecular epidemiology and distribution of serotypes, surface proteins, and antibiotic resistance among group B streptococci in Italy

Group B streptococci (GBS) comprising three different sets of isolates (31 invasive, 36 noninvasive, and 24 colonizing isolates) were collected in Italy during the years 2002 to 2005. Clonal groups were established by pulsed-field gel electrophoresis (PFGE), and selected isolates were studied by multilocus sequence typing (MLST). GBS isolates were also characterized by classical and molecular techniques for serotyping and protein gene and antibiotic resistance profiling. Some serotypes were significantly associated with a particular isolate population: serotype Ia more frequently corresponded to invasive strains than other strains, serotype V was more frequently encountered among noninvasive strains, and nontypeable strains were more common among isolates from carriers. Four major clonal groups accounted for 52.7% of all isolates: PFGE type 1/clonal complex 1 (CC1) comprised mainly serotype V isolates carrying the alp3 gene, PFGE type 2/CC23 encompassed serotype Ia isolates with the alp1 or alpha gene, PFGE type 3/CC17 comprised serotype III isolates carrying the rib gene, and PFGE type 4/CC19 consisted mainly of serotype II isolates possessing the rib gene. The same serotypes were shared by isolates of different clonal groups, and conversely, isolates belonging to the same clonal groups were found to be of different serotypes, presumably due to capsular switching by the horizontal transfer of capsular genes. Erythromycin resistance (prevalence, 16.5%; 15 resistant isolates of 91) was restricted to strains isolated from patients with noninvasive infections and carriers, while tetracycline resistance was evenly distributed (prevalence, 68.1%; 62 resistant isolates of 91). Most erythromycin-resistant GBS strains were of serotype V, were erm(B) positive, and belonged to the PFGE type 1/CC1 group, suggesting that macrolide resistance may have arisen both by clonal dissemination and by the horizontal transfer of resistance genes.

Serotypes, Clones, and Mechanisms of Resistance of Erythromycin-Resistant Streptococcus pneumoniae Isolates Collected in Spain

The aim of this study was to analyze the distributions of antibiotic susceptibility patterns, serotypes, phenotypes, genotypes, and macrolide resistance genes among 125 nonduplicated erythromycin-resistant Streptococcus pneumoniae clinical isolates collected in a Spanish point prevalence study. The prevalence of resistance to macrolides in this study was 34.7%. Multiresistance (to three or more antimicrobials) was observed in 81.6% of these strains. Among 15 antimicrobials studied, cefotaxime, moxifloxacin, telithromycin, and quinupristin-dalfopristin were the most active drugs. The most frequent serotypes of erythromycin-resistant isolates were 19F (25%), 19A (17%), 6B (12%), 14 (10%), and 23F (10%). Of the 125 strains, 109 (87.2%) showed the MLS(B) phenotype [103 had the erm(B) gene and 6 had both erm(B) and mef(E) genes]. Sixteen (12.8%) strains showed the M phenotype [14 with mef(E) and 2 with mef(A)]. All isolates were tested by PCR for the presence of the int, xis, tnpR, and tnpA genes associated with conjugative transposons (Tn916 family and Tn917). Positive detection of erm(B), tet(M), int, and xis genes related to the Tn916 family was found in 77.1% of MLS(B) phenotype strains. In 16 strains, only the tndX, erm(B), and tet(M) genes were detected, suggesting the presence of Tn1116, a transposon recently described for Streptococcus pyogenes. Five clones, namely, Sweden(15A)-25, clone(19F) ST87, Spain(23F)-1, Spain(6B)-2, and clone(19A) ST276, accounted for half of the MLS(B) strains. In conclusion, the majority of erythromycin-resistant pneumococci isolated in Spain had the MLS(B) phenotype, belonged to multiresistant international clones, and carried the erm(B), tet(M), xis, and int genes, suggesting the spread of transposons of the Tn916 family.

Clonal diversity and resistance mechanisms in tetracycline-nonsusceptible Streptococcus pneumoniae isolates in Poland

The frequency of tetracycline resistance in Streptococcus pneumoniae isolates in Poland is one of the highest in Europe. The aim of this study was to analyze the clonal diversity and resistance determinants of tetracycline-nonsusceptible S. pneumoniae isolates identified in Poland and to investigate the effect of tetracycline resistance on their susceptibilities to tigecycline, doxycycline, and minocycline. We have analyzed 866 pneumococcal isolates collected from 1998 to 2003 from patients with respiratory tract diseases, and 242 of these (27.9%) were found to be resistant to tetracycline. All of the resistant isolates were characterized by testing of their susceptibilities to other antimicrobials, serotyping, pulsed-field gel electrophoresis (PFGE), and identification of tetracycline resistance genes and transposons. Selected isolates representing the main PFGE types were analyzed by multilocus sequence typing. Among the isolates investigated, 27 serotypes and 146 various PFGE patterns, grouped into 90 types, were discerned. The most common PFGE type, corresponding to serotype 19F and sequence type 423, was represented by 22.3% of all of the tetracycline-resistant isolates. The tet(M) gene was the sole resistance gene in the group of isolates studied, and in over 96% of the isolates, the Tn916 family of tet(M)-containing conjugative transposons was detected. Several isolates contained specific variants of the transposons, the Tn1545-like, Tn3872-like, or Tn2009-like element. The correlation between the MICs of tetracycline, doxycycline, and minocycline was revealed, whereas no cross-resistance to tetracycline and tigecycline was observed.

The mef(E)-carrying genetic element (mega) of Streptococcus pneumoniae: insertion sites and association with other genetic elements

The structure of the macrolide efflux genetic assembly (mega) element, its genomic locations, and its association with other resistance determinants and genetic elements were investigated in 16 Streptococcus pneumoniae isolates carrying mef(E), of which 1 isolate also carried tet(M) and 4 isolates also carried tet(M) and erm(B). All isolates carried a mega element of similar size and structure that included the operon mef(E)-msr(D) encoding the efflux transport system. Among tetracycline-susceptible isolates, six different integration sites were identified, five of which were recognized inside open reading frames present in the R6 genome. In the five isolates also carrying tet(M), mega was inserted in different genetic contexts. In one isolate, it was part of previously described Tn916-like element Tn2009. In another isolate, mega was inserted in a transposon similar to Tn2009 that also included an erm(B) element. This new composite transposon was designated Tn2010. Neither Tn2009 nor Tn2010 could be transferred by conjugation to pneumococcal or enterococcal recipients. In the three isolates in which mega was not physically linked with tet(M), this gene was associated with erm(B) in transposon Tn3872, a Tn916-like element. Homologies between the chromosomal insertions of these composite transposons and sequences of multidrug-resistant pneumococcal genomes in the databases indicate the presence of preferential sites for the integration of composite Tn916-like elements carrying multiple resistance determinants in S. pneumoniae.

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.

Distribution of serotypes and antimicrobial resistance genes among Streptococcus agalactiae isolates from bovine and human hosts

To better understand the emergence and transmission of antibiotic-resistant Streptococcus agalactiae, we compared phenotypic and genotypic characteristics of 52 human and 83 bovine S. agalactiae isolates. Serotypes found among isolates from human hosts included V (48.1%), III (19.2%), Ia and Ib (13.5% each), and II (5.8%). Among isolates from bovine hosts, molecular serotypes III and II were predominant (53 and 14.5%, respectively). Four and 21 different ribotypes were found among human and bovine isolates, respectively. A combination of ribotyping and serotyping showed that two bovine isolates were indistinguishable from human isolates. Resistance to tetracycline and erythromycin was more common among human (84.6% and 26.9%, respectively) than bovine (14.5% and 3.6%, respectively) isolates. tetM was found in all tetracycline-resistant human isolates, while tetO was the predominant resistance gene among bovine isolates. tet genes were found among various ribotypes. ermB, ermTR, and mefA were detected among erythromycin-resistant human isolates, while ermB was the only erythromycin resistance determinant among isolates from bovine hosts. For isolates from human hosts, erythromycin resistance genes appeared to be associated with specific ribotypes. We conclude that (i) human and bovine S. agalactiae isolates represent distinct populations; (ii) human host-associated S. agalactiae subtypes may occasionally be transmitted to bovines; (iii) while emergence of erythromycin and tetracycline resistance appears to largely occur independently among human and bovine isolates, occasional cross-species transfer of resistant strains or transmission of resistance genes between human- and bovine-associated subtypes may occur; and (iv) dissemination of antibiotic-resistant S. agalactiae appears to include both clonal spread of resistant strains as well as horizontal gene transfer.

Distribution of serotypes and antimicrobial resistance genes among Streptococcus agalactiae isolates from bovine and human hosts

To better understand the emergence and transmission of antibiotic-resistant Streptococcus agalactiae, we compared phenotypic and genotypic characteristics of 52 human and 83 bovine S. agalactiae isolates. Serotypes found among isolates from human hosts included V (48.1%), III (19.2%), Ia and Ib (13.5% each), and II (5.8%). Among isolates from bovine hosts, molecular serotypes III and II were predominant (53 and 14.5%, respectively). Four and 21 different ribotypes were found among human and bovine isolates, respectively. A combination of ribotyping and serotyping showed that two bovine isolates were indistinguishable from human isolates. Resistance to tetracycline and erythromycin was more common among human (84.6% and 26.9%, respectively) than bovine (14.5% and 3.6%, respectively) isolates. tetM was found in all tetracycline-resistant human isolates, while tetO was the predominant resistance gene among bovine isolates. tet genes were found among various ribotypes. ermB, ermTR, and mefA were detected among erythromycin-resistant human isolates, while ermB was the only erythromycin resistance determinant among isolates from bovine hosts. For isolates from human hosts, erythromycin resistance genes appeared to be associated with specific ribotypes. We conclude that (i) human and bovine S. agalactiae isolates represent distinct populations; (ii) human host-associated S. agalactiae subtypes may occasionally be transmitted to bovines; (iii) while emergence of erythromycin and tetracycline resistance appears to largely occur independently among human and bovine isolates, occasional cross-species transfer of resistant strains or transmission of resistance genes between human- and bovine-associated subtypes may occur; and (iv) dissemination of antibiotic-resistant S. agalactiae appears to include both clonal spread of resistant strains as well as horizontal gene transfer.

Prevalence of Streptococcus pneumoniae isolates bearing macrolide resistance genes in association with integrase genes of conjugative transposons in Japan

The relationship between susceptibility to macrolides and tetracycline, and the distribution of the resistance genes erm(B), mef(A) and tet(M) and the integrase gene of the conjugative transposon, Int-Tn, was examined in 43 isolates of Streptococcus pneumoniae from Gunma Prefecture, Japan. Thirty-five isolates were resistant to both macrolides and tetracycline and carried tet(M); erm(B) and mef(A) were detected in 19 and 16, respectively, of these isolates. Sixteen mef(A)-positive isolates were all identified as mef(E) variants. Int-Tn of Tn1545 was associated with 17 erm(B)- and 14 mef(A)-bearing isolates, and Int-Tn of Tn5252 was found in the remaining two mef(A)-carrying isolates. Pneumococcal strains with resistance to macrolides conferred by erm(B) or mef(A) in association with the integrase gene of conjugative transposon Tn1545 or Tn5252 appear to be prevalent in Japan.

Comparison and Transferability of theerm(B) Genes between Human and Farm Animal Streptococci

To obtain better insights into the possible exchange of resistance genes between human and animal streptococci, the sequences of the erm (B) genes of streptococcal isolates from humans, pigs, pork carcasses, chickens, and calves were compared. Identical erm (B) gene sequences were present in strains from humans, pigs, pork carcasses, and calves. During in vitro mating experiments, the erm (B) gene was exchanged between porcine Streptococcus suis and human S. pneumoniae, S. pyogenes, and S. oralis strains. The presence of different tetracycline resistance genes and the int Tn 1545 gene was determined in animal streptococci carrying the erm (B) gene. Although tet(M) and int Tn 1545 genes were detected in 24% of the porcine and pork carcass streptococcal strains, the tet(O) gene was the predominant tetracycline resistance gene in these strains (81%). The latter gene was co-transferred with the erm (B) gene from porcine S. suis strains to human streptococci in the mating experiments. These results show that, identical erm (B) gene sequences were present in animal and human streptococci and that transfer of the erm (B) gene from porcine S. suis to human streptococci and vice versa is possible, but probably occurs at a low frequency.

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.

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.

Rapid and reliable real-time PCR assay for detection of the macrolide efflux gene and subsequent discrimination between its distinct subclasses mef(A) and mef(E)

A real-time PCR assay is described for detection of the macrolide efflux gene, mef. Following amplification, unambiguous discrimination between the two mef subclasses, mef(A) and mef(E), is easily established using a melting curve analysis. The results of this novel assay were 100% concordant with a conventional PCR-RFLP approach but requires far less hands-on time. Furthermore, the real-time format offers semiquantitative results allowing identification of contaminated cultures and/or DNA preparations.

Increase of Macrolide-Resistant Streptococcus pneumoniae-Expressing mefE or ermB Gene in the Nasopharynx among Children with Otitis Media

OBJECTIVE

To evaluate prevalence of macrolide resistant strains and the genotypes of the resistance among Streptococcus pneumoniae isolated from the nasopharynx of children with otitis media.

STUDY DESIGN

Retrospective review.

METHODS

A total of 858 S. pneumoniae isolates were collected from the nasopharynx of pediatric patients with acute otitis media at the clinics of Otolaryngology-Head and Neck Surgery, Wakayama Medical University Hospital and six affiliated hospitals in Wakayama prefecture between January 1998 and December 2002. The antibiotic susceptibility patterns were analyzed for penicillin, erythromycin, and clindamycin according to the National Committee for Clinical Laboratory Standards. Macrolide resistance genes of mefE and ermB were determined by polymerase chain reaction of all S. pneumoniae.

RESULTS

Of 858 clinical isolates, 259 (30.1%) were strains without ermB or mefE gene, 279 (32.5%) carrying mefE, 292 (34.0%) carrying ermB, and 28 (3.4%) carrying both genes. There was a strong correlation between phenotypes and the presence of macrolide resistance genes. The macrolide resistance genes were especially frequently identified among penicillin-resistant S. pneumoniae. Strains carrying ermB gene gradually increased from 25% in 1998 to 45% in 2002, with a concurrent decrease in strains carrying mefE from 36% in 1998 to 1999 to 19% in 2002. Strains having mefE were frequently identified among children younger than 2 years old. The current finding suggested that high-level ermB-mediated macrolide resistance in S. pneumoniae is increasing at an alarming rate in pediatric patients with otitis media, especially among young children. Physicians should pay close attention to such macrolide-resistant bacterial pathogens in the antimicrobial treatment of pediatric patients with otitis media.

Prevalence and molecular analysis of macrolide and fluoroquinolone resistance among isolates of Streptococcus pneumoniae collected during the 2000-2001 PROTEKT US Study

The PROTEKT US (Prospective Resistant Organism Tracking and Epidemiology for the Ketolide Telithromycin in the United States) surveillance program was established to determine the prevalence and mechanisms of antibacterial resistance among bacterial pathogens from patients with community-acquired respiratory tract infections. In year 1 of the PROTEKT US study, 10,103 isolates of Streptococcus pneumoniae, including 3,133 erythromycin-resistant strains and 81 levofloxacin-resistant strains, were collected from 206 centers. We report on the molecular analyses of these resistant strains. The resistance genotypes among the 3,044 typed macrolide-resistant isolates overall were mef(A) (n = 2,157; 70.9%), erm(B) (n = 530; 17.4%), mef(A) erm(B) (n = 304; 10.0%), and erm(A) subclass erm(TR) (n = 5; 0.2%). Fifty (1.6%) macrolide-resistant isolates were negative for the mef and the erm resistance genes. Seventy-eight (96.3%) of the 81 levofloxacin-resistant isolates analyzed possessed multiple mutations in the gyrA, gyrB, parC, and/or parE quinolone resistance-determining regions. A total of 43 known multilocus sequence typing (MLST) profiles (or single- or double-locus variants) accounted for 75 of 81 isolates. There was no evidence of dissemination of fluoroquinolone-resistant clones within the United States; however, 12 isolates with the same MLST profile were located in one center in Massachusetts. Almost 90% of the erythromycin-resistant isolates and approximately one-third of the levofloxacin-resistant isolates were multidrug resistant.

Molecular basis of bacterial resistance to chloramphenicol and florfenicol

Chloramphenicol (Cm) and its fluorinated derivative florfenicol (Ff) represent highly potent inhibitors of bacterial protein biosynthesis. As a consequence of the use of Cm in human and veterinary medicine, bacterial pathogens of various species and genera have developed and/or acquired Cm resistance. Ff is solely used in veterinary medicine and has been introduced into clinical use in the mid-1990s. Of the Cm resistance genes known to date, only a small number also mediates resistance to Ff. In this review, we present an overview of the different mechanisms responsible for resistance to Cm and Ff with particular focus on the two different types of chloramphenicol acetyltransferases (CATs), specific exporters and multidrug transporters. Phylogenetic trees of the different CAT proteins and exporter proteins were constructed on the basis of a multisequence alignment. Moreover, information is provided on the mobile genetic elements carrying Cm or Cm/Ff resistance genes to provide a basis for the understanding of the distribution and the spread of Cm resistance--even in the absence of a selective pressure imposed by the use of Cm or Ff.

Biological counterstrike: antibiotic resistance mechanisms of Gram-positive cocci

The development of antibiotic resistance by bacteria is an evolutionary inevitability, a convincing demonstration of their ability to adapt to adverse environmental conditions. Since the emergence of penicillinase-producing Staphylococcus aureus in the 1940s, staphylococci, enterococci and streptococci have proved themselves adept at developing or acquiring mechanisms that confer resistance to all clinically available antibacterial classes. The increasing problems of methicillin-resistant S. aureus and coagulase-negative staphylococci (MRSA and MRCoNS), glycopeptide-resistant enterococci and penicillin-resistant pneumococci in the 1980s, and recognition of glycopeptide-intermediate S. aureus in the 1990s and, most recently, of fully vancomycin-resistant isolates of S. aureus have emphasised our need for new anti-Gram-positive agents. Antibiotic resistance is one of the major public health concerns for the beginning of the 21st century. The pharmaceutical industry has responded with the development of oxazolidinones, lipopeptides, injectable streptogramins, ketolides, glycylcyclines, second-generation glycopeptides and novel fluoroquinolones. However, clinical use of these novel agents will cause new selective pressures and will continue to drive the development of resistance. This review describes the various antibiotic resistance mechanisms identified in isolates of staphylococci, enterococci and streptococci, including mechanisms of resistance to recently introduced anti-Gram-positive agents.

Use of Macrolides and Tetracyclines for Chronic Inflammatory Diseases

OBJECTIVE:

To review the efficacy of macrolides and tetracyclines in several chronic inflammatory conditions.

DATA SOURCES:

Searches of MEDLINE (1966–March 2004) and an extensive bibliography search were undertaken. Key terms included acne, blepharitis, cardiovascular disease, cystic fibrosis, periodontitis, rosacea, and rheumatoid arthritis.

STUDY SELECTION AND DATA EXTRACTION:

Data were obtained primarily from randomized placebo-controlled trials upon which key recommendations are based.

DATA SYNTHESIS:

Antibiotics are often prescribed for months or even years for treatment of chronic inflammatory conditions such as acne, blepharitis, cardiovascular disease, cystic fibrosis, periodontitis, rosacea, and rheumatoid arthritis. Randomized controlled trials have shown that azithromycin is useful in the management of cystic fibrosis and the tetracyclines are beneficial in the management of rheumatoid arthritis, acne, blepharitis, and periodontitis. Several large, randomized controlled trials have failed to show any benefit of macrolides in the secondary prevention of cardiovascular disease. No randomized placebo-controlled clinical trials have been performed to assess the efficacy of macrolides or tetracyclines in patients with rosacea.

CONCLUSIONS:

The use of tetracyclines and macrolides for rosacea is based primarily on anecdotal reports or open-label trials. Limited clinical trials support the use of tetracyclines or macrolides in acne, blepharitis, periodontitis, rheumatoid arthritis, and cystic fibrosis. Trials to date do not support the use of antibiotics for secondary prevention of cardiovascular disease.

Distribution of theerm(B) Gene,tetracycline Resistance Genes, and Tn1545-like Transposons in Macrolide- and Lincosamide-Resistant Enterococci from Pigs and Humans

The distribution of the erm (B) and the tetracycline resistance genes tet(K), tet(L), tet(M), tet(O), and tet(S) was investigated among macrolide- and lincosamide-resistant enterococci originating from humans, pigs, and pork carcasses. The presence of transposons of the Tn916/Tn1545 family was also traced in these isolates. Furthermore, the porcine strains were tested for the presence of glycopeptide resistance genes vanA and vanB. The erm(B) gene was found in 85% of the porcine and in all human isolates. Ninety-eight percent of the porcine and 89% of the human erm(B)-positive enterococci carried the tet(M) gene. Seventy-seven percent and 70%, respectively, of these strains harbored a Tn1545-like element. Tet(L) was observed in 68% of the porcine and in 65% of the human enterococci. The other tetracycline resistance genes were very rare and the glycopeptide resistance genes vanA and vanB were not detected among the porcine isolates. The similar frequencies of resistance genes and the highly mobile Tn1545-like transposon among porcine and human enterococci might indicate exchange of resistant strains or their resistance genes between humans and pigs or the existence of a common reservoir.

Molecular basis of resistance to macrolides and other antibiotics in commensal viridans group streptococci and Gemella spp. and transfer of resistance genes to Streptococcus pneumoniae

We assessed the mechanisms of resistance to macrolide-lincosamide-streptogramin B (MLS(B)) antibiotics and related antibiotics in erythromycin-resistant viridans group streptococci (n = 164) and Gemella spp. (n = 28). The macrolide resistance phenotype was predominant (59.38%); all isolates with this phenotype carried the mef(A) or mef(E) gene, with mef(E) being predominant (95.36%). The erm(B) gene was always detected in strains with constitutive and inducible MLS(B) resistance and was combined with the mef(A/E) gene in 47.44% of isolates. None of the isolates carried the erm(A) subclass erm(TR), erm(A), or erm(C) genes. The mel gene was detected in all but four strains carrying the mef(A/E) gene. The tet(M) gene was found in 86.90% of tetracycline-resistant isolates and was strongly associated with the presence of the erm(B) gene. The cat(pC194) gene was detected in seven chloramphenicol-resistant Streptococcus mitis isolates, and the aph(3')-III gene was detected in four viridans group streptococcal isolates with high-level kanamycin resistance. The intTn gene was found in all isolates with the erm(B), tet(M), aph(3')-III, and cat(pC194) gene. The mef(E) and mel genes were successfully transferred from both groups of bacteria to Streptococcus pneumoniae R6 by transformation. Viridans group streptococci and Gemella spp. seem to be important reservoirs of resistance genes.

Genetic basis of erythromycin resistance in oral bacteria

We determined the prevalence of erythromycin-resistant bacteria in the oral cavity and identified mef and erm(B) as the most common resistance determinants. In addition, we demonstrate the genetic linkage, on various Tn1545-like conjugative transposons, between erythromycin and tetracycline resistance in a number of isolates.

Macrolide resistance phenotypes of commensal viridans group streptococci and Gemella spp. and PCR detection of resistance genes

One hundred and sixty viridans group streptococci (VGS) and 26 Gemella spp. resistant to erythromycin were studied to detect macrolide lincosamide and streptogramin B (MLS(B)) phenotypes and to investigate resistance rates to other antibiotics. The M phenotype was most prevalent in both bacterial groups (59.6% in VGS, 69.2% in gemellae) and the iMLS(B) phenotype was found least often (9.3 and 13.9%, respectively). All isolates with M phenotype had the mef(A/E) gene, being prevalent the mef(E) subclass. cMLS(B) and iMLS(B) strains contained the erm(B) gene, alone or in combination with the mef(A/E) gene. Thirteen isolates were intermediately resistant to quinupristin/dalfopristin and 11 strains showed low susceptibility to telithromycin. Linezolid was active against all the isolates tested and tetracycline resistance was the major one in VGS (41.6%) and Gemella spp. (46.2%).

Prevalence and identification of tetracycline-resistant oral bacteria in children not receiving antibiotic therapy

The prevalence of tetracycline-resistant oral bacteria in healthy 4- and 6-year-old children who had not received antibiotics during the 3 months prior to sampling was investigated. Of the 47 children sampled, 46 harboured tetracycline-resistant bacteria. The median proportion of cultivable anaerobic and aerobic oral bacteria resistant to tetracycline was 1.1% and the MIC50 of these was 64 microg ml(-1). The majority (56%) of tetracycline-resistant bacteria were resistant to at least one other antibiotic, usually erythromycin. The most commonly identified tetracycline-resistant bacteria were the oral streptococci (65%), the next most prevalent groups were Veillonella spp. (10%) and Neisseria spp. (9%). The most frequently identified tetracycline resistance determinant was tet(M). The results of this study have shown that tetracycline-resistant oral bacteria were widespread amongst the children studied.

The epidemiology of antibiotic resistance in Streptococcus pneumoniae and the clinical relevance of resistance to cephalosporins, macrolides and quinolones

Invasive non-meningeal pneumococcal infections remain a major cause of morbidity and mortality worldwide. The factors affecting the epidemiology and mortality of pneumococcal infections are discussed. The increase and spread of resistance to antimicrobial agents among pneumococci is a cause of concern to the clinician. There are links between the usage of antibacterial agents and the development of resistance. Resistance to penicillin and other beta-lactams has become widespread but this does not appear to have decreased the efficacy of some of these agents against non-meningeal infections. There is evidence that the good pharmacokinetic and pharmacodynamic features of the third generation cephalosporins (cefotaxime and ceftriaxone) contribute to their efficacy in vivo. New breakpoints for cefotaxime and ceftriaxone against non-meningeal pneumococcal isolates were proposed by the National Committee for Clinical Laboratory Standard (NCCLS, US), based on the clinical evidence of the efficacy of these drugs. In contrast there is increasing evidence that resistance to macrolides can lead to a poor clinical response. Fluoroquinolones have been widely used to treat respiratory tract infections among others, and pneumococcal resistance to these agents in vitro, although currently low, is increasing. There are reports that resistance to fluoroquinolones can develop during treatment and may be reflected in a lack of clinical response. Several clinical and epidemiological variables (e.g. prior antibiotic use) can be useful to identify patients at risk from infections with antibiotic-resistant pneumococci. These patients would be those who would benefit the most from a pneumococcal vaccination programme.

Phenotypic and genotypic characterization of two penicillin-susceptible serotype 6B Streptococcus pneumoniae clones circulating in Italy

Twenty-nine penicillin-susceptible serotype 6B strains isolated from patients with invasive diseases and from healthy carriers were examined by different genotyping methods. Ten groups were identified on the basis of the pulsed-field gel electrophoresis (PFGE) profiles, and two of these contained multiple isolates and were analyzed further. PFGE group 1 comprised 12 isolates, the majority of which had a multiresistant phenotype (resistance to erythromycin, clindamycin, tetracycline, chloramphenicol, and trimethoprim-sulfamethoxazole), corresponding to that of a clone previously described in the Mediterranean area and related to penicillin-resistant clone Spain(6B)-2. The pbp2b, pbp2x, dhf, and pspA genes of the isolates had identical restriction profiles; and the partial sequence of pspA was identical to that of clone Spain(6B)-2. In all isolates the resistance determinants erm(B) and tet(M) were inserted in a Tn1545-like element; 11 isolates carried cat as part of the integrated plasmid pC194. Multilocus sequence typing (MLST) performed with two isolates confirmed that their profiles corresponded to that of the Mediterranean clone. PFGE group 2 comprised nine strains, of which the majority showed no antibiotic resistance. Their pspA profiles were different, and the partial sequences obtained for two representative isolates indicated the presence of PspA proteins of different clades. The MLST profile of one strain was identical to that of a serotype 6B strain from the United Kingdom, while two other isolates were novel one-allele variants. This clone appears to be related (five of seven identical alleles) to two other internationally disseminated clones, Hungary(19A)-6 and Poland(23F)-16, both of which are penicillin resistant. The presence of antibiotic-susceptible isolates of this clone suggests that traits other than antibiotic resistance can make a clone successful.

Phenotypic and molecular characterization of tetracycline- and erythromycin-resistant strains of Streptococcus pneumoniae

Sixty-five clinical isolates of Streptococcus pneumoniae, all collected in Italy between 1999 and 2002 and resistant to both tetracycline (MIC, >or=8 microg/ml) and erythromycin (MIC, >or=1 microg/ml), were investigated. Of these strains, 11% were penicillin resistant and 23% were penicillin intermediate. With the use of the erythromycin-clindamycin-rokitamycin triple-disk test, 14 strains were assigned to the constitutive (cMLS) phenotype of macrolide resistance, 44 were assigned to the partially inducible (iMcLS) phenotype, 1 was assigned to the inducible (iMLS) phenotype, and 6 were assigned to the efflux-mediated (M) phenotype. In PCR assays, 64 of the 65 strains were positive for the tetracycline resistance gene tet(M), the exception being the one M isolate susceptible to kanamycin, whereas tet(K), tet(L), and tet(O) were never found. All cMLS, iMcLS, and iMLS isolates had the erythromycin resistance gene erm(B), and all M phenotype isolates had the mef(A) or mef(E) gene. No isolate had the erm(A) gene. The int-Tn gene, encoding the integrase of the Tn916-Tn1545 family of conjugative transposons, was detected in 62 of the 65 test strains. Typing assays showed the strains to be to a great extent unrelated. Of 16 different serotypes detected, the most numerous were 23F (n = 13), 19A (n = 10), 19F (n = 9), 6B (n = 8), and 14 (n = 6). Of 49 different pulsed-field gel electrophoresis types identified, the majority (n = 39) were represented by a single isolate, while the most numerous type included five isolates. By high-resolution restriction analysis of PCR amplicons with four endonucleases, the tet(M) loci from the 64 tet(M)-positive pneumococci were classified into seven distinct restriction types. Overall, a Tn1545-like transposon could reasonably account for tetracycline and erythromycin resistance in the vast majority of the pneumococci of cMLS, iMcLS, and iMLS phenotypes, whereas a Tn916-like transposon could account for tetracycline resistance in most M phenotype strains.

Distribution of tetracycline resistance genes tet(M), tet(O), tet(L) and tet(K) in blood isolates of viridans group streptococci harbouring erm(B) and mef(A) genes. Susceptibility to quinupristin/dalfopristin and linezolid

Susceptibility to erythromycin, tetracycline, clindamycin, quinupristin/dalfopristin and linezolid was investigated using 111 consecutive non-duplicate blood culture isolates of viridans-group streptococci (VGS). The erm(B) and mef(A) genes were detected, either alone or in combination, in the 47 (42%) erythromycin-resistant strains. The tet(M) gene alone was predominant (78%) in the 36 (35%) tetracycline-resistant isolates. Two isolates carried the tet(O) gene alone and two others the tet(L) associated with tet(O) or tet(M). The association between erythromycin and tetracycline resistance was common and the erm(B) and tet(M) determinants seem to be associated in our VGS. We found three isolates resistant to quinupristin/dalfopristin, all of them were erythromycin and tetracycline-resistant. For all isolates tested, linezolid MICs were <or=2 mg/l.

Antibacterial resistance in Streptococcus pneumoniae and Haemophilus influenzae from Italy and Spain: data from the PROTEKT surveillance study, 1999-2000

Antibacterial resistance was evaluated among Streptococcus pneumoniae (n=252) and Haemophilus influenzae (n=202) from two centres in Spain (Barcelona and Madrid) and two centres in Italy (Genoa and Catania) collected during 1999-2000 as part of the ongoing PROTEKT (Prospective Resistant Organism Tracking and Epidemiology for the Ketolide Telithromycin) international surveillance program. Pneumococcal nonsusceptibility to penicillin G was found to be considerably higher in Spain (53.4%) than in Italy (15.1%), whereas erythromycin A resistance was higher in Italy (42.9%) than in Spain (28.6%). Among macrolide-resistant isolates investigated for resistance genes, the prevalence of mefA was higher among isolates from Italy (20/51, 39.2%) than among Spanish isolates (2/38, 5.3%). All other macrolide-resistant isolates possessed ermB. Telithromycin possessed good anti-pneumococcal activity against isolates from both countries (MIC90 0.03 mg/L [Spain]; 0.25 mg/L [Italy]), irrespective of resistance to other antibacterials. Beta-lactamase production among H. influenzae was low: Spain, 10.9%; Italy, 1.8%. With the exception of ampicillin and co-trimoxazole, all H. influenzae isolates were highly susceptible to the antibacterials tested, and all were inhibited by telithromycin at a concentration of < or = 2 mg/L. The findings of PROTEKT 1999-2000 highlight the importance of local resistance patterns in guiding the choice of empirical antibacterials for community-acquired respiratory tract infections.

Phenotypes and genotypes of erythromycin-resistant pneumococci in Italy

Of 120 erythromycin-resistant pneumococci isolated in Italian hospitals, 39 (32.5%) were M-type isolates, carrying the mef gene alone. The mef gene was also detected, together with erm(AM), in one constitutively resistant isolate and in five isolates of the partially inducible phenotype. Among the 45 mef-positive isolates, 25 (55.6%) carried mef(A) and 20 (44.4%) carried mef(E) as observed from PCR-restriction fragment length polymorphism analysis of a 1,743-bp amplicon. The same result was obtained by a similar method applied to a more common 348-bp amplicon.

Molecular epidemiology of erythromycin resistance in Streptococcus pneumoniae isolates from blood and noninvasive sites

Erythromycin-resistant isolates of Streptococcus pneumoniae from blood cultures and noninvasive sites were studied over a 3-year period. The prevalence of erythromycin resistance was 11.9% (19 of 160) in blood culture isolates but 4.2% (60 of 1,435) in noninvasive-site isolates. Sixty-two of the 79 resistant isolates were available for study. The M phenotype was responsible for 76% (47 of 62) of resistance, largely due to a serotype 14 clone, characterized by multilocus sequence typing as ST9, which accounted for 79% (37 of 47) of M phenotype resistance. The ST9 clone was 4.8 times more common in blood than in noninvasive sites. All M phenotype isolates were PCR positive for mef(A), but sequencing revealed that the ST9 clone possessed the mef(A) sequence commonly associated with Streptococcus pyogenes. All M phenotype isolates with this mef(A) sequence also had sequences consistent with the presence of the Tn1207.1 genetic element inserted in the celB gene. In contrast, isolates with the mef(E) sequence normally associated with S. pneumoniae contained sequences consistent with the presence of the mega insertion element. All MLS(B) isolates carried erm(B), and two isolates carried both erm(B) and mef(E). Fourteen of the 15 MLS(B) isolates were tetracycline resistant and contained tet(M). However, six M phenotype isolates of serotypes 19 (two isolates) and 23 (four isolates) were also tetracycline resistant and contained tet(M). MICs for isolates with the mef(A) sequence were significantly higher than MICs for isolates with the mef(E) sequence (P < 0.001). Thus, the ST9 clone of S. pneumoniae is a significant cause of invasive pneumococcal disease in northeast Scotland and is the single most important contributor to M phenotype erythromycin resistance.