In vitro activities of the new ketolide HMR 3647 (telithromycin) in comparison with those of eight other antibiotics against viridans group Streptococci isolated from blood of neutropenic patients with cancer

recA-based PCR assay for accurate differentiation of Streptococcus pneumoniae from other viridans streptococci

Proper identification of Streptococcus pneumoniae by conventional methods remains problematic. The discriminatory power of the 16S rRNA gene, which can be considered the "gold standard" for molecular identification, is too low to differentiate S. pneumoniae from closely related species such as Streptococcus pseudopneumoniae, Streptococcus mitis, and Streptococcus oralis in the routine clinical laboratory. A 313-bp part of recA was selected on the basis of variability within the S. mitis group, showing <95.8% interspecies homology. In addition, 6 signature nucleotides specific for S. pneumoniae were identified within the 313-bp recA fragment. We show that recA analysis is a useful tool for proper identification to species level within the S. mitis group, in particular, for pneumococci.

New species genetic approach to identify strains of mitis group streptococci that are donors of rifampin resistance to Streptococcus pneumoniae

Eight rifampin-resistant streptococci of the mitis group were identified at the species level by using a concatenated 16S rRNA gene-sodA-rpoB-hlpA sequence. Characterization of their rpoB alleles showed single amino acid changes involved in rifampin resistance. Comparison of RpoB sequences from pneumococcal recombinant isolates, viridans isolates, and type strains revealed a species-specific amino acid signature, which allowed it to be ascertained that recombinant RpoBs were originated in genetic interchanges with Streptococcus mitis and Streptococcus oralis.

Antimicrobial resistance of streptococci isolated from mastitic bovine milk samples in Korea

The aim of this study was to determine the antimicrobial resistance of streptococci isolated from mastitic bovine milk samples. A total of 178 isolates belonging to 6 different Streptococcus species were examined: S. uberis (n = 99), S. bovis (n = 30), S. oralis (n = 24), S. salivarius (n = 13), S. intermedius (n = 7), and S. agalactiae (n = 5). Only 8.9% (16/178) of the isolates were susceptible to all antimicrobial agents tested in this study, and S. agalactiae and S. intermedius isolates were all resistant to at least 1 antimicrobial agent tested. Overall, the most frequently observed resistance was to tetracycline (61.2%), followed by lincomycin (43.2%), gentamycin (35.3%), oxacillin (34.3%), and erythromycin (28.6%). Cephalothin and penicillin were the only antimicrobial agents to which most of the streptococci (>or=92%) were susceptible. Wide differences in the prevalence of resistance are apparent among the individual species: S. salivarius displayed exceptionally high resistance to cephalothin (23.0%) and oxacillin (76.9%) and S. agalactiae (20%) and S. intermedius (14.2%) to penicillin. Streptococcus salivarius and S. agalactiae were all susceptible to erythromycin, but others showed various rates of resistance ranging from 12.5% to 42.8%. Resistance to 3 or more of 7 antimicrobial agents was observed in all species (37.6%, 67/178).

Antibiotic Resistance of Non-Pneumococcal Streptococci and Its Clinical Impact

Viridans streptococci (VGS) form a phylogenetically heterogeneous group of species belonging to the genus Streptococcus (1). However, they have some common phenotypic properties. They are alfa- or non-haemolytic. They can be differentiated from S. pneumoniae by resistance to optochin and the lack of bile solubility (2). They can be differentiated from the Enterococcus species by their inability to grow in a medium containing 6.5% sodium chloride (2). Earlier, so-called nutritionally variant streptococci were included in the VGS but based on the molecular data they have now been removed to a new genus Abiotrophia (3) and are not included in the discussion below. VGS belong to the normal microbiota of the oral cavities and upper respiratory tracts of humans and animals. They can also be isolated from the female genital tract and all regions of the gastrointestinal tract (2, 3). Several species are included in VGS and are listed elsewhere (2, 3). Clinically the most important species belonging to the VGS are S. mitis, S. sanguis and S. oralis.

In vitro susceptibility of viridans group streptococci isolated from blood in southwest Finland in 1993-2004

We studied in vitro activity against invasive viridans group streptococci (VGS) of penicillin and 4 newer antibiotics, i.e. telithromycin, linezolid, levofloxacin and quinupristin-dalfopristin. Also 7 other antibiotics were tested. Antibiotic susceptibility of 263 VGS blood isolates, collected from southwest Finland during a 12-y period was determined. We wished to discover whether there is an increasing trend of antimicrobial resistance among VGS in Finland. Our results showed that penicillin is still a good choice for treating VGS infections based on the considerably low resistance percentage, 2.3%. Also newer antibiotics showed good in vitro activity: susceptibilities for telithromycin, linezolid and levofloxacin were 100%, 98.9% and 94.6%, respectively. However, quinupristin-dalfopristin was not as effective as described in previous studies, with only 57% susceptibility.

Viridans Group Streptococcal Infections Among Children With Cancer and the Importance of Emerging Antibiotic Resistance

Viridans group streptococci (VGS) are major pathogens among children with cancer or receiving hematopoietic stem cell transplantation and are associated with considerable morbidity and mortality rates. The incidence and severity of VGS infections have increased during the past 15 years and account for as many as one third of all bacteremic episodes. Risk factors include severe neutropenia, mucositis, gastrointestinal toxicity, pneumonia, younger age, and high-intensity chemotherapy (especially cytosine arabinoside). VGS no longer can be assumed to be susceptible to penicillin because as many as 37 percent of VGS isolates harbor high levels of resistance (minimum inhibitory concentration >4 microg/mL). Furthermore, resistance to multiple classes of antibiotics, including beta-lactams and fluoroquinolones, has now been documented and is increasing in prevalence. In this article, we present a brief overview of VGS, describe the clinical spectrum of VGS-related diseases in children with cancer, and review the recent data regarding the incidence, clinical significance, and management of emerging antibiotic resistance among VGS.

Viridans streptococci isolated by culture from blood of cancer patients: clinical and microbiologic analysis of 50 cases

Clinical and microbiologic studies of 50 cases of viridans streptococcal bacteremia in cancer patients were performed. The bacteria were identified to species level by sequencing analysis of the 16S rRNA gene. At least nine Streptococcus spp. were found, including S. mitis (25 strains, 50.0% of 50); currently unnamed Streptococcus spp. (11 strains); S. parasanguis (five strains); S. anginosus (three strains); S. salivarius (two strains); and one strain each of S. gordonii, S. sanguis, S. sobrinus, and S. vestibularis. There were no S. oralis strains. Among 11 antibiotics of nine classes tested, no resistance to vancomycin, linezolid, or quinupristin-dalfopristin was seen. Resistance to penicillin (MIC, 4 to 12 mug/ml) was noted only among S. mitis strains (28.0%, 7/25) and not non-S. mitis strains (0/25) (P = 0.004). Significantly more S. mitis strains than non-S. mitis strains were resistant to fluoroquinolones and to > or =3 classes of antibiotics. Isolation of quinolone-resistant organisms was associated with the prior usage of quinolones (P = 0.002). Quantitative blood cultures showed that the strains resistant to levofloxacin or gatifloxacin were associated with higher colony counts than were their corresponding nonresistant strains. The young and elderly patients also had higher levels of bacteremia caused predominantly by S. mitis. Septic shock was present in 17 (34.0% of 50) patients, and 13 of those cases were caused by S. mitis (P = 0.007). These results suggest that S. mitis is the most common cause of viridans streptococcal bacteremia in cancer patients and is more resistant to antibiotics than other species.

Evaluation of the BD Phoenix Automated Microbiology System SMIC/ID panel for identification and antimicrobial susceptibility testing of Streptococcus spp

The BD Phoenix Automated Microbiology System SMIC/ID panel was evaluated for identification and antimicrobial susceptibility testing (AST) of various streptococci. A group of 97 consecutive clinical isolates of Streptococcus pneumoniae, 23 Streptococcus pyogenes, 24 Streptococcus agalactiae, and 34 viridans streptococci were collected and comparisons made with routine manual methods used in the clinical microbiology laboratory. Overall, in 162 (91%) of 178 isolates, Phoenix identification results demonstrated agreement. For AST results for the 162 isolates that demonstrated identification concordance, the overall essential agreement rate was 98.5%; the category agreement was 94.9%; and the very major error, major error, and minor error rates were 0%, 0.15%, and 5.8%, respectively. Although relatively high minor error rates were observed with S. pneumoniae and beta-lactams, 79.2% of the 77 minor errors were the result of a single log(2) dilution difference. The Phoenix SMIC/ID panel performed favorably and demonstrated the advantages of automation and simple methodology.

In vitro activity of telithromycin against viridans group streptococci and Streptococcus bovis isolated from blood: antimicrobial susceptibility patterns in different groups of species

The in vitro activities of penicillin, erythromycin, clindamycin, and telithromycin were determined against 155 viridans group streptococci (VGS) and 18 Streptococcus bovis blood isolates. Heterogeneity in the susceptibility patterns and macrolide resistance phenotypes and genotypes in the different groups of VGS was detected. We found seven telithromycin-resistant S. bovis isolates all harboring the erm(B) gene.

In vitro activity of telithromycin against mefA and ermB erythromycin-resistant viridans streptococci isolated from bacteremia of oral origin in Spain

Erythromycin-resistant viridans streptococci are often responsible of bacteremias following dental manipulations. The aim of this study was to evaluate the in vitro activity of telithromycin against erythromycin-susceptible and erythromycin-resistant viridans streptococci. Venous blood samples were collected from 84 patients, 30 s after dental extractions. Viridans streptococci were identified by conventional microbiological techniques. A set of 36 viridans streptococci were selected to investigate the in vitro activity of telithromycin by the agar dilution method. Macrolide resistance genes were amplified with specific primers for the mefA and ermB genes and visualized by electrophoresis. For erythromycin-susceptible viridans streptococci, telithromycin minimal inhibitory concentration90 (MIC90) was <0.008 microg/ml. For erythromycin-resistant viridans streptococci, telithromycin MIC90 was 1 microg/ml. The MIC90 to telithromycin of the mefA-positive and ermB-negative viridans streptococci was lower than that of the mefA-negative and ermB-positive viridans streptococci (0.128 microg/ml versus 1 microg/ml). The in vitro activity of telithromycin was high, irrespective of the erythromycin susceptibility and the mechanism of erythromycin resistance identified.

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%).

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.

What happened to the streptococci: overview of taxonomic and nomenclature changes

Since the division of the Streptococcus genus into enterococci, lactococci, and streptococci in 1984, many changes in the nomenclature and taxonomy of the Streptococcus genus have taken place. The application of genetic comparisons has improved the proper classification of the different species. The Lancefield system of serogrouping the streptococci by the expression of beta-hemolysis on blood agar plates is still very useful for the identification of streptococci for patient management. The Lancefield grouping system cannot be used in itself for accurate identification of specific beta-hemolytic species, but it can be a useful part of the identification procedure. Except for identification of the "Streptococcus bovis group" of species and Streptococcus suis, Lancefield grouping is of little value in identification of the non-beta-hemolytic streptococci and related genera. In fact, identification of the non-beta-hemolytic species is problematic for conventional as well as commercially available identification procedures. A combination of conventional tests and specific chromogenic tests suggested by several investigators is presented and discussed. Tables are included that suggest tests and procedures to guide investigators attempting to identify all the species.

The ketolides: a critical review

Ketolides are a new class of macrolides designed particularly to combat respiratory tract pathogens that have acquired resistance to macrolides. The ketolides are semi-synthetic derivatives of the 14-membered macrolide erythromycin A, and retain the erythromycin macrolactone ring structure as well as the D-desosamine sugar attached at position 5. The defining characteristic of the ketolides is the removal of the neutral sugar, L-cladinose from the 3 position of the ring and the subsequent oxidation of the 3-hydroxyl to a 3-keto functional group. The ketolides presently under development additionally contain an 11, 12 cyclic carbamate linkage in place of the two hydroxyl groups of erythromycin A and an arylalkyl or an arylallyl chain, imparting in vitro activity equal to or better than the newer macrolides. Telithromycin is the first member of this new class to be approved for clinical use, while ABT-773 is presently in phase III of development. Ketolides have a mechanism of action very similar to erythromycin A from which they have been derived. They potently inhibit protein synthesis by interacting close to the peptidyl transferase site of the bacterial 50S ribosomal subunit. Ketolides bind to ribosomes with higher affinity than macrolides. The ketolides exhibit good activity against Gram-positive aerobes and some Gram-negative aerobes, and have excellent activity against drug-resistant Streptococcus pneumoniae, including macrolide-resistant (mefA and ermB strains of S. pneumoniae). Ketolides such as telithromycin display excellent pharmacokinetics allowing once daily dose administration and extensive tissue distribution relative to serum. Evidence suggests the ketolides are primarily metabolised in the liver and that elimination is by a combination of biliary, hepatic and urinary excretion. Pharmacodynamically, ketolides display an element of concentration dependent killing unlike macrolides which are considered time dependent killers. Clinical trial data are only available for telithromycin and have focused on respiratory infections including community-acquired pneumonia, acute exacerbations of chronic bronchitis, sinusitis and streptococcal pharyngitis. Bacteriological and clinical cure rates have been similar to comparators. Limited data suggest very good eradication of macrolide-resistant and penicillin-resistant S. pneumoniae. As a class, the macrolides are well tolerated and can be used safely. Limited clinical trial data suggest that ketolides have similar safety profiles to the newer macrolides. Telithromycin interacts with the cytochrome P450 enzyme system (specifically CYP 3A4) in a reversible fashion and limited clinically significant drug interactions occur. In summary, clinical trials support the clinical efficacy of the ketolides in upper and lower respiratory tract infections caused by typical and atypical pathogens including strains resistant to penicillins and macrolides. Considerations such as local epidemiology, patterns of resistance and ketolide adverse effects, drug interactions and cost relative to existing agents will define the role of these agents. The addition of the ketolides in the era of antibacterial resistance provides clinicians with more options in the treatment of respiratory infections.

Infections caused by viridans streptococci in patients with neutropenia

The frequency of isolation of viridans streptococci from the blood of neutropenic patients with cancer has significantly increased over the course of the last 10-15 years. Risk factors in this patient population include severe neutropenia, oral mucositis, administration of high-dose cytosine arabinoside, and antimicrobial prophylaxis with either trimethoprim-sulfamethoxazole or a fluoroquinolone. In some patients with cancer and neutropenia who develop viridans streptococcal bacteremia, a toxic shock-like syndrome has been described; Streptococcus mitis has been the causative species in most cases. Because resistance of viridans streptococci to a variety of antimicrobial agents is increasingly recognized, penicillin susceptibility cannot be assumed, and empirical vancomycin therapy should be used to treat neutropenic patients with cancer who have shock or are developing acute respiratory distress syndrome. Given the seriousness of septicemia caused by viridans streptococci and the potential for selection of other resistant microorganisms, the routine practice of antimicrobial prophylaxis for neutropenic patients with cancer should be reconsidered.

Ketolides in the treatment of respiratory infections

The ketolides are a new class of macrolides specifically designed to combat respiratory tract pathogens that have acquired resistance to macrolides. The ketolides are semi-synthetic derivatives of the 14-membered macrolide erythromycin A. There are currently two ketolides in the late stages of clinical development in the US (telithromycin [HMR-364, Kelek; Aventis] and ABT-773 [Abbot Laboratories]), as well as newer compounds in earlier stages of testing. Ketolides have a mechanism of action very similar to that of erythromycin A. They potently inhibit protein synthesis by interacting close to the peptidyl transferase site of the bacterial 50S ribosomal subunit. Ketolides bind to ribosomes with higher affinity than macrolides. The ketolides exhibit good activity against Gram-positive and some Gram-negative aerobes and have are active against macrolide-resistant Streptococcus species, including most mef A and erm B strains of Streptococcus pneumoniae. Ketolides have pharmacokinetics which allow once-daily dosing and extensive tissue distribution with very high uptake into respiratory tissues and fluids relative to serum. Evidence suggests the ketolides are primarily metabolised by the cytochrome P450 (CYP) enzyme system in the liver and that elimination is a combination of biliary, hepatic and urinary excretion. Clinical trial data are only available for telithromycin and have focused on respiratory tract infections (RTIs) including community-acquired pneumonia (CAP), acute exacerbations of chronic bronchitis (AECB), sinusitis and streptococcal pharyngitis. Bacteriological and clinical cure rates have been similar to comparators. Ketolides have similar safety profiles to the newer macrolides. In summary, early clinical trials support the clinical efficacy of the ketolides in common RTIs, including activity against macrolide-resistant pathogens.

Ribosomal mutations in Streptococcus pneumoniae clinical isolates

Eleven clinical isolates of Streptococcus pneumoniae, isolated in Finland during 1996 to 2000, had an unusual macrolide resistance phenotype. They were resistant to macrolides and streptogramin B but susceptible, intermediate, or low-level resistant to lincosamides. No acquired macrolide resistance genes were detected from the strains. The isolates were found to have mutations in domain V of the 23S rRNA or ribosomal protein L4. Seven isolates had an A2059C mutation in two to four out of the four alleles encoding the 23S rRNA, two isolates had an A2059G mutation in two alleles, one isolate had a C2611G mutation in all four alleles, and one isolate had a 69GTG71-to-69TPS71 substitution in ribosomal protein L4.

Telithromycin: an oral ketolide for respiratory infections

The ketolides represent a new subclass of antibiotics among the macrolide-lincosamide-streptogramin group. Telithromycin, the first ketolide to be awarded approvable status for clinical use, demonstrates in vitro activity against community-acquired respiratory pathogens including penicillin- and erythromycin-resistant Streptococcus pneumoniae. An extended half-life permits once-daily oral administration. Telithromycin is a substrate for cytochrome P450 (CYP) 3A4 and also inhibits drugs metabolized by CYP3A4. A relatively high frequency of mild-to-moderate gastrointestinal adverse effects has been reported. Similar clinical and microbiologic efficacy has been demonstrated with oral dosing in comparative clinical trials for community-acquired pneumonia, acute sinusitis, acute exacerbations of chronic bronchitis, and pharyngitis. Although limited data on penicillin-resistant S. pneumoniae and erythromycin-resistant Streptococcus pyogenes are available from clinical trials, this drug appears promising for respiratory infections caused by these pathogens.