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

Drug Resistance Characteristics and Macrolide-Resistant Mechanisms of Streptococcus pneumoniae in Wenzhou City, China

Background

Streptococcus pneumoniae (SP) is a Gram-positive, alpha-hemolytic, facultative anaerobic member of the genus Streptococcus. The erythromycin-resistant methylase (erm) gene and macrolide efflux (mef) gene are the 2 main genes that can mediate SP. Transposon (Tn) also plays an important role in the collection and metastasis of the gene. In the present study we investigated the drug resistance characteristics and the macrolide-resistant mechanisms of SP in Wenzhou City, China.

Material/Methods

Sixty-eight strains of SP were isolated from sputum samples of hospitalized children in the Second Affiliated Hospital of Wenzhou Medical University. These strains were analyzed using antimicrobial susceptibility tests to determine their drug resistance to 10 kinds of antibacterials. Macrolide-resistant phenotypes were identified using K-B method. PCR method was used to analyze the erm B gene, mef A gene, and int Tn gene.

Results

Drug resistance rates of 68 strains of SP were 98.5%, 100.0%, 63.2%, 52.9%, 94.1%, 89.7%, 0.0%, 0.0%, 16.2%, and 14.7% for clindamycin, erythromycin, penicillin G, cefotaxime, tetracycline, sulfamethoxazole/trimethoprim, levofloxacin, vancomycin, chloramphenicol, and amoxicillin, respectively. Total detection rates of the erm B gene, mef A gene, and int Tn gene were 98.5%, 91.2%, and 100.0%, respectively.

Conclusions

SP shows significant multi-drug resistance in Wenzhou City, whereas there is no clinical value of macrolides antibiotics for SP. cMLS_B mediated by erm B gene is the most predominant phenotype among macrolide-resistant SP. The int Tn gene may play an important role in horizontal transfer and clonal dissemination of SP drug resistance genes in Wenzhou City.

Serotype Distribution and Antimicrobial Resistance of Streptococcus pneumoniae Isolates Causing Invasive and Noninvasive Pneumococcal Diseases in Korea from 2008 to 2014

Introduction. Streptococcus pneumoniae is an important pathogen with high morbidity and mortality rates. The aim of this study was to evaluate the distribution of common serotypes and antimicrobial susceptibility of S. pneumoniae in Korea. Methods. A total of 378 pneumococcal isolates were collected from 2008 through 2014. We analyzed the serotype and antimicrobial susceptibility for both invasive and noninvasive isolates. Results. Over the 7 years, 3 (13.5%), 35 (10.8%), 19A (9.0%), 19F (6.6%), 6A (6.1%), and 34 (5.6%) were common serotypes/serogroups. The vaccine coverage rates of PCV7, PCV10, PCV13, and PPSV23 were 21.4%, 23.3%, 51.9%, and 62.4% in all periods. The proportions of serotypes 19A and 19F decreased and nonvaccine serotypes increased between 2008 and 2010 and 2011 and 2014. Of 378 S. pneumoniae isolates, 131 (34.7%) were multidrug resistant (MDR) and serotypes 19A and 19F were predominant. The resistance rate to levofloxacin was significantly increased (7.2%). Conclusion. We found changes of pneumococcal serotype and antimicrobial susceptibility during the 7 years after introduction of the first pneumococcal vaccine. It is important to continuously monitor pneumococcal serotypes and their susceptibilities.

Variable recombination dynamics during the emergence, transmission and 'disarming' of a multidrug-resistant pneumococcal clone

BACKGROUND

Pneumococcal β-lactam resistance was first detected in Iceland in the late 1980s, and subsequently peaked at almost 25% of clinical isolates in the mid-1990s largely due to the spread of the internationally-disseminated multidrug-resistant PMEN2 (or Spain6B-2) clone of Streptococcus pneumoniae.

RESULTS

Whole genome sequencing of an international collection of 189 isolates estimated that PMEN2 emerged around the late 1960s, developing resistance through multiple homologous recombinations and the acquisition of a Tn5253-type integrative and conjugative element (ICE). Two distinct clades entered Iceland in the 1980s, one of which had acquired a macrolide resistance cassette and was estimated to have risen sharply in its prevalence by coalescent analysis. Transmission within the island appeared to mainly emanate from Reykjavík and the Southern Peninsular, with evolution of the bacteria effectively clonal, mainly due to a prophage disrupting a gene necessary for genetic transformation in many isolates. A subsequent decline in PMEN2's prevalence in Iceland coincided with a nationwide campaign that reduced dispensing of antibiotics to children in an attempt to limit its spread. Specific mutations causing inactivation or loss of ICE-borne resistance genes were identified from the genome sequences of isolates that reverted to drug susceptible phenotypes around this time. Phylogenetic analysis revealed some of these occurred on multiple occasions in parallel, suggesting they may have been at least temporarily advantageous. However, alteration of 'core' sequences associated with resistance was precluded by the absence of any substantial homologous recombination events.

CONCLUSIONS

PMEN2's clonal evolution was successful over the short-term in a limited geographical region, but its inability to alter major antigens or 'core' gene sequences associated with resistance may have prevented persistence over longer timespans.

Activity of Telithromycin Against Multi-Drug ResistantStreptococcus pneumoniaeand Molecular Characterization of Macrolide and Tetracycline Resistance Determinants

The antistreptococcal activity of telithromycin and 11 different comparators was evaluated in 26 multi-drug resistant (MDR) Streptococcus pneumoniae strains collected during 2002-2003 as part of the ongoing PROTEKT (Prospective Resistant Organism Tracking and Epidemiology for the Ketolide Telithromycin) Italian Surveillance Program. The strains were characterized for their susceptibility to antibiotics both at the phenotypic and genotypic levels; furthermore, the association of erm(B), mef(A) class and tet(M) genes, as well as the mobile elements carrying them were determined. The strains in this study were resistant to penicillin (MIC > or = 2 mg/l) in 23.1% of cases, resistant to tetracycline in 88.4%, to cotrimoxazole in 34.6% and cefuroxime in 26.9% while only telithromycin and levofloxacin retained 100% activity against all microorganisms. Co-existence of different resistance determinants was found in 19.2% of all isolates collected in our laboratory, coming from southern Italy. Twenty-three isolates showing the MLSB phenotype of resistance possessing the erm(B) gene (88.5%), associated with tet(M), were carried on the same Tn1545-like element, while two isolates showing the M phenotype possessing the mef(A) gene alone, were carried on Tn1207.1. In only one strain were mef(E) and tet(M) together carried on Tn2009.

High prevalence of multiresistance in levofloxacin-nonsusceptible Streptococcus pneumoniae isolates in Korea

Korea exhibits the highest rates of multidrug resistance among Streptococcus pneumoniae. The increasing use of levofloxacin has raised concern about the dissemination of levofloxacin resistance in dominant multidrug-resistant (MDR) clones of our pneumococcal population. A total of 50 levofloxacin-nonsusceptible S. pneumoniae (MIC, ≥4 μg/mL) collected from a multihospital network from 1996 to 2006 were analyzed for serotype, antibiotic resistance profile, quinolone resistance-determining region mutation, and multilocus sequence type. Most levofloxacin-nonsusceptible S. pneumoniae (94.0%) exhibited an MDR phenotype. This phenotype was closely associated with a limited number of epidemic MDR clones that are well-known key agents of the global spread of antimicrobial resistance in S. pneumoniae. However, the clonal dissemination of levofloxacin-nonsusceptible S. pneumoniae was rare. Levofloxacin-nonsusceptible clones with nonvaccine serotypes increased during the post-vaccine era in this study. This result suggests that Korean clinicians must be aware of the levofloxacin resistance trend and need to be more prudent for the first choice of fluoroquinolone for empiric treatment of respiratory tract infections in clinical setting. Moreover, the emergence of new clones and their variations may be more frequently associated with resistance under this selective pressure, such as the introduction of a 7-valent pneumococcal conjugate vaccine into our community.

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.

C-9 Alkenylidine bridged macrolides: WO2008061189. Enanta Pharmaceuticals, Inc

Ketolides, which represent the third generation of erythromycin A derivatives, were developed as a result of the need for new and potent antibacterial agents. This class of compounds has a significantly improved pharmacokinetic profile and, above all, shows activity against macrolide-resistant strains. When compared with other macrolides, ketolide structural differences are characterized by the removal of the 3-O-cladinose moiety and by a heteroaryl-alkyl side chain attached to the macrocycle by a flexible linker. The bridged bicyclic ketolides (BBK) are one of the three classes of ketolide; the present application from Enanta Pharmaceuticals, Inc. discloses a series of novel C-9 alkenylidine bridged macrolides belonging to BBK. These compounds are 3,6- and 6,11-bicyclolides, which have the alkenylidine second anchor portion attached to C-9 of the molecule.

In vitro activities of the Rx-01 oxazolidinones against hospital and community pathogens

Rx-01_423 and Rx-01_667 are two members of the family of oxazolidinones that were designed using a combination of computational and medicinal chemistry and conventional biological techniques. The compounds have a two- to eightfold-improved potency over linezolid against serious gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), multidrug-resistant streptococci, and vancomycin-resistant enterococci. This enhanced potency extends to the coverage of linezolid-resistant gram-positive microbes, especially multidrug-resistant enterococci and pneumococci. Compounds from this series expand the spectrum compared with linezolid to include fastidious gram-negative organisms like Haemophilus influenzae and Moraxella catarrhalis. Like linezolid, the Rx-01 compounds are bacteriostatic against MRSA and enterococci but are generally bactericidal against S. pneumoniae and H. influenzae.

Streptococcus pneumoniae choline-binding protein E interaction with plasminogen/plasmin stimulates migration across the extracellular matrix

The virulence mechanisms leading Streptococcus pneumoniae to convert from nasopharyngeal colonization to a tissue-invasive phenotype are still largely unknown. Proliferation of infection requires penetration of the extracellular matrix, which occurs by recruitment of host proteases to the bacterial cell surface. We present evidence supporting the role of choline-binding protein E (CBPE) (a member of the surface-exposed choline-binding protein family) as an important receptor for human plasminogen, the precursor of plasmin. The results of ligand overlay blot analyses, solid-phase binding assays, and surface plasmon resonance experiments support the idea of an interaction between CBPE and plasminogen. We have shown that the phosphorylcholine esterase (Pce) domain of CBPE interacts with the plasminogen kringle domains. Analysis of the crystal structure of the Pce domain, followed by site-directed mutagenesis, allowed the identification of the plasminogen-binding region composed in part by lysine residues, some of which map in a linear fashion on the surface of the Pce domain. The biological relevance of the CBPE-plasminogen interaction is supported by the fact that, compared to the wild-type strain, a mutant of pneumococcus with the cbpE gene deleted (i) displays a reduced level of plasminogen binding and plasmin activation and (ii) shows reduced ability to cross the extracellular matrix in an in vitro model. These results support the idea of a physiological role for the CBPE-plasminogen interaction in pneumococcal dissemination into human tissue.

Prevalence, characteristics, and molecular epidemiology of macrolide and fluoroquinolone resistance in clinical isolates of Streptococcus pneumoniae at five tertiary-care hospitals in Korea

The genes erm(B), mef(A), and both erm(B) and mef(A) were identified in 42.6, 10.1, and 47.3%, respectively, of the erythromycin-resistant Streptococcus pneumoniae isolates. Of the strains, 3.8% were nonsusceptible to levofloxacin and had 1 to 6 amino acid changes in the quinolone resistance-determining region, including a new mutation, Asn94Ser, in the product of parC. Levofloxacin with reserpine was highly specific for efflux screening.

Comparative in vitro and bactericidal activities of telithromycin against penicillin-nonsusceptible, levofloxacin-resistant, and macrolide-resistant Streptococcus pneumoniae by time-kill methodology

Broth microdilution MICs were determined for 14 antimicrobial agents against 296 clinical, non-duplicate isolates of Streptococcus pneumoniae collected at Methodist Hospital (Indianapolis, Indiana, USA) from January 2001 to December 2003. Isolates were categorized as susceptible, intermediate, or resistant using Clinical and Laboratory Standards Institute breakpoints. Time-kill studies were performed to evaluate the bactericidal activity of telithromycin at 1, 2, 4, and 8x MIC against 10 penicillin-nonsusceptible, levofloxacin-resistant, and macrolide-resistant (7 M-phenotype, 3 MLS(B)-phenotype) strains. Bactericidal activity was defined as a >/=3-log(10) reduction in CFU/mL. The prevalence of resistance was highest for the macrolides (32%), followed by penicillin (16.2%), clindamycin (10.8%), amoxicillin+/-clavulanate (4.4%), levofloxacin (3.0%), gatifloxacin and moxifloxacin (2.4%), ceftriaxone and cefotaxime (2.0%), and gemifloxacin (1.4%). None of the isolates tested were resistant to telithromycin. At 24h, telithromycin was bactericidal for 0/10, 2/10, 7/10, and 7/10 isolates at 1x MIC, 2x MIC, 4x MIC, and 8x MIC, respectively. At 4-8x MIC, telithromycin was bactericidal for 7/7 M-phenotype isolates and 0/3 MLS(B)-phenotype isolates. For the MLS(B)-phenotype isolates, colony counts were decreased by 1.3-2.1log(10) colony-forming units/mL after 24h at 8x MIC. Overall, telithromycin was highly active against 296 isolates of S. pneumoniae from our institution and demonstrated bactericidal activity at clinically achievable concentrations for 7 of 10 penicillin-nonsusceptible, levofloxacin-resistant, and macrolide-resistant S. pneumoniae. However, telithromycin was bacteriostatic for the MLS(B)-phenotype isolates.

Optimizing the management of community-acquired respiratory tract infections in the age of antimicrobial resistance

Community-acquired respiratory tract infections (CARTIs) are the most common reason for prescribing antibiotics in the primary care setting. However, over the last decade, the management of CARTIs has become increasingly complicated by the steady increase in prevalence of drug-resistant pathogens responsible for these infections. As a result, significant attention has been directed at understanding the mechanisms of pathogen acquisition of resistance, drivers of resistance and methods for preventing the development of resistance. Data from recent surveillance studies suggest a slowing or decline in resistance rates to agents, such as beta-lactams, macrolides, tetracyclines and folic acid metabolism inhibitors. However, resistance to one antimicrobial family--the fluoroquinolones--while still low, appears to be on the increase. This is of significant concern given the rapid increase in resistance noted with older antibiotics in recent history. While the clinical implications of antibacterial resistance are poorly understood, the overall rates of antimicrobial resistance, as reported in recent surveillance studies, do not correspond to current rates of failure in patients with CARTIs. This disconnection between laboratory-determined resistance and clinical outcome has been termed the in vitro-in vivo paradox and several explanations have been offered to explain this phenomenon. Solving the problem of antimicrobial resistance will be multifactorial. Important factors in this effort include the education of healthcare providers, patients and the general healthcare community regarding the hazards of inappropriate antibiotic use, prevention of infections through vaccination, development of accurate, inexpensive and timely point-of-care diagnostic tests to aid in patient assessment, institution of objective treatment guidelines and use of more potent agents, especially those with a focused spectrum of activity, earlier in the treatment of CARTIs as opposed to reserving them as second-line treatment options. Ultimately, the single-most important factor will be the judicious use of antibiotics, as fewer antibiotic prescriptions lead to fewer antimicrobial-resistant bacteria.

Macrolide efflux in Streptococcus pneumoniae is mediated by a dual efflux pump (mel and mef) and is erythromycin inducible

Macrolide resistance in Streptococcus pneumoniae due to efflux has emerged as an important worldwide clinical problem over the past decade. Efflux is mediated by the genes of the genetic element mega (macrolide efflux genetic assembly) and related elements, such as Tn1207.1. These elements contain two adjacent genes, mef (mefE or mefA) and the closely related mel gene (msrA homolog), encoding a proton motive force pump and a putative ATP-binding cassette transporter homolog, and are transcribed as an operon (M. Del Grosso et al., J. Clin. Microbiol. 40:774-778, 2004; K. Gay and D. S. Stephens, J. Infect. Dis. 184:56-65, 2001; and M. Santagati et al., Antimicrob. Agents Chemother. 44:2585-2587, 2000). Previous studies have shown that Mef is required for macrolide resistance in S. pneumoniae; however, the contribution of Mel has not been fully determined. Independent deletions were constructed in mefE and mel in the serotype 14 macrolide-resistant strains GA16638 (erythromycin [Em] MIC, 8 to 16 microg/ml) and GA17719 (Em MIC, 2 to 4 microg/ml), which contain allelic variations in the mega element. The MICs to erythromycin were significantly reduced for the independent deletion mutants of both mefE and mel compared to those of the parent strains and further reduced threefold to fourfold to Em MICs of <0.15 microg/ml with mefE mel double mutants. Using quantitative reverse transcription-PCR, the expression of mefE in the mel deletion mutants was increased more than 10-fold. However, in the mefE deletion mutants, the expression of mel did not differ significantly from the parent strains. The expression of both mefE and mel was inducible by erythromycin. These data indicate a requirement for both Mef and Mel in the novel efflux-mediated macrolide resistance system in S. pneumoniae and other gram-positive bacteria and that the system is inducible by macrolides.

Infrequent occurrence of single mutations in topoisomerase IV and DNA gyrase genes among US levofloxacin-susceptible clinical isolates of Streptococcus pneumoniae from nine institutions (1999–2003)

OBJECTIVES

Prevalence of single quinolone-resistance determining region (QRDR) mutations in Streptococcus pneumoniae was studied from nine institutions over 5 years to track the incidence of single QRDR mutations.

METHODS

All 1106 levofloxacin-susceptible pneumococci (MICs < or = 2.0 mg/L) identified from 1112 total isolates (99.5% susceptibility) in TRUST 3 (1999), TRUST 5 (2001) and TRUST 7 (2003) surveillance studies from the same nine hospitals in nine states were screened for QRDR mutations. Using pyrosequencing, the strains were screened for mutations corresponding to hot spots Asp-78, Ser-79 and Asp-83 in ParC; Asp-80, Ser-81 and Glu-85 in GyrA; Asp-435 in ParE and Asp-435 in GyrB. DNA sequencing of QRDRs was performed to confirm mutations.

RESULTS

No QRDR mutations were found in any of the isolates with levofloxacin MICs < or = 0.5 mg/L and no gyrA or gyrB QRDR mutations were found in any of the screened isolates (MICs < or = 2 mg/L). Four single-step QRDR mutants with the following amino acid substitutions were found: ParE Asp-435 to Asn (isolated in 1999 in Colorado); ParC Asp-83 to Asn (isolated in 2001 in Kentucky); ParC Ser-79 to Phe (isolated in 2003 in Indiana) and ParC Ser-79 to Tyr (isolated in 2003 in California). These non-clonal strains had levofloxacin MICs of 1 mg/L and were non-susceptible to ciprofloxacin (MIC 2-4 mg/L).

CONCLUSIONS

Overall prevalence of single QRDR mutations in levofloxacin-susceptible S. pneumoniae with MICs of < or = 2 mg/L was 0.4% (4/1106) and has remained <1% within nine institutions over 5 years (1999-2003).

Clinical experience in the management of community-acquired pneumonia: lessons from the use of fluoroquinolones

Community-acquired pneumonia (CAP) remains a major cause of morbidity and mortality worldwide. The treatment of CAP has been complicated by several factors, including the expanding spectrum of causative organisms and the rising prevalence of antibiotic resistance among respiratory pathogens. Initial antimicrobial treatment for patients with CAP is usually selected empirically and should provide appropriate coverage against the most common causative organisms, including resistant strains. Respiratory fluoroquinolones, such as levofloxacin, are the only antimicrobials that are highly active against the pathogens most frequently implicated in CAP, including macrolide-resistant and penicillin-resistant pneumococci, Haemophilus influenzae, Legionella spp., and atypical agents. This paper reviews recent studies involving adult patients with CAP that suggest that levofloxacin, as compared with other conventional antibiotic treatments, may be associated with better clinical outcomes.

Failure of levofloxacin treatment in community-acquired pneumococcal pneumonia

Background

Streptococcus pneumoniae is the leading cause of community-acquired pneumonia (CAP). High global incidence of macrolide and penicillin resistance has been reported, whereas fluoroquinolone resistance is uncommon. Current guidelines for suspected CAP in patients with co-morbidity factors and recent antibiotic therapy recommend initial empiric therapy using one fluoroquinolone or one macrolide associated to other drugs (amoxicillin, amoxicillin/clavulanate, broad-spectrum cephalosporins). Resistance to fluoroquinolones is determined by efflux mechanisms and/or mutations in the parC and parE genes coding for topoisomerase IV and/or gyrA and gyrB genes coding for DNA gyrase. No clinical cases due to fluoroquinolone-resistant S. pneumoniae strains have been yet reported from Italy.

Case presentation

A 72-year-old patient with long history of chronic obstructive pulmonary disease and multiple fluoroquinolone treatments for recurrent lower respiratory tract infections developed fever, increased sputum production, and dyspnea. He was treated with oral levofloxacin (500 mg bid). Three days later, because of acute respiratory insufficiency, the patient was hospitalized. Levofloxacin treatment was supplemented with piperacillin/tazobactam. Microbiological tests detected a S. pneumoniae strain intermediate to penicillin (MIC, 1 mg/L) and resistant to macrolides (MIC >256 mg/L) and fluoroquinolones (MIC >32 mg/L). Point mutations were detected in gyrA (Ser81-Phe), parE (Ile460-Val), and parC gene (Ser79-Phe; Lys137-Asn). Complete clinical response followed treatment with piperacillin/tazobactam.

Conclusion

This is the first Italian case of community-acquired pneumonia due to a fluoroquinolone-resistant S. pneumoniae isolate where treatment failure of levofloxacin was documented. Molecular analysis showed a group of mutations that have not yet been reported from Italy and has been detected only twice in Europe. Treatment with piperacillin/tazobactam appears an effective means to inhibit fluoroquinolone-resistant strains of S. pneumoniae causing community-acquired pneumonia in seriously ill patients.

Therapeutic options among broad-spectrum beta-lactams for infections caused by levofloxacin-nonsusceptible Streptococcus pneumoniae

Streptococcus pneumoniae has consistently become more resistant to primary, orally administered treatment regimens used for community-acquired respiratory tract infections (CARTI; sinusitis, bronchitis, pneumonia). As resistance rates approach 40-50% in the United States and North America for penicillin and macrolides, other agents also have exhibited coresistance rates of 10-20% (tetracycline, clindamycin, trimethoprim/sulfamethoxazole). These facts led to altered clinical treatment guidelines (IDSA) supporting the use of respiratory fluoroquinolones (levofloxacin, gatifloxacin, gemifloxacin, and moxifloxacin). This report from the SENTRY Antimicrobial Surveillance Program lists possible parenterally administered treatment alternatives for the fluoroquinolone (levofloxacin)-nonsusceptible pneumococci. The SENTRY Program isolates from CARTI (1997-2003), totaling 21605 strains from Europe, Asia Pacific, and the Americas, were screened for fluoroquinolone-resistant S. pneumoniae. A total of 157 (0.7%) levofloxacin-nonsusceptible (MIC > or = 4 microg/mL) strains were identified and tested by reference broth microdilution methods against 27 antimicrobials. Quinolone resistance-determining region (QRDR) mutations were determined by PCR amplification and gene sequencing. The entire population of S. pneumoniae had the following antibiogram demographics: penicillin-nonsusceptible (32%), macrolide resistance (24%), tetracycline resistance (21%), clindamycin resistance (11%), trimethoprim/sulfamethoxazole resistance (33%), and 6% of strains were resistant to all 5 drugs. Levofloxacin-resistant strains routinely had 2 or more QRDR mutations most frequently in gyrA at Ser81Phe or Tyr and in parC at Ser79Phe or Tyr and Lys137Asn. Four agents had extremely low rates of resistance when tested against the 157 levofloxacin-nonsusceptible strains (e.g., quinupristin/dalfopristin, 0% resistance; vancomycin, 0%; cefepime, 1%; ceftriaxone, 1%). Levofloxacin-nonsusceptible pneumococcal isolates remain uncommon, but are a growing problem in CARTI (1.4% in 2003), especially in previously fluoroquinolone-treated cases. Parenteral cephalosporins (cefepime or ceftriaxone) continue to be potent and safe for use in hospitalized patients with S. pneumoniae community-acquired pneumonia, used with or without co-drugs according to published guidelines.

Antimicrobial susceptibility of Streptococcus pneumoniae in eight European countries from 2001 to 2003

Susceptibility testing results for Streptococcus pneumoniae isolates (n = 2,279) from eight European countries, examined in the PneumoWorld Study from 2001 to 2003, are presented. Overall, 24.6% of S. pneumoniae isolates were nonsusceptible to penicillin G and 28.0% were resistant to macrolides. The prevalence of resistance varied widely between European countries, with the highest rates of penicillin G and macrolide resistance reported from Spain and France. Serotype 14 was the leading serotype among penicillin G- and macrolide-resistant S. pneumoniae isolates. One strain (PW 158) showed a combination of an efflux type of resistance with a 23S rRNA mutation (A2061G, pneumococcal numbering; A2059G, Escherichia coli numbering). Six strains which showed negative results for mef(A) and erm(B) in repeated PCR assays had mutations in 23S rRNA or alterations in the L4 ribosomal protein (two strains). Fluoroquinolone resistance rates (levofloxacin MIC > or = 4 microg/ml) were low (Austria, 0%; Belgium, 0.7%; France, 0.9%; Germany, 0.4%; Italy, 1.3%; Portugal, 1.2%; Spain, 1.0%; and Switzerland, 0%). Analysis of quinolone resistance-determining regions showed eight strains with a Ser81 alteration in gyrA; 13 of 18 strains showed a Ser79 alteration in parC. The clonal profile, as analyzed by multilocus sequence typing (MLST), showed that the 18 fluoroquinolone-resistant strains were genetically heterogeneous. Seven of the 18 strains belonged to new sequence types not hitherto described in the MLST database. Europe-wide surveillance for monitoring of the further spread of these antibiotic-resistant S. pneumoniae clones is warranted.

Relative fitness of fluoroquinolone-resistant Streptococcus pneumoniae

Fluoroquinolone resistance in Streptococcus pneumoniae is primarily mediated by point mutations in the quinolone resistance–determining regions of gyrA and parC. Antimicrobial resistance mutations in housekeeping genes often decrease fitness of microorganisms. To investigate the fitness of quinolone-resistant S. pneumoniae (QRSP), the relative growth efficiencies of 2 isogenic QRSP double mutants were compared with that of their fluoroquinolone-susceptible parent, EF3030, by using murine nasopharyngeal colonization and pneumonia models. Strains containing the GyrA: Ser81Phe, ParC: Ser79Phe double mutations, which are frequently seen in clinical QRSP, competed poorly with EF3030 in competitive colonization or competitive lung infections. However, they efficiently produced lung infection even in the absence of EF3030. The strain containing the GyrA: Ser81Phe, ParC: Ser79Tyr double mutations, which is seen more frequently in laboratory-derived QRSP than in clinical QRSP, demonstrated reduced nasal colonization in competitive or noncompetitive lung infections. However, the strain was equally able to cause competitive or noncompetitive lung infections as well as EF3030.

High genetic diversity of ciprofloxacin-nonsusceptible isolates of Streptococcus pneumoniae in Poland

We have analyzed the susceptibility to ciprofloxacin of 697 pneumococcal isolates collected in 1998-2002 in Poland from patients with respiratory tract diseases. Thirty-one ciprofloxacin-nonsusceptible isolates (MICs, > or =4 microg/ml) were identified, of which two were resistant to levofloxacin (MIC, 8 microg/ml). Serotyping, pulsed-field gel electrophoresis, multilocus sequence typing, and the analysis of resistance determinants showed their great genetic diversity.

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.