Drug efflux and parC mutations are involved in fluoroquinolone resistance in viridans group streptococci

Role of PatAB Transporter in Efflux of Levofloxacin in Streptococcus pneumoniae

PatAB is an ABC bacterial transporter that facilitates the export of antibiotics and dyes. The overexpression of patAB genes conferring efflux-mediated fluoroquinolone resistance has been observed in several laboratory strains and clinical isolates of Streptococcus pneumoniae. Using transformation and whole-genome sequencing, we characterized the fluoroquinolone-resistance mechanism of one S. pneumoniae clinical isolate without mutations in the DNA topoisomerase genes. We identified the PatAB fluoroquinolone efflux-pump as the mechanism conferring a low-level resistance to ciprofloxacin (8 µg/mL) and levofloxacin (4 µg/mL). Genetic transformation experiments with different amplimers revealed that the entire patA plus the 5'-terminus of patB are required for levofloxacin-efflux. By contrast, only the upstream region of the patAB operon, plus the region coding the N-terminus of PatA containing the G39D, T43A, V48A and D100N amino acid changes, are sufficient to confer a ciprofloxacin-efflux phenotype, thus suggesting differences between fluoroquinolones in their binding and/or translocation pathways. In addition, we identified a novel single mutation responsible for the constitutive and ciprofloxacin-inducible upregulation of patAB. This mutation is predicted to destabilize the putative rho-independent transcriptional terminator located upstream of patA, increasing transcription of downstream genes. This is the first report demonstrating the role of the PatAB transporter in levofloxacin-efflux in a pneumoccocal clinical isolate.

Upregulation of the PatAB Transporter Confers Fluoroquinolone Resistance to Streptococcus pseudopneumoniae

We characterized the mechanism of fluoroquinolone-resistance in two isolates of Streptococcus pseudopneumoniae having fluoroquinolone-efflux as unique mechanism of resistance. Whole genome sequencing and genetic transformation experiments were performed together with phenotypic determinations of the efflux mechanism. The PatAB pump was identified as responsible for efflux of ciprofloxacin (MIC of 4 μg/ml), ethidium bromide (MICs of 8-16 μg/ml) and acriflavine (MICs of 4-8 μg/ml) in both isolates. These MICs were at least 8-fold lower in the presence of the efflux inhibitor reserpine. Complete genome sequencing indicated that the sequence located between the promoter of the patAB operon and the initiation codon of patA, which putatively forms an RNA stem-loop structure, may be responsible for the efflux phenotype. RT-qPCR determinations performed on RNAs of cultures treated or not treated with subinhibitory ciprofloxacin concentrations were performed. While no significant changes were observed in wild-type Streptococcus pneumoniae R6 strain, increases in transcription were detected in the ciprofloxacin-efflux transformants obtained with DNA from efflux-positive isolates, in the ranges of 1.4 to 3.4-fold (patA) and 2.1 to 2.9-fold (patB). Ciprofloxacin-induction was related with a lower predicted free energy for the stem-loop structure in the RNA of S. pseudopneumoniae isolates (-13.81 and -8.58) than for R6 (-15.32 kcal/mol), which may ease transcription. The presence of these regulatory variations in commensal S. pseudopneumoniae isolates, and the possibility of its transfer to Streptococcus pneumoniae by genetic transformation, could increase fluoroquinolone resistance in this important pathogen.

Absence of tmRNA Has a Protective Effect against Fluoroquinolones in Streptococcus pneumoniae

The transfer messenger RNA (tmRNA), encoded by the ssrA gene, is a small non-coding RNA involved in trans-translation that contributes to the recycling of ribosomes stalled on aberrant mRNAs. In most bacteria, its inactivation has been related to a decreased ability to respond to and recover from a variety of stress conditions. In this report, we investigated the role of tmRNA in stress adaptation in the human pathogen Streptococcus pneumoniae. We constructed a tmRNA deletion mutant and analyzed its response to several lethal stresses. The ΔssrA strain grew slower than the wild type, indicating that, although not essential, tmRNA is important for normal pneumococcal growth. Moreover, deletion of tmRNA increased susceptibility to UV irradiation, to exogenous hydrogen peroxide and to antibiotics that inhibit protein synthesis and transcription. However, the ΔssrA strain was more resistant to fluoroquinolones, showing twofold higher MIC values and up to 1000-fold higher survival rates than the wild type. Deletion of SmpB, the other partner in trans-translation, also reduced survival to levofloxacin in a similar extent. Accumulation of intracellular reactive oxygen species associated to moxifloxacin and levofloxacin treatment was also highly reduced (∼100-fold). Nevertheless, the ΔssrA strain showed higher intracellular accumulation of ethidium bromide and levofloxacin than the wild type, suggesting that tmRNA deficiency protects pneumococcal cells from fluoroquinolone-mediated killing. In fact, analysis of chromosome integrity revealed that deletion of tmRNA prevented the fragmentation of the chromosome associated to levofloxacin treatment. Moreover, such protective effect appears to relay mainly on inhibition of protein synthesis, since a similar effect was observed with antibiotics that inhibit that process. The emergence and spread of drug-resistant pneumococci is a matter of concern and these results contribute to a better comprehension of the mechanisms underlying fluoroquinolones action.

Antibiotic Resistance of Non-pneumococcal Streptococci and Its Clinical Impact

The taxonomy of streptococci has undergone major changes during the last two decades. The present classification is based on both phenotypic and genotypic data. Phylogenetic classification of streptococci is based on 16S rRNA sequences [1], and it forms the backbone of the overall classification system of streptococci. Phenotypic properties are also important, especially for clinical microbiologists. The type of hemolysis on blood agar, reaction with Lancefield grouping antisera, resistance to optochin, and bile solubility remain important for grouping of clinical Streptococcus isolates and therefore treatment options [2]. In the following chapter, two phenotypic classification groups, viridans group streptococci (VGS) and beta-hemolytic streptococci, will be discussed.

Alterations in the Quinolone Resistance-Determining Regions and Fluoroquinolone Resistance in Clinical Isolates and Laboratory-Derived Mutants of Mycoplasma bovis: Not All Genotypes May Be Equal

Mycoplasma bovis is considered a major contributor to respiratory diseases in young cattle. Resistant M. bovis isolates have increasingly been reported worldwide due to extensive use of antimicrobials to treat bovine pneumonia. The frequency of isolates resistant to fluoroquinolones varies considerably from one country to another. The MICs of isolates collected in France have only increased from "very low" to "low." The present study was conducted to investigate whether alterations in the quinolone resistance-determining regions (QRDRs) could account for this slight modification in susceptibility. No correlation between QRDR alterations and increased MICs was evidenced in clinical isolates. In addition, all clinical isolates were subtyped, and the tendencies of the different sequence types to develop resistance through mutations in QRDRs under selective pressure in vitro were examined. In vitro, 3 hot spots for mutations in QRDRs (position 83 in GyrA and positions 80 and 84 in ParC) were associated with a high level of resistance when cumulated. We showed that the point mutations in the QRDRs observed in vitro were different (in location and selection rapidity) between the different subtypes. Our in vitro observations were corroborated by the recent detection of a clinical isolate highly resistant to fluoroquinolones (MIC ≥ 16 μg/ml) and belonging to the subtype which easily accumulates QRDR alterations in vitro. The current increased prevalence of this subtype in clinical isolates highlights the urgent need to control fluoroquinolone usage in veterinary medicine.

Emergence of ciprofloxacin-nonsusceptible Streptococcus pyogenes isolates from healthy children and pediatric patients in Portugal

We describe 66 ciprofloxacin-nonsusceptible Streptococcus pyogenes isolates recovered from colonized and infected children. The ParC S79A substitution was frequent and associated with the emm6/sequence type 382 (emm6/ST382) lineage. The ParC D83G substitution was detected in two isolates (emm5/ST99 and emm28/ST52 lineages). One isolate (emm89/ST101) had no quinolone resistance-determining region codon substitutions or other resistance mechanisms. Five of 66 isolates were levofloxacin resistant. Although fluoroquinolones are not used in children, they may be putative disseminators of fluoroquinolone-nonsusceptible strains in the community.

Changes in fluoroquinolone-resistant Streptococcus pneumoniae after 7-valent conjugate vaccination, Spain

Among 4,215 Streptococcus pneumoniae isolates obtained in Spain during 2006, 98 (2.3%) were ciprofloxacin resistant (3.6% from adults and 0.14% from children). In comparison with findings from a 2002 study, global resistance remained stable. Low-level resistance (30 isolates with MIC 4-8 microg/mL) was caused by a reserpine-sensitive efflux phenotype (n = 4) or single topoisomerase IV (parC [n = 24] or parE [n = 1]) changes. One isolate did not show reserpine-sensitive efflux or mutations. High-level resistance (68 isolates with MIC >or=16 microg/mL) was caused by changes in gyrase (gyrA) and parC or parE. New changes in parC (S80P) and gyrA (S81V, E85G) were shown to be involved in resistance by genetic transformation. Although 49 genotypes were observed, clones Spain9V-ST156 and Sweden15A-ST63 accounted for 34.7% of drug-resistant isolates. In comparison with findings from the 2002 study, clones Spain14-ST17, Spain23F-ST81, and ST8819F decreased and 4 new genotypes (ST9710A, ST57016, ST43322, and ST71733) appeared in 2006.

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.

Characterization of fluoroquinolone-resistant beta-hemolytic Streptococcus spp. isolated in North America and Europe including the first report of fluoroquinolone-resistant Streptococcus dysgalactiae subspecies equisimilis: report from the SENTRY Antimicrobial Surveillance Program (1997-2004)

Beta-hemolytic streptococci are common bacterial pathogens that can cause serious invasive disease, and although this group of species has remained susceptible to the fluoroquinolone class, resistant strains have been reported. This multicenter investigation determined the rate of fluoroquinolone-resistant beta-hemolytic streptococci using the SENTRY Antimicrobial Surveillance Program network data (1997-2004). Forty-seven surveillance culture isolates of beta-hemolytic streptococci from North America and Europe with elevated levofloxacin MIC results (2 to >32) microg/mL were tested for susceptibility to other fluoroquinolones including ciprofloxacin, garenoxacin, gatifloxacin, gemifloxacin, and moxifloxacin using reference broth microdilution and Etest (BIODISK, Solna, Sweden) methods. Strains were characterized using polymerase chain reaction and sequencing to detect mutations in the quinolone-resistance determining region (QRDR). The beta-hemolytic streptococci isolates with reduced fluoroquinolone susceptibility included the following Lancefield groups: A (Streptococcus pyogenes; 9 strains), B (Streptococcus agalactiae; 24 strains), C and G (14 strains). Vitek and API 20 strep (bioMerieux, Hazelwood, MO) identification systems, as well as conventional biochemical methods and colony morphology, were used to confirm the organism identifications. The overall potency (MIC90 in microg/mL) for the fluoroquinolones against all tested beta-hemolytic streptococci showed the following rank order: gemifloxacin (0.06) > garenoxacin (0.12) > moxifloxacin (0.25) > gatifloxacin (0.5) > levofloxacin = ciprofloxacin (1). The rate of levofloxacin-resistant beta-hemolytic streptococci in the SENTRY program was 0.14% (Europe) and 0.51% (North America) during the study period. All levofloxacin-resistant strains tested by molecular methods had significant mutations in either parC (position 79 or 83) and/or gyrA (position 81 or 85). All but 2 isolates with high-level resistance to levofloxacin (>32 microg/mL) had gyrA mutations. Strains with lower MIC values to levofloxacin (2-4 microg/mL) only had mutations in parC. The increasing rate of fluoroquinolone-resistant streptococci including Streptococcus pneumoniae, viridans group streptococci, and the more recently reported beta-hemolytic streptococci, is becoming a clinical concern due to the morbidity and mortality caused by these pathogens.

Emergence of quinolone resistance among viridans group streptococci isolated from the oropharynx of neutropenic peripheral blood stem cell transplant patients receiving quinolone antimicrobial prophylaxis

In neutropenic patients receiving quinolone prophylaxis, bacteremia with viridans group streptococci resistant to quinolones is a known complication. The frequency of occurrence of quinolone-resistant organisms colonizing the oropharynx during antibacterial prophylaxis with a quinolone is not well defined. In 48 patients undergoing hematopoietic stem cell transplantation, the prevalence of quinolone resistance in viridans group streptococci colonizing the oropharynx before and during antibacterial prophylaxis with gatifloxacin or moxifloxacin (most with concomitant penicillin) was determined. For quinolone-resistant isolates, mutations in the genes gyrA and parC, which confer resistance to quinolones, were analyzed. Seventy-four isolates before and 27 isolates during quinolone use were recovered from patients' oropharynxes. The numbers of susceptible isolates recovered before versus during quinolone use were as follows: 52 (70%) versus three (11%) for ciprofloxacin, 66 (89%) versus eight (30%) for levofloxacin, 66 (89%) versus ten (37%) for gatifloxacin, and 67 (91%) versus 11 (41%) for moxifloxacin (p<0.0001). Mutations in gyrA and/or parC were detected in quinolone-resistant isolates. Quinolone-resistant viridans group streptococci are frequently found in the oropharynx of neutropenic patients after a brief (median, 8 days) exposure to gatifloxacin or moxifloxacin.

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.

Interspecies recombination in type II topoisomerase genes is not a major cause of fluoroquinolone resistance in invasive Streptococcus pneumoniae isolates in the United States

Mutations in the topoisomerase type II enzymes account for fluoroquinolone resistance in Streptococcus pneumoniae. These mutations can arise spontaneously or be transferred by intraspecies or interspecies recombination, primarily with viridans streptococci. We analyzed the nucleotide sequences of the quinolone resistance-determining regions of 49 invasive levofloxacin-resistant pneumococcal isolates and did not find any evidence for interspecies recombination.

Fluoroquinolone resistance in penicillin-resistant Streptococcus pneumoniae clones, Spain

Among 2,882 Streptococcus pneumoniae sent to the Spanish Reference Laboratory during 2002, 75 (2.6%) were ciprofloxacin-resistant. Resistance was associated with older patients (3.9% in adults and 7.2% in patients > or =65 years of age), with isolation from noninvasive sites (4.3% vs. 1.0%), and with penicillin and macrolide resistance. Among 14 low-level resistant (MIC 4-8 microg/mL) strains, 1 had a fluoroquinolone efflux phenotype, and 13 showed single ParC changes. The 61 high-level ciprofloxacin-resistant (MIC > or =16 microg/mL) strains showed either two or three changes at ParC, ParE, and GyrA. Resistance was acquired either by point mutation (70 strains) or by recombination with viridans streptococci (4 strains) at the topoisomerase II genes. Although 36 pulsed-field gel electrophoresis patterns were observed, 5 international multiresistant clones (Spain23F-1, Spain6B-2, Spain9V-3, Spain14-5 and Sweden15A-25) accounted for 35 (46.7%) of the ciprofloxacin-resistant strains. Continuous surveillance is needed to prevent the dissemination of these clones.

Viridans group streptococci are donors in horizontal transfer of topoisomerase IV genes to Streptococcus pneumoniae

A total of 46 ciprofloxacin-resistant (Cip(r)) Streptococcus pneumoniae strains were isolated from 1991 to 2001 at the Hospital of Bellvitge. Five of these strains showed unexpectedly high rates of nucleotide variations in the quinolone resistance-determining regions (QRDRs) of their parC, parE, and gyrA genes. The nucleotide sequence of the full-length parC, parE, and gyrA genes of one of these isolates revealed a mosaic structure compatible with an interspecific recombination origin. Southern blot analysis and nucleotide sequence determinations showed the presence of an ant-like gene in the intergenic parE-parC regions of the S. pneumoniae Cip(r) isolates with high rates of variations in their parE and parC QRDRs. The ant-like gene was absent from typical S. pneumoniae strains, whereas it was present in the intergenic parE-parC regions of the viridans group streptococci (Streptococcus mitis and Streptococcus oralis). These results suggest that the viridans group streptococci are acting as donors in the horizontal transfer of fluoroquinolone resistance genes to S. pneumoniae.

In vitro antibacterial activity and pharmacodynamics of new quinolones

This synopsis of published literature summarises data on the in vitro antibacterial activity and pharmacodynamics of fluoroquinolones. Data were compiled for ciprofloxacin, levofloxcin, moxifloxacin, gatifloxacin, grepafloxacin, gemifloxacin, trovafloxacin, sitafloxacin and garenoxacin. All of these quinolones are almost equipotent against gram-negative bacteria but demonstrate improved activity against gram-positive species. The new quinolones are uniformly active against gram-positive species except Streptococcus pneumoniae; against which gemifloxacin, sitafloxacin and garenoxacin are one to two dilution steps more active than moxifloxacin. All of the new quinolones except gemifloxacin demonstrate enhanced activity against anaerobes. Since all the new quinolones show similar activity against the major respiratory tract pathogens except Streptococcus pneumoniae and members of the family Enterobacteriaceae, their pharmacokinetics and pharmacodynamics will be clinically relevant differentiators and determinants of their overall activity and efficacy. In vitro simulations of serum concentrations revealed that (i). gemifloxacin and levofloxacin were significantly and gatifloxacin moderately less active than moxifloxacin against Streptococcus pneumoniae and Staphylococcus aureus, and (ii). resistant subpopulations emerged following exposure to levofloxacin and gatifloxacin (gemifloxacin not yet published) but not to moxifloxacin. The emergence of resistance is a function of drug concentrations achievable in vivo and the susceptibility pattern of the target organisms. Therefore, the use of less potent fluoroquinolones with borderline or even suboptimal pharmacokinetic/pharmacodynamic surrogate parameters will inadvertently foster the development of class resistance. Drugs with the most favourable pharmacokinetic/pharmacodynamic characteristics should be used as first-line agents in order to preserve the potential of this drug class and, most importantly, to provide the patient with an optimally effective regimen.

Evidence of active efflux in resistance to ciprofloxacin and to ethidium bromide by Mycoplasma hominis

The uptake of fluoroquinolones was characterized for the fluoroquinolone-susceptible strain PG21 of Mycoplasma hominis. Accumulation of fluoroquinolones appeared to occur by passive diffusion. Addition of arginine as the energizer significantly reduced the uptake of fluoroquinolones, suggesting the presence of an energy-dependent efflux process. Reserpine and orthovanadate, two multidrug pump inhibitors, increased significantly the ciprofloxacin (CIP) uptake. In contrast, such a strong effect was not observed for moxifloxacin and pefloxacin uptakes. Two ethidium bromide (EtBr)-resistant strains, selected in vitro, showed a resistance profile compatible with a multidrug-resistant phenotype, with increased MICs for the hydrophilic fluoroquinolones, CIP and norfloxacin, EtBr, and acriflavine. Taking the EtBr-resistant strain RB1La as a model, a significant decrease of the CIP and EtBr uptakes was observed compared to the reference strain PG21. In the presence of reserpine and orthovanadate, both inhibitors of ATP-dependent efflux pumps, the CIP uptake increased significantly, reaching approximately the same level as that of the susceptible strain. Similar results were obtained with EtBr uptake and efflux experiments. Our data suggest the presence of an active efflux system, possibly an ABC-type efflux pump, implicated in the resistance to CIP and unrelated compounds like EtBr in the human mycoplasma M. hominis.

Interspecies recombination contributes minimally to fluoroquinolone resistance in Streptococcus pneumoniae

Analysis of 71 ciprofloxacin-resistant (MIC > or = 4 microg/ml) Streptococcus pneumoniae clinical isolates revealed only 1 for which the quinolone resistance-determining regions of the parC, parE, and gyrB genes were genetically related to those of viridans group streptococci. Our findings support the occurrence of interspecies recombination of type II topoisomerase genes; however, its contribution to the emergence of quinolone resistance among pneumococci appears to have been minimal.

gyrA mutations associated with quinolone resistance in Bacteroides fragilis group strains

Mutations in the gyrA gene contribute considerably to quinolone resistance in Escherichia coli. Mechanisms for quinolone resistance in anaerobic bacteria are less well studied. The Bacteroides fragilis group are the anaerobic organisms most frequently isolated from patients with bacteremia and intraabdominal infections. Forty-four clinafloxacin-resistant and-susceptible fecal and clinical isolates of the B. fragilis group (eight Bacteroides fragilis, three Bacteroides ovatus, five Bacteroides thetaiotaomicron, six Bacteroides uniformis, and 22 Bacteroides vulgatus) and six ATCC strains of the B. fragilis group were analyzed as follows: (i) determination of susceptibility to ciprofloxacin, levofloxacin, moxifloxacin, and clinafloxacin by the agar dilution method and (ii) sequencing of the gyrA quinolone resistance-determining region (QRDR) located between amino acid residues equivalent to Ala-67 through Gln-106 in E. coli. Amino acid substitutions were found at hotspots at positions 82 (n = 15) and 86 (n = 8). Strains with Ser82Leu substitutions (n = 13) were highly resistant to all quinolones tested. Mutations in other positions of gyrA were also frequently found in quinolone-resistant and -susceptible isolates. Eight clinical strains that lacked mutations in their QRDR were susceptible to at least two of the quinolones tested. Although newer quinolones have good antimicrobial activity against the B. fragilis group, quinolone resistance in B. fragilis strains can be readily selected in vivo. Mutational events in the QRDR of gyrA seem to contribute to quinolone resistance in Bacteroides species.

Overcoming antimicrobial resistance by targeting resistance mechanisms

Three mechanisms of antimicrobial resistance predominate in bacteria: antibiotic inactivation, target site modification, and altered uptake by way of restricted entry and/or enhanced efflux. Many of these involve enzymes or transport proteins whose activity can be targeted directly in an attemptto compromise resistance and, thus, potentiate antimicrobial activity. Alternatively, novel agents unaffected by these resistance mechanisms can be developed. Given the ongoing challenge posed by antimicrobial resistance in bacteria, targeting resistance in this way may be our best hope at prolonging the antibiotic era.

In vitro development of resistance to six quinolones in Streptococcus pneumoniae, Streptococcus pyogenes, and Staphylococcus aureus

Streptococcus pneumoniae, Streptococcus pyogenes, and Staphylococcus aureus isolates were exposed to subinhibitory MICs of ciprofloxacin, sparfloxacin, gatifloxacin, moxifloxacin, clinafloxacin, and gemifloxacin during a 10-day period. Subculturing led to resistance development, regardless of the initial potencies of the quinolones. None of the quinolones was associated with a significantly slower rate of resistance development.

Fluoroquinolone resistance associated with target mutations and active efflux in oropharyngeal colonizing isolates of viridans group streptococci

Oropharyngeal samples from 60 hospitalized patients (30 fluoroquinolone [FQ]-treated and 30 non-FQ-treated patients) and 30 untreated nonhospitalized healthy control subjects yielded 20 isolates of viridans group streptococci with reduced susceptibility to FQ, mostly from the hospitalized patients. An efflux phenotype was commonly encountered, expressed either alone or with topoisomerase mutations. Interspecies transfer of the efflux phenotype was demonstrated via transformation of Streptococcus pneumoniae R6 with DNA from S. mitis and S. oralis.

Horizontal transfer of parC and gyrA in fluoroquinolone-resistant clinical isolates of Streptococcus pneumoniae

We have analyzed genetically three clinical isolates (3180, 3870, and 1244) of Streptococcus pneumoniae with high-level ciprofloxacin resistance. Isolates 3180 and 3870 were atypical because of their insolubility in deoxycholate. However, they hybridized specifically with pneumococcal autolysin and pneumolysin gene probes and have typical pneumococcal atpC and atpA gene sequences. Analysis of the complete sequences of the parC and gyrA genes revealed total variations of 8 and 8.7% (isolate 3180) and 7.4 and 3.6% (isolate 3870), respectively, compared to the wild-type strain R6 sequence. The variations observed between the sequences of R6 and isolate 1244 were less than 0.9%. The structure of the gyrA and parC genes from isolates 3180 and 3870 was organized in sequence blocks that show different levels of divergence, suggesting a pattern of recombination. These results are evidence for recombination at the fluoroquinolone target genes in clinical isolates of S. pneumoniae. The genetically related viridans group streptococci could act as a reservoir for fluoroquinolone resistance genes.