DNA gyrase mutations in quinolone-resistant clinical isolates of Neisseria gonorrhoeae

A Narrative Review of Clinical Treatment Outcomes of Neisseria gonorrhoeae Infection With Ciprofloxacin by Minimum Inhibitory Concentration and Anatomic Site

BACKGROUND

Neisseria gonorrhoeae infections are becoming increasingly resistant to recommended treatments. Resistance-guided therapy may mitigate the continued emergence of resistance by enabling the use of previously recommended treatments like ciprofloxacin. To describe the effectiveness of ciprofloxacin to treat "susceptible" infections, we estimated the clinical efficacy of ciprofloxacin at various minimum inhibitory concentrations (MICs) and anatomic sites.

METHODS

We reviewed publicly available reports using the PubMed.gov database and search terms "gonorrhea/drug therapy"[Mesh] AND "ciprofloxacin". We included clinical treatment studies in which ciprofloxacin was administered alone to treat N. gonorrhoeae, specimens were collected for N. gonorrhoeae culture from each infection, the MIC was determined for ≥90% of infective strains, and individual treatment outcomes were clearly defined. We recorded those data, ciprofloxacin dose and infection site. We calculated the frequency of treatment success and 95% confidence intervals (CIs).

RESULTS

Twenty studies from 1985 to 2020 met our inclusion criteria. Ciprofloxacin at commonly used doses eliminated 99.2% (95% CI, 98.5%-99.6%; n = 1439) of gonococcal infections with MICs <0.125 μg/mL, 76.3% (95% CI, 59.8%-88.6%; n = 38) of infections with MICs from 0.125 to 0.5 μg/mL, and 30.1% (95% CI, 20.5%-41.2%; n = 83) of infections with MICs ≥1 μg/mL across anatomic sites.

CONCLUSIONS

Ciprofloxacin reliably eliminated gonococcal infections with MICs <0.125 μg/mL across anatomic sites. Molecular assays predicting MICs of ciprofloxacin <0.125 μg/mL of gonococcal strains can allow for reintroduction of ciprofloxacin in gonorrhea treatment. Clinicians can confidently use ciprofloxacin to treat susceptible gonococcal infections.

A community-driven resource for genomic epidemiology and antimicrobial resistance prediction of Neisseria gonorrhoeae at Pathogenwatch

BACKGROUND

Antimicrobial-resistant (AMR) Neisseria gonorrhoeae is an urgent threat to public health, as strains resistant to at least one of the two last-line antibiotics used in empiric therapy of gonorrhoea, ceftriaxone and azithromycin, have spread internationally. Whole genome sequencing (WGS) data can be used to identify new AMR clones and transmission networks and inform the development of point-of-care tests for antimicrobial susceptibility, novel antimicrobials and vaccines. Community-driven tools that provide an easy access to and analysis of genomic and epidemiological data is the way forward for public health surveillance.

METHODS

Here we present a public health-focussed scheme for genomic epidemiology of N. gonorrhoeae at Pathogenwatch ( https://pathogen.watch/ngonorrhoeae ). An international advisory group of experts in epidemiology, public health, genetics and genomics of N. gonorrhoeae was convened to inform on the utility of current and future analytics in the platform. We implement backwards compatibility with MLST, NG-MAST and NG-STAR typing schemes as well as an exhaustive library of genetic AMR determinants linked to a genotypic prediction of resistance to eight antibiotics. A collection of over 12,000 N. gonorrhoeae genome sequences from public archives has been quality-checked, assembled and made public together with available metadata for contextualization.

RESULTS

AMR prediction from genome data revealed specificity values over 99% for azithromycin, ciprofloxacin and ceftriaxone and sensitivity values around 99% for benzylpenicillin and tetracycline. A case study using the Pathogenwatch collection of N. gonorrhoeae public genomes showed the global expansion of an azithromycin-resistant lineage carrying a mosaic mtr over at least the last 10 years, emphasising the power of Pathogenwatch to explore and evaluate genomic epidemiology questions of public health concern.

CONCLUSIONS

The N. gonorrhoeae scheme in Pathogenwatch provides customised bioinformatic pipelines guided by expert opinion that can be adapted to public health agencies and departments with little expertise in bioinformatics and lower-resourced settings with internet connection but limited computational infrastructure. The advisory group will assess and identify ongoing public health needs in the field of gonorrhoea, particularly regarding gonococcal AMR, in order to further enhance utility with modified or new analytic methods.

In Vitro and In Vivo Activities of TP0480066, a Novel Topoisomerase Inhibitor, against Neisseria gonorrhoeae

Gonorrhea is a common, sexually transmitted disease caused by Neisseria gonorrhoeae Multidrug-resistant N. gonorrhoeae is an urgent threat, and the development of a new antimicrobial agent that functions via a new mechanism is strongly desired. We evaluated the in vitro and in vivo activities of a DNA gyrase/topoisomerase IV inhibitor, TP0480066, which is a novel 8-(methylamino)-2-oxo-1,2-dihydroquinoline derivative. The MICs of TP0480066 were substantially lower than those of other currently or previously used antimicrobials against gonococcal strains demonstrating resistance to fluoroquinolones, macrolides, β-lactams, and aminoglycosides (MICs, ≤0.0005 μg/ml). Additionally, no cross-resistance was observed between TP0480066 and ciprofloxacin. The frequencies of spontaneous resistance to TP0480066 for N. gonorrhoeae ATCC 49226 were below the detection limit (<2.4 × 10^-10) at concentrations equivalent to 32× MIC. TP0480066 also showed potent in vitro bactericidal activity and in vivo efficacy in a mouse model of N. gonorrhoeae infection. These data suggest that TP0480066 is a candidate antimicrobial agent for gonococcal infections.

In Vitro Activity of Delafloxacin against Clinical Neisseria gonorrhoeae Isolates and Selection of Gonococcal Delafloxacin Resistance

We evaluated the in vitro activity of delafloxacin against a panel of 117 Neisseria gonorrhoeae strains, including 110 clinical isolates collected from 2012 to 2015 and seven reference strains, compared with the activities of seven antimicrobials currently or previously recommended for treatment of gonorrhea. We examined the potential for delafloxacin to select for resistant mutants in ciprofloxacin-susceptible and ciprofloxacin-resistant N. gonorrhoeae We characterized mutations in the gyrA, gyrB, parC, and parE genes and the multidrug-resistant efflux pumps (MtrC-MtrD-MtrE and NorM) by PCR and sequencing and by whole-genome sequencing. The MIC50, MIC90, and MIC ranges of delafloxacin were 0.06 μg/ml, 0.125 μg/ml, and ≤0.001 to 0.25 μg/ml, respectively. The frequency of spontaneous mutation ranged from 10(-7) to <10(-9) The multistep delafloxacin resistance selection of 30 daily passages resulted in stable resistant mutants. There was no obvious cross-resistance to nonfluoroquinolone comparator antimicrobials. A mutant with reduced susceptibility to ciprofloxacin (MIC, 0.25 μg/ml) obtained from the ciprofloxacin-susceptible parental strain had a novel Ser91Tyr alteration in the gyrA gene. We also identified new mutations in the gyrA and/or parC and parE genes and the multidrug-resistant efflux pumps (MtrC-MtrD-MtrE and NorM) of two mutant strains with elevated delafloxacin MICs of 1 μg/ml. Although delafloxacin exhibited potent in vitro activity against N. gonorrhoeae isolates and reference strains with diverse antimicrobial resistance profiles and demonstrated a low tendency to select for spontaneous mutants, it is important to establish the correlation between these excellent in vitro data and treatment outcomes through appropriate randomized controlled clinical trials.

Fluoroquinolone resistance in Neisseria gonorrhoeae after cessation of ciprofloxacin usage in San Francisco: using molecular typing to investigate strain turnover

BACKGROUND

Ciprofloxacin resistance (CipR) among gonococcal strains in San Francisco (SF) increased between 2001 and 2006 and decreased between 2007 and 2009. Molecular typing of isolates obtained from 2005 to 2009 was performed to elucidate changes in CipR prevalence.

METHODS

A total of 2526 samples were collected at the SF City Clinic between 2001 and 2009. Minimum inhibitory concentrations to ciprofloxacin were obtained by agar dilution. Prevalences of CipR strains were determined, with corresponding confidence intervals (CIs). Between 2005 and 2009, 460 isolates were selected for molecular typing using Neisseria gonorrhoeae multiantigen sequence typing.

RESULTS

Between 2001 and 2006, the prevalence of CipR increased from 3.4% (95% CI, 1.3%-5.4%) to 44% (95% CI, 39%-50%). However, in 2007 prevalence began to decrease, reaching 9.6% (95% CI, 6.0%-13%) by 2009. Of the 203 strain types identified between 2005 and 2009, 126 genogroups of closely related strain types were formed (varying by ≤1% at both target loci). Levels of CipR within the data set correlate with the prevalence of 3 major genogroups (G): G437, G1407, and G3112.

CONCLUSIONS

Molecular typing reveals that CipR within the tested population is maintained by strain turnover between resistant genogroups. Despite early recommendation in 2002 to stop ciprofloxacin use in California, CipR in SF increased through 2006. The subsequent decrease in CipR corresponds with the 2007 national recommendation to cease ciprofloxacin treatment of gonorrhea, which suggests that national recommendations are potentially more effective at reducing CipR than regional recommendations in areas with high strain turnover.

Multiplex bead suspension array for screening Neisseria gonorrhoeae antibiotic resistance genetic determinants in noncultured clinical samples

The increasing threat of antibiotic-resistant Neisseria gonorrhoeae highlights the need for new diagnostic options. A high-throughput multiplex bead suspension array assay was developed for profiling 29 N. gonorrhoeae genomic mutations and 2 plasmid genes conferring resistance to 6 antimicrobial agents: penicillin, ciprofloxacin, cefixime, tetracycline, azithromycin, and spectinomycin. The three steps of this assay include amplification of 12 N. gonorrhoeae chromosomal and plasmid loci, multiplex allele-specific primer extension reaction, and multiplex bead suspension array detection. Antibiotic resistance genetic determinants were identified successfully in 239 cervicovaginal N. gonorrhoeae-positive noncultured swab samples. This molecular assay can be used for detection of gonococci in clinical specimens, molecular typing, mutation profiling, and predictive assessment of N. gonorrhoeae susceptibility to antibiotics without the need for culture.

Mutations in the gyrA and parC genes of quinolone-resistant Neisseria gonorrhoeae isolates in India

A dramatic increase in the number of quinolone-resistant Neisseria gonorrhoeae isolates in India and worldwide has been reported recently. This study was undertaken to identify and characterise mutations in the gyrA and parC genes of N. gonorrhoeae resistant to six different quinolone antibiotics. In total, 64 N. gonorrhoeae clinical isolates were obtained during 2007-2009 from patients attending sexually transmitted diseases clinics (New Delhi, 35; Pune, 16; Mumbai, 6; Hyderabad, 6; and Nagpur, 1). Antimicrobial susceptibility was determined by Etest and mutation patterns in gyrA and parC were determined by sequencing analysis. All strains showed varying resistance to different quinolone analogues, ranging from 17.2% (gatifloxacin) to 98.4% (ofloxacin and norfloxacin). Sequencing of gyrA and parC revealed that 100% of strains showed mutations in gyrA and 46.9% showed mutations both in gyrA and parC. All strains showed single or double mutations at Ser-91→Phe, Ser-91→Thr and Asp-95→Gly/Asn in gyrA and at Glu-91→Gly in parC. Asp-95→Asn mutation was the most prevalent in strains isolated from New Delhi, whilst Asp-95→Gly was prevalent in strains isolated from Pune. Strains were categorised into eight different mutation patterns. Resistant strains with high minimum inhibitory concentrations (≥8 μg/mL) showed mutations both in gyrA and parC. The difference in the proportion of strains showing mutations in gyrA and parC was found to be significant (P<0.001). The mutation Asp-95→Asn was restricted to Pune strains only. These results indicate that mutations in quinolone target enzymes may have resulted in the high-level resistance seen in these isolates.

Molecular characterization of quinolone-resistant Neisseria gonorrhoeae isolates from Brazil

Despite the rapid spread of antibiotic resistance among gonococci worldwide, limited reports are available from Brazilian locations. In the present study, 25 quinolone-resistant Neisseria gonorrhoeae (QRNG) strains isolated in Rio de Janeiro, Brazil, were characterized by phenotypic and molecular methods, including analysis of mutations in the gyrA and parC genes. They represented 16.5% of the N. gonorrhoeae isolates obtained during a survey performed from 2006 to 2010. A trend for increasing resistance to ciprofloxacin was observed in the period investigated. The most prevalent pattern of mutation observed among QRNG isolates, Ser-91 to Phe and Asp-95 to Gly in gyrA and Ser-87 to Arg in parC, was detected in 40% of the isolates exhibiting MICs ranging from 4 to >32 μg/ml. Rare types of mutations were found in the gyrA gene (Gln-102 to His [12%] and Asp-95 to Tyr [4%]) and in the parC gene (Ser-88 to Thr [4%]). The genetic relationship of the QRNG isolates, evaluated by pulsed-field gel electrophoresis, suggested that the increase in the frequencies of the QRNG isolates in Rio de Janeiro, Brazil, may have arisen as a result of simultaneous spread of two clonal groups. The results also indicate that fluoroquinolones may no longer be used as first line antibiotics for the treatment of gonorrhea in Rio de Janeiro, and that programs for antimicrobial susceptibility surveillance of N. gonorrhoeae should also be implemented in other regions of Brazil.

Cephalosporin Resistance in Neisseria gonorrhoeae

Gonorrhea, a disease of public health importance, not only leads to high incidence of acute infections and complications but also plays a major role in facilitating human immunodeficiency virus (HIV) acquisition and transmission. One of the major public health needs for gonorrhea control is appropriate, effective treatment. However, treatment options for gonorrhea are diminishing as Neisseria gonorrhoeae have developed resistance to several antimicrobial drugs such as sulfonamides, penicillin, tetracyclines and quinolones. Antimicrobial resistance (AMR) surveillance of N. gonorrhoeae helps establish and maintain the efficacy of standard treatment regimens. AMR surveillance should be continuous to reveal the emergence of new resistant strains, monitor the changing patterns of resistance, and be able to update treatment recommendations so as to assist in disease control. Current treatment guidelines recommend the use of single dose injectable or oral cephalosporins. The emergence and spread of cephalosporin resistant and multi drug resistant N. gonorrhoeae strains, represents a worrying trend that requires monitoring and investigation. Routine clinical laboratories need to be vigilant for the detection of such strains such that strategies for control and prevention could be reviewed and revised from time to time. It will be important to elucidate the genetic mechanisms responsible for decreased susceptibility and future resistance. There is also an urgent need for research of safe, alternative anti-gonococcal compounds that can be administered orally and have effective potency, allowing high therapeutic efficacy (greater than 95.0% cure rate).

Antibacterial susceptibility testing in the clinical laboratory

This article familiarizes the clinician with the principles of bacterial susceptibility testing and reporting to facilitate communication with the clinical microbiology laboratory. As resistance continues to emerge among a wide range of clinically relevant bacteria, the complexity of this communication increases. This updated version provides an overview of the important susceptibility concerns for most commonly isolated bacterial pathogens.

Antimicrobial resistance and genetic characterization of fluoroquinolone-resistant Mannheimia haemolytica isolates from cattle with bovine pneumonia

Antimicrobial susceptibility and molecular characterization of quinolone-resistant Mannheimia haemolytica was conducted. The antimicrobial susceptibility of 229 M. haemolytica isolates which were obtained from cattle with bovine respiratory disease during the period 1984-2006, was determined using 14 antimicrobial agents. Of the 229 isolates, 114 (49.8%) were resistant to at least one agent and resistance rates ranged from 4.8% to 31.4%. Resistance rates for dihydrostreptomycin, oxytetracycline, doxycycline, ampicillin, amoxicillin, thiamphenicol, kanamycin chloramphenicol, nalidixic acid, enrofloxacin, and danofloxacin were 31.4%, 20.5%, 18.3%, 19.2%, 16.6%, 10.9%, 11.4%, 10.5%, 17.0%, 4.8% and 4.8%, respectively. The nucleotide sequences of the quinolone resistance-determining regions of the gyrA and parC genes of nalidixic acid-resistant M. haemolytica were determined. All nalidixic acid-resistant strains possessed at least one amino acid substitution in each of the GyrA and ParC fragments investigated. These results suggest that M. haemolytica require at least one amino acid substitution in both GyrA and ParC in order to attain significant levels of resistance to quinolones. All fluoroquinolone-resistant isolates belonged to serotype 6, and their genotype by PFGE analysis was identical. This result indicates that fluoroquinolone-resistant M. haemolytica strains have clonally expanded.

Fluoroquinolone resistance and mutation patterns in gyrA and parC genes in Neisseria gonorrhoeae isolates from Shanghai, China

In order to study the resistance of Neisseria (N.) gonorrhoeae to the fluoroquinolone and detect mutation patterns of quinolone resistance-determining regions (QRDRs) of clinical isolates in Shanghai, China, a total of 80 clinical isolates of N. gonorrhoeae were consecutively collected from Shanghai. The MIC of fluoroquinolone for the isolates was examined by using the agar dilution method and the mutation profiles of the QRDRs of gyrA and parC were analyzed by sequencing and restriction fragment length polymorphism (RFLP). Chi-square test was used for comparison of the mutation patterns. The results showed that: (1) High percentages of the 8 isolates were resistant to ciprofloxacin (95.0%), ofloxacin (95.0%) and lomefloxacin (97.5%), only one strain was susceptible to the ciprofloxacin. (2) Sensitive strains had a substitute of Asp95-->Ala in the gyrA, and all isolates that were resistant or intermediated to the ciprofloxacin, had a double mutation in the gyrA (Ser91, Ala 92 and Asp95). Some strains also had a mutation in the parC. (3) The MICs of these isolates were significantly associated with the mutation patterns in the gyrA and parC. A double mutation of gyrA combined with parC87 mutation was a predominant pattern in Shanghai and could mediate high level resistance to ciprofloxacin. It suggests that mutations in the QRDRs of gyrA and parC may be responsible for the fluoroquinolone resistance. And fluoroquinolone could not be used as the first line antibiotics for gonorrhea treatment any more in Shanghai, China.

Antimicrobial susceptibility of Neisseria gonorrhoeae strains isolated in 2004-2006 in Bangui, Central African Republic; Yaoundé, Cameroon; Antananarivo, Madagascar; and Ho Chi Minh Ville and Nha Trang, Vietnam

GOAL

To investigate the in vitro antimicrobial susceptibility of Neisseria gonorrhoeae strains isolated in 2004 and 2005 in Bangui, Central African Republic; Yaoundé, Cameroon; Antananarivo, Madagascar; and Ho Chi Minh Ville and Nha Trang, Vietnam.

STUDY DESIGN

Antimicrobial susceptibility testing was performed by both disk diffusion and agar dilution methods according to Clinical and Laboratory Standards Institute (CLSI) recommendations. Minimum inhibitory concentrations (MICs) to 5 antimicrobials (penicillin G, ceftriaxone, ciprofloxacin, spectinomycin, and tetracycline) were determined when feasible. Penicillinase-producing N. gonorrhoeae (PPNG) was analyzed by the paper acidometric method (nitrocefin test).

RESULTS

Thirty N. gonorrhoeae isolates from Bangui could be studied, 79 from Yaoundé, 126 from Antananarivo, 56 from Nha Trang, and 126 from Ho Chi Minh Ville in 2004 and 2005. Unfortunately, because of problems of electricity supply, no strains could be recovered for the determination of MICs in Yaoundé, and only 68 strains could be tested in Antananarivo and 121 in Ho Chi Minh Ville. Patterns of resistance were similar in Antananarivo, Bangui, and Yaoundé but different from those observed in Vietnam. Ciprofloxacin was highly effective in Africa, but nearly all strains in Vietnam were resistant to this drug. Overall, ceftriaxon and spectinomycin were the best antibiotics, with one strain resistant to spectinomycin in Antananrivo and one strain resistant to ceftriaxon in Ho Chi Minh Ville.

CONCLUSIONS

Ciprofloxacin remains highly efficient in Madagascar and Central Africa, ceftriaxone and spectinomycin should be used as the first-line antimicrobial agents in treating gonorrhea in Vietnam.

Direct evaluation of drug resistance parameters in gonococcus

We carried out complex genetic analysis of clinical samples containing N. gonorrhoeae DNA, the genotype and profile of drug resistance of this agent were evaluated. Changes in genes responsible for the formation of N. gonorrhoeae resistance to penicillins, fluoroquinolones, and spectinomycin were detected during minisequencing with subsequent MALDI-TOF mass spectrometry. The sensitivity of gonococcus was evaluated directly in the clinical sample without culturing.

Relation between genetic markers of drug resistance and susceptibility profile of clinical Neisseria gonorrhoeae strains

The main goal of this work is to clarify the predictive value of known genetic markers of Neisseria gonorrhoeae resistance to penicillin, tetracycline, and fluoroquinolones. The correlation between the presence of certain genetic markers and susceptibility of N. gonorrhoeae isolates to penicillin, tetracycline, and fluoroquinolones has been analyzed by means of statistical methods. Susceptibility testing with penicillin, tetracycline, and fluoroquinolones was performed by the agar dilution method. N. gonorrhoeae genomic DNA was isolated. The presence of bla(TEM-1) and tet(M) genes was analyzed by PCR. A novel method of polymorphism discovery based on a minisequencing reaction followed by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry was applied for the analysis of chromosomal N. gonorrhoeae genes involved in antimicrobial resistance development. Clinical N. gonorrhoeae isolates (n = 464) were collected. Susceptibility levels to penicillin, tetracycline, and fluoroquinolones were found to be 25.9%, 35.9%, and 54.1%, respectively. Among the 19 N. gonorrhoeae isolates with penicillin MICs of > or =4 microg/ml, the bla(TEM-1) gene was detected in 12. The Tet(M) determinant was found in 4 of 12 N. gonorrhoeae isolates with tetracycline MICs of > or =16 microg/ml. The chromosomal genetic markers of penicillin and tetracycline resistance were detected especially in isolates with penicillin MICs of 0.25 to 2.0 microg/ml and tetracycline MICs of 0.5 to 4 microg/ml. Mutations in GyrA and ParC were found in 208 of 211 quinolone-resistant N. gonorrhoeae isolates. This work is the first representative molecular research of the N. gonorrhoeae population in Russia. Information about the prevalence of antibiotic resistance mechanisms and the positive predictive value of certain genetic determinants is given. The positive predictive values of the analyzed genetic markers were found to be different for fluoroquinolones (90.3%), penicillin (91.1%), and tetracycline (81.9%).

Molecular characterization of Neisseria gonorrhoeae identifies transmission and resistance of one ciprofloxacin-resistant strain

A highly discriminative and objective genetic characterization of N. gonorrhoeae, which increases our knowledge of strain populations in different geographic areas, is crucial for the development of improved control measures. In the present study, conventional phenotypic characterization and genetic characterization by means of pulsed-field gel electrophoresis (PFGE), sequencing of the entire porB gene, N. gonorrhoeae multiantigen sequence typing (NG-MAST), and pyrosequencing of a quinolone resistance determining region (QRDR) of the gyrA gene of Swedish ciprofloxacin-resistant N. gonorrhoeae serovar IB-10 isolates (n=45) were performed. The genetic characterization identified one widely spread ciprofloxacin-resistant N. gonorrhoeae ST147 strain. In addition, isolates with slightly different genetic characteristics, which presumably reflect the ongoing evolution only, were also identified. All the isolates contained single nucleotide polymorphisms in QRDR of the gyrA gene that are highly correlated with ciprofloxacin resistance. Consequently, comprehensive characterization identified the first confirmed large domestic transmission, mainly among young heterosexuals, of one ciprofloxacin-resistant N. gonorrhoeae strain in Swedish society during 2002-2003. In conclusion, a precise, i.e. genetic, characterization for identification of individual strains is a very valuable support to the crucial active surveillance of the epidemiological characteristics and the antibiotic susceptibility of N. gonorrhoeae in the effective treatment of gonorrhoea.

Rapid detection of the fluoroquinolone resistance-associated ParC mutation in Neisseria gonorrhoeae using TaqMan probes

BACKGROUND

In fluoroquinolone-resistant Neisseria gonorrhoeae, the amino acid mutations in the fluoroquinolone-resistant determining region (QRDR) of the parC gene are an important factor. The aim of the present study was to develop a rapid detection method of a serine 88 to proline substitution in parC which we previously showed as having significantly higher fluoroquinolone minimal inhibitory concentrations (MIC) using the TaqMan discrimination system.

METHODS

We extracted DNA from 90 urine or urethral swab samples obtained from male patients with urethritis caused by N. gonorrhoeae. After DNA extraction, they were subjected to real-time polymerase chain reaction (PCR) using a TaqMan discrimination system and compared with the results of conventional DNA sequencing.

RESULTS

Of the 90 samples, the TaqMan technique result showed 13 samples that were classified as having a serine 88 to proline mutation in parC, and 77 samples that did not have a serine 88 to proline mutation in parC. The classifications of all samples completely corresponded to those determined by conventional DNA sequencing. We also found that N. gonorrhoeae with a serine 88 to proline mutation in parC have a significantly higher MIC to ciprofloxacin than that without a serine 88 to proline mutant in parC.

CONCLUSIONS

The present genotyping method of real-time PCR using a TaqMan discrimination system could be applied to the rapid detection of a serine 88 to proline amino acid mutation in parC of N. gonorrhoeae. This point mutation is significant for the determination of fluoruquinolone resistance. This rapid detection system may lead to the prevention of use of noneffective antimicrobial agents and a decrease of resistant strains.

Activity of gemifloxacin tested against Neisseria gonorrhoeae isolates including antimicrobial-resistant phenotypes

The antigonococcal potency of gemifloxacin and 5 reference comparator antimicrobials was determined for a selected collection of gonococcal isolates. The 250 Neisseria gonorrhoeae strains were inclusive of (1) 50 historic strains from Japan with elevated fluoroquinolone minimal inhibitory concentration values (QRNG) and (2) 200 contemporary strains from clinical specimens in 2004 (176 from 6 sentinel sites in the United States and 24 bacteremic isolates from the SENTRY Antimicrobial Surveillance Program). The rank order of potency of the tested antimicrobials for the entire collection was: ceftriaxone (MIC(90) = 0.06 microg/mL) > gemifloxacin (1 microg/mL) > tetracycline (2 microg/mL) > ciprofloxacin = levofloxacin = penicillin (4 microg/mL). The activity of gemifloxacin was not affected by penicillinase production; however, its activity was decreased for penicillin-resistant strains. Cross-resistance between gemifloxacin and the older fluoroquinolones was present, and the gemifloxacin MIC90 value was higher for the ciprofloxacin-resistant strains compared with the ciprofloxacin-susceptible strains (2 versus 0.016 mug/mL, respectively). More than 20.0% of the recent clinical strains were resistant to penicillin, tetracycline, and ciprofloxacin with >30.0% of gonococci resistant to ciprofloxacin in Washington State and Hawaii. The historic QRNG strains from the Far East were predominantly of intermediate susceptibility (88.0%) to ciprofloxacin, with a gemifloxacin MIC90 value of only 0.25 microg/mL. The bacteremic gonococcal strains were exquisitely susceptible to the 3 quinolones tested (ciprofloxacin, levofloxacin, and gemifloxacin, MIC90 at < or = 0.03 microg/mL) and ceftriaxone (MIC90 = 0.06 microg/mL). In summary, the potency of gemifloxacin was competitive and positioned between that of ceftriaxone and older quinolones or penicillin or tetracycline, irrespective of the gonococcal resistance phenotype. Gemifloxacin should be considered for further development as a therapeutic option to treat uncomplicated infections due to emerging strains resistant to penicillins, tetracycline, and some older fluoroquinolones.

Presence of a mutation in ponA1 of Neisseria gonorrhoeae in numerous clinical samples resistant to various beta-lactams and other, structurally unrelated, antimicrobials

The number of resistant strains in patients with Neisseria gonorrhoeae urethritis has been increasing, making effective treatment difficult. Chromosomally mediated penicillin-resistant N. gonorrhoeae arise through alterations in penicillin-binding proteins (PBPs) and a decrease in outer membrane permeability. To understand the occurrence of penicillin resistance in patients with N. gonorrhoeae infection, we performed this study. In addition, we studied minimum inhibitory concentrations (MICs) of antimicrobials against N. gonorrhoeae strains. We measured the MICs of penicillin G, other beta-lactams, and other kinds of antimicrobials against 53 clinical N. gonorrhoeae isolates from male patients with urethritis in Hyogo and Osaka, Japan. The ponA genes, encoding PBP 1 of these isolates, were sequenced. Of the 53 isolates tested, 41 strains showed some resistance to penicillin G. A mutation in the ponA (ponA1) gene was identified in 46 isolates. There was a tendency that ponA mutant (ponA1) in N. gonorrhoeae led to higher antimicrobial MICs of beta-lactam antimicrobial agents (including penicillin) than those of non-ponA mutants. However, we found lower than expected MICs of penicillin and beta-lactams even in ponA mutants. Therefore, we consider that detailed investigations for the further understanding of the effect of other genes, such as penC (which is reported to be related to ponA1 in achieving high-level penicillin resistance) should be our next step.

Activity of faropenem tested against Neisseria gonorrhoeae isolates including fluoroquinolone-resistant strains

We evaluated the anti-gonococcal potency of faropenem along with 7 comparator reference antimicrobials against a preselected collection of clinical isolates. The 265 isolates were inclusive of 2 subsets: 1) 76 well-characterized resistant phenotypes of gonococcal strains (53 quinolone-resistant strains--31 with documented quinolone resistance-determining region changes from Japan, 15 strains resistant to penicillin and tetracycline, and 8 strains with intermediate susceptibility to penicillin) and 2) 189 recent isolates from clinical specimens in 2004 from 6 states across the United States where quinolone resistance is prevalent. Activity of faropenem was adversely affected by l-cysteine hydrochloride in IsoVitaleX (4-fold increase in [minimal inhibitory concentration] MIC50; 0.06 versus 0.25 microg/mL). The rank order of potency of the antimicrobials for the entire collection was ceftriaxone (MIC90, 0.06 microg/mL) > faropenem (0.25 microg/mL) > azithromycin (0.5 microg/mL) > cefuroxime (1 microg/mL) > tetracycline (2 microg/mL) > penicillin = ciprofloxacin = levofloxacin (4 microg/mL). Using MIC90 for comparison, faropenem was 4-fold more potent than cefuroxime (0.25 versus 1 microg/mL), but was 4-fold less active than ceftriaxone (0.25 versus 0.06 microg/mL). Although the activity of faropenem was not affected by either penicillinase production (MIC90, 0.12 microg/mL, penicillinase-positive) or increasing ciprofloxacin MIC (0.25 microg/mL, ciprofloxacin-resistant), increasing penicillin MIC was associated with an increase in MIC90 values (0.016 microg/mL for penicillin-susceptible to 0.25 microg/mL for penicillin-resistant strains). Among the recent (2004) clinical gonococcal isolates tested, reduced susceptibility to penicillins, tetracycline, and fluoroquinolones was high (28.0-94.2%). Geographic distribution of the endemic resistance rates of gonococci varied considerably, with 16.7-66.7% of the gonococcal isolates being ciprofloxacin-resistant in Oregon, California, Washington, and Hawaii. Faropenem retained its potency against these recent clinical strains and also quinolone-resistant strains from Japan (MIC90, < or =0.25 microg/mL). In summary, the excellent activity of faropenem against the gonococcal strains analyzed irrespective of the resistance phenotype, along with its beta-lactamase stability, makes it an ideal contender for further development as an oral beta-lactam agent to treat uncomplicated gonococcal infections due to strains emerging with resistant to penicillins, tetracyclines, and fluoroquinolones.

Detection of gyrA mutations associated with ciprofloxacin resistance in Neisseria gonorrhoeae by rapid and reliable pre-programmed short DNA sequencing

Quinolone resistance is rapidly increasing in Neisseria gonorrhoeae and is posing a significant public health threat that requires constant surveillance. A rapid and reliable mutation detection assay has been developed. The assay is based on pre-programmed short DNA sequencing and is designed to detect point mutations in the gyrA gene that are highly related to ciprofloxacin resistance, i.e. in codons 91 and 95. By developing an assay based on pyrosequencing and exploiting the pre-programmed nucleotide dispensation capability of this technology, the sequence comprising the mutations will be analysed and promptly reveal whether the N. gonorrhoeae pathogen carries resistance to ciprofloxacin. A panel of 40 N. gonorrhoeae clinical isolates, of which 27 phenotypically displayed decreased susceptibility or resistance to ciprofloxacin, was used in the present study. All point mutations in the short stretch of the N. gonorrhoeae gyrA gene were easily discriminated, and the genotypic results obtained by pre-programmed sequencing were mainly in agreement with the phenotypically identified decreased susceptibility or resistance to ciprofloxacin. The new method used in the present study has the potential for rapid and reliable identification of known as well as previously unknown drug resistance mutations.

In vitro assessment of the further potential for development of fluoroquinolone resistance in Neisseria meningitidis

We examined the potential for the development of fluoroquinolone resistance in Neisseria meningitidis by cultivating two clinical isolates of meningococci in the presence of concentrations of ciprofloxacin at and about the predetermined MIC. The quinolone resistance determining regions (QRDRs) of gyrA and parC of 50 stable quinolone-resistant mutants derived in vitro were sequenced and compared with QRDR alterations reported in clinical isolates of quinolone-resistant meningococci and gonococci. MICs to ciprofloxacin and trovafloxacin were determined and sequence changes were correlated with quinolone MICs. Ciprofloxacin and trovafloxacin MICs of the in vitro-derived quinolone-resistant mutants ranged up to 16 mg/liter. Single GyrA alterations were the first change detected and were accompanied by raised MICs, followed by double GyrA changes and still higher MICs. MICs increased further as single ParC substitutions appeared and these were always in the presence of a single or double GyrA change. GyrA changes occurred at positions 91 and 95 with substitutions of Asp-95-->Asn and Thr-91-->Ala and Ile. Changes in the parC QRDR occurred at positions 85, 86, and 91 with four substitutions, Gly-85-->Asp, Asp-86-->Asn, Glu-91-->Gly, and Glu-91-->Lys, detected. The nature of the individual QRDR substitution appeared to influence the level of quinolone resistance expressed, and this varied with the quinolone agent examined. Close similarities occurred between the sequence and nature of QRDR changes in clinical and in vitro-generated quinolone-resistant mutants and with those previously reported for clinical and in vitro-generated quinolone-resistant gonococci. This suggests that quinolone resistance in meningococci may arise in the same manner and reach similar levels in vivo to those seen in quinolone-resistant Neisseria gonorrhoeae.

Detection of gyrA and parC mutations associated with ciprofloxacin resistance in Neisseria gonorrhoeae by use of oligonucleotide biochip technology

An oligonucleotide biochip that specifically detects point mutations in the gyrA and parC genes of Neisseria gonorrhoeae was designed and subsequently evaluated with 87 untreated clinical specimens. The susceptibilities of the N. gonorrhoeae strains were tested to determine the prevalence of ciprofloxacin-resistant strains in Anhui Province, People's Republic of China. Conventional DNA sequencing was also performed to identify mutations in gyrA and parC and to confirm the biochip data. The study demonstrates that all of the point mutations in the gyrA and parC genes of N. gonorrhoeae were easily discriminated by use of the oligonucleotide biochip. Fifteen different alteration patterns involved in the formation of ciprofloxacin resistance were identified by the biochip assay. Double mutations in both Ser91 and Asp95 of the GyrA protein were seen in all nonsensitive isolates. Double mutations in Ser91 and Asp95 of GyrA plus mutation of Glu91 or Ser87 of the ParC protein lead to significant high-level resistance to ciprofloxacin in N. gonorrhoeae isolates. The results obtained by use of the oligonucleotide biochip were identical to those obtained by use of DNA sequencing. In conclusion, the oligonucleotide biochip technology has potential utility for the rapid and reliable identification of point mutations in the drug resistance genes of N. gonorrhoeae.

High-frequency of quinolone-resistant Neisseria gonorrhoeae in Austria with a common pattern of triple mutations in GyrA and ParC genes

OBJECTIVE

Quinolones have a broad spectrum of antimicrobial activity and are widely used for the treatment of uncomplicated Neisseria gonorrhoeae infections. A dramatic increase in the number of reported N. gonorrhoeae infections as well as quinolone-resistant isolates in Vienna prompted us to investigate the pattern of mutations in these isolates.

GOALS

The goal of this study was to investigate the pattern of mutations in GyrA and ParC genes in quinolone-resistant N. gonorrhoeae clinical isolates in Vienna from 1999 to 2002.

STUDY

The antibiotic susceptibility of N. gonorrhoeae clinical isolates and point mutations of the GyrA and ParC genes of 104 clinical isolates were analyzed.

RESULTS

Quinolone-resistant N. gonorrhoeae isolates increased from 3.9% (3 of 77) in 1999 to 59.4% (120 of 202) in 2002. As expected, none of the 46 N. gonorrhoeae quinolone-sensitive strains showed mutations at these positions of GyrA and ParC genes with the exception of 1 isolate, which had a single mutation at GyrA 91. Unlike what has been previously reported for other geographic areas, 96.6% (56 of 58) of the quinolone-resistant isolates harbored common triple mutations at Gyr 91, 95, and ParC 86. The majority of these isolates (76.8%) belong to the PPNG phenotype.

CONCLUSIONS

Our data indicate that the pattern of mutations in GyrA and ParC subunits of N. gonorrhoeae in Austria differs from that reported from other geographic areas. The differences may either be the result of the difference in bacterial subtypes or various antibiotic regimens used in these regions.

Emergence and spread of Neisseria gonorrhoeae clinical isolates harboring mosaic-like structure of penicillin-binding protein 2 in Central Japan

Of 150 clinical isolates of Neisseria gonorrhoeae recovered in 2001, we examined 55 clinical isolates of N. gonorrhoeae for which cefixime MICs were > or=0.125 microg/ml and randomly selected 15 isolates for which cefixime MICs were < or =0.06 microg/ml for analysis of alterations in the penicillin-binding protein 2 (PBP 2) gene. We found insertion of an extra codon (Asp-345a) in the transpeptidase domain of PBP 2, and this insertion occurred alone or in conjunction with other amino acid substitutions. We also found a mosaic PBP 2 that was composed of fragments of the PBP 2 proteins from Neisseria cinera and Neisseria perflava. This mosaic PBP 2 was significantly associated with decreased susceptibilities to penicillin and cephalosporins, especially oral cephalosporins. For most of the isolates with a mosaic PBP 2, the cefixime MICs were > or =0.5 microg/ml and the cefdinir MICs were > or =1 microg/ml. Analysis of chromosomal DNA restriction patterns by pulsed-field gel electrophoresis revealed that most isolates with the mosaic PBP 2 were genetically similar. The recombination events that generated the mosaic PBP 2 would likely have contributed to the decreased sensitivities to cephalosporins. Isolates with the mosaic PBP 2 appear to threaten the efficacy of the currently recommended regimen with cefixime. The emergence of such strains may be the result of the in vivo generation of clones in which interspecies recombination occurred between the penA genes of N. gonorrhoeae and commensal Neisseria species.

Antibacterial susceptibility testing in the clinical laboratory

This article familiarizes the clinician with the principles of bacterial susceptibility testing and reporting to facilitate communication with the clinical microbiology laboratory. The emergence of resistance in nearly all commonly isolated bacterial organisms has highlighted the need for ongoing dialogue between the laboratory and those who use its services.

Mutations in the gyrA and parC Genes and in vitro Activities of Fluoroquinolones in 91 Clinical Isolates of Neisseria gonorrhoeae in Japan

BACKGROUND AND OBJECTIVES

Fluoroquinolone resistance in Neisseria gonorrhoeae has been associated with alternations in the quinolone-resistance determining regions in the gyrA and parC genes.

GOAL

The goal of this study was to investigate the correlation between fluoroquinolone minimum inhibitory concentrations (MICs) and mutations in the gyrA and parC genes of 91 N. gonorrhoeae clinical isolates from Japan.

STUDY DESIGN

The MICs of fluoroquinolones ciprofloxacin, levofloxacin, and gatifloxacin for 91 clinical isolates from male gonococcal urethritis in Hyogo or Osaka, Japan, were measured, and the gyrA and parC genes of these isolates were sequenced.

RESULTS

Among 91 isolates tested, over 70% isolates were resistant to ciprofloxacin. We found that 4 mutations (Ser-91-Phe, Ser-91-Ile, Asp-95-Gly in gyrA, and Ser-88-Pro in parC) had significant correlation to MICs of fluoroquinolone (ciprofloxacin, levofloxacin, and gatifloxacin).

CONCLUSION

Some mutations in QRDR had a significant relationship to the fluoroquinolone resistance of N. gonorrhoeae clinical isolates from Japan.

Uncommon occurrence of fluoroquinolone resistance-associated alterations in GyrA and ParC in clinical strains of Chlamydia trachomatis

Twenty-three clinical strains of Chlamydia trachomatis were isolated from men with chlamydial nongonococcal urethritis and examined for the presence of fluoroquinolone resistance-associated alterations in GyrA and ParC. The minimum inhibitory concentrations (MICs) of fluoroquinolones, erythromycin, and tetracycline were determined for 6 of the 23 isolates. In 12 of the 23 isolates, a single amino-acid change was found in GyrA, and in 1 isolate, two amino acids were changed. In all 23 isolates, an Arg-83-to-Gly substitution was observed in ParC, and in 3 isolates, an additional amino-acid change was found. Some changes occurred within the quinolone resistance-determining regions (QRDRs) of GyrA and ParC, but not at positions critical for fluoroquinolone resistance. Of the 6 isolates for which MICs of the agents were determined, 1 isolate had a Cys-66 --> Arg substitution in GyrA, and all had the Arg-83 --> Gly substitution in ParC. However, all 6 isolates were susceptible to fluoroquinolones. First-pass urine specimens were obtained from two men who were positive for C. trachomatis after levofloxacin treatment, and the gyrA and parC genes of C. trachomatis were amplified by polymerase chain reaction (PCR) and examined for fluoroquinolone resistance-associated mutations. Pre- and post-treatment C. trachomatis persisting in each of them had identical amino-acid sequences in the QRDR of GyrA and ParC. Further, the substitutions found in GyrA and ParC were not located at positions critical for fluoroquinolone resistance. The present study suggests that fluoroquinolone resistance-associated alterations in GyrA and ParC may be uncommon in clinical strains of C. trachomatis.

Antimicrobial susceptibility of Neisseria gonorrhoeae strains isolated in Guangzhou, China, 1996-2001

OBJECTIVE

To investigate the in vitro antimicrobial susceptibility and resistant trends of Neisseria gonorrhoeae strains isolated in Guangzhou, from 1996 to 2001.

METHODS

The agar dilution method was used to determine the minimum inhibitory concentrations (MICs) to four antimicrobials, penicillin G, ciprofloxacin, ceftriaxone, and spectinomycin. The resistance of all strains to four antibiotics was interpreted according to criteria used in the project of surveillance of gonococcal antibiotic susceptibility in the WHO Western Pacific Region. Penicillinase producing N gonorrhoeae (PPNG) was analysed by the paper acidometric method.

RESULTS

793 consecutive N gonorrhoeae isolates collected in Guangzhou were studied from 1996 to 2001. A total of 55 strains of PPNG were identified and the prevalence rapidly spread from 2% to 21.8%. Of the four antibiotics examined, ceftriaxone and spectinomycin appeared to be the most effective agents although two spectinomycin resistant strains were isolated in 1996. Their MIC(50), MIC(90), and geometric mean MIC (MICmean) were all between the sensitive ranges of the interpretative criteria and remained stable over the years. However, resistance increased continuously to penicillin G and dramatically to ciprofloxacin. In 1996-2001, MIC(50), MIC(90), and MICmean of penicillin G increased from 1 micro g/ml to 2 micro g/ml, 4 micro g/ml to 32 micro g/ml, and 0.68 micro g/ml to 2.35 micro g/ml, respectively; those of ciprofloxacin steeply increased from 0.12 micro g/ml to 4 micro g/ml, 2 micro g/ml to 32 micro g/ml, and 0.14 micro g/ml to 2.62 micro g/ml in 1996-9, respectively, and then declined slightly in 2000-1. The prevalence of resistant isolates spread from 57.2% to 81.8% for penicillin G and from 17.6% to 72.7% for ciprofloxacin over the 6 years.

CONCLUSION

Resistance to penicillin and ciprofloxacin increased greatly during 1996-2001. Ceftriaxone and spectinomycin should be used as the first line agents in treating gonorrhoea. It is of great importance to continuously survey the susceptibilities of N gonorrhoeae to antibiotics in controlling the spread of gonococcal infections.

Molecular characterization of ciprofloxacin resistance of gonococcal strains in Spain

BACKGROUND

Over the past several years, the emergence of gonococcal isolates with intermediate or full resistance to fluoroquinolones has become a significant concern in several countries, including Spain.

GOAL

The goal was to determine the occurrence of ciprofloxacin resistance among Neisseria gonorrhoeae strains in Spain during 2000 to 2001 and determine the frequency and patterns of mutations at gyrA, gyrB, and parC genes in these isolates.

STUDY DESIGN

Eleven ciprofloxacin-resistant strains (with MICs ranging from 1 to 64 micrograms/mL) and two intermediate isolates (with MICs of 0.12 and 0.5 microgram/mL) were found. Mutations were identified by polymerase chain reaction and direct sequencing of the amplified products.

RESULTS AND CONCLUSIONS

Alterations at Ser-91 and Asp-95 in GyrA were detected in all strains except one, an isolate for which the MIC was 0.12 microgram/mL. Alterations in ParC were more variable, and there was no clear correlation between the number of parC mutations and the level of resistance. No alterations at gyrB gene associated with ciprofloxacin resistance were found. The resistance was distributed among different types of strains, suggesting that the increase in the incidence of ciprofloxacin-resistant strains in Spain was not exclusively due to the appearance of a single-strain outbreak.

Mutation patterns in gyrA and parC genes of ciprofloxacin resistant isolates of Neisseria gonorrhoeae from India

AIM

To analyse mutations in the gyrA and parC genes leading to possible increase in ciprofloxacin resistance (high MIC values for ciprofloxacin) in clinical isolates of Neisseria gonorrhoeae in Delhi, India.

METHOD

MIC of ciprofloxacin for 63 clinical isolates of N gonorrhoeae were examined by the Etest method. Subsequently, gyrA and parC genes of these isolates were amplified and sequenced for possible mutations.

RESULTS

Out of the 63 clinical isolates tested, only five (8%) isolates were found to be susceptible to ciprofloxacin (MIC <0.06 micro g/ml). DNA sequence analysis of the gyrA and the parC genes of all these isolates (n = 63) revealed that all isolates which were not susceptible to ciprofloxacin (n=58) had mutation(s) in gyrA and parC genes. 12 isolates (19%) exhibited high resistance with an MIC for ciprofloxacin of 32 micro g/ml. Two out of these 12 isolates (UD62 and UD63), harboured triple mutations (Ser-91 to Phe, Asp-95 to Asn and Val-120 to Leu) in the gyrA gene. The third mutation of Val-120 to Leu, lies downstream of the quinolone resistance determining region (QRDR) of the gyrA and has not been described before in gonococcus. In addition, both these isolates had a Phe-100 to Tyr substitution in the parC, a hitherto unknown mutation.

CONCLUSIONS

Emergence of ciprofloxacin resistance with high levels of MIC values (up to 32 micro g/ml) in India is alarming. Double and triple mutations in gyrA alone or together in gyrA and parC could be responsible for such a high resistance.

Multiclonal increase in ciprofloxacin-resistant Neisseria gonorrhoeae, Thailand, 1998-1999

BACKGROUND

isolates exhibiting clinically significant resistance to fluoroquinolones have been isolated most frequently in Asian and western Pacific countries, including Thailand. In Bangkok, Thailand, ciprofloxacin has been used to treat gonorrhea since 1987.

GOAL

Our goal was to determine the prevalence of isolates of that exhibit resistance to ciprofloxacin in Bangkok and to characterize these strains with regard to ciprofloxacin MICs, auxotype/serovar (A/S) classification, A and C mutations responsible for ciprofloxacin resistance, and outer membrane lipoprotein (Lip) subtype analysis.

STUDY DESIGN

MICs of gonococcal isolates from consecutive patients attending the Bangrak Hospital STD Clinic in Bangkok were determined by agar dilution. A/S class was determined by established procedures. Mutations within A and C were determined by DNA sequencing. Lip subtypes were determined by PCR and DNA sequencing.

RESULTS

In 1998 and 1999, 115 of 168 isolated strains of exhibited decreased susceptibility or resistance to ciprofloxacin, and three cases of possible ciprofloxacin treatment failure were identified. Ciprofloxacin-resistant (CipR) strains increased from 13.8% (8/58) in 1998 to 25.4% (28/110) in 1999 ( = 0.08). Ciprofloxacin MICs of CipR isolates ranged from 1.0 microg/ml to 32.0 microg/ml. CipR strains belonged to a number of A/S classes and Lip subtypes. Different CipR strains contained alterations at both amino acid 91 and amino acid 95 of A and also contained an amino acid alteration in C. These alterations are known to be involved in gonococcal resistance to ciprofloxacin.

CONCLUSIONS

The prevalence of CipR strains of isolated in Bangkok increased substantially in the 1990s. Characterization of the CipR isolates revealed a number of different strain subtypes, indicating that CipR isolates in Bangkok are not from a single clonal source and therefore result from multiple cases of importation or local emergence. Because of the high level of CipR isolates at Bangrak Hospital, in 2000 the Thai Ministry of Public Health issued recommendations against the use of fluoroquinolones for the treatment of gonococcal infection in Thailand.

Rapid detection of quinolone resistance-associated gyrA mutations in Neisseria gonorrhoeae with a LightCycler

Afluorometric real-time polymerase chain-reaction (PCR)-hybridization system, the LightCycler was developed for the detection of Neisseria gonorrhoeae in clinical samples and the analysis of point mutations associated with quinolone resistance in the gyrAgene. This system allowed us to amplify the N. gonorrhoeae-specific gyrA gene from an amount of DNA corresponding to five genome copies per reaction. We were able to detect N. gonorrhoeae in either 55 control strains or 36 nonisolated clinical urethral swab specimens, and to analyze the presence of mutations in codons Ser-91 and Asp-95 of the gyrA gene within 1 h. The mutation status in the gyrA gene assessed by the LightCycler assay was completely in agreement with the results of our previous conventional sequencing analysis, and was associated with the susceptibility to ciprofloxacin.

Development and spread of bacterial resistance to antimicrobial agents: an overview

Resistance to antimicrobial agents is emerging in a wide variety of nosocomial and community-acquired pathogens. The emergence and spread of multiply resistant organisms represent the convergence of a variety of factors that include mutations in common resistance genes that extend their spectrum of activity, the exchange of genetic information among microorganisms, the evolution of selective pressures in hospitals and communities that facilitate the development and spread of resistant organisms, the proliferation and spread of multiply resistant clones of bacteria, and the inability of some laboratory testing methods to detect emerging resistance phenotypes. Twenty years ago, bacteria that were resistant to antimicrobial agents were easy to detect in the laboratory because the concentration of drug required to inhibit their growth was usually quite high and distinctly different from that of susceptible strains. Newer mechanisms of resistance, however, often result in much more subtle shifts in bacterial population distributions. Perhaps the most difficult phenotypes to detect, as shown in several proficiency testing surveys, are decreased susceptibility to beta-lactams in pneumococci and decreased susceptibility to vancomycin in staphylococci. In summary, emerging resistance has required adaptations and modifications of laboratory diagnostic techniques, empiric anti-infective therapy for such diseases as bacterial meningitis, and infection control measures in health care facilities of all kinds. Judicious use is imperative if we are to preserve our arsenal of antimicrobial agents into the next decade.

Quinolone Resistance in Neisseria gonorrhoeae

Single-dose oral quinolones have been recommended for gonorrhea treatment since 1989. The antimicrobial resistance surveillance system has detected several outbreaks of quinolone-resistant gonococcal infections (QRNG), and sporadic treatment failures have been reported from high-incidence areas such as southeast Asia. QRNG may result from mutations that cause structural-functional changes in DNA topoisomerase (the quinolone target enzyme) or by changes in antimicrobial transport into the bacteria. QRNG has occurred sporadically in the United States, predominantly in persons with contact to persons in southeast Asia, and has typically occurred as an epiphenomenon in persons who were treated with other regimens. Nevertheless, this entity warrants close monitoring. The emergence of QRNG is probably related to antimicrobial misuse and overuse, in particular long-term suppressive or subtherapeutic doses.

Correlation of in vitro susceptibilities to newer quinolones of naturally occurring quinolone-resistant Neisseria gonorrhoeae strains with changes in GyrA and ParC

The in vitro activities of ciprofloxacin, trovafloxacin, moxifloxacin, and grepafloxacin against 174 strains of Neisseria gonorrhoeae isolated in Sydney, Australia, were determined. The strains included 84 quinolone-less-sensitive and -resistant N. gonorrhoeae (QRNG) strains for which ciprofloxacin MICs were in the range of 0.12 to 16 microg/ml. The QRNG included strains isolated from patients whose infections were acquired in a number of countries, mostly in Southeast Asia. The gyrA and parC quinolone resistance-determining regions (QRDR) of 18 selected QRNG strains were sequenced, and the amino acid mutations observed were related to the MICs obtained. The activities of moxifloxacin and grepafloxacin against QRNG were comparable to that of ciprofloxacin. Trovafloxacin was more active than the other quinolones against some but not all of the QRNG strains. Increments in ciprofloxacin resistance occurred in a step-wise manner with point mutations initiated in gyrA resulting in amino acid alterations Ser91-to-Phe, Ser91-to-Tyr, Asp95-to-Gly, and Asp95-to-Asn. Single gyrA changes correlated with ciprofloxacin MICs in the range 0.12 to 1 microg/ml. The Ser91 changes in GyrA were associated with higher MICs and further QRDR changes. QRNG strains for which ciprofloxacin MICs were greater than 1 microg/ml had both gyrA and parC QRDR point mutations. ParC alterations were seen in these isolates only in the presence of GyrA changes and comprised amino acid changes Asp86-to-Asn, Ser87-to-Asn, Ser87-to-Arg, Ser88-to-Pro, Glu91-to-Lys, and Glu91-to-Gln. QRNG strains for which MICs were in the higher ranges had double GyrA mutations, but again only with accompanying ParC alterations. Not only did the nature and combination of GyrA and ParC changes influence the incremental increases in ciprofloxacin MICs, but they seemingly also altered the differential activity of trovafloxacin. Our findings suggest that the newer quinolones of the type examined are unlikely to be useful replacements for ciprofloxacin in the treatment of gonorrhea, particularly where ciprofloxacin MICs are high or where resistance is widespread.

Quinolone resistance mutations in the gyrA gene of clinical isolates of Salmonella

S. typhimurium AlhR, S. enteritidis OulR, and S. hadar GueR resistant to fluoroquinolones (QR), ciprofloxacin MICs, 0.25 to 1 microgram/ml; norfloxacin MICs, 0.5 to 4 micrograms/ml; nalidixic acid MIC, 256 micrograms/ml were isolated from urinary tract infections (AlhR and OulR) during FQ therapy in immunocompromised patients infected by the parent FQ-susceptible strains (AlhS and OulS) (ciprofloxacin MICs, 0.032-0.063; norfloxacin MICs, 0.125-0.25; nalidixic acid MICs, 4-8) or from intestinal infection (GueR). Transformation of AlhR, OulR, and GueR by plasmid pJSW101 carrying the wild-type gyrA gene of Escherichia coli resulted in complementation (nalidixic acid MICs, 4 to 8), proving that these strains had a gyrA mutation. A 800-bp fragment of gyrA from the five strains was amplified by PCR. Direct DNA sequencing of 252-bp region of this fragment identified a single point mutation leading to a substitution Ser-83 to Tyr in AlhR and to a substitution Ser-83 to Phe in OulR and in GueR. These results emphasize the potential risk of selection of FQ-resistant Salmonella during FQ therapy in immunocompromised patients and suggest that these strains differ from the parent strains at least by one mutation in the gyrA gene. They also confirm the role of substitutions in position 83 of gyrA in FQ-resistant clinical isolates of Salmonella.

Mechanisms of fluoroquinolone resistance: an update 1994-1998

Fluoroquinolone resistance is mediated by target changes (DNA gyrase and/or topoisomerase IV) and/or decreased intracellular accumulation. The genes (gyrA/gyrB/parC/parE) and proteins of DNA topoisomerase IV show great similarity, both at the nucleotide and amino acid sequence level to those of DNA gyrase. It has been shown that there are hotspots, called the quinolone resistance determining region (QRDR), for mutations within gyrA and parC. Based on the Escherichia coli co-ordinates, the hotspots most favoured for giving rise to decreased susceptibility and/or full resistance to quinolones are at serine 83 and aspartate 87 of gyrA, and at serine 79 and aspartate 83 for parC. Few mutations in gyrB or parE/grlB of any bacteria have been described. Efflux of fluoroquinolones is the major cause of decreased accumulation of these agents; for Staphylococcus aureus, the efflux pump involved in norfloxacin resistance is NorA, and for Streptococcus pneumoniae, PmrA. By analysis of minimum inhibitory concentration (MIC) data derived in the presence and absence of the efflux inhibitor reserpine, it has been shown that up to 50% of ciprofloxacin-resistant clinical isolates of S. pneumoniae may possess enhanced efflux. This suggests that efflux may be an important mechanism of clinical resistance in this species. In Pseudomonas aeruginosa, several efflux operons have been demonstrated genetically and biochemically. These operons are encoded by mex (Multiple EffluX) genes: mexAmexB-oprM, mexCD-OprJ system and mexEF-oprN system. The E. coli efflux pump is the acrAB-tolC system. Both the mar operon and the sox operon can give rise to multiple antibiotic resistance. It has been shown that mutations giving rise to increased expression of the transcriptional activators marA and soxS affect the expression of a variety of different genes, including ompF and acrAB. The net result is that expression of OmpF is reduced and much less drug is able to enter the cell; expression of acrAB is increased, enhancing efflux from the cell.

Comparative in vitro activities of ciprofloxacin, clinafloxacin, gatifloxacin, levofloxacin, moxifloxacin, and trovafloxacin against Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, and Enterobacter aerogenes clinical isolates with alterations in GyrA and ParC proteins

The in vitro activities of ciprofloxacin, clinafloxacin, gatifloxacin, levofloxacin, moxifloxacin, and trovafloxacin were tested against 72 ciprofloxacin-resistant and 28 ciprofloxacin-susceptible isolates of Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, and Enterobacter aerogenes. Irrespective of the alterations in GyrA and ParC proteins, clinafloxacin exhibited greater activity than all other fluoroquinolones tested against K. pneumoniae and E. aerogenes.

Alterations within the quinolone resistance-determining regions of GyrA and ParC of Neisseria gonorrhoeae isolated in the Far East and the United States

The genetic mutations within the quinolone resistance-determining regions (QRDRs) of gyrA and parC of 234 Neisseria gonorrhoeae strains isolated in the Far East and the United States, which exhibited either clinically significant ciprofloxacin resistance (CipR) or intermediate ciprofloxacin resistance (CipI) were characterized. A number of GyrA/ParC amino acid alteration patterns were identified, the most prevalent alteration pattern among CipR isolates being GyrA-91,95/ParC-Asp-86- > Asn (91,95/Asp-86- > Asn). Isolates containing 91,95/Asp-86- > Asn belonged to a number of A/S classes, penicillin/tetracycline resistance phenotypes, and plasmid profiles. These results strongly suggest that the continuing emergence of ciprofloxacin-resistant gonococci is not due to the spread of a single or a few strains but to numerous factors such as 'spread of existing strains, importation of new strains and, possibly, de novo development of ciprofloxacin resistance in previously susceptible strains.

Neisseria gonorrhoeae in Newcastle upon Tyne 1995-1997: increase in ciprofloxacin resistance

Fluoroquinolones and third generation cephalosporins are the most effective antimicrobial agents for the treatment of gonorrhoea. However, clinically significant resistance to fluoroquinolones in Neisseria gonorrhoeae has been reported worldwide including Britain. The aim of this analysis was to study the factors relating to ciprofloxacin resistance and treatment failure. A total of 201 patients attending the Newcastle Genitourinary Medicine (GUM) clinic from 1995-1997 who were diagnosed with culture positive gonorrhoea was analysed. Treatment failure rates for ciprofloxacin were determined and the minimum inhibitory concentration (MIC) was measured for all cases of treatment failure. The case notes of all patients who had strains with MICs of ciprofloxacin in the resistant range (>0.05 microg/ml) were reviewed to determine the clinical outcome. The ciprofloxacin resistance with treatment failure was seen in 5% (8/160). All the 8 cases of treatment failure were heterosexual and had isolates resistant to penicillin and 4 cases (50%) were also resistant to tetracycline. All were sensitive to spectinomycin and ceftriaxone. Most of the cases probably acquired their infection from the Far East. As ciprofloxacin resistance seems to be associated with overseas exposure, changes in the standard treatment of gonorrhoea are not justified but consideration should be given to appropriate alternatives when the infection may have arisen from where such resistant strains are endemic. Monitoring fluoroquinolone resistance is now essential for ensuring adequate treatment of infections with resistant strains and for maximizing the time of usage of fluoroquinolones to treat gonorrhoea.

Alteration in the GyrA subunit of DNA gyrase and the ParC subunit of DNA topoisomerase IV in quinolone-resistant clinical isolates of Staphylococcus epidermidis

We examined 22 clinical isolates of Staphylococcus epidermidis to analyze the association of alterations in GyrA and ParC with fluoroquinolone resistance. The simultaneous presence of GyrA and ParC alterations was associated with a high level of fluoroquinolone resistance in the clinical isolates of S. epidermidis.

Drift in susceptibility of Neisseria gonorrhoeae to ciprofloxacin and emergence of therapeutic failure

Ciprofloxacin, 500 mg, was introduced as the first-line therapy for gonorrhea at St. Mary's Hospital, London, in 1989, when a surveillance program was initiated to detect the emergence of resistance. Isolates of Neisseria gonorrhoeae from consecutive patients attending the Jefferiss Wing, Genitourinary Medicine Clinic at St. Mary's Hospital, between 1989 and 1997 have been tested for susceptibility to ciprofloxacin by using an agar dilution breakpoint technique. Isolates considered potentially resistant (MIC, >0.12 microg/ml) were further characterized by determination of the MICs of ciprofloxacin, nalidixic acid, and penicillin, auxotyped and serotyped, and screened for mutations in the DNA gyrase gene, gyrA, and the topoisomerase IV gene, parC. A total of 4,875 isolates were tested. While the majority of isolates were highly susceptible (MIC, 0.12 microg/ml); all of these belonged to serogroup B, and NR/IB-1 was the most common auxotype/serovar class. The infections in 14 of the 18 patients were known to be acquired abroad, and 5 were known to result in therapeutic failure. The surveillance program has established that ciprofloxacin is still a highly effective antibiotic against N. gonorrhoeae in this population. However, it has identified a drift in susceptibility which may have resulted from increased usage of ciprofloxacin. High-level resistance has now emerged, although treatment failure is still uncommon.