Gonococcal strains from homosexual men have outer membranes with reduced permeability to hydrophobic molecules

The Prevalence of Antibiotic Tolerance in Neisseria gonorrhoeae Varies by Anatomical Site

BACKGROUND

Tolerance enables bacteria to survive intermittent antibiotic exposure without an increase in antimicrobial susceptibility. In this study, we investigated the presence of tolerance to three antimicrobials, ceftriaxone, azithromycin and ciprofloxacin, in clinical isolates and the WHO (World Health Organization) reference panel of Neisseria gonorrhoeae.

METHODS

We used the modified tolerance disk (TD test) to assess for tolerance to ceftriaxone, azithromycin and ciprofloxacin in 14 WHO reference strains and 62 N. gonorrhoeae clinical isolates-evenly divided between anorectal and urogenital infections. The isolates underwent a three-step incubation process wherein the isolates were exposed to an antibiotic disk for 20 h of incubation (Step I), followed by the replacement of the antibiotic disk with a nutrient disk for overnight incubation (Step II) and additional overnight incubation with extra nutrients (Step III).

RESULTS

A total of 4 of the 62 clinical anorectal isolates and none of the urogenital isolates exhibited tolerance to azithromycin (p = 0.033). Tolerance to ceftriaxone and ciprofloxacin was observed in eight and four isolates, respectively, with no difference between infection sites. Tolerance was also detected in 8 (K, M, N, O, P, U, V, W) out of the 14 WHO reference strains, with varying patterns of tolerance to ceftriaxone (n = 8), ciprofloxacin (n = 2) and azithromycin (n = 1).

CONCLUSIONS

This study identified ceftriaxone, azithromycin and ciprofloxacin tolerance in clinical and WHO reference N. gonorrhoeae isolates. Azithromycin tolerance was more common in anorectal than urogenital infections.

Tolerance to Ceftriaxone in Neisseria gonorrhoeae: Rapid Induction in WHO P Reference Strain and Detection in Clinical Isolates

In addition to antimicrobial resistance, bacteria contain other mechanisms to survive antibiotic exposure such as tolerance, defined as the ability to slow metabolism by the extension of the lag phase without altering antimicrobial susceptibility. In a number of bacterial species, tolerance has been associated with treatment failure and infection chronicity and is found to precede and facilitate antimicrobial resistance. It is unknown if tolerance can be induced in Neisseria gonorrhoeae. In this study, we determined if tolerance to ceftriaxone (CRO) can be induced in N. gonorrhoeae and detected in clinical isolates. To induce tolerance, WHO P N. gonorrhoeae reference strain samples were grown under daily 3 h intermittent CRO exposure (10× the MIC), partitioned by overnight growth in GC broth. This cyclic exposure was performed for 7 consecutive days in sextuplicate, with two control cultures to which GC medium without antibiotics was added. To detect tolerance and assess CRO susceptibility, modified Tolerance Disc (TD) and Epsilometer tests were performed on isolates after each CRO exposure cycle. Additionally, this experiment was carried out on 18 clinical N. gonorrhoeae isolates. Tolerance was first detected after two CRO exposure cycles in five out of six samples. The phenotype differed per cycle with no clear pattern. No tolerance was found in control samples but was detected in 10 out of 18 clinical isolates. The present study is the first to demonstrate the induction of tolerance to CRO in N. gonorrhoeae through antibiotic exposure. In addition, tolerance to CRO was found in clinical samples.

Antimicrobial Susceptibility of Urogenital and Extragenital Neisseria gonorrhoeae Isolates Among Men Who Have Sex With Men: Strengthening the US Response to Resistant Gonorrhea and Enhanced Gonococcal Isolate Surveillance Project, 2018 to 2019

BACKGROUND

We investigated differences in gonococcal antimicrobial susceptibility by anatomic site among cisgender men who have sex with men (MSM) using specimens collected through the Centers for Disease Control and Prevention's enhanced Gonococcal Isolate Surveillance Project and Strengthening the US Response to Resistant Gonorrhea.

METHODS

During the period January 1, 2018-December 31, 2019, 12 enhanced Gonococcal Isolate Surveillance Project and 8 Strengthening the US Response to Resistant Gonorrhea sites collected urogenital, pharyngeal, and rectal isolates from cisgender MSM in sexually transmitted disease clinics. Gonococcal isolates were sent to regional laboratories for antimicrobial susceptibility testing by agar dilution. To account for correlated observations, linear mixed-effects models were used to calculate geometric mean minimum inhibitory concentrations (MICs), and mixed-effects logistic regression models were used to calculate the proportion of isolates with elevated or resistant MICs; comparisons were made across anatomic sites.

RESULTS

Participating clinics collected 3974 urethral, 1553 rectal, and 1049 pharyngeal isolates from 5456 unique cisgender MSM. There were no significant differences in the geometric mean MICs for azithromycin, ciprofloxacin, penicillin, and tetracycline by anatomic site. For cefixime and ceftriaxone, geometric mean MICs for pharyngeal isolates were higher compared with anogenital isolates (P < 0.05). The proportion of isolates with elevated ceftriaxone MICs (≥0.125 μg/mL) at the pharynx (0.67%) was higher than at rectal (0.13%) and urethral (0.18%) sites (P < 0.05).

CONCLUSIONS

Based on data collected from multijurisdictional sentinel surveillance projects, antimicrobial susceptibility patterns of Neisseria gonorrhoeae isolates may differ among MSM at extragenital sites, particularly at the pharynx. Continued investigation into gonococcal susceptibility patterns by anatomic site may be an important strategy to monitor and detect the emergence of antimicrobial resistant gonorrhea over time.

Identification of bile acid and fatty acid species as candidate rapidly bactericidal agents for topical treatment of gonorrhoea

BACKGROUND

Novel therapeutic strategies are urgently needed for Neisseria gonorrhoeae, given its increasing antimicrobial resistance. Treatment of oropharyngeal N. gonorrhoeae infections has proven particularly challenging, with most reported treatment failures of the first-line drug ceftriaxone occurring at this site and lower cure rates in recent trials of new antibiotics reported for oropharyngeal infections compared with other sites of infection. However, the accessibility of the oropharynx to topical therapeutics provides an opportunity for intervention. Local delivery of a therapeutic at a high concentration would enable the use of non-traditional antimicrobial candidates, including biological molecules that exploit underlying chemical sensitivities of N. gonorrhoeae but lack the potency or pharmacokinetic profiles required for effective systemic administration.

METHODS

Two classes of molecules that are thought to limit gonococcal viability in vivo, bile acids and short- and medium-chain fatty acids, were examined for rapid bactericidal activity.

RESULTS

The bile acids deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA), but not other bile acid species, exerted extremely rapid bactericidal properties against N. gonorrhoeae, reducing viability more than 100 000-fold after 1 min. The short-chain fatty acids formic acid and hexanoic acid shared this rapid bactericidal activity. All four molecules are effective against a phylogenetically diverse panel of N. gonorrhoeae strains, including clinical isolates with upregulated efflux pumps and resistance alleles to the most widely used classes of existing antimicrobials. DCA and CDCA are both approved therapeutics for non-infectious indications and are well-tolerated by cultured epithelial cells.

CONCLUSIONS

DCA and CDCA are attractive candidates for further development as anti-gonococcal agents.

Gonococcal Adaptation to Palmitic Acid Through farAB Expression and FadD Activity Mutations Increases In Vivo Fitness in a Murine Genital Tract Infection Model

Neisseria gonorrhoeae is a bacterial pathogen that colonizes mucosal epithelia that are rich in antimicrobial molecules such as long-chain fatty acids. Here we studied the mechanisms involved in palmitic acid resistance and their impact on in vivo biological fitness in a murine genital tract infection model. A stable palmitic acid-resistant derivative was obtained by serial passage with incremental palmitic acid concentrations. This derivative outcompeted its parent strain for colonization and survival in the murine infection model. Subsequent whole-genome sequencing resulted in the identification of the 3 resistance-related SNPs ihfAC5T, fadDC772T, and farAG-52T (promoter) that were verified for resistance against palmitic acid. Subsequent characterization of the associated resistance determinants showed that ihfAC5T and farAG-52T induced gene expression of the FarAB efflux pump, whereas fadDC772T increased the maximum enzyme activity of the FadD long-chain fatty acid-coenzyme A ligase. Our results highlight the mechanisms involved in gonococcal adaptation to the murine host environment.

Adaptation to the cervical environment is associated with increased antibiotic susceptibility in Neisseria gonorrhoeae

Neisseria gonorrhoeae is an urgent public health threat due to rapidly increasing incidence and antibiotic resistance. In contrast with the trend of increasing resistance, clinical isolates that have reverted to susceptibility regularly appear, prompting questions about which pressures compete with antibiotics to shape gonococcal evolution. Here, we used genome-wide association to identify loss-of-function (LOF) mutations in the efflux pump mtrCDE operon as a mechanism of increased antibiotic susceptibility and demonstrate that these mutations are overrepresented in cervical relative to urethral isolates. This enrichment holds true for LOF mutations in another efflux pump, farAB, and in urogenitally-adapted versus typical N. meningitidis, providing evidence for a model in which expression of these pumps in the female urogenital tract incurs a fitness cost for pathogenic Neisseria. Overall, our findings highlight the impact of integrating microbial population genomics with host metadata and demonstrate how host environmental pressures can lead to increased antibiotic susceptibility.

The development of mouthwashes without anti-gonococcal activity for controlled clinical trials: an in vitro study

Background: The oropharynx plays a major role in the development and spread of antimicrobial resistant Neisseria gonorrhoeae among men who have sex with men. Trials are currently assessing the efficacy of bactericidal mouthwashes as possible therapeutic or preventive options against these pharyngeal gonococcal infections. Controlled clinical trials require the use of a placebo mouthwash without anti-gonococcal activity. So far, no such placebo mouthwash has been described. We describe the development of a mouthwash for this purpose.

Methods: The in vitro anti-gonococcal activity of Corsodyl®, Listerine Cool Mint®, Biotene®, phosphate buffered saline and six in-house placebo mouthwashes was evaluated. Three gonococcal isolates from patients with pharyngeal infection were exposed to the mouthwashes for a duration ranging from 30 seconds to 60 minutes. Isolates were then plated in duplicate onto blood agar (5% horse blood) and incubated for 24 hours (5-7% CO ₂, 35 ± 2°C). Growth of N. gonorrhoeae was scored on a five-point scale (0 = no growth, to 4 = confluent growth of colonies).

Results: Corsodyl® and Listerine Cool Mint® were bactericidal to all isolates. For the other mouthwashes, the median growth score after 60 minutes of exposure was 4 (interquartile range 4-4) for phosphate buffered saline; 1 (interquartile range 1-3) for Biotene®; and ranged between 0 and 2 for the in-house composed mouthwashes. An in-house composed mouthwash (Placebo 6) performed best, with a growth score of 2.5 (interquartile range 1-3).

Conclusions: All the evaluated potential placebo mouthwashes were bacteriostatic after gonococcal exposure of 30 to 60 minutes. In-house composed Placebo 6 showed less inhibition on gonococcal growth than Biotene® and the other in-house placebos and demonstrates, in our opinion, a good trade-off between anti-gonococcal properties and taste.

Epidemiological Trends of Antibiotic Resistant Gonorrhoea in the United Kingdom

Gonorrhoea is one of the most common sexually-transmitted bacterial infections, globally and in the United Kingdom. The levels of antibiotic resistance in gonorrhoea reported in recent years represent a critical public health issue. From penicillins to cefixime, the gonococcus has become resistant to all antibiotics that have been previously used against it, in each case only a matter of years after introduction as a first-line therapy. After each instance of resistance emergence, the treatment recommendations have required revision, to the point that only a few antibiotics can reliably be prescribed to treat infected individuals. Most countries, including the UK, now recommend that gonorrhoea be treated with a dual therapy combining ceftriaxone and azithromycin. While this treatment is still currently effective for the vast majority of cases, there are concerning signs that this will not always remain the case, and there is no readily apparent alternative. Here, we review the use of antibiotics and epidemiological trends of antibiotic resistance in gonorrhoea from surveillance data over the past 15 years in the UK and describe how surveillance could be improved.

Mutations in Neisseria gonorrhoeae grown in sub-lethal concentrations of monocaprin do not confer resistance

Neisseria gonorrhoeae, due to its short lipooligosaccharide structure, is generally more sensitive to the antimicrobial effects of some fatty acids than most other Gram negative bacteria. This supports recent development of a fatty acid-based potential treatment for gonococcal infections, particularly ophthalmia neonatorum. The N. gonorrhoeae genome contains genes for fatty acid resistance. In this study, the potential for genomic mutations that could lead to resistance to this potential new treatment were investigated. N. gonorrhoeae strain NCCP11945 was repeatedly passaged on growth media containing a sub-lethal concentration of fatty acid myristic acid and monoglyceride monocaprin. Cultures were re-sequenced and assessed for changes in minimum inhibitory concentration. Of note, monocaprin grown cultures developed a mutation in transcription factor gene dksA, which suppresses molecular chaperone DnaK and may be involved in the stress response. The minimum inhibitory concentration after exposure to monocaprin showed a modest two-fold change. The results of this study suggest that N. gonorrhoeae cannot readily evolve resistance that will impact treatment of ophthalmia neonatorum with monocaprin.

Will targeting oropharyngeal gonorrhoea delay the further emergence of drug-resistant Neisseria gonorrhoeae strains?

Gonorrhoea is an important sexually transmitted infection associated with serious complications and enhanced HIV transmission. Oropharyngeal infections are often asymptomatic and will only be detected by screening. Gonococcal culture has low sensitivity (<50%) for detecting oropharyngeal gonorrhoea, and, although not yet approved commercially, nucleic acid amplification tests (NAAT) are the assay of choice. Screening for oropharyngeal gonorrhoea should be performed in high-risk populations, such as men-who-have-sex-with-men(MSM). NAATs have a poor positive predictive value when used in low-prevalence populations. Gonococci have repeatedly thwarted gonorrhoea control efforts since the first antimicrobial agents were introduced. The oropharyngeal niche provides an enabling environment for horizontal transfer of genetic material from commensal Neisseria and other bacterial species to Neisseria gonorrhoeae. This has been the mechanism responsible for the generation of mosaic penA genes, which are responsible for most of the observed cases of resistance to extended-spectrum cephalosporins (ESC). As antimicrobial-resistant gonorrhoea is now an urgent public health threat, requiring improved antibiotic stewardship, laboratory-guided recycling of older antibiotics may help reduce ESC use. Future trials of antimicrobial agents for gonorrhoea should be powered to test their efficacy at the oropharynx as this is the anatomical site where treatment failure is most likely to occur. It remains to be determined whether a combination of frequent screening of high-risk individuals and/or laboratory-directed fluoroquinolone therapy of oropharyngeal gonorrhoea will delay the further emergence of drug-resistant N. gonorrhoeae strains.

The challenge of efflux-mediated antibiotic resistance in Gram-negative bacteria

The global emergence of multidrug-resistant Gram-negative bacteria is a growing threat to antibiotic therapy. The chromosomally encoded drug efflux mechanisms that are ubiquitous in these bacteria greatly contribute to antibiotic resistance and present a major challenge for antibiotic development. Multidrug pumps, particularly those represented by the clinically relevant AcrAB-TolC and Mex pumps of the resistance-nodulation-division (RND) superfamily, not only mediate intrinsic and acquired multidrug resistance (MDR) but also are involved in other functions, including the bacterial stress response and pathogenicity. Additionally, efflux pumps interact synergistically with other resistance mechanisms (e.g., with the outer membrane permeability barrier) to increase resistance levels. Since the discovery of RND pumps in the early 1990s, remarkable scientific and technological advances have allowed for an in-depth understanding of the structural and biochemical basis, substrate profiles, molecular regulation, and inhibition of MDR pumps. However, the development of clinically useful efflux pump inhibitors and/or new antibiotics that can bypass pump effects continues to be a challenge. Plasmid-borne efflux pump genes (including those for RND pumps) have increasingly been identified. This article highlights the recent progress obtained for organisms of clinical significance, together with methodological considerations for the characterization of MDR pumps.

Antimicrobial resistance in Neisseria gonorrhoeae in the 21st century: past, evolution, and future

Neisseria gonorrhoeae is evolving into a superbug with resistance to previously and currently recommended antimicrobials for treatment of gonorrhea, which is a major public health concern globally. Given the global nature of gonorrhea, the high rate of usage of antimicrobials, suboptimal control and monitoring of antimicrobial resistance (AMR) and treatment failures, slow update of treatment guidelines in most geographical settings, and the extraordinary capacity of the gonococci to develop and retain AMR, it is likely that the global problem of gonococcal AMR will worsen in the foreseeable future and that the severe complications of gonorrhea will emerge as a silent epidemic. By understanding the evolution, emergence, and spread of AMR in N. gonorrhoeae, including its molecular and phenotypic mechanisms, resistance to antimicrobials used clinically can be anticipated, future methods for genetic testing for AMR might permit region-specific and tailor-made antimicrobial therapy, and the design of novel antimicrobials to circumvent the resistance problems can be undertaken more rationally. This review focuses on the history and evolution of gonorrhea treatment regimens and emerging resistance to them, on genetic and phenotypic determinants of gonococcal resistance to previously and currently recommended antimicrobials, including biological costs or benefits; and on crucial actions and future advances necessary to detect and treat resistant gonococcal strains and, ultimately, retain gonorrhea as a treatable infection.

Comparison of antimicrobial susceptibilities of pharyngeal, rectal, and urethral Neisseria gonorrhoeae isolates among men who have sex with men

U.S. surveillance for Neisseria gonorrhoeae antimicrobial susceptibilities is based exclusively on male urethral isolates. These data inform gonorrhea treatment guidelines, including recommendations for the treatment of extragenital infections, but data on the susceptibilities of extragenital isolates are limited. We compared the antimicrobial susceptibilities of pharyngeal, rectal, and urethral gonococcal isolates collected from men who have sex with men (MSM), at five sentinel sites throughout the United States. MICs were determined by the agar dilution method. Generalized linear models were used to compare (i) the proportions of isolates with elevated MICs and (ii) geometric mean MICs according to anatomic site, adjusted for city. In December 2011 to September 2013, totals of 205 pharyngeal, 261 rectal, and 976 urethral isolates were obtained. The proportions of isolates with elevated ceftriaxone MICs (≥ 0.125 μg/ml) did not differ according to anatomic site (0.5% of pharyngeal isolates, 1.5% of rectal isolates, and 1.7% of urethral isolates, with a city-adjusted odds ratio [aOR] of 0.4 [95% confidence interval {CI}, 0.0 to 3.9] for pharyngeal versus urethral isolates and an aOR of 0.9 [95% CI, 0.2 to 4.2] for rectal versus urethral isolates). The city-adjusted geometric mean ceftriaxone MICs of pharyngeal (0.0153 μg/ml) and rectal (0.0157 μg/ml) isolates did not differ from that of urethral isolates (0.0150 μg/ml) (ratios of geometric mean MICs of 1.02 [95% CI, 0.90 to 1.17] and 1.05 [95% CI, 0.93 to 1.19], respectively). Similar results were observed for other antimicrobials, including cefixime and azithromycin. These findings suggest that, at the population level, gonococcal antimicrobial susceptibility surveillance based on urethral isolates from MSM adequately reflects the susceptibilities of N. gonorrhoeae strains circulating among MSM.

Certain attributes of the sexual ecosystem of high-risk MSM have resulted in an altered microbiome with an enhanced propensity to generate and transmit antibiotic resistance

Surveillance data from a number of countries have indicated that antibiotic resistance in Neisseriagonorrhoea is strongly associated with men who have sex with men (MSM). This manuscript advances the hypothesis that certain features of the MSM sexual ecosystem may be responsible for this association. It is argued that in comparison with heterosexuals, high-risk MSM (hrMSM) have a higher prevalence of oro-penile, oro-rectal and anal sex which facilitates an enhanced mixing of the pharyngeal, rectal and penile microbiomes. In addition, hrMSM have an increased number of sexual partners per unit time and an increased prevalence of sexual relationships overlapping in time. The increased flux of microbiomes between different body habitats between sexual partners, in combination with the increased connectivity of the sexual network, serve to create a novel high-risk MSM sexual ecosystem with important consequences for the genesis and spread of antibiotic resistance.

Neisseria gonorrhoeae antimicrobial resistance among men who have sex with men and men who have sex exclusively with women: the Gonococcal Isolate Surveillance Project, 2005-2010

BACKGROUND

Gonorrhea treatment has been complicated by antimicrobial resistance in Neisseria gonorrhoeae. Gonococcal fluoroquinolone resistance emerged more rapidly among men who have sex with men (MSM) than men who have sex exclusively with women (MSW).

OBJECTIVE

To determine whether N. gonorrhoeae urethral isolates from MSM were more likely than isolates from MSW to exhibit resistance to or elevated minimum inhibitory concentrations (MICs) of antimicrobials used to treat gonorrhea.

DESIGN

6 years of surveillance data from the Gonococcal Isolate Surveillance Project.

SETTING

Publicly funded sexually transmitted disease clinics in 30 U.S. cities.

PATIENTS

Men with a total of 34 600 episodes of symptomatic urethral gonorrhea.

MEASUREMENTS

Percentage of isolates exhibiting resistance or elevated MICs and adjusted odds ratios for resistance or elevated MICs among isolates from MSM compared with isolates from MSW.

RESULTS

In all U.S. regions except the West, isolates from MSM were significantly more likely to exhibit elevated MICs of ceftriaxone and azithromycin than isolates from MSW (P < 0.050). Isolates from MSM had a high prevalence of resistance to ciprofloxacin, penicillin, and tetracycline and were significantly more likely to exhibit antimicrobial resistance than isolates from MSW (P < 0.001).

LIMITATIONS

Sentinel surveillance may not be representative of all patients with gonorrhea. HIV status, travel history, and antimicrobial use data were missing for some patients.

CONCLUSION

Men who have sex with men are vulnerable to the emerging threat of antimicrobial-resistant N. gonorrhoeae. Because antimicrobial susceptibility testing is not routinely done in clinical practice, clinicians should monitor for treatment failures among MSM diagnosed with gonorrhea. Strengthened prevention strategies for MSM and new antimicrobial treatment options are needed.

Molecular surveillance of clinical Neisseria gonorrhoeae isolates in Russia

The choice of adequate methods for epidemiological purposes remains a challenging problem in Neisseria gonorrhoeae molecular monitoring. In this study, the collection of geographically unrelated gonococci (n = 103) isolated in Russian clinics was comparably tested by (i) a traditional serotyping scheme, (ii) por typing, (iii) Neisseria gonorrhoeae multiantigen sequence typing (NG-MAST), and (iv) multilocus sequence typing (MLST). It is shown that, according to sequencing data, a third of the strains carried new porB1 alleles, as well as tbpB ones, and more than half of the samples had new sequence types (STs) as determined by NG-MAST or MLST. The discriminatory power for each typing method was calculated by using the Hunter-Gaston discriminatory index, D. Commonly, modern nucleic acid-based typing methods (por typing, NG-MAST, and MLST) appeared to be more efficient than the classical serotyping scheme. While the traditional serotyping gave a D value of 0.82, the por typing, NG-MAST, and MLST approaches yielded D values of 0.97, 0.98, and 0.91, respectively. Each typing technique revealed the distribution of gonococci slightly correlated with their geographical sources. However, only the MLST method STs were highly associated with certain phenotypes. Although ST1594, ST1892, and ST6720 were typical for susceptible gonococci, ST1901 and ST6716 were undoubtedly associated with a multidrug-resistant phenotype. We conclude that every tested nucleic acid-based typing method is suitable for N. gonorrhoeae molecular surveillance. However, the MLST method seems to serve large-scale epidemiological purposes, whereas the NG-MAST and por typing approaches are more appropriate for the investigation of local outbreaks.

The transcriptional repressor FarR is not involved in meningococcal fatty acid resistance mediated by the FarAB efflux pump and dependent on lipopolysaccharide structure

Free fatty acids are important antimicrobial substances regulating the homeostasis of colonizing bacteria on epithelial surfaces. Here, we show that meningococci express a functional farAB efflux pump, which is indispensable for fatty acid resistance. However, other than in Neisseria gonorrhoeae, the transcriptional regulator FarR is not involved in regulation of this operon in Neisseria meningitidis. We tested the susceptibility of 23 meningococcal isolates against saturated and unsaturated long-chain fatty acids, proving that meningococci are generally highly resistant, with the exception of serogroup Y strains belonging to sequence type 23. Using genetically determined lipopolysaccharide (LPS)-truncated mutant strains, we show that addition of the LPS core oligosaccharide and hexa-acylation of its membrane anchor lipid A are imperative for fatty acid resistance of meningococci. The sensitivity of the serogroup Y strains is due to naturally occurring mutations within the lpxL1 gene, which is responsible for addition of the sixth acyl chain on the LPS membrane anchor lipid A. Therefore, fatty acid resistance in meningococci is provided by both the active efflux pump FarAB and by the natural permeability barrier of the Gram-negative outer membrane. The transcriptional regulator FarR is not implicated in fatty acid resistance in meningococci, possibly giving rise to a constitutively active FarAB efflux pump system and thus revealing diverse mechanisms of niche adaptation in the two closely related Neisseria species.

Functional role of bacterial multidrug efflux pumps in microbial natural ecosystems

Multidrug efflux pumps have emerged as relevant elements in the intrinsic and acquired antibiotic resistance of bacterial pathogens. In contrast with other antibiotic resistance genes that have been obtained by virulent bacteria through horizontal gene transfer, genes coding for multidrug efflux pumps are present in the chromosomes of all living organisms. In addition, these genes are highly conserved (all members of the same species contain the same efflux pumps) and their expression is tightly regulated. Together, these characteristics suggest that the main function of these systems is not resisting the antibiotics used in therapy and that they should have other roles relevant to the behavior of bacteria in their natural ecosystems. Among the potential roles, it has been demonstrated that efflux pumps are important for processes of detoxification of intracellular metabolites, bacterial virulence in both animal and plant hosts, cell homeostasis and intercellular signal trafficking.

Clusters of circulating Neisseria gonorrhoeae strains and association with antimicrobial resistance in Shanghai

OBJECTIVES

(i) To distinguish Neisseria gonorrhoeae isolates in Shanghai by porB typing; (ii) to ascertain the congruence of porB DNA sequence typing with cases linked epidemiologically; (iii) to determine the association of specific PorB mutations with antimicrobial resistance to penicillin or tetracycline.

METHODS

porB DNA sequences of 174 N. gonorrhoeae isolates, collected from 143 male patients and 31 female sexual partners in Shanghai were determined. Phylogenetic analysis was used to determine sequence associations and concordance with epidemiologically linked cases. PorB protein sequences were compared with the wild-type sequence to identify mutations associated with antimicrobial resistance to penicillin and tetracycline.

RESULTS

porB1a genotypes comprised 27.0% of the isolates and included 15 distinct DNA sequences, while 73.0% of the isolates carried porB1b genotypes with 63 distinct DNA sequences. porB DNA sequence typing was congruent with patient-reported sexual contacts. In addition, porB DNA sequence analysis revealed a number of strains with identical DNA sequences not identified through traditional epidemiological methods. The porB1b isolates had a significantly higher percentage of chromosomally mediated resistance to tetracycline and higher MIC50s to penicillin and ciprofloxacin. G120K/A121D mutations were observed in 71.1% of PIB isolates and were associated with resistance to penicillin and/or tetracycline. The majority of the PIA isolates (82.1%) also carried G120D/A121G double mutations. The index of discrimination for porB DNA sequence analysis was 95%.

CONCLUSIONS

The porB1b genotype was found to be predominant in Shanghai. porB DNA sequence typing was sufficiently discriminatory for differentiating N. gonorrhoeae isolates and was congruent with epidemiological linkages. Novel porB sequences of N. gonorrhoeae and novel mutations of PorB proteins were identified.

Importance of drug resistance in gonococci: from mechanisms to monitoring

Neisseria gonorrhoeae isolates continue to develop an impressive arsenal of resistance mechanisms to antimicrobial agents, including resistance to some of the antibiotics presently recommended for the treatment of gonococcal infections.

Differential regulation of ponA and pilMNOPQ expression by the MtrR transcriptional regulatory protein in Neisseria gonorrhoeae

Neisseria gonorrhoeae utilizes the mtrCDE-encoded efflux pump system to resist not only host-derived, hydrophobic antimicrobials that bathe mucosal surfaces, which likely aids in its ability to colonize and infect numerous sites within the human host, but also antibiotics that have been used clinically to treat infections. Recently, overexpression of the MtrC-MtrD-MtrE efflux pump was shown to be critically involved in the capacity of gonococci to develop chromosomally mediated resistance to penicillin G, which for over 40 years was used to treat gonococcal infections. Mutations in either the promoter or the coding sequence of the mtrR gene, which encodes a repressor of the efflux pump operon, decrease gonococcal susceptibility to penicillin. We now describe the capacity of MtrR to directly or indirectly influence the expression of two other loci that are involved in gonococcal susceptibility to penicillin: ponA, which encodes penicillin-binding protein 1 (PBP 1), and the pilMNOPQ operon, which encodes components of the type IV pilus secretion system, with PilQ acting as a channel for entry for penicillin. We determined that MtrR increases the expression of ponA directly or indirectly, resulting in increased levels of PBP 1, while repressing the expression of the divergently transcribed pilM gene, the first gene in the pilMNOPQ operon. Taken together with other studies, the results presented herein indicate that transcriptional regulation of gonococcal genes by MtrR is centrally involved in determining levels of gonococcal susceptibility to penicillin and provides a framework for understanding how resistance developed over the years.

Epidemiological correlates of asymptomatic gonorrhea

OBJECTIVES

To assess correlates of asymptomatic gonorrhea among patients attending Genitourinary Medicine Clinics participating in the Gonococcal Resistance to Antimicrobials Surveillance Programme (GRASP) in England for 2001-2003.

STUDY DESIGN

GRASP is a sentinel surveillance program that monitors antimicrobial resistance to Neisseria gonorrhoeae. Data collection occurs annually in June to August each year.

RESULTS

Women with previously diagnosed gonorrhea had decreased odds of asymptomatic gonococcal infection, as did women diagnosed with other sexually transmitted infections (all except chlamydia, syphilis, herpes, and warts). Heterosexual men, but not women, coinfected with chlamydia had significantly higher likelihood of being diagnosed with asymptomatic gonorrhea, as did homosexual men coinfected with syphilis and warts.

CONCLUSION

The heterogeneity in correlates of asymptomatic gonorrhea has implications for screening in clinical settings. Such findings also depend on the extent of testing on sexually transmitted infections from different sites of infection, which has particular relevance in homosexual men and would thus need to be investigated in other studies.

Genetic basis of erythromycin resistance in oral bacteria

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

Efflux-mediated drug resistance in bacteria

Drug resistance in bacteria, and especially resistance to multiple antibacterials, has attracted much attention in recent years. In addition to the well known mechanisms, such as inactivation of drugs and alteration of targets, active efflux is now known to play a major role in the resistance of many species to antibacterials. Drug-specific efflux (e.g. that of tetracycline) has been recognised as the major mechanism of resistance to this drug in Gram-negative bacteria. In addition, we now recognise that multidrug efflux pumps are becoming increasingly important. Such pumps play major roles in the antiseptic resistance of Staphylococcus aureus, and fluoroquinolone resistance of S. aureus and Streptococcus pneumoniae. Multidrug pumps, often with very wide substrate specificity, are not only essential for the intrinsic resistance of many Gram-negative bacteria but also produce elevated levels of resistance when overexpressed. Paradoxically, 'advanced' agents for which resistance is unlikely to be caused by traditional mechanisms, such as fluoroquinolones and beta-lactams of the latest generations, are likely to select for overproduction mutants of these pumps and make the bacteria resistant in one step to practically all classes of antibacterial agents. Such overproduction mutants are also selected for by the use of antiseptics and biocides, increasingly incorporated into consumer products, and this is also of major concern. We can consider efflux pumps as potentially effective antibacterial targets. Inhibition of efflux pumps by an efflux pump inhibitor would restore the activity of an agent subject to efflux. An alternative approach is to develop antibacterials that would bypass the action of efflux pumps.

Trends of Chromosomally Mediated Antimicrobial Resistance in Neisseria gonorrhoeae in Canada: 1994–1999

BACKGROUND AND OBJECTIVES

We monitored the trends of chromosomally mediated resistant Neisseria gonorrhoeae (CMRNG) in Canada. Chromosomally resistant N. gonorrhoeae (CMRNG) were defined as having resistance to 3 antibiotics: penicillin (minimum inhibitory concentration [MIC] > or =2.0 mg/L), tetracycline (MIC > or =2.0 mg/L and < or =8.0 mg/L), and erythromycin (MIC > or =2.0 mg/L).

GOAL

The goal was to provide surveillance data for public health interventions for the control of gonococcal infections.

STUDY DESIGN

Antibiotic susceptibility tests were performed on N. gonorrhoeae isolates obtained from 1994 to 1999 in Canada. Strains were further characterized by auxotype (A), serovar (S), and plasmid profile (P).

RESULTS

Between 1994 and 1999, 19.2% of strains were CMRNG, 12.9% had a combined resistance to tetracycline and erythromycin, and 4.7% were resistant to tetracycline. The incidence of ciprofloxacin resistance and azithromycin resistance was 2.3% and 0.8%, respectively.

CONCLUSION

This survey of N. gonorrhoeae provides strain characterization data and temporal trends of strains in the Canadian population. CMRNG strains are on the rise, and the continual monitoring and characterization of these strains is important for the evaluation of current recommended antibiotic therapies used in Canada.

A gonococcal efflux pump system enhances bacterial survival in a female mouse model of genital tract infection

Active efflux of antimicrobial substances is likely to be an important bacterial defense against inhibitory host factors inherent to different body sites. Two well-characterized multidrug resistance efflux systems (MtrCDE and FarAB-MtrE) exist in Neisseria gonorrhoeae, a bacterial pathogen of the human genital mucosae. In vitro studies suggest that the MtrCDE and FarAB-MtrE efflux systems protect the gonococcus from hydrophobic antimicrobial substances that are likely to be present on mucosal surfaces. Here we report that a functional MtrCDE efflux system, but not a functional FarAB-MtrE system, enhances experimental gonococcal genital tract infection in female mice. Specifically, the recovery of mtrD and mtrE mutants, but not a farB mutant, from mice inoculated with mutant or wild-type gonococci was reduced compared with that of the wild-type strain. Competitive-infection experiments confirmed the survival disadvantage of MtrCDE-deficient gonococci. This report is the first direct evidence that a multidrug resistance efflux system enhances survival of a bacterial pathogen in the genital tract. Additionally, experiments using ovariectomized mice showed that MtrCDE-deficient gonococci were more rapidly cleared from mice that were capable of secreting gonadal hormones. MtrCDE-deficient gonococci were more sensitive to nonphysiological concentrations of progesterone in vitro than were wild-type or FarAB-MtrE-deficient gonococci. These results suggest that progesterone may play an inhibitory role in vivo. However, hormonally regulated factors rather than progesterone itself may be responsible for the more rapid clearance of mtr-deficient gonococci from intact mice.

Mutation in 23S rRNA associated with macrolide resistance in Neisseria gonorrhoeae

Fifty-six azithromycin-resistant (MICs, 2.0 to 4.0 micro g/ml) Neisseria gonorrhoeae strains with cross-resistance to erythromycin (MICs, 2.0 to 64.0 micro g/ml), isolated in Canada between 1997 and 1999, were characterized, and their mechanisms of azithromycin resistance were determined. Most (58.9%) of them belonged to auxotype-serotype class NR/IB-03, with a 2.6-mDa plasmid. Based on resistance to crystal violet (MICs >or= 1 micro g/ml), 96.4% of these macrolide-resistant strains appeared to have increased efflux. Nine of the eleven strains selected for further characterization were found to have a promoter region mtrR mutation, a single-base-pair (A) deletion in the 13-bp inverted repeat, which is believed to cause overexpression of the mtrCDE-encoded efflux pump. The two remaining macrolide-resistant strains (erythromycin MIC, 64.0 micro g/ml; azithromycin MIC, 4.0 micro g/ml), which did not have the mutation in the mtrR promoter region, were found to have a C2611T mutation (Escherichia coli numbering) in the peptidyltransferase loop in domain V of the 23S rRNA alleles. Although mutations in domain V of 23S rRNA alleles had been reported in other bacteria, including E. coli, Streptococcus pneumoniae, and Helicobacter pylori, this is the first observation of these mutations associated with macrolide resistance in N. gonorrhoeae.

Epidemiology of anorectal chlamydial and gonococcal infections among men having sex with men in Seattle: utilizing serovar and auxotype strain typing

BACKGROUND

Bacterial sexually transmitted diseases (STDs) among men who have sex with men (MSM) have recently increased in Seattle.

GOALS

Serovar and auxotype typing of strains was used to assess the epidemiology of anorectal chlamydial and gonococcal infections among MSM attending an STD clinic.

STUDY DESIGN

The prevalences of anorectal chlamydial infection and gonorrhea among MSM attending an STD clinic during the period of 1994 to 1996 were compared with prevalences during 1997 to 1999. A retrospective case-control study of MSM attending an STD clinic between 1997 and 1999 was performed. Anorectal chlamydial isolates were characterized by serovar and gonococcal isolates were characterized by serovar and auxotype. Infected MSM were mapped by residence and strain type.

RESULTS

Prevalences of anorectal chlamydial and gonococcal infections increased from 4.0% and 6.3%, respectively, during 1994-1996 to 7.6% and 8.7%, respectively, during 1997-1999 (P = 0.004 and P = 0.013 for chlamydial infection and gonorrhea, respectively). Most chlamydial infections were caused by serovars G (47.9%) and D (29.6%), and most gonococcal infections were caused by auxotype/serovar classes Proto/IB-1 (43.3%), Proto/IB-3 (16.5%), and Proto/IB-2 (10.3%). MSM with anorectal chlamydial infection more often had chlamydial urethritis (P = 0.005) and were not white (P = 0.046), in comparison with controls. MSM with anorectal gonorrhea more often had pharyngeal gonorrhea (P < 0.001), had a history of gonorrhea (P = 0.003), and were younger than age 30 years (P = 0.039), in comparison with controls. Residences of MSM with anorectal gonorrhea were clustered in urban areas, whereas those of MSM with anorectal chlamydial infection were more dispersed.

CONCLUSION

Prevalences of anorectal chlamydial infection and gonorrhea among MSM in Seattle have increased dramatically over the past 3 years. Serovar and auxotype analyses indicate these increases are not clonal but are due to the spread of unique distributions of strains that differ from those causing urogenital infections in the same community.

Gonorrhoea in London: usefulness of first line therapies

OBJECTIVES

To determine the true prevalence and patterns of resistance of Neisseria gonorrhoeae to antimicrobial agents used for therapy in London.

METHODS

A longitudinal study of a representative sample of isolates of N gonorrhoeae linked to demographic data of infected patients was undertaken. Isolates were collected from consecutive patients attending genitourinary medicine clinics in the North and South Thames regions of London during 3 months of each of 4 years, 1997-2000. Prevalence of plasmid mediated resistance to penicillin and chromosomally mediated resistance to penicillin and ciprofloxacin was determined by susceptibility testing. The association of antimicrobial resistance among gonococci with sexual orientation of the patient and country of acquisition of infection was determined.

RESULTS

Numbers of gonococcal isolates collected over the same time period between 1997-2000 have increased by 74%. Plasmid mediated resistance to penicillin was low but has risen above 5% in 2000. Chromosomal resistance to penicillin has fallen below the 5% level but total resistance to penicillin, plasmid and chromosomally mediated, was above 5% in all 4 years. The incidence of resistance and reduced susceptibility to the alternative therapeutic choice, ciprofloxacin, is low but numbers are increasing in each year. High level resistance, to both penicillin and ciprofloxacin, has generally been found among heterosexual men and is often acquired abroad. However, there is some evidence of a change to endemic spread in 2000.

CONCLUSIONS

This surveillance programme shows that the epidemiology of gonorrhoea in London is changing with increasing numbers and changing patterns of resistance. If gonorrhoea is to be controlled and targets set by the sexual health strategy are to be met, intervention with effective and appropriate antimicrobial agents is essential.

Inducible, but not constitutive, resistance of gonococci to hydrophobic agents due to the MtrC-MtrD-MtrE efflux pump requires TonB-ExbB-ExbD proteins

The MtrC-MtrD-MtrE efflux pump possessed by Neisseria gonorrhoeae is very similar to the MexA-MexB-OprM efflux pump of Pseudomonas aeruginosa. Because the antimicrobial resistance property afforded by the MexA-MexB-OprM efflux pump also requires the TonB protein, we asked whether a similar requirement exists for the gonococcal efflux pump. Unlike earlier studies with P. aeruginosa, we found that constitutive levels of gonococcal resistance to hydrophobic antimicrobial agents (i.e., Triton X-100 [TX-100]) did not require the TonB, ExbB, or ExbD protein. However, inducible levels of TX-100 resistance in gonococci had an absolute requirement for the TonB-ExbB-ExbD system, suggesting that such resistance in gonococci has an energy requirement above and beyond that required for constitutive pump activity.

Gonorrhea in the HIV era: a reversal in trends among men who have sex with men

OBJECTIVES

Gonorrhea cases among men who have sex with men (MSM) declined in the early years of the HIV epidemic. We evaluated more recent trends in gonorrhea among MSM through the Centers for Disease Control and Prevention's Gonococcal Isolate Surveillance Project.

METHODS

Isolates and case information were collected from 29 US sexually transmitted disease (STD) clinics. Gonococcal urethritis cases among MSM were compared with those among heterosexual men, and cases among MSM in 1995 to 1999 were compared with earlier MSM cases.

RESULTS

Of 34,942 cases, the proportion represented by MSM increased from 4.5% in 1992 to 13.2% in 1999 (P < .001). Compared with heterosexuals, MSM were older, more often White, and more often had had gonorrhea previously, although fewer had had gonorrhea in the past year. MSM with gonorrhea in 1995 to 1999 were slightly older than those with gonorrhea in 1992 to 1994, and a higher proportion had had gonorrhea in the past year.

CONCLUSIONS

MSM account for an increasing proportion of gonococcal urethritis cases in STD clinics. Given recent evidence that gonorrhea may facilitate HIV transmission, these trends demand increased attention to safe sexual behaviors and reducing STDs among MSM.

Population genetics of the porB gene of Neisseria gonorrhoeae: different dynamics in different homology groups

The porB locus codes for the major outer membrane protein of Neisseria gonorrhoeae. Alleles of this locus have been assigned to two homology groups based on close sequence and immunological relationships and are designated as either PIA or PIB. Several population parameters were estimated and compared among these two groups using a data set of 22 PIA sequences and 91 PIB sequences obtained from diverse geographic localities and from time periods spanning approximately 50 years. Recombination appears to be extensive in the porB gene. While the recombination rates are similar for the PIA and PIB sequences, the relative contribution of recombination to genetic diversity is higher for the PIA sequences. Alleles belonging to the PIB group show greater genetic diversity than do those in the PIA group. Although phylogenetic analysis did not reveal temporal or geographic clustering of sequences, estimates of gene flow and the fixation index suggested that PIB sequences exhibit population substructure based on geographic locality. Selection acts in these homology groups in a different way. While positive Darwinian selection is the dominant force driving the evolution of the PIA sequences, purifying selection operates also on the PIB sequences. These differences may be attributable to the greater propensity of PIA strains, as compared with PIB strains, to cause disseminated gonococcal infection, which would expose the former to intense selection pressure from the host immune system. The molecular evolution of Neisseria gonorrhoeae seems to be driven by the simultaneous action of selection and recombination, but under different rates and selection pressures for the PIA and PIB homology groups.

Decreased azithromycin susceptibility of Neisseria gonorrhoeae due to mtrR mutations

Single-dose azithromycin therapy has recently been used in Uruguay for the treatment of uncomplicated gonococcal infections. As part of an active surveillance study to monitor the emergence of antibiotic resistance in gonococcal isolates, we examined the levels of azithromycin susceptibility in 51 consecutive isolates obtained from males with uncomplicated gonococcal urethritis. Isolates with decreased susceptibility to azithromycin (MICs, 0.25 to 0.5 microg/ml) were common, and these isolates often displayed cross-resistance to hydrophobic antimicrobial agents (erythromycin and Triton X-100). Resistance to erythromycin and Triton X-100 is frequently due to overexpression of the mtrCDE-encoded efflux pump mediated by mutations in the mtrR gene, which encodes a transcriptional repressor that modulates expression of the mtrCDE operon. Accordingly, we questioned whether clinical isolates that express decreased azithromycin susceptibility harbor mtrR mutations. Promoter mutations that would decrease the level of expression of mtrR as well as a missense mutation at codon 45 in the mtrR-coding region that would result in a radical amino acid replacement within the DNA-binding motif of MtrR were found in these strains. When these mutations were transferred into azithromycin-susceptible strain FA19 by transformation, the susceptibility of gonococci to azithromycin was decreased by nearly 10-fold. The mtrCDE-encoded efflux pump system was responsible for this property since insertional inactivation of the mtrC gene resulted in enhanced susceptibility of gonococci to azithromycin. We conclude that the mtrCDE-encoded efflux pump can recognize azithromycin and that the emergence of gonococcal strains with decreased susceptibility to azithromycin can, in part, be explained by mtrR mutations.

Induction of the mtrCDE-encoded efflux pump system of Neisseria gonorrhoeae requires MtrA, an AraC-like protein

The mtr (multiple transferable resistance) gene complex in Neisseria gonorrhoeae encodes an energy-dependent efflux pump composed of the MtrC-MtrD-MtrE cell envelope proteins that serves to export structurally diverse antimicrobial, hydrophobic agents (HAs). Many of these agents have membrane-acting detergent activity. Using Triton X-100 (TX-100) as a representative HA, we found that the mtrCDE efflux pump operon could be induced to higher levels of expression when an HA-sensitive strain was exposed to sublethal concentrations of this non-ionic detergent and the structurally related spermicide, nonoxynol-9. This induction was at the level of mtrCDE gene transcription and was independent of the MtrR repressor, which normally decreases mtrCDE gene expression. However, the enhanced resistance of gonococci to TX-100 was dependent on the expression of a previously undescribed gonococcal protein that belonged to the AraC/XylS family of transcriptional activators. We have termed this protein MtrA to signify its likely role in the activation of mtrCDE gene expression. Taken together with previous studies dealing with the genetic control of mtrCDE gene expression, we propose that gonococci can modulate their resistance to HAs through both positive and negative transcriptional control processes. The action of these regulatory processes is probably of importance in determining the survival capacity of gonococci at mucosal surfaces that contain detergent-like HAs.

The farAB-encoded efflux pump mediates resistance of gonococci to long-chained antibacterial fatty acids

Gonococci often infect mucosal surfaces bathed in antibacterial fatty acids (FAs). Resistance of gonococci to FAs and other antibacterial hydrophobic agents has been attributed to the mtrCDE-encoded efflux pump system and a heretofore undefined mechanism. This alternative resistance mechanism has been suggested to mediate gonococcal resistance to long-chained FAs independently of the mtr efflux pump. We have now identified this alternative FA resistance system in gonococci and report that it bears significant similarity to the emrAB-encoded efflux pump possessed by Escherichia coli and the vceAB-encoded pump of Vibrio cholerae. We termed the gonococcal version of this efflux pump farAB (fatty acid resistance) to signify its involvement in FA resistance expressed by gonococci and to distinguish it from the emrAB- or vceAB-encoded pumps that modulate bacterial susceptibility to uncoupling agents and certain antibiotics. Although the farAB system in gonococci was found to provide resistance to FAs independently of the mtrCDE-encoded efflux pump, its function was dependent on the MtrE outer membrane protein. Moreover, expression of the tandemly linked farA and farB genes was positively associated with the presence of the MtrR transcriptional regulatory protein that normally downregulates the expression of mtrCDE. Thus, the data presented herein suggest that, while the mtrCDE- and farAB-encoded systems act independently to mediate resistance of gonococci to host-derived, hydrophobic antimicrobial agents, their capacity to export these agents is dependent on the same outer membrane protein (MtrE), and their expression may be differentially controlled by the same transcriptional regulatory protein (MtrR).

Erythromycin-resistant Neisseria gonorrhoeae and oral commensal Neisseria spp. carry known rRNA methylase genes

Two Neisseria gonorrhoeae isolates from Seattle and two isolates from Uruguay were resistant to erythromycin (MIC, 4 to 16 microg/ml) and had reduced susceptibility to azithromycin (MIC, 1 to 4 microg/ml) due to the presence of the self-mobile rRNA methylase gene(s) ermF or ermB and ermF. The two Seattle isolates and one isolate from Uruguay were multiresistant, carrying either the 25.2-MDa tetM-containing plasmid (Seattle) or a beta-lactamase plasmid (Uruguay). Sixteen commensal Neisseria isolates (10 Neisseria perflava-N. sicca, 2 N. flava, and 4 N. mucosa) for which erythromycin MICs were 4 to 16 microg/ml were shown to carry one or more known rRNA methylase genes, including ermB, ermC, and/or ermF. Many of these isolates also were multiresistant and carried the tetM gene. This is the first time that a complete transposon or a complete conjugative transposon carrying an antibiotic resistance gene has been described for the genus Neisseria.

Failure of azithromycin therapy in gonorrhea and discorrelation with laboratory test parameters

BACKGROUND

Azithromycin is efficacious in the treatment of chlamydial genital tract infection but less so in gonorrhea. However, MICs of azithromycin for gonococci from previously reported azithromycin treatment failures were consistently below the 'susceptible' MIC level of 2 mg/L.

GOAL OF THIS STUDY

To examine gonococci not eliminated with 1 g azithromycin therapy to establish treatment outcome/MIC correlates in gonorrhea.

STUDY DESIGN

The MICs and phenotypes of gonococci isolated from five cases of treatment failure after 1 g azithromycin therapy were determined and compared with the MICs of a systematic sample of routine isolates.

RESULTS

Azithromycin MICs of gonococci from five cases of failed 1 g azithromycin treatment were 0.125 or 0.25 mg/L, well within the current 'susceptible' MIC range. None of the isolates were of the mtr phenotype. The MIC90 of a systematic sample of 219 gonococcal isolates was 0.25 mg/L.

CONCLUSION

The antibiotic MIC/treatment outcome correlates that are usually found in gonorrhea do not apply for azithromycin. Current MIC criteria do not accurately define susceptibility or resistance of gonococci to azithromycin and by themselves do not predict the likely outcome of therapy. Pharmacokinetic factors may decrease the predictive value of MIC data.

Loss-of-function mutations in the mtr efflux system of Neisseria gonorrhoeae

Resistance of Neisseria gonorrhoeae to antimicrobial hydrophobic agents (HAs) has been ascribed to the mtr (multiple transferable resistance) operon. This operon is composed of the mtrR gene, which encodes a transcriptional repressor (MtrR), and a three-gene complex (mtrCDE), which encodes cell envelope proteins (MtrC-MtrD-MtrE) that form an energy-dependent efflux pump. HA-hypersusceptible strains are often isolated from patients, but the genetic basis for such hypersusceptibility was heretofore unknown. The genetic basis of HA hypersusceptibility in laboratory-derived strains BR54 and BR87 was studied to learn if this trait could be linked to mutations in the mtr operon. Mutations in the mtrR gene of these strains that could be phenotypically suppressed by mutations in their mtrC or mtrD genes were identified. Thus, small deletions (4-10 bp) in the mtrC or mtrD genes of strains BR87 and BR54 that would result in the production of truncated efflux pump proteins that serve as a membrane fusion protein (MtrC) or transporter of HAs (MtrD) were found to be responsible for their HA-hypersusceptible property.

Molecular epidemiology of infections with Neisseria gonorrhoeae among visitors to a sexually transmitted diseases clinic

OBJECTIVES

To identify determinants for plasmid-mediated resistance to penicillin (penicillinase-producing Neisseria gonorrhoeae [PPNG]) and tetracycline (tetracycline-resistant N. gonorrhoeae [TRNG]) among gonococci, to determine the distribution of bacterial characteristics, and to correlate these with antibiograms and patient characteristics.

STUDY DESIGN

Gonococcal isolates from 131 patients attending a sexually transmitted diseases clinic in The Netherlands in 1994 were auxotyped and serotyped and antimicrobial susceptibility was tested. Information on patient characteristics was collected at the initial visit.

RESULTS

The most prevalent serotype, IB-1 (26%), proved to be related to sexual contact with casual partners, especially commercial sex partners. In addition, IB-1 strains were associated with PPNG and displayed higher minimum inhibitory concentrations (MICs) for ceftriaxone, cefuroxime, and ciprofloxacin. Homosexual men were more often infected with nonrequiring, IB-2, and IB-6 strains than heterosexuals. These strains were very sensitive to ceftriaxone and ciprofloxacin. Overall, one strain showed decreased susceptibility to ciprofloxacin (MIC 0.5 microgram/ml), but no resistance to ceftriaxone, ciprofloxacin, or cefuroxime was observed. However, 31% of the isolates were TRNG, PPNG, or both. Determinants for these resistant strains among men were the use of antibiotics (odds ratio [OR] = 4.8, 90% confidence interval [CI] 1.3-19.1), Surinam or Morrocan origin (OR = 3.3, 90% CI 1.3-8.4), and homosexual contacts (OR = 0.1, 90% CI 0.03-0.4).

CONCLUSIONS

Different types, with variable susceptibility, were associated with homosexual and commercial sexual behavior. PPNG and TRNG were more commonly isolated from antibiotic users, heterosexual individuals, and ethnic minorities. Continuous surveillance of susceptibility is needed to follow the spread of PPNG and TRNG and to detect resistance to the currently recommended agents in a timely fashion.

The MtrD protein of Neisseria gonorrhoeae is a member of the resistance/nodulation/division protein family constituting part of an efflux system

The mtr (multiple transferable resistance) system of Neisseria gonorrhoeae mediates resistance of gonococci to structurally diverse hydrophobic agents (HAs) through an energy-dependent efflux process. Recently, complete or partial ORFs that encode membrane proteins (MtrC, MtrD, MtrE) forming an efflux pump responsible for removal of HAs from gonococci were identified and appeared to constitute a single transcriptional unit. In this study, the complete nucleotide sequence of the mtrD gene was determined, permitting the characterization of the MtrD protein. The full-length MtrD protein has a predicted molecular mass of nearly 114 kDa, putatively containing a 56 amino acid signal peptide. MtrD displays significant amino acid sequence similarity to a family of cytoplasmic membrane proteins, termed resistance/nodulation/division (RND) proteins, which function as energy-dependent transporters of antibacterial agents and secrete bacterial products to the extracellular fluid. The predicted topology of the MtrD transporter protein revealed 12 potential membrane-spanning domains, which were clustered within the central and C-terminal regions of the primary sequence. Loss of MtrD due to insertional inactivation of the mtrD gene rendered gonococci hypersusceptible to several structurally diverse HAs, including two fatty acids (capric acid and palmitic acid) and a bile salt (cholic acid), but not hydrophilic antibiotics such as ciprofloxacin and streptomycin. Since gonococci often infect mucosal sites rich in toxic fatty acids and bile salts, the expression of the mtr efflux system may promote growth of gonococci under hostile conditions encountered in vivo.

The MtrR repressor binds the DNA sequence between the mtrR and mtrC genes of Neisseria gonorrhoeae

Gonococcal resistance to antimicrobial hydrophobic agents (HAs) is due to energy-dependent removal of HAs from the bacterial cell by the MtrCDE membrane-associated efflux pump. The mtrR (multiple transferrable resistance Regulator) gene encodes a putative transcriptional repressor protein (MtrR) believed to be responsible for regulation of mtrCDE gene expression. Gel mobility shift and DNase I footprint assays that used a maltose-binding protein (MBP)-MtrR fusion protein demonstrated that the MtrR repressor is capable of specifically binding the DNA sequence between the mtrR and mtrC genes. This binding site was localized to a 26-nucleotide stretch that includes the promoter utilized for mtrCDE transcription and, on the complementary strand, a 22-nucleotide stretch that contains the -35 region of the mtrR promoter. A single transition mutation (A-->G) within the MtrR-binding site decreased the affinity of the target DNA for MtrR and enhanced gonococcal resistance to HAs when introduced into HA-susceptible strain FA19 by transformation. Since this mutation enhanced expression of the mtrCDE gene complex but decreased expression of the mtrR gene, the data are consistent with the notion that MtrR acts as a transcriptional repressor of the mtrCDE efflux pump protein genes.

Involvement of the gonococcal MtrE protein in the resistance of Neisseria gonorrhoeae to toxic hydrophobic agents

Low-level resistance of Neisseria gonorrhoeae to toxic hydrophobic agents (HAs), including some antibiotics, is chromosomally mediated via the multiple transferable resistance (mtr) efflux system. The gene encoding the 48:3 kDa outer-membrane protein MtrE, which is associated with the mtr phenotype, was identified and is homologous to export-associated outer-membrane proteins, including the OprM (formerly OprK) lipoprotein of Pseudomonas aeruginosa. Insertional inactivation of the mtrE gene in N. gonorrhoeae strain FA19 resulted in the loss o the outer-membrane protein, with concomitant hypersusceptibility of the mutant strain to a range of HAs. The properties of this mutant confirmed the role of MtrE in multidrug resistance mediated by an active efflux mechanism. Secondary structure predictions for MtrE indicated a largely hydrophilic protein with a single alpha-helical transmembrane region. A transposon-like element, similar to that found downstream of the region containing the promoters for mtrR and mtrC in Neisseria meningitidis, was identified 63 bp downstream of the mtrE gene.

Proton-dependent multidrug efflux systems

Multidrug efflux systems display the ability to transport a variety of structurally unrelated drugs from a cell and consequently are capable of conferring resistance to a diverse range of chemotherapeutic agents. This review examines multidrug efflux systems which use the proton motive force to drive drug transport. These proteins are likely to operate as multidrug/proton antiporters and have been identified in both prokaryotes and eukaryotes. Such proton-dependent multidrug efflux proteins belong to three distinct families or superfamilies of transport proteins: the major facilitator superfamily (MFS), the small multidrug resistance (SMR) family, and the resistance/ nodulation/cell division (RND) family. The MFS consists of symporters, antiporters, and uniporters with either 12 or 14 transmembrane-spanning segments (TMS), and we show that within the MFS, three separate families include various multidrug/proton antiport proteins. The SMR family consists of proteins with four TMS, and the multidrug efflux proteins within this family are the smallest known secondary transporters. The RND family consists of 12-TMS transport proteins and includes a number of multidrug efflux proteins with particularly broad substrate specificity. In gram-negative bacteria, some multidrug efflux systems require two auxiliary constituents, which might enable drug transport to occur across both membranes of the cell envelope. These auxiliary constituents belong to the membrane fusion protein and the outer membrane factor families, respectively. This review examines in detail each of the characterized proton-linked multidrug efflux systems. The molecular basis of the broad substrate specificity of these transporters is discussed. The surprisingly wide distribution of multidrug efflux systems and their multiplicity in single organisms, with Escherichia coli, for instance, possessing at least nine proton-dependent multidrug efflux systems with overlapping specificities, is examined. We also discuss whether the normal physiological role of the multidrug efflux systems is to protect the cell from toxic compounds or whether they fulfil primary functions unrelated to drug resistance and only efflux multiple drugs fortuitously or opportunistically.

Gonococcal susceptibility to antimicrobials in Baltimore, 1988-1994. What was the impact of ciprofloxacin as first-line therapy for gonorrhea?

BACKGROUND

Single-dose, oral quinolones have been a recommended treatment option for gonorrhea since 1989 and have since been used as first-line therapy for gonorrhea in Baltimore.

METHODS

The impact of this strategy on antimicobial susceptibility patterns in Neisseria gonorrhoeae was assessed utilizing data collected as part of the National Gonococcal Isolate Surveillance system. This system evaluates a systematically collected sample. Minimum inhibitory concentrations to penicillin, tetracycline, ceftriaxone, and ciprofloxacin were determined by agar dilution.

RESULTS

Between January 1988 and September 1994, 1,846 gonococcal isolates were evaluated. The proportion of isolates with plasmid-mediated resistance (penicillinase-producing Neisseria gonorrhoeae or tetracycline-resistant Neisseria gonorrhoeae) increased from 22% in 1988 to 46% in 1992 and then dropped to 20% in 1994. In contrast, the prevalence of chromosomally mediated resistant isolates ranged between 3% and 10%. Between 1988 and 1994, the geometric mean penicillin and tetracycline minimum inhibitory concentrations decreased slightly (penicillin: from 0.509 microgram/ml to 0.369 microgram/ml; tetracycline: from 1.01 micrograms/ml to 0.767 microgram/ml). The mean ceftriaxone MIC increased from 0.005 microgram/ml in 1988 to 0.021 microgram/ml in 1992, and then abruptly decreased. Ciprofloxacin minimum inhibitory concentrations did not change substantially during the study period. Concurrent studies performed in this community suggest that quinolones were infrequently used for infections other than sexually transmitted ones during this time period.

CONCLUSIONS

Single-dose quinolone therapy does not appear to foster development of resistant gonococcal isolates. However, resistance may develop as a result of complex ecological interactions with the community, underscoring the need for continued surveillance.

Transcriptional control of the mtr efflux system of Neisseria gonorrhoeae

The capacity of Neisseria gonorrhoeae to resist structurally diverse hydrophobic agents (HAs) because of the mtr (multiple transferable resistance) efflux system was found to be regulated at the level of transcription by two distinct mechanisms. This was surmised because a deletion that removed > 90% of the coding sequence of the mtrR (multiple transferrable resistance regulator) gene or a single-base-pair deletion within a 13-bp inverted repeat sequence located in its promoter resulted in altered expression of the mtrC gene; mtrC encodes a 44-kDa membrane lipoprotein essential for the efflux of HAs. However, the single-base-pair deletion had the more significant impact on gene expression since it resulted in the loss of expression of mtrR and a threefold increase in the expression of mtrC. Hence, the mtr efflux system in gonococci is subject to both MtrR-dependent and MtrR-independent regulation, and the levels of mtrC mRNA correlate well with HA resistance levels in gonococci.

Importance of lipooligosaccharide structure in determining gonococcal resistance to hydrophobic antimicrobial agents resulting from the mtr efflux system

Levels of gonococcal resistance to antimicrobial hydrophobic agents (HAs) are controlled by the mtr (multiple transferrable resistance) system, composed of the mtrRCDE genes. The mtrR gene encodes a transcriptional repressor that appears to regulate expression of the upstream and divergent mtrCDE operon. The mtrCDE genes encode membrane proteins analogous to the MexABOprK proteins of Pseudomonas aeruginosa that mediate export of structurally diverse antimicrobial agents. In this study we found that a single base pair deletion in a 13 bp inverted repeat sequence within the mtrR promoter resulted in increased resistance of gonococci to both crystal violet (CV) and erythromycin (ERY) as well as to the more lipophilic non-ionic detergent Triton X-100 (TX-100). However, this cross-resistance was contingent on the production of a full-length lipooligosaccharide (LOS) by the recipient strain used in transformation experiments. Introduction of this mutation (mtrR-171) into three chemically distinct deep-rough LOS mutants by transformation resulted in a fourfold increase in resistance to TX-100 compared with a 160-fold increase in an isogenic strain producing a full-length LOS. However, both wild-type and deep-rough LOS strains exhibited an eightfold increase in resistance to CV and ERY as a result of the mtrR-171 mutation. This suggests that gonococci have different LOS structural requirements for mtr-mediated resistance to HAs that differ in their lipophilic properties. Evidence is presented that gonococci exclude HAs by an energy-dependent efflux process mediated by the mtr system.

Temporal changes in the sensitivity of Neisseria gonorrhoeae to penicillin in Edinburgh, Scotland

Increased resistance of Neisseria gonorrhoeae to penicillin has been reported from many centres around the world since the introduction of antibiotic therapy in the 1940s. This study reports the temporal changes in gonococcal penicillin sensitivity over a 3-year period. All patients with a diagnosis of gonorrhoea in the city of Edinburgh, Scotland between 1990 and 1992 were included in the study. Penicillin sensitivity of isolates was analysed in relation to the sex and sexual orientation of the patient and the antibiotic therapy given. Four hundred and twenty-seven new patient episodes of infection occurred of which penicillin sensitivities were available in 426. Eleven episodes of PPNG infection occurred. Chromosomally mediated penicillin resistance did not increase over the study period. No differences were evident in the sensitivity of isolates from homosexual and heterosexual patients. Unlike many other areas the relative resistance of N. gonorrhoeae is not increasing in Edinburgh at present. This may relate to local antibiotic policies combined with intrinsic characteristics of N. gonorrhoeae itself. Unlike previous reports there did not appear to be any increased resistance to penicillin in isolates from gay men.