The distribution of variants of the Tet M determinant in tetracycline-resistant Neisseria gonorrhoeae

Plasmid-mediated penicillin and tetracycline resistance among Neisseria gonorrhoeae isolates in South Africa: prevalence, detection and typing using a novel molecular assay

BACKGROUND

To detect and type plasmids responsible for penicillin and tetracycline resistance in Neisseria gonorrhoeae isolates using a novel duplex polymerase chain reaction (PCR) assay.

METHODS

A duplex PCR assay, to detect and type penicillinase-producing N. gonorrhoeae (PPNG), and plasmid-mediated tetracycline resistant N. gonorrhoeae (TRNG), was developed on the basis of published single assays. Gonococcal Isolate Surveillance Project control strains were used in assay development and then 209 consecutive N. gonorrhoeae isolates, collected from men with urethral discharge in 2008, were tested. Controls included Asia, Africa, and Toronto β-lactamase plasmids, as well as American and Dutch TRNG plasmids. PCR amplicons were detected using an Agilent 2100 Bioanalyzer. Minimum inhibitory concentrations (MIC) were determined with E tests. Penicillinase production was detected using Nitrocefin solution.

RESULTS

Among 209 gonococcal isolates, 54 (25.8%) PPNG and 154 (73.3%) TRNG were detected. The MIC50 and MIC90 values were determined for penicillin (0.19 and 32 mg/L) and tetracycline (6 and 16 mg/L). The assay detected the Africa-type (35.2%), the Toronto-type (44.4%), and a new type (20.3%) of β-lactamase plasmid. The American-type TRNG plasmid was 3-fold more frequent as compared with the Dutch-type. Although there was no overall association between the detection of PPNG and TRNG plasmids, only American type TRNG contained β-lactamase-encoding plasmids (P < 0.0001).

CONCLUSIONS

The prevalence of plasmid-mediated resistance to tetracycline, and to a lesser extent penicillin, is high and neither drug is likely to have any future role in the treatment of gonorrhoea in South Africa. A novel β-lactamase plasmid was detected during the study and requires further characterization.

Changing figures of antimicrobial susceptibility and serovar distribution in Neisseria gonorrhoeae isolated in Greece

OBJECTIVES

To update surveillance data on antimicrobial susceptibility of Neisseria gonorrhoeae isolated in Greece with information for the years 2005 to 2008, and analyze changes occurred from the previous 4-year period.

METHODS

Annual antimicrobial susceptibility rates, susceptibility patterns, and serovars of 635 gonococci isolated in 2005 to 2008 were determined and compared to respective data concerning the gonococcal sample of 2001 to 2004. Genetic similarity of the isolates in phenotypic clusters was investigated by pulsed field gel electrophoresis. Epidemiologic information was also considered.

RESULTS

Despite a reduction in the isolation frequency of penicillinase-producing strains (3.9% vs. 11.6% in the previous period), the rates of resistance and intermediate susceptibility increased for penicillin, as well as for tetracycline, erythromycin, and chloramphenicol, leaving very small proportions of isolates sensitive to these agents (4.3%, 12.8%, 10.2%, and 3.6%, respectively). Resistance to fluoroquinolones increased from 11.3% in 2004 up to 63% in 2008, and strongly correlated with multidrug-resistant isolates of Bropyst serovar, accounting for 72.6% of the quinolone-resistant strains isolated during the last 4 years. All isolates were susceptible to spectinomycin and only 2 exceeded susceptibility breakpoints set for cefotaxime, exhibiting MICs 0.75 to 1 microg/mL. These latter isolates, however, belonged to a cluster of strains with decreased susceptibility to cephalosporins (CDS, cefotaxime MICs >or=0.25 microg/mL) that emerged in late 2006 and increased in frequency up to 20.7% through 2008. Notably, CDS isolates were also quinolone-resistant and multiresistant, further contributing to the increasing rates of quinolone and multidrug resistance in the Greek gonococcal sample.

CONCLUSIONS

Antimicrobial susceptibility figures of Neisseria gonorrhoeae in Greece are worsening due to changes in the synthesis of gonococcal population, resulting from high endemicity rates of multidrug-resistant strains.

Conjugative plasmids of Neisseria gonorrhoeae

Many clinical isolates of the human pathogen Neisseria gonorrhoeae contain conjugative plasmids. The host range of these plasmids is limited to Neisseria species, but presence of a tetracycline (tetM) determinant inserted in several of these plasmids is an important cause of the rapid spread of tetracycline resistance. Previously plasmids with different backbones (Dutch and American type backbones) and with and without different tetM determinants (Dutch and American type tetM determinants) have been identified. Within the isolates tested, all plasmids with American or Dutch type tetM determinants contained a Dutch type plasmid backbone. This demonstrated that tetM determinants should not be used to differentiate between conjugal plasmid backbones. The nucleotide sequences of conjugative plasmids with Dutch type plasmid backbones either not containing the tetM determinant (pEP5233) or containing Dutch (pEP5289) or American (pEP5050) type tetM determinants were determined. Analysis of the backbone sequences showed that they belong to a novel IncP1 subfamily divergent from the IncP1α, β, γ, δ and ε subfamilies. The tetM determinants were inserted in a genetic load region found in all these plasmids. Insertion was accompanied by the insertion of a gene with an unknown function, and rearrangement of a toxin/antitoxin gene cluster. The genetic load region contains two toxin/antitoxins of the Zeta/Epsilon toxin/antitoxin family previously only found in Gram positive organisms and the virulence associated protein D of the VapD/VapX toxin/antitoxin family. Remarkably, presence of VapX of pJD1, a small cryptic neisserial plasmid, in the acceptor strain strongly increased the conjugation efficiency, suggesting that it functions as an antitoxin for the conjugative plasmid. The presence of the toxin and antitoxin on different plasmids might explain why the host range of this IncP1 plasmid is limited to Neisseria species. The isolated plasmids conjugated efficiently between N. gonorrhoeae strains, but did not enhance transfer of a genetic marker.

Antimicrobial susceptibility of Neisseria gonorrhoeae in Greece: data for the years 1994-2004

OBJECTIVES

Surveillance data concerning antimicrobial susceptibilities of Neisseria gonorrhoeae isolated in Greece during the 11 year period 1994-2004 are presented.

METHODS

Antimicrobial susceptibilities of all gonococcal isolates received by the Greek National Reference Center for N. gonorrhoeae during the study period were determined in terms of MICs using Etest. Trends in yearly isolation frequencies by susceptibility category were estimated for defining significant changes in overall susceptibility figures.

RESULTS

Cefotaxime and spectinomycin retained undiminished activity against all isolates throughout the study period. High rates of resistance and intermediate susceptibilities were noticed for penicillin, tetracycline and erythromycin, and even for norfloxacin and ciprofloxacin. A substantial portion (16.5%) of the gonococcal samples consisted of multiresistant strains exhibiting resistance to two or more agents of different antibiotic classes. Although annual rates of low-level chromosomal resistance decreased, high-level resistance owing to the presence of penicillin- and tetracycline-resistance plasmids increased. Fluoroquinolone resistance also showed a significant increasing trend after 1996, reaching a peak rate of 11.3% in 2004.

CONCLUSION

Third-generation cephalosporins and spectinomycin should be considered as first-choice drugs for the empirical treatment of gonorrhoea in Greece.

Molecular epidemiology of Neisseria gonorrheae isolates with plasmid-mediated tetracycline resistance in Canada: temporal and geographical trends (1986-1997)

Plasmid-mediated resistance to tetracycline in Neisseria gonorrhoeae (TRNG) isolates is caused by the acquisition of a 25.2-MDa conjugative, tetM-containing plasmid (TetM plasmid). The presence of the TetM plasmid is the leading cause of gonococcal resistance to tetracycline in most countries. Between 1986 and 1997, 6,306 TRNG isolates were isolated in different Canadian provincial laboratories and subsequently submitted to the national laboratory for further strain characterization. Because nonculture-based identification of N. gonorrhoeae was more widely used after 1995, this snapshot of the molecular epidemiology of TRNG in Canada, which is only possible if bacteria are cultured, represents a comprehensive data baseline that may no longer be achievable. Temporal trends indicate that TRNG isolations peaked in 1994 (18.9% of isolates tested). Antimicrobial susceptibilities (MIC) to tetracycline and penicillin were determined for 4,064 TRNG isolated between 1986 and 1994. The MICs of TRNG isolates ranged from 16 microg/ml to 32 microg/ml of tetracycline, although one isolate had an MIC of 8 microg/ml and the MICs of four isolates were 2 microg/ml. Penicillinase-producing TRNG (i.e., PP/TRNG) comprised 34.1% of all TRNG (n = 1,386) and 52 TRNG isolates exhibited chromosomal resistance to penicillin. Most of the PP/TRNG (94.1%) carried Africa type (3.2 MDa) beta-lactamase-producing plasmids; only 76 (5.5%) PP/TRNG carried Asia type (4.4 MDa) penicillinase-producing plasmids and three isolates carried Toronto type (3.05 MDa) plasmids. TRNG isolates were also retrospectively typed by auxotype (A), serovar (S), and plasmid (P) content analysis. Eleven auxotype/serovar (A/S) groups comprised the majority (93%) of 4,064 typed TRNG isolates with A/S classes NR/IB-2, NR/IB-3, and NR/IB-1 accounting for 75.1% of the strains characterized. Classification of 670 TRNG for tetM type demonstrated that the Dutch (n = 531) type TetM plasmids predominated over the American (n = 139) type TetM plasmids.

Antimicrobial susceptibilities of Neisseria gonorrhoeae strains isolated in Java, Indonesia

BACKGROUND

Despite the rapid spread of antibiotic resistance in gonococci all over Southeast Asia, there is only limited surveillance for antibiotic susceptibility in Indonesia.

GOAL

This study was undertaken to determine the frequency and diversity of antimicrobial resistance in gonococcal isolates from cohorts of female commercial sex workers in Bandung and Jakarta, Indonesia, and to characterize the Tet M plasmid among the tetracycline-resistant strains N gonorrhoeae.

STUDY DESIGN

The antimicrobial susceptibility of 267 strains (85 strains from Bandung and 182 from Jakarta) to penicillin, spectinomycin, tetracycline, ciprofloxacin, cefotaxime, thiamphenicol, kanamycin, azithromycin, and trimethoprim-sulfamethoxazole (TMP-SMZ) was determined by agar dilution. Typing of the Tet M plasmid in tetracycline-resistant isolates was performed by PCR.

RESULTS

Prevalence of penicillin and tetracycline resistance was extremely high: 60.0% of the isolates from Bandung and 70.9% of the isolates from Jakarta were resistant to penicillin. Of these, 60.0% and 62.1%, respectively, were penicillinase-producing N gonorrhoeae (PPNG). All the isolates from Bandung and 98.4% from Jakarta were resistant to tetracycline. All tetracycline-resistant isolates from Bandung and 97.8% from Jakarta carried a PCR fragment characteristic of the "Dutch" type Tet M plasmid. One isolate from Jakarta showed chromosomal resistance to tetracycline (0.6%). Chromosomal resistance to thiamphenicol (MIC, >/=2.0 microg/ml) was significantly higher in Jakarta than in Bandung (P < 0.05). All gonococcal isolates were susceptible to kanamycin, spectinomycin, cefotaxime, ciprofloxacin, and azithromycin.

CONCLUSION

Spectinomycin, fluoroquinolones, and azithromycin are still useful primary drugs for treatment of gonococcal infections in Indonesia. Continued surveillance of antimicrobial susceptibility should be part of gonorrhea control in Indonesia.

Detection of a novel Tet M determinant in tetracycline-resistant Neisseria gonorrhoeae from Uruguay, 1996-1999

BACKGROUND

Determination of the diversity within the tet(M) sequence from N gonorrhoeae is a useful epidemiologic tool for monitoring the movement or importation of strains within a geographic region. Only two distinct tet(M) genes in clinical gonococcal isolates have been described up to now: the Dutch and the American types.

GOAL

The study involved surveillance of the tet(M) gene types in high-level-tetracycline-resistant gonococcal isolates from Uruguay during the period 1996 to 1999.

STUDY DESIGN

Among 181 gonococcal isolates, those showing MICs >/=16 microg/ml to tetracycline were analyzed for detection and characterization of the tet(M) gene by a polymerase chain reaction (PCR) and further HpaII restriction fragment polymorphism methods, respectively. The plasmid content and antibiogram were determined.

RESULTS

Twenty-two of 181 isolates (12%) exhibited high levels of resistance to tetracycline (MICs >/=16 microg/ml) and harbored a putative 25.2-Mda plasmid that contained the tet(M) gene. A high percentage of isolates (95%; 21/22) presented the Dutch type tet(M) gene. One isolate from 1999 revealed a new restriction pattern. Such a pattern had been previously noted in 1991. This new restriction pattern has not been described previously as occurring in isolates of N gonorrhoeae. The tet(M) amplimer sequence showed 100% identity with a previously described tet(M)-carrying plasmid from N meningitidis.

CONCLUSION

A new HpaII restriction pattern of the tet(M) gene is present in low frequency. The tet(M) sequence was different from the gonococcal tet(M) sequences already known and not typable with the use of a differential PCR assay. Accordingly, with the genetic diversity already present within the tet(M) sequence of N gonorrhoeae isolates, we should be aware of the sensitivity of the PCR assays in use for tetracycline-resistant N gonorrhoeae detection.

Molecular epidemiology of tetM genes in Neisseria gonorrhoeae

OBJECTIVE

To examine the epidemiology of the tetM gene in Neisseria gonorrhoeae strains with high level resistance to tetracycline (TRNG) using a polymerase chain reaction (PCR) assay.

METHODS

A single tube PCR was developed which distinguishes between the American and Dutch variants of the tetM gene. Between 1988 and 1995, 518 strains of TRNG (tetracycline MIC > 8.mg/l) were referred to the Gonococcus Reference Unit by other laboratories or isolated from routine swabs taken at local clinics. The strains were analysed for plasmid content, auxotype, serovar, and the tetM gene type. Travel details of the patients were determined by a questionnaire.

RESULTS

A PCR product was obtained from all TRNG examined. 387 TRNG strains produced a 778 bp PCR product (American type tetM) and 131 produced a 443 by PCR product (Dutch type tetM). Infections acquired in the United Kingdom contributed 57% of the TRNG strains included in this study; 82% of these carried the American type of tetM. The number of UK acquired TRNG received by the GRU increased each year except 1993--from four strains received in 1990 to 92 in 1995. After the United Kingdom, Caribbean and African countries contributed most strains, with 56 and 60 TRNG acquired in each area respectively. All strains originating in Africa, except one from South Africa, contained the American type tetM. Infections caught in Nigeria and Kenya contributed most strains (15 and 14 respectively). The TRNG originating from Caribbean countries comprised 36% Dutch tetM type. Infections caught in Jamaica accounted for 82% of the Caribbean strains. All 35 TRNG strains originating in the Far East contained the Dutch type tetM. 25 of the Far East strains were also penicillinase producing (PPNG). Infections originating in Indonesia accounted for 49% of the Far East strains but these belonged to 12 different auxotype/serovar combinations. A geographical variation in the type of penicillinase coding plasmids found in PPNG/TRNG was also detected.

CONCLUSIONS

These data suggest that the Dutch type tetM may have originated in the Far East and the American type in the African continent. Subsequent spread has resulted in a heterogeneous distribution of TRNG types in other parts of the world. At completion of the survey the numbers of TRNG imported each year from the major overseas sources had reached a plateau while UK contracted TRNG continued to rise providing evidence for the establishment of endemic TRNG strains in the United Kingdom.

Antimicrobial resistance of Neisseria gonorrhoeae in Liberia

The prevalence and molecular characteristics of penicillinase-producing Neisseria gonorrhoeae (PPNG) and tetracycline-resistant N. gonorrhoeae (TRNG) were determined in 10 clinics in Monrovia, Liberia, to assess the likely effectiveness of the current standard treatment with penicillin or tetracycline. One hundred gonococcal strains were isolated from 146 urethral swabs and 261 cervical swabs and screened for susceptibility to ceftriaxone, penicillin, spectinomycin and tetracycline by the disk diffusion method; 83% were resistant to penicillin and 63% to tetracycline. Twenty-one strains from 18 men and 3 women with uncomplicated gonorrhoea were subjected to more detailed characterization. These 21 strains belonged to 5 auxotype/serovar classes; 86% were PPNG/TRNG. Three PPNG harboured the 4.4 MDa penicillinase plasmid and 16 the 3.2 MDa plasmid. All TRNG harboured the 25.2 MDa plasmid and their MICs for tetracycline were > 32 mg/L. They gave a PCR product which, according to its restriction pattern, corresponded to the American type tetM gene. By the agar dilution method, all strains exhibited intermediate resistance to sulphamethoxazole-trimethoprim (19:1) (co-trimoxazole) with MICs of 8-32 mg/L. All strains were susceptible to spectinomycin and ciprofloxacin. The MICs for gentamicin were 4-8 mg/L. The use of effective and affordable antimicrobial chemotherapy with either 500 mg ciprofloxacin or a single dose of gentamicin is discussed, with consideration of molecular biological, pharmacological and public health aspects.

Plasmid patterns and antimicrobial susceptibilities of Neisseria gonorrhoeae in Bandung, Indonesia

Antimicrobial susceptibilities of Neisseria gonorrhoeae isolates from female sex workers and from men with urethritis in Bandung, Indonesia, were determined by an agar dilution technique. Typing of the Tet M plasmid in tetracycline-resistant isolates (TRNG) was performed using a polymerase chain reaction (PCR) technique and plasmid profiles of penicillinase-producing isolates (PPNG) were determined. All PPNG possessed the 4.4 MDa beta-lactamase plasmid and all TRNG showed a PCR fragment characteristic of the 'Dutch' type Tet M plasmid. Of the 50 gonococci isolates tested, all were resistant to tetracycline; 47 were TRNG, 26 were PPNG, and 6 were resistant to thiamphenicol. Chromosomal resistance to penicillin was not detected. All isolates were susceptible to ceftriaxone, ciprofloxacin, norfloxacin, ofloxacin, kanamycin, spectinomycin, and trimethoprim/sulfamethoxazole. Spectinomycin and fluoroquinolones are useful primary drugs for treatment of gonococcal infection in Bandung. Continued surveillance of antimicrobial resistance should be part of gonorrhoea control in Indonesia.

New tetracycline resistance determinants coding for ribosomal protection in streptococci and nucleotide sequence of tet(T) isolated from Streptococcus pyogenes A498

An approach based on PCR has been developed to identify new members of the tet gene family in streptococci resistant to tetracycline and minocycline. Degenerate primers, corresponding to portions of the conserved domains of the proteins Tet(M), Tet(O), TeTB(P), Tet(Q), and Tet(S), all specifying the tetracycline-minocycline resistance phenotype, were used to selectively amplify DNA fragments within the coding sequences. Nine streptococcal strains which do not carry the genes tet(M), tet(O), tetB(P), tet(Q), or tet(S) were investigated. Four of them gave no detectable PCR products. The five remaining strains each yielded a PCR product of 1.1 kbp. DNA hybridization experiments showed that these putative Tet determinants fell into four new hybridization classes, of which one, Tet T, was further analyzed. The gene tet(T) was isolated from Streptococcus pyogenes A498, and the nucleotide sequence that was necessary and sufficient for the expression of tetracycline resistance in Escherichia coli was determined. The deduced Tet(T) protein consists of 651 amino acids. The protein most closely related to Tet(T) was Tet(Q), which has 49% identical amino acid residues. A phylogenetic analysis revealed that Tet T represents a novel branching order among the Tet determinants so far described.

Tetracycline-resistant Neisseria gonorrhoeae. Characteristics of patients and isolates at a London Genitourinary Medicine Clinic

OBJECTIVES

To compare auxotypes, serovars, and antibiograms of tetracycline-resistant Neisseria gonorrhoeae (TRNG) and non-TRNG isolated from patients attending an East London Genitourinary Medicine (GUM) Clinic. To obtain plasmid profiles for penicillinase-producing gonococci (PPNG) as well as presumptive TRNG. To identify differences in patient characteristics for the TRNG and non-TRNG patient groups.

STUDY DESIGN

Gonococcal isolates were collected from 400 patients attending the GUM clinic at the Royal London Hospital GUM Clinic over a 1-year period. Isolates (378) were tested for susceptibility to various antibiotics, auxotyped, and serotyped. Plasmid profiles were obtained for PPNG and isolates exhibiting high-level tetracycline resistance (TRNG). The presence of the tet M determinant was confirmed using the polymerase chain reaction (PCR). The PCR product was digested with the restriction endonuclease (RE) Hpa II and electrophoresed on a 2.5% agarose gel to determine an "RE pattern." Patient data were collected by retrospective case-note review.

RESULTS

TRNG (n = 42) accounted for 11% of the 378 isolates tested, and the remaining 336 (89%) isolates were non-TRNG. Non-requiring auxotrophy and P1B-2 serovar expression occurred more frequently among TRNG. PPNG accounted for 31% of TRNG and 5% of non-TRNG. Chromosomal resistance to penicillin (CMRNG) was absent among TRNG but accounted for 11% of non-TRNG. One TRNG isolate showed decreased susceptibility to ciprofloxacin (MIC 0.25 mg/l). All isolates were sensitive to cefotaxime, cefixime, spectinomycin, and azithromycin. All TRNG possessed the 25.2 MDa plasmid and produced a PCR product of appropriate size after tet M gene sequence amplification. RE digests of the PCR product gave a single pattern. None of the TRNG in contrast to 18% of the non-TRNG were acquired homosexually. Ethnic distribution differed between the patients with TRNG and patients without non-TRNG (Afro-Caribbean 81% versus 58%; white 19% versus 36%). Most TRNG were acquired in the United Kingdom.

CONCLUSIONS

TRNG differ from the non-TRNG in their auxotype and serovar distribution. PPNG are more common among the TRNG isolates, whereas CMRNG appear absent. TRNG are isolated more commonly from Afro-Caribbean patients and were not represented among homosexually acquired isolates.