Multiple origins and replication proteins influence biological properties of beta-lactamase-producing plasmids from Neisseria gonorrhoeae

Origin, evolution, and success of pbla, the gonococcal beta-lactamase plasmid, and implications for public health

Neisseria gonorrhoeae is a leading cause of sexually transmitted infection (STI) and a priority AMR pathogen. Two narrow host range plasmids, pbla and pConj, have contributed to ending penicillin and tetracycline therapy, respectively, and undermine current prevention strategies including doxycycline post-exposure prophylaxis (Doxy-PEP). Here, we investigated the origin and evolution of the beta-lactamase plasmid, pbla. We demonstrate that pbla was likely acquired by the gonococcus from Haemophilus ducreyi, and describe the subsequent evolutionary pathways taken by the three major pbla variants. We show that the ability of pConj to spread pbla promotes their co-occurrence in the gonococcal population and the spread of pbla. Changes that mitigate fitness costs of pbla and the emergence of TEM beta-lactamases that confer increased resistance have contributed to the success of pbla. In particular, TEM-135, which has arisen in certain pbla variants, increases resistance to beta-lactams and only requires one amino acid change to become an extended spectrum beta-lactamase (ESBL). The evolution of pbla underscores the threat of plasmid-mediated resistance to current therapeutic and preventive strategies against gonococcal infection. Given the close relationship between pbla and pConj, widespread use of Doxy-PEP is likely to promote spread of both plasmids, strains which carry pConj and are resistant against third generation cephalosporins, and the emergence of plasmid-mediated ESBL in the gonococcus, with significant public health consequences.

Transmission and control strategies of antimicrobial resistance from the environment to the clinic: A holistic review

The environment serves as a significant reservoir of antimicrobial resistance (AMR) microbes and genes and is increasingly recognized as key source of clinical AMR. Modern human activities impose an additional burden on environmental AMR, promoting its transmission to clinical setting and posing a serious threat to human health and welfare. Therefore, a comprehensive review of AMR transmission from the environment to the clinic, along with proposed effective control strategies, is crucial. This review systematically summarized current research on the transmission of environmental AMR to clinical settings. Furthermore, the transmission pathways, horizontal gene transfer (HGT) mechanisms, as well as the influential drivers including triple planetary crisis that may facilitate AMR transfer from environmental species to clinical pathogens are highlighted. In response to the growing trend of AMR transmission, we propose insightful mitigation strategies under the One Health framework, integrating advanced surveillance and tracking technologies, interdisciplinary knowledge, multisectoral interventions, alongside multiple antimicrobial use and stewardship approaches to tacking development and spread of AMR.

Genomic Characterization of a Tetracycline-Resistant Strain of Brochothrix thermosphacta Highlights Plasmids Partially Shared between Various Strains

The Gram-positive bacterium Brochothrix thermosphacta is a spoilage agent commonly found on meat products. While the tet(L) gene, which confers resistance to tetracycline, has been identified in certain strains of B. thermosphacta, only a limited number of studies have investigated this gene and its potential presence on mobile DNA elements. This study aims to analyze the tetracycline-resistant strain B. thermosphacta BT469 at the genomic level to gain insight into the molecular determinants responsible for this resistance. Three plasmids have been identified in the strain: pBT469-1, which contains a tetR gene; pBT469-2, which harbours the tet(L) gene responsible for tetracycline resistance; and pBT469-3, which carries genes encoding for a thioredoxin and a phospholipase A2. Homology searches among sequences in public databases have revealed that the plasmid pBT469-2 is currently unique to the BT469 strain. However, the pBT469-1 plasmid is also found in three other strains of B. thermosphacta. Notably, sequences similar to pBT469-1 and pBT469-2 were also found in other bacterial genera, suggesting that these plasmids may be part of a diverse family present in several bacterial genera. Interestingly, sequences of various strains of B. thermosphacta show a high level of similarity with pBT469-3, suggesting that variants of this plasmid could be frequently found in this bacterium.

There are three major Neisseria gonorrhoeae β-lactamase plasmid variants which are associated with specific lineages and carry distinct TEM alleles

Neisseria gonorrhoeae is a significant threat to global health with an estimated incidence of over 80 million cases each year and high levels of antimicrobial resistance. The gonococcal β-lactamase plasmid, pbla, carries the TEM β-lactamase, which requires only one or two amino acid changes to become an extended-spectrum β-lactamase (ESBL); this would render last resort treatments for gonorrhoea ineffective. Although pbla is not mobile, it can be transferred by the conjugative plasmid, pConj, found in N. gonorrhoeae. Seven variants of pbla have been described previously, but little is known about their frequency or distribution in the gonococcal population. We characterised sequences of pbla variants and devised a typing scheme, Ng_pblaST that allows their identification from whole genome short-read sequences. We implemented Ng_pblaST to assess the distribution of pbla variants in 15 532 gonococcal isolates. This demonstrated that only three pbla variants commonly circulate in gonococci, which together account for >99 % of sequences. The pbla variants carry different TEM alleles and are prevalent in distinct gonococcal lineages. Analysis of 2758 pbla-containing isolates revealed the co-occurrence of pbla with certain pConj types, indicating co-operativity between pbla and pConj variants in the spread of plasmid-mediated AMR in N. gonorrhoeae. Understanding the variation and distribution of pbla is essential for monitoring and predicting the spread of plasmid-mediated β-lactam resistance in N. gonorrhoeae.

Transcriptional Organization of the Stability Module of Broad-Host-Range Plasmid RA3, from the IncU Group

The broad-host-range (BHR) conjugative plasmids have developed diverse adaptive mechanisms defining the range of their promiscuity. The BHR conjugative RA3 plasmid, the archetype of the IncU group, can transfer between, replicate in, and be maintained in representatives of Alpha-, Beta-, and Gammaproteobacteria Its stability module encompasses ten open reading frames (ORFs) apparently organized into five operons, all transcribed in the same direction from several strong promoters that are tightly regulated either by autorepressors or by global plasmid-encoded regulators. In this paper, we demonstrate that owing to an efficient RNA polymerase (RNAP) read-through, the transcription from the first promoter, orf02p, may continue through the whole module. Moreover, an analysis of mRNA produced from the wild-type (WT) stability module and its deletion variants deprived of particular internal transcription initiation sites reveals that in fact each operon may be transcribed from any upstream promoter, giving rise to multicistronic transcripts of variable length and creating an additional level of gene expression control by transcript dosage adjustment. The gene expression patterns differ among various hosts, indicating that promoter recognition, regulation, and the RNAP read-through mechanisms are modulated in a species-specific manner.IMPORTANCE The efficiently disseminating conjugative or mobilizable BHR plasmids play key roles in the horizontal spread of genetic information between closely related and phylogenetically distant species, which can be harmful from the medical, veterinary, or industrial point of view. Understanding the mechanisms determining the plasmid's ability to function in diverse hosts is essential to help limit the spread of undesirable plasmid-encoded traits, e.g., antibiotic resistance. The range of a plasmid's promiscuity depends on the adaptations of its transfer, replication, and stability functions to the various hosts. IncU plasmids, with the archetype plasmid RA3, are considered to constitute a reservoir of antibiotic resistance genes in aquatic environments; however, the molecular mechanisms determining their adaptability to a broad range of hosts are rather poorly characterized. Here, we present the transcriptional organization of the stability module and show that the gene transcript dosage effect is an important determinant of the stable maintenance of RA3 in different hosts.

A β-lactamase-producing plasmid from Neisseria gonorrhoeae carrying a unique 6 bp deletion in blaTEM-1 encoding a truncated 24 kDa TEM-1 penicillinase that hydrolyses ampicillin slowly

BACKGROUND

Seven structurally related β-lactamase-producing plasmids have been characterized in penicillinase-producing Neisseria gonorrhoeae (PPNG) isolates. We characterized a variant (i.e. pJRD20, Canada type) of the Africa-type (pJD5) plasmid isolated from N. gonorrhoeae strain 8903.

OBJECTIVES

To compare the DNA sequence of pJRD20 with that of pJD5 and pJD4 (Asia-type) and their TEM-1 β-lactamases.

METHODS

N. gonorrhoeae 8903 was identified as part of the Gonococcal Antimicrobial Surveillance Program in Canada. β-Lactamase production was assessed using nitrocefin. MICs were determined by agar dilution and Etest methods (CLSI). The DNA sequences of pJRD20, pJD5 and pJD4 were assembled and annotated. The structure of TEM-1 and its penicillin-binding properties were determined by in silico molecular modelling and docking. TEM-1 proteins were characterized by western blot, mass spectrometry and ampicillin hydrolysis assays.

RESULTS

N. gonorrhoeae 8903 exhibited intermediate susceptibility to penicillin with slow β-lactamase activity (i.e. 35 min to hydrolyse nitrocefin). Except for a novel 6 bp deletion starting at the G of the ATG start codon of blaTEM-1, the DNA sequence of pJRD20 was identical to that of pJD5. The TEM-1 β-lactamase produced by pJRD20 is 24 kDa and hydrolyses ampicillin only after several hours.

CONCLUSIONS

This unusual PPNG isolate might have been characterized as a non-PPNG owing to its low MIC of penicillin and its very slow hydrolysis of nitrocefin. Given the unusual nature of its TEM-1 β-lactamase, laboratories might consider extending the duration of nitrocefin hydrolysis assays.

A Meningococcal Native Outer Membrane Vesicle Vaccine With Attenuated Endotoxin and Overexpressed Factor H Binding Protein Elicits Gonococcal Bactericidal Antibodies

BACKGROUND

Meningococcal outer membrane vesicle (OMV) vaccines are prepared with detergents to remove endotoxin, which also remove desirable antigens such as factor H binding protein (FHbp). Native OMV (NOMV) vaccines with genetically attenuated endotoxin do not require detergent treatment and elicit broader serum bactericidal antibody (SBA) responses than OMV or recombinant FHbp (rFHbp) vaccines.

METHODS

We measured human complement-mediated SBA responses in mice immunized with NOMV with overexpressed FHbp subfamily B (NOMV-FHbp), NOMV with FHbp genetically inactivated (NOMV-KO), and/or a control rFHbp vaccine against meningococcal and gonococcal strains.

RESULTS

Despite having 36-fold less FHbp per dose, the NOMV-FHbp vaccine elicited a ≥3-fold higher serum IgG anti-FHbp geometric mean titer than control vaccines containing rFHbp (P ≤ .003). Against 2 meningococcal outbreak strains with mismatched PorA and heterologous FHbp subfamily B sequence variants, the NOMV-FHbp vaccine produced ≥30-fold higher SBA titers than control vaccines. Mice immunized with NOMV-FHbp and NOMV-KO vaccines also elicited SBA against a gonococcal strain (P < .0001 vs the adjuvant-only control group). In contrast, 2 licensed meningococcal serogroup B vaccines, including one containing detergent-extracted OMV, did not produce gonococcal SBA in humans.

CONCLUSIONS

A meningococcal NOMV vaccine elicits SBA against gonococci and with overexpressed FHbp elicits SBA against meningococci.

Identification and sequence analysis of two novel cryptic plasmids isolated from the vaginal mucosa of South African women

The vaginal mucosa is dominated by Gram positive, rod shaped lactobacilli which serve as a natural barrier against infection. In both healthy- and bacterial vaginosis (BV)-infected women Lactobacillus crispatus and Lactobacillus jensenii have been found to be the predominant Lactobacillus species. Many studies have been conducted to assess factors influencing lactobacilli dominance in the vaginal microbiome. In the present study two plasmids, pLc4 and pLc17, isolated from vaginal Lactobacillus strains of both healthy and BV-infected women were characterized. The smaller plasmid, pLc4 (4224 bp), was detected in both L. crispatus and L. jensenii strains, while pLc17 was only detected in L. crispatus. Based on its nucleotide sequence pLc4 appears highly novel, with its replication protein having 44% identity to the replication initiation protein of pSMQ173b_03. Phylogenetic analysis with other Rolling Circle Replication plasmids confirmed that pLc4 shows a low degree of similarity to these plasmids. Plasmid pLc17 (16,663 bp) appears to carry both a RCR replicon and a theta replicon, which is rare in naturally occurring plasmids. pLc4 was maintained at a high copy number of 29, while pLc17 appears to be a medium copy number plasmid maintained at 11 copies per chromosome. While sequence analysis is a valuable tool to study cryptic plasmids, further function-based analysis will be required in order to fully elucidate the role of these plasmids within the vaginal milieu.

Mobile genetic elements in Neisseria gonorrhoeae: movement for change

Neisseria gonorrhoeae, the causative agent of the sexually transmitted disease gonorrhoeae, possesses several mobile genetic elements (MGEs). The MGEs such as transposable elements mediate intrachromosomal rearrangements, while plasmids and the gonococcal genetic island are involved in interchromosomal gene transfer. Additionally, gonococcal MGEs serve as hotspots for recombination and integration of other genetic elements such as bacteriophages, contribute to gene regulation or spread genes through gonococcal populations by horizontal gene transfer. In this review, we summarise the literature on the structure and biology of MGEs and discuss how these genetic elements may play a role in the pathogenesis and spread of antimicrobial resistance in N. gonorrhoeae. Although an abundance of information about gonococcal MGEs exists (mainly from whole genome sequencing and bioinformatic analysis), there are still many open questions on how MGEs influence the biology of N. gonorrhoeae.

Characterisation of blaTEM genes and types of β-lactamase plasmids in Neisseria gonorrhoeae - the prevalent and conserved blaTEM-135 has not recently evolved and existed in the Toronto plasmid from the origin

Background

Antimicrobial resistance (AMR) in Neisseria gonorrhoeae is a major concern worldwide. It has been recently feared that the bla_TEM-1 gene is, via bla_TEM-135, evolving into an extended-spectrum β-lactamase (ESBL), which could degrade all cephalosporins including ceftriaxone. The aims of the present study were to characterize the bla_TEM genes, types of β-lactamase plasmids, the degradation of ampicillin by TEM-135 compared to TEM-1, and to perform molecular epidemiological typing of β-lactamase-producing N. gonorrhoeae strains internationally.

Methods

β-lactamase producing N. gonorrhoeae isolates (n = 139) cultured from 2000 to 2011 in 15 countries were examined using antibiograms, bla_TEM gene sequencing, β-lactamase plasmid typing, and N. gonorrhoeae multiantigen sequence typing (NG-MAST). Furthermore, the bla_TEM gene was sequenced in the first described Toronto plasmid (pJD7), one of the first Asian plasmids (pJD4) and African plasmids (pJD5) isolated in Canada. The degradation of ampicillin by TEM-135 compared to TEM-1 was examined using a MALDI-TOF MS hydrolysis assay.

Results

Six different bla_TEM sequences were identified (among isolates with 125 different NG-MAST STs), i.e. bla_TEM-1 (in 104 isolates), bla_TEM-135 (in 30 isolates), and four novel bla_TEM sequences (in 5 isolates). The bla_TEM-1 allele was only found in the African and Asian plasmids, while all Rio/Toronto plasmids possessed the bla_TEM-135 allele. Most interesting, the first described gonococcal Toronto plasmid (pJD7), identified in 1984, also possessed the highly conserved bla_TEM-135 allele. The degradation of ampicillin by TEM-135 compared to TEM-1 was indistinguishable in the MALDI-TOF MS hydrolysis assay.

Conclusions

bla_TEM-135, encoding TEM-135, is predominantly and originally associated with the Rio/Toronto plasmid and prevalent among the β-lactamase producing gonococcal strains circulating globally. bla_TEM-135 does not appear, as previously hypothesized, to have recently evolved due to some evolutionary selective pressure, for example, by the extensive use of extended-spectrum cephalosporins worldwide. On the contrary, the present study shows that bla_TEM-135 existed in the Toronto plasmid from its discovery and that bla_TEM-135 is highly conserved (not further evolved in the past >30 years). Nevertheless, international studies for monitoring the presence of different bla_TEM alleles, the possible evolution of the bla_TEM-135 allele, and the types of β-lactamase producing plasmids, remain imperative.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2334-14-454) contains supplementary material, which is available to authorized users.

Invasion of E. coli biofilms by antibiotic resistance plasmids

In spite of the contribution of plasmids to the spread of antibiotic resistance in human pathogens, little is known about the transferability of various drug resistance plasmids in bacterial biofilms. The goal of this study was to compare the efficiency of transfer of 19 multidrug resistance plasmids into Escherichia coli recipient biofilms and determine the effects of biofilm age, biofilm-donor exposure time, and donor-to-biofilm attachment on this process. An E. coli recipient biofilm was exposed separately to 19 E. coli donors, each with a different plasmid, and transconjugants were determined by plate counting. With few exceptions, plasmids that transferred well in a liquid environment also showed the highest transferability in biofilms. The difference in transfer frequency between the most and least transferable plasmid was almost a million-fold. The 'invasibility' of the biofilm by plasmids, or the proportion of biofilm cells that acquired plasmids within a few hours, depended not only on the type of plasmid, but also on the time of biofilm exposure to the donor and on the ability of the plasmid donor to attach to the biofilm, yet not on biofilm age. The efficiency of donor strain attachment to the biofilm was not affected by the presence of plasmids. The most invasive plasmid was pHH2-227, which based on genome sequence analysis is a hybrid between IncU-like and IncW plasmids. The wide range in transferability in an E. coli biofilm among plasmids needs to be taken into account in our fight against the spread of drug resistance.

Enhancing gonococcal antimicrobial resistance surveillance: a real-time PCR assay for detection of penicillinase-producing Neisseria gonorrhoeae by use of noncultured clinical samples

With increasing concerns regarding diminishing treatment options for gonorrhea, maintaining the efficacy of currently used treatments and ensuring optimal Neisseria gonorrhoeae antimicrobial resistance surveillance are of the utmost importance. Penicillin is still used to treat gonorrhea in some parts of the world. In this study, we developed and validated a real-time PCR assay for the detection of penicillinase-producing N. gonorrhoeae (PPNG) in noncultured clinical samples with the aim of enhancing penicillin resistance surveillance. The assay (PPNG-PCR2) was designed to be an indirect marker of penicillinase activity, by targeting a region of sequence predicted to be conserved across all N. gonorrhoeae plasmid types harboring the beta-lactamase gene while not specifically targeting the actual beta-lactamase-encoding sequence. The assay was evaluated by using a total of 118 N. gonorrhoeae clinical isolates and 1,194 clinical specimens, including 239 N. gonorrhoeae-positive clinical samples from which N. gonorrhoeae cells were isolated and for which phenotypic penicillinase results are available. Overall, the PPNG-PCR2 assay provided 100% sensitivity and 98.7% specificity compared to bacterial culture results for the detection of PPNG in clinical specimens. PPNG-PCR2 false-positive results, presumably due to cross-reactions with unrelated bacterial species, were observed for up to 1.3% of clinical samples but could be distinguished on the basis of high cycle threshold values. In tandem with phenotypic surveillance, the PPNG-PCR2 assay has the potential to provide enhanced epidemiological surveillance of N. gonorrhoeae penicillin resistance and is of particular relevance to regions where penicillin is still used to treat gonorrhea.

Two internal origins of replication in Streptomyces linear plasmid pFRL1

Previous reports showed that Streptomyces linear plasmids usually contain one internal replication locus. Here, we identified two new replication loci on pFRL1, one (rep1A-ncs1) next to a telomere and another (rep2A-ncs2) approximately 10 kb from it. The rep1A-ncs1 locus was able to direct replication independently in both linear and circular modes, whereas rep2A-ncs2 required an additional locus, rlrA-rorA, in order to direct propagation in linear mode. Rep1A protein bound to ncs1 in vitro. By quantitative reverse transcription-PCR and Northern hybridization, we showed that transcription of rep1A and rep2A varied during development and that each dominated at different time points. pFRL1-derived linear plasmids were inherited through spores more stably than circular plasmids and were more stable with pSLA2 telomeres than with pFRL1 telomeres in Streptomyces lividans.

Variation in Salmonella enterica serovar typhi IncHI1 plasmids during the global spread of resistant typhoid fever

A global collection of plasmids of the IncHI1 incompatibility group from Salmonella enterica serovar Typhi were analyzed by using a combination of DNA sequencing, DNA sequence analysis, PCR, and microarrays. The IncHI1 resistance plasmids of serovar Typhi display a backbone of conserved gene content and arrangement, within which are embedded preferred acquisition sites for horizontal DNA transfer events. The variable regions appear to be preferred acquisition sites for DNA, most likely through composite transposition, which is presumably driven by the acquisition of resistance genes. Plasmid multilocus sequence typing, a molecular typing method for IncHI1 plasmids, was developed using variation in six conserved loci to trace the spread of these plasmids and to elucidate their evolutionary relationships. The application of this method to a collection of 36 IncHI1 plasmids revealed a chronological clustering of plasmids despite their difference in geographical origins. Our findings suggest that the predominant plasmid types present after 1993 have not evolved directly from the earlier predominant plasmid type but have displaced them. We propose that antibiotic selection acts to maintain resistance genes on the plasmid, but there is also competition between plasmids encoding the same resistance phenotype.

Four different integrative recombination events involved in the mobilization of the gonococcal 5.2 kb beta-lactamase plasmid pSJ5.2 in Escherichia coli

We identified and characterized four different recombination mechanisms involved in the cointegrative transfer of the Neisseria gonorrhoeae beta-lactamase plasmid pSJ5.2 by the gonococcal 41 kb tet(M) and the Gram negative self-transmissible plasmids N3 and R64 drd-33 using an Escherichia colirecA-background. Mobilization of pSJ5.2 by the tet(M) plasmid occurred by cointegration through a replicative transposition of two IS1 elements inserted upstream from the beta-lactamase gene of pSJ5.2 and creating a IS1::beta-lactamase hybrid promoter. Two types of recombinational events occurred within the 1.8 kb BamH1-HindIII fragment of pSJ5.2 with the N3 and R64 plasmids. A non-homologous recombination was found at coordinates 1817 and 2849 of pSJ5.2 with sequences from R64. A non-homologous recombination combined with an IS26-mediated one-ended transposition was found at coordinates 1817 and 3010 of pSJ5.2 with N3. In both recombinational events, a deletion of over 1 kb of pSJ5.2 occurred. The fourth recombination event was detected in the 1.0 kb BamH1-HindIII fragment of pSJ5.2 by homologous recombination between DNA from the truncated Tn3 resolvase gene of pSJ5.2 and the resolvase sequences from R64 and N3.

Mobilization of the gonococcal 5.2 kb beta-lactamase plasmid pSJ5.2 into Escherichia coli by cointegration with several gram-conjugative plasmids

We report the mobilization by cointegration of the gonococcal 5.2 kb beta-lactamase plasmid pSJ5.2 in an Escherichia coli background. Transfer of pSJ5.2 was measured by filter mating assays with five different conjugative plasmids from Enterobacteriaceae and the gonococcal 41 kb tet(M). Plasmid pSJ5.2 was mobilized to E. coli at frequencies of 1.7x10(-6), 9.3x10(-8) and 2.7x10(-5) by the tet(M), R64 drd-33 and N3 conjugative plasmids, respectively. Mobilization of pSJ5.2 by the 41 kb tet(M) conjugative plasmid resulted in stable Amp(R) E. coli transconjugants consisting of pSJ5.2 plasmid with an insertion located in the 2.4 kb BamHI-BamHI fragment. Mobilization of pSJ5.2 by R64drd-33 and N3 conjugative plasmids involved stable cointegrates as detected by Southern Blot with a DIG-labelled PstI-digested pSJ5.2 probe. Restriction analysis of the R64::pSJ5.2 and N3::pSJ5.2 cointegrates and Southern Blot with the pSJ5.2 probe showed that cointegrates formed by deletion of DNA regions within the 1.8 kb BamHI-HindIII fragment of pSJ5.2. The plasmid thus appears to use multiple recombination mechanisms for cointegration with different conjugative plasmids. The complete nucleotide sequence of pSJ5.2 was determined, and will be a useful tool to further investigate the molecular mechanisms leading to its cointegrative transfer.

Functional analysis of ori1 and repA of the R-plasmid pSJ5.6 from Neisseria gonorrhoeae

The functional ori1 of the 5.6kb gonococcal R-plasmid pSJ5.6 contains an A-T rich region followed by four 22bp direct repeats and one 19bp inverted repeat. The replication region of the plasmid also contains a gene encoding for a 39kD RepA protein. We have further assessed the functionality of the replication region in pSJ5.6, an-iteron type plasmid, using in vivo complementation assays in Escherichia coli. A 2.1kb PstI-RsaI fragment containing the ori1 and repA gene of pSJ5.6 was cloned into vector pZErO -2 to obtain pZA-MRR. The pUC origin in pZA-MRR was deleted to render the plasmid dependable on the cis-acting ori1 for replication. The resulting plasmid, pMRR, was capable of replication and maintenance in E. coli. We also cloned the ori1 and repA gene separately to obtain pA-Ori and pZG-Rep, respectively. Using in vivo complementation assays, we demonstrated that the ori1(+) plasmid (pA-Ori) was maintained only when the RepA protein was supplied in trans by the high copy number plasmid pZG-Rep.

Molecular analysis of oriT and MobA protein in the 7.4 kb mobilizable beta-lactamase plasmid pSJ7.4 from Neisseria gonorrhoeae

The mobilization region of the 7.4 kb beta-lactamase plasmid pSJ7.4 from Neisseria gonorrhoeae was characterized. The 3.2 kb HindIII-BamHI fragment of pSJ7.4 was mobilized between Escherichia coli strains by conjugative plasmid RK2. Selected restriction enzyme-generated deletions of this fragment were subcloned in pACYC177 to obtain constructs that were suitable for analysis of the mobilization region. Mating experiments showed that a highly conserved 1.9 kb DNA region within coordinates 4096-5997 is required for mobilization of pSJ7.4. This region contains two genes encoding the mobilization protein MobA, another protein, MobC, putatively involved in mobilization from some hosts, and an intergenic oriT. The 168 bp intergenic sequence also contains the promoters for mobA and mobC in an arrangement that suggests divergent transcription and autoregulation from oriT. The 56 kDa MobA was expressed in E. coli as a (6x)His-Tag fusion protein. Purified MobA specifically induced plasmid relaxation by nicking at the oriT. MobA is exceptional because the N-terminal region alone can mobilize pSJ7.4, albeit at a lower frequency than the full-length protein, even in the absence of MobC. The carboxyl terminal region of MobA did not share homology with other mobilization proteins, but may be involved in promoting efficient transfer of pSJ7.4.

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.

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.