Aminoglycoside resistance genes in early members of the Acinetobacter baumannii ST78A (SMAL, Italian clone) reside in an IS26-bounded island in the chromosome

BACKGROUND

The Acinetobacter baumannii isolate called SMAL, previously used to determine the structures of capsular polysaccharide and lipooligosaccharide, was recovered in Pavia, Italy in 2002 among the collection of aminoglycoside-resistant isolates designated as SMAL type. This type was later called the Italian clone, then ST78. ST78 isolates are now widely distributed.

OBJECTIVES

To establish the resistance gene complement and the location and structure of acquired resistance regions in early members of the Italian/ST78 clone.

METHODS

The draft genome of SMAL2002 was assembled from Illumina MiSeq reads. Contigs containing resistance genes were joined and located in the chromosome using PCR with custom primers. The resistance profile was determined using disc diffusion.

RESULTS

SMAL2002 is an ST78A isolate and includes three aminoglycoside resistance genes, aadB (gentamicin, kanamycin, tobramycin) aphA1 (kanamycin, neomycin) and aac(6')-Ian (amikacin, kanamycin, tobramycin). The aadB gene cassette is incorporated at a secondary site in a relative of the aphA1-containing, IS26-bounded pseudo-compound transposon, PTn6020. The aac(6')-Ian gene is in an adjacent IS26-bounded structure that includes sul2 (sulphonamide) and floR (florfenicol) resistance genes. The two pseudo-compound transposons overlap and are in the chromosomal hutU gene flanked by an 8 bp target site duplication. Although aac(6')-Ian was not noticed previously, the same genes and structures were found in several available draft genomes of early ST78A isolates.

CONCLUSIONS

This study highlights the importance of correlating resistance profiles with resistance gene content. The location of acquired resistance genes in the SMAL2002 chromosome represents the original location in the ST78A lineage of ST78.

IS26 and the IS26 family: versatile resistance gene movers and genome reorganizers

SUMMARYIn Gram-negative bacteria, the insertion sequence IS26 is highly active in disseminating antibiotic resistance genes. IS26 can recruit a gene or group of genes into the mobile gene pool and support their continued dissemination to new locations by creating pseudo-compound transposons (PCTs) that can be further mobilized by the insertion sequence (IS). IS26 can also enhance expression of adjacent potential resistance genes. IS26 encodes a DDE transposase but has unique properties. It forms cointegrates between two separate DNA molecules using two mechanisms. The well-known copy-in (replicative) route generates an additional IS copy and duplicates the target site. The recently discovered and more efficient and targeted conservative mechanism requires an IS in both participating molecules and does not generate any new sequence. The unit of movement for PCTs, known as a translocatable unit or TU, includes only one IS26. TU formed by homologous recombination between the bounding IS26s can be reincorporated via either cointegration route. However, the targeted conservative reaction is key to generation of arrays of overlapping PCTs seen in resistant pathogens. Using the copy-in route, IS26 can also act on a site in the same DNA molecule, either inverting adjacent DNA or generating an adjacent deletion plus a circular molecule carrying the DNA segment lost and an IS copy. If reincorporated, these circular molecules create a new PCT. IS26 is the best characterized IS in the IS26 family, which includes IS257/IS431, ISSau10, IS1216, IS1006, and IS1008 that are also implicated in spreading resistance genes in Gram-positive and Gram-negative pathogens.

The RuvABC Holliday Junction Processing System Is Not Required for IS26-Mediated Targeted Conservative Cointegrate Formation

The insertion sequence IS26 plays a key role in the spread of antibiotic resistance genes in Gram-negative bacteria. IS26 and members of the IS26 family are able to use two distinct mechanisms to form cointegrates made up of two DNA molecules linked via directly oriented copies of the IS. The well-known copy-in (formerly replicative) reaction occurs at very low frequency, and the more recently discovered targeted conservative reaction, which joins two molecules that already include an IS, is substantially more efficient. Experimental evidence has indicated that, in the targeted conservative mode, the action of Tnp26, the IS26 transposase, is required only at one end. How the Holliday junction (HJ) intermediate generated by the Tnp26-catalyzed single-strand transfer is processed to form the cointegrate is not known. We recently proposed that branch migration and resolution via the RuvABC system may be needed to process the HJ; here, we have tested this hypothesis. In reactions between a wild-type and a mutant IS26, the presence of mismatched bases near one IS end impeded the use of that end. In addition, evidence of gene conversion, potentially consistent with branch migration, was detected in some of the cointegrates formed. However, the targeted conservative reaction occurred in strains that lacked the recG, ruvA, or ruvC genes. As the RuvC HJ resolvase is not required for targeted conservative cointegrate formation, the HJ intermediate formed by the action of Tnp26 must be resolved by an alternate route. IMPORTANCE In Gram-negative bacteria, the contribution of IS26 to the spread of antibiotic resistance and other genes that provide cells with an advantage under specific conditions far exceeds that of any other known insertion sequence. This is likely due to the unique mechanistic features of IS26 action, particularly its propensity to cause deletions of adjacent DNA segments and the ability of IS26 to use two distinct reaction modes for cointegrate formation. The high frequency of the unique targeted conservative reaction mode that occurs when both participating molecules include an IS26 is also key. Insights into the detailed mechanism of this reaction will help to shed light on how IS26 contributes to the diversification of the bacterial and plasmid genomes it is found in. These insights will apply more broadly to other members of the IS26 family found in Gram-positive as well as Gram-negative pathogens.

Acinetobacter baumannii GC2 Sublineage Carrying the aac(6')-Im Amikacin, Netilmicin, and Tobramycin Resistance Gene Cassette

The aminoglycoside antibiotics amikacin, gentamicin, and tobramycin are important therapeutic options for Acinetobacter iinfections. Several genes that confer resistance to one or more of these antibiotics are prevalent in the globally distributed resistant clones of Acinetobacter baumannii, but the aac(6')-Im (aacA16) gene (amikacin, netilmicin, and tobramycin resistance), first reported in isolates from South Korea, has rarely been reported since. In this study, GC2 isolates (1999 to 2002) from Brisbane, Australia, carrying aac(6')-Im and belonging to the ST2:ST423:KL6:OCL1 type were identified and sequenced. The aac(6')-Im gene and surrounds have been incorporated into one end of the IS26-bounded AbGRI2 antibiotic resistance island and are accompanied by a characteristic 70.3-kbp deletion of adjacent chromosome. The compete genome of the 1999 isolate F46 (RBH46) includes only two copies of ISAba1 (in AbGRI1-3 and upstream of ampC) but later isolates, which differ from one another by <10 single nucleotide differences (SND), carry two to seven additional shared copies. Several complete GC2 genomes with aac(6')-Im in an AbGRI2 island (2004 to 2017; several countries) found in GenBank and two additional Australian A. baumannii isolates (2006) carry different gene sets, KL2, KL9, KL40, or KL52, at the capsule locus. These genomes include ISAba1 copies in a different set of shared locations. The distribution of SND between F46 and AYP-A2, a 2013 ST2:ST208:KL2:OCL1 isolate from Victoria, Australia, revealed that a 640-kbp segment that includes KL2 and the AbGRI1 resistance island replaces the corresponding region in F46. Over 1,000 A. baumannii draft genomes also include aac(6')-Im, indicating that it is currently globally disseminated and significantly underreported. IMPORTANCE Aminoglycosides are important therapeutic options for treatment of Acinetobacter infections. Here, we show that a little-known aminoglycoside resistance gene, aac(6')-Im (aacA16), that confers amikacin, netilmicin, and tobramycin resistance has been circulating undetected for many years in a sublineage of A. baumannii global clone 2 (GC2), generally with a second aminoglycoside resistance gene, aacC1, which confers resistance to gentamicin. These two genes are commonly found together in GC2 complete and draft genomes and globally distributed. One isolate appears to be ancestral, as its genome contains few ISAba1 copies, providing insight into the original source of this insertion sequence (IS), which is abundant in most GC2 isolates. Tracking ISAba1 spread can provide a simple means to track the development and ongoing evolution as well as the dissemination of specific lineages and detect the formation of many sublineages. The complete ancestral genome will provide an essential base point for tracking this process.

Identification of an Outbreak Cluster of Extensively Antibiotic-Resistant GC1 Acinetobacter baumannii Isolates in U.S. Military Treatment Facilities

An outbreak involving an extensively antibiotic-resistant Acinetobacter baumannii strain in three military treatment facilities was identified. Fifty-nine isolates recovered from 30 patients over a 4-year period were found among a large collection of isolates using core genome multilocus sequence typing (MLST). They differed by only 0 to 18 single nucleotide polymorphisms (SNPs) and carried the same resistance determinants except that the aphA6 gene was missing in 25 isolates. They represent a novel sublineage of GC1 lineage 1 that likely originated in Afghanistan. IMPORTANCE A. baumannii is recognized as one of the most important nosocomial pathogens, and carbapenem-resistant strains pose a particularly difficult treatment challenge. Outbreaks linked to this pathogen are reported worldwide, particularly during periods of societal upheaval, such as natural disasters and conflicts. Understanding how this organism enters and establishes itself within the hospital environment is key to interrupting transmission, but few genomic studies have examined these transmissions over a prolonged period. Though historical, this report provides an in-depth analysis of nosocomial transmission of this organism across continents and within and between different hospitals.

Characterisation of an early South African multiply antibiotic-resistant global clone 1 (GC1) Acinetobacter baumannii isolate

OBJECTIVES

To characterise an early clinical multiply antibiotic resistant Acinetobacter baumannii global clone 1 (GC1) isolate from Africa.

METHODS

The draft genome sequence was determined using short-read (Illumina MiSeq) sequence data and compared to other early GC1 isolates. Resistance genes and other features were identified using various bioinformatics tools. Plasmids were visualised.

RESULTS

LUH6050, recovered in South Africa between January1997 to January 1999 is ST1^IP:ST231^Ox:KL1:OCL1. Several antibiotic resistance genes (aacC1, aadA2, aphA1, catA1, sul1, tetA(A)) reside in AbaR32. LUH6050 also includes plasmids pRAY*, carrying the aadB gentamicin and tobramycin resistance gene, and a 29.9 kb plasmid, pLUH6050-3, carrying the msrE-mphE (macrolide resistance) and dfrA44 (trimethoprim resistance) genes and a small cryptic Rep_1 plasmid. Plasmid pLUH6050-3, a cointegrate of pA1-1 (R3-T1; RepAci1) with an R3-T33 type plasmid encoding a different Rep_3 family Rep, carries 15 pdif sites and 13 dif modules including those that carry the mrsE-mphE and dfrA44 genes and three that include toxin-antitoxin gene pairs. The closest relative of pLUH6050-3 found in GenBank was from an unrelated 2013 Tanzanian A. baumannii isolate. The chromosome has an AbaR0-type region in comM and includes no ISAba1 copies. Similar features were found in most other sequenced lineage 1 GC1 isolates recovered prior to 2000.

CONCLUSION

LUH6050 represents an early form of the GC1 lineage 1, adding to limited information about early isolates and isolates from Africa that currently hampers understanding of the emergence, evolution and dissemination of the A. baumannii GC1 clonal complex.

Insertion sequences related to ISAjo2 target pdif and dif sites and belong to a new IS family, the IS1202 family

Several insertion sequences (IS) found in various Acinetobacter species exhibit target specificity. They are found, in the same orientation, 5 bp from the XerC binding site of the pdif sites associated with dif modules in Acinetobacter plasmids, and searches revealed they are also found near chromosomal dif sites of Acinetobacter species. These IS are 1.5 kb long, bounded by 24-26 bp imperfect terminal inverted repeats (TIRs) and encode a large transposase of 441-457 aa. They generate 5 bp target site duplications (TSDs). Structural predictions of the ISAjo2 transposase, TnpAjo2, modelled on TnsB of Tn7 revealed two N-terminal HTH domains followed by an RNaseH fold (DDE domain), a β barrel and a C-terminal domain. Similar to Tn7, the outer IS ends are 5'-TGT and ACA-3', and an additional Tnp binding site, corresponding to the internal portion of the IR, is found near each end. However, the Acinetobacter IS do not encode further proteins related to those required by Tn7 for targeted transposition, and the transposase may interact directly with XerC bound to a dif-like site. We propose that these IS, currently in the IS1202 group in the not characterized yet (NCY) category in ISFinder, are part of a distinct IS1202 family. Other IS listed as in the IS1202 group encode transposases related to TnpAjo2 (25-56 % amino acid identity) and have similar TIRs but fall into three groups based on the TSD length (3-5, >15, 0 bp). Those with 3-5 bp TSDs may also target dif-like sites but targets were not found for the other groups.

IS26-mediated loss of the translocatable unit from Tn4352B requires the presence of the recA1 allele

The pseudo-compound transposon Tn4352B is unusual in that the translocatable unit (TU) consisting of one of the bounding IS26 copies and the central portion containing the aphA1a gene has been found to be readily lost in the Escherichia coli strains used as host. Rapid loss required the presence of an additional 2 G residues adjacent to the internal end of one of the IS26 that flank the central portion and an active Tnp26 transposase. However, Tn4352B was found to be stable in wild-type Klebsiella pneumoniae strains. Though it was concluded that the difference may be due to the species background, the E. coli strains used were recombination-deficient. Here, we have further investigated the requirements for TU loss in E. coli and found that Tn4352B was stable in recombination-proficient strains. Among several recombination-deficient strains examined, rapid loss occurred only in strains that carry the recA1 allele but not in strains carrying different recA alleles, recA13 and a novel recA allele identified here, that also render the strain deficient in homologous recombination. Hence, it appears that a specific property of the RecA1 protein underlies the observed TU loss from Tn4352B.

Mechanisms of IS26-Mediated Amplification of the aphA1 Gene Leading to Tobramycin Resistance in an Acinetobacter baumannii Isolate

Enhanced levels of resistance to antibiotics arising from amplification of an antibiotic resistance gene that impact therapeutic options are increasingly observed. Amplification can also disclose novel phenotypes leading to treatment failure. However, the mechanism is poorly understood. Here, the route to amplification of the aphA1 kanamycin and neomycin resistance gene during tobramycin treatment of an Acinetobacter baumannii clinical isolate, leading to tobramycin resistance and treatment failure, was investigated. In the tobramycin-susceptible parent isolate, MRSN56, a single copy of aphA1 is present in the pseudocompound transposon PTn6020, bounded by directly oriented copies of IS26. For two clinical resistant isolates, new long-read sequence data were combined with available short-read data to complete the genomes. Comparison to the completed genome of MRSN56 revealed that, in both cases, IS26 had generated a circular translocatable unit (TU) containing PTn6020 and additional adjacent DNA. In one case, this TU was reincorporated into the second product generated by the deletion that formed the TU via the targeted conservative route and amplified about 7 times. In the second case, the TU was incorporated at a new location via the copy-in route and amplified about 65 times. Experimental amplification ex vivo by subjecting MRSN56 to tobramycin selection pressure yielded different TUs, which were incorporated at either the original location or a new location and amplified many times. The outcomes suggest that when IS26 is involved, amplification occurs via rolling circle replication of a newly formed TU coupled to the IS26-mediated TU formation or reincorporation step. IMPORTANCE Heteroresistance, a significant issue that is known to impact antibiotic treatment outcomes, is caused by the presence of spontaneously arising cells with elevated levels of resistance to therapeutically important antibiotics in a population of susceptible cells. Gene amplification is one well-documented cause of heteroresistance, but precisely how extensive amplification occurs is not understood. Here, we establish the case for the direct involvement of IS26 activity in the amplification of the aphA1 gene to disclose resistance to tobramycin. The aphA1 gene is usually found associated with IS26 in Gram-negative pathogens and is commonly found in extensively resistant Acinetobacter baumannii strains. IS26 and related IS cause adjacent deletions, forming a nonreplicating circular molecule known as a translocatable unit (TU), and amplification via a rolling circle mechanism appears to be coupled to either IS26-mediated TU formation or reincorporation. Related IS found in Gram-positive pathogens may play a similar role.

OUP accepted manuscript

Objectives

To examine the causes of antibiotic resistance in the extensively resistant global clone 1 (GC1) Acinetobacter baumannii isolate MRSN 56 recovered at a US military treatment facility.

Methods

MRSN 56 was sequenced using MinION (Oxford Nanopore) and the reads combined with available Illumina MiSeq data using Unicycler. Acquired resistance genes were identified using ABRicate and their environment examined. ISAba1 and ISAba125 copies were located.

Results

MRSN 56 is ST1^IP:ST231^Ox:KL1:OCL1 and the complete genome includes four small plasmids, none of which carry resistance genes. The acquired resistance genes were found at four locations in the chromosome in addition to AbaR28 (aphA1, aacC1, aadA1, sul1) in comM. Tn2006 (oxa23, carbapenem resistance) was both in AbaR4 and alone elsewhere. Two copies of Tn7 (dfrA1, sat, aadA1) were identified. One was associated with a 22 852 bp adjacent segment [tetA(B), sul2] derived from the AbGRI1 island, and this novel configuration was designated Tn7+. Tn7+ was incorporated in the position preferred by Tn7, downstream of glmS, by transposition using a sequence in AbGRI1 resembling the Tn7 terminal inverted repeats. Tn7 was found at a secondary site. Fluoroquinolone resistance appears to involve a mutation in gyrA combined with inactivation by ISAba1 of the marR gene in the mar operon and constitutive expression of marA from the promoter internal to ISAba1.

Conclusions

MRSN 56 represents a new sublineage of GC1 lineage 1 with novel features that had not been detected previously. The involvement of the mar operon in fluoroquinolone resistance has not been noted previously.

HI1 and I1 Resistance Plasmids from Salmonella enterica Serovar Typhimurium Strain SRC27 Are Epidemic

Conjugative plasmids are a major contributor to the global spread of antibiotic resistance determinants, but the tracking of their evolutionary history is often neglected. Salmonella enterica serovar Typhimurium (S. Typhimurium) strain SRC27 was isolated from an equine infection in Australia in 1999. SRC27 was known to carry conjugative HI1 and I1 resistance plasmids. In this study, SRC27 was sequenced to determine the relationship between these HI1 and I1 resistance plasmids it was known to carry and HI1 and I1 resistance plasmids circulating worldwide. The resistance genes in the HI1 plasmid, pSRC27-H, are all located in a single complex 34.7 kb resistance region. The backbone sequence and location of the pSRC27-H resistance island were used to identify the most closely related HI1 plasmids among the >90 that have been sequenced since 2011. This defined a sublineage of 20 type 2 HI1 plasmids that have been circulating in Europe, Asia, North America, and Australia since at least 1993. The overall resistance gene content of these HI1 plasmids differs, indicating extensive evolution in situ through the acquisition of additional transposons and deletion or replacement of ancestral regions. The I1 plasmid contains a complete copy of Tn5393a, containing the strAB genes that confer resistance to streptomycin. The precise location of Tn5393a in the backbone also defined a globally disseminated sublineage of I1 plasmids, many of which have also acquired additional resistance determinants. The sequence revealed that SRC27 also carried two additional plasmids, the pSLT-type FIB(S):FII(S) virulence plasmid and a small cryptic theta-replicating Col156 plasmid.

IS26 cannot move alone

BACKGROUND

IS26 plays a major role in the dissemination of antibiotic resistance determinants in Gram-negative bacteria.

OBJECTIVES

To determine whether insertion sequence IS26 is able to move alone (simple transposition) or if it exclusively forms cointegrates.

METHODS

A two-step PCR using outward-facing primers was used to search for circular IS26 molecules. Gibson assembly was used to clone a synthetic IS26 containing a catA1 chloramphenicol resistance gene downstream of the tnp26 transposase gene into pUC19. IS activity in a recA-Escherichia coli containing the non-conjugative pUC19-derived IS26::catA1 construct and the conjugative plasmid R388 was detected using a standard mating-out assay. Transconjugants were screened for resistance.

RESULTS

Circular IS26 molecules that would form with a copy-out route were not detected by PCR. The synthetic IS26::catA1 construct formed CmRTpR transconjugants (where CmR and TpR stand for chloramphenicol resistant and trimethoprim resistant, respectively), representing an R388 derivative carrying the catA1 gene at a frequency of 5.6 × 10-7 CmRTpR transconjugants per TpR transconjugant, which is comparable to the copy-in activity of the unaltered IS26. To test for simple transposition of IS26::catA1 (without the plasmid backbone), 1200 CmRTpR colonies were screened and all were resistant to ampicillin, indicating that the pUC19 backbone was present. Hence, IS26::catA1 had only formed cointegrates.

CONCLUSIONS

IS26 is unable to move alone and cointegrates are the exclusive end products of the reactions mediated by the IS26 transposase Tnp26. Consequently, when describing the formation of complex resistance regions, simple 'transposition' of a single IS26 should not be invoked.

The Complete Nucleotide Sequence of pZM3, a 1970 FIA:FIB:FII Plasmid Carrying Antibiotic Resistance and Virulence Determinants

The multiresistance plasmid, pZM3, from a 1970 Salmonella enterica serovar Wien isolate from Algeria represents the multiresistance FIme-type plasmids conferring resistance to ampicillin, chloramphenicol, kanamycin, neomycin, sulfonamides, streptomycin, spectinomycin, tetracycline, and mercuric ions circulating in the Middle East in the 1970s. pZM3 was sequenced to determine the relationship between IS1936, the IS26-like insertion sequence it carries, and IS26. IS1936 is identical to IS26. pZM3 is a 166.8-kb plasmid with three replicons typed as FIA-1, FIB-1, and FII-1, consistent with other FIme plasmids. However, Tn3, containing the bla_TEM-1a ampicillin resistance gene, disrupts the FII repA gene. pZM3 also contains an IS1-flanked virulence region, including the sit and aerobactin operons, shared with many other FIB-1 virulence plasmids. The remaining resistance genes are located in a 44.7-kb complex resistance island that includes the Tn21-like transposon, Tn1935, identified previously. Relative to Tn21, Tn1935 includes an additional gene cassette, oxa1, and Tn4352 in tniA. Tn1935 is in the same Tn2670 context as Tn21 in NR1, and identity to NR1 extends beyond the IS1 flanking the catA1 gene. On the other side, IS1-mediated events have brought in a Tn10 remnant and inverted part of it, highlighting the role of IS1 in resistance region evolution. The backbone of pZM3 was found to be almost identical to that of pRSB225, recovered in Germany in 2013, and their resistance islands are in the same position. The pRSB225 resistance island has evolved in situ from the pZM3 configuration through an insertion, a replacement, and an inversion.

An analysis of the IS6/IS26 family of insertion sequences: is it a single family?

The relationships within a curated set of 112 insertion sequences (ISs) currently assigned to the IS6 family, here re-named the IS6/IS26 family, in the ISFinder database were examined. The encoded DDE transposases include a helix-helix-turn-helix (H-HTH) potential DNA binding domain N-terminal to the catalytic (DDE) domain, but 10 from Clostridia include one or two additional N-terminal domains. The transposase phylogeny clearly separated 75 derived from bacteria from 37 from archaea. The longer bacterial transposases also clustered separately. The 65 shorter bacterial transposases, including Tnp26 from IS26, formed six clades but share significant conservation in the H-HTH domain and in a short extension at the N-terminus, and several amino acids in the catalytic domain are completely or highly conserved. At the outer ends of these ISs, 14 bp were strongly conserved as terminal inverted repeats (TIRs) with the first two bases (GG) and the seventh base (G) present in all except one IS. The longer bacterial transposases are only distantly related to the short bacterial transposases, with only some amino acids conserved. The TIR consensus was longer and only one IS started with GG. The 37 archaeal transposases are only distantly related to either the short or the long bacterial transposases and different residues were conserved. Their TIRs are loosely related to the bacterial TIR consensus but are longer and many do not begin with GG. As they do not fit well with most bacterial ISs, the inclusion of the archaeal ISs and the longer bacterial ISs in the IS6/IS26 family is not appropriate.

Is aberrant affective cognition an endophenotype for affective disorders? - A monozygotic twin study

BACKGROUND

Identification of endophenotypes can improve prevention, detection and development of new treatments. We therefore investigated whether aberrant affective cognition constitutes an endophenotype for affective disorders by being present in monozygotic (MZ) twins with unipolar or bipolar disorder in partial remission (i.e. affected) and their unaffected co-twins (i.e. high-risk) relative to twins with no family history of affective disorder (i.e. low-risk).

METHODS

We conducted an assessor blind cross-sectional study from 2014 to 2017 of MZ twins using Danish population-based registers in recruitment. Twins attended one test session involving neurocognitive testing, clinical ratings and questionnaires. Main outcomes were attention to and recognition of emotional facial expressions, the memory of emotional self-referential words, emotion regulation and coping strategies.

RESULTS

Participants were 103 affected, 44 high-risk and 36 low-risk MZ twins. Groups were demographically well-balanced and showed comparable non-affective cognitive performance. We observed no aberrant affective cognition in affected and high-risk relative to low-risk twins. However, high-risk twins displayed attentional avoidance of emotional faces (ps ⩽ 0.009) and more use of task-oriented coping strategies (p = 0.01) compared with affected twins. In contrast did affected twins show more emotion-oriented coping than high- and low-risk twins (ps ⩽ 0.004).

CONCLUSIONS

Our findings provide no support of aberrant affective cognition as an endophenotype for affective disorders. High-risk twins' attentional avoidance of emotional faces and greater use of task-oriented coping strategies may reflect compensatory mechanisms.

Neural correlates of improved recognition of happy faces after erythropoietin treatment in bipolar disorder

OBJECTIVE

Bipolar disorder is associated with impairments in social cognition including the recognition of happy faces. This is accompanied by imbalanced cortico-limbic response to emotional faces. We found that EPO improved the recognition of happy faces in patients with bipolar disorder. This randomized, controlled, longitudinal fMRI study explores the neuronal underpinnings of this effect.

METHOD

Forty-four patients with bipolar disorder in full or partial remission were randomized to eight weekly erythropoietin (EPO; 40 000 IU) or saline (NaCl 0.9%) infusions in a double-blind, parallel-group design. Participants underwent whole-brain fMRI at 3T, mood ratings and blood tests at baseline and week 14. During fMRI, participants viewed happy and fearful faces and performed a gender discrimination task.

RESULTS

Thirty-four patients had complete pre- and post-treatment fMRI data (EPO: N = 18, saline: N = 16). Erythropoietin vs. saline increased right superior frontal response to happy vs. fearful faces. This correlated with improved happiness recognition in the EPO group. Erythropoietin also enhanced gender discrimination accuracy for happy faces. These effects were not influenced by medication, mood, red blood cells or blood pressure.

CONCLUSIONS

Together with previous findings, the present observation suggests that increased dorsal prefrontal attention control is a common mechanism of EPO-associated improvements across several cognitive domains.

Evolution and typing of IncC plasmids contributing to antibiotic resistance in Gram-negative bacteria

The large, broad host range IncC plasmids are important contributors to the spread of key antibiotic resistance genes and over 200 complete sequences of IncC plasmids have been reported. To track the spread of these plasmids accurate typing to identify the closest relatives is needed. However, typing can be complicated by the high variability in resistance gene content and various typing methods that rely on features of the conserved backbone have been developed. Plasmids can be broadly typed into two groups, type 1 and type 2, using four features that differentiate the otherwise closely related backbones. These types are found in many different countries in bacteria from humans and animals. However, hybrids of type 1 and type 2 are also occasionally seen, and two further types, each represented by a single plasmid, were distinguished. Generally, the antibiotic resistance genes are located within a small number of resistance islands, only one of which, ARI-B, is found in both type 1 and type 2. The introduction of each resistance island generates a new lineage and, though they are continuously evolving via the loss of resistance genes or introduction of new ones, the island positions serve as valuable lineage-specific markers. A current type 2 lineage of plasmids is derived from an early type 2 plasmid but the sequences of early type 1 plasmids include features not seen in more recent type 1 plasmids, indicating a shared ancestor rather than a direct lineal relationship. Some features, including ones essential for maintenance or for conjugation, have been examined experimentally.

Effect of electroconvulsive therapy on neural response to affective pictures: A randomized, sham-controlled fMRI study

Electroconvulsive therapy (ECT) is the most effective treatment for severe depression but its neurocognitive mechanisms are unclear. This randomized, sham-controlled functional magnetic resonance imaging (fMRI) study explored the effects of a single ECT on neural response to affective pictures. Twenty-seven patients with major depressive disorder were randomized to a single active ECT (N = 15) or sham (N = 12) session in a double-blind, parallel-group design. On the following day, patients underwent fMRI during which they viewed pleasant, unpleasant and neutral pictures and performed a free recall test after the scan. Mood symptoms were assessed before ECT/sham and at the time of fMRI. Subsequently, all patients continued active ECT as usual. Mood symptoms were reassessed after six active ECT sessions. A single ECT vs. sham session reduced neural response to unpleasant vs. pleasant pictures in the medial prefrontal cortex, a region showing greater response in the more depressed patients. This effect occurred in the absence of between-group differences in picture recall, mood symptoms or concomitant medication. In conclusion, modulation of medial prefrontal hyper-activity during encoding of negative affective information may be a common mechanism of distinct biological depression treatments.

Is negative self-referent bias an endophenotype for depression? An fMRI study of emotional self-referent words in twins at high vs. low risk of depression

BACKGROUND

Negative cognitive bias and aberrant neural processing of self-referent emotional words seem to be trait-marks of depression. However, it is unclear whether these neurocognitive changes are present in unaffected first-degree relatives and constitute an illness endophenotype.

METHODS

Fifty-three healthy, never-depressed monozygotic or dizygotic twins with a co-twin history of depression (high-risk group: n = 26) or no first-degree family history of depression (low-risk group: n = 27) underwent neurocognitive testing and functional magnetic imaging (fMRI) as part of a follow-up cohort study. Participants performed a self-referent emotional word categorisation task and free word recall task followed by a recognition task during fMRI. Participants also completed questionnaires assessing mood, personality traits and coping strategies.

RESULTS

High-risk and low-risk twins (age, mean ± SD: 40 ± 11) were well-balanced for demographic variables, mood, coping and neuroticism. High-risk twins showed lower accuracy during self-referent categorisation of emotional words independent of valence and more false recollections of negative words than low-risk twins during free recall. Functional MRI yielded no differences between high-risk and low-risk twins in retrieval-specific neural activity for positive or negative words or during the recognition of negative versus positive words within the hippocampus or prefrontal cortex.

CONCLUSIONS

The subtle display of negative recall bias is consistent with the hypothesis that self-referent negative memory bias is an endophenotype for depression. High-risk twins' lower categorisation accuracy adds to the evidence for valence-independent cognitive deficits in individuals at familial risk for depression.

Evolution in situ of ARI-A in pB2-1, a type 1 IncC plasmid recovered from Klebsiella pneumoniae, and stability of Tn4352B

The IncC plasmid pB2-1, from a Klebsiella pneumoniae isolate recovered in Brisbane prior to 1995, belongs to a subtype of type 1 IncC plasmids, here designated type 1a, that includes those carrying carbapenem resistance genes such as bla_NDM and bla_KPC. pB2-1 carries a 2358bp deletion in the rhs1 gene found in four other type 1a IncC plasmids. pB2-1 confers resistance to ampicillin, gentamicin, kanamycin, neomycin, tobramycin, sulfamethoxazole, tetracycline and trimethoprim. It transferred at a frequency of 4.7×10^-3 transconjugants per donor, similar to that of another type 1a plasmid pDGO100 but ten-fold lower than for its closest relative pRMH760. This difference may be due to a single amino acid substitution in TraL. pB2-1 has an ISEc52 insertion in the dsbC gene, demonstrating that dsbC is not essential for transfer. pB2-1 lacks the ARI-B insertion and hence the sul2 gene. The resistance genes sul1, dfrA10, aphA1a, bla_TEM, aadB, and tetA(B) are all in the ARI-A island, in a configuration that has evolved from ARI-A of pRMH760 in two steps. A 10.3kb segment extending from the catA1 gene to the end of pDUmer module was lost via homologous recombination between two copies of IS4321. In addition, a 5.3kb segment extending from IS1326 to the left end of Tn4352B was replaced with an 18.7kb tet(B)-containing segment bounded on one end by IS1 and on the other by IS26. The IS26-bounded transposon Tn4352B was shown to be stable in K. pneumoniae in contrast to the high instability observed in E. coli.

Differences in neural and cognitive response to emotional faces in middle-aged dizygotic twins at familial risk of depression

BACKGROUND

Negative bias and aberrant neural processing of emotional faces are trait-marks of depression but findings in healthy high-risk groups are conflicting.

METHODS

Healthy middle-aged dizygotic twins (N = 42) underwent functional magnetic resonance imaging (fMRI): 22 twins had a co-twin history of depression (high-risk) and 20 were without co-twin history of depression (low-risk). During fMRI, participants viewed fearful and happy faces while performing a gender discrimination task. After the scan, they were given a faces dot-probe task, a facial expression recognition task and questionnaires assessing mood, personality traits and coping.

RESULTS

Unexpectedly, high-risk twins showed reduced fear vigilance and lower recognition of fear and happiness relative to low-risk twins. During face processing in the scanner, high-risk twins displayed distinct negative functional coupling between the amygdala and ventral prefrontal cortex and pregenual anterior cingulate. This was accompanied by greater fear-specific fronto-temporal response and reduced fronto-occipital response to all emotional faces relative to baseline. The risk groups showed no differences in mood, subjective state or coping.

CONCLUSIONS

Less susceptibility to fearful faces and negative cortico-limbic coupling during emotional face processing may reflect neurocognitive compensatory mechanisms in middle-aged dizygotic twins who remain healthy despite their familial risk of depression.

pIP40a, a type 1 IncC plasmid from 1969 carries the integrative element GIsul2 and a novel class II mercury resistance transposon

The 167.5kb sequence of the conjugative IncC plasmid pIP40a, isolated from a Pseudomonas aeruginosa in 1969, was analysed. pIP40a confers resistance to kanamycin, neomycin, ampicillin, sulphonamides and mercuric ions, and several insertions in a type 1 IncC backbone were found, including copies of IS3, Tn1000 and a novel mercury resistance transposon, Tn6182. The antibiotic resistance genes were in two locations. Tn6023, containing the aphA1 kanamycin and neomycin resistance gene, is in a partial copy of Tn1/Tn2/Tn3 (bla_TEM, ampicillin resistance) in the kfrA gene, and the sul2 sulphonamide resistance gene is in the integrative element GIsul2 in the position of ARI-B islands. The 11.5kb class II transposon Tn6182 is only distantly related to other class II transposons, with at most 33% identity between the TnpA of Tn6182 and TnpA of other group members. In addition, the inverted repeats are 37bp rather than 38bp, and the likely resolution enzyme is a tyrosine recombinase (TnpI). Re-annotation of GIsul2 revealed genes predicted to confer resistance to arsenate and arsenite, but resistance was not detected. The location of GIsul2 confirms it as the progenitor of the ARI-B configurations seen in many IncC plasmids isolated more recently. However, GIsul2 has integrated at the same site in type 1 and type 2 IncC plasmids, indicating that it targets this site. Analysis of the distribution of GIsul2 revealed that it in addition to its chromosomal integration site at the 3'-end of the guaA gene, it has also integrated into other plasmids, increasing its mobility.

Associations between mood instability and emotional processing in a large cohort of bipolar patients

BACKGROUND

Aberrant emotional biases have been reported in bipolar disorder (BD), but results are inconsistent. Despite the clinical relevance of chronic mood variability in BD, there is no previous research investigating how the extent of symptom fluctuations in bipolar disorder might relate to emotional biases. This exploratory study investigated, in a large cohort of bipolar patients, whether instability in weekly mood episode symptoms and other clinical and demographic factors were related to emotional bias as measured in a simple laboratory task.

METHOD

Participants (N = 271, BDI = 206, BDII = 121) completed an 'emotional categorization and memory' task. Weekly self-reported symptoms of depression and mania were collected prospectively. In linear regression analyses, associations between cognitive bias and mood variability were explored together with the influence of demographic and clinical factors, including current medication.

RESULTS

Greater accuracy in the classification of negative words relative to positive words was associated with greater instability in depressive symptoms. Furthermore, greater negative bias in free recall was associated with higher instability in manic symptoms. Participants diagnosed with BDII, compared with BDI, showed overall better word recognition and recall. Current antipsychotic use was associated with reduced instability in manic symptoms but this did not impact on emotional processing performance.

CONCLUSIONS

Emotional processing biases in bipolar disorder are related to instability in mood. These findings prompt further investigation into the underpinnings as well as clinical significance of mood instability.

Effects of erythropoietin on memory-relevant neurocircuitry activity and recall in mood disorders

OBJECTIVE

Erythropoietin (EPO) improves verbal memory and reverses subfield hippocampal volume loss across depression and bipolar disorder (BD). This study aimed to investigate with functional magnetic resonance imaging (fMRI) whether these effects were accompanied by functional changes in memory-relevant neuro-circuits in this cohort.

METHOD

Eighty-four patients with treatment-resistant unipolar depression who were moderately depressed or BD in remission were randomized to eight weekly EPO (40 000 IU) or saline infusions in a double-blind, parallel-group design. Participants underwent whole-brain fMRI at 3T, mood ratings, and blood tests at baseline and week 14. During fMRI, participants performed a picture encoding task followed by postscan recall.

RESULTS

Sixty-two patients had complete data (EPO: N = 32, saline: N = 30). EPO improved picture recall and increased encoding-related activity in dorsolateral prefrontal cortex (dlPFC) and temporo-parietal regions, but not in hippocampus. Recall correlated with activity in the identified dlPFC and temporo-parietal regions at baseline, and change in recall correlated with activity change in these regions from baseline to follow-up across the entire cohort. The effects of EPO were not correlated with change in mood, red blood cells, blood pressure, or medication.

CONCLUSION

The findings highlight enhanced encoding-related dlPFC and temporo-parietal activity as key neuronal underpinnings of EPO-associated memory improvement.

pDGO100, a type 1 IncC plasmid from 1981 carrying ARI-A and a Tn1696-like transposon in a novel integrating element

Most A/C plasmids sequenced to date were recovered in the last two decades. To gain insight into the evolution of this group, the IncC plasmid pDGO100, found in a multiply antibiotic-resistant Escherichia coli strain isolated in 1981, was sequenced. pDGO100 belongs to the type 1 lineage and carries an ARI-A antibiotic resistance island but not an ARI-B island. The A/C2 backbone of pDGO100 has a deletion in the rhs1 gene previously found in pRMH760 and differs by only six single base pair substitutions from pRMH760, recovered at the same hospital 16years later. This confirms that the separation of type 1 and type 2 IncC plasmids is long standing. The ARI-A islands are also closely related, but pRMH760 contains Tn4352B in tniA of Tn402, while in pDGO100, Tn4352 has inserted into merA of pDUmer. pDGO100 also carries an additional 46kb insertion that includes a Tn1696-like transposon with the dfrB3 gene cassette. This insertion was identified as a novel integrating element, with an int gene at one end, and also includes the fec iron uptake operon that has been acquired from the E. coli chromosome. Related integrating elements carrying the same int gene were found in A/C2, IncHI1, and IncHI2 plasmids, and in the chromosomes of Enterobacter cloacae, Klebsiella oxytoca, and Cronobacter sakazakii isolates. In the Enterobacteriaceae chromosomes, these integrating elements appear to target a gene encoding a radical SAM superfamily protein. In the A/C2, IncHI1, and IncHI2 plasmids, genes encoding a phosphoadenosine phosphosulfate reductase were interrupted. The extremities of the integrating element are highly conserved, whilst the internal gene content varies. The detection of integrative elements in plasmids demonstrates an increased range of locations into which this type of mobile element can integrate and insertion in plasmids is likely to assist their spread.

Neural correlates of improved executive function following erythropoietin treatment in mood disorders

BACKGROUND

Cognitive dysfunction in depression and bipolar disorder (BD) is insufficiently targeted by available treatments. Erythropoietin (EPO) increases neuroplasticity and may improve cognition in mood disorders, but the neuronal mechanisms of these effects are unknown. This functional magnetic resonance imaging (fMRI) study investigated the effects of EPO on neural circuitry activity during working memory (WM) performance.

METHOD

Patients with treatment-resistant major depression, who were moderately depressed, or with BD in partial remission, were randomized to eight weekly infusions of EPO (40 000 IU) (N = 30) or saline (N = 26) in a double-blind, parallel-group design. Patients underwent fMRI, mood ratings and blood tests at baseline and week 14. During fMRI patients performed an n-back WM task.

RESULTS

EPO improved WM accuracy compared with saline (p = 0.045). Whole-brain analyses revealed that EPO increased WM load-related activity in the right superior frontal gyrus (SFG) compared with saline (p = 0.01). There was also enhanced WM load-related deactivation of the left hippocampus in EPO-treated compared to saline-treated patients (p = 0.03). Across the entire sample, baseline to follow-up changes in WM performance correlated positively with changes in WM-related SFG activity and negatively with hippocampal response (r = 0.28-0.30, p < 0.05). The effects of EPO were not associated with changes in mood or red blood cells (p ⩾0.08).

CONCLUSIONS

The present findings associate changes in WM-load related activity in the right SFG and left hippocampus with improved executive function in EPO-treated patients.

CLINICAL TRIAL REGISTRATION

clinicaltrials.gov: NCT00916552.

A randomised trial of hypertonic saline during hospitalisation for exacerbation of cystic fibrosis

BACKGROUND

The mucoactive effects of hypertonic saline should promote exacerbation resolution in people with cystic fibrosis (CF).

OBJECTIVES

To determine the effects of hypertonic saline inhalation during hospitalisation for exacerbation of CF on length of stay, lung function, symptoms, oxygenation, exercise tolerance, quality of life, bacterial load and time to next hospitalisation.

METHODS

132 adults with an exacerbation of CF were randomised to inhale three nebulised doses a day of either 4 mL 7% saline or a taste-masked control of 0.12% saline, throughout the hospital admission. The primary outcome measure was length of hospital stay.

RESULTS

All participants tolerated their allocated saline solution. There was no significant difference in length of stay, which was 12 days in the hypertonic saline group and 13 days in controls, with a mean between-group difference (MD) of 1 day (95% CI 0 to 2). The likelihood of regaining pre-exacerbation FEV1 by discharge was significantly higher in the hypertonic saline group (75% vs 57%), and the number needed to treat was 6 (95% CI 3 to 65). On a 0-100 scale, the hypertonic saline group had significantly greater reduction in symptom severity than the control group at discharge in sleep (MD=13, 95% CI 4 to 23), congestion (MD=10, 95% CI 3 to 18) and dyspnoea (MD=8, 95% CI 1 to 16). No significant difference in time to next hospitalisation for a pulmonary exacerbation was detected between groups (HR=0.86 (CI 0.57 to 1.30), p=0.13). Other outcomes did not significantly differ.

CONCLUSIONS

Addition of hypertonic saline to the management of a CF exacerbation did not reduce the length of hospital stay. Hypertonic saline speeds the resolution of exacerbation symptoms and allows patients to leave hospital with greater symptom resolution.

TRIAL REGISTRATION NUMBER

ACTRN12605000780651.

Effective emotion regulation strategies improve fMRI and ECG markers of psychopathology in panic disorder: implications for psychological treatment action

Impairments in emotion regulation are thought to have a key role in the pathogenesis of anxiety disorders, but the neurobiological underpinnings contributing to vulnerability remain poorly understood. It has been a long-held view that exaggerated fear is linked to hyperresponsivity of limbic brain areas and impaired recruitment of prefrontal control. However, increasing evidence suggests that prefrontal-cortical networks are hyperactive during threat processing in anxiety disorders. This study directly explored limbic-prefrontal neural response, connectivity and heart-rate variability (HRV) in patients with a severe anxiety disorder during incidental versus intentional emotion regulation. During 3 Tesla functional magnetic resonance imaging, 18 participants with panic disorder and 18 healthy controls performed an emotion regulation task. They either viewed negative images naturally (Maintain), or they were instructed to intentionally downregulate negative affect using previously taught strategies of cognitive reappraisal (Reappraisal). Electrocardiograms were recorded throughout to provide a functional measure of regulation and emotional processing. Compared with controls, patients showed increased neural activation in limbic-prefrontal areas and reduced HRV during incidental emotion regulation (Maintain). During intentional regulation (Reappraisal), group differences were significantly attenuated. These findings emphasize patients' ability to regulate negative affect if provided with adaptive strategies. They also bring prefrontal hyperactivation forward as a potential mechanism of psychopathology in anxiety disorders. Although these results challenge models proposing impaired allocation of prefrontal resources as a key characteristic of anxiety disorders, they are in line with more recent neurobiological frameworks suggesting that prefrontal hyperactivation might reflect increased utilisation of maladaptive regulation strategies quintessential for anxiety disorders.

Acute fluoxetine modulates emotional processing in young adult volunteers

BACKGROUND

Fluoxetine is generally regarded as the first-line pharmacological treatment for young people, as it is believed to show a more favourable benefit:risk ratio than other antidepressants. However, the mechanisms through which fluoxetine influences symptoms in youth have been little investigated. This study examined whether acute administration of fluoxetine in a sample of young healthy adults altered the processing of affective information, including positive, sad and anger cues.

METHOD

A total of 35 male and female volunteers aged between 18 and 21 years old were randomized to receive a single 20 mg dose of fluoxetine or placebo. At 6 h after administration, participants completed a facial expression recognition task, an emotion-potentiated startle task, an attentional dot-probe task and the Rapid Serial Visual Presentation. Subjective ratings of mood, anxiety and side effects were also taken pre- and post-fluoxetine/placebo administration.

RESULTS

Relative to placebo-treated participants, participants receiving fluoxetine were less accurate at identifying anger and sadness and did not show the emotion-potentiated startle effect. There were no overall significant effects of fluoxetine on subjective ratings of mood.

CONCLUSIONS

Fluoxetine can modulate emotional processing after a single dose in young adults. This pattern of effects suggests a potential cognitive mechanism for the greater benefit:risk ratio of fluoxetine in adolescent patients.

Different neural and cognitive response to emotional faces in healthy monozygotic twins at risk of depression

BACKGROUND

Negative cognitive bias and aberrant neural processing of emotional faces are trait-marks of depression. Yet it is unclear whether these changes constitute an endophenotype for depression and are also present in healthy individuals with hereditary risk for depression.

METHOD

Thirty healthy, never-depressed monozygotic (MZ) twins with a co-twin history of depression (high risk group: n = 13) or without co-twin history of depression (low-risk group: n = 17) were enrolled in a functional magnetic resonance imaging (fMRI) study. During fMRI, participants viewed fearful and happy faces while performing a gender discrimination task. After the scan, they were given a faces dot-probe task, a facial expression recognition task and questionnaires assessing mood, personality traits and coping strategies.

RESULTS

High-risk twins showed increased neural response to happy and fearful faces in dorsal anterior cingulate cortex (ACC), dorsomedial prefrontal cortex (dmPFC), pre-supplementary motor area and occipito-parietal regions compared to low-risk twins. They also displayed stronger negative coupling between amygdala and pregenual ACC, dmPFC and temporo-parietal regions during emotional face processing. These task-related changes in neural responses in high-risk twins were accompanied by impaired gender discrimination performance during face processing. They also displayed increased attention vigilance for fearful faces and were slower at recognizing facial expressions relative to low-risk controls. These effects occurred in the absence of differences between groups in mood, subjective state or coping.

CONCLUSIONS

Different neural response and functional connectivity within fronto-limbic and occipito-parietal regions during emotional face processing and enhanced fear vigilance may be key endophenotypes for depression.

A type 2 A/C2 plasmid carrying the aacC4 apramycin resistance gene and the erm(42) erythromycin resistance gene recovered from two Salmonella enterica serovars

OBJECTIVES

To determine the relationships between RepA/C2 plasmids carrying several antibiotic resistance genes found in isolates of Salmonella enterica serovars Ohio and Senftenberg from pigs.

METHODS

Illumina HiSeq was used to sequence seven S. enterica isolates. BLAST searches identified relevant A/C2 plasmid contigs and contigs were assembled using PCR.

RESULTS

Two serovar Ohio isolates were ST329 and the five Senftenberg isolates were ST210. The A/C2 plasmids recovered from the seven isolates belong to type 2 and contain two resistance islands. Their backbones are closely related, differing by five or fewer SNPs. The sul2-containing resistance island ARI-B is 19.9 kb and also contains the kanamycin and neomycin resistance gene aphA1, the tetracycline resistance gene tetA(D) and an erythromycin resistance gene, erm(42), not previously seen in A/C2 plasmids. A second 30.3 kb resistance island, RI-119, is in a unique location in the A/C2 backbone 8.2 kb downstream of rhs. RI-119 contained genes conferring resistance to apramycin, netilmicin and tobramycin (aacC4), hygromycin (hph), sulphonamides (sul1) and spectinomycin and streptomycin (aadA2). In one of the seven plasmids, this resistance region contained two IS26-mediated deletions. A discrete 5.7 kb segment containing the aacC4 and hph genes and bounded by IS26 on one side and the inverted repeat of Tn5393 on the other was identified.

CONCLUSIONS

The presence of almost identical A/C2 plasmids in two serovars indicates a common origin. Type 2 A/C2 plasmids continue to evolve via addition of new resistance regions such as RI-119 and evolution of existing ones.

Paradoxical effects of short-term antidepressant treatment in fMRI emotional processing models in volunteers with high neuroticism

BACKGROUND

Short-term antidepressant administration has been reported to decrease amygdala response to threat in healthy volunteers and depressed patients. Neuroticism (N) is a risk factor for depression but has also been associated with slow or incomplete remission with antidepressant drug treatment. Our aim was to investigate early selective serotonin reuptake inhibitor (SSRI) administration neural effects on implicit processing of fearful facial expressions in volunteers with high levels of N.

METHOD

Highly neurotic subjects received 20 mg/day citalopram versus placebo for 7 days in a double-blind, between-groups design. On the last day haemoperfusion and functional magnetic resonance imaging (fMRI) data during a gender discrimination task with fearful and happy faces were acquired. A control group of non-neurotic volunteers was also tested.

RESULTS

High-N volunteers had reduced responses to threatening facial expressions across key neural circuits compared to low-N volunteers. SSRI treatment was found to elevate resting perfusion in the right amygdala, increase bilateral amygdalae activation to positive and negative facial expressions and increase activation to fearful versus happy facial expressions in occipital, parietal, temporal and prefrontal cortical areas.

CONCLUSIONS

These results suggest that 7 days of SSRI administration can increase neural markers of fear reactivity in subjects at the high end of the N dimension and may be related to early increases in anxiety and agitation seen early in treatment. Such processes may be involved in the later therapeutic effects through decreased avoidance and increased learning about social 'threat' cues.

Antidepressant treatment and emotional processing: can we dissociate the roles of serotonin and noradrenaline?

The ability to match individual patients to tailored treatments has the potential to greatly improve outcomes for individuals suffering from major depression. In particular, while the vast majority of antidepressant treatments affect either serotonin or noradrenaline or a combination of these two neurotransmitters, it is not known whether there are particular patients or symptom profiles which respond preferentially to the potentiation of serotonin over noradrenaline or vice versa. Experimental medicine models suggest that the primary mode of action of these treatments may be to remediate negative biases in emotional processing. Such models may provide a useful framework for interrogating the specific actions of antidepressants. Here, we therefore review evidence from studies examining the effects of drugs which potentiate serotonin, noradrenaline or a combination of both neurotransmitters on emotional processing. These results suggest that antidepressants targeting serotonin and noradrenaline may have some specific actions on emotion and reward processing which could be used to improve tailoring of treatment or to understand the effects of dual-reuptake inhibition. Specifically, serotonin may be particularly important in alleviating distress symptoms, while noradrenaline may be especially relevant to anhedonia. The data reviewed here also suggest that noradrenergic-based treatments may have earlier effects on emotional memory that those which affect serotonin.

The effect of the serotonin transporter polymorphism (5-HTTLPR) on amygdala function: a meta-analysis

The 5-HTTLPR polymorphism has been widely regarded as a potential genetic risk factor for affective disorders. Consistent with this, this polymorphism has been associated with altered amygdala responses at rest and in response to aversive stimuli. However, the strength of this association remains uncertain. We sought to synthesize existing data on the association between the 5-HTTLPR polymorphism and amygdala activation and ascertain the strength of evidence for this association. Meta-analytic techniques were applied to data from relevant published studies and unpublished data sets to obtain an estimate of the likely magnitude of effect of any association. The large number of studies allowed us to apply a formal test of publication bias, as well as explore the impact of various study-level characteristics on the magnitude of the observed effect size. Our meta-analysis indicated that there is a statistically significant but small effect of 5-HTTLPR on left and right amygdala activity. However, there was considerable between-study heterogeneity, which could not be fully accounted for by the study design and sample characteristics that we investigated. In addition, there was evidence of excess statistical significance among published studies. These findings indicate that the association between the 5-HTTLPR and amygdala activation is smaller than originally thought, and that the majority of previous studies have been considerably under powered to reliably demonstrate an effect of this size.

Using an experimental medicine model to understand the antidepressant potential of the N-Methyl-D-aspartic acid (NMDA) receptor antagonist memantine

There is growing interest in the role of the glutamatergic system both in depression and as a novel target for treatments. Preclinical studies suggested that the non-competitive N-Methyl-D-aspartic acid (NMDA) receptor antagonist memantine might have antidepressant properties, but a randomised controlled trial failed to support this. A healthy volunteer model of emotional processing was used to assess the neuropsychological profile of action of memantine. Healthy volunteers (n=32) were randomised to receive a single dose of memantine (10 mg) or placebo, and subsequently completed a battery of tasks measuring emotional processing, including facial expression recognition, emotional memory, dot-probe and emotion-potentiated startle tasks, as well as working and verbal memory. Memantine treated volunteers showed an increased emotion-potentiated startle, and a reduced bias for negative items in emotional recognition memory. There were no effects of the drug on any other aspect of emotional or non-emotional information processing. These results suggest that a single dose of memantine produces an early anxiogenic response in the emotion-potentiated startle similar to that seen following a single dose of the selective serotonin reuptake inhibitor, citalopram. However, the overall profile of effects is more limited than that which might be expected in response to a conventional antidepressant.

Negative ion treatment increases positive emotional processing in seasonal affective disorder

BACKGROUND

Antidepressant drug treatments increase the processing of positive compared to negative affective information early in treatment. Such effects have been hypothesized to play a key role in the development of later therapeutic responses to treatment. However, it is unknown whether these effects are a common mechanism of action for different treatment modalities. High-density negative ion (HDNI) treatment is an environmental manipulation that has efficacy in randomized clinical trials in seasonal affective disorder (SAD).

METHOD

The current study investigated whether a single session of HDNI treatment could reverse negative affective biases seen in seasonal depression using a battery of emotional processing tasks in a double-blind, placebo-controlled randomized study.

RESULTS

Under placebo conditions, participants with seasonal mood disturbance showed reduced recognition of happy facial expressions, increased recognition memory for negative personality characteristics and increased vigilance to masked presentation of negative words in a dot-probe task compared to matched healthy controls. Negative ion treatment increased the recognition of positive compared to negative facial expression and improved vigilance to unmasked stimuli across participants with seasonal depression and healthy controls. Negative ion treatment also improved recognition memory for positive information in the SAD group alone. These effects were seen in the absence of changes in subjective state or mood.

CONCLUSIONS

These results are consistent with the hypothesis that early change in emotional processing may be an important mechanism for treatment action in depression and suggest that these effects are also apparent with negative ion treatment in seasonal depression.

Decreased heart rate variability during emotion regulation in subjects at risk for psychopathology

BACKGROUND

Dysfunctions in the regulation of emotional responses are related to poor psychological well-being and increased impact of cardiovascular disease. It has been suggested that the relationship between negative affect and higher morbidity could be mediated by a dysregulation of the autonomic nervous system (ANS), for example, of heart rate variability (HRV). Neuroticism is a personality trait associated with a maladaptive emotion regulation and also with alterations in ANS function. However, it is unknown whether subjects with high neuroticism present with specific biases in emotion regulation associated with reduced HRV.

METHOD

In total, 33 healthy subjects (n=13, highly neurotic) performed an emotion regulation task, during which they were instructed to either passively view negative pictures or attempt to down-regulate the affect elicited by the images. During the task an electrocardiogram was recorded and HRV was measured by calculation of the high frequency spectrum (HF-HRV).

RESULTS

A significant interaction between task condition and personality group was observed on HF-HRV measures (F 1,31=6.569, p=0.016). This was driven by subjects with low neuroticism presenting higher HF-HRV during down-regulation compared to passive exposure to negative stimuli, while subjects with high neuroticism reported an opposite tendency.

CONCLUSIONS

Our results show reduced HF-HRV during cognitive reappraisal of negative stimuli in high neuroticism and indicate a specific link between loss of flexibility in the parasympathetic cardiovascular tone and emotion regulation, consistent with previous work. Such findings support the importance of exploring the combination of ANS adaptability and emotional dysregulation in neuroticism as different facets of a common psychosomatic vulnerability factor.

Short-term antidepressant administration reduces negative self-referential processing in the medial prefrontal cortex in subjects at risk for depression

Depression has been associated with changes in responses within the medial prefrontal cortex (mPFC) during emotional information processing. Antidepressant drug treatment has been shown to modify neural responses in healthy volunteers early in treatment within similar circuitry. It is unclear, however, whether the same early effect occurs in depressed patients, before changes in mood. The current study therefore investigated the effects of 7-days administration of the selective serotonin-uptake inhibitor citalopram vs placebo in volunteers (n=29) at a high risk for the development of depression, using the personality phenotype of high neuroticism in a double-blind, between-groups design. On the last day of treatment, resting haemoperfusion and functional magnetic resonance imaging (MRI) data were acquired during a self-referential words categorisation task. A significant activation in a cluster of mPFC areas, including dorsal anterior cingulate and right orbitofrontal cortex was revealed, driven by decreased responses to the negative self-descriptors following citalopram compared with placebo, in the absence of any mood differences. These findings show a normalisation of neural abnormalities in- and at-risk population early in treatment, supporting the theory that antidepressants may indeed act by modifying specific neural dysfunctions correlated to negative cognitive biases.

Effects of low dose tryptophan depletion on emotional processing in dieters

Biased processing of ED-relevant stimuli (eg Fairburn, Shafran, & Cooper, 1999) and 5-HT function (Kaye, Fudge, & Paulus, 2009) are implicated in vulnerability to and the maintenance of eating disorders (EDs), but it is not known if these findings are connected: Could manipulating 5-HT function affect the processing of ED-relevant stimuli? To address this question we assessed emotional processing in female dieters (T+n=12, T-n=14) following acute low dose tryptophan depletion. ATD increased interference in the masked condition of the emotional Stroop to all negative emotional stimuli, in the absence of any other differences in emotional processing. These results suggest that ATD affects the processing of some negative (including ED-relevant) stimuli, and that reduced 5-HT function may be involved in some aspects of psychological vulnerability to EDs.

Neural response to angry and disgusted facial expressions in bulimia nervosa

BACKGROUND

Processing emotional facial expressions is of interest in eating disorders (EDs) as impairments in recognizing and understanding social cues might underlie the interpersonal difficulties experienced by these patients. Disgust and anger are of particular theoretical and clinical interest. The current study investigated the neural response to facial expressions of anger and disgust in bulimia nervosa (BN).

METHOD

Participants were 12 medication-free women with BN in an acute episode (mean age 24 years), and 16 age-, gender- and IQ-matched healthy volunteers (HVs). Functional magnetic resonance imaging (fMRI) was used to examine neural responses to angry and disgusted facial expressions.

RESULTS

Compared with HVs, patients with BN had a decreased neural response in the precuneus to facial expressions of both anger and disgust and a decreased neural response to angry facial expressions in the right amygdala.

CONCLUSIONS

The neural response to emotional facial expressions in BN differs from that found in HVs. The precuneus response may be consistent with the application of mentalization theory to EDs, and the amygdala response with relevant ED theory. The findings are preliminary, but novel, and require replication in a larger sample.

A cognitive neuropsychological model of antidepressant drug action

The psychological mechanisms by which antidepressant drugs act to improve mood remain underspecified. In this paper we consider the evidence to suggest that early changes in emotional processing underlie subsequent mood improvement following antidepressant treatment. Negative biases in information processing are consistently found in depression, and we argue that primary mode of action of antidepressant drugs may be to remediate these biases providing a more positive social environment in which the patient can relearn emotional associations fostering later improvement in mood. Evidence from behavioural and functional magnetic resonance imaging studies supports this hypothesis. Experimental medicine models developed under this premise have the potential to screen for new treatments, to predict individual treatment response and to consider the effects of pharmacological vs psychological treatments.