Direct immunofluorescence (DIF) techniques were compared with conventional cell culture for the diagnosis of ocular infections with Chlamydia trachomatis. The DIF test was found to have a sensitivity of 100% and a specificity of 97.5%. Of 178 patients studied, 19 patients (11%) were positive by DIF and 15 (8.4%) by conventional cell culture technique. Four patients who had previous treatment with chloramphenicol eye drops were negative by cell culture but positive by the DIF test. The DIF test is considered to be a rapid, accurate test with a number of advantages over culture techniques for the detection of C. trachomatis. The importance of appropriate referral of positive patients to prevent more serious sequelae due to C. trachomatis infection is discussed.

OBJECTIVE: To estimate the prevalence of Chlamydia trachomatis, C. psittaci and C. pneumoniae antibodies in sera from altogether 931 blood donors, patients with symptoms of urethritis, assumed salpingitis and sexually acquired reactive arthritis (SARA), and women with fertility problems. METHODS: IgG antibodies to C. trachomatis, C. psittaci and C. pneumoniae were determined by microimmunofluorescence (MIF) tests. All patients were also tested for genital C. trachomatis infection using direct immunofluorescence (DIF) tests. RESULTS: The DIF-positive cases had a significantly (p < 0.0001) higher prevalence of C. trachomatis antibodies than the DIF negatives, i.e. 88.5% versus 14% in men with urethritis, 94.3% versus 36.4% in women with salpingitis, 66.7% versus 16.7% in SARA patients and 90.6% versus 20.8% in women with fertility problems. Antibody reactivity to all three chlamydial species was found significantly (p < 0.0001) more often in the patient groups and in those with a DIF-confirmed genital C. trachomatis infection than in blood donors. CONCLUSIONS: Presence of serum antibodies to C. trachomatis is tightly associated with the presence of chlamydiae in the genital tract, which also influences the cross-reactivities occurring in the MIF tests between chlamydial species.

A new diagnostic tool for the identification of differential item functioning (DIF) is proposed. Classical approaches to DIF allow to consider only few subpopulations like ethnic groups when investigating if the solution of items depends on the membership to a subpopulation. We propose an explicit model for differential item functioning that includes a set of variables, containing metric as well as categorical components, as potential candidates for inducing DIF. The ability to include a set of covariates entails that the model contains a large number of parameters. Regularized estimators, in particular penalized maximum likelihood estimators, are used to solve the estimation problem and to identify the items that induce DIF. It is shown that the method is able to detect items with DIF. Simulations and two applications demonstrate the applicability of the method.

Dinucleotide frequency (DiF) and codon usage (cu) were analysed in gene sequences from four parasitic protozoa, Babesia bovis, Theileria parva, Toxoplasma gondii and Eimeria tenella, of the phylum Apicomplexa. In keeping with the 'genome hypothesis', cu was found to be non-random and species specific in these organisms, although cu among members of the same subclass was found to be very similar. Several low-usage (lu) codons were identified, and the usage of lu codons appears to be related to the taxonomic position of the organisms under study. A comparison of the observed/expected DiF ratios obtained from gene coding regions revealed a low frequency of the TA and CG dinucleotides in all organisms studied. A comparison of these DiF ratios with those found in rRNA-encoding genes and in introns, showed that in the parasites, B. bovis and Th. parva (representing the piroplasms), the low frequency of dinucleotides appeared to be the result of coding pressure alone. In T. gondii and E. tenella (representing the coccidia), however, coding pressure could not completely explain differences in DiF.

In the present study, the defense styles were assessed in alcohol-dependent patients to verify whether they used less adaptive defense mechanisms compared with healthy controls and to evaluate if immature defense styles (IDSs) are related with alexithymia, while controlling the effect of age, temperament, and character on this relationship in male alcohol-dependent inpatients. Participants were consecutively admitted 118 male alcohol-dependent inpatients and 60 healthy controls. Patients were investigated with the Defense Style Questionnaire, the Toronto Alexithymia Scale, and the Temperament and Character Inventory. The alcohol-dependent patients were using neurotic defense style, some IDSs (projection, acting out, splitting, and somatization) more, and the mature defense style humor less than the control group. Together with higher age, IDS discriminated alcohol dependents from the control group (higher age, acting out, and splitting and lower humor in the second regression model). Immature defense style was positively correlated with novelty seeking, harm avoidance, self-transcendence, difficulty in identifying feelings (DIF), difficulty in describing feelings, external oriented thinking, and total alexithymia score in the present study, whereas it was negatively correlated with self-directedness and cooperativeness. Mean scores of neurotic and IDS were higher in the alexithymic group than the nonalexithymic group, and alexithymia was correlated with some IDSs. Higher difficulty in describing feelings predicted mature defense style, higher harm avoidance and DIF predicted neurotic defense style, and lower cooperativeness and self-transcendence and higher DIF predicted IDS. These suggest that alcohol dependents are using maladaptive IDS more, which can be taken into account in the development of therapeutic programs for these patients. In addition, IDS seems to be related with alexithymia, particularly DIF factor, whereas low cooperativeness and high self-transcendence are significant covariants. Thus, these results could indicate the use of specific strategies in the clinical and psychotherapeutic management of patients with alexithymic feature and IDS.

BACKGROUND

Previous studies found that depression is associated with a broad impairment in quality of life (QOL). This finding might be associated to a measurement overlap.

METHODS

The objective of this study was to verify whether the items of the World Health Organization Quality of Life Instrument-Abbreviated version (WHOQOL-BREF), a measure of generic QOL, are invariant among patients having a current major depressive episode who come from primary care services. We investigated data from primary care services from the 6 countries (Australia, Brazil, Israel, Russia, Spain, and the United States) involved in the baseline sample of the Longitudinal Investigation of Depression Outcomes. The Rasch model was used to analyze items exhibiting differential item functioning (DIF) as a way of assessing invariance in relation to a depression factor defined by the diagnosis of depression using the Composite International Diagnostic Interview. In addition, the Center for Epidemiological Studies-Depression Scale (CES-D) score was correlated with the item and domain scores of the WHOQOL-BREF using the Pearson coefficient.

RESULTS

The sample consisted of 2359 subjects, of which 1193 had a confirmed diagnosis of a current major depressive episode. Of the 26 items of the WHOQOL-BREF, 11 showed DIF due to the depression factor, and the physical domain presented more items displaying DIF. All Pearson coefficients between the WHOQOL-BREF item and domain scores and the CES-D score were weak and moderate (r = -0.13 to r = 0.43).

CONCLUSIONS

Our findings indicate that most WHOQOL-BREF items do not exhibit DIF for a current major depressive episode and the variance associated with depression in this generic QOL measure is restricted to some facets of this construct. Thus, we recommend this restricted adjustment for depression in future analyses of this measure. Furthermore, our study indicates that researchers must measure QOL regardless of depression severity.

Many constructs are measured using multi-item data collection instruments. Differential item functioning (DIF) occurs when construct-irrelevant covariates interfere with the relationship between construct levels and item responses. DIF assessment is an active area of research, and several techniques are available to identify and account for DIF in cross-sectional settings. Many studies include data collected from individuals over time; yet appropriate methods for identifying and accounting for items with DIF in these settings are not widely available. We present an approach to this problem and apply it to longitudinal Modified Mini-Mental State Examination (3MS) data from English speakers in the Canadian Study of Health and Aging. We analyzed 3MS items for DIF with respect to sex, birth cohort and education. First, we focused on cross-sectional data from a subset of Canadian Study of Health and Aging participants who had complete data at all three data collection periods. We performed cross-sectional DIF analyses at each time point using an iterative hybrid ordinal logistic regression/item response theory (OLR/IRT) framework. We found that item-level findings differed at the three time points. We then developed and applied an approach to detecting and accounting for DIF using longitudinal data in which covariation within individuals over time is accounted for by clustering on person. We applied this approach to data for the "entire" dataset of English speaking participants including people who later dropped out or died. Accounting for longitudinal DIF modestly attenuated differences between groups defined by educational attainment. We conclude with a discussion of further directions for this line of research.

Studies of the site-specific recombinase Cre suggest a key role for interactions between the C-terminus of the protein and a region located about 30 residues from the C-terminus in linking in a cyclical manner the four recombinase monomers present in a recombination complex, and in controlling the catalytic activity of each monomer. By extrapolating the Cre DNA recombinase structure to the related site-specific recombinases XerC and XerD, it is predicted that the extreme C-termini of XerC and XerD interact with alpha-helix M in XerD and the equivalent region of XerC respectively. Consequently, XerC and XerD recombinases deleted for C-terminal residues, and mutated XerD proteins containing single amino acid substitutions in alphaM or in the C-terminal residues were analysed. Deletion of C-terminal residues of XerD has no measurable effect on co-operative interactions with XerC in DNA-binding assays to the recombination site dif, whereas deletion of 5 or 10 residues of XerC reduces co-operativity with XerD some 20-fold. Co-operative interactions between pairs of truncated proteins during dif DNA binding are reduced 20- to 30-fold. All of the XerD mutants, except one, were catalytically proficient in vitro; nevertheless, many failed to mediate a recombination reaction on supercoiled plasmid in vivo or in vitro, implying that the ability to form a productive recombination complex and/or mediate a controlled recombination reaction is impaired.

It has been discovered recently in experiments that the dendritic integration of excitatory glutamatergic inputs and inhibitory GABAergic inputs in hippocampus CA1 pyramidal neurons obeys a simple arithmetic rule as V(S)(Exp) ≈ V(E)(Exp) + V(I)(Exp) + kV(E)(Exp) V(I)(Exp), where V(S)(Exp), V(E)(Exp) and V(I)(Exp) are the respective voltage values of the summed somatic potential, the excitatory postsynaptic potential (EPSP) and the inhibitory postsynaptic potential measured at the time when the EPSP reaches its peak value. Moreover, the shunting coefficient k in this rule only depends on the spatial location but not the amplitude of the excitatory or inhibitory input on the dendrite. In this work, we address the theoretical issue of how much the above dendritic integration rule can be accounted for using subthreshold membrane potential dynamics in the soma as characterized by the conductance-based integrate-and-fire (I&F) model. Then, we propose a simple I&F neuron model that incorporates the spatial dependence of the shunting coefficient k by a phenomenological parametrization. Our analytical and numerical results show that this dendritic-integration-rule-based I&F (DIF) model is able to capture many experimental observations and it also yields predictions that can be used to verify the validity of the DIF model experimentally. In addition, the DIF model incorporates the dendritic integration effects dynamically and is applicable to more general situations than those in experiments in which excitatory and inhibitory inputs occur simultaneously in time. Finally, we generalize the DIF neuronal model to incorporate multiple inputs and obtain a similar dendritic integration rule that is consistent with the results obtained by using a realistic neuronal model with multiple compartments. This generalized DIF model can potentially be used to study network dynamics that may involve effects arising from dendritic integrations.

Variation of the equatorial diffraction spacing of soft type I collagen tissues with water content using X-rays has been known for many years. Recently, a generalized model for collagen molecule packing within fibrils was deduced from this information for different collagenous tissues. It is now known that the eq. diff. sp. of mineralized tissues can be less than for soft tissues and is inversely dependent on the wet density. A determination of the eq. dif. sp. dependence on water content using neutron diffraction of fully mineralized cow bone was undertaken for comparison. Specimens with various partial water content between 0 and 100% were tested. Data show collagen molecules pack more closely together as water content decreases, just as for soft tissues.

On the basis of our studies, we conclude that RA is a potent promoter of differentiation of EC cells. We have demonstrated that the tumorigenicity of PCC4-azalR EC cultures can be effectively reduced following exposure of the cells to RA. This is presumably a result of differentiation of the EC cells to nontumorigenic derivatives. However, even after several weeks of exposure to RA, there remains in the culture a subpopulation of unresponsive EC cells. The reason why these cells do not differentiate in the presence of RA is currently under investigation. We have also derived by mutagen treatment and clonal selection EC cells that fail to respond to RA. Preliminary indications are that these cells have lost the capacity to differentiate when subjected to other manipulations which stimulate differentiation of the parental EC cells. This is an important observation since the mutants were selected only by their lack of response to RA. Unlike the parental cells, which have relatively large amounts of RABP, dif- cells appear either to lack RABP or to possess an altered binding protein which has a greatly reduced affinity for RA. These observations are consistent with the view that some function of the RA-RABP complex is critical in the sequence of events leading to differentiation of EC cells. However, further studies are required before we can establish the generality of this proposal. We are presently investigating whether the level and/or function of RA-RABP complexes in cells from the EC lines listed in TABLE 1 can explain their varying tendencies to differentiate.

In Dictyostelium development, prestalk cells first differentiate at scattered positions in the aggregate and then sort out, probably by chemotaxis to cAMP. They may regulate their proportions by selective depletion of the stalk cell inducer, DIF-1. Once sorted, prestalk cells form a DIF-1 sink, which can produce gradients of DIF-1 and its metabolites in the slug. Global movements of cells in the slug may be regulated by cAMP signals, as in aggregation. Terminal differentiation of stalk and spore cells requires activation of cAMP-dependent protein kinase, possibly brought about by ammonia depletion. Finally, a technique for insertional mutagenesis promises the ready isolation of developmental genes.

The objective of this study was to analyse the different immunoreactants at the dermo-epidermal junction (DEJ) of patients with cutaneous lupus erythematosus (CLE). Sun-protected non lesional (SPNL) skin biopsies from 65 patients with specific cutaneous manifestations of LE and from 18 patients with other dermatologic diseases were tested using the direct immunofluorescence (DIF) technique. Nineteen out of 65 patients with CLE were affected by systemic LE (SLE). We used the conventional chi-squared test to analyse statistical differences between CLE-SLE and CLE-non-SLE groups in the immunological composition of lupus band test (LBT). C3 was the most common component while IgM were the most frequent immunoglobulins (Igs) of LBT in LE patients. No immunoreactants could be demonstrated at the DEJ in patients with other dermatologic diseases. No statistical differences could be found between CLE-SLE and CLE-non-SLE groups as regards the detection of the different immunoreactants at the DEJ. A positive LBT (even for the presence of only one immunoreactant at the DEJ) performed on SPNL skin represents a useful and specific criterion to distinguish patients with lupus erythematosus (LE) from those without LE. We also believe in a prognostic value of a positive LBT on SPNL skin when the deposition of at least two immunoreactants is demonstrated, and especially if the deposits are composed of IgG.

We evaluated the psychometric properties of the Cambridge Face Memory Test (CFMT; Duchaine & Nakayama, 2006). First, we assessed the dimensionality of the test with a bifactor exploratory factor analysis (EFA). This EFA analysis revealed a general factor and 3 specific factors clustered by targets of CFMT. However, the 3 specific factors appeared to be minor factors that can be ignored. Second, we fit a unidimensional item response model. This item response model showed that the CFMT items could discriminate individuals at different ability levels and covered a wide range of the ability continuum. We found the CFMT to be particularly precise for a wide range of ability levels. Third, we implemented item response theory (IRT) differential item functioning (DIF) analyses for each gender group and 2 age groups (age ≤ 20 vs. age>> 21). This DIF analysis suggested little evidence of consequential differential functioning on the CFMT for these groups, supporting the use of the test to compare older to younger, or male to female, individuals. Fourth, we tested for a gender difference on the latent facial recognition ability with an explanatory item response model. We found a significant but small gender difference on the latent ability for face recognition, which was higher for women than men by 0.184, at age mean 23.2, controlling for linear and quadratic age effects. Finally, we discuss the practical considerations of the use of total scores versus IRT scale scores in applications of the CFMT.

A patient with clinical findings of dermatitis herpetiformis (DH), negative direct immunofluorescent (DIF) findings for junctional IgA deposits in 2 biopsy specimens, and positive for IgA endomysial (AEmA) and tissue transglutaminase (tTG) antibodies responded initially to dapsone. After dapsone had to be discontinued because of side effects, a gluten-free diet and supportive therapy controlled the disease; the AEmA and tTG antibodies became negative. Our data on 10 consecutive DH cases examined by DIF and by serum studies for AEmA and antibodies to tTG, point to frequencies of 90% DIF positive and 70% AEmA and tTG positive cases. The use of both DIF and serum tests for AEmA and tTG reveals DH cases not detected by DIF alone that respond to gluten-free diet. Findings on autoantibodies to tTG, an enzyme that metabolizes gliadin, points to a role of tTG in the immunopathology of gluten-sensitive enteropathy and helps to explain the need for a gluten-free diet in the management of DH cases.

Knowledge is a prerequisite for promoting well-informed decision-making. Nevertheless, there is no validated and standardized test to assess the level of knowledge among renal patients regarding kidney disease and all treatment options. Therefore, the objective of this study was to investigate the psychometric properties of such a questionnaire for use in research and practice. A 30-item list was validated in four groups: (1) 187 patients on dialysis, (2) 82 patients who were undergoing living donor kidney transplantation the following day, (3) the general population of Dutch residents (n = 515) and (4) North American residents (n = 550). The psychometric properties of the questionnaire were examined using multidimensional item response theory (MIRT). Norm references were also calculated. Five items were found to distort ability estimates (Differential item functioning; DIF). MIRT analyses were subsequently carried out for the remaining 25 items. Almost all items showed good discrimination and difficulty parameters based on the fitted model. Two stable dimensions with 21 items were retrieved for which norm references for the Dutch and North American, dialysis and transplantation groups were calculated. This study resulted in a thorough questionnaire, the Rotterdam renal replacement knowledge-test, which enables reliable testing of patient's knowledge on kidney disease and treatment options in clinic and research.

This report summarizes and compares the results of complement fixation test (CFT), virus isolation (VI), and direct immunofluorescence test (DIF) for the antigen detection of respiratory syncytial virus (RSV), influenza A virus (Flu A), and adenovirus in 62 children with acute lower respiratory tract infections (ALRI) in Kuwait. It includes, as well, CFT results for parainfluenza virus and Mycoplasma pneumoniae. Combining the three methods, a potential causative agent was identified in 56 (90 per cent) children, of whom 14 (22 per cent) had evidence of infection with more than one pathogen. RSV was most frequently identified followed by Flu A, parainfluenza, Mycoplasma pneumoniae and adenovirus. Virus isolation proved the best method for identification of RSV, Flu A, and adenovirus [identified 52 (84 per cent) cases]. DIF was sensitive for RSV detection (sensitivity 84 per cent, specificity 94 per cent), and less sensitive for Flu A (sensitivity 62 per cent, specificity 98 per cent). However, DIF was completely insensitive to adenovirus (no positives). CFT was positive for the five pathogens in 44 (71 per cent) of the population studied; therefore, almost 20 per cent of positive identifications would have been missed if VI and DIF were not done. The sensitivity and specificity of CFT for RSV, adenovirus and Flu A were 71, 75, and 31 per cent, and 94, 96, and 94 per cent, respectively. Based on the results of this pilot study, it appears that a combination of the three tests yields the best rate of virus detection. Cell culture cannot be discarded for the identification of some respiratory viruses, especially adenovirus, until better techniques, or more sensitive reagents are applied. However, since RSV is the virus most commonly involved in children with ALRI, we recommend using DIF on routine basis for diagnosis. Its results compare well with virus isolation; it is simple, rapid, and inexpensive.

The differentiation-inducing factor-1 (DIF-1) is a signal molecule that induces stalk cell differentiation in the cellular slime mold Dictyostelium discoideum. In addition, DIF-1 is a potent antileukemic agent that induces growth arrest in K562 cells. In this study, we investigated the mechanism of action of DIF-1 in K562 cells in the light of cell-cycle regulators such as cyclins, retinoblastoma protein (pRb), and the mitogen-activated protein kinase (MAPK) family. DIF-1 down-regulated cyclins D/E and a phosphorylated form of pRb (p-pRb), and thereby induced G(1) arrest of the cell cycle. DIF-1 inactivated the extracellular signal-regulated kinase (ERK) in a biphasic manner but did not affect the c-Jun N-terminal kinase (JNK) or p38 MAPK. The MEK (MAPK kinase) inhibitor, U0126, which has been shown to induce growth arrest, inactivated ERK and down-regulated cyclins D and E. Although DIF-1 activated the phosphatidylinositol 3-kinase (PI-3K)/Akt pathway, neither wortmannin nor 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002; PI-3K inhibitors) cancelled DIF-1-induced growth arrest. The present results suggest that ERK inactivation may be involved in DIF-1-induced growth arrest and that PI-3K activity is not required for DIF-1-induced growth arrest in K562 cells.

Direct and indirect immunofluorescent studies (DIF, IIF) were performed on 24 pemphigus vulgaris patients who were in a state of clinical remission. The tests were repeated after an interval of 6 months. All the patients were on maintenance therapy with oral prednisone. The DIF in eight patients showed negative results among whom seven remained negative. Six patients out of 24 showed weakly positive fluorescence and ten patients showed strong positive fluorescence. The IIF was negative in 17 patients and positive in seven patients who also showed positive DIF. During a follow-up period of 20 months, one of eight patients with negative DIF relapsed compared with two of six patients with weak positive DIF and five of 10 patients with strong DIF. Five patients with strong DIF for IgG also had C3, of whom three relapsed, compared with five of 19 patients who were negative for C3. Four of seven patients with positive IIF relapsed compared with four of 17 with negative IIF. It is suggested that repeated DIF tests in pemphigus patients, who are in clinical remission, may serve as an indicator for the immunological activity and be of help in the management of these cases.

The dif site is located in the replication terminus region of bacterial chromosomes, having a function of resolving dimeric chromosomes formed during replication. We demonstrate that filamentous bacteriophages of vibrios, such as f237 (Vibrio parahaemolyticus) and CTXphi (V. cholerae), are integrated into the dif-like site of host chromosome.

OBJECTIVE

To evaluate the equivalence of the PROMIS® wave 1 physical functioning item bank, by age (50 years or older versus 18-49).

METHODS

A total of 114 physical functioning items with 5 response choices were administered to English- (n=1504) and Spanish-language (n=640) adults. Item frequencies, means and standard deviations, item-scale correlations, and internal consistency reliability were estimated. Differential Item Functioning (DIF) by age was evaluated.

RESULTS

Thirty of the 114 items were fagged for DIF based on an R-squared of 0.02 or above criterion. The expected total score was higher for those respondents who were 18-49 than those who were 50 or older.

CONCLUSIONS

Those who were 50 years or older versus 18-49 years old with the same level of physical functioning responded differently to 30 of the 114 items in the PROMIS® physical functioning item bank. This study yields essential information about the equivalence of the physical functioning items in older versus younger individuals.

BACKGROUND

Direct immunofluorescence (DIF) is a valuable tool in the diagnosis of cutaneous lupus erythematosus (LE). Our goal was to characterize the most frequent immune reactants in the skin biopsies of cutaneous LE and identify the most common immunofluorescence staining patterns.

METHODS

DIF results of immunoglobulin G (IgG), IgA, IgM, C3, and fibrinogen from 199 patients between 1989 and 1998 were retrospectively analyzed. Confirmatory clinical and serological diagnosis of LE subtype was available for 95 patients. Intensity of staining was ranked from 0 to 4+ but only included as significant if>>/=2+. Laboratory values were gathered and analyzed for all patients who had distinct granular immune deposition for Ig and/or complement.

RESULTS

The most commonly detected individual Ig was IgM in 149 (75%) specimens. IgM and C3 combination was the most common pair expressed with 98 (49%) specimens. The most common triplet was IgM, C3, and fibrinogen in 63 (32%) specimens. The most common quadruplet was the combination of IgG, IgM, C3, and fibrinogen in 42 (21%) specimens. All the five immunoreactants were detected in only 25 (13%) specimens. Systemic LE patients had a higher percent of abnormal laboratory values compared to discoid LE (DLE) and subacute LE (SCLE) patients (p = 0.02). Fibrinogen staining was found to be significantly higher in DLE patients and lowest in SCLE patients (p = 0.05).

CONCLUSIONS

This study demonstrates a marked predominance of IgM +/- C3 in cutaneous LE. When used in conjunction with other data, DIF is an extremely powerful tool in the routine evaluation of the LE patient. Our report emphasizes the importance of IgM expression in the diagnosis of LE by DIF and how positive staining with multiple conjugates can raise its sensitivity.

Plasma, urine, and skin drug concentrations were determined for dogs (n=12) given five daily oral doses of marbofloxacin (MAR) (2.75 mg/kg), enrofloxacin (ENR) (5.0 mg/kg) or difloxacin (DIF) (5.0 mg/kg). Concentrations of the active metabolite of ENR, ciprofloxacin (CIP), were also determined. The three-period, three-treatment crossover experimental design included a 21-day washout period between treatments. Area under the plasma drug concentration vs. time curve (AUC0-last, microg/mLxh of MAR was greater than for ENR, CIP, ENR/CIP combined, and DIF. Maximum concentration (Cmax) of MAR was greater than ENR, CIP, and DIF. Time of maximum plasma concentration (Tmax) was similar for MAR and DIF; Tmax occurred earlier for ENR and later for CIP. Plasma half-life (t1/2) of MAR was longer than for ENR, CIP, and DIF. Urine concentrations of DIF were less than MAR or ENR/CIP combined, but urine concentrations of MAR and ENR/CIP combined did not differ. DIF skin concentrations were less than the concentrations of MAR or ENR/CIP combined 2 h after dosing, but skin concentrations of MAR and ENR/CIP combined did not differ.

Circular chromosomes can form dimers during replication and failure to resolve those into monomers prevents chromosome segregation, which leads to cell death. Dimer resolution is catalysed by a highly conserved site-specific recombination system, called XerCD-dif in Escherichia coli. Recombination is activated by the DNA translocase FtsK, which is associated with the division septum, and is thought to contribute to the assembly of the XerCD-dif synapse. In our study, direct observation of the assembly of the XerCD-dif synapse, which had previously eluded other methods, was made possible by the use of Tethered Particle Motion, a single molecule approach. We show that XerC, XerD and two dif sites suffice for the assembly of XerCD-dif synapses in absence of FtsK, but lead to inactive XerCD-dif synapses. We also show that the presence of the γ domain of FtsK increases the rate of synapse formation and convert them into active synapses where recombination occurs. Our results represent the first direct observation of the formation of the XerCD-dif recombination synapse and its activation by FtsK.