High Prevalence and High Rate of Antibiotic Resistance of Mycoplasma genitalium Infections in Men Who Have Sex With Men: A Substudy of the ANRS IPERGAY Pre-exposure Prophylaxis Trial.

BACKGROUND: Mycoplasma genitalium (MG) is an emerging pathogen among men who have sex with men (MSM) with raising rates of antibiotic resistance. This study assessed the prevalence and incidence of MG infection in MSM enrolled in the open-label phase of the ANRS IPERGAY trial with on-demand tenofovir disoproxil fumarate/emtricitabine for human immunodeficiency virus prevention and the impact of doxycycline post-exposure prophylaxis (PEP). METHODS: 210 subjects were tested at baseline and at 6 months by real-time PCR assays for MG detection in urine samples and oropharyngeal and anal swabs. Resistance to azithromycin (AZM), to fluoroquinolones (FQs), and to doxycycline was investigated in the French National Reference Center of Bacterial Sexually Transmitted Infections (STIs). RESULTS: The all-site prevalence of MG at baseline was 10.5% (6.3% in urine samples, 4.3% in anal swabs, 0.5% in throat swabs) and remained unchanged at 6 months whether or not PEP was used: 9.9% overall, 10.2% with PEP, 9.6% without. The overall rate of MG resistance (prevalent and incident cases) to AZM and FQs was 67.6% and 9.1%, respectively, with no difference between arms. An in vivo mutation of the MG 16S rRNA, which could be associated with tetracycline resistance, was observed in 12.5% of specimens tested. CONCLUSIONS: The prevalence of MG infection among MSM on pre-exposure prophylaxis was high and its incidence was not decreased by doxycycline prophylaxis with a similar high rate of AZM and FQ resistance, raising challenging issues for the treatment of this STI and supporting current recommendations to avoid testing or treatment of asymptomatic MG infection.

Faecal calprotectin and gut microbiota do not predict enteropathy in very preterm infants.

AIM: Very preterm birth is associated with a high risk of enteropathies. Diagnosis is challenging, especially in mild forms, leading to unnecessary periods of cessation of enteral feeding. This study aimed at establishing a prognosis score of enteropathy combining clinical parameters and faecal calprotectin concentration. METHODS: This prospective multicentric study included preterm neonates born at a gestational age of 33 weeks or less. Stools were collected weekly until hospital discharge, and daily in case of digestive events for calprotectin measurement (ELISA and immunochromatography) and microbiota analyses (16S rRNA gene sequencing). RESULTS: Among the 121 neonates included, 21 experienced at least one episode of enteropathy, mainly mild forms. By ELISA testing, median faecal calprotectin was 88 (8-798) µg/g faeces. No statistically significant association was found between the outset of enteropathy and maternal and neonatal characteristics, and calprotectin levels. The agreement between ELISA and immunochromatography assay was moderate (intra-class correlation coefficient 0.58, 95%CI [0.47-0.66]). Comparison of species diversity and relative bacterial abundance profiles between infants with or without enteropathy revealed no specific alterations associated with enteropathy. CONCLUSION: The study failed to propose a prognostic score of enteropathy, probably due the large inter- and intra-individual variability of faecal calprotectin in very preterm neonates.

Folliculitis decalvans is characterized by a persistent, abnormal subepidermal microbiota.

Folliculitis decalvans (FD) is a chronic inflammatory disease of unknown aetiology. Although Staphylococcus aureus, frequently found on lesional skin, is thought to play a causal role, the importance of its involvement remains controversial. To examine the role of S aureus, we compared superficial and subepidermal microbiota in 20 FD patients who had S aureus on lesional skin and in 20 healthy controls using culture techniques and genomic identification, before and after an anti-staphylococcal treatment; we also screened for S aureus virulence factors. When present on lesional skin, S aureus colonized non-lesional and subepidermal skin in 80% of cases. These data imply a break in the epidermal barrier integrity and that an abnormal non-lesional skin microbiota persists in FD. S aureus had no superantigenic toxin in 31% of cases and no toxin specificity. Clinical improvement obtained in most cases upon treatment was associated with the disappearance of S aureus in all studied areas, with an incomplete restoration of normal microbiota and a significant increase in negative bacterial samples. This persistent unbalanced, subepidermal microbiota may act as a reservoir of abnormal flora and explain the chronicity of FD, suggesting new avenues of research to restore normal microbiota.

Variable spectrum of disease and risk factors of peripartum Clostridium difficile infection: report of 14 cases from French hospitals and literature review.

Our aim was to study Clostridium difficile infection (CDI) in peripartum women in France and compare them to cases published in the literature. We characterize these infections regarding clinico-biological features and specific risk factors in order to raise awareness for obstetricians and midwifes. Eight antepartum and six post-partum CDI cases were retrospectively studied in 6 French centers during the period between 2008 and 2013. In addition, 59 literature cases were reviewed. Cases were identified with CDI clinical symptoms associated to characteristic imagery or detection of C. difficile toxins. The key risk factors of CDI (antibiotherapy, hospitalization) and other risk factors (cesarean section, obstetric complications, corticotherapy, and underlying disease) were retrospectively collected. Most of the cases were exposed to at least one key risk factor of CDI: previous exposure to antibiotics and/or hospitalization. The post-partum cases often had cesarean section: 67% (4/6) in French cases and 89% (31/35) in literature cases. Metronidazole was the most used antibiotic. Relapses occurred in two French cases and in nine published cases. Two French cases and 15 literature cases were reported to have complications (pseudomembranous colitis, toxic megacolon, death…). Diverse C. difficile PCR ribotypes were involved, but the BI/NAP1/027 strain was not detected in the French case series contrary to the literature cases. The delay for diagnosis CDI could be long and peripartum CDI could be severe. In case of unexplained diarrhea in pregnant women, clinicians need to consider CDI and ask for research of C. difficile and its toxins in stool.

Preterm infants with necrotising enterocolitis demonstrate an unbalanced gut microbiota.

AIM: This Lebanese study tested the hypothesis that differences would exist in the gut microbiota of preterm infants with and without necrotising enterocolitis (NEC), as reported in Western countries. METHODS: This study compared 11 infants with NEC and 11 controls, all born at 27-35 weeks, in three neonatal intensive care units between January 2013 and March 2015. Faecal samples were collected at key time points, and microbiota was analysed by culture, quantitative PCR (qPCR) and temperature temporal gel electrophoresis (TTGE). RESULTS: The cultures revealed that all preterm infants were poorly colonised and harboured no more than seven species. Prior to NEC diagnosis, significant differences were observed by qPCR with a higher colonisation by staphylococci (p = 0.034) and lower colonisations by enterococci (p = 0.039) and lactobacilli (p = 0.048) in the NEC group compared to the healthy controls. Throughout the study, virtually all of the infants were colonised by Enterobacteriaceae at high levels. TTGE analysis revealed no particular clusterisation, showing high interindividual variability. CONCLUSION: The NEC infants were poorly colonised with no more than seven species, and the controls had a more diversified and balanced gut microbiota. Understanding NEC aetiology better could lead to more effective prophylactic interventions and a reduced incidence.

Establishment and development of the intestinal microbiota of preterm infants in a Lebanese tertiary hospital.

The establishment and development of the intestinal microbiota is known to be associated with profound short- and long-term effects on the health of full-term infants (FTI), but studies are just starting for preterm infants (PTI). The data also mostly come from western countries and little information is available for the Middle East. Here, we determined the composition and dynamics of the intestinal microbiota during the first month of life for PTI (n = 66) and FTI (n = 17) in Lebanon. Fecal samples were collected weekly and analyzed by quantitative PCR (q-PCR) and temporal temperature gradient gel electrophoresis (TTGE). We observed differences in the establishment and composition of the intestinal microbiota between the two groups. q-PCR showed that PTI were more highly colonized by Staphylococcus than FTI in the first three weeks of life; whereas FTI were more highly colonized by Clostridium clusters I and XI. At one month of life, PTI were mainly colonized by facultative anaerobes and a few strict anaerobes, such as Clostridium cluster I and Bifidobacterium. The type of feeding and antibiotic treatments significantly affected intestinal colonization. TTGE revealed low species diversity in both groups and high inter-individual variability in PTI. Our findings show that PTI had altered intestinal colonization with a higher occurrence of potential pathogens (Enterobacter, Clostridium sp) than FTI. This suggests the need for intervention strategies for PTI to modulate their intestinal microbiota and promote their health.

Clostridium difficile carriage in healthy infants in the community: a potential reservoir for pathogenic strains.

BACKGROUND: Clostridium difficile has long been considered to be a nosocomial pathogen but has emerged in the community in recent years. During infancy, asymptomatic C. difficile colonization is common. However, knowledge of colonization determinants and strain characteristics is limited. We studied the dynamics of C. difficile colonization in healthy infants from the community. Determinants of colonization and strain genotypes were also determined in a cohort of infants attending day nurseries. METHODS: A 1-year follow-up study involving 10 healthy infants was performed to determine the incidence and kinetics of intestinal C. difficile colonization. In addition, a 1-point study involving 85 healthy infants (age, 0-3 years) from 2 day nurseries was performed. C. difficile isolates were typed by polymerase chain reaction-ribotyping and analyzed for the presence of toxin genes. RESULTS: During the follow-up study, all infants acquired C. difficile and were colonized for several months. An early (neonatal) and a late (4-6 months of age) acquisition period were identified. In day nurseries, 38 infants (45%) carried C. difficile, with 11 (13%) carrying a toxigenic isolate. Age and several environmental factors were associated with the C. difficile carrier state. Strains causing disease in adults were identified in infants. Interestingly, no infant carried the common epidemic 027 or 078 strains. CONCLUSIONS: This study provides information on the dynamics of colonization in infants in the community and on the genotype of involved strains. C. difficile colonization appears mainly as an age-dependent process. Pathogenic strains circulate in asymptomatic infants from the community, who represent a potential reservoir of pathogenic strains.

Clostridium difficile colonization in early infancy is accompanied by changes in intestinal microbiota composition.

Clostridium difficile is a major enteric pathogen responsible for antibiotic-associated diarrhea. Host susceptibility to C. difficile infections results partly from inability of the intestinal microbiota to resist C. difficile colonization. During early infancy, asymptomatic colonization by C. difficile is common and the intestinal microbiota shows low complexity. Thus, we investigated the potential relationship between the microbiota composition and the implantation of C. difficile in infant gut. Fecal samples from 53 infants, ages 0 to 13 months, 27 negative and 26 positive for C. difficile, were studied. Dominant microbiota profiles were assessed by PCR-temporal temperature gradient gel electrophoresis (TTGE). Bacterial signatures of the intestinal microbiota associated with colonization by C. difficile were deciphered using principal component analysis (PCA). Resulting bands of interest in TTGE profiles were excised, sequenced, and analyzed by nucleotide BLAST (NCBI). While global biodiversity was not affected, interclass PCA on instrumental variables highlighted significant differences in dominant bacterial species between C. difficile-colonized and noncolonized infants (P = 0.017). Four bands were specifically associated with the presence or absence of C. difficile: 16S rRNA gene sequences related to Ruminococcus gnavus and Klebsiella pneumoniae for colonized infants and to Bifidobacterium longum for noncolonized infants. We demonstrated that the presence of C. difficile in the intestinal microbiota of infants was associated with changes in this ecosystem's composition. These results suggest that the composition of the gut microbiota might be crucial in the colonization process, although the chronology of events remains to be determined.

Functional and phylogenetic alterations in gut microbiome are linked to graft-versus-host disease severity.

Acute graft-versus-host disease (aGVHD) is the main complication of hematopoietic stem cell transplantation (HSCT). Changes in gut microbiota composition have been associated with subsequent aGVHD, and reconstitution of healthy microbiota is currently being explored as a therapeutic approach. However, the specific actors in the intestinal ecosystem involved in the pathologic process at the time of aGVHD onset are not yet fully known. We prospectively collected stool samples from patients who underwent allogeneic HSCT. Patients sampled at aGVHD onset were compared with non-GVHD patients. To identify phylogenetic and functional signatures of the disease process, we determined fecal short-chain fatty acid (SFCA) profiles and used high-throughput DNA sequencing and real-time quantitative polymerase chain reaction to assess the microbiota composition. Microbiota alterations were highly specific of gastrointestinal (GI) aGVHD severity. Bacterial biomass and α-diversity were lower in severe aGVHD. We identified several bacterial signatures associated with severe aGVHD at disease onset; a negative correlation was observed with anaerobic bacteria of the Lachnospiraceae, especially the Blautia genus, and Ruminococcaceae families. In parallel, in severe aGVHD patients, we showed a dramatic decrease in the levels of the main SFCAs: acetate (75.8%), propionate (95.8%), and butyrate (94.6%). Mild aGVHD patients were characterized by conserved levels of propionate and Blautia propionate producers. Butyrate was significantly decreased in all GI aGVHD stages, representing a potential diagnostic marker of the disease. Specific microbiota and metabolic alterations were thus associated with aGVHD severity and may be useful for diagnostic and pathophysiologic purposes.

Assessment of Neonatal Intensive Care Unit Practices and Preterm Newborn Gut Microbiota and 2-Year Neurodevelopmental Outcomes.

Importance: In very preterm newborns, gut microbiota is highly variable with major dysbiosis. Its association with short-term health is widely studied, but the association with long-term outcomes remains unknown. Objective: To investigate in preterm newborns the associations among practice strategies in neonatal intensive care units (NICUs), gut microbiota, and outcomes at 2 years. Design, Setting, and Participants: EPIFLORE is a prospective observational cohort study that includes a stool sample collection during the fourth week after birth. Preterm newborns of less than 32 weeks of gestational age (GA) born in 2011 were included from 24 NICUs as part of the French nationwide population-based cohort, EPIPAGE 2. Data were collected from May 2011 to December 2011 and analyzed from September 2016 to December 2018. Exposures: Eight NICU strategies concerning sedation, ventilation, skin-to-skin practice, antibiotherapy, ductus arteriosus, and breastfeeding were assessed. A NICU was considered favorable to a practice if the percentage of that practice in the NICU was more than the expected percentage. Main Outcomes and Measures: Gut microbiota was analyzed by 16S ribosomal RNA gene sequencing and characterized by a clustering-based method. The 2-year outcome was defined by death or neurodevelopmental delay using a Global Ages and Stages questionnaire score. Results: Of 577 newborns included in the study, the mean (SD) GA was 28.3 (2.0) weeks, and 303 (52.5%) were male. Collected gut microbiota was grouped into 5 discrete clusters. A sixth cluster included nonamplifiable samples owing to low bacterial load. Cluster 4 (driven by Enterococcus [n = 63]), cluster 5 (driven by Staphylococcus [n = 52]), and cluster 6 (n = 93) were significantly associated with lower mean (SD) GA (26.7 [1.8] weeks and 26.8 [1.9] weeks, respectively) and cluster 3 (driven by Escherichia/Shigella [n = 61]) with higher mean (SD) GA (29.4 [1.6] weeks; P = .001). Cluster 3 was considered the reference. After adjustment for confounders, no assisted ventilation at day 1 was associated with a decreased risk of belonging to cluster 5 or cluster 6 (adjusted odds ratio [AOR], 0.21 [95% CI, 0.06-0.78] and 0.19 [95% CI, 0.06-0.62], respectively) when sedation (AOR, 10.55 [95% CI, 2.28-48.87] and 4.62 [1.32-16.18], respectively) and low volume of enteral nutrition (AOR, 10.48 [95% CI, 2.48-44.29] and 7.28 [95% CI, 2.03-26.18], respectively) was associated with an increased risk. Skin-to-skin practice was associated with a decreased risk of being in cluster 5 (AOR, 0.14 [95% CI, 0.04-0.48]). Moreover, clusters 4, 5, 6 were significantly associated with 2-year nonoptimal outcome (AOR, 6.17 [95% CI, 1.46-26.0]; AOR, 4.53 [95% CI, 1.02-20.1]; and AOR, 5.42 [95% CI, 1.36-21.6], respectively). Conclusions and Relevance: Gut microbiota of very preterm newborns at week 4 is associated with NICU practices and 2-year outcomes. Microbiota could be a noninvasive biomarker of immaturity.

Incidence, risk factors and outcome of multi-drug resistant Acinetobacter baumannii nosocomial infections during an outbreak in a burn unit.

BACKGROUND: Multidrug-Resistant Acinetobacter baumannii (MR-AB) can cause outbreaks in burn units. We aimed to study the incidence, risk factors and outcome of MR-AB infections in a burn unit (BU). METHODS: A prospective study was conducted from April to November, 2014 during an outbreak in a BU in Paris. Weekly surveillance cultures were performed to determine MR-AB colonization. MR-AB nosocomial infections, discharge or death without MR-AB infection were considered as competing events. To identify risk factors for MR-AB infection, baseline characteristics and time-dependent variables were investigated in univariate analyses using Cox models. RESULTS: Eighty-six patients admissions were analyzed during the study period. Among them, 15 (17%) acquired MR-AB nosocomial infection. Median time to infection was 22days (interquartile range: 10-26 days). Cumulative incidence of MR-AB infections was 15% at 28days (95% CI=8-24). Risk factors for MR-AB infection in univariate analysis were SAPS II (Hazard Ratio (HR):1.08; 95% CI:1.05-1.12; P<0.0001) and ABSI (Abbreviated Burn Severity Index) scores (HR:1.32; 95% CI:1.12-1.56; P=0.001), MR-AB colonization (HR:10.2; 95%CI:2.05-50.3; P=0.004), invasive procedures (ventilation, arterial and/or venous catheter) (P=0.0001) and ≥2 skin grafts (HR:10.2; 95% CI:1.76-59.6; P=0.010). MR-AB infection was associated with an increased risk of death (HR: 7.11; 95%CI: 1.52-33.2; P=0.013) and longer hospital stay with a median estimated increase of 10days (IQR: 6; 14). CONCLUSIONS: Incidence of MR-AB nosocomial infection was high during this outbreak, and was associated with prolonged hospitalization and increased risk of death. High patient severity scores, prior MR-AB colonization, invasive procedures and repeated skin grafts were associated with an increased risk of nosocomial infection.

Impact of an Acinetobacter baumannii outbreak on kidney events in a burn unit: A targeted machine learning analysis.

BACKGROUND: Multidrug-resistant (MDR) bacteria outbreaks represent a major threat in intensive care units. Patients may then be exposed to drug-related direct toxicity during such outbreaks. The objective of this study was to explore the impact of an outbreak of imipenem-resistant Acinetobacter baumannii (IR-AB) on renal outcomes. METHODS: We performed a before-and-after observational study in a French burn intensive care unit during an IR-AB outbreak: a 13-month period before (period A, October 2013-October 2014) and a 13-month period after outbreak control (period B, December 2014-December 2015). A total of 409 patients were included, 195 during period A and 214 during period B. The main endpoint was major adverse kidney events at day 90 (MAKE 90). Secondary endpoints were acute kidney injury (AKI) and persistent renal dysfunction. RESULTS: Incidence of MAKE 90 was 15.9% during period A versus 11.2% during period B (P = .166) and AKI 28.2% versus 18.7% (P = .023). The use of colistin was associated with renal outcomes in univariate analysis. After adjustment of potential confounding factors using a targeted Machine Learning Analysis (ie, IR-AB-related infection, septic shock, severity scores, other nephrotoxics, chronic kidney disease, serum creatinine at admission, Staphylococcus aureus), colistin remained associated with the risk of MAKE and AKI (relative risk = 2.909, 95% confidence interval [CI] [1.364, 6.204], P = .006 for MAKE 90, and relative risk = 2.14, 95% CI [1.52, 3.02], P<.0001 for AKI). CONCLUSIONS: The episode of IR-AB outbreak was associated with an increased risk of kidney events, which appears to be driven by the use of colistin.

The eukaryotic gut virome in hematopoietic stem cell transplantation: new clues in enteric graft-versus-host disease.

Much attention has been focused on the role of the bacterial microbiome in human health, but the virome is understudied. Although previously investigated in individuals with inflammatory bowel diseases or solid-organ transplants, virome dynamics in allogeneic hematopoietic stem cell transplantation (HSCT) and enteric graft-versus-host disease (GVHD) remain unexplored. Here we characterize the longitudinal gut virome in 44 recipients of HSCT using metagenomics. A viral 'bloom' was identified, and significant increases were demonstrated in the overall proportion of vertebrate viral sequences following transplantation (P = 0.02). Increases in both the rates of detection (P < 0.0001) and number of sequences (P = 0.047) of persistent DNA viruses (anelloviruses, herpesviruses, papillomaviruses and polyomaviruses) over time were observed in individuals with enteric GVHD relative to those without, a finding accompanied by a reduced phage richness (P = 0.01). Picobirnaviruses were detected in 18 individuals (40.9%), more frequently before or within a week after transplant than at later time points (P = 0.008). In a time-dependent Cox proportional-hazards model, picobirnaviruses were predictive of the occurrence of severe enteric GVHD (hazard ratio, 2.66; 95% confidence interval (CI) = 1.46-4.86; P = 0.001), and correlated with higher fecal levels of two GVHD severity markers, calprotectin and α1-antitrypsin. These results reveal a progressive expansion of vertebrate viral infections over time following HSCT, and they suggest an unexpected association of picobirnaviruses with early post-transplant GVHD.

First case of chancroid in 14 years at the largest STI clinic in Paris, France.

We report the first case of chancroid seen at our clinic in 14 years. It was diagnosed by nuclear acid amplification test in a male patient returning from Madagascar. Although the disease is considered on the verge of disappearance even in tropical countries, its real potential for reemergence - due to new strains of Haemophilus ducreyi, underreporting and a lack of widespread use of molecular testing - could be underestimated.

Comparison of commercial molecular assays for toxigenic Clostridium difficile detection in stools: BD GeneOhm Cdiff, XPert C. difficile and illumigene C. difficile.

Three commercial molecular assays were evaluated for toxigenic Clostridium difficile detection in stools. As compared to toxigenic culture, BD GeneOhm Cdiff (BD Diagnostics), XPert C. difficile (Cepheid) and illumigene C. difficile (Meridian Bioscience) demonstrated respectively a sensitivity of 95.5%, 97.8% and 86.7% and a specificity of 97.9%, 97.9% and 100%.

Prevalence and diversity of Clostridium difficile strains in infants.

During early infancy asymptomatic intestinal colonization by Clostridium difficile is frequent. To update information on infant colonization prevalence and to characterize infant strains, in terms of their virulence factors and their phylogenetic diversity, a prospective screening of C. difficile in the stools of infants 0 to 2 years old was conducted at Jean Verdier Hospital (Hôpital Jean Verdier) over an 18 month period. C. difficile was screened by toxigenic culture, and molecular characterization was performed by PCR-ribotyping and multilocus sequence typing (MLST). The overall C. difficile colonization prevalence was 33.7 % (99/294). The colonization rate by a toxigenic strain was 7.1 % (21/294). Community-acquired C. difficile accounted for 66.7 % (66/99) of cases. Molecular typing was performed on 90 isolates from Jean Verdier Hospital and 8 additional isolates from another hospital in Versailles (Centre Hospitalier de Versailles). Among these isolates, 23 were toxigenic (21 tcdA(+)/tcdB(+) and 2 tcdA(-)/tcdB(+)). All the isolates were negative for the binary toxin genes. Seventeen PCR ribotypes (PRs) were identified, with five PRs accounting for 82.7 % (81/98) of the isolates. MLST generated 15 different sequence types (STs). The predominant genotype, PRJV11-ST38 (33.7 %), included only non-toxigenic strains. Toxigenic strains were distributed in eight genotypes. Neither PR027-ST3, nor PR078/126-ST49 were identified but some PRs/STs corresponded to well-known adult infectious strains. These results indicate that infants are widely colonized by non-toxigenic strains. However, toxigenic adult infectious strains circulate in asymptomatic infants even in the community; thus, infants may be a reservoir for adult infectious strains.

Identification of a novel transcriptional regulator involved in pilC1 regulation in Neisseria meningitidis.

Type IV pili are crucial for the virulence of Neisseria meningitidis. PilC proteins belong to the complex protein machinery required for pili biosynthesis. The expression of the pilC1 gene is known to be induced during host cell contact and to be tightly controlled through four promoters, two transcription factors and a two-component signal transduction system. By screening of an insertional-mutant library, we identified a novel regulatory protein, i.e. NMA1805, involved in the pilC1 complex regulation. Increased transcription of gene NMA1805 was shown to result in augmented expression of the pilC1 gene, whereas abrogated expression of gene NMA1805 was associated with an absence of pilC1 induction upon contact with host cells. Moreover, we demonstrated that the NMA1805 gene displayed two promoters. The NMA1805 regulatory protein was evidenced to interact with one of them.

A two-component system is required for colonization of host cells by meningococcus.

In order to adapt to changing environments, bacteria have evolved two-component systems (TCSs) that are able to sense and respond to environmental stimuli. The signal perception relies on a sensor protein whose activation allows rapid adaptation through transcriptional regulation achieved by the regulatory protein. The ability to adhere to and grow on the surface of human host cells is an absolute requirement for many pathogens, including Neisseria meningitidis, in order to colonize new hosts and to disseminate inside their host. Among the four TCSs encoded in the meningococcus genome, only the PhoQ (MisS)/PhoP (MisR) system has been shown to constitute a functional signal transduction circuit. To investigate the involvement of this TCS in the adaptation process requisite for host cell colonization, we have tested the ability to grow on host cells of a mutant inactivated for the sensor of the TCS. Our results demonstrate the involvement of the TCS in the adaptation of the meningococcus to growth on host cells. We show that the expression of the PhoQ (MisS)/PhoP (MisR) TCS is cell-contact controlled. Furthermore, this TCS controls the regulation of a group of genes, the REP2 regulon, previously shown to be cell-contact regulated and to encode functions crucial for the adaptation of the bacterium to host cell colonization. Thus, we provide evidence that one of the four TCSs existing in N. meningitidis contributes to the adaptation of the pathogen to growth on host cells.