Group B streptococcus infections of soft tissue and bone in California adults, 1995-2012

A group B Streptococcus indexed transposon mutant library to accelerate genetic research on an important perinatal pathogen

IMPORTANCE

Group B Streptococcus (GBS) is a significant global cause of serious infections, most of which affect pregnant women, newborns, and infants. Studying GBS genetic mutant strains is a valuable approach for learning more about how these infections are caused and is a key step toward developing more effective preventative and treatment strategies. In this resource report, we describe a newly created library of defined GBS genetic mutants, containing over 1,900 genetic variants, each with a unique disruption to its chromosome. An indexed library of this scale is unprecedented in the GBS field; it includes strains with mutations in hundreds of genes whose potential functions in human disease remain unknown. We have made this resource freely available to the broader research community through deposition in a publicly funded bacterial maintenance and distribution repository.

Nitric Oxide Production and Effects in Group B Streptococcus Chorioamnionitis

Intrauterine infection, or chorioamnionitis, due to group B Streptococcus (GBS) is a common cause of miscarriage and preterm birth. To cause chorioamnionitis, GBS must bypass maternal-fetal innate immune defenses including nitric oxide (NO), a microbicidal gas produced by nitric oxide synthases (NOS). This study examined placental NO production and its role in host-pathogen interactions in GBS chorioamnionitis. In a murine model of ascending GBS chorioamnionitis, placental NOS isoform expression quantified by RT-qPCR revealed a four-fold expression increase in inducible NOS, no significant change in expression of endothelial NOS, and decreased expression of neuronal NOS. These NOS expression results were recapitulated ex vivo in freshly collected human placental samples that were co-incubated with GBS. Immunohistochemistry of wild type C57BL/6 murine placentas with GBS chorioamnionitis demonstrated diffuse inducible NOS expression with high-expression foci in the junctional zone and areas of abscess. Pregnancy outcomes between wild type and inducible NOS-deficient mice did not differ significantly although wild type dams had a trend toward more frequent preterm delivery. We also identified possible molecular mechanisms that GBS uses to survive in a NO-rich environment. In vitro exposure of GBS to NO resulted in dose-dependent growth inhibition that varied by serovar. RNA-seq on two GBS strains with distinct NO resistance phenotypes revealed that both GBS strains shared several detoxification pathways that were differentially expressed during NO exposure. These results demonstrate that the placental immune response to GBS chorioamnionitis includes induced NO production and indicate that GBS activates conserved stress pathways in response to NO exposure.

Expanding the definition beyond surveillance criteria reveals a large burden of osteomyelitis caused by group B Streptococcus in the United States Veterans Health Administration

Background

Population-based surveillance studies may underestimate osteomyelitis caused by Group B Streptococcus (GBS). We analyzed cases of GBS osteomyelitis, including patients diagnosed using an expanded case definition that incorporates cultures from non-sterile sites, as well as cultures from normally sterile sites.

Methods

We retrospectively examined a cohort of veterans with the diagnosis of osteomyelitis between 2008 and 2017. Cases of definite GBS osteomyelitis required GBS isolation from normally sterile sites, (e.g., blood or bone). Cases of probable GBS osteomyelitis permitted GBS isolation from non-sterile sites (e.g., surgical sites, wounds). We compared comorbid conditions, lower extremity amputation and mortality rates in these groups.

Results

Among 1281 cases of GBS osteomyelitis, the median age was 63 years, 87% had diabetes mellitus and 37% had peripheral vascular disease. Similar characteristics were found in 768 (60%) cases classified as definite and 513 (40%) classified as probable GBS osteomyelitis. Polymicrobial infection was less frequent in patients with definite than with probable GBS osteomyelitis (45% vs. 85%; P < 0.001). Mortality rates within 1-year were similar for definite and probable GBS osteomyelitis (12% vs. 10%). Amputation within 1-year occurred in 21% of those with definite and 10% of those with probable GBS osteomyelitis of the lower extremity, with comparable rates in the subset with monomicrobial infection.

Conclusions

Expanding the definition of GBS osteomyelitis to include cases with cultures from non-sterile sites may be warranted, increasing the estimated burden of GBS osteomyelitis. This can help guide preventive efforts to reduce the impact of GBS osteomyelitis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07238-0.

Prevalence, population structure, distribution of serotypes, pilus islands and resistance genes among erythromycin-resistant colonizing and invasive Streptococcus agalactiae isolates recovered from pregnant and non-pregnant women in Isfahan, Iran

Background

The information on antibiotic resistance and molecular features of Group B Streptococcus (GBS) are essential for epidemiological purposes as well as vaccine development. Therefore, we aimed to assess the antimicrobial resistance profiles and molecular characteristics of GBS isolates in Isfahan, Iran. A total number of 72 colonizing and invasive GBS were collected from pregnant and non-pregnant women. The GBS isolates were analyzed for resistance profiles, capsular genotyping, and detection of PI-1, PI-2a, PI-2b, hvgA, ermB, ermTR, lnuB and, mefA genes. Besides, erythromycin-resistant strains were subjected to multilocus sequence typing (MLST).

Results

The prevalence of colonizing and invasive GBS were 11 and 0.05%, respectively. The frequency of capsular serotypes was as follows: III (26.3%), Ia (20.83%), Ib and V (each 15.2%), IV (9.7%), II (8.3%), VII (2.7%), and VI (1.3%). Overall frequencies of PIs were as follows: PI-1, 37.5%, PI-1 + PI-2a, 30.5%, PI-1 + PI-2b, 29.1% and PI-2b, 2.7%. Two maternal colonizing GBS (2.6%) were hvgA positive and were belonged to ST-17/CPS-III/PI-1 + PI-2b lineage. Among 30(41.6%) erythromycin resistant GBS, 21 isolates (70%) harbored ermB gene, followed by ermTR (23.3%) and mefA (10%). One clindamycin-resistant isolate harbored the lnuB gene. MLST analysis revealed the following five clonal complexes (CCs) and nine STs: (CC-19/ST-335, ST-19, and ST-197), (CC-12/ST-43, ST-12), (CC-23/ST-163, ST-23), (CC-17/ST-17) and (CC-4/ST-16).

Conclusion

The study shows an alarmingly high prevalence of erythromycin-resistant GBS in Iran. In addition, we report dissemination of ST-335/CPS-III clone associated with tetracycline and erythromycin resistance in our region. The distribution of capsular and pilus genotypes varies between invasive and colonizing GBS that could be helpful for vaccine development.

Genome-Wide fitness analysis of group B Streptococcus in human amniotic fluid reveals a transcription factor that controls multiple virulence traits

Streptococcus agalactiae (group B Streptococcus; GBS) remains a dominant cause of serious neonatal infections. One aspect of GBS that renders it particularly virulent during the perinatal period is its ability to invade the chorioamniotic membranes and persist in amniotic fluid, which is nutritionally deplete and rich in fetal immunologic factors such as antimicrobial peptides. We used next-generation sequencing of transposon-genome junctions (Tn-seq) to identify five GBS genes that promote survival in the presence of human amniotic fluid. We confirmed our Tn-seq findings using a novel CRISPR inhibition (CRISPRi) gene expression knockdown system. This analysis showed that one gene, which encodes a GntR-class transcription factor that we named MrvR, conferred a significant fitness benefit to GBS in amniotic fluid. We generated an isogenic targeted deletion of the mrvR gene, which had a growth defect in amniotic fluid relative to the wild type parent strain. The mrvR deletion strain also showed a significant biofilm defect in vitro. Subsequent in vivo studies showed that while the mutant was able to cause persistent murine vaginal colonization, pregnant mice colonized with the mrvR deletion strain did not develop preterm labor despite consistent GBS invasion of the uterus and the fetoplacental units. In contrast, pregnant mice colonized with wild type GBS consistently deliver prematurely. In a sepsis model the mrvR deletion strain showed significantly decreased lethality. In order to better understand the mechanism by which this newly identified transcription factor controls GBS virulence, we performed RNA-seq on wild type and mrvR deletion GBS strains, which revealed that the transcription factor affects expression of a wide range of genes across the GBS chromosome. Nucleotide biosynthesis and salvage pathways were highly represented among the set of differentially expressed genes, suggesting that MrvR may be involved in regulating nucleotide availability.

Group B Streptococcus (GBS) is a species of Gram-positive bacteria that often colonizes the healthy adult intestinal and reproductive tracts without causing serious symptoms. During pregnancy, however, GBS can invade the pregnant uterus, where it can cause infection of the placenta, fetal membranes, and fetus—a condition known as chorioamnionitis. Chorioamnionitis is associated with serious adverse pregnancy outcomes, including stillbirth, preterm labor, and severe infection of the newborn. GBS can survive in human amniotic fluid, which is low in bacterial nutrients and contains immune molecules that limit microbial persistence, and this ability likely contributes to GBS chorioamnionitis. This study is focused on a single GBS gene that encodes a genetic regulator we called MrvR, which we show is important for GBS resistance to human amniotic fluid. Using a series of genetic techniques combined with animal models of GBS colonization and infection, we show that MrvR also plays a key role in allowing GBS to invade the bloodstream and trigger the inflammatory responses that lead to preterm labor and stillbirth. The study concludes with a survey of other GBS genes whose activity is regulated by MrvR, which seems to be an important contributor to GBS virulence.

Invasive Bacterial Infections in Subjects with Genetic and Acquired Susceptibility and Impacts on Recommendations for Vaccination: A Narrative Review

The WHO recently endorsed an ambitious plan, “Defeating Meningitis by 2030”, that aims to control/eradicate invasive bacterial infection epidemics by 2030. Vaccination is one of the pillars of this road map, with the goal to reduce the number of cases and deaths due to Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae and Streptococcus agalactiae. The risk of developing invasive bacterial infections (IBI) due to these bacterial species includes genetic and acquired factors that favor repeated and/or severe invasive infections. We searched the PubMed database to identify host risk factors that increase the susceptibility to these bacterial species. Here, we describe a number of inherited and acquired risk factors associated with increased susceptibility to invasive bacterial infections. The burden of these factors is expected to increase due to the anticipated decrease in cases in the general population upon the implementation of vaccination strategies. Therefore, detection and exploration of these patients are important as vaccination may differ among subjects with these risk factors and specific strategies for vaccination are required. The aim of this narrative review is to provide information about these factors as well as their impact on vaccination against the four bacterial species. Awareness of risk factors for IBI may facilitate early recognition and treatment of the disease. Preventive measures including vaccination, when available, in individuals with increased risk for IBI may prevent and reduce the number of cases.

A Case Report of Cerebral Meningitis Caused by Penicillin-Non-Susceptible Group B Streptococcus in an Immunocompromised Adult Patient

Streptococcus agalactiae, also known as Group B Streptococcus (GBS), is the leading cause of bacteremia and meningitis in neonates; however, it also causes meningitis in adults, although much less frequently. After the detection of penicillin-non-susceptible GBS (PRGBS) for the first time in 2008 by Japanese researchers, clinical PRGBS isolates have been reported worldwide. These isolates need to be given due attention for being non-susceptible to multiple drugs. Herein, we present the first clinical report of meningitis caused by PRGBS. A 41-year-old Japanese male receiving an immunosuppressant visited hospital complaining of fever. Although he did not have meningitis-related symptoms or physical findings, determination of the cause of fever by Gram-staining of the spinal fluid revealed gram-positive cocci in pairs and chains. Initially, he was hospitalized on the diagnosis of cerebral meningitis caused by Streptococcus pneumoniae. However, culture of the spinal fluid revealed the β-hemolytic colonies on blood agar. Biochemical testing and mass spectrometry revealed the isolated organism as GBS (serotype Ib). The minimum inhibitory concentration (MIC) of penicillin G for the isolated strain was 0.5 μg/mL, which is greater than the MIC criteria for “susceptibility” to penicillin G for beta-hemolytic streptococci according to Clinical and Laboratory Standards Institute standards. The isolated strain was also resistant to macrolide (MIC ≥ 8 μg/mL) and fluoroquinolone (MIC ≥ 8 μg/mL). The patient recovered without neurologic sequelae upon treatment with ceftriaxone, vancomycin, and corticosteroids for 4 days, and subsequently with ampicillin for 17 days. The rate of isolation of PRGBS in the clinics has gradually increased, particularly in Japan. Although PRGBS isolated in the present case was susceptible to ampicillin and cephalosporins, strains not susceptible to ampicillin, cefotaxime, and ceftriaxone have already been isolated, indicating the prospects for limited range of effective antibiotics against PRGBS infections, including meningitis, in the near future.

Burden of Adults Hospitalized with Group B Streptococcal Infection

Background

The burden of noninvasive group B Streptococcus (GBS) infections in adults is unknown. We determined population-based rates of hospitalization where invasive or noninvasive GBS infections were identified among US adults in a defined catchment area.

Methods

We identified adults with clinical and laboratory-confirmed evidence of GBS infection from January 2014 through December 2016 from 6 hospitals in Louisville, Kentucky. Invasive disease was defined as GBS isolated from a normally sterile site.

Results

Among 1076 adults with GBS infection, the median age was 52 years, 51% were male, and 89% had ≥1 chronic medical condition. The most prevalent infection sites were skin and soft tissue (39%), urinary tract (23%), bone and joint (16%), and bloodstream (11%). Forty percent of infections were polymicrobial. The annual incidence of GBS-associated hospitalization was 73 per 100 000 adults and 68 and 100 per 100 000 for patients aged 18–64 and ≥ 65 years, respectively. For every invasive GBS infection, 3.7 noninvasive infections occurred.

Conclusions

Our population-based study outlines the full burden of GBS-associated hospitalization in adults and found incidence rates comparable to those of pneumococcal disease, where vaccines are recommended. Noninvasive disease was 3–4 times more common than invasive disease, suggesting that the GBS burden among adults is considerably greater than previously recognized.

Epidemiology of Invasive Group B Streptococcal Infections Among Nonpregnant Adults in the United States, 2008-2016

Importance

Group B Streptococcus (GBS) is an important cause of invasive bacterial disease. Previous studies have shown a substantial and increasing burden of GBS infections among nonpregnant adults, particularly older adults and those with underlying medical conditions.

Objective

To update trends of invasive GBS disease among US adults using population-based surveillance data.

Design, Setting, and Participants

In this population-based surveillance study, a case was defined as isolation of GBS from a sterile site between January 1, 2008, and December 31, 2016. Demographic and clinical data were abstracted from medical records. Rates were calculated using US Census data. Antimicrobial susceptibility testing and serotyping were performed on a subset of isolates. Case patients were residents of 1 of 10 catchment areas of the Active Bacterial Core surveillance (ABCs) network, representing approximately 11.5% of the US adult population. Patients were included in the study if they were nonpregnant, were 18 years or older, were residents of an ABCs catchment site, and had a positive GBS culture from a normally sterile body site.

Main Outcomes and Measures

Trends in GBS cases overall and by demographic characteristics (sex, age, and race), underlying clinical conditions of patients, and isolate characteristics are described.

Results

The ABCs network detected 21 250 patients with invasive GBS among nonpregnant adults from 2008 through 2016. The GBS incidence in this population increased from 8.1 cases per 100 000 population in 2008 to 10.9 in 2016 (P = .002 for trend). There were 3146 cases reported in 2016 (59% male; median age, 64 years; age range, 18-103 years). The GBS incidence was higher among men than women and among blacks than whites and increased with age. Projected to the US population, an estimated 27 729 cases of invasive disease and 1541 deaths occurred in the United States in 2016. Ninety-five percent of cases in 2016 occurred in someone with at least 1 underlying condition, most commonly obesity (53.9%) and diabetes (53.4%). Resistance to clindamycin increased from 37.0% of isolates in 2011 to 43.2% in 2016 (P = .02). Serotypes Ia, Ib, II, III, and V accounted for 86.4% of isolates in 2016; serotype IV increased from 4.7% in 2008 to 11.3% in 2016 (P < .001 for trend).

Conclusions and Relevance

The public health burden of invasive GBS disease among nonpregnant adults is substantial and continues to increase. Chronic diseases, such as obesity and diabetes, may contribute.

A Counterselectable Sucrose Sensitivity Marker Permits Efficient and Flexible Mutagenesis in Streptococcus agalactiae

Streptococcus agalactiae (group B Streptococcus [GBS]) is a cause of severe infections, particularly during the newborn period. While methods exist for generating chromosomal mutations in GBS, they are cumbersome and inefficient and present significant challenges if the goal is to study subtle mutations, such as single-base-pair polymorphisms. To address this problem, we have developed an efficient and flexible GBS mutagenesis protocol based on sucrose counterselection against levansucrase (SacB) expressed from a temperature-selective shuttle vector. GBS containing the SacB expression cassette demonstrates lethal sensitivity to supplemental sucrose whether the plasmid DNA is replicating outside of the chromosome or has been integrated during a crossover event. Transmission electron microscopy shows that SacB-mediated lethal sucrose sensitivity results from the accumulation of inclusion bodies that eventually lead to complete degradation of normal cellular architecture and subsequent lysis. We used this new mutagenesis technique to generate an in-frame, allelic exchange knockout of the GBS sortase gene srtA, demonstrating that >99% of colonies that emerge from our protocol had the expected knockout phenotype and that among a subset tested by sequencing, 100% had the correct genotype. We also generated barcoded nonsense mutations in the cylE gene in two GBS strains, showing that the approach can be used to make small, precise chromosomal mutations.IMPORTANCE The ability to generate chromosomal mutations is fundamental to microbiology. Historically, however, GBS pathogenesis research has been made challenging by the relative genetic intractability of the organism. Generating a single knockout in GBS using traditional techniques can take many months, with highly variable success rates. Furthermore, traditional methods do not offer a straightforward way to generate single-base-pair polymorphisms or other subtle changes, especially to noncoding regions of the chromosome. We have developed a new sucrose counterselection-based method that permits rapid, efficient, and flexible GBS mutagenesis. Our technique requires no additional equipment beyond what is needed for traditional approaches. We believe that it will catalyze rapid advances in GBS genetics research by significantly easing the path to generating mutants.

A comparison of Streptococcus agalactiae septic arthritis and non-Streptococcus agalactiae septic arthritis

INTRODUCTION

Streptococcus agalactiae (Group B Streptococcus, GBS) is an uncommon cause of septic arthritis in the adult population. In recent years, there has been an increase in the incidence of GBS septic arthritis. This study aims to compare the clinical presentation, investigations, microbiology and outcome of management in patients with GBS and non-GBS septic arthritis.

METHODS

Retrospective review of hospital surgical records was done to identify all patients treated surgically at our institution from January 2011 to January 2016 for primary septic arthritis. Patients were categorised into two groups: those with culture-proven GBS septic arthritis and those with causative pathogens that were not GBS. Patients who were medically unfit for surgical intervention as well as those who declined interventional procedures were excluded from the study.

RESULTS

A total of 83 patients were included in the study: 62 (74.7%) had non-GBS septic arthritis and 21 (25.3%) had GBS septic arthritis. Patients with GBS septic arthritis were more likely to have polyarticular involvement (p < 0.001) and involvement of less common sites such as the elbow joint. They were also more likely to have elevated inflammatory markers (C-reactive protein > 150 mg/L; p = 0.017) and positive blood cultures (p = 0.02), and were typically healthy adults with no medical comorbidities (p = 0.012).

CONCLUSION

Patients with GBS septic arthritis were more likely to present with polyarticular involvement, positive blood cultures and higher levels of C-reactive protein on admission, and tended to be healthier individuals with no medical comorbidities.

Intrinsic Maturational Neonatal Immune Deficiencies and Susceptibility to Group B Streptococcus Infection

Although a normal member of the gastrointestinal and vaginal microbiota, group B Streptococcus (GBS) can also occasionally be the cause of highly invasive neonatal disease and is an emerging pathogen in both elderly and immunocompromised adults. Neonatal GBS infections are typically transmitted from mother to baby either in utero or during passage through the birth canal and can lead to pneumonia, sepsis, and meningitis within the first few months of life. Compared to the adult immune system, the neonatal immune system has a number of deficiencies, making neonates more susceptible to infection. Recognition of GBS by the host immune system triggers an inflammatory response to clear the pathogen. However, GBS has developed several mechanisms to evade the host immune response. A comprehensive understanding of this interplay between GBS and the host immune system will aid in the development of new preventative measures and therapeutics.

Examining the association of MMP-1 gene -1607 (2G/1G) and -519 (A/G) polymorphisms with the risk of osteomyelitis: A case-control study

To investigate the effects of matrix metalloproteinase-1 (MMP-1) gene polymorphisms on the onset of osteomyelitis in Chinese Han population.In all, 80 osteomyelitis patients (case group) and 81 healthy people (control group) were recruited into this case-control study. Polymerase chain reaction-restriction fragment length polymorphism method was utilized to examine the genotypes of MMP-1 polymorphisms (-1607 2G/1G and -519A/G) in the 2 groups. Genotype and allele differences between the case and control groups were analyzed by chi-square test. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated to present the association strength between MMP-1 gene polymorphisms and osteomyelitis.Frequencies of -1607 2G/2G genotype between the case and control groups were statistically significant (P = .025). Compared with 1G/1G genotype carriers, the 2G/2G genotype carriers had 1.605 times risk of developing osteomyelitis (OR 2.605, 95% CI 1.116-6.082). Meanwhile, the 2G allele significantly associated with the risk of osteomyelitis (OR 1.735, 95% CI 1.115-2.701). In addition, frequency of -519GG genotype was obviously higher in case group than that in control group (P = .024), and GG genotype related to an increased risk of osteomyelitis (OR 2.792, 95% CI 1.127-6.917). Whereas, the -519G allele may be a susceptible factor for osteomyelitis (OR 1.622, 95% CI 1.038-2.536).The MMP-1 -1607 (2G/1G) and -519 (A/G) polymorphisms may contribute to the onset of osteomyelitis.

A preliminary in vitro evaluation of the bioactive potential of cryogel scaffolds incorporated with Manuka honey for the treatment of chronic bone infections

Previous studies have identified honey as an agent in bacterial inhibition and a mediator in lowering the pH at the wound site. Manuka honey (MH), indigenous to New Zealand, contains a Unique Manuka Factor that provides an additional antibacterial agent. While there are many potential benefits to incorporating MH into wounds, there is currently no ideal way to deliver the material to the site of injury. Cryogels are a type of scaffold that possess high porosity, mechanical stability, and a sponge-like consistency. This study uniquely incorporates varying amounts of MH into cryogel scaffolds, utilizing its properties in a sustained release fashion to assist in the overall healing process, while using the cryogel structure as a tissue template. All cryogels were evaluated to determine the effects of MH on porosity, swelling potential, mechanical durability, and cell compatibility. The release of MH was also quantified to evaluate bacterial clearance potential, and the scaffolds were mineralized to replicate native bone. It was determined that a 5% MH silk fibroin cryogel has the potential to inhibit bacterial growth while still maintaining adequate porosity, mechanical properties, and cell infiltration. Such a scaffold would have use in a number of applications, including bone regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1918-1933, 2018.

A case of infected schwannoma mimicking malignant tumor

BACKGROUND

Infected schwannoma has been reported, this being one of the four cases published in the literature. Infected schwannoma has proven to be a tough diagnostic challenge to the treating tumor surgeon, mimicking infectious entities and most essentially, a malignant tumor.

CASE PRESENTATION

The authors report the case of a 64-year-old male with a soft tissue mass in his right gluteal area that presented initially with right leg pain, then later with signs of inflammation on the tumor area. Magnetic resonance imaging (MRI), computed tomography (CT), and thallium-201 scintigraphy studies confirm the presence of soft tissue mass which had continuity with sciatic nerve, with subsequent serial MRI findings suggesting tumor enlargement with cystic degeneration. Increased level of C-reactive protein (CRP) was observed before surgery. During an open biopsy upon tissue sampling, exudates with necrotic tissue were seen. Increased level of CRP and necrotic change suggested the possibility of malignant tumor. Histopathological diagnosis was schwannoma, and group B Streptococcus was detected by culture. After the confirmation of infected schwannoma, enucleation of the tumor was performed.

CONCLUSIONS

The report concludes that establishment of a benign pathology is essential when presented with similar clinical findings prior to definitive enucleation of an infected schwannoma.

Temporal trends of β-haemolytic streptococcal osteoarticular infections in western Norway

BACKGROUND

Beta-haemolytic streptococci are important contributors to the global burden of osteoarticular infections (OAI). Knowledge on the disease traits specific for streptococcal OAI, however, remains scarce. We wished to explore temporal trends of OAI caused by Group A Streptococci (GAS), Group B Streptococci (GBS) and Group C and G Streptococci (GCGS), and furthermore, to describe the associated host and pathogen characteristics.

METHODS

All cases of microbiologically verified β-haemolytic streptococcal OAI in Health Region Bergen, Norway, in the period 1999-2013 were retrospectively identified. Clinical data were extracted from medical records. Microbial isolates were submitted to antibiotic susceptibility testing and molecular typing.

RESULTS

A total of 24 GAS, 45 GBS and 42 GCGS acute OAI were identified. The cumulative incidence of GCGS OAI, but not GAS or GBS OAI, increased significantly from the first to the last 5-year period (IRR 5.7, p = 0.0003), with the annual incidence peaking at 1.9/100 000 in 2013. GAS OAI generally produced the most acute and severe clinical presentation, whereas GBS and GCGS predominantly affected the elderly, and were significantly associated with the presence of host risk factors of systemic and focal origin, respectively.

CONCLUSIONS

We found a significantly increasing incidence of GCGS OAI, likely related to the presence of host susceptibility factors, including prosthetic material and pre-existing joint disease. With an increasing application of therapeutic and diagnostic bone and joint procedures, the rising trend of OAI caused by GCGS is likely to continue. Sustained epidemiological attentiveness to GCGS seems warranted.

The essential genome of Streptococcus agalactiae

BACKGROUND

Next-generation sequencing of transposon-genome junctions from a saturated bacterial mutant library (Tn-seq) is a powerful tool that permits genome-wide determination of the contribution of genes to fitness of the organism under a wide range of experimental conditions. We report development, testing, and results from a Tn-seq system for use in Streptococcus agalactiae (group B Streptococcus; GBS), an important cause of neonatal sepsis.

METHODS

Our method uses a Himar1 mini-transposon that inserts at genomic TA dinucleotide sites, delivered to GBS on a temperature-sensitive plasmid that is subsequently cured from the bacterial population. In order to establish the GBS essential genome, we performed Tn-seq on DNA collected from three independent mutant libraries-with at least 135,000 mutants per library-at serial 24 h time points after outgrowth in rich media.

RESULTS

After statistical analysis of transposon insertion density and distribution, we identified 13.5 % of genes as essential and 1.2 % as critical, with high levels of reproducibility. Essential and critical genes are enriched for fundamental cellular housekeeping functions, such as acyl-tRNA biosynthesis, nucleotide metabolism, and glycolysis. We further validated our system by comparing fitness assignments of homologous genes in GBS and a close bacterial relative, Streptococcus pyogenes, which demonstrated 93 % concordance. Finally, we used our fitness assignments to identify signal transduction pathway components predicted to be essential or critical in GBS.

CONCLUSIONS

We believe that our baseline fitness assignments will be a valuable tool for GBS researchers and that our system has the potential to reveal key pathogenesis gene networks and potential therapeutic/preventative targets.