Journal of Medical Microbiology - Current Issue

Clostridioides difficile (formerly known as Clostridium difficile) is a significant cause of healthcare-associated infection with symptoms ranging from diarrhoea and abdominal pain to pseudomembranous colitis and toxic megacolon. Severe disease can pose a significant morbidity and mortality risk and is to be considered a medical emergency. The emergence of a new C. difficile ribotype with an estimated mortality rate of 20% (ribotype 995) has prompted a re-review of the evidence and guidelines around managing severe C. difficile infections (CDI). International guidance on the management of CDI varies regarding first-line antibiotic choice. Metronidazole is no longer favoured as first line due to concerns around resistance, and vancomycin and fidaxomicin are now recommended as first line options. Antibiotic therapy should be used in conjunction with good supportive measures and early consideration of surgical management. Faecal microbiota transplant can be utilized in recurrent CDI and may be useful in severe disease. Severe CDI is a significant ongoing threat to public health, and further research into effective management is essential to ensure the best possible outcomes for patients.

Mycoplasma genitalium is characterized by a small genome and a lack of a cell wall, contributing to its unique biology. It is associated with reproductive tract infections, including non-gonococcal urethritis and pelvic inflammatory disease. It is nearly as common as chlamydia in most studies from high-income countries. The emergence of antimicrobial resistance in M. genitalium raises concern about the long-term efficacy of current therapeutic strategies. Understanding its genomic intricacies and pathogenic mechanisms is crucial for developing targeted interventions to address the growing public health impact of this elusive microbe.

Introduction. Infections caused by Mycobacterium abscessus, an environmentally prevalent, rapidly growing mycobacteria, are increasingly frequent in developed countries.

Objective. To analyse the drug susceptibility profiles of M. abscessus isolated in the state of São Paulo from 2008 to 2024.

Methods. Of the 2,402 M. abscessus isolates identified during those 17 years, 558 (23.2%) met the American Thoracic Society’s microbiologic and clinical criteria for drug susceptibility testing (DST), which was performed for five agents – clarithromycin, amikacin, cefoxitin, ciprofloxacin, and doxycycline.

Results. Clarithromycin showed a dramatic increase in resistance phenotype from ≤10% in the early period to 73–90% over the last 8 years. Over half those isolates demonstrated inducible resistance. Resistance to amikacin was found in fewer than 5% of isolates from 2016 to 2021. In 2022, that result increased to 13%, but for 2023 and 2024, it had fallen back to 2%. Over the past decade, cefoxitin DST has reported the majority of isolates as intermediate, a problematic result in M. abscessus group (MAG) infections, which typically require long-term treatment for successful outcomes. Since 2018, the annual susceptibility rate has been ≤18%, and in five of the 7 years, ≤7%. Ciprofloxacin was typically assessed as susceptible from 2009 to 2011, then decreased sharply to ≤20% over the next several years, and since 2018, the rate has been less than 5%. Through the entire study, doxycycline resistance has remained consistently high; in the years since 2018, ≤6% of isolates have been susceptible.

Conclusion. This study demonstrates wide variation among MAG clinical isolates in the frequency of susceptibility, both across different agents and within individual agents over time. These results emphasize the importance of performing high-quality DST on MAG clinical isolates and suggest the need to consider revising the standard panel of drugs tested.

Introduction. Accumulating evidence indicates a significant association between gut microbiota and the risk of developing pyogenic arthritis (PA). However, their causal relationship has yet to be elucidated.

Hypothesis. The gut microbiota is causally associated with the risk of PA.

Aim. The Mendelian randomization (MR) methodology was employed to assess the potential causal effects of gut microbiota on the susceptibility to PA.

Methodology. A two-sample MR study was performed using the summary statistics of gut microbiota from the largest available genome-wide association study meta-analysis (n=13,266) conducted by the MiBioGen consortium. The summary statistics of PA were obtained from the R11 release data provided by the FinnGen consortium (2,441 cases and 2,87,796 controls). Inverse-variance weighted (IVW) model, weighted median estimator model, weighted model-based method and MR-Egger regression (MER) model were used to examine the causal association between gut microbiota and PA. To assess the heterogeneity and pleiotropic effects of the identified instrumental variables (IVs), we utilized several analytical methods, including the leave-one-out sensitivity analysis, the MR Pleiotropy Residual Sum and Outlier test and Cochran’s Q test.

Results. Utilizing the IVW method, we identified six bacterial traits that were negatively correlated with PA: Eubacterium eligens group [OR: 0.6057; 95 % confidence interval (CI): 0.4525 to 0.8107; P=0.0007], Barnesiella (OR: 0.7456; 95 % CI: 0.5760 to 0.9651; P=0.0258), Coprococcus2 (OR: 0.7257; 95 % CI: 0.5352 to 0.9840; P=0.0391), Ruminococcaceae UCG005 (OR: 0.7562; 95 % CI: 0.5920 to 0.9660; P=0.0252), E. oxidoreducens group (OR: 0.7311; 95 % CI: 0.5547 to 0.9637; P=0.0262) and Lachnospiraceae FCS020 group (OR: 0.7825; 95 % CI: 0.6135 to 0.9981; P=0.0482), respectively. On the contrary, four bacterial traits were positively correlated with PA: Adlercreutzia (OR 1.3210, 95 % CI 1.0181–1.7141, P=0.0362), Holdemania (OR 1.2239, 95 % CI 1.0013–1.4960, P=0.0485), Anaerostipes (OR 1.3614, 95 % CI 1.0189–1.8191, P=0.0369) and Butyricimonas (OR 1.2627, 95 % CI 1.0016–1.5921, P=0.0484), respectively. No significant heterogeneity among IVs or evidence of horizontal pleiotropy was detected.

Conclusion. Our research demonstrates a potential causal link between various gut microbiota and the risk of PA. Further research is imperative to elucidate the mechanisms by which gut microbiota influence the pathogenesis of PA.

Introduction. Enterococcus faecium clade B has recently been re-classified as Enterococcus lactis. Although E. lactis was previously associated with food products and probiotics, the recent re-classification has prompted the need for the accurate identification of this species and re-interpretation of its disease-causing ability. Since the re-classified E. lactis can currently only be identified by molecular techniques such as whole-genome sequencing, we constructed a MALDI Biotyper® custom database to rapidly identify and differentiate E. lactis causing bacteraemia from E. faecium.

Hypothesis/Gap statement. The re-classification of E. faecium clade B as E. lactis warrants the development of rapid and accurate identification methods to distinguish these species, particularly in clinical settings where E. lactis may be misidentified as E. faecium.

Aim. The aim of this study was to construct a MALDI Biotyper® custom database to rapidly identify and differentiate E. lactis causing bacteraemia from E. faecium.

Methodology. A total of 97 enterococcal isolates, including 38 E. lactis, 51 E. faecium and 8 non-E. faecium non-E. lactis enterococci (E. avium, E. casseliflavus, E. cecorum, E. durans, E. faecalis, E. faecium, E. gallinarum, E. lactis, E. mundtii and E. raffinosus) were investigated. Whole-genome sequence analysis was used to confirm the species of each isolate. A MALDI Biotyper® in-house database was constructed using 29 E. lactis isolates and the ethanol/formic acid/acetonitrile preparation protocol. The in-house database was validated using the 97 enterococcal isolates and the extended direct transfer preparation protocol.

Results. Our in-house database correctly identified all isolates at the species level, including the E. lactis isolates, all of which were misidentified as E. faecium by the BioTyper® MBT Compass reference library (2022). Of the 38 E. lactis isolates, 84.2% (n=32) were identified at the high probable species level (score ≥2.300), while the remaining 15.8% (n=6) were identified at the probable species level (score 2.000–2.299). Similarly, all E. faecium isolates (n=51) were accurately identified, including 84.3% (n=43/51) identified at the high probable species level and 15.7% (n=8/51) identified at the probable species level.

Conclusion. Our study provides a ready-to-use custom MALDI spectral database that can be implemented in clinical diagnostic and research laboratories to accurately identify E. lactis, which is currently misidentified as E. faecium by the standard spectrum database available on commercial platforms.

Introduction. Previous studies have shown vast differences in the skin and oral microbiomes of newborns based on delivery method [Caesarean section (C-section) vs vaginal]. Exposure to or absence of certain bacteria during delivery can impact the neonate’s future susceptibility to infections, allergies or autoimmunity by altering immune functions. Few studies have focused on the impact of maternal obesity on the variations of newborn skin and oral microbiomes. Obese pregnant women typically have a higher vaginal microbiome diversity, and their pregnancies are at higher risk for adverse outcomes and complications.

Hypothesis. We hypothesized that the skin and oral microbiomes of newborns born to obese mothers would include more diverse, potentially pathogenic bacteria and that the skin and oral microbiome in C-section delivered newborns would be less diverse than vaginally delivered newborns.

Aim. We aim to begin to establish maternal obesity and mode of delivery as factors contributing to increased risk for negative newborn outcomes through impacts on newborn bacterial dysbiosis.

Methodology. A skin swab was collected immediately following delivery of 39 newborns from 13 healthy weight body mass index (BMI 18.50–24.99), 11 overweight (BMI 25.0–29.99) and 15 obese (BMI ≥30.00) pregnant participants. An oral swab was collected immediately following delivery for 38 of these newborns from 13 healthy weight, 10 overweight and 15 obese pregnant participants. Bacterial genera were identified via 16S rRNA amplicon sequencing.

Results. The newborn skin microbiome was comprised of typical skin bacteria (i.e. Corynebacterium). Newborns of obese participants had a higher relative abundance of Peptoniphilus in their skin microbiome compared to newborns of healthy weight participants (P=0.007). Neonates born via C-section had a higher relative abundance of Ureaplasma in their oral microbiome compared to neonates delivered vaginally (P=0.046).

Conclusion. We identified differences in the newborn skin and oral microbiomes based on pre-pregnancy BMI and method of delivery. These differences could be linked to an increased risk of allergies, autoimmune disease and infections. Future longitudinal studies will be crucial in determining the long-term impact of these specific genera on newborn outcomes. Understanding these connections could lead to targeted interventions that reduce the risk of adverse outcomes and improve overall health trajectory.

Introduction. Relapse of melioidosis is not uncommon and can occur due to shorter oral antibiotic therapy in the first episode. In such isolates, low mutation rates were identified amongst paired clinical isolates during relapse, but large-scale structural variants were also common.

Hypothesis. Using pair-wise comparison, a low number of mutations, especially amongst the virulence and antibiotic resistance genes, may be present amongst the paired isolates obtained during the study period.

Aim. A pair of clinical isolates obtained from a patient with recurrent melioidosis during the study period (January 2018 to June 2021) was analysed for identifying the genomic relatedness and DNA changes that may have caused the relapse.

Methodology. Using paired-end Illumina sequencing, following appropriate data quality checks, the genomes were assembled using Shovill pipeline, whilst the variants were called using Snippy. Structural variants were detected using TIDDIT, and functional associations were identified using the STRING database searches.

Results. One of the isolates (from the second episode) had a highly fragmented genome, but very few structural variants and SNPs were identified. Both the isolates had similar virulence and antibiotic resistance genes; however, owing to the few structural changes, a slightly lower number of virulence genes were observed. Together, they shared 99.8% of the proteomes, and most variants identified spanned either hypothetical proteins or un-annotated regions.

Conclusions. Based on comprehensive genome analysis the two strains were genetically similar, with a few structural variants, implying the second episode to be a relapse rather than a re-infection. There was no difference in the antibiotic resistance or virulence genes that may have explained the relapse.

Introduction. Depression has become one of the mental diseases that seriously affect human health. Its mechanism is very complex, and many factors influence the condition. An imbalance of the gut microbiota is being considered as a factor that impacts the occurrence and progression of depression. Future therapies may therefore tap into this connection, treating depression through manipulation of the gut microbiome.

Hypothesis/Gap Statement. Latroeggtoxin-VI (LETX-VI), a proteinaceous neurotoxin from Latrodectus tredecimguttatus eggs, was previously demonstrated to inhibit excessive inflammation and improve depression behaviours, suggesting that it might be able to regulate the balance of gut microbiota. The aim of this study was to explore the effects of LPS and LETX-VI on depressive behaviours and gut microbiota and to analyse correlations between changes in the gut microbiota and depressive behaviours.

Methodology. A murine model of depression was established, and the effects of LPS and LETX-VI treatment on depressive behaviours and gut microbiota were investigated.

Results. In the murine model, depressive behaviour was induced by LPS; the ratio of Firmicutes to Bacteroidetes (F/B) and the number of pro-inflammatory bacteria in the gut microbiota increased (P<0.01), while butyric acid-producing bacteria with anti-inflammatory effect decreased (P<0.05). Furthermore, the metabolic function of the gut microbiota was disrupted, and the level of virulence factors among gut microbiota was up-regulated (P<0.05). Association analysis showed that the changes in the composition and function of gut microbiota were closely related to the depression phenotype of mice, suggesting that the abnormal function of gut microbiota is linked to depression. However, when LETX-VI was applied before LPS injection, the LPS-induced changes in the gut microbiota were alleviated, and the depressive behaviour greatly improved.

Conclusion. LETX-VI can prevent depressive behaviour by regulating the composition and/or function of the gut microbiota.