- Volume 72, Issue 8, 2023

  Bacillus anthracis   has a wide host range among warm-blooded animals and causes the disease anthrax. This manifests in localized forms (skin, alimentary) and as septicaemia, the latter typically being fatal.   Bacillus anthracis   forms robust and long-lived endospores, which constitute the environmental phase of its lifecycle and are the key infective agents. Elaboration of plasmid-encoded binary toxin complex and a capsule are fundamental to pathogenicity. Epidemiology in animals is typified by prolonged environmental quiescence and acute systemic disease. Human disease is non-contagious and derives usually from contact with livestock or animal products, although military or terrorist dispersal of spores remains a threat.

Introduction. Tigecycline is one of the important antibiotics available for treating infection caused by multiple-drug resistant pathogens. However, the conventional AST methods which are commonly used in clinical microbiology laboratories usually lead to false intermediate or resistant results in testing tigecycline susceptibility, and further mislead clinical antimicrobial therapies.

Hypothesis. The modified Kirby-Bauer disc diffusion (mKB) method was performed based on the traditional standard Kirby-Bauer disc diffusion (sKB) method.

Aim. To evaluate a modified Kirby-Bauer disc diffusion (mKB) method for tigecycline susceptibility testing, for the purpose of providing accurate tigecycline susceptibility results in clinical practice.

Methodology. A total of 4271 nonduplicate clinical strains were isolated from 37 hospitals across China to perform the mKB method, standard Kirby–Bauer disc diffusion (sKB) method, comparing with the reference broth microdilution (BMD) according to the CLSI. Parameters of categorical agreement (CA), minor errors (mE), major errors (ME), and very major errors (VME) were used in this methodological evaluation research.

Results. BMD testing showed that 91.3–98.9 % of the A. baumannii , K. pneumoniae, E. coli, E. cloacae, S. marcescens, and C. freundii strains were susceptible, while 0–3.1% strains were resistant to tigecycline. When testing A. baumannii , mKB demonstrated higher CA than sKB (90.6 % vs 44.8 %) compared to reference BMD. The mE (9.0 % vs 45.2 %), ME (0.5 % vs 10.6 %) and VME (both 0 %) all satisfied the acceptability criteria. mKB also showed higher CA (87.2 % vs 52.0 %) than sKB in comparison with BMD when testing Enterobacterales (mainly K. pneumonia). The ME (0.45 % vs 8.1 %) and VME (both 0 %) but not mE (12.4 % vs 40.4 %) met the acceptability criteria.

Conclusion. The mKB method can test bacterial susceptibility to tigecycline more accurately than sKB. For the tigecycline-intermediate or -resistant strains by sKB method, BMD or mKB method should be used to verify the results and report reliable tigecycline susceptibility results.

The identification of the novel pneumococcal serotype 7D by Neufeld quellung reaction requires significant expertise. To circumvent this, we developed a simple serotype-specific PCR method to discriminate serotype 7D from the closely related serotypes 7C, 7B and 40. The established PCR was validated with the strain collection of the German National Reference Center for Streptococci (GNRCS). However, no isolate initially assigned as serotype 7B, 7C or 40 was identified as serotype 7D.

Introduction. Invasive mucormycosis (IM) is a potentially fatal infection caused by fungi of the order Mucorales. Histopathology, culture, and radiology are the mainstays of diagnosis, but they are not sufficiently sensitive, resulting in delayed diagnosis and intervention. Recent studies have shown that PCR-based techniques can be a promising way to diagnose IM.

Hypothesis/Gap Statement. Early diagnosis of fungal infections using molecular diagnostic techniques can improve patient outcomes, especially in invasive mucormycosis.

Aim. The aim of this study was to evaluate the utility of our in-house mould-specific real time PCR assay (qPCR) in comparison with the commercially available real time PCR (MucorGenius PCR), for the early diagnosis of mucormycosis in tissue samples from patients with suspicion of invasive mucormycosis (IM). This in-house assay can detect and distinguish three clinically relevant mould species, e.g. Aspergillus spp., Mucorales and Fusarium spp. in a single reaction with only one pair of primers, without the need for sequencing.

Methodology. We enrolled 313 tissue samples from 193 patients with suspected IM in this prospective study. All cases were classified using EORTC/MSGERC guidelines. All samples were tested using traditional methods, in-house qPCR, and MucorGenius PCR.

Results. Using direct microscopy as a gold standard, the overall sensitivity and specificity of in-house qPCR for detection of IM was 92.46% and 80% respectively, while that of the MucorGenius PCR was 66.67% and 90% respectively. However, co-infection of IM and IA adversely affected the performance of MucorGenius PCR in detection of IM.

The in-house PCR detected Aspergillus spp. in 14 cases and Fusarium spp. in 4 cases which showed clinical and radiological features of fungal sinusitis. The in-house qPCR also performed better in detecting possible cases of IM. This aids early diagnosis and appropriate treatment to improve patient outcomes.

Conclusion. Because the in-house PCR is not only sensitive and specific, but also entirely based on SYBR Green for detection of targets, it is less expensive than probe-based assays and can be used on a regular basis for the diagnosis of IM in resource-constrained settings. It can be used to distinguish between mucormycosis and fungal sinusitis caused by Aspergillus and Fusarium in high-risk patients, as well as to accurately detect Mucorales in fungal co-infection cases.

Introduction. The human oocyte microenvironment is follicular fluid, which is important for follicle growth, ovulation and maturation of the oocyte. The micro-organisms present in follicular fluid could be a predictor of in vitro fertilization outcomes.

Hypothesis/Gap Statement. Women with follicular fluid colonized with micro-organisms can be asymptomatic, but the presence of some genera in the follicular fluid correlates with in vitro fertilization.

Aim. To confirm the existence of micro-organisms in follicular fluid, and to profile the micro-organisms present in follicular fluid sampled from women undergoing in vitro fertilization with different outcomes.

Methodology. Women undergoing in vitro fertilization (n=163) were divided into different subgroups according to their in vitro fertilization outcomes. Their follicular fluid samples were collected, and among them, 157 samples were analysed by 16S rDNA sequencing, and 19 samples were analysed using culturomics.

Results. The culturomics results suggested that the 19 follicular fluid samples were not sterile. The isolation rates for Streptococcus , Finegoldia and Peptoniphilus were >50 % in the 19 samples. Linear discriminant analysis effect size analysis showed differential bacteria abundance according to the pregnancy rate, the rate of normal fertilization, the rate of high-quality embryos and the rate of available oocytes. The sequencing results showed that micro-organisms could be detected in all 157 samples. Pseudomonas , Lactobacillus , Comamonas , Streptococcus and Acinetobacter were detected in all of the samples, but with a wide range of relative abundance. Pseudomonas , Lactobacillus , Ralstonia and Vibrio constituted a notable fraction of the microbiota.

Conclusions. Follicular fluid is not sterile. Micro-organisms in follicular fluid could be a predictor of in vitro fertilization outcomes.

Introduction. Cancer patients with Clostridioides difficile infection (CDI) are at a higher risk for adverse outcomes. In addition, a high prevalence of Clostridioides difficile asymptomatic colonization (CDAC) has been reported in this vulnerable population.

Gap Statement. The molecular characteristics and potential role of CDAC in healthcare-related transmission in the cancer population have been poorly explored.

Aim. We aimed to compare the molecular and genotypic characteristics of C. difficile isolates from cancer patients with CDAC and CDI.

Method. We conducted a prospective cohort study of cancer patients with CDAC or CDI from a referral centre. Molecular characterization, typification and tcdC gene expression of isolates were performed.

Results. The hospital-onset and community-onset healthcare facility-associated CDI rates were 4.5 cases/10 000 patient-days and 1.4 cases/1 000 admissions during the study period. Fifty-one C. difficile strains were isolated: 37 (72 %) and 14 (28 %) from patients with CDI or CDAC, respectively. All isolates from symptomatic patients were tcdA+/tcdB+, and four (10 %) were ctdA+/ctdB+. In the CDAC group, 10 (71 %) isolates were toxigenic, and none were ctdA+/ctdB+. The Δ18 in-frame tcdC deletion and two transition mutations were found in five isolates. After bacterial typing, 60 % of toxigenic isolates from asymptomatic carriers were clonal to those from patients with C. difficile -associated diarrhoea. No NAP1/027/BI strains were detected.

Conclusions. We found a clonal association between C. difficile isolates from patients with CDAC and CDI. Studies are needed to evaluate the potential role of asymptomatic carriers in the dynamics of nosocomial transmission to support infection control measures and reduce the burden of CDI in high-risk groups.

Introduction. Caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, coronavirus disease 2019 (COVID-19) has threatened global public health. Immune damage mechanisms are essential guidelines for clinical treatment and immune prevention.

Hypothesis. The dysregulated type I interferon (IFN-I) responses, lymphocytopenia and hypercytokinemia during SARS-CoV-2 infection have been reported. However, whether there is a correlation between levels of IFN-I and the severity of COVID-19 has not been reported yet.

Aim. To investigate the source of IFN-I and detect the exact roles of them in the pathogenesis of COVID-19.

Methodology. Here ELISA was used to detect serum IFN-I (IFN-α and IFN-β) for 137 cases with laboratory-confirmed COVID-19 admitted into one hospital in Wuhan from December 2019 to March 2020, and the relationships between IFN-α/β concentrations and patients’ clinical parameters were conducted by statistical analysis.

Results. Both IFN-α and IFN-β concentrations dramatically increased in COVID-19 patients, especially in old patients (>80 years) and severe cases. Statistical analysis demonstrated that serum IFN-α/β concentrations were negatively correlated with the counts of total CD3 + T, CD4+ and CD8+T cells, especially in critically ill cases. Moreover, serum IFN-α levels were positively correlated to IL-6 and TNF-α. Finally, immunofluorescent double staining showed that IFN-α and IFN-β are major secretions from macrophages and dendritic cells (DCs) in lymph nodes from COVID-19 autopsies.

Conclusion. These results demonstrate that macrophages and DCs are the main origination of IFN-I, and serum levels of IFN-I are positively associated with lymphopenia and cytokine storm, suggesting that IFN-α/β deteriorated the severity of COVID-19. Anti-interferon or IFN-I signalling block drugs are needed to treat ICU patients.