Novel Ralstonia species from human infections: improved matrix-assisted laser desorption/ionization time-of-flight mass spectrometry-based identification and analysis of antimicrobial resistance patterns

A collection of 161 Ralstonia isolates, including 90 isolates from persons with cystic fibrosis, 27 isolates from other human clinical samples, 8 isolates from the hospital environment, 7 isolates from industrial samples, and 19 environmental isolates, was subjected to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) identification and yielded confident species level identification scores for only 62 (39%) of the isolates, including four that proved misidentified subsequently. Whole-genome sequence analysis of 32 representative isolates for which no confident MALDI-TOF MS species level identification was obtained revealed the presence of seven novel Ralstonia species, including three and four that were isolated from cystic fibrosis or other human clinical samples, respectively, and provided the basis for updating an in-house MALDI-TOF MS database. A reanalysis of all mass spectra with the updated MALDI-TOF MS database increased the percentage of isolates with confident species level identification up to 77%. The antimicrobial susceptibility of 30 isolates mainly representing novel human clinical and environmental Ralstonia species was tested toward 17 antimicrobial agents and demonstrated that the novel Ralstonia species were generally multi-resistant, yet susceptible to trimethoprim/sulfamethoxazole, ciprofloxacin, and tigecycline. An analysis of genomic antimicrobial resistance genes in 32 novel and publicly available genome sequences revealed broadly distributed beta-lactam resistance determinants.IMPORTANCEThe present study demonstrated that a commercial matrix-assisted laser desorption/ionization time-of-flight mass spectrometry identification database can be tailored to improve the identification of Ralstonia species. It also revealed the presence of seven novel Ralstonia species, including three and four that were isolated from cystic fibrosis or other human clinical samples, respectively. An analysis of minimum inhibitory concentration values demonstrated that the novel Ralstonia species were generally multi-resistant but susceptible to trimethoprim/sulfamethoxazole, ciprofloxacin, and tigecycline.

Aztreonam-avibactam synergy, a validation and comparison of diagnostic tools

INTRODUCTION

Antimicrobial resistance is a growing problem that necessitates the development of new therapeutic options. Cefiderocol and aztreonam (AT) are often the last active β-lactams for treating metallo-β-lactamases (MBL)-producing Gram-negative bacilli. In these difficult-to-treat bacterial strains, AT resistance is frequently attributed to the co-occurrence of other resistance mechanisms. In the case of β-lactamases they can often be inhibited by avibactam. In the present study, we evaluated the use of the double-disc synergy test (DDST) as a screening tool for the detection of synergy between AT-avibactam (ATA). We validated both the Gradient Diffusion Strips (GDSs) superposition method and the commercially available Liofilchem's ATA GDS.

MATERIALS AND METHODS

We tested AT susceptibility in combination with ceftazidime-avibactam for 65 strains, including 18 Serine-β-Lactamase (SBL)- and 24 MBL-producing Enterobacterales, 12 MBL-producing P. aeruginosa, and 11 S. maltophilia isolates. Interpretation was done with EUCAST breakpoints (version 13.0), AT breakpoints being used for ATA. The accuracy and validity of the GDSs superposition method and ATA GDS were evaluated using an AT GDS applied on Mueller Hinton Agar plates supplemented with avibactam (MH-AV). A DDST was performed to screen for synergy between antibiotic combinations.

RESULTS

Using MH-AV, all SBL- and MBL-positive Enterobacterales were susceptible or susceptible at increased exposure to the combination AT-avibactam. In contrast, only 2 out of the 12 (17%) P. aeruginosa strains and 9/11 (82%) of the S. maltophilia strains were susceptible- or susceptible at increased exposure for the combination of AT-avibactam. The DDST detected all synergies, demonstrating a 100% sensitivity and 100% negative predictive value for all bacterial strains.

CONCLUSION

The DDST is a sensitive tool for screening for antibiotic synergy. Unlike S. maltophilia and SBL- and MBL-positive Enterobacterales, most MBL-positive P. aeruginosa strains remain resistant to AT-avibactam. ATA GDS should be preferred for MIC determination of the AT-avibactam combination, while the GDSs superposition method can be used as an alternative to the commercial test.

Comparing Vaginal and Endometrial Microbiota Using Culturomics: Proof of Concept

It is generally accepted that microorganisms can colonize a non-pathological endometrium. However, in a clinical setting, endometrial samples are always collected by passing through the vaginal-cervical route. As such, the vaginal and cervical microbiomes can easily cross-contaminate endometrial samples, resulting in a biased representation of the endometrial microbiome. This makes it difficult to demonstrate that the endometrial microbiome is not merely a reflection of contamination originating from sampling. Therefore, we investigated to what extent the endometrial microbiome corresponds to that of the vagina, applying culturomics on paired vaginal and endometrial samples. Culturomics could give novel insights into the microbiome of the female genital tract, as it overcomes sequencing-related bias. Ten subfertile women undergoing diagnostic hysteroscopy and endometrial biopsy were included. An additional vaginal swab was taken from each participant right before hysteroscopy. Both endometrial biopsies and vaginal swabs were analyzed using our previously described WASPLab-assisted culturomics protocol. In total, 101 bacterial and two fungal species were identified among these 10 patients. Fifty-six species were found in endometrial biopsies and 90 were found in vaginal swabs. On average, 28 % of species were found in both the endometrial biopsy and vaginal swab of a given patient. Of the 56 species found in the endometrial biopsies, 13 were not found in the vaginal swabs. Of the 90 species found in vaginal swabs, 47 were not found in the endometrium. Our culturomics-based approach sheds a different light on the current understanding of the endometrial microbiome. The data suggest the potential existence of a unique endometrial microbiome that is not merely a presentation of cross-contamination derived from sampling. However, we cannot exclude cross-contamination completely. In addition, we observe that the microbiome of the vagina is richer in species than that of the endometrium, which contradicts the current sequence-based literature.

Culturomics to Investigate the Endometrial Microbiome: Proof-of-Concept

The microbiome of the reproductive tract has been associated with (sub)fertility and it has been suggested that dysbiosis reduces success rates and pregnancy outcomes. The endometrial microbiome is of particular interest given the potential impact on the embryo implantation. To date, all endometrial microbiome studies have applied a metagenomics approach. A sequencing-based technique, however, has its limitations, more specifically in adequately exploring low-biomass settings, such as intra-uterine/endometrial samples. In this proof-of-concept study, we demonstrate the applicability of culturomics, a high-throughput culturing approach, to investigate the endometrial microbiome. Ten subfertile women undergoing diagnostic hysteroscopy and endometrial biopsy, as part of their routine work-up at Brussels IVF, were included after their informed consent. Biopsies were used to culture microbiota for up to 30 days in multiple aerobic and anaerobic conditions. Subsequent WASPLab®-assisted culturomics enabled a standardized methodology. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) or 16S rRNA sequencing was applied to identify all of bacterial and fungal isolates. Eighty-three bacterial and two fungal species were identified. The detected species were in concordance with previously published metagenomics-based endometrial microbiota analyses as 77 (91%) of them belonged to previously described genera. Nevertheless, highlighting the added value of culturomics to identify most isolates at the species level, 53 (62.4%) of the identified species were described in the endometrial microbiota for the first time. This study shows the applicability and added value of WASPLab®-assisted culturomics to investigate the low biomass endometrial microbiome at a species level.

Validation of Rapid Antimicrobial Susceptibility Testing directly from blood cultures using WASPLab®, including Colibrí™ and Radian® in-Line Carousel

With the increase in antimicrobial resistance, fast reporting of antimicrobial susceptibility testing (AST) results is becoming increasingly important. EUCAST developed a method for rapid AST (RAST) directly from the broth of positive blood cultures (BC). Inhibition zones are read after 4, 6, and 8 h, with specific breakpoints per time point. We evaluated the RAST method based on EUCAST disk diffusion methodology with inoculation of BC broth using WASPLab^® (inclusive Colibrí^™ and Radian^®). Forty-nine non-duplicate strains were tested: Escherichia coli n = 17, Klebsiella pneumoniae n = 7, Pseudomonas aeruginosa n = 4, Acinetobacter baumannii n = 2, Staphylococcus aureus n = 10, Enterococcus faecalis n = 6, and Enterococcus faecium n = 3. Results were compared to direct AST and standardized AST. Good categorical agreement was obtained at all time points for all groups, except P. aeruginosa. RAST cut-offs for extended-spectrum β-lactamase (ESBL)-producing Enterobacterales enabled the detection of all included ESBL isolates (n = 5) at all time points, except for 1 E. coli ESBL after 4 h. RAST cut-offs for carbapenemase-producing Enterobacterales enabled the detection of only one carbapenemase after 6 h. However, all carbapenemases (n = 3) were correctly detected after 8 h. Two methicillin-resistant S. aureus were included; both were correctly categorized as cefoxitin-resistant at 6 and 8 h. At 4 h, there was insufficient growth for inhibition zone interpretation. EUCAST RAST is a fast supplementary tool for direct AST of positive BC. WASPLab^® provides a significant advantage as pictures are made automatically implicating that we are not strictly bound to the time points for inhibition zone interpretation.

Anaerobic bacteraemia: a 10-year retrospective epidemiological survey

In order to identify current trends in anaerobic bacteraemia, a 10-year retrospective study was performed in the University Hospital Brussel, Belgium. All clinically relevant bacteraemia detected from 2004 until 2013 were included. Medical records were reviewed in an attempt to define clinical parameters that might be associated with the occurrence of anaerobic bacteraemia. 437 of the isolated organisms causing anaerobic bacteraemia were thawed, subcultured and reanalyzed using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). There were an average of 33 cases of anaerobic bacteraemia per year during 2004-2008 compared to an average of 27 cases per year during 2009-2013 (P = 0.017), corresponding to a decrease by 19% between the first and the latter period. Also, the total number of cases of anaerobic bacteraemia per 100,000 patient days decreased from 17.3 in the period from 2004 to 2008 to 13.7 in the period 2009 to 2013 (P = 0.023). Additionally, the mean incidence of anaerobic bacteraemia decreased during the study period (1.27/1000 patients in 2004 vs. 0.94/1000 patients in 2013; P = 0.008). In contrast, the proportion of isolated anaerobic bacteraemia compared to the number of all bacteraemia remained stable at 5%. Bacteroides spp. and Parabacteroides spp. accounted for 47.1% of the anaerobes, followed by 14.4% Clostridium spp., 12.6% non-spore-forming Gram-positive rods, 10.5% anaerobic cocci, 8.2% Prevotella spp. and other Gram-negative rods and 7.1% Fusobacterium spp. The lower gastrointestinal tract (47%) and wound infections (10%) were the two most frequent sources for bacteraemia, with the origin remaining unknown in 62 cases (21%). The overall mortality rate was 14%. Further studies focusing on the antimicrobial susceptibility and demographic background of patients are needed to further objectify the currently observed trends.

Fourth Belgian multicentre survey of antibiotic susceptibility of anaerobic bacteria

Objectives

To collect recent data on the susceptibility of anaerobes to antimicrobial agents with known activity against anaerobes, and to compare them with results from previous Belgian multicentre studies.

Methods

Four hundred and three strict anaerobic clinical isolates were prospectively collected from February 2011 to April 2012 in eight Belgian university hospitals. MICs were determined by one central laboratory for 11 antimicrobial agents using Etest methodology.

Results

According to EUCAST breakpoints, >90% of isolates were susceptible to amoxicillin/clavulanate (94%), piperacillin/tazobactam (91%), meropenem (96%), metronidazole (92%) and chloramphenicol (98%), but only 70% and 40% to clindamycin and penicillin, respectively. At CLSI recommended breakpoints, only 71% were susceptible to moxifloxacin and 79% to cefoxitin. MIC₅₀/MIC₉₀ values for linezolid and for tigecycline were 1/4 and 0.5/4 mg/L, respectively. When compared with survey data from 2004, no major differences in susceptibility profiles were noticed. However, the susceptibility of Prevotella spp. and other Gram-negative bacilli to clindamycin decreased from 91% in 1993–94 and 82% in 2004 to 69% in this survey. Furthermore, the susceptibility of clostridia to moxifloxacin decreased from 88% in 2004 to 66% in 2011–12 and that of fusobacteria from 90% to 71%.

Conclusions

Compared with previous surveys, little evolution was seen in susceptibility, except a decline in activity of clindamycin against Prevotella spp. and other Gram-negative bacteria, and of moxifloxacin against clostridia. Since resistance was detected to all antibiotics, susceptibility testing of anaerobic isolates is indicated in severe infections to confirm appropriateness of antimicrobial therapy.

Staphylococcus jettensis sp. nov., a coagulase-negative staphylococcal species isolated from human clinical specimens

Eight coagulase-negative, novobiocin-susceptible staphylococcal strains were isolated from human clinical specimens at two different Belgian medical facilities. All strains were non-motile, Gram-stain-positive, catalase-positive cocci. DNA G+C content, peptidoglycan type, menaquinone pattern, the presence of teichoic acid and cellular fatty acid composition were in agreement with the characteristics of species of the genus Staphylococcus . Sequencing of the 16S rRNA gene and four housekeeping genes (dnaJ, tuf, gap and rpoB) demonstrated that these strains constitute a separate taxon within the genus Staphylococcus . Less than 41 % DNA–DNA hybridization with the most closely related species of the genus Staphylococcus ( Staphylococcus haemolyticus , Staphylococcus hominis and Staphlococcus lugdunensis ) was observed. Key biochemical characteristics that allowed these bacteria to be distinguished from their nearest phylogenetic neighbours are arginine dihydrolase positivity, ornithine decarboxylase negativity and inability to produce acid aerobically from d-mannose, α-lactose and turanose. Acid is produced aerobically from trehalose. Based on these results, a novel species of the genus Staphylococcus is described and named Staphylococcus jettensis sp. nov. The type strain is SEQ110T ( = LMG 26879T = CCUG 62657T = DSM 26618T).

Prevalence of Bordetella holmesii and Bordetella bronchiseptica in respiratory tract samples from Belgian patients with pertussis-like symptoms by sensitive culture method and mass spectrometry

Insertion sequences IS481 and IS1001 are targets for molecular detection of respectively Bordetella pertussis and Bordetella parapertussis. There is a raising concern about specificity of these targets due to sequence similarity with Bordetella holmesii and Bordetella bronchiseptica. The likelihood of false (para)pertussis diagnoses should be correlated with the prevalence of these organisms in the respiratory tract (RT). From October 2010 until September 2011, 2,207 RT samples were submitted to the Belgian reference laboratory for pertussis diagnosis. End-point IS481/IS 1001 PCR and culture were performed for B. pertussis and B. parapertussis. We developed a sensitive culture method followed by screening with matrix-assisted laser desorption/ionisation- time of flight mass spectrometry (MALDI-TOF MS) to look for B. holmesii and B. bronchiseptica in our samples,. Only one B. bronchiseptica and no B. holmesii were detected in RT samples from Belgian patients with pertussis-like symptoms.

Third Belgian multicentre survey of antibiotic susceptibility of anaerobic bacteria

OBJECTIVES

To collect recent data on the susceptibility of anaerobes and to compare them with results from previous studies.

METHODS

Four hundred and forty-three anaerobic clinical isolates from various body sites were prospectively collected from October 2003 to February 2005 in nine Belgian hospitals. MICs were determined for nine anti-anaerobic and three recently developed antibiotics.

RESULTS

Most gram-negative bacilli except Fusobacterium spp. were resistant to penicillin. Piperacillin/tazobactam, metronidazole, chloramphenicol, meropenem and amoxicillin/clavulanic acid were very active against all groups, but only 86% of Bacteroides fragilis group strains were susceptible to the latter. Cefoxitin, cefotetan and clindamycin were less active. In particular, only 62%, 52% and 48% of B. fragilis group strains were susceptible, respectively. Clindamycin shows a continuing decrease in activity, as 83% were still susceptible in 1987 and 66% in 1993-94. Anti-anaerobic activity of the new antibiotics is interesting, with MIC50 and MIC90 of 1 and >32 mg/L for moxifloxacin, 2 and 4 mg/L for linezolid and 0.5 and 8 mg/L for tigecycline.

CONCLUSIONS

The susceptibility of anaerobic bacteria remains stable in Belgium, except for clindamycin, which shows a continuous decrease in activity. However, for each of the tested antibiotics, at least a few resistant organisms were detected. Consequently, for severe infections involving anaerobic bacteria, it could be advisable to perform microbiological testing instead of relying on known susceptibility profiles. Periodically monitoring background susceptibility remains necessary to guide empirical therapy.

Septicemia due to Solobacterium moorei in a patient with multiple myeloma

We report a case of bacteremia caused by Solobacterium moorei, an anaerobic, non-sporulated Gram-positive bacillus in a patient with a multiple myeloma. The source of infection was presumably related to multiple dento-alveolar abscesses. This is the first recovery of S. moorei from blood cultures.

In vitro activity of ertapenem against anaerobes isolated from the respiratory tract

Ertapenem is a novel parenteral carbapenem with a long serum half-life. Its spectrum of activity is similar to that of imipenem and meropenem against Gram-positive bacteria, Enterobacteriaceae and fastidious Gram-negative bacteria but it is less active against Pseudomonas aeruginosa and Acinetobacter spp. Several studies were performed in the United States but only one European study has shown that ertapenem has an excellent activity against anaerobes. The objectives of the present study were to test the activity of ertapenem against anaerobes isolated prospectively from the lower and upper respiratory tracts, and to compare their susceptibility with that of anaerobic isolates from other body sites. Fifty-three isolates from the respiratory tract, as well as 50 isolates from various other body sites were tested with E-tests against six antibiotics. For respiratory isolates and for isolates from other sites, MIC 90 values (mg/l) were, respectively, >32 and >32 for penicillin, 0.38 and 0.75 for amoxicillin/clavulanate, 48 and >256 for ceftriaxone, 0.12 and 0.75 for ertapenem, 12 and >256 for clindamycin and 2 and 12 for moxifloxacin. The higher susceptibility of respiratory tract isolates was mainly due to the different distribution of isolated species: only three respiratory isolates but 22 other isolates belonged to the Bacteroides fragilis group. This study confirms the excellent anti-anaerobic activity of ertapenem against anaerobic isolates from the respiratory tract.

Prevalence of fragilysin gene in Bacteroides fragilis isolates from blood and other extraintestinal samples

Of 166 Bacteroides fragilis isolates, 26.2% of 103 isolates from blood and 20.6% of 63 extraintestinal isolates harbored the fragilysin gene (difference not statistically significant). Clinical characteristics and evolution were comparable in patients with B. fragilis bacteremia with or without this enterotoxin. Fragilysin seems not to be an important virulence factor in B. fragilis disease.