Actinobaculum schaalii: A truly emerging pathogen?: Actinobaculum schaalii: un pathogène réellement émergent?

Microbiological Characterization of Actinotignum schaalii Strains Causing Invasive Infections during a Multiyear Period in a Large Canadian Health Care Region

Actinotignum schaalii is an underrecognized Gram-positive bacillus that is associated with urinary tract infections and cutaneous abscesses. The role of A. schaalii in invasive infections continues to be unappreciated because the bacteria can be isolated from a diverse spectrum of clinical specimens, ranging from being a single pathogen in urine and blood cultures to being deemed a colonizer in polymicrobial anaerobic cultures of sterile fluids and tissues. We conducted a microbiological analysis of clinical isolates obtained from 2012 through 2019. A total of 86 isolates were analyzed; 37 (43%) were from blood cultures, 35 (41%) were from deep wounds and abscesses, 6 (7%) were from urine samples, and the rest were recovered from peritoneal, kidney, and scrotal fluid samples. Urinary tract infections were clinically identified as the source of most cases of bacteremia, although no simultaneous urine cultures yielded positive results. The 16S rRNA gene sequences were available for 32 isolates (37%). Phylogenetic analysis revealed that AS.1/AS.2 strains caused a larger proportion of bloodstream infections (BSIs) (100% versus 52% [P = 0.01]) and trended toward a higher rate of hospitalization (91% versus 76% [P = 0.18]) but had a lower clindamycin MIC90 (0.12 versus >256 μg/mL). Our study emphasizes the emergence of A. schaalii as a pathogen in human urine samples, BSIs, and skin and soft tissue infections. It highlights the pitfalls of current laboratory methods in recovering and identifying this organism from clinical specimens, particularly urine samples. Phylogenetic analysis showed unique genotypic sequences for A. schaalii AS.1/AS.2 strains causing urosepsis, which requires further study to identify potential virulence factors. IMPORTANCE Actinotignum schaalii is an underrecognized Gram-positive bacillus due to its special growth requirements and prior phenotypic identification methods, and it is often mistaken as a contaminant. It has been associated with various clinical syndromes, from urinary tract infections to cutaneous infections. The widespread use of molecular diagnostic methods allowed for improved detection. However, its role in invasive infections remains underappreciated. We conducted a detailed microbiological analysis to improve our understanding of this organism's genotypic and phenotypic characteristics. Our results highlight the pitfalls of clinical laboratory recovery, particularly from urine cultures. Although most BSIs were caused by urinary tract infections, no simultaneous urine cultures identified A. schaalii, largely due to the failure of phenotypic methods to reliably isolate and identify this organism. Additionally, this is the first study demonstrating A. schaalii strains with differences in clinical and microbiological characteristics, raising the possibility of potential bacterial virulence factors contributing to invasive infections.

Characterizing Actinotignum schaalii infections in a large Canadian healthcare region

Aims: We characterize the epidemiology of Actinotignum schaalii within a large Canadian region after implementation of improved identification methods. Patients & methods: Positive cultures for A. schaalii from a centralized microbiology laboratory in Canada were analyzed. Clinical data were retrieved through administrative databases and chart reviews. Primary outcome was incidence of A. schaalii infections; secondary outcomes included mortality, hospital admission and length of stay. Results & conclusions: 86 unique isolates were studied, 37 bloodstream infections (BSI) and 49 non-BSIs. Patients with BSIs were older with more comorbidities, with urinary tract infections implicated as the most frequent source; skin abscesses caused the most non-BSIs. Hospitalization and 90-day mortality was higher in the BSI group. A. schaalii is an important community-acquired pathogen with the potential to cause invasive infections.

Actinotignum schaalii infection - a case series from a tertiary hospital in Greece

Introduction

Actinotignum schaalii is a small Gram-positive facultative anaerobic coccoid rod that was reclassified in 1997 from the genus Actinomyces and is difficult to culture with usual microbiological techniques, as it is slowly growing. A. schaalii is an emerging human pathogen that is most commonly implicated in urinary tract infections (UTIs), but has also been isolated less frequently from abscesses of various sites (such as the skin, the genitourinary tract, surgical sites or intraabdominal).

Methods

All cases where A. schaalii was identified during a 6-year period (January 2016 - January 2022) in the University Hospital of Heraklion were reviewed.

Results

A. schaalii was isolated in 11 cultures from 10 patients. The site of infection was skin and soft tissue in nine out of eleven cultures (81.8%) and the bone was the site of infection in two patients (18.2%). Most cultures were polymicrobial. The median age of patients was 55.5 years (interquartile range 34-63 years), and 80% (n=8) were male. A. schaalii was susceptible to beta-lactams, quinolones and vancomycin, but resistant to clindamycin, erythromycin and metronidazole. Moreover, two cases of diabetic patients diagnosed with polymicrobial diabetic foot osteomyelitis from this organism are presented in detail. Both patients were successfully managed with targeted antimicrobial treatment and prompt surgical management.

Conclusions

A. schaalii is an emerging pathogen that is likely under-reported due to difficulties in isolation and identification. Herein two cases of diabetic foot osteomyelitis are also presented in detail, successfully managed with targeted antimicrobial therapy and surgical debridement.

Actinotignum schaalii: Relation to Concomitants and Connection to Patients' Conditions in Polymicrobial Biofilms of Urinary Tract Catheters and Urines

Actinotignum schaalii is an emerging, opportunistic pathogen and its connection to non-infectious diseases and conditions, such as prostate or bladder cancer, or chronic inflammation has been proposed. Here, we analyzed 297 urine, ureteral and urinary catheter samples from 128 patients by Polymerase Chain Reaction followed by Denaturing Gradient Gel Electrophoresis and Sequencing (PCR-DGGE-S), and culture, and 29 of these samples also by 16S rRNA Illumina sequencing, to establish A. schaalii’s prevalence in urinary tract-related samples, its relation to other bacteria, and its potential association with patients’ conditions and samples’ characteristics. A. schaalii-positive samples were significantly more diverse than A. schaalii negative and between-group diversity was higher than intra-group. Propionimicrobium lymphophilum, Fusobacterium nucleatum, Veillonella sp., Morganella sp., and Aerococcus sp. were significantly more often present in A. schaalii-positive samples; thus, we suggest these species are A. schaalii’s concomitants, while Enterobacter and Staphylococcaceae were more often identified in A. schaalii-negative samples; therefore, we propose A. schaalii and these species are mutually exclusive. Additionally, a significantly higher A. schaalii prevalence in patients with ureter stricture associated hydronephrosis (p = 0.020) was noted. We suggest that A. schaalii could be an early polybacterial biofilm colonizer, together with concomitant species, known for pro-inflammatory features.

The Pathogenic Role of Actinomyces spp. and Related Organisms in Genitourinary Infections: Discoveries in the New, Modern Diagnostic Era

Actinomycosis is a chronic, suppurative, granulomatous infectious disease, caused by different species of Actinomyces bacteria. To date, 26 validly published Actinomyces species have been described as part of a normal human microbiota or from human clinical specimens. Due to the rapid spread of new, modern diagnostic procedures, 13 of 26 of these species have been described in this century and the Actinomycetaceae family has undergone several taxonomic revisions, including the introduction of many novel species termed Actinomyces-like organisms (ALOs). There is scarce data available on the role of these novel bacterial species in various infectious processes in human medicine. The aim of this review is to provide a comprehensive overview of Actinomyces and closely related organisms involved in human diseases-with a special focus on newly described species-in particular their role in genitourinary tract infections in females and males.

Actinotignum schaalii Abscess in a Patient with Common Variable Immunodeficiency

Actinotignum schaalii is an anaerobic, gram-positive commensal organism of the urogenital tract. A. schaalii typically causes urinary tract infections, predominantly in the elderly. Here, we describe the first case of A. schaalii infection presenting as cellulitis and abscess in a patient with common variable immunodeficiency. The patient was successfully treated with an incision and drainage and a prolonged antibiotic course. A. schaalii infection should be considered in sterile abscesses, and anaerobic cultures should be requested in the absence of positive routine cultures.

Actinobaculum massiliense Proteome Profiled in Polymicrobial Urethral Catheter Biofilms

Actinobaculum massiliense, a Gram-positive anaerobic coccoid rod colonizing the human urinary tract, belongs to the taxonomic class of Actinobacteria. We identified A. massiliense as a cohabitant of urethral catheter biofilms (CB). The CBs also harbored more common uropathogens, such as Proteus mirabilis and Aerococcus urinae, supporting the notion that A. massiliense is adapted to a life style in polymicrobial biofilms. We isolated a clinical strain from a blood agar colony and used 16S rRNA gene sequencing and shotgun proteomics to confirm its identity as A. massiliense. We characterized this species by quantitatively comparing the bacterial proteome derived from in vitro growth with that of four clinical samples. The functional relevance of proteins with emphasis on nutrient import and the response to hostile host conditions, showing evidence of neutrophil infiltration, was analyzed. Two putative subtilisin-like proteases and a heme/oligopeptide transporter were abundant in vivo and are likely important for survival and fitness in the biofilm. Proteins facilitating uptake of xylose/glucuronate and oligopeptides, also highly expressed in vivo, may feed metabolites into mixed acid fermentation and peptidolysis pathways, respectively, to generate energy. A polyketide synthase predicted to generate a secondary metabolite that interacts with either the human host or co-colonizing microbes was also identified. The product of the PKS enzyme may contribute to A. massiliense fitness and persistence in the CBs.

Native aortic endocarditis due to an unusual pathogen: Actinotignum schaalii

We report a case of aortic native valve endocarditis due to Actinotignum schaalii in an 89-year-old man with prostatism history but no signs of urinary infection. Actinotignum schaalii was isolated not only from positive blood culture but also from cardiac valve culture using mass spectrometry and 16S rDNA sequencing. Actinotignum schaalii is recognized as commensal of genitourinary tract, but it was underdiagnosed. The advances in bacterial identification such as MALDI-TOF MS probably explain the increasing described cases of infections due to A. schaalii these last years.

Laboratory diagnosis of urinary tract infections: Towards a BILULU consensus guideline

Urinary tract infections (UTI) are very common throughout life and account for the majority of the workload in the clinical microbiology laboratory. Clear instructions for the interpretation of urine cultures by the laboratory technicians are indispensable to obtain standardized, reliable, and clinically useful results. In literature, there is often a lack of evidence-based practice in processing urinary samples in the laboratory. In this consensus document, the BILULU Study Group presents a practical approach for the implementation of existing guidelines for the culture of urine in the microbiology laboratory and offers answers for issues where no clear solution is available in the guidelines.

The urinary microbiota: a paradigm shift for bladder disorders?

PURPOSE OF REVIEW

A resident microbial community [the female urinary microbiota (FUM)] exists within the female bladder of many adult women. Information about the FUM is likely to modify the diagnosis, prevention and treatment of adult women with urinary disorders. This review highlights key findings from recent literature relevant to adult, nonpregnant women.

RECENT FINDINGS

Similar to other human microbial communities, the FUM varies in its characteristics, including organism diversity and predominant organism identity. Recent literature reveals previously undetected organisms and community characteristics that appear associated with certain urinary symptoms, including urinary tract infection and urgency urinary incontinence. The role of individual organisms may range from beneficial to pathogenic and may vary on the basis of an individual's FUM characteristics. The simple dichotomy of 'infected' or 'sterile' no longer sufficiently captures the microbiological complexity of the female bladder.

SUMMARY

Deeper understanding of the FUM should yield better methods to restore the microbiota to a healthy state, providing symptom relief. Opportunities to modify the FUM without antibiotic use are exciting possibilities for future research; stand-alone antibiotic use may be reevaluated to improve treatment precision. Long-standing nomenclature for conditions such as asymptomatic bacteriuria and urinary tract infection will likely require modification.

The Female Urinary Microbiota/Microbiome: Clinical and Research Implications

The changing science of the urinary microbiota and microbiome has both clinical and research implications. This review paper provides an overview of the state of this science, as well as a discussion of the potential for prevention, diagnosis, and treatment of human disease. The history of techniques used for clinical detection of infection are placed into context along with the modern methods of bacterial detection and identification.

Actinotignum schaalii subcutaneous abscesses in a patient with hidradenitis suppurativa: Case report and literature review

Actinotignum schaalii (formerly Actinobaculum schaalii) is a Gram-positive, facultative anaerobic rod that is typically involved in urinary tract infections in elderly patients or those with underlying urological pathologies. In contrast, abscess formation caused by A. schaalii is very rare. We present a case of multiple abscesses in the perineal area in a young patient with hidradenitis suppurativa associated with A. schaalii and Prevotella melaninogenica and review the relevant literature on the topic.