Differential Antimicrobial Susceptibilities of Granulicatella adiacens and Abiotrophia defectiva

Epidemiology, clinical characteristics, and outcome of infective endocarditis due to Abiotrophia and Granulicatella in a Tertiary Hospital in China, 2015-2023: a retrospective study

BACKGROUND

Abiotrophia (ABI) and Granulicatella (GRA) are rare causative pathogens in infective endocarditis (IE). This study aims to describe the epidemiology, clinical characteristics, and outcome of ABI/GRA-IE. The main features of ABI/GRA-IE were compared with Viridans group streptococci (VGS) IE.

METHODS

From January 2015 to December 2023, a total of 1531 definite IE in Zhongshan Hospital, Fudan University, Shanghai, China were retrospectively enrolled in this study. Clinical and laboratory data were collected.

RESULTS

Forty-five ABI/GRA-IE cases were identified, representing 2.9% of all IE cases in Zhongshan Hospital between 2015 and 2023, compared to 20.1% of VGS-IE. ABI and GRA IE shared similar clinical characteristics. Congenital valvulopathy was reported in 21 (46.7%) ABI/GRA-IE and 85 (28.8%) VGS-IE (P = 0.025). Pulmonary valve was more frequently affected in ABI/GRA-IE (6 [13.3%]) than VGS-IE (7 [2.4%]) (P = 0.002). Congestive heart failure was observed in 30 (66.7%) ABI/GRA-IE and 103 (34.9%) VGS-IE (P < 0.001). Systemic embolization excluding central nervous system (CNS) occurred in 13 (28.9%) ABI/GRA-IE and 39 (13.2%) VGS-IE (P = 0.012). In-hospital mortality was reported as 4.4% in ABI/GRA-IE and 3.7% in VGS-IE (P = 0.854).

CONCLUSION

GRA/ABI-IE was approximately one-seventh as prevalent as VGS-IE. Congestive heart failure and systemic embolization (excluding CNS) were more frequent in GRA/ABI-IE compared to VGS-IE. Mortality of ABI/GRA-IE in this study was comparable to that of VGS-IE and lower than previously reported results.

When less is more: the art of communicating clinical microbiology results

The clinical microbiology laboratory is capable of identifying microorganisms in clinical specimens faster and more accurately than ever before. At face value, this should enable patient care providers to make better-informed decisions and target antimicrobial therapies to deliver individualized care. Ironically, more complete and specific reporting of microorganisms isolated from specimens may result in overtreatment based on the presence of a pathogen, even in the absence of clear signs of clinical infection. This conundrum calls into question the role of the laboratory in contributing to care through selective or "exception" reporting whereby some results are selectively withheld when there is a low probability that laboratory findings correlate with the clinical infection. In a recent article published in the Journal of Clinical Microbiology, Bloomfield et al. (J Clin Microbiol 62:e00342-24, 2024, https://doi.org/10.1128/jcm.00342-24) examine the impact and safety of an exception reporting strategy applied to wound swab specimens. Canonical pathogens associated with skin and soft tissue infections including S. aureus and beta-hemolytic streptococci are withheld from the laboratory report if certain patient criteria are met that would put them at low risk of adverse outcomes if untreated, or if treated with guideline-recommended empiric therapy. Their central finding was an approximately 50% reduction in post-laboratory report antibiotic initiation without adverse events or increased 30-day admission rate (indicative of infection-related complications, e.g., disseminated disease). While effectively achieving their goal, the premise of exception reporting and other modified reporting strategies raises questions about the potential risk of underreporting and how to ensure that the message is being interpreted, and acted upon, by care providers as was intended by the laboratory.

A Case of Granulicatella adiacens Osteomyelitis and Mitral Valve Endocarditis

Granulicatella adiacens is a nutritionally variant streptococci (NVS) that can cause various infections, including but not limited to endocarditis, osteomyelitis, pneumonia, and abscess. We report a case of an 80-year-old male who was found to have Granulicatella adiacens osteomyelitis and mitral valve endocarditis. Also included is a systematic review of osteomyelitis caused by Granulicatella adiacens.

Arteriovenous Graft Infection Due to Granulicatella adiacens

Granulicatella adiacens is a gram-positive coccus that is normally found in the human oral cavity and gastrointestinal and urogenital tracts but can rarely cause infection. When it does cause infection, Granulicatella adiacens has been most associated with bacteremia and endovascular infection, but to our knowledge, there are no previously documented cases of arteriovenous graft (AVG) infection. We present a case of Granulicatella adiacens bacteremia with associated AVG infection.

An Aminoglycoside-Sparing Regimen with Double Beta-Lactam to Successfully Treat Granulicatella adiacens Prosthetic Aortic Valve Endocarditis-Time to Change Paradigm?

(1) Background: Granulicatella adiacens is a former nutritionally variant streptococci (NVS). NVS infective endocarditis (IE) is generally characterized by a higher rate of morbidity and mortality, partially due to difficulties in choosing the most adequate microbiological culture method and the most effective treatment strategy, and partially due to higher rates of complications, such as heart failure, peripheral septic embolism, and peri-valvular abscess, as well as a higher rate of valve replacement. Depending on the affected valve (native valve endocarditisNVE, or prosthetic valve endocarditisPVE), the American Heart Association (AHA) 2015 treatment guidelines (GLs) suggest penicillin G, ampicillin, or ceftriaxone plus gentamicin (2 weeks for NVE and up to 6 weeks for PVE), while vancomycin alone may be a reasonable alternative in patients who are intolerant of β-lactam therapy. The European Society of Cardiology (ESC) 2023 GLs recommend treating NVE with penicillin G, ceftriaxone, or vancomycin for 6 weeks, suggesting combined with an aminoglycoside (AG) for at least the first 2 weeks only for PVE; likewise, the same recommendations for IE due to Enterococcus faecalis. (2) Methods: Starting from the case of a 51-year-old man with G. adiacens aortic bio-prosthesis IE who was successfully treated with aortic valve replacement combined with double beta-lactams, an AG-sparing regimen, we performed microbiology tests in order to validate this potential treatment change. (3) Results: As for E. faecalis IE, we found that the combination of ampicillin plus cephalosporines (like ceftriaxone or ceftobiprole) showed a synergistic effect in vitro, probably due to wider binding to penicillin-binding proteins (PBPs), thus contributing to enhanced bacterial killing and good clinical outcome, as well as avoiding the risk of nephrotoxicity due to AG association therapy. (4) Conclusions: Further studies are required to confirm this hypothesis, but double beta-lactams and an adequate sourcecontrol could be a choice in treating G. adiacens IE.

Clinical characteristics and outcome of infective endocarditis due to Abiotrophia and Granulicatella compared to Viridans group streptococci

OBJECTIVE

To describe the clinical characteristics and outcome of Abiotrophia and Granulicatella infective endocarditis and compare them with Viridans group streptococci infective endocarditis.

METHODS

All patients in the International Collaboration on Endocarditis (ICE) - prospective cohort study (PCS) and the ICE-PLUS cohort were included (n=8112). Data from patients with definitive or possible IE due to Abiotrophia species, Granulicatella species and Viridans group streptococci was analyzed. A propensity score (PS) analysis comparing the ABI/GRA-IE and VGS-IE groups according to a 1:2 ratio was performed.

RESULTS

Forty-eight (0.64%) cases of ABI/GRA-IE and 1,292 (17.2%) VGS-IE were included in the analysis. The median age of patients with ABI/GRA-IE was lower than VGS-IE (48.1 years vs. 57.9 years; p=0.001). Clinical features and the rate of in-hospital surgery was similar between ABI/GRA-IE and VGS-IE (52.1% vs. 45.4%; p=0.366). Unadjusted in-hospital death was lower in ABI/GRA-IE than VGS-IE (2.1% vs. 8.8%; p=0.003), and cumulative six-month mortality was lower in ABI/GRA-IE than VGS-IE (2.1% vs. 11.9%; p<0.001). After PS analysis, in-hospital mortality was similar in both groups, but six-month mortality was lower in the ABI/GRA IE group (2.1% vs. 10.4%; p=0.029).

CONCLUSIONS

Patients with ABI/GRA-IE were younger, had similar clinical features and rates of surgery and better prognosis than VGS-IE.

Development of high level daptomycin resistance (HLDR) in Abiotrophia and Granulicatella spp isolates from patients with infective endocarditis (IE)

Abiotrophia and Granulicatella species are fastidious organisms, representing around 1%-3% of infective endocarditis (IE). Little is known about the optimal antibiotic treatment of these species, and daptomycin has been suggested as a therapeutic option. We describe the antimicrobial profile in Abiotrophia and Granulicatella IE isolates, investigate high-level daptomycin resistance (HLDR) development and evaluate daptomycin activity in combination therapy. In vitro studies with 16 IE strains (6 A. defectiva, 9 G. adiacens and 1 G. elegans) were performed using microdilution to determine minimal inhibitory concentration (MIC) and time-kill methodology to evaluate combination therapy. Daptomycin non-susceptibility (DNS; MIC≥ 2 mg/L) and HLDR (MIC≥256 mg/L) were based on existing Clinical and Laboratory Standards (CLSI) breakpoints for viridans streptococci. All isolates were susceptible to vancomycin: G. adiacens was more susceptible to penicillin and ampicillin than A. defectiva (22% vs. 0%, and 67% vs. 33%) but less susceptible to ceftriaxone and daptomycin (56% vs. 83%, and 11% vs. 50%). HLDR developed in both A. defectiva (33%) and G. adiacens (78%) after 24h exposure to daptomycin. Combination therapy did not prevent the development of daptomycin resistance with ampicillin (2/3 strains), gentamicin (2/3 strains), ceftriaxone (2/3 strains) or ceftaroline (2/3 strains). Once developed, HLDR was stable for a prolonged time (>3 weeks) in G. adiacens, whereas in A. defectiva the HLDR it reversed to baseline MIC at day 10. This study is first to demonstrate rapid HLDR development in Abiotrophia and Granulicatella species in vitro. Resistance was stable, and most combination therapies did not prevent it.

In vitro antimicrobial activity against Abiotrophia defectiva and Granulicatella elegans biofilms

OBJECTIVES

To determine the efficacy of different antibiotics (alone or in combination) against Abiotrophia defectiva and Granulicatella elegans biofilms and to investigate the anti-biofilm activity of gentamicin alone versus blood culture isolates from both species.

METHODS

The activity of benzylpenicillin, clindamycin, daptomycin, fosfomycin, gentamicin, levofloxacin and rifampicin against 24-hour-old biofilms of A. defectiva and G. elegans was investigated in vitro by conventional microbiological methods and isothermal microcalorimetry.

RESULTS

For planktonic bacteria, the MIC values of tested antibiotics ranged from 0.016 to 64 mg/L, as determined by microcalorimetry. Higher antibiotic concentrations, ranging from 1 to >1024 mg/L, were needed to produce an effect on biofilm bacteria. Gentamicin was an exception as it was active at 1 mg/L against both planktonic and biofilm G. elegans. A synergistic effect was observed when daptomycin was combined with benzylpenicillin, gentamicin or rifampicin against A. defectiva biofilms and when gentamicin was combined with rifampicin or levofloxacin against G. elegans biofilms. A. defectiva clinical isolates displayed greater variability in gentamicin susceptibility as compared with G. elegans strains.

CONCLUSIONS

Antimicrobial susceptibility profiles vary widely between Abiotrophia and Granulicatella biofilms, and synergistic effects of the tested antibiotics were heterogeneous. The clinical relevance of these in vitro observations needs to be confirmed in experimental in vivo conditions and human trials, before guidelines for the treatment of A. defectiva and G. elegans infections are established. This study suggests the benefit of further clinical exploration of antibiotic combinations with anti-biofilm effect.

Infective endocarditis due to Granulicatella elegans presenting with musculoskeletal symptoms

A 62-year-old man with essential hypertension and right L4-L5 hemilaminectomy was referred to rheumatology for evaluation of severe arthralgia and myalgia for 12 months. Review of symptoms was significant for night sweats and 20 pounds unintentional weight loss. Physical examination was significant for holosystolic murmur best heard at the cardiac apex of unclear chronicity. Laboratory investigations revealed elevated inflammatory markers, white blood cell count and B-type natriuretic peptide. Transoesophageal echocardiogram showed flail posterior mitral leaflet with severe mitral regurgitation and two vegetations (2.5×1 cm and 1.6×0.3 cm). Abdominal CT showed new focal splenic infarcts, and a brain MRI revealed subacute infarcts, consistent with the embolic phenomenon. Blood cultures grew Granulicatella elegans The patient underwent mitral valve replacement surgery followed by 6 weeks of parenteral therapy with vancomycin and gentamicin, with full recovery at a 3-month follow-up.

Native Valve Infective Endocarditis with Osteomyelitis and Brain Abscess Caused by Granulicatella adiacens with Literature Review

Granulicatella adiacens is a type of NVS (nutritionally variant streptococci) rarely causing infective endocarditis (IE). NVS are fastidious and unable to sustain growth on routine culture media due to lack of specific nutrients. Endocarditis caused by NVS due to their virulence is associated with higher treatment failures and mortality rates. New antimicrobial susceptibility patterns are indicative of a significant rise in penicillin resistance and susceptibility differences between NVS subspecies. Initial empirical therapy is essential as a delay in using the appropriate agent leads to poor results. We present a case of an immunocompetent young female with recent intravenous drug abuse resulting in native mitral valve endocarditis with ruptured chordae tendineae and septic embolization, causing brain abscess and lumbar spine osteomyelitis. She was transferred to a tertiary center where she underwent mitral valve replacement successfully and treated with six weeks of intravenous vancomycin and ertapenem. To our knowledge, ours is the first case report of G. adiacens endocarditis in an adult with brain abscess and osteomyelitis with an excellent response to antibiotic therapy. Based on our case report, literature review, and new antimicrobial susceptibility patterns, updates to treatment guidelines are suggested to improve the therapeutic outcomes.

Granulicatella adiacens and Abiotrophia defectiva Native Vertebral Osteomyelitis: Three Cases and Literature Review of Clinical Characteristics and Treatment Approach

Granulicatella adiacens and Abiotrophia defectiva are an increasingly recognized cause of osteoarticular infections. We describe two cases of G. adiacens and one case of A. defectiva native vertebral osteomyelitis (NVO) and review all published cases. Nine cases of G. adiacens NVO and two cases of A. defectiva NVO were previously described. Patients were usually middle-aged men, and classical risk factors for NVO were present in half of the cases. Concomitant bacteremia was reported in 78.6% of cases, and concurrent infective endocarditis occurred in 36.4% of this sub-group of patients. Many different antibiotic schemes were recorded, with median treatment duration of 6 weeks. In the most recent reports, glycopeptides represented the most frequent empirical therapy, possibly due to the increasing emergence of G. adiacens and A. defectiva penicillin-resistant strains. Stabilization surgery was rarely required (14.3% of cases), and clinical cure was generally achieved. In conclusion, Granulicatella spp. and Abiotrophia spp. NVO is rare but increasingly described. A total antibiotic course of six weeks seems to be appropriate for noncomplicated cases, and clinical outcome is generally favorable.

Aortitis caused by Abiotrophia defectiva: Description of two cases

Abiotrophia defectiva is a well-known endocarditis pathogen, however it has never been described as a cause of primary aortitis. Here we describe the first published case of thoracic aortitis and an unusual case of aortic graft infection due to A. defectiva, which were both managed conservatively.

Antimicrobial Susceptibility Patterns among a Large, Nationwide Cohort of Abiotrophia and Granulicatella Clinical Isolates

Antimicrobial susceptibility patterns from 599 A. defectiva, G. adiacens, and G. elegans clinical isolates were determined by broth microdilution. We observed significant differences in susceptibility across species, particularly to penicillin and ceftriaxone, and across geographical regions. A. defectiva was the least susceptible species overall to penicillin. All isolates were susceptible to vancomycin and >90% were susceptible to levofloxacin.