The amazing world of obligate anaerobic Gram positive cocci: a critical analysis of 598 infectious episodes in the era of MALDI-TOF MS

Authors:
Aaron George, Hugo Bonatti, Joel Grunhut, Pooja Ajith

Body of Abstract:
Background: Peptostrepotococci have been known as 2nd most common anaerobic bacteria causing diseases in humans. Better microbiology testing systems have allowed for better distinguishing the different species and genus of Gram positive obligate anaerobic cocci (GPAC). The currently accepted classification distinguishes between Peptostreptococcus anaerobius (PA), Finegoldia magna (FM), Parvimonas micra (PM), Peptionphilus asaccharolyticus (PAs) and Anaerococcus prevotii (AP), however, this list is expanding.
Patients and Methods: Our institutional database was searched for all infections caused by GPAC during a 4-year period. Identification was done using biochemical assays during the first 2 years and thereafter, using MALDI-TOF.
Results: In total, 714 isolates of GPAC in 597 patients (52.3% male) were identified. Table 1 shows demographic, clinical and microbiology data for the different GPAC: PA (90), FM (212), PM (74), PAs (125) and AP (146); in 50 cases (8%) two different GPAC were isolated. Median age was 56.5 (range 1 day to 98.8) years including 16 pediatric and 53 octogenarian patients. Median BMI was 30.8 (range 11.5 – 77.5) kg/m2 with a 56% obesity rate; 37% were diabetic and 35% active smokers. Drained abscesses/fluid collections and tissue samples accounted for 84%% of specimens, wound cultures for 5% and blood cultures for 11% of specimens; 57% of GPAC isolates were identified since MALDI-TOF introduction. Infection locations were head/neck 4%, trunk 35%, upper extremity 3%, lower extremity 36%, intraabdominal 11%, chest 1% and blood stream 11%. Microscopy of 530 specimens revealed WBC in 78%, Gram positive cocci in 78%, Gram negative rods in 38% and Gram positive rods in 29%. Normal flora, in addition to GPAC was reported in 54% of specimens. In 25% EC was a single isolate; spectrum of pathogens isolated in addition to GPAC in 446 mixed infections included staphylococci (127), streptococci (103), enterococci (18), Gram negative rods (161), other anaerobes (264), and yeast (10). Treatment consisted of surgical drainage/debridement during which samples for microbiology were taken and antibiotics with anaerobic activity.
Conclusion: GPAC are a diverse group of pathogen and have remained an important cause of serious surgical infections. PM was more commonly found in intraabdominal infections and together with AP had the highest propensity to invade the blood stream. FM on the other hand is most commonly found in soft tissue infections.