Susceptibility of 45 Streptococcus bovis isolates to five antibiotic agents

An Overview on Streptococcus bovis/Streptococcus equinus Complex Isolates: Identification to the Species/Subspecies Level and Antibiotic Resistance

Streptococcus bovis/Streptococcus equinus complex (SBSEC), a non-enterococcal group D Streptococcus spp. complex, has been described as commensal bacteria in humans and animals, with a fecal carriage rate in humans varying from 5% to over 60%. Among streptococci, SBSEC isolates represent the most antibiotic-resistant species—with variable resistance rates reported for clindamycin, erythromycin, tetracycline, and levofloxacin—and might act as a reservoir of multiple acquired genes. Moreover, reduced susceptibility to penicillin and vancomycin associated with mobile genetic elements have also been detected, although rarely. Since the association of SBSEC bacteremia and colon lesions, infective endocarditis and hepatobiliary diseases has been established, particularly in elderly individuals, an accurate identification of SBSEC isolates to the species and subspecies level, as well as the evaluation of antibiotic resistance, are needed. In this paper, we reviewed the major methods used to identify SBSEC isolates and the antimicrobial resistance rates reported in the scientific literature among SBSEC species.

Identification, antimicrobial resistance and molecular characterization of the human emerging pathogen Streptococcus gallolyticus subsp. pasteurianus

This study aimed to retrospectively identify 22Streptococcus bovis clinical strains based on the new taxonomy, as well as to investigate their antibiotic-resistance and clonality. Strains were identified by Phoenix100 system, 16S rRNA sequencing, and two MALDI-TOF MS platforms (Bruker Biotyper, Vitek MS). Antibiotic resistance was determined both phenotypically and genotypically, and clonality was assessed by PFGE. Most of strains (63.6%) were isolated from urine, and diabetes was the most common underlying disease (31.8%). Phoenix100 system revealed all strains belonged to biotype II, and 16S rRNA sequencing identified all strains as S. gallolyticus subsp pasteurianus (SGSP). Although both MALDI-TOF MS systems correctly identified isolates to the species level, only Bruker Biotyper accurately identified to the subspecies level. Erythromycin-resistant strains (31.8%) were also clindamycin-resistant and positive for erm(B). Strains resistant to tetracycline (68.2%) were also resistant to erythromycin. PFGE showed high genetic variability identifying 17 different pulsotypes, most of which single.

Association of Streptococcus bovis presence in colonic content with advanced colonic lesion

AIM: To prospectively examine the association between presence of Streptococcus bovis (S. bovis) in colonic suction fluid and the endoscopic findings on colonoscopy.

METHODS: From May 2012 to March 2013, 203 consecutive patients who underwent colonoscopy for any reason were enrolled in the study. Exclusion criteria included: antibiotic use in the previous month, age younger than 18 years, and inadequate preparation for colonoscopy. The colonoscopy was performed for the total length of the colon or to the occluding tumor. The endoscopic findings were registered. Samples were obtained proximal to the colonoscopic part of the suction tube from each patient and sent to the clinical microbiology laboratory for isolation and identification of S. bovis. Samples were incubated in enrichment media with addition of antibiotic disks for inhibition of growth of Gram-negative rods. The samples were seeded on differential growth media; suspected positive colonies were isolated and identified with Gram staining, catalase, and pyrrolidonyl arylamidase tests, and further identified using a VITEK2 system. Statistical analyses were performed using the Student’s t and χ² tests.

RESULTS: Of the 203 patients recruited, 49 (24%) patients were found to be S. bovis carriers; of them, the endoscopic findings included: 17 (34.7%) cases with malignant tumors, 11 (22.4%) with large polyps, 5 (10.2%) with medium-sized polyps, 6 (12.2%) with small polyps, 4 (8.1%) with colitis, and 6 (12.2%) normal colonoscopies. Of 154 patients found negative for S. bovis, the endoscopic findings included: none with malignant tumors, 9 (5.8%) cases with large polyps, 11 (7.1%) with medium-sized polyps, 26 (16.9%) with small polyps, 7 (4.5%) with colitis, and 101 (65.6%) normal colonoscopies. S. bovis (Gram-positive coccus) is considered part of the normal intestinal flora. There is an association between S. bovis bacteremia and colonic neoplasia. It is not well understood whether the bacterium has a pathogenetic role in the development of neoplasia or constitutes an epiphenomenon of colorectal neoplasms. There was a clear relationship between positivity for S. bovis in colonic suction fluid and findings of malignant tumors and large polyps in the colon.

CONCLUSION: There is an association between S. bovis bacteremia and malignant colonic lesions; this should prompt for development of a reliable screening method for advanced colonic lesions.

Genomics, evolution, and molecular epidemiology of the Streptococcus bovis/Streptococcus equinus complex (SBSEC)

The Streptococcus bovis/Streptococcus equinus complex (SBSEC) is a group of human and animal derived streptococci that are commensals (rumen and gastrointestinal tract), opportunistic pathogens or food fermentation associates. The classification of SBSEC has undergone massive changes and currently comprises 7 (sub)species grouped into four branches based on sequences identities: the Streptococcus gallolyticus, the Streptococcus equinus, the Streptococcus infantarius and the Streptococcus alactolyticus branch. In animals, SBSEC are causative agents for ruminal acidosis, potentially laminitis and infective endocarditis (IE). In humans, a strong association was established between bacteraemia, IE and colorectal cancer. Especially the SBSEC-species S. gallolyticus subsp. gallolyticus is an emerging pathogen for IE and prosthetic joint infections. S. gallolyticus subsp. pasteurianus and the S. infantarius branch are further associated with biliary and urinary tract infections. Knowledge on pathogenic mechanisms is so far limited to colonization factors such as pili and biofilm formation. Certain strain variants of S. gallolyticus subsp. macedonicus and S. infantarius subsp. infantarius are associated with traditional dairy and plant-based food fermentations and display traits suggesting safety. However, due to their close relationship to virulent strains, their use in food fermentation has to be critically assessed. Additionally, implementing accurate and up-to-date taxonomy is critical to enable appropriate treatment of patients and risk assessment of species and strains via recently developed multilocus sequence typing schemes to enable comparative global epidemiology. Comparative genomics revealed that SBSEC strains harbour genomics islands (GI) that seem acquired from other streptococci by horizontal gene transfer. In case of virulent strains these GI frequently encode putative virulence factors, in strains from food fermentation the GI encode functions that are pivotal for strain performance during fermentation. Comparative genomics is a powerful tool to identify acquired pathogenic functions, but there is still an urgent need for more physiological and epidemiological data to understand SBSEC-specific traits.