Laboratory Diagnosis, Antimicrobial Susceptibility And Genuine Clinical Spectrum of Streptococcus anginosus Group; Our Experience At A University Hospital

Abstract

Background: Streptococcus anginosus group (SAG) may be unrecognized or misidentified in the Clinical Microbiology Laboratory resulting in under-reporting. Consequently, their role as genuine pathogens remains underestimated.

Objectives: The aim of this study is to suggest a reasonable identification approach that is suitable for laboratories of limited resources, to detect any possible emerging antimicrobial resistance, and to assess the genuine clinical spectrum of infections that are caused solely by SAG.

Methods: Our research included 190 bacterial isolates from 190 patients. The isolates were examined by colonies' morphology, odor, hemolytic pattern on 5% sheep Blood agar and Gram staining. Lancefield serogrouping was determined by agglutination test. Antimicrobial susceptibility testing (AST) was performed by disc diffusion method. The isolates were subjected to automated identification and AST by Vitek 2 compact instrument. The collected patients' data included age, gender, clinical condition and/or site of infection, and probable predisposing factor.

Results: All isolates produced minute-sized colonies that consistently generated distinct odor. The isolates showed variable hemolytic patterns, and the majority (74.7%) were non-hemolytic. The isolates showed different Lancefield serogroups, and the commonest was group F (54.2%). A total of 188 (98.9%) isolates were identified by Vitek 2 compact instrument at ≥95% confidence. The isolates showed high rates of antimicrobial susceptibility, however the highest rate of antimicrobial resistance was detected to gentamicin (60.5%). A total of 98 (51.6%) strains were isolated from superficial non-invasive skin and soft tissue infections, 67 (35.3%) strains from deep invasive and sterile body fluids' infections, and 25 (13.1%) strains from upper respiratory tracts' infections.

Conclusion: a combination of phenotypic characteristics could still represent a reasonable Laboratory identification battery. There was no significant emerging antimicrobial resistance detected. A broad genuine spectrum of clinical infections that are caused solely by SAG was reported in our institution.

Keywords: Streptococcus anginosus group; antimicrobial susceptibility testing; clinical infections; laboratory diagnosis.