Group G Beta-Hemolytic Streptococcal Bacteremia Characterized by 16S Ribosomal RNA Gene Sequencing

Little is known about the relative importance of the four species of Lancefield group G beta-hemolytic streptococci in causing bacteremia and the factors that determine the outcome for patients with group G beta-hemolytic streptococcal bacteremia. From 1997 to 2000, 75 group G beta-hemolytic streptococcal strains were isolated from the blood cultures of 66 patients. Sequencing of the 16S rRNA genes of the group G beta-hemolytic streptococci showed that all 75 isolates were Streptococcus dysgalactiae subspecies equisimilis. The API system (20 STREP) and Vitek system (GPI) successfully identified 65 (98.5%) and 62 (93.9%) isolates, respectively, as S. dysgalactiae subspecies equisimilis with >95% confidence, whereas the ATB Expression system (ID32 STREP) only successfully identified 49 isolates (74.2%) as S. dysgalactiae subspecies equisimilis with >95% confidence. The median age of the patients was 76 years (range, 33 to 99 years). Fifty-six patients (85%) were over 60 years old. All patients had underlying diseases. No source of the bacteremia was identified (primary bacteremia) in 34 patients (52%), whereas 17 (26%) had cellulitis and 8 (12%) had bed sore or wound infections. Fifty-eight patients (88%) had community-acquired group G streptococcal bacteremia. Sixty-two patients (94%) had group G Streptococcus recovered in one blood culture, whereas 4 patients (6%) had it recovered in multiple blood cultures. Fifty-nine patients (89%) had group G Streptococcus as the only bacterium recovered in their blood cultures, whereas in 7 patients other bacteria were recovered concomitantly with the group G Streptococcus in the blood cultures (Staphylococcus aureus in 3, Clostridium perfringens in 2, Citrobacter freundii in 1, and Bacteroides fragilis in 1). Overall, 10 patients (15%) died. Male sex, diagnosis other than cellulitis, hospital-acquired bacteremia, and multiple positive blood cultures were associated with mortality {P < 0.005 (relative risk [RR] = 7.6), P < 0.05 (RR = 3.7), P < 0.005 (RR = 5.6), and P < 0.05 (RR = 5.6), respectively}. Unlike group C beta-hemolytic streptococcal bacteremia, group G beta-hemolytic streptococcal bacteremia is not a zoonotic infection in Hong Kong.

目前学界对兰斯菲尔德G群β溶血性链球菌（Lancefield group G beta-hemolytic streptococci）的四个菌种在引发菌血症中的相对重要性，以及G群β溶血性链球菌菌血症患者的预后影响因素，仍知之甚少。1997年至2000年间，研究人员从66例患者的血培养标本中分离获得75株G群β溶血性链球菌。对该类菌株的16S rRNA基因（16S rRNA gene）测序结果显示，全部75株分离株均为停乳链球菌似马亚种（Streptococcus dysgalactiae subspecies equisimilis）。API 20 STREP鉴定系统（API system (20 STREP)）与Vitek GPI鉴定系统（Vitek system (GPI)）分别以>95%的置信度成功鉴定出65株（98.5%）与62株（93.9%）为停乳链球菌似马亚种；而ATB Expression ID32 STREP鉴定系统（ATB Expression system (ID32 STREP)）仅以>95%的置信度成功鉴定出49株（74.2%）为该亚种。本队列患者的中位年龄为76岁（年龄范围33~99岁），其中56例（85%）年龄超过60岁；所有患者均合并基础疾病。34例患者（52%）未明确菌血症感染源，即原发性菌血症（primary bacteremia）；17例（26%）合并蜂窝织炎（cellulitis），8例（12%）存在压疮（bed sore）或伤口感染。58例患者（88%）为社区获得性（community-acquired）G群链球菌菌血症。62例（94%）仅在1套血培养中检出G群链球菌，4例（6%）在多套血培养中检出该菌。59例（89%）的血培养中仅检出G群链球菌，另有7例患者血培养中同时检出其他细菌：3株金黄色葡萄球菌（Staphylococcus aureus）、2株产气荚膜梭菌（Clostridium perfringens）、1株弗氏柠檬酸杆菌（Citrobacter freundii）与1株脆弱拟杆菌（Bacteroides fragilis）。总体而言，10例患者（15%）死亡。单因素分析显示，男性性别、非蜂窝织炎诊断、医院获得性（hospital-acquired）菌血症以及多套血培养阳性与死亡率显著相关（分别对应P<0.005，相对危险度[RR]=7.6；P<0.05，RR=3.7；P<0.005，RR=5.6；P<0.05，RR=5.6）。与C群β溶血性链球菌菌血症不同，在香港地区，G群β溶血性链球菌菌血症并非人畜共患病（zoonotic infection）。