Group Milleri Streptococci in Surgical Patients: A Review of 367 Patients from a Single Center

Research Article

Austin J Surg. 2018; 5(2): 1126.

Group Milleri Streptococci in Surgical Patients: A Review of 367 Patients from a Single Center

Bonatti H¹* and Stelzmueller I²

¹Unversity of Maryland Community Medical Group Surgical Care, Easton, USA

²Praxis DOZ. DR. Ingrid STELZMüLLER, Salzburg, Austria

*Corresponding author: Hugo Bonatti, Unversity of Maryland Community Medical Group Surgical Care, USA

Received: December 13, 2017; Accepted: January 12, 2018; Published: February 09, 2018


Background: Group Milleri streptococci (GMS) also known as Group anginosus streptococci comprise a heterogeneous subgroup of Gram-positive cocci, which are capable to cause severe purulent infections and abscesses.

Patients and Methods: This is a retrospective study of infections due to 637 consecutive GMS isolates in 448 patients during a four year period. Eight patient subgroups were created: primary non surgical (18%), ENT/dental (16%), upper GI tract (5%), lower GI tract diseases (8%), appendicitis (9%), anorectal (10%), biliary (27%), thoracic (3%) and miscellaneous infections (4%).

Results: Overall, 346 patients had a single isolate, 71 had two, 18 had three and 21 had four or more isolates. Median patient age was 51.1 years (range 0.1-94), 58.6% were male. Significant co-morbidities were present in 19.2% of patients, 17.9% were immunocompromised, 11.6% had cancer and 10.9% were solid organ recipients. Swabs accounted for 51.8% of isolates, bile for 19%, aspirates for 13.7%, blood cultures for 7.8% and the remaining specimens were from miscellaneous sites. Mixed infections were found in 48% with E. coli and Bacteroides fragilis being the predominant secondary pathogens. Of the surgically treated patients, 70% also received antibiotics [mean duration of treatment was 6 days). Recurrent infections developed in 5.8% and persistent infection requiring repeat surgery and/or prolonged antibiotic therapy in 11.2%. During the study period, 20 patients died, GMS infection accounted for a 2.5% mortality rate. Resistance rates to penicillin G, piperacillin/tazobactam, carbapenems and clindamycin was <5%, for cephalosporins and quinolones resistance ranged between 5% and 40%.

Conclusion: GMS are significant surgical pathogens. They should be distinguished from viridans streptococci. Most GMS infections require combined surgical/interventional treatment and antimicrobial chemotherapy.

Keywords: Streptococcus group Milleri; Streptococcus group anginosus; Sepsis; Abscess; Antibiotic; Surgical infection, Immunosuppression


Pyogenic infections may be caused by a multitude of different microorganisms, may affect everybody site [1-3] and are commonly polymicrobial [2,4,5]. Some infections only require antibiotics and many can be treated with drainage alone but for most pyogenic infections treatment includes drainage, source control and antimicrobial therapy [6,7].

Until the 1970s viridans streptococci were rarely associated with purulent infections except endocarditis [8]. Viridans streptococci including Group Milleri Streptococci (GMS) can cause purulent infections of various internal organs [8-11]. GMS - in the US referred as to Group anginosus streptococci - comprise a heterogeneous group of streptococci including the species Streptococcus anginosus, Streptococcus constellatus, Streptococcus intermedius and certain β-haemolytic streptococci from Lancefield groups C, F and G [1,12]. The relevance of GMS within viridans streptococci with regard to surgical infections may have been underestimated. GMS have a propensity to cause purulent infections and form deep seated abscesses, are frequently isolated as part of polymicrobial infections and have a high recurrence rate if not treated properly [13-19]. In 1956, Guthof first described Streptococcus milleri in abscesses of the oral cavity [20]; subsequently, GMS were isolated from liver and central nervous system abscesses and in patients suffering from appendicitis, peritonitis, pleural empyema, Ear-Nose-Throat (ENT) and dental infections [20-25]. They also may cause endocarditis and bacteraemia [10,26,27]. Very recently, worldwide an increasing interest in GMS can be observed with multiple new reports being available [28-36]. Some of these reports focus on previously described GMS infections others emphasize the significance of GMS in thus far poorly studied patient populations such as those with pulmonary disease or GMS in the setting of vascular graft infection [30,36].

In this retrospective study the significance of GMS in a cohort of patients from a single center was analyzed (637 consecutive GMS isolates in 448 patients).

Patients and Methods

Patient identification, data collection, statistical analysis

For identification of patients the computerized database of the Institute for Hygiene and Microbiology was screened for GMS isolates. Clinical data were retrieved from electronic and paper charts and entered into an MS EXCEL database. The work was conducted according to the rules of the local ethics committee; subsets of this series have been reported previously.

Infection was assumed if GMS was isolated from otherwise sterile body sites together with clinical signs of infection such as fever, cough or purulent discharge and/or radiological signs such as abscess formation and/or laboratory findings indicative for acute infection including leucocytosis and/or elevated C-reactive protein.

Eight patient subgroups were created: primary non surgical (18%), ENT/dental (16%), upper GI tract (5%) and lower GI tract diseases (8%), appendicitis (9%), anorectal (10%), biliary (27%), thoracic (3%) and miscellaneous infections (4%).

For non surgical patients only limited clinical data could be obtained. Data are reported as total numbers and percentage for discreet and median/mean with range for continuous parameters. Statistical analysis was performed using SPSS. A p-value of <0.05 was considered statistically significant.

Microbiological analysis

The microbiology database was queried for all isolates of GMS from a collection of approximately 430.000 processed samples during a four year period. Isolation and identification of GMS were performed according to the Clinical and Laboratory Standards Institute (CLSI). Aerobic and anaerobic testing was performed. Specimens were incubated on Columbia agar containing 5% sheep red blood cells and incubated in a CO2-enriched atmosphere for 48 hours. Streptococci were identified by morphology, colony size, and hemolysis pattern. GMS were identified using the API 20 Strep Bio Merieux® (Marcyl ´Etoile, France) assay. Antimicrobial susceptibility testing was performed using the disc diffusion assay according to CLSI guidelines (CLSI 2004 Performance Standards for Antimicrobial Susceptibility Testing; Fourteenth Informational Supplement CLSI, Wayne, Pa). Subsets of isolates were subtyped; Streptococcus intermedius and constellatus were identified but not Streptococcus anginosus.


Clinical Data

A total of 637 GMS isolates in 448 patients could be identified. The majority of patients (65%) were treated at various surgical services. Twenty percent of isolates originated from non-surgical services including internal medicine (12%), gynecology and urology (4%), neurology (2%), dermatology and pediatrics (1% each). Figure 1a shows distribution within surgical services. Approximately 80% of all isolates were isolated from general surgical and transplant patients. Figure 1b displays distribution of GMS isolates according to the site of infection. The biliary tract was the most common infection site with 27% followed by ENT/dental infections with 16%; all other infections accounted for <10% of cases.