Incidence and Epidemiology of Streptococcus pseudoporcinus in the Genital Tract

Abstract

Streptococcus pseudoporcinus, a beta-hemolytic microorganism first isolated from the female gastrourinary tract in 2006, cross-reacts with serogrouping kits for group B Streptococcus (GBS) and could be misidentified in the laboratory. The epidemiologic characteristics of this species have not been reported previously, but this organism is thought to be rare. Paired vaginal and rectal samples were collected from 663 nonpregnant women enrolled in a phase II clinical vaccine trial of a GBS type III capsular polysaccharide-protein conjugate vaccine, and isolates initially identified as S. pseudoporcinus were collected for further testing. A total of 120 isolates of S. pseudoporcinus were recovered from 36 unique individuals with 5.4% of 663 women having this organism recovered at least once during follow-up. All of these isolates cross-reacted with a commercially available GBS serogrouping kit. Women colonized with isolates confirmed as S. pseudoporcinus by genotypic and phenotypic methodologies were compared to women who were not colonized to determine whether there were any significant factors associated with acquisition of S. pseudoporcinus. Acquisition of S. pseudoporcinus vaginally and/or rectally was 36 per 846.0 women-years of follow-up for an annual incidence of 4 per 100 woman-years of follow-up. Acquisition of S. pseudoporcinus was independently associated with black women, being 30 to 40 years of age, recent Trichomonas vaginalis infection, primary or recurrent genital herpes, having bacterial vaginosis by Nugent criteria, and having had two or more male sexual partners since the last visit. This study suggests that S. pseudoporcinus is not rare, especially among black women, and could be misidentified as GBS.Streptococcus pseudoporcinus is a facultative Gram-positive cocci usually characterized by a large zone of beta-hemolysis. It was initially thought to be Streptococcus porcinus, an organism in serological groups E, P, U, and V and found in the upper respiratory and genital tracts of swine (3), but in 2005, Duarte et al. demonstrated that strains of S. porcinus isolated from humans had unique pulsed-field gel electrophoresis profiles of the chromosomal DNA compared to the nonhuman strains and the majority of the human isolates belonged to serogroup NG1 (5). In 2006, Bekal et al. using 16S rRNA gene sequencing demonstrated that the organism found in humans had biochemical characteristics similar to those of S. porcinus but were genetically unique and proposed the name Streptococcus pseudoporcinus (1). Thompson and Facklam from the Centers for Disease Control and Prevention tested human strains of S. porcinus (serogroup NG1) with the group B reagents of 12 commercial Streptococcus test kits and reported that all of the kits evaluated cross-reacted with one or more of the isolates (17). Because S. pseudoporcinus cross-reacts with serogrouping kits for group B Streptococcus (GBS), S. pseudoporcinus may be misidentified as GBS in clinical settings.S. pseudoporcinus has been isolated from multiple specimen ...

The Brief Case: Too Beta To Be a “B”

“…Like S. agalactiae, S. pseudoporcinus produces large colonies (typically Ͼ0.5 mm) after 24 h of incubation (which is useful for differentiating beta-hemolytic streptococci prior to Lancefield antigen typing because it excludes the possibility of beta-hemolytic strains of members of the Streptococcus anginosus group, whose colonies are characteristically smaller [Յ0.5 mm]), is CAMP factor positive, and is bacitracin resistant, and both species are most commonly isolated from the female genitourinary tract (1, 2). Although, unlike S. agalactiae, S. pseudoporcinus does not contain Lancefield group B antigen, it cross-reacts with group B antigen agglutination reagents in Streptococcus serogrouping kits (1,(4)(5)(6)(7)(8). Furthermore, colonies of S. pseudoporcinus have been reported as indistinguishable from those of S. agalactiae when chromogenic agars designed for the detection of S. agalactiae are utilized (6).…”

“…Although, unlike S. agalactiae, S. pseudoporcinus does not contain Lancefield group B antigen, it cross-reacts with group B antigen agglutination reagents in Streptococcus serogrouping kits (1,(4)(5)(6)(7)(8). Furthermore, colonies of S. pseudoporcinus have been reported as indistinguishable from those of S. agalactiae when chromogenic agars designed for the detection of S. agalactiae are utilized (6). Taken together, this can make differentiation between S. pseudoporcinus and S. agalactiae difficult and has probably led to an underestimation of the former's role and frequency in human colonization and disease.…”

“…Taken together, this can make differentiation between S. pseudoporcinus and S. agalactiae difficult and has probably led to an underestimation of the former's role and frequency in human colonization and disease. Frequency may also be underestimated because molecular screening tests to detect S. agalactiae do not detect S. pseudoporcinus (6).…”

“…The acquisition of S. pseudoporcinus has been independently associated with black women, aged 21 to 43 years, who have ever reported genital herpes simplex virus infection, recent Trichomonas vaginalis infection, bacterial vaginosis by the Nugent criteria, or obesity or who have had two or more male sexual partners during the 1 or 2 months since their last health clinic visit (i.e., increased numbers of sexual partners) (1,6). Therefore, based on some of these findings, it has been suggested that S. pseudoporcinus may be associated with sexually transmitted infections (STIs).…”

Recognition of Streptococcuspseudoporcinus Colonization in Women as a Consequence of Using Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry for Group B Streptococcus Identification

“…The prevalence and clinical significance of genitourinary S. pseudoporcinus and its relationship to peripartum neonatal and maternal infections are not currently known (2,3). In 2011, Stoner et al (4) sought to identify the prevalence and epidemiology of S. pseudoporcinus in the genital tracts of nonpregnant women. They found that 5.4% of the women in their study had genital cultures positive for this bacterium.…”