Changing epidemiology of group B streptococcal infections among adults in Iceland: 1975-2014

Genetic evidence for a novel variant of the pilus island 1 backbone protein in group B Streptococcus

PURPOSE

Pili contribute significantly to the pathogenesis of infection of group B Streptococcus (GBS) by facilitating adhesion and invasion of host cells. GBS pilin subunits (the backbone pilin protein, BP, and the ancillary pilin proteins, AP) as well as the specific enzymes required for pilus assembly are encoded by genes located in two separate genomic regions, known as pilus island 1 (PI-1) and PI-2. Our aim was to characterize the pilus profile of a collection of GBS isolates from metropolitan Toronto, Canada.

METHODOLOGY

The pilus profile of 1332 invasive and colonizing GBS isolates was determined by PCR and, in selected cases, by whole genome sequencing.

RESULTS

While investigating the pilus profile of a collection of GBS organisms, we discovered that 51 isolates possessed a novel variant of the PI-1 BP, which we named BP-1b. The predicted translated sequences of archetypical GBS BP-1 and novel BP-1b variants shared only 63 % amino acid sequence homology. The novel BP-1b variant was most common among strains of serotype Ib and VI, but was also found among strains of serotypes Ia, II, III and VIII.

CONCLUSION

We describe a relatively frequent occurrence of a novel PI-1 BP that cannot be detected by a commonly used multiplex PCR scheme, which could lead to strains being mistyped as PI-1 negative. We present PCR primers that can easily be incorporated into the multiplex PCR assay to identify strains with novel BP-1b variant.

Cross-resistance to lincosamides, streptogramins A and pleuromutilins in Streptococcus agalactiae isolates from the USA

Background

Streptococcus agalactiae (Group B Streptococcus, GBS) is a leading cause of meningitis, sepsis and pneumonia in neonates in the United States. GBS also causes invasive disease in older infants, pregnant women, children and young adults with underlying medical conditions, and older adults. Resistance to lincosamides in the absence of erythromycin resistance is rare in GBS, but has been previously reported in clinical isolates, both on its own or in combination with resistance to streptogramins A and pleuromutilins (L/LSA/LSAP phenotypes).

Objectives

To retrospectively screen the Active Bacterial Core surveillance (ABCs) GBS isolate collection for these phenotypes in order to identify the causal genetic determinants and determine whether their frequency is increasing.

Methods

Based on MIC data, 65 (0.31%) isolates susceptible to erythromycin (MIC ≤0.25 mg/L) and non-susceptible to clindamycin (MIC ≥0.5 mg/L) were identified among 21 186 GBS isolates. Genomic DNA was extracted and WGS was performed. The presence of 10 genes previously associated with LSA resistance was investigated by read mapping.

Results

Forty-nine (75%) isolates carried the lsa (C) gene and expressed the LSAP phenotype, and 12 (18%) carried both the lnu (B) and lsa (E) genes and expressed the LSAP phenotype. The four remaining isolates were negative for all determinants investigated.

Conclusions

While the overall observed frequency of these phenotypes among our GBS isolates was quite low (0.31%), this frequency has increased in recent years. To the best of our knowledge, this is the first time the LSAP phenotype has been reported among GBS isolates from the USA.

Molecular Characteristics of Group B Streptococci Isolated from Adults with Invasive Infections in Japan

Streptococcus agalactiae (group B streptococcus) isolates (n = 443) obtained from Japanese adults with invasive infections between April 2010 and March 2013 were analyzed for capsular serotype, multilocus sequence type (ST), antibiotic susceptibility, and resistance genes. Among these cases, bacteremia without primary focus was the most common variety of infection (49.9%), followed by cellulitis (12.9%) and pneumonia (9.0%). Concerning patient age (18 to 59, 60 to 69, 70 to 79, 80 to 89, and 90 years old or older), the incidence of pneumonia increased in patients in their 70s and 80s (P < 0.001), while younger patients (18 to 59 and 60 to 69 years old) were more likely to have abscesses (P < 0.05). The mortality rate was 10.2% for all ages. The most common capsular serotype was Ib (39.5%), followed by V (16.0%), III (13.8%), VI (9.5%), and Ia (8.6%). The main ST of serotype Ib strains was ST10, which belonged to clonal complex 10 (88.0%). The predominant clonal complexes of serotypes V and III, respectively, were 1 (78.9%) and 19 (75.4%). Among these isolates, 9 strains (2.0%) were identified as group B streptococci with reduced penicillin susceptibility, reflecting amino acid substitutions in penicillin-binding protein 2X (PBP2X). In addition, 19.2% of all strains possessed mef(A/E), erm(A), or erm(B) genes, which mediate macrolide resistance, while 40.2% of strains were resistant to quinolones resulting from amino acid substitutions in GyrA and ParC. Our data argue strongly for the continuous surveillance of microbial characteristics and judicious antibiotic use in clinical practice.