Molecular typing and antimicrobial resistance of group B Streptococcus clinical isolates in Saudi Arabia

Recent development and fighting strategies for lincosamide antibiotic resistance

SUMMARYLincosamides constitute an important class of antibiotics used against a wide range of pathogens, including methicillin-resistant Staphylococcus aureus. However, due to the misuse of lincosamide and co-selection pressure, the resistance to lincosamide has become a serious concern. It is urgently needed to carefully understand the phenomenon and mechanism of lincosamide resistance to effectively prevent and control lincosamide resistance. To date, six mobile lincosamide resistance classes, including lnu, cfr, erm, vga, lsa, and sal, have been identified. These lincosamide resistance genes are frequently found on mobile genetic elements (MGEs), such as plasmids, transposons, integrative and conjugative elements, genomic islands, and prophages. Additionally, MGEs harbor the genes that confer resistance not only to antimicrobial agents of other classes but also to metals and biocides. The ultimate purpose of discovering and summarizing bacterial resistance is to prevent, control, and combat resistance effectively. This review highlights four promising strategies, including chemical modification of antibiotics, the development of antimicrobial peptides, the initiation of bacterial self-destruct program, and antimicrobial stewardship, to fight against resistance and safeguard global health.

Genomic insights into the diversity, virulence, and antimicrobial resistance of group B Streptococcus clinical isolates from Saudi Arabia

Introduction

Detailed assessment of the population structure of group B Streptococcus (GBS) among adults is still lacking in Saudi Arabia. Here we characterized a representative collection of isolates from colonized and infected adults.

Methods

GBS isolates (n=89) were sequenced by Illumina and screened for virulence and antimicrobial resistance determinants. Genetic diversity was assessed by single nucleotide polymorphisms and core-genome MLST analyses.

Results

Genome sequences revealed 28 sequence types (STs) and nine distinct serotypes, including uncommon serotypes VII and VIII. Majority of these STs (n=76) belonged to the human-associated clonal complexes (CCs) CC1 (33.71%), CC19 (25.84%), CC17 (11.24%), CC10/CC12 (7.87%), and CC452 (6.74%). Major CCs exhibited intra-lineage serotype diversity, except for the hypervirulent CC17, which exclusively expressed serotype III. Virulence profiling revealed that nearly all isolates (94.38%) carried at least one of the four alpha family protein genes (i.e., alphaC, alp1, alp2/3, and rib), and 92.13% expressed one of the two serine-rich repeat surface proteins Srr1 or Srr2. In addition, most isolates harbored the pilus island (PI)-2a alone (15.73%) or in combination with PI-1 (62.92%), and those carrying PI-2b alone (10.11%) belonged to CC17. Phylogenetic analysis grouped the sequenced isolates according to CCs and further subdivided them along with their serotypes. Overall, isolates across all CC1 phylogenetic clusters expressed Srr1 and carried the PI-1 and PI-2a loci, but differed in genes encoding the alpha-like proteins. CC19 clusters were dominated by the III/rib/srr1/PI-1+PI-2a (43.48%, 10/23) and V/alp1/srr1/PI-1+PI-2a (34.78%, 8/23) lineages, whereas most CC17 isolates (90%, 9/10) had the same III/rib/srr2/P1-2b genetic background. Interestingly, genes encoding the CC17-specific adhesins HvgA and Srr2 were detected in phylogenetically distant isolates belonging to ST1212, suggesting that other highly virulent strains might be circulating within the species. Resistance to macrolides and/or lincosamides across all major CCs (n=48) was associated with the acquisition of erm(B) (62.5%, 30/48), erm(A) (27.1%, 13/48), lsa(C) (8.3%, 4/48), and mef(A) (2.1%, 1/48) genes, whereas resistance to tetracycline was mainly mediated by presence of tet(M) (64.18%, 43/67) and tet(O) (20.9%, 14/67) alone or in combination (13.43%, 9/67).

Discussion

These findings underscore the necessity for more rigorous characterization of GBS isolates causing infections.

Re-framing the importance of Group B Streptococcus as a gut-resident pathobiont

Streptococcus agalactiae (Group B Streptococcus, GBS) is a Gram-positive bacterial species that causes disease in humans across the lifespan. While antibiotics are used to mitigate GBS infections, it is evident that antibiotics disrupt human microbiomes (which can predispose people to other diseases later in life), and antibiotic resistance in GBS is on the rise. Taken together, these unintended negative impacts of antibiotics highlight the need for precision approaches for minimizing GBS disease. One possible approach involves selectively depleting GBS in its commensal niches before it can cause disease at other body sites or be transmitted to at-risk individuals. One understudied commensal niche of GBS is the adult gastrointestinal (GI) tract, which may predispose colonization at other body sites in individuals at risk for GBS disease. However, a better understanding of the host-, microbiome-, and GBS-determined variables that dictate GBS GI carriage is needed before precise GI decolonization approaches can be developed. In this review, we synthesize current knowledge of the diverse body sites occupied by GBS as a pathogen and as a commensal. We summarize key molecular factors GBS utilizes to colonize different host-associated niches to inform future efforts to study GBS in the GI tract. We also discuss other GI commensals that are pathogenic in other body sites to emphasize the broader utility of precise de-colonization approaches for mitigating infections by GBS and other bacterial pathogens. Finally, we highlight how GBS treatments could be improved with a more holistic understanding of GBS enabled by continued GI-focused study.

Capsular gene distribution and RAPD typing of Streptococcus agalactiae isolated from pregnant women

Streptococcus agalactiae has different virulence factors, from which the capsule has the most significant role in the pathogenesis of this organism. We aimed to investigate the distribution of more prevalent capsular genes among different Random Amplified Polymorphic DNA (RAPD) types of S. agalactiae isolated from pregnant women. A total of 106 isolates were collected from 420 vaginal and rectal swabs obtained from pregnant women. The specimens were transferred using Todd Hewitt Broth and were cultured on a blood agar containing antibiotics. The S. agalactiae isolates were identified by the standard microbiological and biochemical tests. The genomic DNAs of S. agalactiae isolates were extracted using an extraction kit. Then, the PCR method was used to detection of the capsular genes. Moreover, The RAPD PCR was used to genotyping of the isolates. The colonization rate of the pregnant women was 25.23%, and there was a statistically significant correlation between the weeks of gestation and the probability of colonization (p-value < 0.05). Also, 31 (29.24%) and 18 (16.98%) pregnant women had a history of abortion and membrane rupture, respectively. In addition, 20 (18.86%), 32 (30.18%), 4 (3.77%), and 6 (5.66%) isolates carried genes encoding capsular types Ia, Ib, III, and V, respectively. None isolates had the type II capsular gene, and other 44 isolates were non-typeable. Nine clones (clusters) of S. agalactiae were observed in the present study with 70% similarity, and 53 different types were identified among the isolates. Except for capsular types III and V that belonged to clones 3, 5, 7, and 9, other capsular types were detected in different RAPD types. We found that the capsular types Ib and Ia were predominant among pregnant women in this area, indicating their significance for vaccine designation. Also, our isolates showed a lower genotypic diversity in RAPD typing. This may be due to the same sources of most isolates.