MALDI-TOF MS based typing of GBS as an alternative to MLST molecular method

Safa Maarouf

Studenteropgave: Speciale


Asymptomatic vaginal carriage of group b streptococcus (GBS) constitutes the main risk factor for vertical transmission of GBS from mothers to their babies. GBS is associated with invasive neonatal diseases, particularly early-onset diseases, which constitute 60-70% of neonatal early-onset diseases. By treating pregnant women with intrapartum antibiotic prophylaxis (IAP) during the birth, it is possible to prevent the vertical transmission of GBS and thus the potential neonatal early-onset disease cases. According to the CDC guidelines, it is recommended that all GBS-colonized pregnant women should receive the IAP during the birth. As a result, the incidence of early-onset neonatal GBS diseases has decreased significantly. However, the CDC guidelines do not take in consideration that the majority of the GBS isolates in pregnant women act as commensals since the risk of early-onset GBS diseases in newborns which may be caused by pathogenic GBS isolates is only 1-2%. Thus, an excessive use of antibiotics exposes many women and their babies to the risk of adverse effects. The aim of this master’s thesis was to develop a typing system that can differentiate between commensal and pathogenic GBS isolates obtained from colonized pregnant women such that IAP is only used to prevent the vertical transfer of pathogenic GBS isolates. The GBS isolates obtained from GBS-colonized pregnant women are generally not typed routinely since the generally accepted standard molecular typing method multi locus sequence typing (MLST) is time-consuming and costly and thus not feasible for routine use. Therefore, the quick, simple, and inexpensive Whole-cell MALDI-TOF MS, which is currently widely employed for routine bacterial species identification, was used for the typing purpose in this thesis. The MALDI-TOF MS typing system was developed and validated based on a global collection of 55 GBS isolates that had been previously studied by MLST. These GBS isolates included the five most common disease-causing capsular serotypes (Ia, Ib, II, III, and V). The typing system was then applied to type 745 GBS isolates obtained from clinical samples of GBS-colonized Danish pregnant women and 33 GBS isolates from Danish neonates with early- and late-onset GBS diseases. The 55 GBS isolates were differentiated in 16 MALDI-TOF groups. The MALDI-TOF groups were both stable and reproducible. However, a lack of correlation between the identified MALDI-TOF groups and MLST sequence types was recognized. Based on the clinical samples, several MALDI-TOF groups were associated with pathogenic GBS isolates including MALDI-TOF group 5, which was associated with 48% of the pathogenic GBS isolates. The majority of the GBS isolates among pregnant women were distributed in the MALDI-TOF groups that were associated with pathogenic GBS isolates. In addition several GBS isolates could not be assigned to any MALDI-TOF group.

UddannelserMolekylærbiologi, (Bachelor/kandidatuddannelse) Kandidat
Udgivelsesdato10 mar. 2017
VejledereOle Skovgaard