An exemption is the PBP dedicated to build the septal PG required to separate daughter cells during cell division. This dispensability has led to the widely accepted concept of functional redundancy for many PBPs. On an average, bacterial genomes harbour a minimum of 10 PBP-encoding genes, most of them non-essential. TP reactions, involving cleavage of the terminal D‑Ala-D-Ala bond in the stem peptide, are carried out by enzymes known generically as penicillin-binding proteins (PBPs) due to their capacity to bind β‑lactam antibiotics, which are D‑Ala-D-Ala structural analogues. The building subunits -muropeptides- are incorporated into the growing macromolecule by transglycolyslation (TG) and transpeptidation (TP) reactions, which constitute the last biosynthetic steps. The PG is synthesized by a stepwise process that includes cytosolic and periplasmic reactions. The major component of the cell wall is the peptidoglycan (PG) a giant macromolecule formed by glycan chains cross-linked by short peptides. These isolates were more frequent among non-invasive isolates.The bacterial cell wall preserves cell integrity in response to external insults and the internal turgor pressure. In particular, ftsI alleles that harboured the mutations D350N, S357N, M377I and S385T were resistant to ampicillin and third generation cephalosporins.

BLNAR isolates were linked to modification in the ftsI gene encoding the penicillin binding protein 3 (PBP3). Moreover, the proportion of beta-lactamase negative ampicillin resistant isolates (BLNAR) was significantly higher among non-invasive isolates compared to that of invasive isolates (24% versus 7%, p < 0.001). Antibiotic susceptibility testing indicated that 24% of the invasive isolates were resistant to ampicillin but this percentage was significantly higher (51%, p < 0.001) among the non-invasive isolates. Non-typeable isolates showed extensive heterogeneity. WGS analysis suggested a serotype b to a capsule switching event.

Serotype f was the most frequently observed but serotypes b and a were also present among invasive isolates. Most of the non-invasive isolates were non-typeable (99%) and this proportion was significantly less among invasive isolates 75%, p < 0.0001).

Pbp3 ftsi