| Sulphonamides | | None known |
| Penicillins | penA mutations cause 4–8 fold MIC increases as a result of (i) insertion of an asparagine molecule at amino acid position 345 and (ii) mutations near the C terminus of PBP-2 which lower the rate of acylation for penicillin penB mutations result in G120K/G120D and A121D substitutions in PorB1b penC (pilQ gene) mutation results in the E666K substitution that interferes with the formation of the PilQ secretin complex reducing penicillin entry (penB and mtrR mutations are required for the penC mutation effect)—observed only in the laboratory and probably not important in the clinical scenario ponA mutations lower the rate of acylation by penicillin deletion or insertional mutations in the mtrR promoter or in the mtrR gene result in increased expression of the MtrC-MtrD-MtrE efflux pump. pem modifies the expression of penA, penB and mtr
| Several types of penicillinase-producing plasmids: |
| Tetracyclines | rpsJ mutation leads to the V57M substitution resulting in ribosomal protection penB mutations result in G120D and A121D substitutions in PorB1b penC (pilQ2) mutation results in the E666K substitution that interferes with the formation of the PilQ secretin complex reducing tetracycline entry (penB and mtrR mutations are required for the penC mutation effect)—observed only in the laboratory and probably not important in the clinical scenario deletion or insertional mutations in the mtrR promoter or in the mtrR gene results in increased expression of the MtrC-MtrD-MtrE efflux pump tem gene modifies the expression of penB and mtr
| Two main types of TetM-encoding plasmid: |
| Spectinomycin | | None known |
| Kanamycin | | None known |
| Gentamicin | | None known |
| Erythromycin | ermB, ermC and ermF genes encode methylases responsible for modification of the ribosomal target C2599T mutation in the peptidyltransferase loop of domain V of 23S rRNA Deletion or insertional mutations in the mtrR promoter or in the mtrR gene result in increased expression of the MtrC-MtrD-MtrE efflux pump mef gene encodes for another macrolide efflux pump of uncertain significance
| None known |
| Azithromycin | Similar mechanisms as for erythromycin 23S rRNA rrl gene mutations reported independently at positions C2599T and A2143G 153 base-pair insertion sequence located between the mtrR/mtrC promoter and the mtrC gene
| None known |
| Quinolones | | None known |
| Cephalosporins | Mosaic penA genes derived from exchange of DNA with commensal organisms (G545S, I312M and V316T appear to be important amino acid substitutions) penA point mutations (A501V and A501T) reduce susceptibility in non-mosaic PBP-2 isolates Deoxyadenylate nucleotide deletion in the mtrR promoter mtrR mutation results in a G45D substitution in the DNA binding motif of MtrR penB mutations resulting in alterations in amino acid residues 101 and 102 in the putative loop 3 of PorB1b ponA mutation resulting in a L421P substitution in PBP-1 reported but significance uncertain
| None known |