Novel mechanism responsible for high-level macrolide resistance in Moraxella catarrhalis

Figures & data

Table 1 MICs and mechanisms underlying macrolide resistance in parent strains, in vitro erythromycin-resistant spontaneous mutants, and transformants of Moraxella catarrhalis

Strain	Origin	MIC (mg/L)				Mutation in 23S rRNA gene, domain V^a				Change in ribosomal protein
		ERY	CLR	AZM	CLI	Allele 1	Allele 2	Allele 3	Allele 4	L4	L22
25238	ATCC	0.06	0.06	0.03	0.5	-^b	-	-	-	-	-
S25-32-afl0	ERY-selected mutant of 25238	>256	l28	64	l	—	-	-	-	Q61R	Ins98SRADRIS
25238-L4tf	Transformant of 25238	32	l6	l6	0.5	—	-	-	-	Q61R	-
25238-L22tf	Transformant of 25238	8	8	8	0.5	-	-	-	-	-	Ins98SRADRIS
25238-L4L22tf	Transformant of 25238-L4tf	128	64	64	0.5	-	-	-	-	Q61R	Ins98SRADRIS
Mcl9	Clinical isolate	0.06	0.03	0.0l6	0.5	-	-	-	-	-	-
S 19-256-aflO	ERY-selected mutant of Mcl9	>256	>256	2	l	C2611T	C2611T	C2611T	-	G65A	-
Mcl9-L4tf	Transformant of Mcl9	l	l	0.5	l	-	-	-	-	G65A	-
Mcl9-C2611Ttf	Transformant of Mcl9	4	2	l	l	C2611T	C2611T	C2611T	C2611T	-	-
Mcl9-L4C2611Ttf	Transformant of Mcl9-C26llTtf	256	256	2	l	C2611T	C2611T	C2611T	C2611T	G65A	-

Notes: ^aEscherichia coli numbering (GenBank accession number V00331);

b no mutation detected.

Abbreviations: ATCC, American Type Culture Collection; MIC, minimum inhibitory concentration; ERY, erythromycin; CLR, clarithromycin; AZM, azithromycin; CLI, clindamycin; Ins, insert.