Microbiological characterization of Streptococcus pneumoniae and non-typeable Haemophilus influenzae isolates as primary causes of acute otitis media in Bulgarian children before the introduction of conjugate vaccines

Table 2 Antimicrobial susceptibility of 128 S. pneumoniae isolates from middle ear fluids and trends in antibiotic nonsusceptibility divided in two periods depending on year of strain isolation

Antibiotics	MICs (μg/mL)		Overall% susceptibility n = 128			NS rates in 1994–2005 n = 49	NS rates in 2006-2011n = 79
	MIC_50/90	MIC range	S	I	R	%	%
Penicillin	0.12/4.0	0.01 - 8.0	31.2	40.6	28.1	73.5	65.8
Amoxicillin	0.12/4.0	0.01 - 8.0	89.1	6.2	4.7	8.2	12.7
Cefuroxime sodium	≤0.5/8.0	≤0.5- ≥ 16.0	63.3	5.5	31.2	28.6	41.8
Ceftriaxone	0.06/1.0	0.03-4.0	93.0	4.7	2.3	4.1	8.9
Erythromycin	≤0.25/≥64.0	≤0.25- ≥ 64.0	53.1	0.0	46.9	36.7	53.2
Clindamycin	0.06/≥64.0	0.01- ≥ 64.0	66.4	0.8	32.8	22.4	40.5
Levofloxacin	1.0/1.0	0.5 - 2.0	100.0	0.0	0.0	0.0	0.0
Tetracycline	2.0/≥8.0	0.25- ≥ 8.0	50.8	0.8	48.4	46.9	50.6
Chloramphenicol	4.0/≥8.0	0.5- ≥ 8.0	84.4	-	15.6	24.5	10.1
Trimeth/Sulfameth	2.0/≥4.0	0.06- ≥ 4.0	35.2	22.7	42.2	65.3	64.6

MICs-minimal inhibitory concentracions; MIC_50/90, MICs for 50% and 90% of the isolates, respectively; R-resistant; I-intermediate; S-susceptible (Interpretation according to CLSI, 2010); NS - nonsusceptibility; The following breakpoints (μg/mL) for penicillin (oral penicillin V) were used: susceptible ≤ 0.06; intermediate ≥ 0.12 - 1.0; resistant ≥ 2; Trimethoprim/Sulfamethoxazole (1:19 ratio), MIC refers to trimethoprim value.

ISSN: 1476-0711