ANTIMICROBIAL SUSCEPTIBILITY OF STREPTOCOCCUS-PNEUMONIAE, HAEMOPHILUS-INFLUENZAE AND MORAXELLA (BRANHAMELLA) CATARRHALIS ISOLATED IN THE UK FROM SPUTA

Four hundred and thirty-one Streptococcus pneumroniae, 1272 Haenophilus influenzae and 305 Moraxella (Branhamella) catarrhalis were isolated from sputa and identified in 28 UK laboratories during a ten week period in 1990. Disc diffusion susceptibility testing was performed in each centre using identical methods. Species-speafic susceptibility breakpoints applied to data for six antimicrobial agents were determined from the distribution of isolates according to zone diameters of inhibition measured in participating laboratories and were correlated with minimum inhibitory concentration data obtained with 302 isolates ant to the coordinating centre. Inter-laboratory reproducibility was estimated by comparing peripheral and coordinating centre results for these 302 isolates and by distributing five reference strains to all laboratories for testing. Reduced susceptibility to ampicillin and amoxycillin-clavulanate was detected in < 3% of S. pneumoniae, but 8·1% were resistant to tetracycline and 6·5% to erythromycin. Resistance to ampicillin due to production of β-lactamase occurred in 9·4% of H. influenzae, another 5·2% were resistant to ampicillin and amoxycillin-clavulanate but were β-lactamase-negative. 4·5% were resistant to tetracycline and most (86·6%) had MICs ≥ 1 mg/L of erythromycin. Zonc diameters around ampicillin discs were ≥ 10 mm smaller than those around amoxycillin-clavulanate discs for 241 (79%) of M. catarrhalis. Although only 193/241 had been reported to be β-lactamase positive by participating laboratories, data obtained at the coordinating centre confirmed that ≥ 10 mm and ≤ 3 mm zone size differences correlated with β-lactamase positive and -negative isolates respectively. No M. catarrhalis were resistant to amoxycillin-clavulanate and < 4% were resistant to either tetracycline or erythromycin. The prevelence of resistance to cefaclor was highest among H. influenzae (5·2%) and lowest among S. pneumoniae (0·9%). Only seven of 2008 isolates (two to three per species) were resistant to cefixime. The data suggest that the prevalence of resistance to ampicillin, tetracycline and erythromycin must be taken into consideration when treating respiratory infections. © 1991, by The British Society for Antimicrobial Chemotheraphy.