Increase in penicillin resistance rates in Belgium due to clonal spread of a penicillin-resistant 23F Streptococcus pneumoniae strain

In 1994 a sudden increase in penicillin resistance was observed in Belgium among invasive pneumococci. To determine whether this increase was due to clonal spread of a resistant strain or to de novo acquisition of penicillin resistance, pneumococci of capsular types 23F, 19, 14, 9, and 6 isolated in 1993 and 1994, were analyzed by capsular serotyping and DNA macrorestriction analysis, resolved by pulsed-field gel electrophoresis. Furthermore, pneumococcal isolates from northern France, a region with a high prevalence of penicillin resistance, and from southern Belgium, a region with a low but increasing prevalence of penicillin resistance, were analyzed. The rate of resistance of invasive pneumococci to penicillin increased from 2.3% in 1993 to 7.6% in 1994. Pneumococcal serotype 23F represented 26.7% of the penicillin-resistant isolates in 1993 and 40.4% in 1994, while the prevalence of serotype 23F decreased from 10.9% in 1993 to 8.8% in 1994. In 1994 up to 35.8% of serotype 23F isolates were penicillin resistant. The Belgian penicillin-resistant 23F isolates from 1994 were genetically closely related to the French 23F penicillin-resistant isolates and, as clones were clearly distinct from the other serotypes as well as from the penicillin-susceptible 23F isolates. These data demonstrate the important contribution of the clonal spread of a penicillin-resistant pneumococcal strain in the overall increase of penicillin resistance in our country.