[Streptococcus pyogenes: in vitro susceptibility and role of beta-lactamase producing bacteria in the persistence of streptococcal pharyngotonsillitis].

OBJECTIVE

To assess the frequency of association between Streptococcus pyogenes and beta-lactamase-producing-bacteria in the pharyngotonsillitis and the evaluate the in vitro susceptibility.

DESIGN

Prospective, descriptive, transverse study.

SETTING

The present study was carried out in the Health Center Dr. José Castro Villagrana, in Tlalpan, México, D.F., from Juanary, 1996 to February 1999.

PARTICIPANTS

In three hundred and ninety four patients with pharyngotonsillitis diagnosis we isolated the same number of Streptococcus pyogenes, and possible beta-lactamase-producing-bacteria.

RESULTS

In 180 patients (45.7%) we isolated at least one possible beta-lactamase-producing-bacteria. Of these, in 138 patients (35%) were confirmed the enzyme presence. In total, we isolated 218 possible beta-lactamase-producing bacteria, and 152 (69.7%) were beta-lactamase positive. We found no significant change in the in vitro susceptibility of group A Streptococcus to penicillin, but erythromycin resistance is relatively common, approximately 10% in this study.

CONCLUSIONS

Streptococcus pyogenes was uniformly susceptible to all penicillins and cephalosporins in vitro. Erythromycin treatment should not be promoted as first-line therapy because the consequent increase of bacterial resistance could create difficulty in treating penicillin-allergic patients. Because of the poor activity of trimetoprimsulfametoxazol, this drug no longer can be considered the drug of choice for the management of group A Streptococcal infections.