Susceptibility to new beta-lactams of enterobacterial extended-spectrum beta-lactamase (ESBL) producers and penicillin-resistant Streptococcus pneumoniae in Mexico.

The activities of several beta-lactam antimicrobial agents, aminoglycosides and ciprofloxacin, were determined against 62 clinical isolates of enterobacteria resistant to oxyimino cephalosporins (extended-spectrum beta-lactamase producers), collected during 1991 to 1993, and 16 penicillin-resistant invasive isolates of Streptococcus pneumoniae collected during 1994-1996. The numbers and percentages of susceptible enterobacterial strains to tested antibiotics were: imipenem 60 (97%), ciprofloxacin 57 (92%), cefepime 56 (90%), cefpirome 34 (55%), aztreonam 13 (21%), cefotaxime 7 (11%), ceftazidime 0 (0%), amikacin 11 (18%) and gentamicin 16 (26%). Despite the fact that these strains had never been exposed previously to cefepime or cefpirome, the susceptibility was 90% and 55%, respectively. No penicillin-resistant strains of S. pneumoniae were susceptible to cefotaxime, imipenem or cefepime. Only one strain was susceptible to ceftazidime and 4 (25%) were susceptible to cefpirome. Erythromycin showed the greatest activity with 12 (75%) susceptible strains.