Correlation between β-lactamase activity and antibiotic sensitivity of clinical pathogens isolated from sputum

We investigated the correlation between β-lactamase activity and disk-sensitivity of 271 clinical pathogens isolated from the sputum of patients in Sendai Kosei Hospital during the period from January to June 1988. The β-lactamase activity was qualitated by the pH-disk method using bromocresol purple as pH-indicator and penicillin G or cefazolin as substrate. Antibiotic sensitivity was measured by sensitivity disks (SHOWA, Japan) containing ampicillin (ABPC), piperacillin (PIPC), cefazolin (CEZ), cefotiam (CTM), cefmetazole (CMZ), cefoperazone (CPZ), latamoxef (LMOX = moxalactam), cefuzonam (CZON), imipenem (IPM) and sulbactam/cefoperazone (SBT/CPZ). Of 271 isolates, 171 (63.1%) were positive for β-lactamase activity, as were 122 (61.3%) of 199 strains of Gram-negative bacteria and 49 (68. 1%) of 72 strains of Gram-positive cocci. Forty-nine (55.1%) of 89 strains isolated from outpatients and 122 (67.0%) of 182 strains isolated from inpatients produced β-Iactamase. As compared with β-lactamase non-producing strains, β-lactamase producing strains were generally less sensitive to ABPC and CEZ. Some were less sensitive to PIPC, CTM, CMZ, CPZ, LMOX and ■CZON. On the other hand, both the β-lactamase positive and negative strains were usually very sensitive to IPM and SBT/CPZ. We conclude from the above results that IPM and SBT/CPZ are more effective than other antibiotics against infections in immunocompromised hosts in whom the majority of pathogens are presumably producing β-lactamase.