Susceptibility to cephalosporins of penicillin-susceptible and penicillin-resistant strains of Neisseria gonorrhoeae from Philadelphia

Abstract

Using agar dilution, we determined MICs of penicillin, cefoxitin, ceftriaxone, cefmetazole, tetracycline, and spectinomycin for 129 strains of Neisseria gonorrhoeae. All strains were susceptible to ceftriaxone (MIC range, .0.008 to 0.06 ,ug/ml) and spectinomycin (16 to 32 ,ug/ml). The MICs for 50, 90, and 100% of strains tested were 1.0, 2.0, and >8.0 ,ug/ml; 0.12, 1.0, and >8.0 ,Ig/ml; 0.5, 1.0, and 2.0 ,ug/ml; and 1.0, 2.0, and >8.0 ,ug/ml for cefmetazole, penicillin, cefoxitin, and tetracycline, respectively. Seven strains were Il-lactamase producers; eight were chromosomally resistant to penicillin. There was a log-linear relation for non-P-lactamase-producing strains between the MICs of cefmetazole, cefoxitin, and tetracycline and the MIC of penicillin (Pearson r = 0.787, 0.544, and 0.358, respectively).The treatment strategy for presumed or microbiologically documented gonorrheal infection has changed in the light of new information regarding the susceptibility of Neisseria gonorrhoeae to penicillin and tetracycline (6). Most laboratories do not test each strain for antimicrobial susceptibilities; thus clinicians rely on epidemiologic data from regional or national authorities to guide therapy. Cephalosporins such as cefoxitin and ceftriaxone have been widely used as primary therapy for gonorrhea. The purpose of our study was to determine the susceptibility patterns of N. gonorrhoeae, collected from men seen at clinics in two urban Philadelphia neighborhoods, to five drugs commonly used in the treatment of gonorrhea: penicillin, tetracycline, spectinomycin, cefoxitin, and ceftriaxone. We also tested the activity of cefmetazole, a novel cephalosporin being used in clinical trials, as chemotherapy for gonorrhea. We determined the incidence of penicillin resistance due to ,-lactamase production, and we examined the relation between susceptibility to penicillin and susceptibility to other antibiotics among non-3-lactamase-producing strains. MATERIALS AND METHODSBetween March and October 1987, isolates of N. gonorrhoeae were collected from men seen at Episcopal Hospital and women seen at Temple University Hospital, both in north Philadelphia. The isolates were identified in the clinical microbiology laboratories by growth on Thayer-Martin agar, Gram stain appearance, oxidase activity, and coagglutination with monoclonal antibodies (Phadebact Monoclonal GC Omni Test; Pharmacia Diagnostics, Piscataway, N.J.) or by carbohydrate utilization (Fastidious Fermenters Duo Tubes and Trio Tubes; Carr-Scarborough Microbiologicals, Inc., Decatur, Ga.). Isolates were frozen at -70°C in 1-ml samples of Trypticase soy broth (BBL Microbiology Systems, Cockeysville, Md.) with 20% glycerol until they were thawed for batch susceptibility testing. The control strain was a laboratory isolate whose susceptibilities to penicillin and tetracycline were determined by agar dilution in a previous experiment (data not published). ,-Lactamase activity was * Corresponding author. determined by the chromogenic cephalosporin assay (Cefinase; B...

Antimicrobial susceptibility testing of Neisseria gonorrhoeae and implications for epidemiology and therapy

“…In the large cooperative study designed to set up quality control criteria for disk diffusion and agar dilution AST, the r values were 0.97 for penicillin, 0.88 for tetracycline, and 0.65 for ceftriaxone (57). In our study in 1991, the r values were 0.96 for penicillin, 0.94 for tetracycline, 0.62 for ceftriaxone, and 0.62 for cefpodoxime (34). Similar findings were reported for two other very potent cephalosporins: cefotaxime had an r value of 0.79, and ceftazidime had a value of 0.63 (55).…”

Susceptibility of Neisseria gonorrhoeae to cefpodoxime: determination of MICs and disk diffusion zone diameters

“…Furthermore, if there is emergence of strains with diminished susceptibilities to ceftriaxone, cefpodoxime may also be of limited value. In an earlier study, we found a similar association between MICs for cefoxitin and cefmetazole in ,-lactamase-negative strains (6). The ultimate determination of MIC breakpoints and disk diffusion zone diameter cutoffs for cefpodoxime will best be made when clinical data reg4rding the correlation of cure rates with MICs are available.…”

“…In many geographic areas, penicillin and tetracycline are very likely to result in failure of therapy because of the high prevalence of resistant strains. Penicillin and tetracycline MICs can be well estimated by using disk diffusion as in previous studies (6,8). The accuracy of disk diffusion testing for ceftriaxone and cefpodoxime is somewhat less, but it is still reproducible.…”

Antimicrobial susceptibility testing of Neisseria gonorrhoeae and implications for epidemiology and therapy.

“…One of the concerns about the 1-lactamase-stable cephalosporins is that, for non-PPNG strains, the MIC of penicillin is highly correlated with the MIC of the cephalosporin. In Philadelphia in 1989, we showed a strong log-linear correlation between penicillin and cefmetazole MICs for 122 non-PPNG strains (Pearson r = 0.787) (34). Several strains had cefmetazole MICs of .4 ,ug/ml, suggesting that they might not be eradicated with single-dose cefmetazole.…”