Lack of in vitro activity of cefoxitin, cefamandole, cefuroxime, and piperacillin against Chlamydia trachomatis

In Vitro Susceptibility Testing of Clinical Isolates of Chlamydia trachomatis

Penicillin class antibiotics have demonstrated varying degrees of in vivo and in vitro success when tested against Chlamydia trachomatis. The activity of ampicillin-sulbactam, an agent commonly utilized in the treatment of pelvic infections, was tested to ascertain if any antichlamydial activity is present. Up to six endocervical isolates of C. trachomatis were tested against each of five antibiotics including doxycycline, erythromycin, clindamycin, ampicillin/sulbactam, and sulbactam alone. McCoy cell monolayers were inoculated with high inclusion counts of 10,000–30,000 inclusion-forming units (IFU) per coverslip, and exposed to each antibiotic. Up to nine subsequent antibiotic free culture passes were performed to assess the viability of abnormal inclusions. Doxycycline, erythromycin, and clindamycin achieved 100% eradication of inclusions at concentrations of 4.0, 2.0, and 1.0 µg/mL. Exposure to ampicillin/sulbactam resulted in a greater than 99% reduction in the inclusion count at 32.0 µg/mL, while sulbactam by itself demonstrated considerably less activity. Abnormal inclusions were noted only in the ampicillin/sulbactam exposed cells, and these, plus all inclusions remaining following sublethal exposure to the other antibiotics, resulted in regrowth to control levels in subsequent passes. Doxycycline and erythromycin demonstrated excellent activity. Clindamycin and ampicillin/sulbactam also significantly reduced inclusion formation, and therefore may provide adequate C. trachomatis coverage in patients receiving these antibiotics for pelvic infections.

In vitro activity of beta-lactam drugs and sulbactam against Chlamydia trachomatis

We tested the in vitro activity of ampicillin, ampicillin-sulbactam, cefoperazone, cefoperazone-sulbactam, and sulbactam against 18 recent clinical isolates of Chlamydia trachomatis and two ATCC strains. Ampicillin (MIC50, 256 micrograms/ml) and sulbactam (MIC50, 128 micrograms/ml) demonstrated some activity against C. trachomatis, but cefoperazone had little to no activity. At 2-3 dilutions below the MIC, C. trachomatis treated with ampicillin or sulbactam, but not cefoperazone, formed small inclusions that remained small on passage onto antibiotic-free McCoy cells. It appears that ampicillin and sulbactam suppress rather than kill C. trachomatis.

Role of cephalosporins in gonorrhoea and other sexually transmitted diseases

Cephalosporins have a role in the treatment of gonorrhoea, and especially infections caused by strains that are penicillin-resistant, either because they produce plasmid-mediated beta-lactamase or they have chromosomally mediated diminished permeability or modified penicillin-binding proteins. Although none of the oral or Group I agents are useful, most of the Group II, III and IV agents are, and especially cefuroxime, cefotaxime, ceftriaxone and cefoxitin. In addition to uncomplicated urethral, cervical or rectal infections, appropriate regimens are also effective for the treatment of pharyngeal infections, disseminated infections and gonococcal ophthalmia. The cephalosporins have no clear role in the treatment of syphilis, granuloma inguinale, Mycoplasma or chlamydial infections or bacterial vaginosis, but ceftriaxone may be effective in chancroid, and cefoxitin in combination with an antichlamydial agent (such as a tetracycline) might be used for the treatment of pelvic inflammatory disease.

In vitro activity of clavulanic acid, amoxicillin, and ticarcillin against Chlamydia trachomatis

In vitro, growth of Chlamydia trachomatis was not entirely eliminated by 960 micrograms of ticarcillin per ml, 64 micrograms of amoxicillin per ml, 32 micrograms of clavulanic acid per ml, a combination of ticarcillin (480 micrograms/ml) and clavulanic acid (32 micrograms/ml), and a combination of amoxicillin (32 micrograms/ml) and clavulanic acid (8 micrograms/ml). However, a greater than or equal to 99% decrease in the number of inclusions was obtained at concentrations readily attainable in serum.

In vitro activity of a group of broad-spectrum cephalosporins and other beta-lactam antibiotics against Chlamydia trachomatis

The activities of seven broad spectrum cephalosporins, four other beta-lactam antibiotics, and one monobactam against Chlamydia trachomatis were measured in a cell culture system. The minimal inhibitory concentration of four of the seven cephalosporins was greater than or equal to 128 micrograms/ml; those of the other three were from 16 to 32 micrograms/ml. Of the other agents, only mecillinam had activity against C. trachomatis comparable to that reported for ampicillin (minimal inhibitory concentration, less than or equal to 0.5 micrograms/ml).