Antimicrobial drug susceptibility of 15 strains of Chlamydia trachomatis recently isolated from cases of non-gonococcal urethritis, in Italy

Detection of nucleotide variability in rpoB in both rifampin-sensitive and rifampin-resistant strains of Chlamydia trachomatis

A 656-bp PCR fragment from rpoB was sequenced from five rifampin-resistant Chlamydia trachomatis variants selected in vitro from a wild-type parent with a surprising level of genetic variability in this region. Three variants (MIC, 4 microg/ml) showed Ala522-->Val in cluster I (codons 507 to 533), which harbors mutations in most rifampin-resistant bacteria. Two high-level resistance variants (MICs, 64 and 256 microg/ml) showed His526-->Tyr in cluster I with additional genetic variation, some of which resulted in amino acid substitutions. None of the latter was situated in clusters related to rifampin resistance in other bacteria.

Effects of azithromycin and rifampin on Chlamydia trachomatis infection in vitro

An in vitro cell culture model was used to investigate the long-term effects of azithromycin, rifampin, and the combination of azithromycin and rifampin on Chlamydia trachomatis infection. Although standard in vitro susceptibility testing indicated efficient inhibition by azithromycin, prolonged treatment did not reveal a clear elimination of chlamydia from host cells. Chlamydia were temporarily arrested in a persistent state, characterized by culture-negative, but viable, metabolically active chlamydia, as demonstrated by the presence of short-lived rRNA transcripts. Additionally, azithromycin induced generation of aberrant inclusions and an altered steady-state level of chlamydial antigens, with the predominance of Hsp60 protein compared to the level of the major outer membrane protein. Treatment with azithromycin finally resulted in suppression of rRNA synthesis. Chlamydial lipopolysaccharide and processed, functional rRNA were detectable throughout the entire incubation period. These in vitro data show a good correlation to those from some recent clinical investigations that have reported on the persistence of chlamydia, despite appropriate antibiotic treatment with azithromycin. Rifampin was highly active by in vitro susceptibility testing, but prolonged exposure to rifampin alone for up to 20 days resulted in the emergence of resistance. No development of resistance to rifampin was observed when chlamydia-infected cells were incubated with a combination of azithromycin and rifampin. This combination was shown to be more efficient than azithromycin alone, in that suppression of rRNA synthesis occurred earlier. Thus, such a combination may prove more useful than azithromycin alone.

In-vitro activity of ofloxacin against Chlamydia trachomatis

The in-vitro activity of ofloxacin was evaluated against recently isolated Chlamydia trachomatis strains from patients suffering from non-gonococcal urethritis. The minimal inhibitory concentration (MIC) proved to be 1 mg/l against 8 of the 10 strains assayed (the MICs for the other two strains were 0.5 and 2 mg/l). The data obtained confirm that ofloxacin is active against Chlamydia trachomatis at concentrations achievable with the routine dosage regimen. The drug may thus be regarded as potentially useful for the treatment of non-gonococcal urethritis due to Chlamydia.

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.

Chlamydia trachomatis: in vitro susceptibility to antibiotics singly and in combination

Decreased susceptibility in vitro to erythromycin has been demonstrated for few C. trachomatis isolates outside Scandinavia, making local susceptibility-screening indicated. Eleven recent isolates of C. trachomatis found in a Danish hospital have been examined for susceptibility, expressed as minimal inhibitory concentration (MIC) to antibacterial agents commonly used in genito-urinary infections. Full susceptibility to doxycycline and erythromycin was demonstrated. Clindamycin and ampicillin showed moderate activity, and sulfamethizole had a MIC value in the border area of what is needed for therapeutic effect in non-urinary infections. C. trachomatis, being a major pathogen in pelvic inflammatory disease, makes combination chemotherapy desirable in order to protect against resistance development, to obtain synergistic effect and to ensure effect in infections of mixed etiology - provided antagonism could not be anticipated. In three checkerboard trials, with the combinations doxycycline plus ampicillin, erythromycin plus sulfamethizole and ampicillin plus sulfamethizole, using MIC as end-point, neither synergism nor antagonism could be demonstrated in the concentration range from 1/8 to 4 times the MIC values of each drug.

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

Newer penicillins and cephalosporins are being evaluated in many infections. One of these infections, acute pelvic inflammatory disease, can be caused by Chlamydia trachomatis. This study demonstrated that cefoxitin, cefamandole, cefuroxime, and piperacillin had no effective in vitro activity against C. trachomatis.