In vitro activity of azithromycin (CP-62,993) against Chlamydia trachomatis and Chlamydia pneumoniae

Liposomal Encapsulation Increases the Efficacy of Azithromycin against Chlamydia trachomatis

Chlamydia trachomatis (C. trachomatis) is an obligate intracellular bacterium linked to ocular and urogenital infections with potentially serious sequelae, including blindness and infertility. First-line antibiotics, such as azithromycin (AZT) and doxycycline, are effective, but treatment failures have also been reported. Encapsulation of antibiotics in liposomes is considered an effective approach for improving their local effects, bioavailability, biocompatibility and antimicrobial activity. To test whether liposomes could enhance the antichlamydial action of AZT, we encapsulated AZT in different surface-charged elastic liposomes (neutral, cationic and anionic elastic liposomes) and assessed their antibacterial potential against the C. trachomatis serovar D laboratory strain as well as the clinical isolate C. trachomatis serovar F. A direct quantitative polymerase chain reaction (qPCR) method was used to measure chlamydial genome content 48 h post infection and to determine the recoverable chlamydial growth. All the liposomes efficiently delivered AZT to HeLa 229 cells infected with the laboratory Chlamydia strain, exhibiting the minimal inhibitory concentrations (MIC) and the minimal bactericidal concentrations (MBC) of AZT even 4–8-fold lower than those achieved with the free AZT. The tested AZT-liposomes were also effective against the clinical Chlamydia strain by decreasing MIC values by 2-fold relative to the free AZT. Interestingly, the neutral AZT-liposomes had no effect on the MBC against the clinical strain, while cationic and anionic AZT-liposomes decreased the MBC 2-fold, hence proving the potential of the surface-charged elastic liposomes to improve the effectiveness of AZT against C. trachomatis.

Mathematical modelling of the role of mucosal vaccine on the within-host dynamics of Chlamydia trachomatis

A mathematical model of the within-host replicative dynamics of C. trachomatis infection and its interactions with the immune system, in the presence of a mucosal vaccine, is presented. Our aim is to estimate the requisite efficacy of an efficacious mucosal vaccine that could promote a stable disease-free state in vivo. Sensitivity analysis was used to quantify how variability in the model parameters influence the value of the disease threshold R₀. This shows that the two most important factors to be considered for achieving a disease-free state state in vivo, based on their influence on R₀, are the efficacy of the Chlamydia vaccine, and the rate at which the humoral immune response protects healthy epithelial cells from infection. Numerical simulations of the model show that a vaccine with a minimum efficacy of 86% may be required for the in vivo control of Chlamydia burden. Such effective but imperfect Chlamydia vaccine could confer long-term protective immunity to genital Chlamydia infections. Conditions under which lower vaccine efficacies may suffice are also explored.

Evaluating the Antibiotic Susceptibility of Chlamydia - New Approaches for in Vitro Assays

Pigs are the natural hosts of Chlamydia suis, the only Chlamydia species known to spontaneously acquire homotypic resistance conferred by a class C tetracycline resistance gene. Various susceptibility assays have existed for several years, but there is no widely accepted, standardized assay to determine chlamydial antibiotic susceptibility. In this study, we developed new approaches to determine the in vitro susceptibility of Chlamydia to different antibiotics in view of existing protocols. Specifically, the minimal inhibitory concentration (MIC) is based on a consensus of both inclusion number reduction and alteration of inclusion size and morphology upon antibiotic exposure. In addition to these, we employed a recovery assay, allowing observation of the chlamydial response to drug removal and subsequent recovery, as compared to both continued exposure and to the unexposed control. We propose a simple and fast screening method to detect tetracycline resistant C. suis strains within 2 to 3 days with minimal use of consumables. For proof of principle, we evaluated the susceptibility of three C. suis field strains and the reference strain S45/6 to tetracycline, sulfamethoxazole, and penicillin, antibiotics commonly used to prevent respiratory and gastrointestinal diseases on fattening pig farms. We found that tetracycline sensitive strains can easily be distinguished from resistant strains using the evaluation parameters proposed in this study. Moreover, we report that S45/6 is sensitive to sulfamethoxazole while all evaluated C. suis field strains showed some degree of sulfamethoxazole resistance. Finally, we confirm that Penicillin G induces the chlamydial stress response in all evaluated C. suis strains.

Antimicrobial activity of bitespiramycin, a new genetically engineered macrolide

The antimicrobial activity of bitespiramycin (BT) against Chlamydia trachomatis (Ct), Chlamydia pneumoniae (Cp), Ureaplasma urealyticum (Uu), and Mycoplasma pneumoniae (Mp), was compared with those of azithromycin (AZM) and acetylspiramycin (AT-SP) in vitro. Furthermore, the anti-Mp activities of BT and AZM were evaluated in a hamster model. The activities of BT in vitro were similar to those of AZM but were more effective than those of AT-SP. BT effectively inhibited Mp infection at a dose of 200mg/kg in a hamster model.

On the pathway to better birth outcomes? A systematic review of azithromycin and curable sexually transmitted infections

The WHO recommends the administration of sulfadoxine-pyrimethamine (SP) to all pregnant women living in areas of moderate (stable) to high malaria transmission during scheduled antenatal visits, beginning in the second trimester and continuing to delivery. Malaria parasites have lost sensitivity to SP in many endemic areas, prompting the investigation of alternatives that include azithromycin-based combination (ABC) therapies. Use of ABC therapies may also confer protection against curable sexually transmitted infections and reproductive tract infections (STIs/RTIs). The magnitude of protection at the population level would depend on the efficacy of the azithromycin-based regimen used and the underlying prevalence of curable STIs/RTIs among pregnant women who receive preventive treatment. This systematic review summarizes the efficacy data of azithromycin against curable STIs/RTIs.

Lack of macrolide resistance in Chlamydia trachomatis after mass azithromycin distributions for trachoma

We investigated antimicrobial drug resistance in ocular Chlamydia trachomatis 18 months after 4 biannual communitywide distributions of antimicrobial drugs in a region of Ethiopia where ocular strains of C. trachomatis are highly endemic. We found no significant differences in susceptibilities to azithromycin and doxycycline in 6 posttreatment and 4 pretreatment samples.

Azithromycin reduces Chlamydia pneumoniae-induced attenuation of eNOS and cGMP production by endothelial cells

BACKGROUND

Intracellular infections with cytomegalovirus (CMV) or Chlamydia pneumoniae (Cp) may play a role in the aetiology of atherosclerosis. Nitric oxide (NO) is a key regulator of endothelial function. Under pathological conditions uncoupling of endothelial nitric oxide synthase (eNOS) leads to vessel damage as a result of production of oxygen radicals instead of NO. We hypothesized that infection-induced atherosclerosis is initiated by changes in NO metabolism and may be reversed by azithromycin treatment.

METHODS

Confluent human umbilical vein endothelial cells (HUVECs) were infected with Cp or CMV. After 48 h of infection, production of eNOS, cyclic guanosine monophosphate (cGMP) and reactive oxygen species (ROS) was measured. Detection of cGMP was used as a reporter assay for the bioavailability of NO. Subsequently, Cp- and CMV-infected HUVECs were coincubated with 0.016 mg L(-1) and 1 mg L(-1) azithromycin.

RESULTS

Infection with Cp (MOI 1 and MOI 0.1) and CMV (MOI 1) caused a dose- and time-dependent reduction of eNOS production in the HUVECs: Cp MOI 1: 1141 +/- 74 pg mL(-1) (P < 0.01); Cp MOI 0.1: 3189 +/- 30 pg mL(-1) (P < 0.01); CMV: 3213 +/- 11 pg mL(-1) (P < 0.01) vs. 3868 +/- 83 pg mL(-1) for uninfected HUVECs. Chlamydia pneumoniae- but not CMV-infection also reduced cGMP-production (Cp: 0.195 +/- 0.030 pmol mL(-1) (P < 0.01); CMV: 0.371 +/- 27 pmol mL(-1) (P > 0.05) vs. 0.378 +/- 0.019 pmol mL(-1) for uninfected HUVECs). CMV-infection did not affect ROS production either, but Cp-infection reduced ROS-production by 21% (P > 0.05; Cp MOI 0.1) to 68% (P < 0.01; Cp MOI 1). Azithromycin treatment restored Cp-induced eNOS, cGMP and ROS production in a dose-dependent manner.

CONCLUSIONS

Infection with Cp in endothelial cells in vitro attenuates eNOS, cGMP and ROS production in HUVECs and azithromycin reverses Cp-induced effects on eNOS, cGMP and ROS-production. The results from our in vitro research support the role of antibiotic therapy for infection-induced atherosclerosis by indicating that azithromycin does actually improve endothelial function.

International guidelines for the treatment of community-acquired pneumonia in adults: the role of macrolides

The significance of community-acquired pneumonia (CAP) has led to the publication of guidelines from numerous international organisations. Because the macrolide class of antimicrobials is active against most of the key pathogens associated with CAP, agents from this class are commonly included in recommendations from these guidelines. However, there are differences among the various guidelines concerning the positioning of the macrolides for empirical therapy. An important factor concerning the use of macrolides for CAP is the emergence of resistance of Streptococcus pneumoniae over the past decade. The rate of S. pneumoniae resistance to macrolides ranges from 4 to 70% of strains in worldwide surveillance studies. The most common mechanisms of resistance include methylation of a ribosomal target encoded by the erm gene and efflux of the macrolides by a cell membrane protein transporter, encoded by the mef gene. S. pneumoniae strains with the mef gene are resistant at a lower level (with minimum inhibitory concentration [MIC] values generally 1-16 microg/ml) than erm resistant strains; and it is possible that such strains may be inhibited if sufficiently high levels of macrolide can be obtained at the infected site. Currently mef-associated resistance predominates in North America, whereas erm predominates in Europe. Until recently, reports of failure of treatment of CAP with macrolides has been rare, particularly for patients with low-risk for drug-resistant strains. However, since 2000, several patients treated with an oral macrolide who have subsequently required admission to the hospital for macrolide-resistant S. pneumoniae (MRSP) bacteraemia have been reported in the literature. Major issues, which are fundamental to the use of the macrolides as recommended in the various guidelines, include the importance of providing therapy for 'atypical' pathogens and the clinical significance of MRSP. Presently, the macrolides are more prominently recommended in the North American guidelines than in other parts of the world. The difference in the emphasis placed on the importance of the atypical pathogens as well as the expression of MRSP in North America compared with Europe partly explains this variance.

Antibiotic susceptibilities of Parachlamydia acanthamoeba in amoebae

Parachlamydia acanthamoeba are intracellular bacteria of amoebae and are considered potential etiological agents of human pneumonia. We have determined the in vitro antibiotic susceptibilities of two strains (strain Bn(9) and Hall's coccus) in Acanthamoeba polyphaga. The two strains were susceptible to tetracyclines, macrolides, and rifampin, but resistant to fluoroquinolones.

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.

Clinical efficacy of intravenous followed by oral azithromycin monotherapy in hospitalized patients with community-acquired pneumonia. The Azithromycin Intravenous Clinical Trials Group

The purpose of this study was to evaluate intravenous (i.v.) azithromycin followed by oral azithromycin as a monotherapeutic regimen for community-acquired pneumonia (CAP). Two trials of i.v. azithromycin used as initial monotherapy in hospitalized CAP patients are summarized. Clinical efficacy is reported from an open-label randomized trial of azithromycin compared to cefuroxime with or without erythromycin. Bacteriologic and clinical efficacy results are also presented from a noncomparative trial of i.v. azithromycin that was designed to give additional clinical experience with a larger number of pathogens. Azithromycin was administered to 414 patients: 202 and 212 in the comparative and noncomparative trials, respectively. The comparator regimen was used as treatment for 201 patients; 105 were treated with cefuroxime alone and 96 were given cefuroxime plus erythromycin. In the comparative trial, clinical outcome data were available for 268 evaluable patients with confirmed CAP at the 10- to 14-day visit, with 106 (77%) of the azithromycin patients cured or improved and 97 (74%) of the comparator patients cured or improved. Mean i.v. treatment duration and mean total treatment duration (i.v. and oral) for the clinically evaluable patients were significantly (P < 0.05) shorter for the azithromycin group (3.6 days for the i.v. group and 8.6 days for the i.v. and oral group) than for the evaluable patients given cefuroxime plus erythromycin (4.0 days for the i.v. group and 10.3 days for the i.v. and oral group). The present comparative study demonstrates that initial therapy with i.v. azithromycin for hospitalized patients with CAP is associated with fewer side effects and is equal in efficacy to a 1993 American Thoracic Society-suggested regimen of cefuroxime plus erythromycin when the erythromycin is deemed necessary by clinicians.

Pharyngeal colonization prevalence rates for Streptococcus pyogenes and Streptococcus pneumoniae in a respiratory chemoprophylaxis intervention study using azithromycin

OBJECTIVES

A prospective assessment of the pharyngeal colonization prevalence rates for Streptococcus pyogenes and Streptococcus pneumoniae before and after an azithromycin chemoprophylaxis intervention clinical trial in a cohort of US Marine Corps trainees. In addition, the minimum inhibitory concentrations (MICs) for all streptococcal isolates, for azithromycin, penicillin, erythromycin and cefotaxime are reported.

METHODS

Between November 1994 and March 1995, 1108 asymptomatic male US Marine Corps trainees, located in Southern California, were randomly assigned to one of three intervention groups: (1) weekly oral azithromycin, 500 mg (n = 362); (2) 1.2 MU benzathine penicillin G, intramuscularly once (n = 374); or (3) no chemoprophylaxis (n = 372). Subjects provided both a pre- and post-training pharyngeal culture and microbial analysis was conducted to determine the colonization status of each study subject.

RESULTS

The pretraining colonization prevalence was 1.2% for S. pneumoniae and 2.4% for S. pyogenes. There was no statistical difference in pretraining prevalence between the three treatment groups for either organism. Post-training pharyngeal cultures revealed an overall prevalence of 1.1% with no difference between treatment arms. However, the overall post-training prevalence of S. pyogenes colonization increased to 4.8%, with the azithromycin group having significant evidence of protection (0.7%) in comparison with the no-treatment group (8.2%). The Etest method demonstrated no significant difference in the MIC50, MIC90, and MIC ranges between pre- and post-training isolates for any of the tested drugs.

CONCLUSION

The use of azithromycin as a chemoprophylactic agent to reduce the colonization and subsequent infection of streptococcal respiratory disease among healthy adult male military recruits may be beneficial.

In vitro susceptibilities of Chlamydia pneumoniae isolates from German patients and synergistic activity of antibiotic combinations

The susceptibilities of six Chlamydia pneumoniae type strains and of six German patient isolates to erythromycin, azithromycin, roxithromycin, clarithromycin, doxycycline, ofloxacin, and rifampin were investigated. MICs and minimal chlamydicidal concentrations were all within the ranges reported previously. Combinations of azithromycin with either ofloxacin, doxycycline, or rifampin, as well as combinations of three antibiotics (rifampin, azithromycin, and ofloxacin or doxycycline), showed synergistic activity against C. pneumoniae.

The macrolides: erythromycin, clarithromycin, and azithromycin

In addition to erythromycin, macrolides now available in the United States include azithromycin and clarithromycin. These two new macrolides are more chemically stable and better tolerated than erythromycin, and they have a broader antimicrobial spectrum than erythromycin against Mycobacterium avium complex (MAC), Haemophilus influenzae, nontuberculous mycobacteria, and Chlamydia trachomatis. All three macrolides have excellent activity against the atypical respiratory pathogens (C. pneumoniae and Mycoplasma species) and the Legionella species. Azithromycin and clarithromycin have pharmacokinetics that allow shorter dosing schedules because of prolonged tissue levels. Both azithromycin and clarithromycin are active agents for MAC prophylaxis in patients with late-stage acquired immunodeficiency syndrome (AIDS), although azithromycin may be the preferable agent because of fewer drug-drug interactions. Clarithromycin is the most active MAC antimicrobial agent and should be part of any drug regimen for treating active MAC disease in patients with or without AIDS. Although both azithromycin and clarithromycin are well tolerated by children, azithromycin has the advantage of shorter treatment regimens and improved tolerance, potentially improving compliance in the treatment of respiratory tract and skin or soft tissue infections. Intravenously administered azithromycin has been approved for treatment of adults with mild to moderate community-acquired pneumonia or pelvic inflammatory diseases. An area of concern is the increasing macrolide resistance that is being reported with some of the common pathogens, particularly Streptococcus pneumoniae, group A streptococci, and H. influenzae. The emergence of macrolide resistance with these common pathogens may limit the clinical usefulness of this class of antimicrobial agents in the future.

Azithromycin. A review of its use in paediatric infectious diseases

Azithromycin is an azalide antimicrobial agent active in vitro against major pathogens responsible for infections of the respiratory tract, skin and soft tissues in children. Pathogens that are generally susceptible to azithromycin include Haemophilus influenzae (including ampicillin-resistant strains), Moraxella catarrhalis, Chlamydia pneumoniae, Chlamydia trachomatis, Mycoplasma pneumoniae, Legionella spp., Streptococcus pyogenes and Streptococcus agalactiae. Azithromycin is also generally active against erythromycin- and penicillin-susceptible Streptococcus pneumoniae and methicillin-susceptible Staphylococcus aureus. Azithromycin is administered once daily, achieves clinically relevant concentrations at sites of infection, is slowly eliminated from the body and has few drug interactions. In children, azithromycin is usually given as either a 3-day course of 10 mg/kg/day or a 5-day course with 10 mg/kg on the first day, followed by 5 mg/kg/day for a further 4 days. These standard regimens were as effective as amoxicillin/clavulanic acid, clarithromycin, cefaclor and amoxicillin in the treatment of children with otitis media. Azithromycin was also as effective as either phenoxymethylpenicillin (penicillin V), erythromycin, clarithromycin or cefaclor against streptococcal pharyngitis or tonsillitis in children, but appears to result in more recurrence of infection than phenoxymethylpenicillin in this indication, necessitating a dosage of 12 mg/kg/day for 5 days. Community-acquired pneumonia, bronchitis and other respiratory tract infections in children responded as well to azithromycin as to amoxicillin/clavulanic acid, cefaclor, erythromycin or josamycin. Azithromycin was similar or superior to ceftibuten in mixed general practice populations of patients. However, symptoms of lower respiratory tract infections resolved more rapidly with azithromycin than with erythromycin, josamycin or cefaclor. Skin and soft tissue infections responded as well to azithromycin as to cefaclor, dicloxacillin or flucloxacillin, and oral azithromycin was as effective as ocular tetracycline in treating trachoma. Although not as well tolerated as phenoxymethylpenicillin in the treatment of streptococcal pharyngitis, azithromycin is at least as well tolerated as most other agents used to treat respiratory tract and other infections in children and was better tolerated than amoxicillin/clavulanic acid. Adverse events that do occur are mostly gastrointestinal and tend to be mild to moderate in severity.

CONCLUSIONS

Azithromycin is an effective and well tolerated alternative to first-line agents in the treatment of respiratory tract, skin and soft tissue infections in children, offerring the convenience of a short, once-daily regimen.

Susceptibility of Chlamydia pneumoniae to azithromycin and doxycycline: methodological aspects on the determination of minimal inhibitory and minimal bactericidal concentrations

An in vitro assay for measuring and comparing the efficacy of different antimicrobial agents against Chlamydia pneumoniae was developed. Azithromycin, a representative of the new azalide group of antibiotics, and doxycycline were evaluated with respect to their antibacterial effect and capacity for intracellular killing under different experimental conditions. For both study drugs, the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values increased significantly with longer bacterial preincubation time. The effect of different exposure times of antibiotics on the bacteria was also studied.

The treatment of non-gonococcal urethritis with single dose oral azithromycin

In an uncontrolled study, the efficacy of azithromycin in the treatment of non-gonococcal urethritis was assessed in 41 male patients aged between 20 and 40 years with a mean age of 27 +/- 5 years. Clinical and microbiological diagnosis confirmed that 28 men were found positive for Chlamydia trachomatis, 10 for Ureaplasma urealyticum and three for both C. trachomatis and U. urealyticum. All patients received 1 g azithromycin orally (four 250 mg capsules). The length of time between the treatment and following visits were 7-10 days and 14-21 days for second and third visits, respectively. Complete eradication was achieved in 27 out of 41 patients. Of the remaining 14, six were found positive for C. trachomatis and were excluded as they did not return for the follow-up visit, one patient did not achieve complete eradication, one patient infected with both C. trachomatis and U. urealyticum failed to achieve complete eradication, and six patients infected with U. urealyticum failed to be completely cured. No adverse effects were reported in any patient. Single dose administration of 1 g azithromycin appears to be an effective and well-tolerated treatment for chlamydial urethritis and an advantage in terms of patient compliance.

Chlamydia pneumoniae and chronic pharyngitis

Chlamydia pneumoniae has been implicated as an etiological agent for both upper and lower respiratory tract infections. We describe 4 cases of chronic pharyngitis where Chlamydia pneumoniae appears to be the etiological agent. All the patients were non-smokers, and had symptoms of more than 6 months' duration. Disease symptoms seemed to resolve following appropriate antibiotic treatment.

In vitro and in vivo activities of azithromycin, a new azalide antibiotic, against chlamydia

The in vitro and in vivo activities of azithromycin against chlamydia were investigated. The MIC of azithromycin for five standard strains of different species of chlamydia and six wild-type strains of Chlamydia pneumoniae was 0.125 microgram/ml, which was superior to that of erythromycin but inferior to those of clarithromycin and minocycline. However, the therapeutic effect of a 7-day course of azithromycin at a dose of 10 mg/kg of body weight administered orally once daily to mice with experimental Chlamydia psittaci pneumonia was excellent, with a 100% survival rate at 14 days after infection, which was the same as that for treatment with minocycline administered at 10 mg/kg twice daily; all erythromycin treated animals died within 10 days. When treatment was discontinued 3 days after the infection, the survival rate for mice treated with azithromycin was 90% and that for mice administered minocycline was 30%. These results suggest that azithromycin may be useful in the treatment of respiratory infections caused by intracellular pathogens, including chlamydia because of its excellent accumulation within host cells.