Mycobacterium tuberculosis gene expression at different stages of hypoxia-induced dormancy and upon resuscitation

The physiology of dormant Mycobacterium tuberculosis was studied in detail by examining the gene expression of 51 genes using quantitative Reverse-Transcription Polymerase Chain Reaction. A forty-day period of dormancy in the Wayne culture model depicted four major transcription patterns. Some sigma factors and many metabolic genes were constant, whereas genes belonging to the dormancy regulon were activated on day 9. In particular, alpha-crystallin mRNA showed more than a 1,000-fold increase compared to replicating bacilli. Genes belonging to the enduring hypoxic response were up-regulated at day 16, notably, transcription factors sigma B and E. Early genes typical of log-phase bacilli, esat-6 and fbpB, were uniformly down-regulated during dormancy. Late stages of dormancy showed a drop in gene expression likely due to a lack of substrates in anaerobic respiration as demonstrated by the transcriptional activation observed following nitrates addition. Among genes involved in nitrate metabolism, narG was strongly up-regulated by nitrates addition. Dormant bacilli responded very rapidly when exposed to oxygen and fresh medium, showing a transcriptional activation of many genes, including resuscitation-promoting factors, within one hour. Our observations extend the current knowledge on dormant M. tuberculosis gene expression and its response to nutrients and to aerobic and anaerobic respiration.

Infection of human THP-1 cells with dormant Mycobacterium tuberculosis

Dormant, non-replicating Mycobacterium tuberculosis H37Rv strain cultured in hypoxic conditions was used to infect THP-1 cells. CFUs counting, Kinyoun staining and electron microscopy showed that dormant bacilli infected THP-1 cells at a rate similar to replicating M. tuberculosis, but failed to grow during the first 6 days of infection. The absence of growth was specific to the intracellular compartment, as demonstrated by efficient growth in liquid medium. Quantification of β-actin mRNA recovered from infected cells showed that, in contrast with log-phase bacteria, infection with dormant bacilli determined a reduced THP-1 cell death. Gene expression of intracellular non-replicating bacteria showed a pattern typical of a dormant state. Intracellular dormant bacteria induced the activation of genes associated to a proinflammatory response in THP-1 cells. Though, higher levels of TNFα, IL-1β and IL-8 mRNAs compared to aerobic H37Rv infected cells were not paralleled by increased cytokine accumulation in the supernatants. Moreover, dormant bacilli induced a higher expression of inducible cox-2 gene, accompanied by increased PGE2 secretion. Overall, our data describe a new model of in vitro infection using dormant M. tuberculosis that could provide the basis for understanding how non-replicating bacilli survive intracellularly and influence the maintenance of the hypoxic granuloma.

Characteristics of drug-resistant tuberculosis in Abkhazia (Georgia), a high-prevalence area in Eastern Europe

Although multidrug-resistant (MDR) tuberculosis (TB) is a major public health problem in Eastern Europe, the factors contributing to emergence, spread and containment of MDR-TB are not well defined. Here, we analysed the characteristics of drug-resistant TB in a cross-sectional study in Abkhazia (Georgia) between 2003 and 2005, where standard short-course chemotherapy is supplemented with individualized drug-resistance therapy. Drug susceptibility testing (DST) and molecular typing were carried out for Mycobacterium tuberculosis complex strains from consecutive smear-positive TB patients. Out of 366 patients, 60.4% were resistant to any first-line drugs and 21% had MDR-TB. Overall, 25% of all strains belong to the Beijing genotype, which was found to be strongly associated with the risk of MDR-TB (OR 25.9, 95% CI 10.2-66.0) and transmission (OR 2.8, 95% CI 1.6-5.0). One dominant MDR Beijing clone represents 23% of all MDR-TB cases. The level of MDR-TB did not decline during the study period, coinciding with increasing levels of MDR Beijing strains among previously treated cases. Standard chemotherapy plus individualized drug-resistance therapy, guided by conventional DST, might be not sufficient to control MDR-TB in Eastern Europe in light of the spread of "highly transmissible" MDR Beijing strains circulating in the community.

The toll-like receptor 2/6 ligand MALP-2 reduces the viability of Mycobacterium tuberculosis in murine macrophages

Toll-like receptors (TLRs) sense conserved structures of pathogens and influence macrophage functions. Here we investigated the impact of TLR signaling on the modulation of macrophage defense mechanisms against infection of Mycobacterium tuberculosis (MTB), the causative agent of tuberculosis. We found that a synthetic derivative of the TLR2/6 agonist MALP-2 and the potent TLR4 agonist lipopolysaccharide inhibited the intracellular growth of MTB in murine macrophages. Likely the microbicidal effect was mediated by production of nitric oxide while it is still unclear the role played by release of TNF-α , IL-6, MIP-1β and IL-10. These results suggest that the activation of microbicidal defense via TLR ligands is an appealing target for the establishment on immune intervention against tuberculosis.

External quality control of Mycobacterium tuberculosis drug susceptibility testing: results of two rounds in endemic countries

SETTING

Quality assurance for the World Health Organization (WHO)/International Union Against Tuberculosis and Lung Disease (The Union) global tuberculosis (TB) drug resistance surveillance programme.

OBJECTIVE

To monitor the quality of drug susceptibility testing (DST) in different countries.

METHODS

In 2002-2003 and 2005-2006, 20 Mycobacterium tuberculosis strains were sent by the WHO/Union Supranational Reference Laboratory of Rome to TB reference laboratories in Albania, Bahrain, Kosovo, Mozambique, Oman, Qatar and Turkey for external quality control (EQC).

RESULTS

In 2002-2003, the specificity, sensitivity, efficiency, reproducibility and predictive values for resistance/susceptibility were >or=90% for streptomycin (SM), isoniazid (INH) and ethambutol (EMB). In 2005-2006, all statistical values were >or=96% for SM, INH, rifampicin and EMB.

CONCLUSION

EQC improved the quality of M. tuberculosis DST in the participating countries.

Validation of the agar proportion and 2 liquid systems for testing the susceptibility of Mycobacterium tuberculosis to moxifloxacin

Moxifloxacin (MOX), an 8-methoxyquinolone compound, is now widely used for the treatment of bacterial infections and also accepted as 2nd-line drug for the treatment of multidrug-resistant (MDR) tuberculosis. To tentatively correlate the clinical outcome with in vitro results, we sought to set up susceptibility test conditions for Mycobacterium tuberculosis against MOX by using the reference agar proportion method, the BACTEC 460 radiometric system, and the recently validated nonradiometric BACTEC MGIT 960 system. Our aim was to determine the critical MOX test concentration to be used with the abovementioned methods for routine susceptibility testing. MICs were determined for 20 pan-susceptible strains, 10 MDR strains, and 10 fluoroquinolone-resistant strains with defined gyrA mutations. MOX MICs resulted in a bimodal pattern with values for gyrA mutants considerably higher than those for pan-susceptible and MDR strains. Our data showed that a concentration of 0.5 microg/mL allowed a clear-cut separation between susceptible and resistant strains when tested by all the studied methods. Confirmatory test with a subset of pan-susceptible and MDR isolates appeared to validate the selected critical concentration. The MOX-resistant strains were almost isolated from patients with prior fluoroquinolone exposure.

The Ag85B protein of Mycobacterium tuberculosis may turn a protective immune response induced by Ag85B-DNA vaccine into a potent but non-protective Th1immune response in mice

Clarifying how an initial protective immune response to tuberculosis may later loose its efficacy is essential to understand tuberculosis pathology and to develop novel vaccines. In mice, a primary vaccination with Ag85B-encoding plasmid DNA (DNA-85B) was protective against Mycobacterium tuberculosis (MTB) infection and associated with Ag85B-specific CD4+ T cells producing IFN-gamma and controlling intramacrophagic MTB growth. Surprisingly, this protection was eliminated by Ag85B protein boosting. Loss of protection was associated with a overwhelming CD4+ T cell proliferation and IFN-gamma production in response to Ag85B protein, despite restraint of Th1 response by CD8+ T cell-dependent mechanisms and activation of CD4+ T cell-dependent IL-10 secretion. Importantly, these Ag85B-responding CD4+ T cells lost the ability to produce IFN-gamma and control MTB intramacrophagic growth in coculture with MTB-infected macrophages, suggesting that the protein-dependent expansion of non-protective CD4+ T cells determined dilution or loss of the protective Ag85B-specific CD4+ induced by DNA-85B vaccination. These data emphasize the need of exerting some caution in adopting aggressive DNA-priming, protein-booster schedules for MTB vaccines. They also suggest that Ag85B protein secreted during MTB infection could be involved in the instability of protective anti-tuberculosis immune response, and actually concur to disease progression.

Isolation of Nocardia asiatica from cutaneous ulcers of a human immunodeficiency virus-infected patient in Italy

A strain of Nocardia was isolated from cutaneous ulcers of a human immunodeficiency virus-infected patient in Italy. Comparative 16S rRNA gene sequence analysis revealed that the isolate represented a strain of Nocardia asiatica. Antimicrobial susceptibility testing was essential to guide the clinicians to successfully treat this infection.

BCG-infected adherent mononuclear cells release cytokines that regulate group 1 CD1 molecule expression

Increasing evidence is now available showing that CD1-restricted T cell responses against non-peptide mycobacterial antigens could play a role in the immune resistance against tuberculosis. BCG, widely used in anti-tubercular vaccination, shares various constituents with Mycobacterium tuberculosis, but does not provide full protection. In the present study we have investigated the pattern of group 1 CD1 molecule expression in adherent mononuclear cells (AMNC) of human peripheral blood, infected in vitro with BCG. Shortly after exposure to BCG, both BCG-positive and BCG-negative AMNC showed a moderate CD1 expression elicited by BCG-induced release of GM-CSF presumably acting through an autocrine and a paracrine mechanism. This was demonstrated using two-color flow cytometry with green fluorescent BCG and anti-CD1 PE-labeled antibodies. However, high CD1 expression induced by exogenously added GM-CSF in AMNC was reduced if target cells were cocultivated with BCG. Monoclonal antibodies against IL-10 partially restored CD1 expression, thus showing that IL-10, released from infected AMNC, is involved, at least in part, in CD1 negative modulation. Therefore, through a complex cytokine network, including not yet identified factor(s), BCG triggers but does not allow full expression of CD1 on AMNC. It cannot be excluded that this mechanism could play a role in the limited efficiency of BCG vaccination.

Metronidazole plus rifampin sterilizes long-term dormant Mycobacterium tuberculosis

Long-term nonreplicating (dormant) Mycobacterium tuberculosis populations (26-day-old cells) were sterilized by metronidazole plus rifampin, but not by metronidazole or rifampin alone, after 7 and 11 days of exposure to the drugs. Lower or no drug activity was observed against 19- or 12-day-old dormant or 5-day-old actively replicating populations.

Immune response and protection by DNA vaccines expressing antigen 85B of Mycobacterium tuberculosis

A plasmid DNA containing two different expression cassettes was prepared to independently drive antigen 85B (85B) of Mycobacterium tuberculosis and HIV-Tat in C57BL/6 mice. In vivo expression of the plasmid was demonstrated by efficient transcription of 85B and Tat mRNAs in mouse fibroblasts. DNA-85B or DNA-(85B-Tat) were immunogenic and protected mice to the same extent against M. tuberculosis infection, with a decrease in the numbers of CFU lung-1 in comparison with nonimmunized animals down to levels (0.64 log10 CFU) not significantly different from protection conferred by bacillus Calmette-Guérin vaccine (0.97 log10 CFU decrease). Multipromoter plasmids, which permit the reduction of the total amount of DNA injected, can be useful for DNA vaccination against tuberculosis.

Infection of human dendritic cells with a Mycobacterium tuberculosis sigE mutant stimulates production of high levels of interleukin-10 but low levels of CXCL10: impact on the T-cell response

The Mycobacterium tuberculosis genome encodes 13 sigma factors. We have previously shown that mutations in some of these transcriptional activators render M. tuberculosis sensitive to various environmental stresses and can attenuate the virulence phenotype. In this work, we focused on extracytoplasmic factor sigmaE and studied the effects induced by the deletion of its structural gene (sigE) in the infection of human monocyte-derived dendritic cells (MDDC). We found that the wild-type M. tuberculosis strain (H37Rv), the sigE mutant (ST28), and the complemented strain (ST29) were able to infect dendritic cells (DC) to similar extents, although at 4 days postinfection a reduced ability to grow inside MDDC was observed for the sigE mutant ST28. After mycobacterium capture, the majority of MDDC underwent full maturation and expressed both inflammatory cytokines, such as tumor necrosis factor alpha, and the regulatory cytokines interleukin-12 (IL-12), IL-18, and beta interferon (IFN-beta). Conversely, a higher level of production of IL-10 was observed in ST28-infected MDDC compared to H37Rv- or ST29-infected cell results. However, in spite of the presence of IL-10, supernatants from ST28-infected DC induced IFN-gamma production by T cells similarly to those from H37Rv-infected DC culture. On the other hand, IL-10 impaired CXCL10 production in sigE mutant-infected DC and, indeed, its neutralization restored CXCL10 secretion. In line with these results, supernatants from ST28-infected cells showed a decreased capability to recruit CXCR3+ CD4+ T cells compared to those obtained from H37Rv-infected DC culture. Thus, our findings suggest that the sigE mutant-induced secretion of IL-10 inhibits CXCL10 expression and, in turn, the recruitment of activated-effector cells involved in the formation of granulomas.

Does one size fit all? Drug resistance and standard treatments: results of six tuberculosis programmes in former Soviet countries

SETTING

After the collapse of the Soviet Union, countries in the region faced a dramatic increase in tuberculosis cases and the emergence of drug resistance.

OBJECTIVE

To discuss the relevance of the DOTS strategy in settings with a high prevalence of drug resistance.

DESIGN

Retrospective analysis of one-year treatment outcomes of short-course chemotherapy (SCC) and results of drug susceptibility testing (DST) surveys of six programmes located in the former Soviet Union: Kemerovo prison, Russia; Abkhasia, Georgia; Nagorno-Karabagh, Azerbaijan; Karakalpakstan, Uzbekistan; Dashoguz Velayat, Turkmenistan; and South Kazakhstan Oblast, Kazakhstan. Results are reported for new and previously treated smear-positive patients.

RESULTS

Treatment outcomes of 3090 patients and DST results of 1383 patients were collected. Treatment success rates ranged between 87% and 61%, in Nagorno-Karabagh and Kemerovo, respectively, and failure rates between 7% and 23%. Any drug resistance ranged between 66% and 31% in the same programmes. MDR rates ranged between 28% in Karakalpakstan and Kemerovo prison and 4% in Nagorno-Karabagh.

CONCLUSION

These results show the limits of SCC in settings with a high prevalence of drug resistance. They demonstrate that adapting treatment according to resistance patterns, access to reliable culture, DST and good quality second-line drugs are necessary.

Drug resistance evolution of a Mycobacterium tuberculosis strain from a noncompliant patient

The emergence and spread of multidrug-resistant (MDR) Mycobacterium tuberculosis (MT) represents a worldwide health care problem because of the difficulty in treating these infections. Development of drug resistance in MT arises mainly by mutation of chromosomal genes. To investigate the evolution of a MT population during a long-lasting infection, the phenotypic and genotypic changes in the drug resistance of 10 sequential MT isolates from a noncompliant chronically infected patient were investigated. During more than 12 years of active disease, a MDR population developed; molecular typing showed one single parental strain that infected the patient and persisted throughout the disease. Molecular analysis of the drug resistance-related genes revealed that discrete subpopulations evolved over time from the parental strain by acquiring and accumulating resistance-conferring mutations to isoniazid, rifampin, and streptomycin. Overall, these observations indicate that during a chronic infection, several subpopulations may coexist in the same patient with different drug susceptibility profiles.

Evaluation of a new line probe assay for rapid identification of gyrA mutations in Mycobacterium tuberculosis

Resistance of Mycobacterium tuberculosis to fluoroquinolones (FQ) results mostly from mutations in the gyrA gene. We developed a reverse hybridization-based line probe assay in which oligonucleotide probes carrying the wild-type gyrA sequence, a serine-to-threonine (S95T) polymorphism, and gyrA mutations (A90V, A90V-S95T, S91P, S91P-S95T, D94A, D94N, D94G-S95T, D94H-S95T) were immobilized on nitrocellulose strips and hybridized with digoxigenin-labeled PCR products obtained from M. tuberculosis strains. When a mutated PCR product was used, hybridization occurred to the corresponding mutated probe but not to the wild-type probe. A panel of M. tuberculosis complex strains including 19 ofloxacin-resistant (OFL-R) and 9 ofloxacin-susceptible (OFL-S) M. tuberculosis strains was studied for detection and identification of gyrA mutations by the line probe assay and nucleotide sequencing, in comparison with testing of in vitro susceptibility to FQ. Results were 100% concordant with those of nucleotide sequencing. The S95T polymorphism, which is not related to FQ resistance, was found in 5 OFL-S and 2 OFL-R strains; the other 17 OFL-R strains harbored single mutations associated with serine or threonine at codon 95. No mutations were found in the other OFL-S strains. Overall, on the basis of the MICs on solid medium, the new line probe assay correctly identified all OFL-S and 17 out of 19 (89.5%) OFL-R strains. A nested-PCR protocol was also evaluated for the assay to amplify PCR products from M. tuberculosis-spiked sputa, with a good specificity and a sensitivity of 2 x 10(3) M. tuberculosis CFU per ml of sputum.

Bacillus Calmette-Guérin shares with virulent Mycobacterium tuberculosis the capacity to subvert monocyte differentiation into dendritic cell: implication for its efficacy as a vaccine preventing tuberculosis

The only available vaccine against tuberculosis (TB) is Bacillus Calmette-Guérin (BCG) whose efficacy in preventing pulmonary tuberculosis is however controversial. Here, we show that BCG infection of monocytes causes their differentiation into mature dendritic cells (DCs) lacking CD1 molecules expression, coupled with suboptimal up-regulation of HLA class II, CD80 and CD40 molecules and a marked unresponsiveness to lipopolysaccharide stimulation. In addition, alloreactive naïve T lymphocytes primed by these subverted DCs did not undergo defined functional polarization, as witnessed by their inability to produce IFN-gamma. Since efficient antigen presentation and IFN-gamma production by mycobacterial-specific T lymphocytes are required for protection against Mycobacterium tuberculosis, our data might provide additional explanation for the low efficacy of BCG vaccination.

Cetyl-pyridinium chloride is useful for isolation of Mycobacterium tuberculosis from sputa subjected to long-term storage

Recovery of Mycobacterium tuberculosis from sputa treated with cetyl-pyridinium chloride (CPC) and stored for 20 +/- 9 days was significantly higher than that from sputa that were untreated and processed by the N-acetyl-L-cisteine-NaOH method. Addition of CPC is useful for isolation of M. tuberculosis from sputa subjected to long-term storage received from remote areas of the world.

Mycobacterium tuberculosis diverts alpha interferon-induced monocyte differentiation from dendritic cells into immunoprivileged macrophage-like host cells

Dendritic cells (DCs) are critical for initiating a pathogen-specific T-cell response. During chronic infections the pool of tissue DCs must be renewed by recruitment of both circulating DC progenitors and in loco differentiating monocytes. However, the interaction of monocytes with pathogens could affect their differentiation. Mycobacterium tuberculosis has been shown to variably interfere with the generation and function of antigen-presenting cells (APCs). In this study we found that when alpha interferon (IFN-alpha) is used as an inductor of monocyte differentiation, M. tuberculosis inhibits the generation of DCs, forcing the generation of immunoprivileged macrophage-like cells instead. Cells derived from M. tuberculosis-infected monocyte-derived macrophages (M. tuberculosis-infected MoMphi) retained CD14 without acquiring CD1 molecules and partially expressed B7.2 but did not up-regulate B7.1 and major histocompatibility complex (MHC) class I and II molecules. They synthesized tumor necrosis factor alpha and interleukin-10 (IL-10) but not IL-12. They also showed a reduced ability to induce proliferation and functional polarization of allogeneic T lymphocytes. Thus, in the presence of IFN-alpha, M. tuberculosis may hamper the renewal of potent APCs, such as DCs, generating a safe habitat for intracellular growth. M. tuberculosis-infected MoMphi, in fact, showed reduced expression of both signal 1 (CD1, MHC classes I and II) and signal 2 (B7.1 and B7.2), which are essential for mycobacterium-specific T-lymphocyte priming and/or activation. These data further suggest that M. tuberculosis has the ability to specifically interfere with monocyte differentiation. This ability may represent an effective M. tuberculosis strategy for eluding immune surveillance and persisting in the host.

The extra cytoplasmic function sigma factor sigma(E) is essential for Mycobacterium tuberculosis virulence in mice

The virulence of a Mycobacterium tuberculosis H37Rv sigE mutant was studied in immunodeficient and immunocompetent mice. The mutant was strongly attenuated in both animal models and induced formation of granulomas with different characteristics than those induced by the wild-type strain.

An anti-inflammatory role for V alpha 14 NK T cells in Mycobacterium bovis bacillus Calmette-Guérin-infected mice

The possible contribution of NKT cells to resistance to Mycobacterium tuberculosis infection remains unclear. In this paper we characterized the Valpha14 NKT cell population following infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG). BCG infection determined an early expansion of Valpha14 NKT cells in liver, lungs, and spleen, which peaked on day 8 and was sustained until day 30. However, an NK1.1(+) Valpha14 NKT population preferentially producing IFN-gamma predominated at an early stage (day 8), which was substituted by an NK1.1(-) population preferentially producing IL-4 at later stages (day 30). Despite the fact that Valpha14 NKT cell-deficient mice eliminated BCG as did control mice, they had significantly higher numbers of granulomas in liver and lungs. Additionally, while control mice developed organized small granulomas, those in Valpha14 NKT-deficient mice had signs of caseation, large cellular infiltrates, and some multinucleated macrophages, suggesting that Valpha14 NKT cells may actually work as anti-inflammatory cells by limiting excessive lymphocyte influx and tissue pathology. In agreement, we found an increased spontaneous production and mRNA expression of TNF-alpha in liver and lungs of Valpha14 NKT-deficient mice, whose neutralization in vivo by anti-TNF-alpha mAbs consistently reduced the number of granulomas in liver and lungs. Together, our results support a regulatory role for Valpha14 NKT cells in the course of BCG infection through their ability to limit the extent of inflammatory response and point to an important role for this cell subset as a regulator of the balance between protective responses and immunopathology.

IFN-alpha beta released by Mycobacterium tuberculosis-infected human dendritic cells induces the expression of CXCL10: selective recruitment of NK and activated T cells

We recently reported that dendritic cells (DC) infected with Mycobacterium tuberculosis (Mtb) produce Th1/IFN-gamma-inducing cytokines, IFN-alpha beta and IL-12. In the present article, we show that maturing Mtb-infected DC express high levels of CCR7 and they become responsive to its ligand CCL21. Conversely, CCR5 expression was rapidly lost from the cell surface following Mtb infection. High levels of CCL3 and CCL4 were produced within 8 h after infection, which is likely to account for the observed CCR5 down-modulation on Mtb-infected DC. In addition, Mtb infection stimulated the secretion of CXCL9 and CXCL10. Interestingly, the synthesis of CXCL10 was mainly dependent on the Mtb-induced production of IFN-alpha beta. Indeed, IFN-alpha beta neutralization down-regulated CXCL10 expression, whereas the expression of CXCL9 appeared to be unaffected. The chemotactic activity of the Mtb-infected DC supernatants was evaluated by migration assays using activated NK, CD4(+), and CD8(+) cells that expressed both CCR5 and CXCR3. Mtb-induced expression of CCL3, CCL4, CXCL9, and CXCL10 was involved in the stimulation of NK and T cell migration. In accordance with the data on the IFN-alpha beta-induced expression of CXCL10, neutralization of IFN-alpha beta significantly reduced the chemotactic activity of the supernatant from Mtb-infected DC. This indicates that IFN-alpha beta may modulate the immune response through the expression of CXCL10, which along with CXCL9, CCL3, and CCL4 participates in the recruitment and selective homing of activated/effector cells, which are known to accumulate at the site of Mtb infection and take part in the formation of the granulomas.

Activities of moxifloxacin alone and in combination with other antimicrobial agents against multidrug-resistant Mycobacterium tuberculosis infection in BALB/c mice

The activity of moxifloxacin was enhanced by the addition of ethionamide but not by that of cycloserine, thiacetazone, capreomycin, para-aminosalicylic acid, or linezolid in BALB/c mice infected with a strain of Mycobacterium tuberculosis resistant to isoniazid, rifampin, and six other drugs. These observations are important for the therapy of multidrug-resistant tuberculosis.

Involvement of the fadD33 gene in the growth of Mycobacterium tuberculosis in the liver of BALB/c mice

The potential pathogenic role of Mycobacterium tuberculosis H37Rv fadD33, a gene encoding an acyl-CoA synthase that is underexpressed in the attenuated strain H37Ra, was investigated. In a first approach, fadD33 was cloned and expressed in strain H37Ra to restore gene expression and fadD33-complemented bacteria were used to investigate whether fadD33 might confer any growth advantage to M. tuberculosis H37Ra in an infection model of BALB/c mice. No differences were found in the growth rates of M. tuberculosis H37Rv, H37Ra and fadD33-complemented H37Ra in the lungs and spleen. In contrast, in the liver, where the attenuated strain H37Ra showed impaired growth compared to the virulent strain H37Rv, complementation of the attenuated strain H37Ra with fadD33 restored bacterial replication. In a further approach, the fadD33 gene of strain H37Rv was disrupted by allelic exchange mutagenesis and the virulence of the mutant strain was tested by mouse infection. It was found that disruption of fadD33 decreased M. tuberculosis H37Rv growth in the liver, but not in the lungs or spleen, and complementation of the fadD33-disrupted mutant with fadD33 restored bacterial replication in the liver, but did not affect replication in the lungs and spleen. These findings suggest that fadD33 plays a role in M. tuberculosis virulence by supporting bacterial growth in the liver.

Recombinant GroES in combination with CpG oligodeoxynucleotides protects mice against Mycobacterium avium infection

The groES gene of Mycobacterium avium strain 485 was cloned and expressed in Escherichia coli and the recombinant GroES protein was purified by affinity chromatography. The GroES preparation showed high purity by electrophoresis and immunoblotting. Immuno-electron microscopy showed that GroES was located both in the cytoplasm and on the surface of the mycobacterial cells and thus is readily available to interact with the host immune system. BALB/c mice were immunised intranasally with recombinant GroES, alone or in combination with a synthetic oligodeoxynucleotide containing unmethylated CpG motifs, and tested for protection against infection with M. avium. Neither GroES nor CpG alone provided any protection against subsequent challenge with M. avium, whereas a combination of the two significantly protected the lungs and spleen against colonisation by M. avium after intranasal challenge with a low dose of the organism. This indicates that intranasal administration of GroES and CpG oligodeoxynucleotides increases the resistance of BALB/c mice to M. avium infection.

Mycobacterium tuberculosis subverts the differentiation of human monocytes into dendritic cells

Intracellular pathogens have developed strategies for evading elimination by the defenses of the host immune system. Here we describe an escape mechanism utilized by Mycobacterium tuberculosis that involves the interference with the generation of fully competent DC from monocytes. We show that monocytes infected with live M. tuberculosis differentiated into mature, CD83+ and CCR7+ DC (Mt-MoDC), but were characterized by a selective failure in the expression of the family of CD1 molecules. These cells also showed levels of MHC class II and CD80 (B7.1) that were reduced in comparison with LPS-matured DC. In addition, Mt-MoDC produced TNF-alpha and IL-10, but were unable to secrete IL-12. The generation of Mt-MoDC required the infection of monocytes with live M. tuberculosis, since infection with heat-killed bacteria partially abrogated the effects on monocyte differentiation. Interestingly, Mt-MoDC revealed an impaired antigen-presentation function as assessed by the reduced capability to induce proliferation of cord blood T lymphocytes. Further, naive T lymphocytes expanded by Mt-MoDC were unable to secrete cytokines, in particular IL-4 and IFN-gamma, suggesting that they could be ineffective in helping the macrophage-mediated killing of intracellular mycobacteria. Our results suggest that the interference with monocyte differentiation into fully competent DC is an evasion mechanism of M. tuberculosis that could contribute to its intracellular persistence by avoiding immune recognition.

Exposure of BALB/c mice to low doses of Mycobacterium avium increases resistance to a subsequent high-dose infection

BALB/c mice exposed intranasally (i.n.), intradermally (i.d.) or intraperitoneally (i.p.) to low doses of Mycobacterium avium (20 c.f.u. at three different times two weeks apart) showed an increased resistance to a subsequent high-dose (10(5) c.f.u.) infection. I.n.-exposed mice had few mycobacteria in the tissues (>100 c.f.u.) and showed an expansion of CD4(+) T cells associated with overproduction of IL-12 and IFN-gamma, but not IL-4 and IgG antibodies. Parenterally (i.p. and i.d.) exposed animals showed c.f.u. numbers higher than i.n.-exposed mice, together with overproduction of IL-12, IFN-gamma and IL-4 in the case of i.p.-exposed mice, and of IL-12, IFN-gamma and IgG2a and IgG1 antibodies in the case of i.d.-exposed mice. Low-dose exposures were not contained by athymic BALB/c nude mice; however, naive nude mice reconstituted with i.n.-primed CD4(+) T cells of BALB/c mice were protected against high-dose infection, indicating that CD4(+) T cells are essential to control even low-dose infections by M. avium. Overall, these data suggest that continuous i.n. exposure to M. avium doses commonly found in the environment may play a role in determining the natural resistance of normal hosts against this organism.

Prevalence of resistance to anti-tuberculosis drugs: results of the 1998/99 national survey in Italy

OBJECTIVE

To determine the prevalence of resistance to the main anti-tuberculosis drugs in newly and previously treated tuberculosis patients in Italy and to evaluate the contribution of foreign-born and human immunodeficiency virus (HIV) positive cases to drug resistance.

METHODS

Methods and definitions were derived from the WHO/IUATLD Global Project on Anti-tuberculosis Drug Resistance Surveillance. Univariate and multivariate analysis was used to study prevalence rates of drug resistance in risk groups.

RESULTS

In a national survey in Italy, 810 initial isolates of Mycobacterium tuberculosis (683 from new cases, 115 from retreatment cases and 12 from patients whose treatment history was unknown/dubious) were analysed. Low prevalence of drug and multidrug resistance was found in the new cases (isoniazid 2.9%; rifampicin 0.8%; multidrug resistance 1.2%; any drug resistance 12.3%). The prevalence of resistance to isoniazid and rifampicin was significantly higher in immigrants and HIV-positive subjects, respectively. A high prevalence of drug resistance was found in cases with previous treatment failure or default (isoniazid 5.2%; rifampicin 4.3%; multidrug resistance 36.5%; any drug resistance 61.7%).

RECOMMENDATIONS

Special efforts are necessary to monitor trends in drug resistance and to ensure favourable treatment outcomes among immigrants and HIV-positive tuberculosis cases.

Influence of Mycobacterium bovis bacillus Calmette Guérin on in vitro induction of CD1 molecules in human adherent mononuclear cells

Nonpeptide antigens (including glycolipids of microbial origin) can be presented to T cells by CD1 molecules expressed on monocyte-derived dendritic cells. These HLA unrestricted responses appear to play a role in host immunity against Mycobacterium tuberculosis and other pathogenic bacteria. It is known that vaccination with Mycobacterium bovis bacillus Calmette-Guérin (BCG) has limited efficacy in many clinical settings, although the reasons for its inadequacy remain unclear. Here we have investigated the influence of BCG on the induction of CD1b on human monocytes by granulocyte-macrophage colony-stimulating factor (GM-CSF), which is believed to be the principal inducer of this antigen-presenting molecule. Although BCG alone led to a slight induction of CD1b expression, this agent reduced markedly the ability of GM-CSF to induce high levels of CD1b that were typically observed in uninfected cells. Inhibition of CD1b expression in BCG-infected monocytes was apparent at both the mRNA transcript and CD1b protein levels. Down-regulation of CD1b expression by BCG was mediated, at least in part, by one or more soluble factors and could not be reversed with high concentrations of GM-CSF or a variety of other cytokines. The present results suggest that BCG could diminish the efficiency of CD1-restricted T-cell responses against nonpeptide mycobacterial antigens by reducing CD1 expression on antigen-presenting cells. These findings have potential implications for understanding the nature of the immune response elicited by BCG in humans and suggest potential strategies that could be important for the development of better vaccines for the prevention of tuberculosis.

Infection of human macrophages and dendritic cells with Mycobacterium tuberculosis induces a differential cytokine gene expression that modulates T cell response

Macrophages and dendritic cells (DC) play an essential role in the initiation and maintenance of immune response to pathogens. To analyze early interactions between Mycobacterium tuberculosis (Mtb) and immune cells, human peripheral blood monocyte-derived macrophages (MDM) and monocyte-derived dendritic cells (MDDC) were infected with Mtb. Both cells were found to internalize the mycobacteria, resulting in the activation of MDM and maturation of MDDC as reflected by enhanced expression of several surface Ags. After Mtb infection, the proinflammatory cytokines TNF-alpha, IL-1, and IL-6 were secreted mainly by MDM. As regards the production of IFN-gamma-inducing cytokines, IL-12 and IFN-alpha, was seen almost exclusively from infected MDDC, while IL-18 was secreted preferentially by macrophages. Moreover, Mtb-infected MDM also produce the immunosuppressive cytokine IL-10. Because IL-10 is a potent inhibitor of IL-12 synthesis from activated human mononuclear cells, we assessed the inhibitory potential of this cytokine using soluble IL-10R. Neutralization of IL-10 restored IL-12 secretion from Mtb-infected MDM. In line with these findings, supernatants from Mtb-infected MDDC induced IFN-gamma production by T cells and enhanced IL-18R expression, whereas supernatants from MDM failed to do that. Neutralization of IFN-alpha, IL-12, and IL-18 activity in Mtb-infected MDDC supernatants by specific Abs suggested that IL-12 and, to a lesser extent, IFN-alpha and IL-18 play a significant role in enhancing IFN-gamma synthesis by T cells. During Mtb infection, macrophages and DC may have different roles: macrophages secrete proinflammatory cytokines and induce granulomatous inflammatory response, whereas DC are primarily involved in inducing antimycobacterial T cell immune response.

Bacillus Calmette-Guerin down-regulates CD1b induction by granulocyte-macrophage colony stimulating factor in human peripheral blood monocytes

Non-peptide antigens (e.g. glycolipids of microbial origin) presented by monocyte-associated CD1 molecules to T cells appear to play an important role in host immunity against tuberculosis and other pathogenic bacteria. Since vaccination with Bacillus Calmette-Guerin (BCG) has limited efficacy, the influence of viable BCG organisms on the induction of CD1b antigen by granulocyte macrophage-colony stimulating factor (GM-CSF) has been tested in adherent mononuclear cells obtained from peripheral blood of healthy donors. The results indicate that the vaccine reduces substantially CD1b induction by GM-CSF. On the other hand, BCG was found to promote a slight increase in the expression of this molecule on target cells not exposed to GM-CSF. Attempts to reverse the antagonistic effects of BCG on GM-CSF with high concentrations of GM-CSF, alone, or associated with IL-4, were unsuccessful. Moreover, mycobacteria suppression by 10 microg/ml of rifampin, did not affect BCG influence on CD1b induction. The present results suggest that mycobacterium-induced impairment of the CD1 system could play a role in the unsatisfactory results obtained with BCG vaccination.

Virulence and drug susceptibility of Mycobacterium celatum

The virulence and drug susceptibility of a clinical isolate of Mycobacterium celatum which showed smooth transparent (ST) and smooth opaque (SO) colonies were studied. While ST cells multiplied intracellularly and maintained their coccobacillary form in a human macrophage model of infection, SO cells formed long filaments and completely destroyed the phagocytes. In BALB/c mice, the ST variant, but not the SO variant, grew efficiently in the spleen, liver and lung. The ST variant was usually more resistant in vitro than the SO variant to drugs, with MIC values for clarithromycin (CLA), azithromycin (AZI), ciprofloxacin, sparfloxacin, amikacin, clofazimine, ethambutol and isoniazid being higher than those of the SO variant. In beige mice infected with the more highly virulent variant ST, CLA and AZI were the most active drugs in terms of viable count reduction in organs and mutant selection. Together, these observations indicate that the ST variant of M. celatum is a virulent form that can be efficiently inhibited in vivo by CLA and AZI.

Activity of 16 antimicrobial agents against drug-resistant strains of Mycobacterium tuberculosis

The in vitro activity of 16 antimicrobial agents against 46 drug-resistant strains of Mycobacterium tuberculosis recently isolated from Italian patients was determined. As for first-line antituberculosis drugs, while isoniazid was ineffective against all the strains tested, resistance to streptomycin, rifampicin, pyrazinamide, and ethambutol was 80.4%, 71.7%, 39.1%, and 8.7%, respectively. Among second-line antituberculous drugs, resistance to ciprofloxacin, ofloxacin, and sparfloxacin and to amikacin and kanamycin was around 20%. About 10% of the strains were resistant to capreomycin and cycloserine and 4.3% were resistant to ethionamide; no strain was found to be resistant to thiacetazone, para-aminosalicylic acid, and viomycin. Although all strains displayed a rather continuous distribution of minimal inhibitory concentrations (MICs), a bimodal distribution was observed for rifampicin, amikacin, and kanamicin, with very high MIC values for resistant strains; relatively low MICs were found for fluoroquinolone-resistant strains. Among the small number of strains resistant to second-line agents, low resistant levels were observed. Restriction fragment length polymorphism analysis showed few strain clusters with resistance to first-line antituberculous drugs and aminoglycosides, fluoroquinolones, or both. Altogether, these results showed that second-line agents were still active against the isoniazid-resistant and multiply first-line resistant strains tested, with none or low resistance levels; these observations can be of importance for the treatment of multidrug-resistant tuberculosis in Italy.

Activities of eighteen antimicrobial regimens against Mycobacterium avium infection in beige mice

The therapeutic effect of 18 anti-Mycobacterium avium regimens was examined in beige mice after 91 days of infection. Treatments included monotherapy with clarithromycin (CLA), ethambutol (EMB), amikacin (AMI), rifabutin (RFB), ciprofloxacin (CIP), clofazimine (CLO), and combinations of CLA, CLA-EMB, or CLA-AMI with one of the other drugs. After monotherapy, only AMI and CLA displayed bacteriostatic and/or moderate bactericidal effects in spleens and lungs, while CIP and RFB were totally inactive and CLO and EMB showed intermediate effects against the isolate tested. Resistant mutants were isolated in spleens of mice treated with EMB, CIP, RFB, and CLO-Among two-drug combinations, CLA-RFB, CLA-CIP, and CLA-CLO were significantly more active than RFB, CIP, CLO, respectively, but not more active than CLA alone, in both organs; CLA-AMI and CLA-EMB were bactericidal in spleens and lungs, respectively. Although activity of CLA-EMB was significantly potentiated by RFB and CLO in spleens and lungs, that of CLA-AMI was significantly increased by RFB and CLO only in lungs. The most active regimen in spleens and lungs on day 91 was the combination of all three, namely CLA-AMI-EMB, which reduced the CFU numbers of 2.7 and 7.5 log10, in comparison with day 1 and day 91 counts in untreated control mice, respectively.

Mycobacterium avium infection in BALB/c and SCID mice

BALB/c and severe combined immunodeficient (SCID) mice were inoculated intraperitoneally with Mycobacterium avium and the numbers of cfu were monitored for 70 days in spleen, liver, lung, kidney, brain and peritoneum. While BALB/c mice formed typical granulomas and controlled bacterial growth in organs, a delay in development of lesions and a modest containment of infection were observed in SCID mice. In the spleen of BALB/c mice, in which bacterial growth was contained, macrophages (Mo) and natural killer (NK) cell numbers increased > or = 4.2 times and T- and B-cell numbers increased > or = 1.8 times after 42 days of infection; conversely, a low recruitment of mononuclear cells was observed in the spleen of SCID mice, where M. avium proliferated efficiently. Unlike visceral organs, a pronounced decrease in the number of cfu was observed in the peritoneum of BALB/c mice, concomitantly with a > or = 31.7-fold increase in Mo and NK cells and a > or = 9.1-fold increase in T and B cells. In the peritoneum of SCID mice only a bacteriostatic effect was observed despite a > or = 56.7-fold increase in Mo and NK cells and a > or = 22.3-fold increase in T and B cells. These results suggest that while an intact immune response can efficiently control M. avium infection in the spleen and peritoneum of BALB/c mice, cells of the innate immune system such as Mo and NK cells play a role in the containment of bacterial growth in the peritoneum, but not spleen, of SCID mice.

rpoB mutations in multidrug-resistant strains of Mycobacterium tuberculosis isolated in Italy

Mutations of rpoB associated with rifampin resistance were studied in 37 multidrug-resistant (MDR) clinical strains of Mycobacterium tuberculosis isolated in Italy. At least one mutated codon was found in each MDR strain. It was always a single-base substitution leading to an amino acid change. Nine different rpoB alleles, three of which had not been reported before, were found. The relative frequencies of specific mutations in this sample were different from those previously reported from different geographical areas, since 22 strains (59.5%) carried the mutated codon TTG in position 531 (Ser-->Leu) and 11 (29.7%) had GAC in position 526 (His-->Asp).

Typing of human Mycobacterium avium isolates in Italy by IS1245-based restriction fragment length polymorphism analysis

All but 2 of 63 Mycobacterium avium isolates from distinct geographic areas of Italy exhibited markedly polymorphic, multibanded IS1245 restriction fragment length polymorphism (RFLP) patterns; 2 isolates showed the low-number banding pattern typical of bird isolates. By computer analysis, 41 distinct IS1245 patterns and 10 clusters of essentially identical strains were detected; 40% of the 63 isolates showed genetic relatedness, suggesting the existence of a predominant AIDS-associated IS1245 RFLP pattern.

Antimicrobial activity of fluoroquinolones and other antibiotics on 1,116 clinical gram-positive and gram-negative isolates

A total of 1,116 clinically isolated strains belonging to Staphylococcus aureus (200), Staphylococcus epidermidis (200), Streptococcus pneumoniae (20), Escherchia coli (200), Klebsiella spp. (177), Serratia marcescens (22), Pseudomonas aeruginosa (224), Haemophilus influenzae (35) and Salmonella (38) from the Department of Infectious Diseases, La Sapienza University in Rome (Italy) were tested against three fluoroquinolones (ofloxacin, ciprofloxacin and levofloxacin) and 10 other antibiotics (augmentin, ampicillin, cefaclor, cefixime, cefotaxime, cotrimoxazole, gentamicin, minocycline, oxacillin and vancomycin). Fluoroquinolones inhibited essentially about 100% of H. influenzae, Salmonella and S. pneumoniae, more than 75% of Staphylococcus including methicillin-resistant strains, and about 90% of Enterobacteriaceae and 50% of P. aeruginosa. Minimal inhibitory concentration values ranged from < 0.015 to > 32 micrograms/ml for Klebsiella, S. aureus and epidermidis, E. coli and P. aeruginosa; from < 0.015 to 2 micrograms/ml for Salmonella; from 0.03 to 16 micrograms/ml for Serratia; from < 0.015 to 1 microgram/ml for Haemophilus; and from 0.5 to 2 micrograms/ml for S. pneumoniae. Levofloxacin and to a lesser extent ofloxacin and ciprofloxacin, generally exhibited a greater activity than the other agents against both Gram-positive and Gram-negative bacteria. Regarding the distribution of resistant strains in Italy, we found a peculiar pattern of resistance as far as E. coli and P. aeruginosa were concerned. Quality control parameters are also summarized. S. epidermidis resulted as a new emergent pathogen especially in immunocompromised patients and its level of sensitivity has been modified over the last few years. In fact, the percentage of resistant strains to antibiotics or the percentage of methicillin-resistant isolates (in our study 35%), has gradually increased. Levofloxacin and ofloxacin showed good activity against staphylococcal strains compared with the majority of other antibiotics. These results suggest that the newer quinolones are promising antimicrobial agents for various infections.

Activities of isoniazid alone and in combination with other drugs against Mycobacterium avium infection in beige mice

Monotherapy with isoniazid or amikacin or clarithromycin or combinations of two of these drugs showed nil to modest therapeutic activity in beige mice infected with Mycobacterium avium. However, the combination of all three, isoniazid-amikacin-clarithromycin, markedly reduced CFUs in both spleens and lungs after 91 days of infection.

The influence of the SOS response on the activity of 4-quinolones and zidovudine against some strains of Enterobacteria

The 4-Quinolones are known to induce the SOS response. This should also be the case with AZT (Zidovudine) which has the same bactericidal mechanism. SOS response might make the bacteria more sensitive or more resistant to subsequent doses of quinolones and AZT. NA (Nalidixic acid), the first quinolone of the early 1960s, sensitises a strain of E. coli isolated from the urine of patients with cystopyelitis and the E. coli AB1157 wild type strain which is a well-known SOS inducer. In this case, the SOS system is not involved but only the recombination repair mechanisms which make the bacteria more susceptible to further damage by NA. On the contrary, CPX (Ciprofloxacin) protects E. coli from further exposure to antibiotics. Therefore the SOS response induction assists the bacteria in recovering from the DNA damage caused by CPX. The SOS response induced by AZT in the tested E. coli strains does not seem to either contribute to the lethality of the drug or to be involved in protecting bacteria from the damage caused by AZT. In fact, the percentage of killing was the same for both pre-treated and non pre-treated bacteria (p = 0.5). On the contrary, it was found that in Salmonella typhimurium belonging to blood of a patient with recurrent bacteriaemia, the CPX added to pre-treated bacteria with AZT was less lethal than when it was added to non pre-treated bacteria. The SOS response, in this case, protects bacteria from the damage caused by AZT.

["Killing" of pseudomonas aeruginosa isolated from patients with critical post-operative complications. Effect of various antibiotics]

We undertook this study to estimate phagocytic killing by neutrophils (PMNs) of Pseudomonas aeruginosa pre-exposed to sub-inhibitory concentration of Amikacin and Imipenem. In particular, we have isolated bacteria from endotracheal aspirates of post-operative patients mechanically ventilated admitted to an ICU with respiratory failure. PMNs were obtained both from these patients (Group A, n. 6) as well as from subjects submitted to surgery with uncomplicated post-operative period (Group B, n. 8). From specimens tested, 6 strains of Pseudomonas aeruginosa were isolated. Results showed that the rate of killing of bacteria treated with Amikacin was no different from that of untreated bacteria, whichever the source of PMNs, either from Group A or Group B patients. On the other hand, the microbicidal effect on P. aeruginosa exposed to Imipenem was significantly enhanced when PMNs were obtained from Group B patients. In the mixture bacteria, Imipenem and PMNs obtained from Group A the rate of killing was low, similar to the controls without antibiotics. Such a finding suggests a possible impairment of PMNs due to the critical disease and in some way responsible for the host adverse interaction between granulocytes, antibiotics and pathogens. The underlying mechanisms remain to be clarified and further studies are required to understand the possible clinical implications.

Type frequency and antimicrobial susceptibility of Mycobacterium avium-intracellulare complex strains isolated in Italy from AIDS and non-AIDS patients

Typing of the glycopeptidolipid antigens performed by thin layer chromatography on 59 Mycobacterium avium-intracellulare (MAC) strains isolated in Italy from AIDS patients showed that the most frequent types were 1, 4, 3, 8, and 21 (24, 19, 14, 14 and 8% of the strains, respectively). Among non-AIDS patients, types 1, 4 and 8 were also frequently found. The antimicrobial susceptibility tested in agar and/or liquid media to a panel of drugs indicated in clofazimine and rifabutin effective agents against both AIDS and non-AIDS strains. The data obtained show that MAC type distribution in Italy appears to be different from that reported for other countries. No major differences in drug susceptibility between AIDS and non-AIDS related strains were found.

Rapid detection of mycobacteria by combining a radiometric detection system with DNA probes

Forty-four Mycobacterium-spp. were isolated in 33 patients from an infectious diseases ward. All patients were HIV-positive and most of them were drug-abusers. M. avium-intracellulare was the most common type of MOTT (Mycobacteria other than tuberculosis) detected and the only microorganism isolated in patients with mycobacteriaemia. The radiometric method performed by the Bactec system enhanced the isolation rate of mycobacteria, especially from the bloodstream. The Gen-probe DNA hybridization system proved to be rapid diagnostic tool for the identification of strains.

Activity of antimicrobial drugs evaluated by agar dilution and radiometric methods against strains of Nocardia asteroides isolated in Italy from immunocompromised patients

Benzylpenicillin, amoxicillin, amoxicillin plus clavulanic acid, cephalothin, cephaloridine, cefotaxime, imipenem, erythromycin, clarithromycin, azithromycin, amikacin, ciprofloxacin and trimethoprim-sulfamethoxazole were tested in vitro by the agar dilution method against eleven strains of Nocardia asteroides isolated both from AIDS and other immunocompromised patients. Imipenem, amikacin and trimethoprim-sulfamethoxazole were shown to be the most active drugs with minimum inhibitory concentrations (MIC) values nearly always lower than concentrations achievable in blood. Ciprofloxacin, cephaloridine and cefotaxime were moderately active, while the remaining drugs were totally ineffective. When susceptibility was assessed by the radiometric method the MIC90 values were uniformly lower than those in the agar method, possibly due to lower inactivation of drugs during incubation. The two methods showed a good correlation only for imipenem, amikacin and ciprofloxacin. The results obtained by the radiometric method seem to indicate that, as for mycobacteria, this method may also give a more accurate evaluation of the antimicrobial susceptibility of Nocardiae.

In vitro activity of zidovudine alone and in combination with ciprofloxacin against Salmonella and Escherichia coli

The in vitro antibacterial activity of zidovudine alone and in combination with ciprofloxacin was investigated. Zidovudine showed a good activity against Escherichia coli and Salmonella (MIC range 0.5-8 micrograms/ml and 1.5-62 micrograms/ml respectively) isolated from biological samples of HIV-infected patients. These strains proved to be extremely susceptible to ciprofloxacin alone. The interaction between zidovudine and ciprofloxacin ranged from additive activity to indifference. No antagonism was observed: the FIC index for every combination resulted < or = 1.5. The addition of AZT 1 mg/l (clinically achievable plasma concentration after therapeutic doses of 1200 mg/day) did not affect the bactericidal activity of ciprofloxacin; on the contrary, in some cases we observed an increase of bactericidal effect of the quinolone. These data have to be considered in patients with AIDS who can be treated concomitantly with zidovudine and ciprofloxacin.

In vitro activity of clarithromycin alone or in combination with other antimicrobial agents against Mycobacterium avium-intracellulare. Complex strains isolated from AIDS patients

The activity of clarithromycin and five other antimicrobial agents, namely amikacin, rifampicin, rifabutin, clofazimine and ciprofloxacin, was assessed both by an agar dilution and a radiometric method in broth on 11 Mycobacterium avium-intracellulare complex (MAC) strains, recently isolated from AIDS patients. Minimum inhibitory concentrations (MICs) radiometrically determined were, in general, several times lower than MICs assessed in agar, probably because of a partial degradation of antimicrobials during the long incubation period needed for tests in solid medium. When tested in broth, rifabutin and clofazimine showed very low MICs 90 (0.24 and 0.78 microgram/ml, respectively). Ciprofloxacin and clarithromycin also had MICs90 in the range of peak serum levels (1.93 and 3.76 micrograms/ml, respectively). Moreover, all these antimicrobials are known to concentrate several times in macrophages. MICs90 were higher for amikacin (11 micrograms/ml) and for rifampicin (8 micrograms/ml). When clarithromycin was tested against three MAC strains in combination with another drug, it showed a synergistic effect only when combined with rifampicin. Some synergistic effect was observed also when combining clarithromycin with rifampicin and amikacin, whereas in combination with rifabutin and clofazimine there was only an additive effect.

Evaluation of vaginal microflora in patients infected with HIV

HIV infection is thought to exacerbate the virulence of normal saprophytic vaginal microflora. We studied the vaginal ecosystem of HIV patients to detect the quantitative and qualitative variation of vaginal microorganisms. 15 patients (5 with AIDS and 10 with ARC) were investigated. Vaginal candidiasis was more frequent in this group than in the control groups. Gardnerella was present in 60% of patients generally in association with anaerobic bacteria and Mycoplasma. Among anaerobia, Bacteroides sp and other Gram-negative rods were the most common bacteria. Neisseria gonorrhoeae was absent in all patients tested. Chlamydia trachomatis was recovered in two out of the 15 HIV-positive patients. Aerobic Gram-negative flora was 100-fold that of the control group and anaerobic Gram-negative flora 10-fold.