Franco Ciuchini

Molecular Epidemiological and Antibiotic Susceptibility Characterization of Brucella Isolates from Humans in Sicily, Italy

ABSTRACT Brucellosis is a serious problem in Sicily. Brucella melitensis was identified as the species most frequently isolated in humans in Italy. No data, however, are available about the molecular epidemiological characterization of Brucella isolates from humans. We have conducted this study to molecularly characterize clinical isolates of Brucella spp. and to evaluate their antimicrobial susceptibilities. Twenty Brucella isolates were studied. Differential growth characteristics and DNA polymorphisms such as the restriction patterns of the PCR-amplified omp2a and omp2b genes, rpoB nucleotide sequencing, and multiple-locus variable-number tandem repeat analysis of 16 loci (MLVA-16) were used to characterize the strains. In vitro antibiotic susceptibility was determined by the E-test method on two different agar media, and the results were compared. All isolates were identified as B. melitensis biovar 3. rpoB nucleotide sequence analysis allowed the identification of two different genotypes of B. melitensis biovar 3. On the other hand, the MLVA-16 typing assay recognized 17 distinct genotypes. All isolates were sensitive to all tested antibiotics (rifampin, doxycycline, ciprofloxacin, ceftriaxone, and trimethoprim-sulfamethoxazole), and the Mueller-Hinton agar plate is recommended for antibiotic susceptibility testing by the E-test method. Our findings identify B. melitensis biovar 3 as the etiological agent isolated in Sicily and encourage the use of both molecular methods, and in particular of the MLVA-16 assay, in epidemiological trace-back analysis. This study represents the first epidemiological data from molecular typing of Brucella strains circulating in Italy and, in particular, in eastern Sicily.

Genetic Bases of the Rifampin Resistance Phenotype in Brucella spp.

ABSTRACT Rifampin is one of the most potent and broad-spectrum antibiotics against bacterial pathogens. Its bactericidal activity is due to its ability to bind to the β subunit of the DNA-dependent RNA polymerase encoded by the rpoB gene. Mutations of the rpoB gene have been characterized in rifampin-resistant (Rifr) strains of Escherichia coli and Mycobacterium tuberculosis. The genetic bases of Rifr in Brucella spp. are still unknown. In the present study, the nucleotide sequences of the rpoB gene of the Rifr vaccine strain Brucella abortus RB51 and of 20 Rifr clones derived in our laboratory from two Brucella melitensis isolates were determined. These sequences were then compared to those of the respective rifampin-susceptible (Rifs) parental strains and to the published B. melitensis strain 16M. All Rifr strains carried one or more missense mutations mapping in two regions of the rpoB gene. These two “hot” regions were investigated in eight additional RifrBrucella laboratory mutants and in 20 reference RifsBrucella strains. rpoB mutations were found in all Rifr mutants. In contrast, no missense mutations were found in any analyzed Rifs strains. Our results represent the first from a study of the molecular characterization of rpoB mutations in resistant Brucella strains and provide an additional proof of the association of specific rpoB mutations with the development of the Rifr phenotype in prokaryotes. In addition, because of the relationship between Rifr and the attenuation of virulence in Brucella spp., studies of virulence in these mutants may provide useful information about the genetic basis of pathogenesis in Brucella.

PCR Assay To Detect Bacillus anthracis Spores in Heat-Treated Specimens

ABSTRACT Recent interest in anthrax is due to its potential use in bioterrorism and as a biowarfare agent against civilian populations. The development of rapid and sensitive techniques to detect anthrax spores in suspicious specimens is the most important aim for public health. With a view to preventing exposure of laboratory workers to viable Bacillus anthracis spores, this study evaluated the suitability of PCR assays for detecting anthrax spores previously inactivated at 121°C for 45 min. The results indicate that heat treatment ensures the complete inactivation of B. anthracis spores without significantly affecting the efficiency of PCR assays.

Mouse cytokine profiles associated with Brucella abortus RB51 vaccination or B. abortus 2308 infection

ABSTRACT This study indicated that mice immunized with Brucella abortus RB51 bacteria and subsequently challenged with B. abortus 2308 were protected from reinfection. After vaccination, both Th1 and Th2 cytokine patterns were observed. Of those, the early production of gamma interferon seems to have the prominent role in inducing an immunologically based protection.

Protective Properties of Rifampin-Resistant Rough Mutants of Brucella melitensis

ABSTRACT Vaccination against Brucella infections in animals is usually performed by administration of live attenuated smooth B. abortus strain S19 and B. melitensis strain Rev1. They are proven effective vaccines against B. abortus in cattle and against B. melitensis and B. ovis in sheep and goats, respectively. However, both vaccines have the main drawback of inducing O-polysaccharide-specific antibodies that interfere with serologic diagnosis of disease. In addition, they retain residual virulence, being a cause of abortion in pregnant animals and infection in humans. To overcome these problems, one approach is to develop defined rough mutant Brucella strains lacking O antigen of lipopolysaccharide. B. abortus rough strain RB51, a rifampin-resistant mutant of virulent strain B. abortus 2308, is used as a vaccine against B. abortus infection in cattle in some countries. However, RB51 is not effective in sheep, and there is only preliminary evidence that it is effective in goats. In this study, we tested the efficacies of six rifampin-resistant rough strains of B. melitensis in protecting BALB/c mice exposed to B. melitensis infection. The protective properties, as well as both humoral and cellular immune responses, were assessed in comparison with those provided by B. melitensis Rev1 and B. abortus RB51 vaccines. The results indicated that these rough mutants were able to induce a very good level of protection against B. melitensis infection, similar to that provided by Rev1 and superior to that of RB51, without inducing antibodies to O antigen. In addition, all B. melitensis mutants were able to stimulate good production of gamma interferon. The characteristics of these strains encourage further evaluation of them as alternative vaccines to Rev1 in primary host species.

Brucella abortus RB51 Induces Protection in Mice Orally Infected with the Virulent Strain B. abortus 2308

ABSTRACT Brucellae are gram-negative, facultative intracellular bacteria which are one of the most common causes of abortion in animals. In addition, they are the source of a severe zoonosis. In this trial, we evaluated the effect of oral inoculation of Brucella abortus RB51 in mice against a challenge infection with B. abortus 2308. First, we showed that a gastric acid neutralization prior to the oral inoculation contributed to a more homogeneous and consistent infection with both vaccine strain B. abortus RB51 and virulent strain B. abortus 2308. Successively, we assessed the clearance and the immune response following an oral infection with B. abortus RB51. Oral inoculation gave a mild infection which was cleared 42 days after infection, and it induced a delayed humoral and cell-mediated immune response. Finally, we immunized mice by oral inoculation with B. abortus RB51, and we challenged them with the virulent strain B. abortus 2308 by an oral or intraperitoneal route 42 days after vaccination. Oral inoculation of B. abortus RB51 was able to give protection to mice infected with the virulent strain B. abortus 2308 by the oral route but not to mice infected intraperitoneally. Our results indicate that oral inoculation of mice with B. abortus RB51 is able to give a protective immunity against an oral infection with virulent strains, and this protection seems to rely on an immune response at the mucosal level.

Evaluation of Brucella melitensis B115 as rough-phenotype vaccine against B. melitensis and B. ovis infections.

Brucella melitensis strain Rev1 is used as vaccine for the prophylaxis of brucellosis in sheep and goats. Because of its smooth phenotype, however, it induces antibodies directed to the O-polysaccharide (O-PS) of the lipopolysaccharide (LPS), thus unabling to distinguish between vaccinated and infected animals. It has been speculated that alternative vaccines could be live, attenuated Brucella rough strains, which are devoid of the O-PS. B. melitensis B115 is a natural, attenuated, rough strain. The O-PS is not exposed at the surface but is present in the cytoplasm. We tested the protective activity of B115 against B. melitensis and B. ovis infections in mice, in comparison with that of Rev1. The residual virulence and the humoral response following B115 vaccination were also evaluated. Vaccination with B115 conferred significant protective immunity against B. melitensis 16M and B. ovis challenge strains, equivalent to that provided by Rev1. No interfering antibodies to O-PS were detected, while the B115 vaccination was monitored by a specific B115-based complement fixation test. These promising features suggest further evaluation of B. melitensis B115 as vaccine for target animal hosts.

Effect of Exogenous Interleukin-18 (IL-18) and IL-12 in the Course of Brucella abortus 2308 Infection in Mice

ABSTRACT In this study we demonstrated that combined inoculation of interleukin-12 (IL-12) and IL-18 reduced the number of bacteria in the spleens of mice infected with Brucella abortus 2308 and that the effect of the treatment was mediated by an increased capability of spleen cells to produce gamma interferon at the early phase of infection.

Field Validation of the Use of RB51 as Antigen in a Complement Fixation Test To Identify Calves Vaccinated with Brucella abortus RB51

ABSTRACT In order to confirm the efficiency of an experimental RB51-based complement fixation (CF) test in identifying cattle vaccinated withBrucella abortus strain RB51, 831 sera from 110 vaccinated and 48 unvaccinated Hereford heifers of Iowa, collected for studies conducted in different years, were sent to Italy without coding to be tested in a CF test using RB51 as antigen. Most of the calves, aged from 3 to 10 months, were vaccinated subcutaneously with the recommended dosage of 1010 CFU of RB51 commercial vaccine, while only six calves received 109 CFU of the same vaccine. Serum samples for serologic testing, collected until 16 postinoculation weeks (PIW), were also tested by routine surveillance tests for brucellosis such as rose bengal plate and CF tests performed withB. abortus smooth strain 99 as control antigen. RB51 CF test results obtained by testing sera from cattle vaccinated in 1999 indicate that the sensitivity of the reaction is 97% at 2 to 3 PIW and 90% until 8 PIW and decreases to 65% at 12 PIW, the specificity remaining at 100%. Collectively, the results of this study confirm that serologic standard tests fail to detect antibodies to RB51 while the RB51-based CF test is able to monitor antibody responses to RB51 until 15 to 16 PIW with a specificity of 100%. In addition, unlike the RB51-based dot blot assay, which is the only test currently used to monitor antibody responses to RB51, the CF test also detected specific responses following vaccination with 109 CFU of RB51, although seroconversion was only 50% at 8 PIW. In conclusion, because of high specificity and sensitivity, the CF test described here can be used to efficaciously monitor serologic responses following RB51 vaccination in cattle and could also be employed to detect RB51 infection in humans exposed to this strain.

Brucella melitensis B115‐based complement fixation test to detect antibodies induced by Brucella rough strains

Aims:  To assess the efficiency of a Brucella melitensis B115 rough strain, naturally devoid of anticomplementary activity, used as antigen in a complement fixation test (CFT) to detect antibodies induced by Brucella strains with rough phenotype, such as Brucella abortus RB51, Brucella ovis and Brucella canis.