Human case of autochthonous West Nile virus lineage 2 infection in Italy, September 2011

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Effects of fluoroquinolones on bacterial adhesion and on preformed biofilm of strains isolated from urinary double J stents

The activity of levofloxacin and ulifloxacin on biofilm formation and persistence was evaluated on microorganisms isolated from urinary double-J-stents. We analyzed 51 bacterial strains and their susceptibility to different antimicrobial classes was determined. We evaluated the bacterial ability to form biofilm and the effects of different concentrations of levofloxacin and ulifloxacin on bacterial adhesion and biofilm persistence. Most of the strains were biofilm producers with no relevant difference in biofilm production at 24 or 48 hours. The fluoroquinolones were able to prevent biofilm formation, but not to eradicate the preformed biofilm. On the basis of our data we advise that antibiotic prophylaxis with fluoroquinolones may be most helpful if given at the time of stent insertion and at high dosage.

Antibiotic susceptibility and serotype distribution in Streptococcus pneumoniae circulating in Italy: results of the SEMPRE surveillance study (2000-2002)

During 2000-2002, 20 clinical microbiology centres collected 1623 Streptococcus pneumoniae isolates. Susceptibility to penicillin, amoxicillin, amoxicillin/clavulanic acid, cefaclor, cefuroxime, cefotaxime, clarithromycin, ciprofloxacin, levofloxacin, rifampicin and teicoplanin was determined locally by the Etest and/or by the microdilution method by three co-ordinating centres. Total resistance to penicillin increased from 15.2% to 16.1% and macrolide resistance increased from 37.9% to 43.7%. Overall, the most effective drugs (>99% susceptible strains) were amoxicillin, amoxicillin/clavulanic acid, levofloxacin and rifampicin. The most frequent serotypes were: 23F (15.8%), 3 (10.8%) 14 (9.1%), 19F (9.1%), 6B (7.2%), 19A (6.9%) and 6A (4.8%). In conclusion, penicillin and macrolide resistance is increasing in Italy, whilst fluoroquinolone currently remains active. The most common serotypes circulating are included in the heptavalent conjugate vaccine, with the exception of type 3.

Interpretive criteria for disk diffusion susceptibility testing of ulifloxacin, the active metabolite of prulifloxacin

Prulifloxacin, a new fluoroquinolone, is a prodrug whose active compound, ulifloxacin, is derived from its transformation after oral administration and intestinal absorption. Based on early pharmacokinetic and pharmacodynamic data, the following MIC breakpoints have tentatively been proposed: < or = 1 microg/ml, susceptible; 2 microg/ml, intermediate; and > or = 4 microg/ml, resistant. In this report, ulifloxacin MIC vs. zone diameter scattergrams and discrepancy rates were analyzed in 461 freshly isolated clinical strains (237 Enterobacteriaceae, 101 nonfermenters, and 123 Gram-positive bacteria). In agreement with the guidelines of the National Committee for Clinical Laboratory Standards, a modification of the error rate-bounded method was used to select disk diffusion test breakpoints. The following zone diameter breakpoints were chosen and are proposed herein for the interpretation of ulifloxacin disk (5 microg) test results: < or = 15 and > or = 19 mm for Enterobacteriaceae, < or = 16 and > or = 20 mm for nonfermenters, and < or = 14 and > or = 18 mm for Gram-positive bacteria. By applying these breakpoint values, no very major errors were detected, while major and minor errors were largely below the accepted discrepancy rates.

Epidemiology of methicillin-resistant staphylococci in Europe

Methicillin-resistant staphylococci are mostly resistant not only to all beta-lactams but also to a wide range of other antibiotics, and have emerged as major nosocomial pathogens during the past two decades. Considerable variations in the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) exist between institutions and between geographic areas. In Europe, in general, a north-south gradient is observed, MRSA strains being rare in Scandinavian hospitals (<2%) and far more prevalent in Mediterranean hospitals (>40%). Whether low or high, the rates of MRSA prevalence in European countries have remained approximately the same during the last decade. Recent findings suggest that MRSA might also be emerging as a community-acquired pathogen. The first stage in the emergence of MRSA is its acquisition by methicillin-susceptible S. aureus, and the integration into its chromosome, of the mecA gene, which, together with the other mec genes, is carried on a mobile genetic element, the staphylococcal chromosomal cassette mec (SCCmec). The origin of SCCmec elements as well as the mechanisms of their acquisition remain unknown. Molecular epidemiology studies using different techniques clearly indicate that the massive geographic spread of MRSA results from the dissemination of relatively few highly epidemic clones. Five major lineages (the so-called Iberian, Brazilian, Hungarian, New York/Japan and pediatric pandemic MRSA clones) have been defined. In Europe, the Iberian clone has been reported in several countries; the Brazilian, pediatric and Hungarian clones have also been detected, but less frequently. A unique Italian clone is predominant in Italy. As with S. aureus, coagulase-negative staphylococci (CNS) represent a serious concern in hospital-acquired infections. Despite marked geographic variations, in some areas of Europe high proportions (60-70%) of CNS are methicillin resistant. The formation of biofilm is a key virulence factor of S. epidermidis, the prominent CNS pathogen, which is the most common cause of bacteremia in device-related infections. Another emerging nosocomial pathogen, S. hemolyticus, is characterized by a tendency to develop multiple antibiotic resistances, with a unique predisposition to glycopeptide resistance.

Humoral immune response against hepatitis C virus

Antibodies are in several instances a reliable marker indicating vigorous immune response against infectious agents and in several viral diseases presence in the blood of specific anti-viral antibodies indicates an effective protection. However, this is not always true. For example, in the case of hepatitis C virus (HCV) an important human pathogen considered the causative agent of the nonA- nonB hepatitis, in spite of an intense antibody response there is no protection against a new infection and in the majority of infected individuals the virus overcomes host defences establishing a persistent infection. Here we describe how the dissection of the humoral immune response against HCV glycoprotein E2 of infected patients was useful for a better comprehension of the virus-host interplay. Cross-reactive antibodies directed against E2 are produced by the HCV-infected patient, but not all of them are protective, and some could even result to be detrimental for the patient. The cross-reactive anti-HCV/E2 humoral antibody response is complex and not necessarily completely beneficial to the host.

Heterogeneity of the humoral anti-HCV/E2 response in persistently infected patients as demonstrated by divergent patterns of inhibition of the binding of anti-HCV/E2 human monoclonal antibodies

A complete understanding of the molecular features of humoral immune response could be of pivotal importance in the management of persistent viruses as HCV. In this study, 24 HCV-positive samples, characterized by classical virological parameters, are evaluated using a new assay for the quantitation of antibody subpopulations directed against discrete epitopes on surface glycoprotein E2, a key viral protein. The results, besides confirming the usefulness of this new approach, highlight the extreme heterogeneity of anti-HCV/E2 response as far as single epitopes are concerned. The specific epitopes under study are also demonstrated to be widely shared among different genotypes.

Conjugative transfer of the erm(A) gene from erythromycin-resistant Streptococcus pyogenes to macrolide-susceptible S. pyogenes, Enterococcus faecalis and Listeria innocua

In mating experiments, the erythromycin resistance methylase gene erm(A) was successfully transferred from erm(A)-positive clinical isolates of Streptococcus pyogenes to macrolide-susceptible recipients of S. pyogenes, Enterococcus faecalis and Listeria innocua. Compared with the SmaI macrorestriction pattern of the S. pyogenes recipient, the patterns of S. pyogenes transconjugants shared the lack of a fragment and the appearance of a new, larger fragment. This is the first experimental evidence that the erm(A) gene can be transferred from erythromycin-resistant S. pyogenes to macrolide-susceptible S. pyogenes as well as to other Gram-positive recipients.

In vitro antibacterial activities of AF 3013, the active metabolite of prulifloxacin, against nosocomial and community Italian isolates

AF 3013, the active metabolite of prulifloxacin, was tested to determine its inhibitory and bactericidal activities against 396 nosocomial and 258 community Italian isolates. Compared with that of ciprofloxacin, its activity (assessed in MIC and minimal bactericidal concentration tests) was generally similar or greater against gram-positive bacteria and greater against gram-negative bacteria. In time-kill assays using selected isolates, its bactericidal activity was comparable to that of ciprofloxacin.

Identification of six putative novel human papillomaviruses (HPV) and characterization of candidate HPV type 87

Six putative novel human papillomavirus (HPV) types were detected by using general primers for a conserved L1 HPV region in patients examined in gynecologic centers. One of the isolates, detected in samples from 4 patients with koilocytic atypia at cervical cytology (3 of whom were also infected with human immunodeficiency virus type 1), was completely sequenced, identified as a new HPV genotype, and designated candidate HPV87 (candHPV87) by the Reference Center for Human Papillomavirus. candHPV87 shows the classic HPV genome organization and the absence of a functional E5 coding region. Phylogenetic analysis documented that the candHPV87 genome clusters within the A3 group of HPVs, together with HPV61, HPV72, HPV83, HPV84 and candHPV86, which have been completely sequenced, and a number of other putative novel genotypes (two of which are described in this work), which have been partially characterized. To address the growth-enhancing potential of candHPV87, the E6 and E7 putative coding regions were cloned and expressed in tissue cultures. The data indicate that both proteins stimulate cell division in tissue cultures more than those of low-risk HPVs, though not as much as those of HPV16. Taken together, the clinical, molecular, and biological data suggest that the novel papillomavirus characterized in the present study is a low- to intermediate-risk HPV.

A multicenter study on central venous catheter-associated infections in Italy

In a 1-year multicenter study the microbial colonization of 1154 central venous catheters (CVCs) was investigated. Catheters explanted either from immunocompromised or immunocompetent patients were collected and analyzed by five clinical microbiology laboratories located in Ancona, Aviano, Catania, Pavia and Rome, Italy. A further aim was to investigate, by scanning electron microscopy, the features of currently used catheters, both new and explanted from patients, analyzing their surface quality, the influence of the host protein biofilm on their microbial colonization, the modifications caused by their permanence in the body and the relationship between these factors and the occurrence of infections.

Mapping B-cell epitopes of hepatitis C virus E2 glycoprotein using human monoclonal antibodies from phage display libraries

Clinical and experimental evidence indicates that the hepatitis C virus (HCV) E2 glycoprotein (HCV/E2) is the most promising candidate for the development of an effective anti-HCV vaccine. Identification of the human epitopes that are conserved among isolates and are able to elicit protective antibodies would constitute a significant step forward. This work describes the mapping of the B-cell epitopes present on the surface of HCV/E2, as recognized by the immune system during infection, by the analysis of the reciprocal interactions of a panel of human recombinant Fabs derived from an HCV-infected patient. Three unrelated epitopes recognized by antibodies with no neutralization-of-binding (NOB) activity were identified; a fourth, major epitope was defined as a clustering of minor epitopes recognized by Fabs endowed with strong NOB activity.

Nonneutralizing human antibody fragments against hepatitis C virus E2 glycoprotein modulate neutralization of binding activity of human recombinant Fabs

Evidence from clinical and experimental studies indicates that hepatitis C virus E2 (HCV/E2) glycoprotein is the major target of a putatively protective immune response. However, even in the presence of a vigorous production of anti-HCV/E2 antibodies, reinfection can occur. Dissection of the human immune response against HCV/E2 indicated that blocking of binding of HCV/E2 to target cells [neutralization of binding (NOB) activity] varies widely among antibody clones. Moreover, in vivo, simultaneous binding of antibodies to distinct epitopes can induce conformational changes and synergies that may be relevant to understanding the anti-HCV immune response. In this study, human recombinant Fabs were generated by affinity-selecting a phage display repertoire library with antibody-coated HCV/E2. These Fabs, which share the same complementarity-determining region DNA sequences, had higher affinity than other anti-HCV/E2 Fabs but showed no NOB activity even at the highest concentrations. Binding of Fabs to HCV/E2 caused conformational changes modifying Fab-binding patterns and reducing, with a negative synergistic effect, Fab-mediated NOB activity. These data suggest that some antibody clones have the potential to modify HCV/E2 conformation and that, in this state, binding of this glycoprotein to its cellular target is less prone to inhibition by some antibody clones. This can explain why high anti-HCV/E2 antibody titers do not directly correlate with protection from infection. Information on the interactions among different antibody clones can contribute to understanding virus-host interplay and developing more effective vaccines.

SmaI macrorestriction analysis of Italian isolates of erythromycin-resistant Streptococcus pyogenes and correlations with macrolide-resistance phenotypes

High rates of erythromycin resistance among Streptococcus pyogenes strains have been reported in Italy in the last few years. In this study, 370 erythromycin-resistant (MIC, > or = 1 microg/mL) Italian isolates of this species obtained in 1997-1998 from throat swabs from symptomatic patients were typed by analyzing SmaI macrorestriction fragment patterns by pulsed-field gel electrophoresis (PFGE). Among the typable isolates (n = 341; the genomic DNA of the remaining 29 isolates was not restricted by SmaI), 48 distinct PFGE types were recognized, of which 31 were recorded in only one isolate (one-strain types). Fifty-two percent of typable isolates fell into three type clusters and 75% into six, suggesting that erythromycin-resistant group A streptococci circulating in Italy are polyclonal, but the majority of them probably derives from the spread of a limited number of clones. In parallel experiments, the 370 test strains were characterized for the macrolide resistance phenotype: 80 were assigned to phenotype cMLS, 89 to phenotype iMLS-A, 33 to phenotype iMLS-B, 11 to phenotype iMLS-C, and 157 to phenotype M. There was a close correlation between these phenotypic data and the genotypic results of PFGE analysis, the vast majority of the isolates assigned to individual PFGE classes belonging usually to a single phenotype of macrolide resistance. All of the 29 untypable isolates belonged to the M phenotype. Further correlations were observed with tetracycline resistance.

Recovery from a single blood culture of two enterococcus gallinarum isolates carrying both vanC-1 and vanA cluster genes and differing in glycopeptide susceptibility

Two Enterococcus gallinarum isolates distinguished by different colony sizes were recovered from the same blood culture from a woman with acute myeloid leukemia. They were designated E31 (the one with larger colonies) and E32 (the one with smaller colonies). Both isolates were glycopeptide resistant, but the MICs of vancomycin and teicoplanin for E31 (32 and 2 microg/ml, respectively, consistent with the VanC phenotype) and E32 (128 and 16 microg/ml, respectively, consistent with the VanA phenotype) were different. E31 and E32 had the same plasmid profile and showed identical pulsed-field gel electrophoresis patterns after digestion of total DNA with NotI and a two-band variation after digestion with SmaI. Polymerase chain reaction experiments showed that both isolates had both the vanC-1 and vanA genes and carried a Tn1546-related transposon lacking orf1, vanY, and vanZ. The absence of these three genes was confirmed by Southern analysis with appropriate probes. Southern hybridization experiments using a vanA probe showed that this atypical Tn1546-related element appeared to be located on the chromosome. In both E31 and E32, the vanA probe hybridized to EcoRV and HindIII fragments larger in size than the hybridizing fragments observed in the VanA prototype strain Enterococcus faecium BM4147, suggesting the lack of the relevant EcoRV and HindIII restriction sites.

Differentiation of resistance phenotypes among erythromycin-resistant Pneumococci

Laboratory differentiation of erythromycin resistance phenotypes is poorly standardized for pneumococci. In this study, 85 clinical isolates of erythromycin-resistant (MIC > or = 1 microg/ml) Streptococcus pneumoniae were tested for the resistance phenotype by the erythromycin-clindamycin double-disk test (previously used to determine the macrolide resistance phenotype in Streptococcus pyogenes strains) and by MIC induction tests, i.e., by determining the MICs of macrolide antibiotics without and with pre-exposure to 0.05 microg of erythromycin per ml. By the double-disk test, 65 strains, all carrying the erm(AM) determinant, were assigned to the constitutive macrolide, lincosamide, and streptogramin B resistance (cMLS) phenotype, and the remaining 20, all carrying the mef(E) gene, were assigned to the recently described M phenotype; an inducible MLS resistance (iMLS) phenotype was not found. The lack of inducible resistance to clindamycin was confirmed by determining clindamycin MICs without and with pre-exposure to subinhibitory concentrations of erythromycin. In macrolide MIC and MIC-induction tests, whereas homogeneous susceptibility patterns were observed among the 20 strains assigned to the M phenotype by the double-disk test, two distinct patterns were recognized among the 65 strains assigned to the cMLS phenotype by the same test; one pattern (n = 10; probably that of the true cMLS isolates) was characterized by resistance to rokitamycin also without induction, and the other pattern (n = 55; designated the iMcLS phenotype) was characterized by full or intermediate susceptibility to rokitamycin without induction turning to resistance after induction, with an MIC increase by more than three dilutions. A triple-disk test, set up by adding a rokitamycin disk to the erythromycin and clindamycin disks of the double-disk test, allowed the easy differentiation not only of pneumococci with the M phenotype from those with MLS resistance but also, among the latter, of those of the true cMLS phenotype from those of the iMcLS phenotype. While distinguishing MLS from M resistance in pneumococci is easily and reliably achieved, the differentiation of constitutive from inducible MLS resistance is far more uncertain and is strongly affected by the antibiotic used to test inducibility.

In vitro activity of ketolides telithromycin and HMR 3004 against italian isolates of Streptococcus pyogenes and Streptococcus pneumoniae with different erythromycin susceptibility

Two ketolides, telithromycin and HMR 3004, were evaluated for their in vitro activity against erythromycin-susceptible and -resistant strains of Streptococcus pyogenes and Streptococcus pneumoniae. On the basis of their resistance to macrolide, lincosamide and streptogramin (MLS) antibiotics, erythromycin-resistant test strains were assigned to the constitutive resistance (cMLS) phenotype, the inducible resistance (iMLS) phenotype or the M phenotype. iMLS S. pyogenes strains were further subdivided into the three recently described subtypes iMLS-A, -B and -C. Telithromycin and HMR 3004 were uniformly and highly active against pneumococci (regardless of their susceptibility or resistance to erythromycin and/or penicillin), erythromycin-susceptible S. pyogenes and erythromycin-resistant S. pyogenes strains of the M phenotype (in which resistance is mediated by an efflux system) or iMLS-B or -C phenotype (in which resistance is mediated by a methylase encoded by the ermTR gene). Both ketolides were less active against erythromycin-resistant S. pyogenes strains with the cMLS phenotype or the iMLS-A subtype (where resistance is mediated by a methylase encoded by the ermAM gene), these strains ranging in phenotype from the upper limits of susceptibility to low-level resistant.

Glycopeptide susceptibility profiles of Staphylococcus haemolyticus bloodstream isolates

Twelve clinical strains of Staphylococcus haemolyticus (eight methicillin resistant and three methicillin susceptible), isolated from blood cultures between 1982 and 1997, were investigated for teicoplanin and vancomycin susceptibility profiles. On the basis of conventional MIC tests and breakpoints, four isolates were susceptible (MICs, 1 to 8 microgram/ml) and eight were resistant (MICs, 32 to 64 microgram/ml) to teicoplanin while all were susceptible to vancomycin (MICs, 1 to 2 microgram/ml). All four strains for which the conventional teicoplanin MICs were within the range of susceptibility expressed heterogeneous resistance to teicoplanin and homogeneous vancomycin susceptibility. Of the eight strains for which the conventional teicoplanin MICs were within the range of resistance, six expressed heterogeneous and two expressed homogeneous teicoplanin resistance while seven showed heterogeneous vancomycin resistance profiles (with subpopulations growing on 8 microgram of the drug per ml at frequencies of >/=10(-6) for six strains and 10(-7) for one) and one demonstrated homogeneous vancomycin susceptibility. Of six bloodstream isolates of other staphylococcal species (S. aureus, S. epidermidis, and S. simulans), for all of which the conventional teicoplanin MICs were >/=4 microgram/ml and the vancomycin MICs were </=2 microgram/ml, none exhibited heterogeneous susceptibility profiles for teicoplanin while three showed homogeneous and three showed heterogeneous susceptibility profiles for vancomycin (with subpopulations growing on 8 microgram of the drug per ml found for only one strain). The results of this study indicate that a heterogeneous response to glycopeptides is a common feature of S. haemolyticus isolates and suggest that susceptibility to glycopeptides as determined by conventional MIC tests may not be predictive of the outcome of glycopeptide therapy.

Multicenter evaluation of the new HIV DUO assay for simultaneous detection of HIV antibodies and p24 antigen

A multicenter survey was performed to evaluate a new semi-automated human immunodeficiency virus fourth generation antibodies and antigen simultaneous assay. This assay showed a sensitivity of 100% and specificity of 99.6% among sera obtained from hospitalized patients or blood donors. Sera obtained from commercially available as well as in-house seroconversions were tested showing that HIV DUO is able to reveal an infected state in 11 out of 14 cases earlier than conventional tests. This new assay improves old test performances in terms of sensitivity, maintaining specificity at very high levels.

Molecular epidemiology of an outbreak of fulminant hepatitis B

A nosocomial outbreak of hepatitis B occurred among the inpatients of a hematology unit. Nine of the 11 infected patients died from fulminant hepatitis. An investigation was conducted to identify the source of infection and the route of transmission. Two clusters of nosocomial hepatitis B were identified. The hepatitis B virus (HBV) genome from serum samples of all case patients, of one HBsAg-positive patient with acute reactivation of the infection, and of eight acutely infected, unrelated cases was identified by PCR amplification of viral DNA and was entirely sequenced. Transmission was probably associated with breaks in infection control practices, which occurred as single events from common sources or through a patient-to-patient route, likely the result of shared medications or supplies. Sequence analysis evidenced close homology among the strains from the case patients and that from the patient with reactivation, who was the likely source of infection. Molecular analysis of viral isolates evidenced an accumulation of mutations in the core promoter/precore region, as well as several nucleotide substitutions throughout the genome. The sequences of all patients were compared with published sequences from fulminant and nonfulminant HBV infections.

In vitro activity of monoclonal and recombinant yeast killer toxin-like antibodies against antibiotic-resistant gram-positive cocci

BACKGROUND

Monoclonal (mAbKT) and recombinant single-chain (scFvKT) anti-idiotypic antibodies were produced to represent the internal image of a yeast killer toxin (KT) characterized by a wide spectrum of antimicrobial activity, including gram-positive cocci. Pathogenic eukaryotic and prokaryotic microorganisms, such as Candida albicans, Pneumocystis carinii, and a multidrug-resistant strain of Mycobacterium tuberculosis, presenting specific, although yet undefined, KT-cell wall receptors (KTR), have proven to be killed in vitro by mAbKT and scFvKT. mAbKT and scFvKT exert a therapeutic effect in vivo in experimental models of candidiasis and pneumocystosis by mimicking the functional activity of protective antibodies naturally produced in humans against KTR of infecting microorganisms. The swelling tide of concern over increasing bacterial resistance to antibiotic drugs gives the impetus to develop new therapeutic compounds against microbial threat. Thus, the in vitro bactericidal activity of mAbKT and scFvKT against gram-positive, drug-resistant cocci of major epidemiological interest was investigated.

MATERIALS AND METHODS

mAbKT and scFvKT generated by hybridoma and DNA recombinant technology from the spleen lymphocytes of mice immunized with a KT-neutralizing monoclonal antibody (mAb KT4) were used in a conventional colony forming unit (CFU) assay to determine, from a qualitative point of view, their bactericidal activity against Staphylococcus aureus, S. haemolyticus, Enterococcus faecalis, E. faecium, and Streptococcus pneumoniae strains. These bacterial strains are characterized by different patterns of resistance to antibiotics, including methicillin, vancomycin, and penicillin.

RESULTS

According to the experimental conditions adopted, no bacterial isolate proved to be resistant to the activity of mAbKT and scFvKT.

CONCLUSIONS

scFvKT exerted a microbicidal activity against multidrug resistant bacteria, which may represent the basis for the drug modeling of new antibiotics with broad antibacterial spectra to tackle the emergence of microbial resistance.

Quantitative evaluation of the recombinant HIV-1 phenotype to protease inhibitors by a single-step strategy

OBJECTIVE

To develop and optimize a fast and quantitative recombinant strategy for evaluating the HIV-1 phenotype to protease inhibitors (PI).

DESIGN AND METHODS

A non-replicative HIV-1 molecular vector (designated pdelta prodelta env) capable of expressing exogenous HIV-1 protease-encoding sequences was developed in this study. The HIV-1 protease sequences were amplified from either viral isolates or plasma samples (both from 21 HIV-1-infected individuals, 19 of whom were failing different anti-HIV-1 combination treatments) and cloned in the pdelta prodelta env backbone. The HIV-1 recombinant phenotype to PI was determined directly after transfection of viral chimeric clones by measuring protease activity and calculating a percentage sensitivity index (SI%; the ratio between the results from each clone and those from a PI-sensitive reference strain).

RESULTS

The SI% values obtained from the recombinant clones paralleled the IC50 results of the viral isolates and documented different degrees of resistance and cross-resistance to PI, compatible, with few exceptions, with the respective genotype. Interestingly, an inverse correlation between SI% values and the presence of primary mutations for resistance to PI (P = 0.0038 and P = 0.0414, for indinavir and ritonavir, respectively) and a difference in SI% between samples harbouring an increasing number of mutations (indinavir, P = 0.022; ritonavir, P = 0.0466) were observed.

CONCLUSION

The data substantiate the reliability of the novel strategy for a fast (5 day) quantitative evaluation of HIV-1 phenotype to PI, and indicate that this method may contribute to the understanding of mechanisms of virus resistance to PI.

Glycopeptide resistance in coagulase-negative staphylococci

Coagulase-negative staphylococci (CNS) were the first organisms in which acquired glycopeptide resistance was recognized. Ever since the early reports, it has been apparent that resistance to teicoplanin is more common than that to vancomycin and that resistance occurs mostly in species such as Staphylococcus haemolyticus and Staphylococcus epidermidis. The minimum inhibitory concentrations (MICs) of teicoplanin for CNS usually fall over a wide range, and, especially in some methicillin-resistant isolates of the two above-mentioned species, they can reach and even exceed the resistance breakpoint, whereas vancomycin MICs tend to remain more stable over a narrower range within the limits of susceptibility. CNS strains intermediately susceptible and even resistant not only to teicoplanin but also to vancomycin have, however, been isolated, most frequently from patients subjected to prolonged glycopeptide treatment. Laboratory detection of glycopeptide-resistant CNS may be problematic, mainly because susceptibility tests, particularly those for teicoplanin, are influenced by various technical factors, and agar diffusion tests may yield false susceptibility data. In studies with experimental glycopeptides, some molecules have exhibited improved in vitro activity compared with teicoplanin and vancomycin, but these encouraging microbiological findings have not usually been followed by in vivo trials. Stepwise and single-step exposure to teicoplanin and vancomycin has allowed stable clones for which glycopeptide MICs are increased to be obtained from susceptible CNS strains, particularly strains of Staphylococcus haemolyticus and Staphylococcus epidermidis. In these studies, resistance to teicoplanin was generally easier to obtain than resistance to vancomycin, and the levels of teicoplanin resistance were higher. Population studies have demonstrated the usually heterogeneous nature of glycopeptide resistance in CNS. Although glycopeptide-resistant CNS have been shown to differ in several features from their glycopeptide-susceptible counterparts, the exact mechanism of staphylococcal glycopeptide resistance remains unknown.

An electron microscopic study of clinical and laboratory-derived strains of teicoplanin-resistant Staphylococcus haemolyticus

Staphylococcal resistance to glycopeptides (which involves more teicoplanin than vancomycin) is uncommon and largely confined to Staphylococcus haemolyticus, an emerging nosocomial pathogen with a tendency to develop antibiotic resistance. In this study, six S. haemolyticus strains, including two isogenic pairs of teicoplanin-susceptible/-resistant strains and two resistant clinical isolates, were used in a morphologic and morphometric electron microscope investigation. Cells from both clinical and laboratory-derived teicoplanin-resistant strains exhibited abnormally roughened, irregular outlines when observed by transmission electron microscopy. However, no significant differences in cell wall thickness resulted from morphometric analysis when the susceptible/resistant cells of the two isogenic pairs were compared. By scanning electron microscopy, an abnormally roughened, blistered surface was associated with teicoplanin-resistant cocci. A certain variability was noted between strains, not clearly related to the resistance level. In freeze-fracture investigations, a higher number per square micrometer of intramembrane particles, more significant in the E than in the P membrane fracture face, was observed in the laboratory-derived resistant clones as compared to susceptible parent strains. Further studies are needed to understand the cause-effect relation between these ultrastructural alterations and staphylococcal resistance to teicoplanin (but not to vancomycin).

Genotypic characterization of a nosocomial outbreak of VanA Enterococcus faecalis

Despite growing concern about vancomycin-resistant enterococci (VRE) as nosocomial pathogens, especially in the United States, in Italy VRE still represent an uncommon and occasional experience for most diagnostic laboratories. We report a genotypic characterization of the first reported nosocomial outbreak of VRE in Italy. Some experiments, including plasmid analysis and pulsed-field gel electrophoresis (PFGE) assays, aimed at investigating the genetic relatedness of the VRE isolates. Other experiments, based on hybridization and polymerase chain reaction (PCR) assays, aimed at characterizing the vancomycin resistance determinants. Over a 6-month period, 21 VRE, all identified as Enterococcus faecalis, were isolated from eight patients (all treated earlier with glycopeptide antibiotics) in a neurosurgical intensive care unit. All isolates had the same biochemical profile and antibiotic susceptibility pattern, including high-level resistance to aminoglycosides and vancomycin and teicoplanin MICs of 256 and 128 micrograms/ml, respectively. Three plasmids, one strongly hybridizing with a vanA probe, were detected in all but the last of the 21 VRE isolates. The last isolate of the cluster lacked the smallest of the three plasmids. Similar restriction profiles were obtained after plasmid DNA digestion with several endonucleases, with minor differences appreciated only in the first and last isolates. Analysis of genomic DNA restriction fragment patterns by PFGE confirmed that the reported cluster of VRE isolations was due to a single nosocomial strain of E. faecalis, despite some modifications in plasmid DNA at the beginning and at the end of the outbreak. Completely different PFGE patterns were yielded by vancomycin-susceptible E. faecalis strains isolated during the same period from inpatients in the same intensive care unit. Hybridization experiments with vanA and vanS-vanH probes and DNA amplification assays using 14 PCR primer pairs specific for vanA cluster genes (vanR, vanS, vanH, vanA, and vanY), orf1, orf2, vanB, and vanC showed identical organization of resistance determinants in all epidemic VRE isolates. This organization appeared to be the same as that described for Tn1546 in VanA prototype strain E. faecium BM4147.

Borderline susceptibility to methicillin in Staphylococcus aureus: a new mechanism of resistance?

Staphylococcus aureus strains with borderline levels of susceptibility or resistance to antistaphylococcal penicillinase-resistant penicillins (PRPs) were initially reported as neither heteroresistant nor multiply resistant organisms, producing large amounts of beta-lactamase, and becoming fully susceptible to PRPs in the presence of beta-lactamase inhibitors. This borderline susceptibility or low-level resistance was suggested to be due to beta-lactamase hyperproduction: according to this hypothesis, the staphylococcal beta-lactamase, when hyperproduced, would succeed in partially hydrolyzing methicillin and related PRPs. However, later studies demonstrated that borderline PRP susceptibility cannot be explained soley on this basis, beta-lactamase hyperproduction being neither sufficient nor necessary to determine the borderline phenotype. Intrinsic mechanisms have also been reported to be associated with some borderline PRP susceptible S. aureus strains. The more recent discovery of a PRP-hydrolyzing beta-lactamase (methicillinase) produced, in addition to the conventional penicillinase, by borderline S. aureus strains suggests that this second, more specific beta-lactamase is more likely to be responsible for the borderline phenotype than an increased amount of the penicillinase. The slow kinetics of PRP hydrolysis by methicillinase is consistent with its association with reduced susceptibility rather than true resistance to PRPs. The combined effect of methicillinase plus penicillinase on some common substrates might explain the increased beta-lactamase activity often observed in borderline S. aureus strains.

In vitro activity of levofloxacin against gram-positive bacteria

The in vitro activity of levofloxacin was investigated against 256 clinical strains of four gram-positive genera (Staphylococcus, Streptococcus, Enterococcus, and Listeria). Ofloxacin and ciprofloxacin were used as comparators. Uniform susceptibility to levofloxacin was recorded among methicillin-susceptible staphylococci, streptococci other than Streptococcus agalactiae, regardless of their being susceptible, intermediate, or resistant to penicillin (S. pneumoniae) or erythromycin (S. pyogenes and S. pneumoniae), in enterococci other than Enterococcus faecalis and E. faecium, and in Listeria monocytogenes isolates. Moreover, 1 of 22 S. agalactiae isolates and 1 of 19 E. faecium isolates was resistant, and 2 of 19 were intermediate. Resistances to levofloxacin with MIC90s in the resistance range were only observed in methicillin-resistant staphylococci and E. faecalis isolates. In any case, the MICs of ofloxacin and ciprofloxacin were usually 2-4 times higher than those of levofloxacin. In time-kill assays using three test strains (a methicillin-susceptible Staphylococcus aureus isolate, a penicillin-susceptible Streptococcus pneumoniae isolate, and an E. faecalis isolate), the bactericidal activity of levofloxacin was greater than that of ciprofloxacin.

Nationwide survey in Italy of treatment of Streptococcus pyogenes pharyngitis in children: influence of macrolide resistance on clinical and microbiological outcomes. Artemis-Italy Study Group

Throat swab specimens were obtained from 3,227 children with symptoms of acute pharyngotonsillitis. After 14 to 21 days, a second throat swab specimen was obtained at a follow-up visit. Over 42% of the 934 strains of Streptococcus pyogenes isolated in the primary study were resistant to erythromycin, azithromycin, and clarithromycin. Eradication rates among the 668 patients who entered the follow-up study were as follows: 84.1%, penicillin recipients; 82.7%, cephalosporin recipients; and 71.7%, macrolide recipients. Among patients treated with macrolides, the eradication rate was approximately 80% when the infecting organisms were erythromycin-susceptible and approximately 60% when they were erythromycin-resistant. These results indicate substantial in vitro macrolide resistance among Italian isolates of S. pyogenes. However, at least for a minor self-limiting condition such as acute S. pyogenes pharyngitis, our findings point to a limited overall correlation between in vitro susceptibility (to penicillins, cephalosporins, or macrolides) and eradication in patients treated with these drugs and an even weaker correlation between in vitro resistance (to macrolides) and noneradication in patients receiving macrolide therapy.

Phenotypes and genotypes of erythromycin-resistant Streptococcus pyogenes strains in Italy and heterogeneity of inducibly resistant strains

A total of 387 clinical strains of erythromycin-resistant (MIC, >/=1 microg/ml) Streptococcus pyogenes, all isolated in Italian laboratories from 1995 to 1998, were examined. By the erythromycin-clindamycin double-disk test, 203 (52.5%) strains were assigned to the recently described M phenotype, 120 (31.0%) were assigned to the inducible macrolide, lincosamide, and streptogramin B resistance (iMLS) phenotype, and 64 (16.5%) were assigned to the constitutive MLS resistance (cMLS) phenotype. The inducible character of the resistance of the iMLS strains was confirmed by comparing the clindamycin MICs determined under normal testing conditions and those determined after induction by pregrowth in 0.05 microg of erythromycin per ml. The MICs of erythromycin, clarithromycin, azithromycin, josamycin, spiramycin, and the ketolide HMR3004 were then determined and compared. Homogeneous susceptibility patterns were observed for the isolates of the cMLS phenotype (for all but one of the strains, HMR3004 MICs were 0.5 to 8 microg/ml and the MICs of the other drugs were >128 microg/ml) and those of the M phenotype (resistance only to the 14- and 15-membered macrolides was recorded, with MICs of 2 to 32 microg/ml). Conversely, heterogeneous susceptibility patterns were observed in the isolates of the iMLS phenotype, which were subdivided into three distinct subtypes designated iMLS-A, iMLS-B, and iMLS-C. The iMLS-A strains (n = 84) were highly resistant to the 14-, 15-, and 16-membered macrolides and demonstrated reduced susceptibility to low-level resistance to HMR3004. The iMLS-B strains (n = 12) were highly resistant to the 14- and 15-membered macrolides, susceptible to the 16-membered macrolides (but highly resistant to josamycin after induction), and susceptible to HMR3004 (but intermediate or resistant after induction). The iMLS-C strains (n = 24) had lower levels of resistance to the 14- and 15-membered macrolides (with erythromycin MICs increasing two to four times after induction), were susceptible to the 16-membered macrolides (but resistant to josamycin after induction), and remained susceptible to HMR3004, also after induction. The erythromycin resistance genes in 100 isolates of the different groups were investigated by PCR. All cMLS and iMLS-A isolates tested had the ermAM (ermB) gene, whereas all iMLS-B and iMLS-C isolates had the ermTR gene (neither methylase gene was found in isolates of other groups). The M isolates had only the macrolide efflux (mefA) gene, which was also found in variable proportions of cMLS, iMLS-A, iMLS-B, and iMLS-C isolates. The three iMLS subtypes were easily differentiated by a triple-disk test set up by adding a josamycin disk to the erythromycin and clindamycin disks of the conventional double-disk test. Tetracycline resistance was not detected in any isolate of the iMLS-A subtype, whereas it was observed in over 90% of both iMLS-B and iMLS-C isolates.

A new subtraction technique for molecular cloning of rare antiviral antibody specificities from phage display libraries

The preparation of random combinatorial libraries exposed on the surface of phage provides a route for the selection of diverse high affinity human monoclonal antibodies. However, in particular settings, the isolation of genes coding for a rare antibody can be elusive because some epitopes are predominant and because, in the case of impure antigens, the protein or any compound of interest can be present in relatively minimal amount. In this paper, we describe the successful utilization of a new strategy of "preadsorption" panning that allowed us to clone a rare human monoclonal antibody fragment and to access a different antibody repertoire. The procedure is easy, fast, inexpensive, can be used together with other panning techniques and can be particularly useful in cloning antibodies against rare or unknown determinants.

Dissection of human humoral immune response against hepatitis C virus E2 glycoprotein by repertoire cloning and generation of recombinant Fab fragments

Demonstration of antibodies inhibiting key viral functions is the basis for the design of an effective vaccine. Dissection of the human antibody response by repertoire cloning may be a powerful means to address this issue. In this study, a panel of human monoclonal recombinant Fab fragments specific for hepatitis C virus (HCV) E2 envelope protein was generated. The selection procedure was designed to select for cross-genotype reactive antibodies. Sequences coding five different human recombinant Fabs specific for the HCV/E2 protein were cloned and characterized. The ability of the cloned antibody fragments to inhibit adhesion of recombinant envelope E2 protein to target cells was assayed. While affinity of the different antibody fragments appeared similar, activity in inhibiting E2 binding to target cells varied considerably from one Fab fragment to another. Two Fabs were not able to inhibit E2 binding at high concentration (40 microg/mL), while three other Fab clones were active in neutralizing 50% of the E2 binding at concentrations ranging from 3 to 0.35 microg/mL.

In vitro antibacterial activity of trovafloxacin and five other fluoroquinolones

The in vitro inhibitory and bactericidal activities of the investigational fluoroquinolone trovafloxacin were studied and compared with those of five other fluoroquinolones (ciprofloxacin, ofloxacin, pefloxacin, rufloxacin and sparfloxacin) against a wide range of clinical isolates from Italian hospitals. Against gram-positive bacteria, trovafloxacin was overall more active than the other antibiotics tested, including sparfloxacin, another gram-positive-oriented fluoroquinolone, and was active against all ciprofloxacin-resistant streptococci, enterococci, and listeriae, all ciprofloxacin-resistant Staphylococcus aureus isolates and most ciprofloxacin-resistant coagulase-negative staphylococci. Its antistaphylococcal activity was not affected by oxacillin resistance or susceptibility of the isolates, nor was its antipneumococcal activity affected by whether isolates were susceptible or resistant to penicillin. Against gram-negative bacteria, trovafloxacin retained a high potency mostly comparable with that of ciprofloxacin. Rufloxacin and pefloxacin were less active than the other fluoroquinolones against most test strains of both gram-positive and gram-negative organisms. Trovafloxacin minimal bactericidal concentrations usually equalled or exceeded by 2-4 times the minimal inhibitory concentration values, indicating that the compound is overall highly bactericidal.

In vitro extracellular and intracellular activity of two newer and two earlier fluoroquinolones against Listeria monocytogenes

Two new fluoroquinolones (trovafloxacin and sparfloxacin) with enhanced activity against gram-positive pathogens and two earlier compounds (ciprofloxacin and ofloxacin) were tested for their in vitro inhibitory and bactericidal activity against 80 strains of Listeria monocytogenes. All strains were uniformly highly susceptible to trovafloxacin, the MIC90 being 0.25 mg/l. Resistance to sparfloxacin was not detected, however the MIC90 of sparfloxacin was eight times that of trovafloxacin. A few strains were resistant to ciprofloxacin and ofloxacin (MIC90 4 mg/l for both drugs). MBCs usually exceeded MICs by 2 to 4 times. The MBC90 of trovafloxacin (1 mg/l) was lower than that of the other three drugs (8 mg/l). After checking their ability to enter and grow within human enterocyte-like Caco-2 cells, four strains were used to study the intracellular activity and eradicating power of the four quinolones. Trovafloxacin was more active than sparfloxacin and the earlier fluoroquinolones in terms of both intracellular killing and inhibition of a cytopathogenic effect. The uniform high-level activity of trovafloxacin against Listeria monocytogenes isolates in conventional in vitro assays and its extracellular and intracellular killing of invasive strains suggest that this and maybe other new fluoroquinolones should be further investigated as possible anti-listerial agents.

In vitro antibacterial activity of LY333328, a new semisynthetic glycopeptide

LY333328 is a semisynthetic N-alkyl derivative of LY264826, a naturally occurring structural analog of vancomycin. LY333328 was evaluated for its in vitro inhibitory and bactericidal activities in comparison with those of the two currently available glycopeptides (vancomycin and teicoplanin). Glycopeptide-susceptible test strains included a total of 311 isolates (most of clinical origin) from the genera Staphylococcus, Enterococcus, Streptococcus, Aerococcus, Gemella, Lactococcus, Listeria, Corynebacterium, and Clostridium. Test strains resistant or intermediate to vancomycin and/or teicoplanin included 56 clinical isolates of Enterococcus (of the VanA, VanB, and VanC phenotypes) and 32 clinical isolates of Staphylococcus (S. haemolyticus, S. epidermidis, and S. aureus), 31 strains of gram-positive genera outside the spectrum of activity of vancomycin (Leuconostoc, Pediococcus, Lactobacillus, and Erysipelothrix), and laboratory-derived organisms obtained after exposure of susceptible Staphylococcus isolates to teicoplanin (6 strains) or laboratory-derived organisms with resistance determinants received from VanA enterococci (2 Enterococcus and 25 Listeria transconjugants). LY333328 was highly active against staphylococci, enterococci, and listeriae (whether they were clinical or laboratory-derived strains) resistant to the currently available glycopeptides. In particular, the MICs of LY333328 did not vary substantially between teicoplanin-susceptible and teicoplanin-resistant staphylococci and between vancomycin-susceptible and vancomycin-resistant enterococci. LY333328 demonstrated fairly good inhibitory activity even against most strains of Leuconostoc, Pediococcus, and Erysipelothrix (MIC range, 1 to 8 microg/ml), whereas it proved less active (although much more active than vancomycin or teicoplanin) against Lactobacillus strains. In minimal bactericidal concentration (MBC) and time-kill studies, LY333328 demonstrated excellent bactericidal activity; enterococci, in particular, which were largely tolerant of vancomycin and teicoplanin, were uniformly killed by LY333328, with MBC-to-MIC ratios of 4 to 8 for most vancomycin-susceptible and vancomycin-resistant strains. In attempts to select for resistant clones, no survivors stably growing in the presence of 10 microg of LY333328 per ml were obtained from the Staphylococcus and Enterococcus test strains exposed to the drug.

Dynamic features of human immunodeficiency virus type 1 (HIV-1) viremia: kinetics of cell-free HIV-1 RNA after therapeutic plasma exchange

To gain insight into the variables that influence the dynamics of human immunodeficiency virus type 1 (HIV-1) viremia levels, HIV-1 RNA molecules were quantified in plasma from an infected patient undergoing therapeutic plasma exchange (TPEx). After each TPEx procedure (2000 mL of fluid exchanged per session), HIV-1 genome molecule levels dropped to 58%-63% of the basal level but rapidly reverted to pre-TPEx values (doubling time = 3.50-4.04 h). Of interest, mobilization of extravascular cell-free virions (on average, 5.15 x 10(4) viral genome molecules/h) had already occurred during TPEx. After three daily TPEx procedures, HIV-1 viremia rebounded to basal values, while HIV-1 proviruses and viral transcripts in peripheral blood lymphocytes constantly tested at stable levels. Overall, this study extends previous analyses of the rate of HIV-1 turnover, using an alternative approach to the use of antiretroviral drugs, and it provides, albeit indirectly, insights into the amount and dynamic features of extravascular cell-free virus.

An improved phage display vector for antibody repertoire cloning by construction of combinatorial libraries

Phagemid pComb3 is a widely used vector for molecular cloning of the antibody repertoire and for production of phage display libraries. However, in practical use, the utilization of this vector has some drawbacks. In this work we describe the construction of pComb3/TIG, an improved, easily manipulated vector for the cloning and display of antibody fragment libraries on the surface of filamentous phage. The two small "stuffer" fragments at the cloning sites were replaced with long DNA fragments, for easier differentiation of the correctly cut forms of the vector. Moreover, in pComb3/TIG the fragment at the heavy-chain-fragment cloning site contains an acid phosphatase-encoding gene. This feature allows the easy distinction of the Escherichia coli cells containing the unmodified form of the phagemid instead of the heavy-chain fragment coding cDNA in a simple plate histochemical assay.

Borderline methicillin-susceptible Staphylococcus aureus strains have more in common than reduced susceptibility to penicillinase-resistant penicillins

Ten epidemiologically unrelated Staphylococcus aureus isolates with borderline levels of susceptibility to antistaphylococcal penicillinase-resistant penicillins (PRPs) were investigated together with appropriate S. aureus control strains. By a nitrocefin microplate assay, all borderline PRP-susceptible test strains were found to produce comparable amounts of beta-lactamase. Hydrolytic activity against another chromogenic substrate (PADAC) and against the PRPs was also demonstrated in membrane preparations from induced cells of 9 of the 10 borderline test strains. When bacterial membranes were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, two methicillin-inducible bands of about 32 and 31 kDa were detected, after Coomassie blue staining, in the membrane protein patterns of the same nine borderline test strains. By gel renaturation and zymographic detection of beta-lactamase activity, both methicillin-inducible membrane proteins were detected with nitrocefin as a substrate, whereas only one band (presumably the smaller protein) was detected with PADAC. With the remaining borderline test strain (a40), only the larger band was detected in the renatured gels with nitrocefin as a substrate. Plasmid DNA analysis revealed that the borderline susceptible test strains, again with the exception of a40, shared a 17.2-kb plasmid yielding four HindIII fragments of 7.0, 5.3, 3.5, and 1.4 kb. In Western blot (immunoblot) experiments using rabbit antiserum to penicillin-binding protein (PBP) 2a, test strain a40, which did not share a number of features characteristically associated with the other borderline test strains, was eventually shown to produce PBP 2a. Five other S. aureus strains, belonging to phage group 94/96, were found to display the borderline phenotype, including such distinguishing features as the membrane-associated PRP- and PADAC-hydrolyzing activity, the two methicillin-inducible membrane proteins, and the 17.2-kb plasmid. These results suggest that borderline susceptible S. aureus strains share more common features than reduced susceptibility to PRPs.

Dynamics and modulation of human immunodeficiency virus type 1 transcripts in vitro and in vivo

The dynamics of human immunodeficiency virus type 1 (HIV-1) transcription was analyzed in vitro and in vivo by using a specific molecular approach which allows accurate quantitation of the different classes of viral mRNAs. Unspliced (US) and multiply spliced (MS) HIV-1 transcripts were assayed by competitive reverse transcription (cRT)-PCR, using a single competitor RNA bearing in tandem internally deleted sequences of both template species. Acute HIV-1 infection of primary peripheral blood mononuclear cells (PBMCs), monocytes/macrophages cells, and the A3.01 T-lymphocyte-derived cell line was studied; both classes of HIV-1 mRNAs increased exponentially (r2 > 0.98) at days 1 to 3 and 1 to 4 postinfection in HIV(IIIB)-infected A3.01 cells and PBMCs, respectively, whereas monocytes/macrophages infected with monocytotropic HIV(BaL) exhibited a linear (r2 = 0.81 to 0.94) accumulation of US and MS transcripts. Following induction of chronically infected ACH-2 cells, MS transcripts increased 2 h postinduction and peaked at 5 h (doubling time, 58 min), while at 24 h, US mRNAs increased 3,053-fold compared with basal time (doubling time, 137 min). To address the biopathological significance of HIV-1 expression pattern during infection progression, pilot cross-sectional and longitudinal analyses were carried out with samples from untreated and treated HIV-1-infected patients. In almost all untreated (recently infected, long-term nonprogressor, and progressor) patients, MS transcript levels followed the general trend of systemic HIV-1 activity. In patients under treatment with powerful antiretroviral compounds, viral MS transcripts rapidly fell to undetectable levels, indicating that in vivo, levels of MS mRNAs in PBMCs are closely associated with the number of newly infected cells and suggesting a new role for the quantitative analysis of HIV-1 transcription in infected patients.

Transferable erythromycin resistance in Listeria spp. isolated from food

An erythromycin-resistant (Emr) Listeria innocua and an Emr Listeria monocytogenes isolate both carried ermC genes, which code for rRNA methylases. The ermC genes were transferable by conjugation to recipient L. monocytogenes, Listeria ivanovii, and Enterococcus faecalis but did not appear to be associated with conjugative plasmids.

Lysozyme inhibitors enhance immune response in mice

The effect of hen egg-white lysozyme (HEWL) inhibitors (such as heparin, histidine methylester, chitotriose, chitobiose) on immune response was evaluated by measuring antibody-producing cells and circulating antibodies in mice inoculated with these substances and the test antigen (SRBC or BSA). It was found that these compounds have an immuno-enhancing effect which is directly proportional to their inhibitory activity on HEWL. Conversely, HEWL inhibited the immunoenhancing effect of these compounds when injected together with these and the test antigen. The results suggest that one possible mechanism by which adjuvants stimulate immune response may be the inhibition of endogenous lysozyme.

Modulatory effects of hen egg-white lysozyme on immune response in mice

The effect of her egg-white lysozyme (HEWL) on immune response was evaluated by measuring antibody-producing cells and circulating antibodies in mice inoculated with the test antigen (SRBC or BSA) and HEWL at the same time but in a separate body area. HEWL caused a premature decline in SRBC-specific plaque forming cells (PFC) and a reduction in the total amount of these cells. HEWL inhibited antibody production against BSA in the primary response, but was devoid of any effect on the secondary response elicited in the same mice by a second inoculation of the test antigen. The inhibitory effect of HEWL was dose-dependent, being maximal with 300 micrograms, required an enzymatically active protein and was not shown by other basic proteins. HEWL also abolished the enhancing effect of LPS and CFA on anti-BSA antibody production. The inhibitory activity of HEWL was further increased by hydrolyzed peptidoglycan. These results suggest that HEWL modulates the immune response in mice and performs this function through activation of non-specific suppression mechanisms.

In vitro conjugative transfer of VanA vancomycin resistance between Enterococci and Listeriae of different species

In a study designed to gain data on the in vitro transferability of vancomycin resistance from enterococci of the VanA phenotype to listeriae of different species, three clinical Enterococcus isolates-Enterococcus faecium LS10, Enterococcus faecalis LS4, and Enterococcus faecalis A3208, all harboring a plasmid that strongly hybridized with a vanA probe-were used as donors in transfer experiments. Strains of five Listeria species were used as recipients. From Enterococcus faecium LS10, glycopeptide resistance was transferred to Listeria monocytogenes, Listeria ivanovii, and Listeria welshimeri recipients, whereas no transfer occurred to Listeria seeligeri or Listeria innocua strains. From the two Enterococcus faecalis isolates, no transfer occurred to any Listeria recipient. MICs of both vancomycin and teicoplanin were > or = 256 mg/l for all transconjugants tested. Furthermore, all transconjugants harbored a plasmid that strongly hybridized with the vanA probe, with vanA consistently located in an EcoRI fragment of about 4 kb. Exposure of Listeria transconjugants to vancomycin resulted in synthesis of a membrane protein similar in size (39 kDa) to a vancomycin-induced membrane protein of Enterococcus faecium LS10. In retransfer experiments with Listeria transconjugants used as donors, glycopeptide resistance was transferred to all Listeria recipients tested, including strains of Listeria innocua and Listeria seeligeri, which were unable to receive the resistance from Enterococcus faecium LS10. The frequency of vanA transfer to listerial recipients was greater in retransfer experiments than in the primary matings. These findings suggest that the vanA resistance determinant might spread to the established pathogen Listeria monocytogenes, both directly from a resistant enterococcus and through strains of nonpathogenic Listeria species acting as intermediate resistance vehicles.

Quantitative molecular monitoring of human immunodeficiency virus type 1 activity during therapy with specific antiretroviral compounds

Methods for the absolute quantitation of nucleic acids present in small amounts in biological samples (competitive PCR and competitive reverse transcription PCR) were applied to the direct monitoring of specific anti-human immunodeficiency virus type 1 (HIV-1) therapy. With these techniques, different parameters of HIV-1 activity (including genomic RNA copy numbers in plasma, proviral and late transcript copy numbers in peripheral blood lymphocytes, and mean transcriptional activity per each HIV-1 provirus) were monitored during therapy with azidothymidine or ddI. In most of these treated patients, a direct response to the antiretroviral compounds employed was detected during the first few weeks of treatment, as documented by a fast decrease of all molecular indexes of HIV-1 activity. However, residual viral replication (albeit at minimal levels) was documented during therapy in all subjects monitored in this study. In a minority of the patients under study (3 of 12), the drug-dependent viral inhibition was maintained throughout the observation time (213 to 791 days), but in 9 patients a rebound in viremia level was detected during therapy with competitive reverse transcription PCR. Sequencing analysis of a portion of the HIV-1 gene pol from cell-free virions showed that circulating viral variants bearing at least two mutations compatible with azidothymidine or ddI resistance were detectable in the patients who exhibited a rebound in cell-free HIV-1 genomic RNA copy numbers in plasma but not in one patient who maintained (for 455 days) lowered levels of viral load during ddI treatment.

Interactions with lectins and agglutination profiles of clinical, food, and environmental isolates of Listeria

On the basis of preliminary trials with 14 collection strains of Listeria, five lectins (Canavalia ensiformis, concanavalin A; Griffonia simplicifolia lectin I; Helix pomatia agglutinin; Ricinus communis agglutinin; and Triticum vulgaris wheat germ agglutinin) were selected to set up a microtiter agglutination assay. The lectin agglutination profiles of 174 clinical, food, and environmental strains of Listeria monocytogenes, Listeria innocua, and Listeria seeligeri were investigated. Data on the standard determination of the antigenic structure were available for clinical strains; nonclinical isolates were assigned to serogroup 1 or 4 with commercial antisera. The listeria-lectin interaction was related to serological type rather than species; in particular, the strains assigned to serogroup 1 or belonging to serovars 1/2a, 1/2b, 1/2c, 3a, 3b, and 7 were never agglutinated by G. simplicifolia lectin I. The five-lectin set proved to be capable of detecting differences between serologically identical isolates of L. monocytogenes. Of the 150 isolates of this species, 144 were distributed over 15 different lectin agglutination profiles and 6 autoagglutinated, the overall typeability being 96%. However, the profiles encountered among L. monocytogenes isolates were not randomly distributed. With strains assigned to serogroup 1 or belonging to serovars 1/2a, 1/2b, 1/2c, and 3b, the clinical isolates fell into only two of the eight patterns recorded overall; with strains of serogroup 4 and serovar 4b, food and environmental isolates were distributed over eight of the nine patterns found in total, while clinical isolates were distributed over five patterns. In a comparative study of 15 epidemiologically relevant isolates of L. monocytogenes from five distinct outbreaks, strains with identical phage types and/or DNA fingerprints displayed identical lectin profiles. The heterogeneity of agglutination profiles may form the basis of a new approach to L. monocytogenes typing.