Alessandra Zanchi

Staphylococcus aureus nasal carriage in the community: a survey from central Italy.

Recently, concern has increased regarding the spread of methicillin-resistant Staphylococcus aureus (MRSA) in the community. We studied 812 subjects from central Italy to establish the rates of nasal carriage of S. aureus, and antibiotic susceptibility patterns, in the community. The prevalence of S. aureus nasal carriage was 30.5%. Only one subject, with predisposing risk factors for acquisition, was identified as carrier of MRSA (prevalence of 0.12%). The presence of MRSA in the community of our area still appears to be a rare event. Among methicillin-susceptible S. aureus (MSSA) isolates, a surprisingly high rate (18%) of resistance to rifampin was observed.

Immunity to diphtheria in a sample of adult population fron central Italy

A sample of 643 healthy subjects from central Italy aged 20 to 80, were screened for diphtheria antitoxin. Serum diphtheria antitoxin was assayed by a new passive haemagglutination technique using turkey red blood cells sensitized with diphtheria toxoid, after having performed a correlation study between this technique and the reference in vivo neutralization test. Of the studied population 26.7% showed a lack of serum antitoxin titres considered to be protective. The rate of susceptible subjects increased with age, showing the highest value (38.9%) in the sixth decade of age. Males proved less protected than females; 53.2% of the male population aged 50-59 were lacking a protective anti-diphtheria immunity. On the basis of present results, a periodical revaccination of the entire adult population with reduced doses of diphtheria toxoid would be advisable.

Resistance Determinants and Clonal Diversity in Group A Streptococci Collected during a Period of Increasing Macrolide Resistance

ABSTRACT Susceptibility to macrolides and lincosamides was investigated with 299 consecutive nonduplicate Streptococcus pyogenes clinical isolates collected over a 6-year period (1992 to 1997) from an area of central Italy. During this period, macrolide resistance rates steadily increased (from 9% in 1992 to 53% in 1997; P < 0.001). The increase was caused by isolates with a macrolide-lincosamide-streptogramin B resistance phenotype, carrying mostly erm(B) but also erm(TR) genes, that were not detected in the first 2 years and were detected with increasing prevalence (8, 5, 26, and 37%, respectively) during the following 4 years. During the same period, the prevalence of isolates with a macrolide resistance phenotype, carrying mef(A) determinants, did not vary significantly; on average it was 13%, with modest rate fluctuations in different years and no definite trend. Molecular typing revealed a remarkable clonal diversity among susceptible and resistant isolates and a notable heterogeneity of the genetic environment of the resistance genes. The analysis of clonal diversity in relation with resistance phenotypes and genotypes revealed that increased macrolide resistance rates were due to a complex interplay of different mechanisms, with a relevant contribution played by an “epidemic” spread of genetic elements carrying the erm(B) gene among the circulating streptococcal population.

Distribution of cphA or related carbapenemase-encoding genes and production of carbapenemase activity in members of the genus Aeromonas.

The prevalence of the cphA gene or related carbapenemase-encoding genes was investigated in 114 Aeromonas strains belonging to the six species of major clinical interest. A species-related distribution of cphA-related sequences was observed. Similar sequences were found in A. hydrophila, A. veronii bv. sobria, A. veronii bv. veronii, and A. jandaei, but not in A. caviae, A. trota, or A. schubertii. However, a single A. caviae strain (of 62 tested) was found carrying cphA-related sequences, suggesting the possibility of the horizontal transfer of this gene to species which normally do not carry it. Production of carbapenemase activity was detectable in 83% of the hybridization-positive strains but in none of the hybridization-negative ones. When it was present, carbapenemase activity was always inhibitable by EDTA. Either carbapenemase-producing or not, Aeromonas strains appeared to be susceptible to imipenem when in vitro susceptibility testing was performed with inocula of conventional size (10(5) CFU), for which MICs were always < or = 1 microgram/ml. With a larger inoculum (10(8) CFU), the MICs for carbapenemase-negative strains always remained < or = 1 microgram/ml, while those for carbapenemase-producing strains were always > or = 4 micrograms/ml, being usually higher than the breakpoint for susceptibility. The present results indicate that the production of metallocarbapenemase activity, apparently encoded by cphA homologs, is widespread among some of the Aeromonas species of clinical interest (A. hydrophila, A. veronii bv. sobria, A. veronii bv. veronii, and A. jandaei) and that imipenem MICs for carbapenemase-producing strains are subjected to a relevant inoculum size effect.

Large Oligoclonal Outbreak Due to Klebsiella pneumoniae ST14 and ST26 Producing the FOX-7 AmpC β-Lactamase in a Neonatal Intensive Care Unit

ABSTRACT A large outbreak caused by expanded-spectrum cephalosporin-resistant Klebsiella pneumoniae (ESCRKP) was observed in a neonatal intensive care unit (NICU) in central Italy. The outbreak involved 127 neonates (99 colonizations and 28 infections, with seven cases of sepsis and two deaths) over a period of more than 2 years (February 2008 to April 2010). Characterization of the 92 nonredundant isolates that were available for further investigation revealed that all of them except one produced the FOX-7 AmpC-type β-lactamase and belonged to either sequence type 14 (ST14) or ST26. All of the FOX-7-positive isolates were resistant to cefotaxime, ceftazidime, and piperacillin-tazobactam, while 76% were susceptible to cefepime, 98% to ertapenem, 99% to meropenem, and 100% to imipenem. The two carbapenem-nonsusceptible isolates had alterations in the genes encoding outer membrane proteins K35 and K36, which resulted in truncated and likely nonfunctional proteins. The outbreak was eventually controlled by the reinforcement of infection control measures based on a multitiered interventional approach. This is the first report of a large NICU outbreak caused by ESCRKP producing an AmpC-type enzyme. This study demonstrates that AmpC-type enzyme-producing strains can cause large outbreaks with significant morbidity and mortality effects (the mortality rate at 14 days was 28.5% for episodes of sepsis), and it underscores the role of laboratory-based surveillance and infection control measures to contain similar episodes.

Erythromycin Resistance in Streptococcus pyogenes and Macrolide Consumption in a Central Italian Region

AbstractBackground:The study investigated macrolide resistance in Streptococcus pyogenes in a central Italian area from 2001 to 2006 and the possible correlation between antibiotic consumption and fluctuations of resistance percentages.Materials and Methods:Macrolide and lincosamide susceptibility of 1,419 S. pyogenes isolates was tested by Kirby Bauer method. Macrolide consumption was valuated as defined daily dose/1,000 inhabitants per day (DID), according to the World Health Organization anatomic therapeutic chemical classification. Spearman’s correlation coefficient was used to assess the association between resistance and use of (1) all macrolides pooled, (2) once daily, (3) twice daily, and (4) three times daily dosage regimens.Results:In total, 320 strains (22.6%) were erythromycinresistant, 11.4% with the M phenotype and 11.2% with the MLS phenotype. There was a significant decrease in erythromycin resistance during the study period—from 28.1% in 2001 to 15.6% in 2006 (p < 0.01). No significant correlation was found between erythromycin resistance and local overall macrolide consumption, neither during the same year nor during the previous year. In contrast, a significant correlation was found between resistance rates and oncedaily macrolide use during the preceding 6 months in Siena r = 0.747, p = 0.008).Conclusion:The known greater selective effect of longacting agents could establish a pressure outcome, resulting in a specific local epidemiology during a relatively short time gap.

Pneumococcal disease in a paediatric population in a hospital of central Italy : A clinical and microbiological case series from 1992 to 2006

OBJECTIVES Streptococcus pneumoniae is frequently isolated from carrier children, but it also causes localized and invasive diseases. Increasing incidence of chemoresistance can affect the efficacy of empiric therapy and it motivates interest in primary prophylaxis. The study aims to investigate clinical and microbiological features of paediatric pneumococcal infections in an Italian province. METHODS Retrospective clinical analysis of 640 children, hospitalized from 1992 to 2006 with one culture positive for S. pneumoniae, was performed. Chemosusceptibility tests and serotyping were carried out on isolates; statistical analysis was applied to compare variables. RESULTS Overall, 47.8% were carriers, 49% and 3.2% had, respectively, a localized or invasive disease; S. pneumoniae aetiology accounted for 25% of meningitis and 16% of sepsis. On the total isolates, 10.2% were penicillin non-susceptible, 35.15% were erythromycin resistant, with increasing rates over years. Prevalent invasive serotypes were 1 (38.1%) and 7F (9.5%). CONCLUSIONS The study sustains pneumococcal disease relevance in children, on the strength of a 15 year observation. Long time period can represent a limit due to population characteristics changing; a selection bias could also be present due to hospitalized only patient analysis. However, we documented variable evolution of chemoresistance and a peculiar serotype spreading, offering microbiological basis for an appropriate clinical approach.

MOLECULAR EPIDEMIOLOGY OF NASOPHARYNGEAL CORYNEBACTERIA IN HEALTHY ADULTS FROM AN AREA WHERE DIPHTHERIA VACCINATION HAS BEEN EXTENSIVELY PRACTICED

In addition to conventional biochemical tests, a DNA probe specific for Corynebacterium diphtheriae was used to characterize 53 cystinase-positive and urease-negative corynebacteria strains isolated from pharyngeal and nasal swabs obtained from 515 healthy adults living in an urban area of central Italy. No Corynebacterium diphtheriae strain was found. Six “atypical” strains were isolated, which could not be classified in any of the species so far defined in the Corynebacterium genus. These strains appeared to be biochemically close to Corynebacterium pseudodiphtheriticum and genetically close to Corynebacterium diphtheriae, since their DNAs strongly hybridized, under relatively low stringency conditions, with a Corynebacterium diphtheriae-specific probe and since insertion sequences which are usually found in Corynebacterium diphtheriae genomes were also found to be present in their genomes. No one of these six strains was either toxigenic or susceptible to lysogenization by β-corynephage carrying the tox gene. Therefore, they do not seem to have any epidemiological relevance as possible hosts for β-phages.

Antimicrobial susceptibility of Streptococcus pyogenes and Streptococcus pneumoniae: surveillance from 1993 to 2004 in Central Italy.

Abstract The susceptibility of 1870 Streptococcus pyogenes and 1595 Streptococcus pneumoniae to macrolides and lincosamides has been monitored from 1993 to 2004 in Central Italy. Among S. pyogenes, 30.2% were erythromycin resistant; 18.5% were also resistant to josamycin and clindamycin (MLS phenotype). After an increasing erythromycin resistance rate in 1993-1997 (maximum 53.16%), a definite decrease was observed since 2001 with resistance rates always less than 30%. Thirty six percent of pneumococcal isolates were erythromycin-resistant, with minor temporal fluctuations; the MLS phenotype was the most prevalent overall (32.6%) and in individual years. S. pneumoniae strains were also tested for susceptibility to b-lactams and other antimicrobial agents: 11.2% were penicillin non-susceptible, with a gradually increasing prevalence after 2001 (maximum rate 17.3% in 2004), 31.15% were resistant to tetracycline, 4.9% to chloramphenicol, 0.74% to rifampin. All pneumococcal isolates were susceptible to teicoplanin and 99.9% to ceftriaxone and ofloxacin.

Specific antibody patterns over a two-year period after rubella immunization with RA 27/3 live attenuated vaccine.

Screening for rubella antibodies was carried out on 1557 schoolgirls aged 9-20. Of seronegative subjects 70% (442/631) were immunized with RA 27/3 rubella vaccine and some of the vaccinees underwent a serological and clinical follow-up over a two year period. Adverse reactions occurred in 27% of vaccinees, usually 1-2 weeks after immunization; late reactions were never observed. The vaccine-induced seroconversion rate evaluated at 4-5 weeks after immunization was 99.7%. Both one and two years after immunization the seropositivity rate of vaccinees was 100%. The maximum geometric mean antibody titre (GMT) was observed at 4-5 weeks after vaccination and a significant GMT decrease was evident on both the following annual controls. Specific antibody patterns in vaccinees were highly variable and in a small number of subjects a remarkable antibody titre decrease was noticed.