77 research outputs found
Dynamics of pneumococcal colonization in healthy Dutch children
No full textA recent study of pneumococcal colonization in 3198 healthy children of 1-19 years of age in The Netherlands showed pneumococcal colonization in 19 % of the children, with a peak incidence of 55 % at the age of 2 years; an age-related serotype distribution was also found. In the present study, the genetic background and resistance profiles of 578 pneumococcal isolates from the latter study were characterized by means of chromosomal genotyping and susceptibility testing. In contrast to the age-related serotype distribution observed previously, the genetic background of the strains was not age related. Few strains were found showing close homology (>95 %) with the international clones Spain(9V)-3 (ten isolates showed homology), England(14)-9 (four isolates), Tennessee(23F)-4 (two isolates), CSR(14)-10 (one isolate) and Sweden(15A)-25 (one isolate). In total, 19 % of strains showed resistance to one or more antibiotics. Resistance to cotrimoxazole, tetracycline, erythromycin and penicillin was found in 12.9, 5.6, 5.0 and 2.7 % of isolates, respectively. Multidrug resistance was found in 1.9 % of strains. In conclusion, pneumococcal colonization isolates from healthy Dutch children represent a heterogeneous, mostly antibiotic susceptible, genetic population.<br/
Tolerance of staphylococcus aureus to ß-lactam antibiotics
No full textPenicillin has a bactericidal action on actively dividing bacteria. If
protein synthesis of bacteria exposed to penicillin is inhibited, for
example by the addition of chloramphenicol or the omission of an
essential amino acid from the medium, the bactericidal action of penicillin
changes into bacteriostasis (6). Rogers (10) and Shockman (11) found with S. aureus and Streptococcus faecalis respectively that
inhibition of protein synthesis by chloramphenicol was accompanied by
a sharp decline in the autolytic activity of the cells. These results
supported their hypothesis that bacteria are lysed under the influence
of penicillin because the equilibrium between peptidoglycan synthesis
and autolysis shifts in the direction of the latter process as a
result of the action of the ß-lactam antibiotic. The correctness of
the hypothesis of Rogers and Shockman was supported by the work of
Tomasz et al. (13), who isolated an autolysin-deficient mutant of
Streptococcus pneumoniae which was not killed after exposure to
penicillin. Tomasz et al. (13) called the absence of the bactericidal
action of penicillin, tolerance for this agent. Since then, tolerant
strains belonging to various species of bacteria have been isolated
from clinical material. In previous studies (3,4) we showed that
S. aureus strains can be divided into tolerant and nontolerant strains
on the basis of their survival in vitro in the presence of high
concentrations of methicillin ( >:- 64 .ug/ml). According to the observations
of Rogers (10), the mechanism of the reduced lysis in tolerant
S. aureus strains exposed to high concentrations of methicillin could
be based on inhibition of protein synthesis. The existence of such a
link has already been demonstrated by Mychajlonka et al. (8) for
tolerant Streptococcus mutans strains. In the present study we
investigated peptidoglycan, RNA and protein synthesis in two tolerant
and two nontolerant S. aureus strains after exposure to a low and a
high concentration of methicillin
Optimization of the pre-treatment section
No full textDe begeleider en/of auteur heeft geen toestemming gegeven tot het openbaar maken van de scriptie.
The supervisor and/or the author did not authorize public publication of the thesis.
Industrial Drying Processes
No full textDe begeleider en/of auteur heeft geen toestemming gegeven tot het openbaar maken van de scriptie.
The supervisor and/or the author did not authorize public publication of the thesis.
Antimicrobial resistance trends in blood culture positive Salmonella Typhi isolates from Pondicherry, India, 2005–2009
No full textAbstractTyphoid fever is caused by Salmonella enterica serovar Typhi, a major public health concern in developing countries. Recently, there has been an upsurge in the occurrence of bacterial isolates that are resistant to ciprofloxacin, and the emergence of broad spectrum β-lactamases in typhoidal salmonellae constitutes a new challenge for the clinician. A total of 337 blood culture isolates of S. Typhi, isolated from Pondicherry, India, between January 2005 and December 2009, were investigated using phenotypic, molecular and serological methods. Of the 337 isolates, 74 (22%) were found to be multidrug resistant (MDR) and 264 (78%) nalidixic acid resistant (NAR). Isolates with reduced susceptibility to ciprofloxacin possessed single mutations in the gyrA gene. A high rate of resistance (8%) was found to ciprofloxacin. All isolates with a ciprofloxacin MIC ≥ 4 mg/L possessed both double mutations in the QRDR of the gyrA gene and a single mutation in the parC gene. Active efflux pump mechanisms were also found to be involved in ciprofloxacin resistance. Finally, a large number of PFGE patterns (non-clonal genotypes) were observed among the S. Typhi isolates. In conclusion, a high rate of ciprofloxacin resistance was observed in comparison to other endemic areas in blood culture isolates of S. Typhi from Pondicherry, India, with steadily increasing NAR but decreasing MDR isolations over the study period. This is most likely to be due to an increased use of ciprofloxacin as a first-line drug of choice over more traditional antimicrobial agents for the treatment of typhoid fever
Improved performance of PACE 2 with modified collection system in combination with probe competition assay for detection of Chlamydia trachomatis in urethral specimens from males
No full textThe Gen-Probe PACE 2 assay (GP) in combination with a modified collection
system was compared with cell culture (CC) for the detection of Chlamydia
trachomatis in urethral specimens from males. Analysis of discordant
results was performed by PCR. The modifications, i.e., application of a
more rigid swab type and a 50% reduction in the amount of transport
medium, were made to improve the sensitivity of the assay. By using the
modified GP on 302 urethral specimens from males, a sensitivity of 89.5%
and a specificity of 100% were determined. In addition, performance of a
probe competition assay on all GP samples with a result > 0.6 and < 1.0
times the cutoff factor (gray zone) detected three more true-positive
samples. The sensitivity of GP in combination with the probe competition
assay increased to 94.9%, with a specificity of 100%. This was identical
to the performance of CC. The modified GP offers a very sensitive and
specific alternative to CC
In vitro activity of trovafloxacin against Bacteroides fragilis in mixed culture with either Escherichia coli or a vancomycin- resistant strain of Enterococcus faecium determined by an anaerobic time-kill technique.
No full textTo determine the efficacy of trovafloxacin as a possible treatment for
intra-abdominal abscesses, we have developed an anaerobic time-kill
technique using different inocula to study the in vitro killing of
Bacteroides fragilis in pure culture or in mixed culture with either
Escherichia coli or a vancomycin-resistant strain of Enterococcus faecium
(VREF). With inocula of 5 x 10(5) CFU/ml and trovafloxacin concentrations
of /=6.1 (log(10)
CFU/ml) was attained with all pure and mixed cultures within 24 h. With
inocula of 10(8) CFU/ml, a similar E(max) and a similar concentration to
produce 50% of E(max) (EC(50)) for B. fragilis were found in both pure
cultures and mixed cultures with E. coli. However, to produce a similar
killing of B. fragilis in the mixed cultures with VREF, a 14-fold increase
in the concentration of trovafloxacin was required. A
vancomycin-susceptible strain of E. faecium and a trovafloxacin-resistant
strain of E. coli were also found to confer a similar "protective" effect
on B. fragilis against the activity of trovafloxacin. Using inocula of
10(9) CFU/ml, the activity of trovafloxacin was retained for E. coli and
B. fragilis and was negligible against VREF. We conclude that this is a
useful technique to study the anaerobic killing of mixed cultures in vitro
and may be of value in predicting the killing of mixed infections in vivo.
The importance of using mixed cultures and not pure cultures is clearly
shown by the difference in the killing of B. fragilis in the mixed
cultures tested. Trovafloxacin will probably be ineffective in the
treatment of infections involving large numbers of enterococci. However,
due to its ability to retain activity against large cultures of B.
fragilis and E. coli, trovafloxacin could be beneficial in the treatment
of intra-abdominal abscesses
Molecular epidemiology of pneumococcal colonization in response to pneumococcal conjugate vaccination in children with recurrent acute otitis media
No full textContains fulltext :
32756.pdf (Publisher’s version ) (Open Access)A randomized double-blind trial with a 7-valent pneumococcal conjugate vaccine was conducted in The Netherlands among 383 children, aged 1 to 7 years, with a history of recurrent acute otitis media. No effect of vaccination on the pneumococcal colonization rate was found. However, a shift in serotype distribution was clearly observed (R. Veenhoven et al., Lancet 361:2189-2195, 2003). We investigated the molecular epidemiology of 921 pneumococcal isolates retrieved from both the pneumococcal vaccine (PV) and control vaccine (CV) groups during the vaccination study. Within individuals a high turnover rate of pneumococcal restriction fragment end labeling genotypes, which was unaffected by vaccination, was observed. Comparison of the genetic structures before and after completion of the vaccination scheme revealed that, despite a shift in serotypes, there was clustering of 70% of the pneumococcal populations. The remaining isolates (30%) were equally observed in the PV and CV groups. In addition, the degree of genetic clustering was unaffected by vaccination. However, within the population genetic structure, nonvaccine serotype clusters with the serotypes 11, 15, and 23B became predominant over vaccine-type clusters after vaccination. Finally, overall pneumococcal resistance was low (14%), and, albeit not significant, a reduction in pneumococcal resistance as a result of pneumococcal vaccination was observed. Molecular surveillance of colonization in Dutch children shows no effect of pneumococcal conjugate vaccination on the degree of genetic clustering and the genetic structure of the pneumococcal population. However, within the genetic pneumococcal population structure, a clear shift toward nonvaccine serotype clusters was observed
Distinguishing Complicated from Uncomplicated Bacteremia Caused by Staphylococcus aureus: The Value of "New" and "Old" Serological Tests
No full textAntibody responses to staphylococcal α-toxin, cell wall teichoic acid, and cell
wall peptodoglycan were measured in 259 serum samples from 74 consecutive
patients with Staphylococcus aureus bacteremia. All patients with complicated
bacteremia were seropositive in at least one of three tests, and 18 (72%) of 25
were positive two or three assays; six (75%) of eight patients with
endocarditis were positive for all three tests. In contrast, 15 (75%) of 20
patients with uncomplicated bacteremia were positive in only one or none of the
tests. These differences in antibody response patterns were statistically
significant (Xsup2 = 18.33, P < .001). Patients with complicated bacteremia had
peak antibody titers that were significantly higher than those of patients with
uncomplicated bacteremia. The assay for antibody α-toxin was as sensitive as
the assays for antibody to cell wall antigens but had less specificity for
complicated bacteremia. The clinical severity of the bacteremia did not
correlate with a complicated vs. uncomplicated nature of the infection but was
predictive of early death due to staphylococcemia. The calculated predictive
values suggest that the serology of S. aureus bacteremia may be clinical
valuable when multiple tests are performed in paired serum samples
The accuracy of four commercial broth microdilution tests in the determination of the minimum inhibitory concentration of colistin
No full textColistin is considered as one of the last-resort antibiotics and reliable antimicrobial susceptibility testing is therefore crucial. The reference standard for AST according to EUCAST and CLSI is broth microdilution (BMD). However, BMD is labor intensive to perform. Commercial antimicrobial susceptibility tests derived from BMD method are available. We investigated the performance of four different commercial tests: Sensititre™, SensiTest™ Colistin, Micronaut MIC Strip Colistin and UMIC Colistin using 70 clinical isolates (half of them was deemed by VITEK2 as resistant), including isolates from cystic fibrosis patients and mcr-1 bearing isolates. We used two reference standards: BMD and composite MIC as determined by all four tests. Sensititre™ had essential agreement (EA, defined as minimum inhibitory concentration within ± 1 dilution) of 87% and 89% compared to BMD and composite reference standard, respectively. For SensiTest™, the EA’s were 93% and 90%. For UMIC, 87% and 90%, and for Micronaut, 83% and 84%. All four tests demonstrated categorical agreement (CA) above 90%. CA for SensiTest™ and Micronaut was both 96%, UMIC 94%, and Sensititre™ 93%. All tests were reproducible as tested in two quality control isolates. In conclusion, in clinical isolates from a large referral center, the four commercial tests for determination of colistin minimum inhibitory concentrations showed acceptable performance
- …
