43 research outputs found
Tolerance of staphylococcus aureus to ĂŸ-lactam antibiotics
Penicillin 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 ĂŸ-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
Improved performance of PACE 2 with modified collection system in combination with probe competition assay for detecti
The 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
Rapid detection of methicillin resistance in Staphylococcus aureus isolates by the MRSA-screen latex agglutination test
The slide agglutination test MRSA-Screen (Denka Seiken Co., Niigata,
Japan) was compared with the mecA PCR ("gold standard") for the detection
of methicillin resistance in Staphylococcus aureus. The MRSA-Screen test
detected the penicillin-binding protein 2a (PBP2a) antigen in 87 of 90
genetically diverse methicillin-resistant S. aureus (MRSA) stock culture
strains, leading to a sensitivity of 97%. The three discrepant MRSA
strains displayed positive results only after induction of the mecA gene
by exposure to methicillin. Both mecA PCR and MRSA-Screen displayed
negative results among the methicillin-susceptible S. aureus strains (n =
106), as well as for Micrococcus spp. (n = 10), members of the family
Enterobacteriaceae (n = 10), Streptococcus pneumoniae (n = 10), and
Enterococcus spp. (n = 10) (specificity = 100%). Producing the same PBP2a
antigen, all 10 methicillin-resistant Staphylococcus epidermidis strains
score positived in both the latex test and the mecA PCR. Consequently, the
MRSA-Screen test should be applied only after identification of the MRSA
strain to the species level to rule out coagulase-negative staphylococci.
In conclusion, due to excellent specificity and sensitivity the
MRSA-Screen latex test has the potential to be successfully used for
routine applications in the microbiology laboratory
Comparative study of the effects of ceftizoxime, piperacillin, and piperacillin-tazobactam concentrations on antibacterial activity and selection of antibiotic-resistant mutants of Enterobacter cloacae and Bacteroides fragilis in vitro and in vivo in mixed-infection abscesses
The effects of ceftizoxime (CZX), piperacillin (PIP), and PIP-tazobactam
(PT) concentrations on the antibacterial activity and selection of
resistant mutants of Bacteroides fragilis and Enterobacter cloacae were
investigated in vitro in a mixed-culture anaerobic time-kill study and in
vivo in a mixed-infection abscess model. Mixed cultures were incubated for
24 h with 0.125 to 512 micro g of CZX per ml or 0.125 to 2,048 micro g of
PIP or PT per ml. Mice were treated every 2 h for 24 h with CZX at 6 to
1,536 mg/kg/day or with PIP or PT at 24 to 6,144 mg/kg/day starting 30 min
before inoculation with different B. fragilis-E. cloacae combinations.
There was a good correlation between the in vitro and in vivo activities
of the antibiotics and their MICs obtained with high inocula (10(8)
CFU/ml). The respective 50% effective doses (milligrams per kilogram per
day) with B. fragilis and E. cloacae 22491 were 771 and 521 for CZX, 416
and 643 for PIP, and 85 and 554 for PT, and with the B. fragilis-E.
cloacae 032349 combination, they were 81 and 21 for CZX and 77 and 766 for
PT. Resistant mutants of E. cloacae 22491 were preferentially selected in
vitro with 2 to 64 micro g of CZX per ml and in vivo with CZX at 12 to 384
mg/kg/day. There was no preferential selection of CZX-resistant B.
fragilis or E. cloacae 032349. For CZX-resistant E. cloacae 22491, we
found a 16- to 512-fold increase in the MIC of CZX and increased MICs of
other expanded-spectrum cephalosporins, owing in part to the production of
a stably derepressed cephalosporinase. In vitro and in vivo, PT did not
select resistant mutants of E. cloacae and B. fragilis. Results
demonstrate the adverse microbiological outcome of choosing an
expanded-spectrum cephalosporin like CZX for empirical treatment of mixed
infections involving a susceptible Enterobacter strain
The accuracy of four commercial broth microdilution tests in the determination of the minimum inhibitory concentration of colistin
Colistin 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
Direct detection of extended-spectrum beta-lactamases (CTX-M) from blood cultures by LC-MS/MS bottom-up proteomics
Rapid bacterial species identification and antibiotic susceptibility testing in positive blood cultures have an important impact on the antibiotic treatment for patients. To identify extended-spectrum beta-lactamases (ESBL) directly in positive blood culture bottles, we developed a workflow of saponin extraction followed by a bottom-up proteomics approach using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The workflow was applied to positive blood cultures with Escherichia coli and Klebsiella pneumoniae collected prospectively in two academic hospitals over a 4-month period. Of 170 positive blood cultures, 22 (12.9%) contained ESBL-positive isolates based on standard susceptibility testing. Proteomic analysis identified CTX-M ESBLs in 95% of these isolates directly in positive blood cultures, whereas no false positives were found in the non-ESBL producing positive blood cultures. The results were confirmed by molecular characterisation of beta-lactamase genes. Based on this proof-of-concept study, we conclude that LC-MS/MS-based protein analysis can directly identify extended-spectrum beta lactamases in E. coli and K. pneumoniae positive blood cultures, and could be further developed for application in routine diagnostics
Molecular typing of Salmonella typhi strains from Dhaka (Bangladesh) and development of DNA probes identifying plasmid-encoded multidrug-resistant isolates
Seventy-eight Salmonella typhi strains isolated in 1994 and 1995 from
patients living in Dhaka, Bangladesh, were subjected to phage typing,
ribotyping, IS200 fingerprinting, and PCR fingerprinting. The collection
displayed a high degree of genetic homogeneity, because restricted numbers
of phage types and DNA fingerprints were observed. A significant number of
the S. typhi strains (67%) were demonstrated to be multiple drug resistant
(MDR). The vast majority of the MDR strains were resistant to
chloramphenicol, ampicillin, trimethoprim, streptomycin, sulfamethoxazole,
and tetracycline (R type CATmSSuT), a resistance phenotype that has also
frequently been observed in India. Only two strains displayed a distinct
MDR phenotype, R type AT-mSSuT. Pulsed-field gel electrophoresis
demonstrated the presence of large plasmids exclusively in the MDR strains
of both R types. The plasmids present in the S. typhi strains of R type
CATmSSuT could be conjugated to Escherichia coli and resulted in the
complete transfer of the MDR phenotype. PCR fingerprinting allowed
discrimination of MDR and susceptible strains. The DNA fragments enabling
discrimination of MDR and susceptible S. typhi strains by PCR were useful
genetic markers for identifying MDR encoded by large plasmids of the H1
incompatibility group
PCR monitoring of response to liposomal amphotericin B treatment of systemic candidiasis in neutropenic mice
When a diagnosis of invasive candidiasis has been made, treatment with
toxic fungicidal agents is inevitable. The crucial decision of when to
stop such treatment is difficult to make, because cultures are often
negative despite ongoing invasive candidiasis and can therefore not be
used as a reliable parameter of effective therapy. In the present study,
the use of PCR in monitoring the therapeutic efficacy of antifungal
treatment with liposomal amphotericin B was evaluated by using neutropenic
mice with systemic candidiasis. Blood cultures of infected mice treated
with different doses of liposomal amphotericin B were only positive at the
early onset of the infection process and became sterile within 3 days;
this was true even with mice treated with 1 mg of liposomal amphotericin B
per kg of body weight that experienced a relapse of infection 14 days
later. A significant correlation between presence of Candida albicans in
the kidneys and PCR results obtained with blood was demonstrated. Thus,
PCR results obtained with blood samples correlated well with the
therapeutic efficacy of antifungal treatment
Amoxicillin pharmacokinetics in preterm infants with gestational ages of less than 32 weeks
The multiple-dose pharmacokinetics of amoxicillin (AM [administered twice
daily in a 25-mg/kg of body weight intravenous dose]) in 17 preterm
infants (11 males; gestational age, 29 +/- 1.9 weeks; birth weight, 1,175
+/- 278 g) were evaluated on day 3 of life. Blood samples were collected
from an arterial catheter at 0, 0.5, 1, 2, 4, 8, and 12 h after the
intravenous dose. A high-performance liquid chromatography method was used
to determine AM concentrations in serum. AM pharmacokinetics followed a
one-compartment open model. The glomerular filtration rates of all
patients were simultaneously studied by means of the 24-h continuous
inulin infusion technique. The elimination half-life, apparent volume of
distribution, and total body clearance of AM (mean +/- standard deviation)
were 6.7 +/- 1.7 h, 584 +/- 173 ml, and 62.4 +/- 23.3 ml/h, respectively.
The mean (+/- standard deviation) AM peak and trough levels were 53.6 +/-
9.1 and 16.0 +/- 4.9 mg/liter, respectively. All infants had a serum
trough level above 5 mg/liter. The total body clearance and apparent
volume of distribution of AM and the clearance of inulin increased
significantly with increasing gestational age. The total bod
Improved detection of Candida albicans by PCR in blood of neutropenic mice with systemic candidiasis
A PCR using primers aimed at the multicopy gene coding for the small
subunit rRNA and resulting in the synthesis of a 180-bp fragment was
evaluated for its use in diagnosing invasive candidiasis in comparison
with blood culture. With the use of a C. albicans-specific probe, +/- 10
to 15 C. albicans cells are detected in 100 microliters of whole blood by
Southern analysis. A DNase pretreatment was critical in the purification
process of yeast DNA from whole blood. Omission of the DNase pretreatment
decreased assay sensitivity 10-fold. PCR analysis of blood specimens
collected from mice with invasive candidiasis is more sensitive than blood
culture (100 versus 67%, respectively) at 72 h after intravenous (i.v.)
inoculation with C. albicans. Furthermore, the intensity of the
hybridization signals increased with the progression of infection. In
contrast, multiple blood samples from gastrointestinally colonized mice
were all negative by PCR, indicating that the PCR assay is also specific
and may, therefore, make a positive contribution to the detection and
follow-up of invasive candidiasis