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A Tomasz

Publications and source records attributed to A Tomasz.

At least 109 records · Page 6Linked to original sources
PubMed1995

Drastic changes in the peptidoglycan composition of penicillin resistant laboratory mutants of Streptococcus pneumoniae.

The penicillin MIC of 2 Streptococcus pneumoniae clinical isolates was increased 100-fold (from 0.02 to 2.0 micromilligrams) and 20-fold (from 0.5 to 10.0 micromilligrams) through gradual exposure of the bacteria to increasing concentrations of penicillin in the laboratory. In both mutants the affinity of all four high molecular mass penicillin binding proteins (PBPs) for penicillin was drastically reduced accompanied by major changes in the composition of peptidoglycan as resolved by HPLC. The ratio of crosslinked to monomeric peptides became virtually inverted in the resistant cell walls with monomers representing two-thirds of the muropeptide species. The proportion of the crosslinked tri-tetra dimer, a major component of the cell wall of the original isolates, decreased to one-third or one-sixth of its normal representation, while the amounts of tripeptide monomers with an alanyl-serine substitution on the lysine epsilon amino group increased by close to a factor of two. The growth rates of both mutants decreased by a factor of approximately two, as compared to the original bacteria.

Amino Acid Sequence↗
PubMed1995

A Staphylococcus aureus autolysin that has an N-acetylmuramoyl-L-alanine amidase domain and an endo-beta-N-acetylglucosaminidase domain: cloning, sequence analysis, and characterization.

The Tn551 insertion site of the autolysis-deficient Staphylococcus aureus mutant RUSAL2 was cloned and used to identify the autolysis gene atl in the parent strain, RN450. The open reading frame for atl was 3768 bp in length, encoding a deduced protein of 1256 amino acids and molecular size of 137,381 Da. The atl gene product is a bifunctional protein that has an amidase domain and an endo-beta-N-acetylglucosaminidase domain which must undergo proteolytic processing to generate the two extracellular lytic enzymes found in the culture broth of S. aureus.

Amino Acid Sequence↗
PubMed1995

Beta-Lactam antibiotic resistance in gram-positive bacterial pathogens of the upper respiratory tract: a brief overview of mechanisms.

Streptococcus pneumoniae and Group A Streptococci are frequent colonizers and major causative agents of disease in the upper respiratory tract of humans. In spite of the immense and common selective pressure of beta-lactam antibiotics against both of these bacterial species during the last four to five decades, penicillin-resistant strains of group A streptococci have not been described in the clinical literature as of 1994. This is particularly puzzling since penicillin-resistant mutants of this bacterium have been isolated repeatedly in the laboratory and such mutants carry altered penicillin-binding proteins (PBPs) with reduced drug affinities, i.e., a basic mechanism identical to the one seen in penicillin-resistant isolates of Streptococcus pneumoniae that have emerged in large numbers and at numerous locations and have spread explosively all over the globe by the beginning of the 1990s. The reasons for this contrasting situation are not clear. In Streptococcus pneumoniae the resistance mechanism to penicillin appears to originate in recombinational events between ancestral pneumococcal cells and as yet unidentified extra species DNA donors and probably involves the process of genetic transformation for which this bacterium has a remarkable hormonally controlled mechanism. The integration of foreign DNA sequences in the pneumococcal PBP genes leads to the remodeling of at least four of the five PBPs that change in their kinetic properties and increase in the penicillin resistance level of the bacteria also seems to involve increased production of the low-affinity binding proteins.

Animals↗
PubMed1995

Penicillin-resistant and multidrug-resistant Streptococcus pneumoniae in a pediatric hospital in Zagreb, Croatia.

Sixty-four penicillin-resistant Streptococcus pneumoniae isolates [benzylpenicillin minimal inhibitory concentrations (MICs) between 0.05 and 1.6 micrograms/ml] recovered at the Pediatric Hospital "Dr. Fran Mihaljevic" in Zagreb, Croatia between October 1990 and March 1993 were analyzed for serotype, antibiotic susceptibility patterns, and chromosomal relatedness using pulsed-field gel electrophoretic (PFGE) analysis of chromosomal DNA fragmented by digestion with the SmaI endonuclease. Hospital "Dr. Fran Mihaljevic" services the capital of Croatia and its vicinity. Most of the isolates were from nasopharyngeal carriage, but several isolates were from otitis media, sinusitis, and meningitis. Most isolates belonged to either serotype 23F (36/64) or 19F (12/64); the rest, including three 15C isolates, were in 11 additional distinct serotypes. The overwhelming majority (25/36) of the serotype 23F isolates had penicillin MIC values of 1-2 micrograms/ml and shared variants of a common PFGE pattern, closely related to the PFGE identified in multiresistant pneumococci of the same serotype with wide geographic spread to Spain, Portugal, France, and the United States. This group of bacteria was also resistant to tetracycline, chloramphenicol, and sulfamethoxazole/trimethoprim. In contrast to the relative genetic and phenotypic homogeneity of the more highly penicillin resistant isolates, pneumococci with penicillin MICs between 0.5 and 0.4 microgram/ml (29/64) were distributed in 13 different serotypes and as many as 20 distinct PFGE patterns.

Autolysis↗
PubMed1995

Antibiotic susceptibility of Streptococcus pneumoniae isolates in Portugal. A multicenter study between 1989 and 1993.

A total of 1,104 strains of Streptococcus pneumoniae were isolated from hospitalized patients (75.5%) and from colonization sites at the Public Health Institute (24.5%) during the last 4 years (1989-1993). Penicillin resistance (defined as MIC > or = 0.1 microgram/liter) was found to increase in time: 4.6% in 1989, 4.9% in 1990, 6.4% in 1991, 11.3% in 1992, and 17% in 1993. In 1992, 0.8% of the strains had penicillin MIC = 2 mg/liter. Increase in penicillin resistance was also evident among invasive strains [blood, cerebrospinal fluid (CSF), pleura]: 2/92 isolates from 1989-1992 (2.3%) were penicillin resistant as compared to 7/101 isolates from 1992 (6.9%). Multiresistance (resistance to three or more antibiotics) was 4.4% with penicillin, tetracycline, chloramphenicol being the predominant resistant phenotype at the end of 1992. In 1993, strains with resistance to penicillin plus chloramphenicol plus tetracycline increased further. Erythromycin resistance was usually associated with clindamycin resistance, but the majority of such strains remained susceptible to penicillin. Drift in the direction of increasing MIC values was also noted during this 3-year period among "susceptible" isolates: bacteria with MIC of 6-10 ng/ml representing the majority of isolates in 1990-1991 decreased and were replaced by cells with MIC of 20 ng/ml. The most frequent pneumococcal serotypes were 23, 19, 3, 6, 14, 9, and 8, with the frequency of type 9 increasing from 2.9% (in 1989) through 3.2% (1990) to 6.4% (1992). Among all antibiotic resistant strains, the prevalent serotypes were 23, 9, 14, and 6. The chromosomal backgrounds of resistant isolates tested by pulsed-field gel electrophoresis showed close resemblance to the background of the serotype 23F multiresistant clone first identified in Spain. The data suggest that the recent large increase in the frequency of penicillin-resistant pneumococci represents the import of this clone into Portugal during the early 1990s. The increased frequency of drug-resistant pneumococci highlights the importance of continued surveillance of these dangerous pathogens.

Drug Resistance, Microbial↗
PubMed1995

Novel penicillin-resistant clones of Streptococcus pneumoniae in the Czech Republic and in Slovakia.

Seventy-two penicillin-resistant Streptococcus pneumoniae isolates collected from clinical specimens in the Czech and Slovakian Republics between 1990 and 1992 were analyzed by a variety of molecular techniques. Most of the highly resistant isolates (40/72) (penicillin MIC between 1 up to 16 micrograms/ml) were represented by two distinct pneumococcal clones, and most of these isolates (35/40) were also resistant to at least two other antibiotics (tetracycline plus chloramphenicol or erythromycin). All 17 isolates belonging to the first clone were of serotype 14, had very high penicillin MICs (8-12 micrograms/ml), shared a common, abnormal penicillin-binding protein (PBP) pattern and one of two related pulsed-field gel electrophoretic (PFGE) patterns. The 15 isolates belonging to the second clone were all of serotype 19A, had penicillin MICs between 1 and 4 micrograms/ml, shared a unique, abnormal PBP pattern, and could be divided into two subgroups on the basis of PFGE patterns, one of which was indistinguishable from the PFGE pattern of a multiresistant capsular type 19A clone of S. pneumoniae already identified earlier in Hungary. Thirty-two of the 72 pneumococcal isolates had lower penicillin MICs (0.1-0.5 microgram/ml), and these isolates differed from the more highly resistant ones in several respects: They belonged to seven different serotypes, showed large variation in PFGE patterns (20 patterns in 32 isolates) and most of them (21/32) were resistant to penicillin only. Tentative explanations for these findings, in terms of epidemiological and molecular mechanisms, are considered.

Bacterial Proteins↗
PubMed1995

Transmission of multidrug-resistant serotype 23F Streptococcus pneumoniae in group day care: evidence suggesting capsular transformation of the resistant strain in vivo.

Surveillance for nasopharyngeal colonization with Streptococcus pneumoniae was maintained in a research day care center between 1985 and 1992. An outbreak of nasal carriage of a multi-drug-resistant (MDR) serotype 23F organism occurred between May 1990 and December 1991 involving 14 of 52 children. Electrophoresis of penicillin-binding proteins (PBP) and pulsed-field gel electrophoresis (PFGE) of chromosomal DNA indicated that the MDR serotype 23F organism was closely related to a serotype 23F MDR clone that has been prevalent in Spain since the early 1980s. In June 1991, an MDR serotype 14 organism was isolated from a child who had previously carried the MDR serotype 23F strain. PFGE and PBP typing revealed that the MDR serotype 14 organism was very similar to the circulating MDR serotype 23F strain, suggesting serotype transformation. Dissemination of MDR pneumococcal strains and possibly spread of the MDR phenotype to additional serotypes may be facilitated in group day care.

Anti-Bacterial Agents↗
PubMed1995

Selective lysis of cultures and cell walls of penicillin-resistant but not penicillin-susceptible Streptococcus pneumoniae strains by a murein hydrolase complex.

A murein hydrolase complex selectively lysed cultures of penicillin-resistant pneumococci and their cell walls in which the majority of muropeptide subunits were indirectly cross-linked through oligopeptide substituents (alanyl-alanine or alanyl-serine) on the epsilon-amino group of the stem peptide lysine residues. Walls of penicillin-susceptible strains were not hydrolyzed.

Amino Acid Sequence↗
PubMed1995

Evidence for the geographic spread of a methicillin-resistant Staphylococcus aureus clone between Portugal and Spain.

Methicillin-resistant Staphylococcus aureus (MRSA) isolates collected during a 7-month period in 1992 and 1993 at Hospital Pulido Valente (340 beds), Lisbon, Portugal, were characterized by a combination of genotypic and phenotypic methods. Clonal identities were determined by probing ClaI digests (i) with a mecA probe and (ii) with a Tn554 probe and (iii) by pulsed-field gel electrophoresis (PFGE) patterns of chromosomal SmaI digests. mecA-ClaI type I was predominant among these isolates (38 of 43). Most of these (37 of 38 [97.4%]) were associated with a single Tn554 pattern, pattern E, and the majority (23 of 38 [61%]) also showed a relatively uniform chromosomal background, as indicated by PFGE (PFGE pattern A). The major clone (mecA-ClaI type I::Tn554 type E and PFGE pattern A) at Hospital Pulido Valente was indistinguishable by these molecular typing criteria from the dominant clone that had been identified in two major current outbreaks of MRSA disease in Spain (Barcelona and Madrid). The Portuguese and Spanish clones also had a common heterogeneous class 3 phenotype and identical multidrug resistance patterns. The data presented in this work support the notion that MRSA clones can spread across considerable geographic distances.

Cross Infection↗
PubMed1995

Geographic spread of epidemic multiresistant Staphylococcus aureus clone in Brazil.

Staphylococcus aureus isolates from five large teaching hospitals and one medium-size community hospital located in geographically distant parts of Brazil, in the south and southeast (Rio de Janeiro, Niteroi, Sao Paulo, Porto Alegre) and in the north (Manaus), were tested for their antibiotic resistance patterns and genetic backgrounds. Eighty-five of the 152 isolates were identified as methicillin-resistant S. aureus (MRSA) by using a combination of an agar dilution screen and a mecA gene-specific DNA probe. All MRSA isolates were resistant to penicillin, erythromycin, gentamicin, oxacillin, and cephalothin, and the majority of isolates (74%) were also resistant to chloramphenicol, sulfamethoxazole-trimethoprim, ciprofloxacin, and clindamycin as well and were susceptible only to vancomycin. Isolates obtained from hospitals in Sao Paulo, Rio de Janeiro, Niteroi, and Porto Alegre (1,600 km from one another) and Manaus (3,700 km from Rio de Janeiro) were examined by a variety of molecular fingerprinting techniques: the nature of the mecA polymorph and Tn554 attachment sites and restriction fragment length polymorphism of genomic DNAs after SmaI restriction and separation of the digested DNA by pulsed-field gel electrophoresis. The overwhelming majority of the isolates shared a common pulsed-field gel electrophoresis pattern and carried mecA polymorph III in combination with Tn554 pattern B, indicating the presence of a single, epidemic MRSA clone spread over large geographic distances of Brazil.

Brazil↗
PubMed1994

Reduced methicillin resistance in a new Staphylococcus aureus transposon mutant that incorporates muramyl dipeptides into the cell wall peptidoglycan.

Screening of a new Tn551 library constructed in the background of a highly methicillin-resistant Staphylococcus aureus strain identified a new insertion site located on the SmaI B-fragment of the chromosome that reduced the minimal inhibitory concentration of the parent (1600 micrograms/ml) to 25-50 micrograms/ml in the mutant and caused heterogeneous expression of resistance and abnormality in peptidoglycan composition (absence of the unsubstituted pentapeptide and incorporation of alanylglutamate- and alanylisoglutamate-containing muropeptides). There was an accumulation of large amounts of the UDP-linked muramyl dipeptide in the cytoplasmic wall precursor pool of the mutant. Reduced (heterogeneous) antibiotic resistance and all the biochemical abnormalities were reproduced in genetic backcrosses by transduction with phage 80 alpha. Mutant RUSA235 appears to be impaired in the biosynthesis of the staphylococcal cell wall precursor muropeptide before the lysine addition step. We propose to provisionally call the gene inactivated in this mutant femF.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1994

Methylprednisolone attenuates inflammation, increase of brain water content and intracranial pressure, but does not influence cerebral blood flow changes in experimental pneumococcal meningitis.

We investigated the effect of methylprednisolone on pathophysiological alterations in experimental pneumococcal meningitis. Untreated rats injected with pneumococcal cell wall components after hydrolization with M1 muramidase (PCW-M) developed an increase of regional cerebral blood flow (rCBF; 165.0 +/- 12.8%, baseline 100%, mean +/- S.E.M.), brain water content (79.23 +/- 0.10%), intracranial pressure (ICP; 11.9 +/- 1.0 mmHg) and white blood cell (WBC) count in the cerebrospinal fluid (CSF) (2,709 +/- 482 cells/microliters) within 8 h after intracisternal (i.c.) challenge. Pretreatment with methylprednisolone or administration of methylprednisolone 4 h after i.c. challenge significantly attenuated the increase of brain water content (78.88 +/- 0.08% and 78.82 +/- 0.05%, resp.), ICP (7.7 +/- 1.1 mmHg and 4.9 +/- 0.8 mmHg, resp.) and CSF WBC count (1,257 +/- 168 cells/microliters and 976 +/- 105 cells/microliters, resp.). However, methylprednisolone did not inhibit the increase of rCBF (163.5 +/- 13.7% and 160.9 +/- 6.8%, resp.), whereas dexamethasone significantly attenuated microvascular changes. Hypercapnia-induced reactivity of cerebral vessels tested 8 h after i.c. injection was preserved in all groups. In conclusion, we found that methylprednisolone significantly attenuated the increase of brain water content, ICP and CSF WBC count, but had no effect on microvascular changes during the early phase of experimental pneumococcal meningitis.

Animals↗
PubMed1994

Methicillin-resistant Staphylococcus aureus disease in a Portuguese hospital: characterization of clonal types by a combination of DNA typing methods.

Fifteen pediatric patients as well as the five nursing staff of the Burn Unit of the Hospital D. Estefania in Lisbon, Portugal, were assayed at weekly intervals over a five-month period in order to identify the nature and number of methicillin-resistant Staphylococcus aureus (MRSA) clones associated with colonization and wound infection. Methicillin resistance was confirmed by a mec-specific DNA probe. MRSA isolates were classified into chromosomal types (clones) on the basis of a variety of techniques: (i) ribotyping; (ii) restriction digestion by the endonuclease ClaI followed by Southern hybridization with the mecA-specific DNA probe and (iii) by hybridization with Tn554; and (iv) pulsed-field electrophoresis (PFE) of SmaI digests followed by (v) Southern hybridization with the mecA DNA probe. A sixth, physiological technique (population analysis) was used to define the mode of phenotypic expression of methicillin resistance in each isolate. All isolates carried a single, common polymorph (ClaI type III) of the mecA gene. Hybridization with Tn554 resolved these isolates to two novel patterns (alpha and beta), of which one (Tn554 alpha) was predominant (90%). This pattern could be further resolved to four closely related PFE types (A through D). In contrast, all isolates with the Tn554 beta pattern belonged to an additional, grossly different PFE type E. The Tn554 beta class was also unique in that these bacteria carried the mecA gene in a SmaI fragment smaller (about 170 kb) than that found in the alpha type strains (194 kb). Most isolates (83%) showed a single heterogeneous (population analysis Class 3) mode of resistance expression. The data demonstrate the full capacity of the globally rare (ClaI type III) MRSA clone for colonization and virulence. The results also document the stability of the complex heterogeneous resistance phenotype as well as the stability of the chromosomal types under conditions of in vivo carriage over a period of several months. In a few isolates the same mecA polymorph was present in several, grossly different genetic backgrounds, suggesting horizontal transfer of the mecA gene.

Adult↗
PubMed1994

CD14 is a pattern recognition receptor.

Septic shock caused by a diverse group of bacterial pathogens is a serious human disease. Recognition of bacterial envelope constituents is one mechanism used by mammalian cells to initiate responses leading to bacterial killing or, unfortunately, responses that also cause fatal septic shock. Here we show that CD14 plays a key role in initiating cell activation by a group of bacterial envelope components from Gram-negative and Gram-positive microorganisms, as well as mycobacteria. We propose that CD14 is a receptor used by mammalian cells to recognize and signal responses to a diverse array of bacterial constituents. This finding defines the molecular basis for innate microbial immunity; implicit in these findings are new possibilities for therapeutics.

Animals↗
PubMed1994

Mechanisms of brain injury in bacterial meningitis: workshop summary.

Morbidity and mortality associated with bacterial meningitis remain high, although antibiotic therapy has improved during recent decades. The major intracranial complications of bacterial meningitis are cerebrovascular arterial and venous involvement, brain edema, and hydrocephalus with a subsequent increase of intracranial pressure. Experiments in animal models and cell culture systems have focused on the pathogenesis and pathophysiology of bacterial meningitis in an attempt to identify the bacterial and/or host factors responsible for brain injury during the course of infection. An international workshop entitled "Bacterial Meningitis: Mechanisms of Brain Injury" was organized by the Department of Neurology at the University of Munich and was held in Eibsee, Germany, in June 1993. This conference provided a forum for the exchange of current information on bacterial meningitis, including data on the clinical spectrum of complications, the associated morphological alterations, the role of soluble inflammatory mediators (in particular cytokines) and of leukocyte-endothelial cell interactions in tissue injury, and the molecular mechanisms of neuronal injury, with potential mediators such as reactive oxygen species, reactive nitrogen species, and excitatory amino acids. It is hoped that a better understanding of the pathophysiological events that take place during bacterial meningitis will lead to the development of new therapeutic regimens.

Animals↗