SUMMARY Genomic studies have revealed the presence of Ser/Thr kinases and phosphatases in many bacterial species, although their physiological roles have largely been unclear. Here we review bacterial Ser/Thr kinases (eSTKs) that show homology in their catalytic domains to eukaryotic Ser/Thr kinases and their partner phosphatases (eSTPs) that are homologous to eukaryotic phosphatases. We first discuss insights into the enzymatic mechanism of eSTK activation derived from structural studies on both the ligand-binding and catalytic domains. We then turn our attention to the identified substrates of eSTKs and eSTPs for a number of species and to the implications of these findings for understanding their physiological roles in these organisms.
The emergence of coagulase-negative staphylococci not only as human pathogens but also as reservoirs of antibiotic resistance determinants requires the deployment and development of methods for their rapid and reliable identification. Internal transcribed spacer-PCR (ITS-PCR) was used to identify a collection of 617 clinical staphylococcal isolates. The amplicons were resolved in high-resolution agarose gels and visually compared with the patterns obtained for the control strains of 29 staphylococcal species. Of the 617 isolates studied, 592 (95.95%) were identified by ITS-PCR and included 11 species: 302 isolates of Staphylococcus epidermidis, 157 of S. haemolyticus, 79 of S. aureus, 21 of S. hominis, 14 of S. saprophyticus, 8 of S. warneri, 6 of S. simulans, 2 of S. lugdunensis, and 1 each of S. caprae, S. carnosus, and S. cohnii. All species analyzed had unique ITS-PCR patterns, although some were very similar, namely, the group S. saprophyticus, S. cohnii, S. gallinarum, S. xylosus, S. lentus, S. equorum, and S. chromogenes, the pair S. schleiferi and S. vitulus, and the pair S. piscifermentans and S. carnosus. Four species, S. aureus, S. caprae, S. haemolyticus, and S. lugdunensis, showed polymorphisms on their ITS-PCR patterns. ITS-PCR proved to be a valuable alternative for the identification of staphylococci, offering, within the same response time and at lower cost, higher reliability than the currently available commercial systems.
We constructed a conditional mutant of pbpA in which transcription of the gene was placed under the control of an IPTG (isopropyl--D-thiogalactopyranoside)-inducible promoter in order to explore the role of PBP1 in growth, cell wall structure, and cell division. A methicillin-resistant strain and an isogenic methicillinsusceptible strain, each carrying the pbpA mutation, were unable to grow in the absence of the inducer. Conditional mutants of pbpA transferred into IPTG-free medium underwent a four-to fivefold increase in cell mass, which was not accompanied by a proportional increase in viable titer. Examination of thin sections of such cells by transmission electron microscopy or fluorescence microscopy of intact cells with Nile red-stained membranes showed a morphologically heterogeneous population of bacteria with abnormally increased sizes, distorted axial ratios, and a deficit in the number of cells with completed septa. Immunofluorescence with an antibody specific for PBP1 localized the protein to sites of cell division. No alteration in the composition of peptidoglycan was detectable in pbpA conditional mutants grown in the presence of a suboptimal concentration of IPTG, which severely restricted the rate of growth, and the essential function of PBP1 could not be replaced by PBP2A present in methicillin-resistant cells. These observations suggest that PBP1 is not a major contributor to the cross-linking of peptidoglycan and that its essential function must be intimately integrated into the mechanism of cell division.Penicillin-binding proteins (PBPs) are enzymes involved in the last stages of peptidoglycan biosynthesis. There are four native PBPs, PBP1 to PBP4, in Staphylococcus aureus and an additional PBP, PBP2A, in methicillin-resistant S. aureus (MRSA) strains (1,5,11). This extra PBP is encoded by the exogenous gene mecA and, in contrast to the native PBPs, shows low affinity for -lactams, ensuring continued cell wall synthesis in the presence of otherwise lethal concentrations of these antibiotics (11,25).The primary amino acid structure of PBP1 shows a high degree of similarity to the sequences of PBP2B and SpoVD from Bacillus subtilis, PBP2X from Streptococcus pneumoniae, and PBP3 from Escherichia coli (33). All of these proteins are high-molecular-weight (HMW) class B PBPs, composed of a C-terminal domain with conserved transpeptidase motifs and an N-terminal domain of as-yet-unknown function (6, 7). Several lines of evidence indicate that PBP2B of B. subtilis, the pneumococcal PBP2X, and PBP3 of E. coli are involved in cell division (2,20,27,34), consistent with their location in division and cell wall (dcw) synthesis clusters on the chromosome (28).An earlier study by Pucci and colleagues has determined the chromosomal location of S. aureus pbpA in a dcw cluster together with other determinants, such as mraY, divIB, ftsA, and ftsZ (28), and a role for PBP1 in cell division of S. aureus has been proposed (22).PBP1 of S. aureus was reported to be essential for growth because disruption of the ...
Denmark and Iceland are countries where the frequency of methicillin-resistant Staphylococcus aureus is very low due to strict infection control and restrictive antibiotic use policies. In contrast, methicillin-resistant S. epidermidis (MRSE) continues to be isolated as a nosocomial pathogen. The molecular typing by pulsed-field gel electrophoresis (PFGE) of 136 MRSE isolates from five hospitals in Denmark and 94 MRSE isolates from one hospital in Iceland collected in 1997 and 1998 defined 40 different patterns. Closely related PFGE types were found in isolates recovered in Iceland, Denmark, Mexico, Uruguay, Greece, and Cape Verde, evidencing for the first time the geographic clonal dissemination of MRSE strains. The large majority (87.4%) of the MRSE isolates studied were multiresistant.
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