Differentiation of Haemonchus placei from Haemonchus contortus by PCR and by morphometrics of adult parasites and third stage larvae / Identificação de Haemonchus placei e Haemonchus contortus por PCR e por análise morfológica de parasitas adultos e larvas infectantes

Molecular and morphological methods were evaluated to distinguish between Haemonchus contortus and Haemonchus placei species. A total of 141 H. contortus and 89 H. placei male adult specimens collected from artificially infected lambs were identified individually by PCR analysis, using a species-specific primer pair. These PCR results were used as gold standard for Haemonchus spp. identification. Haemonchus placei presented higher mean spicule and barb lengths than H. contortus (P<0.05). However, some measurements overlapped. For this reason, a discriminate function did not allow the correct identification of 13 H. contortus and one H. placei specimen. The sheath tail length of the third stage larvae (L3), which comprises the distance between the tip of the larval tail and the end of the sheath tail, were measured. Only three of the 485 H. placei larvae (0.619%) had a sheath tail shorter than 85 µm, while only four of the 500 H. contortus larvae (0.8%) presented a sheath tail longer than 85 µm. The results indicated that 6.09% of the male adult specimens would be misclassified based on the discriminate function, while only 0.71% of infective larvae would be misclassified. Therefore, identification of L3 can be used as the first method to indicate the presence of H. placei and/or H. contortus in a population of domestic ruminants.

Métodos moleculares e morfológicos foram avaliados para a identificação de Haemonchus contortus e Haemonchus placei. No total, 141 H. contortus e 89 H. placei machos adultos, obtidos de cordeiros artificialmente infectados, foram identificados individualmente por PCR com o emprego de um par de “primers” espécie-específico. Esses resultados da análise por PCR foram considerados como padrão para a identificação das espécies de Haemonchus. Haemonchus placei apresentou valores médios de espículos e ganchos superiores aos de H. contortus (P<0,05). Entretanto, houve sobreposição de alguns valores. Por essa razão, a função discriminante não permitiu a identificação correta de 13 exemplares de H. contortus e de um, de H. placei. Foi medida a cauda da bainha de larvas infectantes (L3), que compreende a distância entre a ponta da cauda da larva e a ponta da cauda da bainha. Apenas três das 485 L3 de H. placei (0,619%) apresentaram a cauda da bainha com medida inferior a 85 µm e somente em quatro das 500 L3 de H. contortus (0,8%) essa medida foi superior a 85 µm. Os resultados demonstraram que 6,09% dos machos adultos seriam identificados erroneamente com base na função discriminante, enquanto a identificação incorreta de L3 seria de apenas 0,71%. Portanto, a identificação de L3 pode ser utilizada como método inicial para indicar a presença de H. placei e/ou H. contortus em uma população de ruminantes domésticos.

Staphylococcus aureus Penicillin-Binding Protein 2 Can Use Depsi-Lipid II Derived from Vancomycin-Resistant Strains for Cell Wall Synthesis.

Vancomycin-resistant Staphylococcus aureus (S. aureus) (VRSA) uses depsipeptide-containing modified cell-wall precursors for the biosynthesis of peptidoglycan. Transglycosylase is responsible for the polymerization of the peptidoglycan, and the penicillin-binding protein 2 (PBP2) plays a major role in the polymerization among several transglycosylases of wild-type S. aureus. However, it is unclear whether VRSA processes the depsipeptide-containing peptidoglycan precursor by using PBP2. Here, we describe the total synthesis of depsi-lipid I, a cell-wall precursor of VRSA. By using this chemistry, we prepared a depsi-lipid II analogue as substrate for a cell-free transglycosylation system. The reconstituted system revealed that the PBP2 of S. aureus is able to process a depsi-lipid II intermediate as efficiently as its normal substrate. Moreover, the system was successfully used to demonstrate the difference in the mode of action of the two antibiotics moenomycin and vancomycin.

Peptidoglycan assembly machines: the biochemical evidence.

To make progress in understanding peptidoglycan metabolism, we will reconstitute in vitro the assembly process and the molecular machineries that carry out this formidable task. We review here the reports of isolation of complexes comprising penicillin-binding proteins (PBPs), the enzymes that synthesize the peptidoglycan from its lipid-linked precursor.

Novel mechanism of resistance to glycopeptide antibiotics in Enterococcus faecium.

Glycopeptides and beta-lactams are the major antibiotics available for the treatment of infections due to Gram-positive bacteria. Emergence of cross-resistance to these drugs by a single mechanism has been considered as unlikely because they inhibit peptidoglycan polymerization by different mechanisms. The glycopeptides bind to the peptidyl-D-Ala(4)-D-Ala(5) extremity of peptidoglycan precursors and block by steric hindrance the essential glycosyltransferase and D,D-transpeptidase activities of the penicillin-binding proteins (PBPs). The beta-lactams are structural analogues of D-Ala(4)-D-Ala(5) and act as suicide substrates of the D,D-transpeptidase module of the PBPs. Here we have shown that bypass of the PBPs by the recently described beta-lactam-insensitive L,D-transpeptidase from Enterococcus faecium (Ldt(fm)) can lead to high level resistance to glycopeptides and beta-lactams. Cross-resistance was selected by glycopeptides alone or serially by beta-lactams and glycopeptides. In the corresponding mutants, UDP-MurNAc-pentapeptide was extensively converted to UDP-MurNAc-tetrapeptide following hydrolysis of D-Ala(5), thereby providing the substrate of Ldt(fm). Complete elimination of D-Ala(5), a residue essential for glycopeptide binding, was possible because Ldt(fm) uses the energy of the L-Lys(3)-D-Ala(4) peptide bond for cross-link formation in contrast to PBPs, which use the energy of the D-Ala(4)-D-Ala(5) bond. This novel mechanism of glycopeptide resistance was unrelated to the previously identified replacement of D-Ala(5) by D-Ser or D-lactate.

Murein (peptidoglycan) binding property of the essential cell division protein FtsN from Escherichia coli.

The binding of the essential cell division protein FtsN of Escherichia coli to the murein (peptidoglycan) sacculus was studied. Soluble truncated variants of FtsN, including the complete periplasmic part of the protein as well as a variant containing only the C-terminal 77 amino acids, did bind to purified murein sacculi isolated from wild-type cells. FtsN variants lacking this C-terminal region showed reduced or no binding to murein. Binding of FtsN was severely reduced when tested against sacculi isolated either from filamentous cells with blocked cell division or from chain-forming cells of a triple amidase mutant. Binding experiments with radioactively labeled murein digestion products revealed that the longer murein glycan strands (>25 disaccharide units) showed a specific affinity to FtsN, but neither muropeptides, peptides, nor short glycan fragments bound to FtsN. In vivo FtsN could be cross-linked to murein with the soluble disulfide bridge containing cross-linker DTSSP. Less FtsN, but similar amounts of OmpA, was cross-linked to murein of filamentous or of chain-forming cells compared to levels in wild-type cells. Expression of truncated FtsN variants in cells depleted in full-length FtsN revealed that the presence of the C-terminal murein-binding domain was not required for cell division under laboratory conditions. FtsN was present in 3,000 to 6,000 copies per cell in exponentially growing wild-type E. coli MC1061. We discuss the possibilities that the binding of FtsN to murein during cell division might either stabilize the septal region or might have a function unrelated to cell division.

FtsZ collaborates with penicillin binding proteins to generate bacterial cell shape in Escherichia coli.

The mechanisms by which bacteria adopt and maintain individual shapes remain enigmatic. Outstanding questions include why cells are a certain size, length, and width; why they are uniform or irregular; and why some branch while others do not. Previously, we showed that Escherichia coli mutants lacking multiple penicillin binding proteins (PBPs) display extensive morphological diversity. Because defective sites in these cells exhibit the structural and functional characteristics of improperly localized poles, we investigated the connection between cell division and shape. Here we show that under semipermissive conditions the temperature-sensitive FtsZ84 protein produces branched and aberrant cells at a high frequency in mutants lacking PBP 5, and this phenotype is exacerbated by the loss of additional peptidoglycan endopeptidases. Surprisingly, certain ftsZ84 strains lyse at the nonpermissive temperature instead of filamenting, and inhibition of wild-type FtsZ forces some mutants into tightly wound spirillum-like morphologies. The results demonstrate that significant aspects of bacterial shape are dictated by a previously unrecognized relationship between the septation machinery and ostensibly minor peptidoglycan-modifying enzymes and that under certain circumstances improper FtsZ function can destroy the structural integrity of the cell.

Expression and characterization of the isolated glycosyltransferase module of Escherichia coli PBP1b.

The enzymes involved in the biosynthesis of peptidoglycan are targets for the development of new antibiotics. The bifunctional high molecular weight (HMW) penicillin-binding proteins (PBPs), which contain both glycosyltransferase (GTase) and transpeptidase (TPase) activities, are particularly attractive targets because of their extracellular location. However, there is limited mechanistic or structural information about the GTase modules of these enzymes. In this paper, we describe the overexpression and characterization of the GTase module of Escherichia coli PBP1b, a paradigm of the HMW PBPs. We define the C-terminal boundary of the GTase module and show that the isolated module can be overexpressed at significantly higher levels than the full-length protein. The catalytic efficiency and other characteristics of the isolated module are comparable in most respects to the full-length enzyme. This work lays the groundwork for mechanistic and structural analysis of GTase modules.

Structural determinants required to target penicillin-binding protein 3 to the septum of Escherichia coli.

In Escherichia coli, cell division is mediated by the concerted action of about 12 proteins that assemble at the division site to presumably form a complex called the divisome. Among these essential division proteins, the multimodular class B penicillin-binding protein 3 (PBP3), which is specifically involved in septal peptidoglycan synthesis, consists of a short intracellular M1-R23 peptide fused to a F24-L39 membrane anchor that is linked via a G40-S70 peptide to an R71-I236 noncatalytic module itself linked to a D237-V577 catalytic penicillin-binding module. On the basis of localization analyses of PBP3 mutants fused to green fluorescent protein by fluorescence microscopy, it appears that the first 56 amino acid residues of PBP3 containing the membrane anchor and the G40-E56 peptide contain the structural determinants required to target the protein to the cell division site and that none of the putative protein interaction sites present in the noncatalytic module are essential for the positioning of the protein to the division site. Based on the effects of increasing production of FtsQ or FtsW on the division of cells expressing PBP3 mutants, it is suggested that these proteins could interact. We postulate that FtsQ could play a role in regulating the assembly of these division proteins at the division site and the activity of the peptidoglycan assembly machineries within the divisome.

Resistance to beta-lactam antibiotics.

beta-lactams have a long history in the treatment of infectious diseases, though their use has been and continues to be confounded by the development of resistance in target organisms. beta-lactamases, particularly in Gram-negative pathogens, are a major determinant of this resistance, although alterations in the beta-lactam targets, the penicillin-binding proteins (PBPs), are also important, especially in Gram-positive pathogens. Mechanisms for the efflux and/or exclusion of these agents also contribute, though often in conjunction these other two. Approaches for overcoming these resistance mechanisms include the development of novel beta-lactamase-stable beta-lactams, beta-lactamase inhibitors to be employed with existing beta-lactams, beta-lactam compounds that bind strongly to low-affinity PBPs and agents that potentiate the activity of existing beta-lactams against low-affinity PBP-producing organisms.

An internationally spread clone of Streptococcus pneumoniae evolves from low-level to higher-level penicillin resistance by uptake of penicillin-binding protein gene fragments from nonencapsulated pneumococci.

Low-level penicillin resistance in an international Streptococcus pneumoniae serotype 19F clone emerging in Switzerland was characterized by mutations in the penicillin-binding protein PBP2x. Some isolates of this clone had evolved to higher resistance levels (penicillin MICs of 0.094 and 1 microg/ml), probably by acquisition of pbp2x fragments from local nonencapsulated pneumococci.

Molecular epidemiology of penicillin-resistant Streptococcus pneumoniae in a university hospital, Ankara, Turkey.

Penicillin-resistant Streptococcus pneumoniae isolates (n = 76) from clinical samples of patients admitted to Hacettepe University Hospital between January 1997 and December 2001 were included in the study. MICs of penicillin G, erythromycin A, clindamycin, cefaclor, cefotaxime, vancomycin, chloramphenicol, tetracycline, ciprofloxacin and rifampicin were determined by agar dilution. The isolates were serogrouped on the basis of the Neufeld Quellung reaction and were typed by BOX-PCR. Genetic polymorphism of the penicillin resistance genes pbp2b and pbp2x was investigated by restriction fragment length polymorphism (RFLP) analysis. Of the 76 isolates tested, 64 (84.2%) showed intermediate resistance to penicillin, while 12 (15.8%) were resistant to higher levels of penicillin (MIC > or = 2 mg/L). The resistance patterns of the isolates revealed six different resistance profiles. There were 22 different serotypes, with c. 55% of the isolates belonging to serotypes 23B, 19A, 19F, 14, 6 A and 9V. Five distinct patterns for pbp2b and 12 distinct patterns for pbp2x were obtained by RFLP analysis of penicillin-binding protein genes. The combination of these patterns allowed isolates to be classified into 22 fingerprint subgroups. BOX-PCR analysis showed that the isolates fell into 14 distinct BOX genotypes, with 33 subtypes. Serotype 9V isolates with pbp genotype 2-6 and BOX-PCR type 4, 4.1 or 4.2 were related to the pandemic clone Spain(9V)-3. No relatedness to other international clones was detected among the other study strains, but genetic relatedness was observed among some of the serotype 19A and 23B isolates. Overall, the results demonstrated that most of the penicillin-resistant pneumococcal isolates in Turkey, other than those belonging to serotypes 9V, 19A and 23B, were derived from several independent clones, possibly resulting from multiple importation of strains originating from outside the country. Differences in pbp patterns, serotypes and resistance profiles among isolates that showed similar BOX-PCR patterns supported the hypothesis that horizontal transfer of capsular genes, pbp genes and other genetic determinants between S. pneumoniae and viridans group streptococci may have occurred.

SOS response induction by beta-lactams and bacterial defense against antibiotic lethality.

The SOS response aids bacterial propagation by inhibiting cell division during repair of DNA damage. We report that inactivation of the ftsI gene product, penicillin binding protein 3, by either beta-lactam antibiotics or genetic mutation induces SOS in Escherichia coli through the DpiBA two-component signal transduction system. This event, which requires the SOS-promoting recA and lexA genes as well as dpiA, transiently halts bacterial cell division, enabling survival to otherwise lethal antibiotic exposure. Our findings reveal defective cell wall synthesis as an unexpected initiator of the bacterial SOS response, indicate that beta-lactam antibiotics are extracellular stimuli of this response, and demonstrate a novel mechanism for mitigation of antimicrobial lethality.

[Analysis of the resistance gene in Streptococcus pneumoniae].

Resistance genes were determinded for 81 strains of Streptococcus pneumoniae isolated from Ehime University hospital, during 2002 and 2003 by various clinical material. In penicillin-binding proteins of mutation, there were 74 strains; pbp2x mutation 23 strains (28.4%), pbp2b mutation one strain (1.2%), pbp1a + pbp2x mutations 5 strains (6.2%), pbp2x + pbp2b mutations 18 strains (22.2%) and all mutations 27 strains (33.3%). As for the result of macrolide resistance genes, there were 67 strains; mefA gene 20 strains (24.7%), ermB gene 46 strains (56.8%) and both gene one strain (1.2%). In the analysis of gyrA gene and parC gene, 3 strains (3.7%) had both gene mutations, and 26 strains (32.1%) had only parC gene mutation. There was more of an increase than before in isolates, two or more mutation strains with PBPs gene, ermB gene holding strains and the levofloxacin resistance strain. These results suggest that the gyrA gene or parC gene mutation strains hold PBPs gene mutation and macrolide resistance genes in a high rate, and there will be more drug resistance in the future.

In vitro activities of ME1036 (CP5609), a novel parenteral carbapenem, against methicillin-resistant staphylococci.

ME1036, formerly CP5609, is a novel parenteral carbapenem with a 7-acylated imidazo[5,1-b]thiazole-2-yl group directly attached to the carbapenem moiety of the C-2 position. The present study evaluated the in vitro activities of ME1036 against clinical isolates of gram-positive and gram-negative bacteria. ME1036 displayed broad activity against aerobic gram-positive and gram-negative bacteria. Unlike other marketed beta-lactam antibiotics, ME1036 maintained excellent activity against multiple-drug-resistant gram-positive bacteria, such as methicillin-resistant staphylococci and penicillin-resistant Streptococcus pneumoniae (PRSP). The MICs of this compound at which 90% of isolates were inhibited were 2 microg/ml for methicillin-resistant Staphylococcus aureus (MRSA), 2 microg/ml for methicillin-resistant coagulase-negative staphylococci, and 0.031 microg/ml for PRSP. In time-kill studies with six strains of MRSA, ME1036 at four times the MIC caused a time-dependent decrease in the numbers of viable MRSA cells. The activity of ME1036 against MRSA is related to its high affinity for penicillin-binding protein 2a, for which the 50% inhibitory concentration of ME1036 was approximately 300-fold lower than that of imipenem. In conclusion, ME1036 demonstrated a broad antibacterial spectrum and high levels of activity in vitro against staphylococci, including beta-lactam-resistant strains.

Impact of specific pbp5 mutations on expression of beta-lactam resistance in Enterococcus faecium.

We tested the impact of individual PBP 5 mutations on expression of ampicillin resistance in Enterococcus faecium using a shuttle plasmid designed to facilitate expression of cloned pbp5 in ampicillin-susceptible E. faecium D344SRF. Substitutions that had been implicated in contributing to the resistance of clinical strains conferred only modest levels of resistance when they were present as single point mutations. The levels of resistance were amplified when some mutations were present in combination. In particular, a methionine-to-alanine change at position 485 (in close proximity to the active site) combined with the insertion of a serine at position 466 (located in a loop that forms the outer edge of the active site) was associated with the highest levels of resistance to all beta-lactams. Affinity for penicillin generally correlated with beta-lactam MICs for the mutants, but these associations were not strictly proportional.

The basis for resistance to beta-lactam antibiotics by penicillin-binding protein 2a of methicillin-resistant Staphylococcus aureus.

Penicillin-binding protein 2a (PBP2a) of Staphylococcus aureus is refractory to inhibition by available beta-lactam antibiotics, resulting in resistance to these antibiotics. The strains of S. aureus that have acquired the mecA gene for PBP2a are designated as methicillin-resistant S. aureus (MRSA). The mecA gene was cloned and expressed in Escherichia coli, and PBP2a was purified to homogeneity. The kinetic parameters for interactions of several beta-lactam antibiotics (penicillins, cephalosporins, and a carbapenem) and PBP2a were evaluated. The enzyme manifests resistance to covalent modification by beta-lactam antibiotics at the active site serine residue in two ways. First, the microscopic rate constant for acylation (k2) is attenuated by 3 to 4 orders of magnitude over the corresponding determinations for penicillin-sensitive penicillin-binding proteins. Second, the enzyme shows elevated dissociation constants (Kd) for the non-covalent pre-acylation complexes with the antibiotics, the formation of which ultimately would lead to enzyme acylation. The two factors working in concert effectively prevent enzyme acylation by the antibiotics in vivo, giving rise to drug resistance. Given the opportunity to form the acyl enzyme species in in vitro experiments, circular dichroism measurements revealed that the enzyme undergoes substantial conformational changes in the course of the process that would lead to enzyme acylation. The observed conformational changes are likely to be a hallmark for how this enzyme carries out its catalytic function in cross-linking the bacterial cell wall.

Genomic analysis of penicillin-resistant Streptococcus pneumoniae in Southeastern Michigan.

OBJECTIVE: The emergence of multidrug resistance within Streptococcus pneumoniae population was analysed, correlating penicillin resistance Pen(R) with secondary antibiotic resistance, capsular serotype, and genetic diversity among isolates. METHODS: DNA fingerprinting, following macro-restriction enzyme digestion and pulse field gel electrophoresis (PFGE), and restriction fragment analysis of the PBP 2b gene, following PCR amplification, were performed on the Pen(R) S. pneumoniae, among 377 clinical isolates obtained from the clinical microbiology laboratory (University of Michigan Medical Center). RESULTS: Overall 35% of the isolates were Pen(R) of which 45% demonstrated high-level penicillin (Pen(R)-R, MIC>1). Respiratory isolates were more likely to be Pen(R) (p <0.001) than non-respiratory isolates and the rate of Pen(R)-R was significantly increased in children <10 years of age (59.6%, p <0.02). Secondary antibiotic resistance was more frequently associated with Pen(R)-R. Genomic DNA fingerprinting analysis and restriction fragment analysis of the PBP 2b gene demonstrated genomic divergence with discrete conserved pattern in the PBP 2b gene among the resistant isolates. CONCLUSION: The emergence of multidrug resistance in the S. pneumoniae population in SE Michigan is not due to expansion of a single or limited number of resistant clones, is occurring most frequently in the paediatric population and is associated with a decreased susceptibility to penicillin.

Role of penicillin-binding protein 5 C-terminal amino acid substitutions in conferring ampicillin resistance in Norwegian clinical strains of Enterococcus faecium.

The importance of amino acid sequence differences in the C-terminal part and levels of mRNA expression of penicillin-binding protein 5 (PBP5) for ampicillin resistance in Enterococcus faecium was investigated. Seventeen isolates from Norwegian hospitalized patients (ampicillin MIC 0.064->256 mg/L) with different C-terminal pbp5 DNA sequences encoding 11 different amino acid sequences were analyzed with a 14C-radiolabeled penicillin- binding assay to PBP5 and with real-time PCR quantification of pbp5 mRNA expression. Using multiple logistic regression analysis the amino acid substitution Met 485 was linked to ampicillin MIC and levels of 14C-radiolabeled penicillin bound to PBP5; however, there were isolates with identical PBP5 alleles and different ampicillin MICs. There was no relation between the quantity of pbp5 mRNA transcripts and ampicillin resistance. The results cannot explain ampicillin resistance in Norwegian clinical strains of E. faecium and indicate that other factors besides the properties of the C-terminal part of PBP5 are most likely involved.

Mixed quantum mechanical/molecular mechanical (QM/MM) study of the deacylation reaction in a penicillin binding protein (PBP) versus in a class C beta-lactamase.

The origin of the substantial difference in deacylation rates for acyl-enzyme intermediates in penicillin-binding proteins (PBPs) and beta-lactamases has remained an unsolved puzzle whose solution is of great importance to understanding bacterial antibiotic resistance. In this work, accurate, large-scale mixed ab initio quantum mechanical/molecular mechanical (QM/MM) calculations have been used to study the hydrolysis of acyl-enzyme intermediates formed between cephalothin and the dd-peptidase of Streptomyces sp. R61, a PBP, and the Enterobacter cloacae P99 cephalosporinase, a class C beta-lactamase. Qualitative and, in the case of P99, quantitative agreement was achieved with experimental kinetics. The faster rate of deacylation in the beta-lactamase is attributed to a more favorable electrostatic environment around Tyr150 in P99 (as compared to that for Tyr159 in R61) which facilitates this residue's function as the general base. This is found to be in large part accomplished by the ability of P99 to covalently bind the ligand without concurrent elimination of hydrogen bonds to Tyr150, which proves not to be the case with Tyr159 in R61. This work provides an essential foundation for further work in this area, such as selecting mutations capable of converting the PBP into a beta-lactamase.

[Methicillin resistance detection in Staphylococcus aureus: comparison between conventional methods and MRSA-Screen latex agglutination technique]. / Detección de meticilino-resistencia en Staphylococcus aureus: comparación de métodos convencionales y aglutinación con MRSA-Screen latex.

Methicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen that has emerged over the last four decades, causing both nosocomial and community-acquired infections. Rapid and accurate detection of methicillin resistance in S. aureus is important for the use of appropriate antimicrobial therapy and for the control of nosocomial spread of MRSA strains. We evaluated the efficiency of conventional methods for detection of methicillin resistance such as the disk diffusion, agar dilution, oxacillin agar screen test, and the latex agglutination test MRSA-Screen latex, in 100 isolates of S. aureus, 79 mecA positive and 21 mecA negative. The MRSA-Screen latex (Denka Seiken, Niigata, Japón), is a latex agglutination method that detects the presence of PLP-2a, product of mecA gene in S. aureus. The PCR of the mecA gene was used as the "gold standard" for the evaluation of the different methods tested. The percentages of sensitivity and specificity were as follows: disk difusión 97 and 100%, agar dilution 97 and 95%, oxacillin agar screen test 100 and 100%, and MRSA-Screen latex, 100 and 100 %. All methods presented high sensitivity and specificity, but MRSA-Screen latex had the advantage of giving a reliable result, equivalent to PCR, in only 15 minutes.