Antigenic variation of penicillin-binding proteins from penicillin-resistant clinical strains of Streptococcus pneumoniae

Growing and Characterizing Biofilms Formed by Streptococcus pneumoniae

It is estimated that over 80% of bacterial infections are associated with biofilm formation. Biofilms are organized bacterial communities formed on abiotic surfaces, such as implanted or inserted medical devices, or on biological surfaces, such as epithelial linings and mucosal surfaces. Biofilm growth is advantageous for the bacterial organism as it protects the bacteria from antimicrobial host factors and allows the bacteria to reside in the host without causing excessive inflammation. Like many other opportunistic pathogens of the respiratory tract, Streptococcus pneumoniae forms biofilms during asymptomatic carriage, which promotes, among other things, persistence in the niche, intraspecies and interspecies communication, and spread of bacterial DNA. Changes within the colonizing environment resulting from host assaults, such as virus infection, can induce biofilm dispersion where bacteria leave the biofilm and disseminate to other sites with ensuing infection. In this chapter, we present methodology to form complex biofilms in the nasopharynx of mice and to evaluate the biofilm structure and function in this environment. Furthermore, we present methods that recapitulate this biofilm phenotype in vitro by incorporating crucial factors associated with the host environment and describe how these models can be used to study biofilm function, transformation, and dispersion.

Insights into the antibacterial mechanism of PEGylated nano-bacitracin A against Streptococcus pneumonia: both penicillin-sensitive and penicillin-resistant strains

Background

Multidrug-resistant (MDR) Streptococcus pneumonia constitute a major worldwide public health concern.

Materials and methods

In our preliminary study, PEGylated nano-self-assemblies of bacitracin A (PEGylated Nano-BA_12K) showed strong antibacterial potency against reference S. pneumonia strain (ATCC 49619). In this study, the possibility of applying PEGylated Nano-BA_12K against penicillin-resistant S. pneumonia was further investigated. In addition, the underlying antibacterial mechanism of PEGylated Nano-BA_12K against both sensitive and resistant S. pneumonia was also clarified systematically, since S. pneumonia was naturally resistant to its unassembled counterpart bacitracin A (BA).

Results

PEGylated Nano-BA_12K showed strong antibacterial potency against 13 clinical isolates of S. pneumonia, including five penicillin-resistant strains. Structural changes, partial collapse, and even lysis of both penicillin-sensitive and penicillin-resistant bacteria were observed after incubation with PEGylated Nano-BA_12K via transmission electron microscopy and atomic force microscopy. Thus, the cell wall or/and cell membrane might be the main target of PEGylated Nano-BA_12K against S. pneumonia. PEGylated Nano-BA_12K exhibited limited effect on the permeabilization and peptidoglycan content of cell wall. Surface pressure measurement suggested that PEGylated Nano-BA_12K was much more tensioactive than BA, which was usually translated into a good membranolytic effect, and is helpful to permeabilize the cell membrane and damage membrane integrity, as evidenced by depolarization of the membrane potential, permeabilization of membrane and leakage of calcein from liposomes.

Conclusion

Collectively, great cell membrane permeability and formidable membrane disruption may work together for the strong antibacterial activity of PEGylated Nano-BA_12K against S. pneumonia. Taken together, PEGylated Nano-BA_12K has excellent potential against both penicillin-sensitive and penicillin-resistant S. pneumonia and might be suitable for the treatment of S. pneumonia infectious diseases.

The Growing Threat of Antibiotic Resistance in Children

Antimicrobial resistance is a global public health threat and a danger that continues to escalate. These menacing bacteria are having an impact on all populations; however, until recently, the increasing trend in drug-resistant infections in infants and children has gone relatively unrecognized. This article highlights the current clinical and molecular data regarding infection with antibiotic-resistant bacteria in children, with an emphasis on transmissible resistance and spread via horizontal gene transfer.

Pneumococcus

Pneumococcus is one of the most common bacterial pathogens encountered in medicine. This article summarizes the risk factors, pathogenesis, treatment, and prevention of the spectrum of disease caused by pneumococcus with particular emphasis on antibiotic resistance as well as immunization. This information is useful for physicians caring for patients both as inpatients and outpatients as well as for those concerned with public health and disease prevention.

The multidrug-resistant PMEN1 pneumococcus is a paradigm for genetic success

BACKGROUND

Streptococcus pneumoniae, also called the pneumococcus, is a major bacterial pathogen. Since its introduction in the 1940s, penicillin has been the primary treatment for pneumococcal diseases. Penicillin resistance rapidly increased among pneumococci over the past 30 years, and one particular multidrug-resistant clone, PMEN1, became highly prevalent globally. We studied a collection of 426 pneumococci isolated between 1937 and 2007 to better understand the evolution of penicillin resistance within this species.

RESULTS

We discovered that one of the earliest known penicillin-nonsusceptible pneumococci, recovered in 1967 from Australia, was the likely ancestor of PMEN1, since approximately 95% of coding sequences identified within its genome were highly similar to those of PMEN1. The regions of the PMEN1 genome that differed from the ancestor contained genes associated with antibiotic resistance, transmission and virulence. We also revealed that PMEN1 was uniquely promiscuous with its DNA, donating penicillin-resistance genes and sometimes many other genes associated with antibiotic resistance, virulence and cell adherence to many genotypically diverse pneumococci. In particular, we describe two strains in which up to 10% of the PMEN1 genome was acquired in multiple fragments, some as long as 32 kb, distributed around the recipient genomes. This type of directional genetic promiscuity from a single clone to numerous unrelated clones has, to our knowledge, never before been described.

CONCLUSIONS

These findings suggest that PMEN1 is a paradigm of genetic success both through its epidemiology and promiscuity. These findings also challenge the existing views about horizontal gene transfer among pneumococci.

High levels of genetic recombination during nasopharyngeal carriage and biofilm formation in Streptococcus pneumoniae

Transformation of genetic material between bacteria was first observed in the 1920s using Streptococcus pneumoniae as a model organism. Since then, the mechanism of competence induction and transformation has been well characterized, mainly using planktonic bacteria or septic infection models. However, epidemiological evidence suggests that genetic exchange occurs primarily during pneumococcal nasopharyngeal carriage, which we have recently shown is associated with biofilm growth, and is associated with cocolonization with multiple strains. However, no studies to date have comprehensively investigated genetic exchange during cocolonization in vitro and in vivo or the role of the nasopharyngeal environment in these processes. In this study, we show that genetic exchange during dual-strain carriage in vivo is extremely efficient (10⁻²) and approximately 10,000,000-fold higher than that measured during septic infection (10⁻⁹). This high transformation efficiency was associated with environmental conditions exclusive to the nasopharynx, including the lower temperature of the nasopharynx (32 to 34°C), limited nutrient availability, and interactions with epithelial cells, which were modeled in a novel biofilm model in vitro that showed similarly high transformation efficiencies. The nasopharyngeal environmental factors, combined, were critical for biofilm formation and induced constitutive upregulation of competence genes and downregulation of capsule that promoted transformation. In addition, we show that dual-strain carriage in vivo and biofilms formed in vitro can be transformed during colonization to increase their pneumococcal fitness and also, importantly, that bacteria with lower colonization ability can be protected by strains with higher colonization efficiency, a process unrelated to genetic exchange.

Although genetic exchange between pneumococcal strains is known to occur primarily during colonization of the nasopharynx and colonization is associated with biofilm growth, this is the first study to comprehensively investigate transformation in this environment and to analyze the role of environmental and bacterial factors in this process. We show that transformation efficiency during cocolonization by multiple strains is very high (around 10⁻²). Furthermore, we provide novel evidence that specific aspects of the nasopharyngeal environment, including lower temperature, limited nutrient availability, and epithelial cell interaction, are critical for optimal biofilm formation and transformation efficiency and result in bacterial protein expression changes that promote transformation and fitness of colonization-deficient strains. The results suggest that cocolonization in biofilm communities may have important clinical consequences by facilitating the spread of antibiotic resistance and enabling serotype switching and vaccine escape as well as protecting and retaining poorly colonizing strains in the pneumococcal strain pool.

The human milk protein-lipid complex HAMLET sensitizes bacterial pathogens to traditional antimicrobial agents

The fight against antibiotic resistance is one of the most significant challenges to public health of our time. The inevitable development of resistance following the introduction of novel antibiotics has led to an urgent need for the development of new antibacterial drugs with new mechanisms of action that are not susceptible to existing resistance mechanisms. One such compound is HAMLET, a natural complex from human milk that kills Streptococcus pneumoniae (the pneumococcus) using a mechanism different from common antibiotics and is immune to resistance-development. In this study we show that sublethal concentrations of HAMLET potentiate the effect of common antibiotics (penicillins, macrolides, and aminoglycosides) against pneumococci. Using MIC assays and short-time killing assays we dramatically reduced the concentrations of antibiotics needed to kill pneumococci, especially for antibiotic-resistant strains that in the presence of HAMLET fell into the clinically sensitive range. Using a biofilm model in vitro and nasopharyngeal colonization in vivo, a combination of HAMLET and antibiotics completely eradicated both biofilms and colonization in mice of both antibiotic-sensitive and resistant strains, something each agent alone was unable to do. HAMLET-potentiation of antibiotics was partially due to increased accessibility of antibiotics to the bacteria, but relied more on calcium import and kinase activation, the same activation pathway HAMLET uses when killing pneumococci by itself. Finally, the sensitizing effect was not confined to species sensitive to HAMLET. The HAMLET-resistant respiratory species Acinetobacter baumanii and Moraxella catarrhalis were all sensitized to various classes of antibiotics in the presence of HAMLET, activating the same mechanism as in pneumococci. Combined these results suggest the presence of a conserved HAMLET-activated pathway that circumvents antibiotic resistance in bacteria. The ability to activate this pathway may extend the lifetime of the current treatment arsenal.

Molecular mechanisms of β-lactam resistance in Streptococcus pneumoniae

Alterations in the target enzymes for β-lactam antibiotics, the penicillin-binding proteins (PBPs), have been recognized as a major resistance mechanism in Streptococcus pneumoniae. Mutations in PBPs that confer a reduced affinity to β-lactams have been identified in laboratory mutants and clinical isolates, and document an astounding variability of sites involved in this phenotype. Whereas point mutations are selected in the laboratory, clinical isolates display a mosaic structure of the affected PBP genes, the result of interspecies gene transfer and recombination events. Depending on the selective β-lactam, different combinations of PBP genes and mutations within are involved in conferring resistance, and astoundingly in non-PBP genes as well.

Pneumococcal interactions with epithelial cells are crucial for optimal biofilm formation and colonization in vitro and in vivo

The human nasopharynx is the main reservoir for Streptococcus pneumoniae (the pneumococcus) and the source for both horizontal spread and transition to infection. Some clinical evidence indicates that nasopharyngeal carriage is harder to eradicate with antibiotics than is pneumococcal invasive disease, which may suggest that colonizing pneumococci exist in biofilm communities that are more resistant to antibiotics. While pneumococcal biofilms have been observed during symptomatic infection, their role in colonization and the role of host factors in this process have been less studied. Here, we show for the first time that pneumococci form highly structured biofilm communities during colonization of the murine nasopharynx that display increased antibiotic resistance. Furthermore, pneumococcal biofilms grown on respiratory epithelial cells exhibited phenotypes similar to those observed during colonization in vivo, whereas abiotic surfaces produced less ordered and more antibiotic-sensitive biofilms. The importance of bacterial-epithelial cell interactions during biofilm formation was shown using both clinical strains with variable colonization efficacies and pneumococcal mutants with impaired colonization characteristics in vivo. In both cases, the ability of strains to form biofilms on epithelial cells directly correlated with their ability to colonize the nasopharynx in vivo, with colonization-deficient strains forming less structured and more antibiotic-sensitive biofilms on epithelial cells, an association that was lost when grown on abiotic surfaces. Thus, these studies emphasize the importance of host-bacterial interactions in pneumococcal biofilm formation and provide the first experimental data to explain the high resistance of pneumococcal colonization to eradication by antibiotics.

Current concepts in antimicrobial therapy against select gram-positive organisms: methicillin-resistant Staphylococcus aureus, penicillin-resistant pneumococci, and vancomycin-resistant enterococci

Gram-positive bacteria cause a broad spectrum of disease in immunocompetent and immunocompromised hosts. Despite increasing knowledge about resistance transmission patterns and new antibiotics, these organisms continue to cause significant morbidity and mortality, especially in the health care setting. Methicillin-resistant Staphylococcus aureus poses major problems worldwide as a cause of nosocomial infection and has emerged as a cause of community-acquired infections. This change in epidemiology affects choices of empirical antibiotics for skin and skin-structure infections and community-acquired pneumonia in many settings. Throughout the world, the treatment of community-acquired pneumonia and other respiratory tract infections caused by penicillin-resistant Streptococcus pneumoniae has been complicated by resistance to β-lactam and macrolide antibacterial drugs. Vancomycin-resistant enterococci are a major cause of infection in the hospital setting and remain resistant to treatment with most standard antibiotics. Treatment of diseases caused by resistant gram-positive bacteria requires appropriate use of available antibiotics and stewardship to prolong their effectiveness. In addition, appropriate and aggressive infection control efforts are vital to help prevent the spread of resistant pathogens.

GenHtr: a tool for comparative assessment of genetic heterogeneity in microbial genomes generated by massive short-read sequencing

Background

Microevolution is the study of short-term changes of alleles within a population and their effects on the phenotype of organisms. The result of the below-species-level evolution is heterogeneity, where populations consist of subpopulations with a large number of structural variations. Heterogeneity analysis is thus essential to our understanding of how selective and neutral forces shape bacterial populations over a short period of time. The Solexa Genome Analyzer, a next-generation sequencing platform, allows millions of short sequencing reads to be obtained with great accuracy, allowing for the ability to study the dynamics of the bacterial population at the whole genome level. The tool referred to as Gen^Htr was developed for genome-wide heterogeneity analysis.

Results

For particular bacterial strains, Gen^Htr relies on a set of Solexa short reads on given bacteria pathogens and their isogenic reference genome to identify heterogeneity sites, the chromosomal positions with multiple variants of genes in the bacterial population, and variations that occur in large gene families. Gen^Htr accomplishes this by building and comparatively analyzing genome-wide heterogeneity genotypes for both the newly sequenced genomes (using massive short-read sequencing) and their isogenic reference (using simulated data). As proof of the concept, this approach was applied to SRX007711, the Solexa sequencing data for a newly sequenced Staphylococcus aureus subsp. USA300 cell line, and demonstrated that it could predict such multiple variants. They include multiple variants of genes critical in pathogenesis, e.g. genes encoding a LysR family transcriptional regulator, 23 S ribosomal RNA, and DNA mismatch repair protein MutS. The heterogeneity results in non-synonymous and nonsense mutations, leading to truncated proteins for both LysR and MutS.

Conclusion

Gen^Htr was developed for genome-wide heterogeneity analysis. Although it is much more time-consuming when compared to Maq, a popular tool for SNP analysis, Gen^Htr is able to predict potential multiple variants that pre-exist in the bacterial population as well as SNPs that occur in the highly duplicated gene families. It is expected that, with the proper experimental design, this analysis can improve our understanding of the molecular mechanism underlying the dynamics and the evolution of drug-resistant bacterial pathogens.

Binding of ceftaroline to penicillin-binding proteins of Staphylococcus aureus and Streptococcus pneumoniae

OBJECTIVES

This study evaluated the affinity of ceftaroline and comparator beta-lactams for penicillin-binding proteins (PBPs) of methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA) and Streptococcus pneumoniae with varying susceptibility to penicillin. Ceftaroline is currently in Phase 3 development for the treatment of complicated skin and skin structure infections and community-acquired pneumonia, including infections caused by MRSA and multidrug-resistant S. pneumoniae.

METHODS

Binding affinities (IC(50)s) of ceftaroline, ceftriaxone, oxacillin and penicillin G for PBPs were measured in a competition assay by adding various concentrations of the test drugs to membranes or whole cells. PBPs were labelled using the fluorescent reporter molecule Bocillin FL.

RESULTS

Overall, ceftaroline exhibited greater binding affinity for the range of PBPs tested, as compared with comparator beta-lactams. The high affinity of ceftaroline for PBPs 1-3 of MSSA and PBP2a of MRSA correlates well with its efficacy against these organisms, as determined by MIC. Similarly, efficient binding of ceftaroline to key S. pneumoniae PBPs, such as PBP2x/2a/2b, taken together, correlates well with its low MICs for penicillin-resistant isolates of S. pneumoniae.

CONCLUSIONS

The high affinities of ceftaroline for MRSA PBP2a, MSSA PBPs 1-3 and S. pneumoniae PBP2x/2a/2b support the potential efficacy of ceftaroline in the treatment of infections caused by MRSA and S. pneumoniae.

Streptococcus pneumoniae surface protein PcpA elicits protection against lung infection and fatal sepsis

Previous studies have suggested that pneumococcal choline binding protein A (PcpA) is important for the full virulence of Streptococcus pneumoniae, and its amino acid sequence suggests that it may play a role in cellular adherence. PcpA is under the control of a manganese-dependent regulator and is only expressed at low manganese concentrations, similar to those found in the blood and lungs. PcpA expression is repressed under high manganese concentrations, similar to those found in secretions. In this study, we have demonstrated that PcpA elicits statistically significant protection in murine models of pneumonia and sepsis. In the model of pneumonia with each of four challenge strains, statistically fewer S. pneumoniae cells were recovered from the lungs of mice immunized with PcpA and alum versus mice immunized with alum only. The immunizations reduced the median CFU by 4- to 400-fold (average of 28-fold). In the model of sepsis using strain TIGR4, PcpA expression resulted in shorter times to become moribund and subcutaneous immunization with PcpA increased survival times of mice infected with wild-type PcpA-expressing pneumococci.

Multidrug-resistant Streptococcus pneumoniae infections: current and future therapeutic options

Antibacterial resistance in Streptococcus pneumoniae is increasing worldwide, affecting principally beta-lactams and macrolides (prevalence ranging between approximately 1% and 90% depending on the geographical area). Fluoroquinolone resistance has also started to emerge in countries with high level of antibacterial resistance and consumption. Of more concern, 40% of pneumococci display multi-drug resistant phenotypes, again with highly variable prevalence among countries. Infections caused by resistant pneumococci can still be treated using first-line antibacterials (beta-lactams), provided the dosage is optimised to cover less susceptible strains. Macrolides can no longer be used as monotherapy, but are combined with beta-lactams to cover intracellular bacteria. Ketolides could be an alternative, but toxicity issues have recently restricted the use of telithromycin in the US. The so-called respiratory fluoroquinolones offer the advantages of easy administration and a spectrum covering extracellular and intracellular pathogens. However, their broad spectrum raises questions regarding the global risk of resistance selection and their safety profile is far from optimal for wide use in the community. For multi-drug resistant pneumococci, ketolides and fluoroquinolones could be considered. A large number of drugs with activity against these multi-drug resistant strains (cephalosporins, carbapenems, glycopeptides, lipopeptides, ketolides, lincosamides, oxazolidinones, glycylcyclines, quinolones, deformylase inhibitors) are currently in development. Most of them are only new derivatives in existing classes, with improved intrinsic activity or lower susceptibility to resistance mechanisms. Except for the new fluoroquinolones, these agents are also primarily targeted towards methicillin-resistant Staphylococcus aureus infections; therefore, demonstration of their clinical efficacy in the management of pneumococcal infections is still awaited.

Analysis of mutations in the pbp genes of penicillin-non-susceptible pneumococci from Turkey

Sequence analysis of the pbp genes from 20 Streptococcus pneumoniae isolates from Turkey (eight with high-level penicillin-resistance, nine with low-level penicillin-resistance, and three that were penicillin-susceptible) was performed and phylogenetic trees were constructed. Most isolates clustered together within a single branch that was distinct from sequences deposited previously in GenBank, which suggests that these isolates have probably evolved following new recombination events. The most prominent active-site mutations, which have also been associated previously with resistance, were T371A in PBP1a, E481G followed by T451A in PBP2b, and T338A in PBP2x. All isolates also possessed a (570)SVES/TK(574) block in the PBP2b sequence, instead of the QLQPT sequence of R6, which is fairly uncommon in GenBank sequences. This is the first study to analyse alterations in the pbp sequences of pneumococci isolated in Turkey.

RWJ-54428 (MC-02,479), a new cephalosporin with high affinity for penicillin-binding proteins, including PBP 2a, and stability to staphylococcal beta-lactamases

RWJ-54428 (MC-02,479) is a new cephalosporin active against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). The potency of this new cephalosporin against MRSA is related to a high affinity for penicillin-binding protein 2a (PBP 2a), as assessed in a competition assay using biotinylated ampicillin as the reporter molecule. RWJ-54428 had high activity against MRSA strains COL and 67-0 (MIC of 1 micro g/ml) and also showed affinity for PBP 2a, with a 50% inhibitory concentration (IC(50)) of 0.7 micro g/ml. RWJ-54428 also displayed excellent affinity for PBP 5 from Enterococcus hirae R40, with an IC(50) of 0.8 micro g/ml and a MIC of 0.5 micro g/ml. The affinity of RWJ-54428 for PBPs of beta-lactam-susceptible S. aureus (MSSA), enterococci (E. hirae), and Streptococcus pneumoniae showed that the good affinity of RWJ-54428 for MRSA PBP 2a and E. hirae PBP 5 does not compromise its binding to susceptible PBPs. RWJ-54428 showed stability to hydrolysis by purified type A beta-lactamase isolated from S. aureus PC1. In addition, RWJ-54428 displayed low MICs against strains of S. aureus bearing the four classes of staphylococcal beta-lactamases, including beta-lactamase hyperproducers. The frequency of isolation of resistant mutants to RWJ-54428 from MRSA strains was very low. In summary, RWJ-54428 has high affinity to multiple PBPs and is stable to beta-lactamase, properties that may explain our inability to find resistance by standard methods. These data are consistent with its excellent activity against beta-lactam-resistant gram-positive bacteria.

Multidrug-resistant Pathogens: Mechanisms of Resistance and Epidemiology

Resistance to antimicrobial agents among bacteria and fungi is a persistent problem complicating the management of critically ill patients. To understand the issues involved in resistance in critical care, it is essential to understand the epidemiology and mechanisms of resistance. beta-lactam resistance in pneumococci, and penicillin and chloramphenicol resistance in Neisseria meningitidis, have complicated the management of meningitis. Vancomycin resistance in enterococci and methicillin resistance in Staphylococcus aureus have disseminated among hospitals, nursing homes and, in some cases, community patients. Glycopeptide resistance in S. aureus has recently been described in clinical isolates; the potential for spread of this resistance trait is concerning. Resistance to broad-spectrum cephalosporins is a persistent challenge in the management of infections caused by Pseudomonas areuginosa, and Enterobacter species, as well as other Enterobacteriaceae. Azole resistance in Candida species. has also complicated the treatment of nosocomial infections. Resistance to antimicrobial drugs is a persistent and emerging problem and presents major therapeutic challenges.

Pathogens resistant to antimicrobial agents. Epidemiology, molecular mechanisms, and clinical management

The emergence of resistance to antimicrobial agents continues to be a major problem in the nosocomial setting and now in nursing homes and the community as well. Bacteria use a variety of strategies to avoid the inhibitory effects of antibiotic agents and have evolved highly efficient means for the dissemination of resistance traits. Control of antibiotic-resistant pathogens provides a major challenge for both the medical community and society in general. To control the emergence of resistant pathogens, CDC and infection control guidelines must be adhered to, and antibiotics must be used more judiciously.

In vitro development of resistance of Streptococcus pneumoniae to beta-lactam antibiotics

In recent years, increasing numbers of Streptococcus pneumoniae strains displaying relative resistance to penicillin have been reported. Epidemiological studies have shown a correlation between aminopenicillin administration and resistance. We investigated the development of resistance in six strains (four sensitive and two intermediate-resistant to penicillin) by serial daily passages in subinhibitory concentrations of amoxicillin (AMX), amoxicillin + clavulanic acid (AMC), imipenem (IMP), cefixime (CFM), cefatrizine (CTZ), cefadroxil (CDX), and cefuroxime (CXM). MICs were determined by the macrodilution method in brain-heart broth for each daily passage. The number of daily passages needed to increase the MIC by a factor of 8 was achieved with AMX, AMC, and CFM for most of the strains after a mean of 24, 20, and 11 passages, respectively, and for one-third of the strains, with CDX, IMP, and CTZ after 11, 11, and 21 passages, respectively. Decreased susceptibility to breakpoints for intermediate-resistant S. pneumoniae populations was noted for all strains with CFM, AMX, and AMC after a mean of 10, 18, and 21 serial passages, respectively, and for four of five strains with IMP and CTZ after 12 and 13 passages. CTZ-, CDX-, and CXM-passaged variants had increased MIC values only for cephalosporins, while AMX-, AMC-, IMP-, and CFM-passaged variants exhibited increased MICs to all antibiotics tested. These in vitro data appear to be in agreement with epidemiological studies and warrant further exploration with respect to possible clinical implications.

Structural organization of the Streptococcus pneumoniae chromosome and relatedness of penicillin-sensitive and -resistant strains in type 9V

Fragmentation of Streptococcus pneumoniae genomic DNA with low-frequency-cleavage restriction endonucleases and separation of the fragments by field-inversion gel electrophoresis (FIGE) provides a DNA-fingerprint of a strain. This method enables us to construct a physical and genetic map of the R6 laboratory strain what will be presented. The origin of replication containing several Dna boxes was located in the dnaA region. It was of interest to compare the profiles of subclones. Two clones of strain R36A (R6 and C13) were cultivated separately for more than 15,000 generations in two laboratories. FIGE profiles differed by only one band. Another R36A descendant, isolated in 1958 by Ravin, strain Rx was of interest since it was deficient in Dpn restriction enzymes and methylases and in the hex B function. Its origin was questionable; its profile is identical to others R6 descendants, demonstrating that Rx is derived from R36A. FIGE analysis was carried out on several penicillin-resistant strains of type 9V because penicillin-resistance in this type increased recently. The profiles of a collection of a number of these resistant isolates were very similar, showing that they result from a clone. The profiles of penicillin sensitive isolates of the same type are very similar to the resistant isolates. This suggests that the 9V type has spread recently from a clone, and the resistance genes have mutated and were selected when penicillin was extensively used.

Penicillin-binding proteins as resistance determinants in clinical isolates of Streptococcus pneumoniae

Altered penicillin-binding proteins (PBPs) with reduced affinity for penicillin are encoded by mosaic genes in penicillin-resistant clinical isolates of Streptococcus pneumoniae. Generally, members of one bacterial clone contain the same mosaic gene. We report here on a serotype 19A clone of penicillin- and multiple-resistant S. pneumoniae prevalent in Hungary, members of which are exceptionally diverse in terms of PBP properties. The pbp2x gene of four 19A isolates was sequenced, and a distinct mosaic structure detected in each case. The pbp2x genes also differed from a homologous gene of a high-level penicillin-resistant S. mitis from Hungary. The contribution of PBPs to resistance development was studied on transformation experiments using the laboratory strain R6 as recipient, and PBP genes from the type 19A isolate Hu11. pbp2x and pbp2b function as primary resistance determinants for different beta-lactams. Secondary transformation with pbp1a increased the resistance level considerably for penicillins and cefotaxime. Chromosomal DNA of a high-level penicillin- and cefotaxime-resistant S. mitis from Hungary also transformed the R6 strain to increased resistance levels, and PBP2x and PBP2b functioned as primary resistance determinants as above. In contrast, high-level cefotaxime resistance appeared to be due to a low affinity PBP2a, indicating that this PBP can also function as a resistance determinant.

Pneumococcal diversity: considerations for new vaccine strategies with emphasis on pneumococcal surface protein A (PspA)

Streptococcus pneumoniae is a problematic infectious agent, whose seriousness to human health has been underscored by the recent rise in the frequency of isolation of multidrug-resistant strains. Pneumococcal pneumonia in the elderly is common and often fatal. Young children in the developing world are at significant risk for fatal pneumococcal respiratory disease, while in the developed world otitis media in children results in substantial economic costs. Immunocompromised patients are extremely susceptible to pneumococcal infection. With 90 different capsular types thus far described, the diversity of pneumococci contributes to the challenges of preventing and treating S. pneumoniae infections. The current capsular polysaccharide vaccine is not recommended for use in children younger than 2 years and is not fully effective in the elderly. Therefore, innovative vaccine strategies to protect against this agent are needed. Given the immunogenic nature of S. pneumoniae proteins, these molecules are being investigated as potential vaccine candidates. Pneumococcal surface protein A (PspA) has been evaluated for its ability to elicit protection against S. pneumoniae infection in mouse models of systemic and local disease. This review focuses on immune system responsiveness to PspA and the ability of PspA to elicit cross-protection against heterologous strains. These parameters will be critical to the design of broadly protective pneumococcal vaccines.

Epidemiology, laboratory detection, and therapy of penicillin-resistant streptococcal infections

Streptococci cause a wide range of infections in humans including respiratory tract infections, endocarditis, meningitis, bacteremias, and skin and soft tissue lesions. Mutations in the penicillin binding proteins target sites in these organisms have recently caused resistance to penicillins and cephalosporins. The passage of resistant genetic material from one streptococcal species to another has been recognized as one of the mechanisms by which this resistance has occurred and spread. Such resistance has been a particular problem in Streptococcus pneumoniae and viridans group streptococci with penicillin resistance levels in excess of 25%, now common in both groups of organisms worldwide. Fourth-generation cephalosporins, with their enhanced antibacterial activity against Gram-positive organisms (cefpirome > cefepime) and their increased stability to the beta-lactamases produced by many bacterial species, offer a new option for the treatment of potentially life-threatening infections such as pneumococcal pneumonia and meningitis with or without bacteremia. Clinical trials are currently in place to evaluate the role of these agents in these, and other, indications of Gram-positive infections. Prior studies of cefpirome therapy for infections caused by Streptococcus spp. were successful, and recent expanded in vitro investigations profess a future for expanded use of cefpirome to treat infections produced by several Gram-positive species.

Alterations in PBP 1A essential-for high-level penicillin resistance in Streptococcus pneumoniae

High-level penicillin resistance in pneumococci is due to alterations in penicillin-binding proteins (PBPs) 2X, 2B, and 1A. We have sequenced the penicillin-binding domain of PBP 1A from penicillin-resistant South African pneumococcal isolates and have identified amino acid substitutions which are common to all the resistant isolates analyzed. Site-directed mutagenesis was then used to determine whether particular amino acid substitutions at specific positions in PBP 1A mediate penicillin resistance. PCR was used to isolate PBP 2X, 2B, and 1A genes from clinical isolate 8303 (penicillin MIC, 4 micrograms/ml). These wild-type PBP genes were cloned into pGEM-3Zf and were used as the transforming DNA. Susceptible strain R6 (MIC, 0.015 microgram/ml) was first transformed with PBP 2X and 2B DNA, resulting in PBP 2X/2B-R6 transformants for which MICs were 0.25 microgram/ml. When further transformed with PBP 1A DNA, 2X/2B/1A-R6 transformants for which MICs were 1.5 micrograms/ml were obtained. Site-directed mutagenesis of the PBP 1A gene from isolate 8303 was then used to reverse particular amino acid substitutions, followed by transformation of PBP 2X/2B-R6 transformants with the mutagenized PBP 1A DNA. For PBP 2X/2B/1A-R6 transformants, the introduction of the reversal of Thr-371 by Ser or Ala in PBP 1A decreased the MIC from 1.5 to 0.5 micrograms/ml, whereas the reversal of four consecutive amino acid substitutions (Thr-574 by Asn, Ser-575 by Thr, Gln-576 by Gly, and Phe-577 by Tyr) decreased the MIC from 1.5 to 0.375 micrograms/ml. These data reveal that amino acid residue 371 and residues 574 to 577 of PBP 1A are important positions in PBP 1A with respect to the interaction with penicillin and the development of resistance.

Evolving clinical problems with Streptococcus pneumoniae: increasing resistance to antimicrobial agents, and failure of traditional optochin identification in Chicago, Illinois, between 1993 and 1996

Infections due to multidrug-resistant pneumococci are a growing concern. Through December 1995, over 85% of isolates recovered from our patients in Chicago, Illinois, were fully susceptible to penicillin, and only a rare resistant strain was recovered from blood or cerebrospinal fluid (CSF). In December 1995, we began to observe bloodstream infections due to Streptococcus pneumoniae with penicillin MICs that represented either intermediate or full resistance to penicillin. S. pneumoniae isolated between January 1, 1993, and December 31, 1996, were tested against 11 different antimicrobial agents. There were 158 from blood or CSF, and 303 from other (primarily respiratory) sources. During 1996, 46% of our total S. pneumoniae isolates were no longer fully susceptible to penicillin, representing a threefold increase from the previous year's experience. In isolates from blood and CSF, more than 90% of strains had been fully susceptible to penicillin through 1995, but since the start of 1996, 29% of our invasive isolates were no longer fully susceptible to penicillin. During 1996, vancomycin was the only currently approved agent that was active against all recovered isolates. We also noted two isolates during 1996 where optochin testing did not accurately identify strains as S. pneumoniae. A major problem with multidrug-resistant S. pneumoniae causing both respiratory and invasive diseases appears to have now reached the Chicago area. Laboratories need to be aware of a continued increase in antimicrobial agent resistance exhibited by this pathogen, as well as potential difficulties that can be encountered using traditional laboratory identification methods.

Clonal distribution of penicillin-resistant Streptococcus pneumoniae 23F in France

We studied the clonality of clinical isolates of Streptococcus pneumoniae 23F, the serotype most often associated with penicillin resistance in France. Clinical isolates obtained between November 1992 and April 1993 from nasopharyngeal samples from children with acute otitis media from different regions of the country were analyzed. The genetic polymorphism of penicillin-susceptible and -resistant 23F isolates (MIC, 2 mg/liter) was studied by pulsed-field gel electrophoresis. The resistant isolates were closely related, whereas the susceptible isolates were genetically heterogeneous. PCR amplification and restriction of the genes encoding penicillin-binding proteins (PBPs) 1A, 2B, and 2X also showed that the 24 resistant isolates had similar patterns which were very different from those of the susceptible isolates. All resistant isolates gave the same PBP pattern, with low affinities of PBPs for penicillin. Our results indicate that, in contrast to penicillin-susceptible 23F isolates, the penicillin-resistant 23F isolates have a single clonal origin, suggesting the rapid clonal spread of a resistant epidemic strain throughout the country.

Evidence of recombination and an antigenically diverse immunoglobulin A1 protease among strains of Streptococcus pneumoniae

The genetic relationships among 114 isolates of Streptococcus pneumoniae representing mainly nine serotypes that frequently cause severe childhood disease in Northern Europe were examined by use of multilocus enzyme electrophoresis. A comparison was made of the corresponding antigenic variations of excreted immunoglobulin A1 (IgA1) proteases detected by enzyme neutralization assays. Allelic variation at 13 gene loci among 70 electrophoretic types disclosed a comparatively low mean genetic diversity per locus (H = 0.319). In contrast, IgA1 proteases showed extensive antigenic diversity as 17 different inhibition types were distinguished. A lack of overall clonality was apparent from the linkage equilibrium of alleles harbored by 28 isolates chosen to represent the genetic diversity of the study population. However, certain clones, such as those marked by identical electrophoretic type, serotype, and IgA1 protease type, persisted for a sufficiently long time to enable clonal spread between distant geographic areas. Among clonally related isolates, examples illustrating a shift of capsular serotype or IgA1 protease type supported the view that recombination occurs in vivo in corresponding genes. In conclusion, over time, horizontal genetic exchange appears to be sufficiently frequent to disrupt the clonal structure otherwise generated by binary fission in natural populations of S. pneumoniae. The clonal instability combined with considerable antigenic heterogeneity renders the pneumococcal IgA1 protease less attractive as a potential component of future vaccines.

Origin and molecular epidemiology of penicillin-binding-protein-mediated resistance to beta-lactam antibiotics

Resistance to beta-lactam antibiotics in some naturally transformable bacterial pathogens has arisen by interspecies recombinational events that have generated hybrid penicillin-binding proteins with reduced affinity for the antibiotics. This type of resistance is of particular concern in pneumococci, in which it is increasing worldwide.

Emerging problems of antimicrobial resistance

The incidence of organisms resistant to various antimicrobial agents has risen over the last several years, resulting in an increase in morbidity and mortality and overall treatment costs. The emergence of virtually untreatable infections has focused the medical community's attention on this issue. This paper reviews common pathogens (both nosocomial and community-acquired infections) that have become resistant to antimicrobial drugs. Approaches that may prevent or retard the development, of resistance among these organisms are discussed.

Penicillin resistance among Streptococcus pneumoniae in Europe

Penicillin resistance in Streptococcus pneumoniae, which has been occasionally described in European isolates since the early 1970s, presently constitutes a general problem, although its rate may vary largely between countries and areas. Spain and Hungary show the highest rates of resistance and were probably the starting point for further dissemination to adjacent and distant countries. In Europe, resistant strains belong predominantly to serotypes 6, 9, 14, 19, and 23, and are isolated more frequently from pediatric than from adult patients, and from respiratory and CSF samples rather than blood. Although penicillin resistance in pneumococci is usually a well-recognized problem, some difficulties, mainly related to methodologic aspects of in vitro susceptibility testing, still subsist for its proper surveillance, but may be overcome through the adoption of adequate diagnostic protocols and tools.

Antimicrobial susceptibility of bacterial isolates in south Sweden including a 13-year follow-up study of some respiratory tract pathogens

The antibiotic susceptibility of consecutive isolates of the upper respiratory tract pathogens Streptococcus pyogenes, Streptococcus pneumoniae, Haemophilus influenzae, Branhamella catarrhalis, and Staphylococcus aureus, (100 strains of each species collected each year during March through April 1985, 1988 and 1992) to penicillin V, amoxycillin, cefaclor, cefuroxime, doxycycline, erythromycin, and cotrimoxazole was investigated by MIC determination on PDM and PDM II agar. The MICs of the upper respiratory isolates from 1992 supplemented with 100 isolates each of Escherichia coli, Klebsiella spp., Enterobacter cloacae, Proteus mirabilis and Staphylococcus saprophyticus collected during 1992 were determined against the above antibiotics plus cefadroxil, cefpodoxime, roxithromycin, ciprofloxacin, ofloxacin, and BAY Y 3118. Beta-lactamase production was found in 10% of H. influenzae and 80-90% of S. aureus and B. catarrhalis in 1992. Among H. influenzae isolates, non-beta-lactamase-induced resistance to all beta-lactam antibiotics was first detected in 1988 and amounted to 3% of isolates in 1992. Decreased susceptibility of S. preumoniae to penicillin (> or = 0.12 mg/l), co-trimoxazole > or = 32 mg/l, doxycycline (> or = 2 ml/l) and erythromycin (> or = 1 mg/l) was detected in 11%, 7%, and 8%, respectively, in 1992, which is significantly higher than in previous years at the same laboratory. Decreased susceptibility of S. pyogenes to doxycycline and erythromycin was detected in 11% and 9% in 1992. The two most recently developed antibiotics, cefpodoxime and BAY Y 3118, showed high antibacterial activity. The study emphasizes the need to screen for resistance mechanisms such as beta-lactamase production and lowered penicillin affinity.

Genetic identification of exported proteins in Streptococcus pneumoniae

A strategy was developed to mutate and genetically identify exported proteins in Streptococcus pneumoniae. Vectors were created and used to screen pneumococcal DNA in Escherichia coli and S. pneumoniae for translational gene fusions to alkaline phosphatase (PhoA). Twenty five PhoA+ pneumococcal mutants were isolated and the loci from eight of these mutants showed similarity to known exported or membrane-associated proteins. Homologues were found to: (i) protein-dependent peptide permeases, (ii) penicillin-binding proteins, (iii) Clp proteases, (iv) two-component sensor regulators, (v) the phosphoenolpyruvate: carbohydrate phosphotransferases permeases, (vi) membrane-associated dehydrogenases, (vii) P-type (E1E2-type) cation transport ATPases, (viii) ABC transporters responsible for the translocation of the RTX class of bacterial toxins. Unexpectedly one PhoA+ mutant contained a fusion to a member of the DEAD protein family of ATP-dependent RNA helicases suggesting export of these proteins.

Genetic diversity of penicillin-binding protein 2B and 2X genes from Streptococcus pneumoniae in South Africa

Streptococcus pneumoniae (the pneumococcus) is believed to have developed resistance to penicillin by the production of altered forms of penicillin-binding proteins (PBPs) that have decreased affinity for penicillin. Sixty-eight clinical isolates of serogroup 6 and 19 pneumococci (MICs, < 0.015 to 8 micrograms/ml) were randomly selected from hospitals across South Africa which are at substantial geographic distance from each other. The polymerase chain reaction was used to isolate the penicillin-binding domain of PBPs 2B and 2X from the chromosomal DNAs of the bacteria; the purified PBP DNA was digested with restriction enzymes, the fragments were end-labelled and separated on polyacrylamide gels, and the DNA fingerprints were visualized following autoradiography. Fingerprint analysis revealed that at least 19 PBP 2B gene variants occur in the serogroup 6 and 19 pneumococci. The PBP 2B gene revealed a uniform profile among penicillin-susceptible isolates, with variation from this profile occurring only in isolates for which MICs were > or = 0.06 micrograms/ml. Analysis of the PBP 2X gene revealed a greater diversity in the population with 26 variant genes, including some diversity among susceptible isolates. Discrete profiles of both genes were found only within narrow bands of the penicillin MIC, so that the gene pattern predicted the MIC. PBP 2X gene variation and the lack of variability among PBP 2B genes in pneumococci inhibited at low MICs confirm that PBP 2X alteration may be responsible for low-level penicillin resistance, while alterations in both PBP 2B and PBP 2X are required for high-level resistance. The extensive diversity of PBP genes in South African serogroup 6 and 19 strains suggests that altered PBP genes have arisen frequently in this population.

Genetic relationships of penicillin-susceptible and -resistant Streptococcus pneumoniae strains isolated on different continents

Sixty-six strains of Streptococcus pneumoniae isolated in different parts of the world, 46 resistant and 22 susceptible to penicillin, were subdivided by multilocus enzyme electrophoresis into 28 distinct electrophoretic types (ETs). The ETs to which penicillin-susceptible strains were assigned differed from those containing resistant isolates of the same serotype. Five common clones could be recognized among the penicillin-resistant bacteria by combining the ETs, the antigenic properties of penicillin-binding proteins PBP 1a and 2b, and the tetracycline and chloramphenicol resistance profiles. Two clones were found in Finland and were associated with capsular serotypes 6B and 23F, respectively. Two clones were from Spain (type 6B and 9V, respectively). The fifth clone was isolated in South Africa and in Spain and contained both serotype 23F isolates and one type 19F strain. The other resistant strains were represented by rare isolates distributed among 12 other ETs, confirming that resistance to penicillin has evolved by multiple branches. Because capsular type was mixed in several ETs, the results also demonstrate that it may vary among very closely related pneumococci.

The crisis in antibiotic resistance

The synthesis of large numbers of antibiotics over the past three decades has caused complacency about the threat of bacterial resistance. Bacteria have become resistant to antimicrobial agents as a result of chromosomal changes or the exchange of the exchange of genetic material via plasmids and transposons. Streptococcus pneumoniae, Streptococcus pyogenes, and staphylococci, organisms that cause respiratory and cutaneous infections, and members of the Enterobacteriaceae and Pseudomonas families, organisms that cause diarrhea, urinary infection, and sepsis, are now resistant to virtually all of the older antibiotics. The extensive use of antibiotics in the community and hospitals has fueled this crisis. Mechanisms such as antibiotic control programs, better hygiene, and synthesis of agents with improved antimicrobial activity need to be adopted in order to limit bacterial resistance.

Purification and partial characterization of a penicillin-binding protein from Mycobacterium smegmatis

Penicillin-binding proteins (PBPs), although characterized from several organisms, have so far not been studied in mycobacteria. The present study is the first characterization of a PBP from Mycobacterium smegmatis. The PBP was purified by solubilization of the membranes with Triton X-100 and successive chromatography of the solubilized proteins on ampicillin-linked CH Sepharose 4B and DE-52. The purified PBP (M(r), 49,500) catalyzed a model transpeptidase reaction with the tripeptide acetyl2-L-Lys-D-Ala-D-Ala as the substrate and Gly-Gly as the acceptor. The transpeptidase activity was inhibited by 50% at a benzylpenicillin concentration of 1.8 x 10(-7) M, which was similar to the concentration (1.1 x 10(-7) M) of benzylpenicillin required to saturate to 50% this PBP. Of several antibiotics tested, the concentration of antibiotic required to inhibit [35S]penicillin binding by 90% was found to be the lowest for cefoxitin and Sch 34343.