Trends in incidence and resistance patterns of Staphylococcus aureus bacteremia.

BACKGROUND: Staphylococcus aureus bacteremia (SAB) causes a significant burden on the population. Several infection control measures have been implemented in Pirkanmaa county to combat a local epidemic with methicillin-resistant Staphylococcus aureus (MRSA). We aimed to study the epidemiology of SAB and antibiotic resistance of S. aureus and the possible influence of improved infection control. METHODS: Register data from 2005 to 2015 were retrospectively analysed to study the antimicrobial susceptibility, the incidence and mortality in SAB in a population-based setting. RESULTS: The incidence of SAB increased during the study period from 21.6 to 35.8/100,000 population. The number of both health care-associated (HA) and community-associated (CA) cases has increased. The incidence of MSSA bacteremia increased from 19.9 to 35.2/100,000 population in Pirkanmaa in parallel to other parts of Finland. The incidence of MRSA bacteremia was 10-fold (4.5/100,000 population) higher in 2011 than in other parts of the country, but sank to the national level (0.59/100,000 population) in 2015. The fatality rate decreased from 22% to 17%. The proportion of penicillin-susceptible Staphylococcus aureus (PSSA) increased from 23.9% in 2008 to 43.1% in 2015. CONCLUSION: The incidence of both HA and CA SAB has increased since 2005. Conversely, the proportion of MRSA and PRSA bacteremia has decreased. Promotion of infection control measures may have reduced the incidence of MRSA bacteremia but not the overall incidence of SAB. The rising proportion of PSSA enables the use of targeted, narrow spectrum antimicrobials.

Peptidoglycan Branched Stem Peptides Contribute to Streptococcus pneumoniae Virulence by Inhibiting Pneumolysin Release.

Streptococcus pneumoniae (the pneumococcus) colonizes the human nasopharynx and is a significant pathogen worldwide. Pneumolysin (Ply) is a multi-functional, extracellular virulence factor produced by this organism that is critical for pathogenesis. Despite the absence of any apparent secretion or cell surface attachment motifs, Ply localizes to the cell envelope of actively growing cells. We sought to characterize the consequences of this surface localization. Through functional assays with whole cells and subcellular fractions, we determined that Ply activity and its release into the extracellular environment are inhibited by peptidoglycan (PG) structure. The ability of PG to inhibit Ply release was dependent on the stem peptide composition of this macromolecule, which was manipulated by mutation of the murMN operon that encodes proteins responsible for branched stem peptide synthesis. Additionally, removal of choline-binding proteins from the cell surface significantly reduced Ply release to levels observed in a mutant with a high proportion of branched stem peptides suggesting a link between this structural feature and surface-associated choline-binding proteins involved in PG metabolism. Of clinical relevance, we also demonstrate that a hyperactive, mosaic murMN allele associated with penicillin resistance causes decreased Ply release with concomitant increases in the amount of branched stem peptides. Finally, using a murMN deletion mutant, we observed that increased Ply release is detrimental to virulence during a murine model of pneumonia. Taken together, our results reveal a novel role for branched stem peptides in pneumococcal pathogenesis and demonstrate the importance of controlled Ply release during infection. These results highlight the importance of PG composition in pathogenesis and may have broad implications for the diverse PG structures observed in other bacterial pathogens.

Penicillin-binding proteins: evergreen drug targets.

The penicillin-binding proteins (PBPs) are well known targets for the ß-lactam antibiotics. They continue to be a focus of interest for pharmaceutical design, as exemplified by the number of new agents under clinical investigation as well as novel experimental molecules. Considerable advances have been made in understanding the structure and function of this family of enzymes, through high-resolution structural studies and mechanistic studies in solution. These studies have thrown light on role of the high molecular mass PBPs in mediating ß-lactam resistance, although much work remains to be done to enable a full description of the mechanisms by which these proteins modulate their sensitivity towards ß-lactams while retaining their essential activity in cell wall biosynthesis.

Structural effect of the Asp345a insertion in penicillin-binding protein 2 from penicillin-resistant strains of Neisseria gonorrhoeae.

A hallmark of penicillin-binding protein 2 (PBP2) from penicillin-resistant strains of Neisseria gonorrhoeae is insertion of an aspartate after position 345. The insertion resides on a loop near the active site and is immediately adjacent to an existing aspartate (Asp346) that forms a functionally important hydrogen bond with Ser363 of the SxN conserved motif. Insertion of other amino acids, including Glu and Asn, can also lower the rate of acylation by penicillin, but these insertions abolish transpeptidase function. Although the kinetic consequences of the Asp insertion are well-established, how it impacts the structure of PBP2 is unknown. Here, we report the 2.2 Å resolution crystal structure of a truncated construct of PBP2 containing all five mutations present in PBP2 from the penicillin-resistant strain 6140, including the Asp insertion. Commensurate with the strict specificity for the Asp insertion over similar amino acids, the insertion does not cause disordering of the structure, but rather induces localized flexibility in the ß2c-ß2d loop. The crystal structure resolves the ambiguity of whether the insertion is Asp345a or Asp346a (due to the adjacent Asp) because the hydrogen bond between Asp346 and Ser362 is preserved and the insertion is therefore Asp346a. The side chain of Asp346a projects directly toward the ß-lactam-binding site near Asn364 of the SxN motif. The Asp insertion may lower the rate of acylation by sterically impeding binding of the antibiotic or by hindering breakage of the ß-lactam ring during acylation because of the negative charge of its side chain.

Comparison of microdilution and standard agar dilution method for determining Penicillin resistance among S.pneumoniae.

BACKGROUND: Antibiotic resistance among different microbial organisms is increasing. No study exists from Pakistan comparing methods of determining antibiotic resistance among bacterial isolates. METHODS: Ten clinical patient sample strains of S.pneumoniae were used to compare agar dilution with broth microdilution method for determining Minimum Inhibitory Concentrations (MICs) of Penicillin G. Agar dilution was conducted as per National Committee for Clinical Laboratory Standards. Broth microdilution was performed in Brain Heart Infusion broth using sterile plastic microtiter trays with 96 U-shaped wells. In both methods, concentration of Penicillin G ranged from 0.03 to 16µg/mL and S.aureus ATCC 29213 with an MIC of 0.25µg/mL was used as a control. MIC ≤0.06µg/mL was considered sensitivity to antibiotic, MIC 0.12-1.0 intermediate resistance and MIC ≥2 full resistance. RESULTS: Good agreement was found between two methods. Four strains gave identical MICs in both. The other six strains agreed to within one log2 dilution step. Both methods categorized same five strains as Penicillin sensitive and four as Penicillin resistant; one strain was classified as sensitive on agar dilution but resistant on broth microdilution. Broth microdilution was more expensive, tedious and time consuming than the agar dilution with multipoint inoculator. This would limit its clinical applicability in a busy diagnostic lab with a large sample turnover. CONCLUSIONS: We propose agar dilution for the clinical labs in developing countries that use Kirby-Bauer disk diffusion method and want to initiate MIC determination of antibiotics for patient samples.

Lipid II-independent trans editing of mischarged tRNAs by the penicillin resistance factor MurM.

Streptococcus pneumoniae is a causative agent of nosocomial infections such as pneumonia, meningitis, and septicemia. Penicillin resistance in S. pneumoniae depends in part upon MurM, an aminoacyl-tRNA ligase that attaches L-serine or L-alanine to the stem peptide lysine of Lipid II in cell wall peptidoglycan. To investigate the exact substrates the translation machinery provides MurM, quality control by alanyl-tRNA synthetase (AlaRS) was investigated. AlaRS mischarged serine and glycine to tRNA(Ala), as observed in other bacteria, and also transferred alanine, serine, and glycine to tRNA(Phe). S. pneumoniae tRNA(Phe) has an unusual U4:C69 mismatch in its acceptor stem that prevents editing by phenylalanyl-tRNA synthetase (PheRS), leading to the accumulation of misaminoacylated tRNAs that could serve as substrates for translation or for MurM. Although the peptidoglycan layer of S. pneumoniae tolerates a combination of both branched and linear muropeptides, deletion of MurM results in a reversion to penicillin sensitivity in strains that were previously resistant. However, because MurM is not required for cell viability, the reason for its functional conservation across all strains of S. pneumoniae has remained elusive. We now show that MurM can directly function in translation quality control by acting as a broad specificity lipid-independent trans editing factor that deacylates tRNA. This activity of MurM does not require the presence of its second substrate, Lipid II, and can functionally substitute for the activity of widely conserved editing domain homologues of AlaRS, termed AlaXPs proteins, which are themselves absent from S. pneumoniae.

Mechanisms of action of systemic antibiotics used in periodontal treatment and mechanisms of bacterial resistance to these drugs.

Antibiotics are important adjuncts in the treatment of infectious diseases, including periodontitis. The most severe criticisms to the indiscriminate use of these drugs are their side effects and, especially, the development of bacterial resistance. The knowledge of the biological mechanisms involved with the antibiotic usage would help the medical and dental communities to overcome these two problems. Therefore, the aim of this manuscript was to review the mechanisms of action of the antibiotics most commonly used in the periodontal treatment (i.e. penicillin, tetracycline, macrolide and metronidazole) and the main mechanisms of bacterial resistance to these drugs. Antimicrobial resistance can be classified into three groups: intrinsic, mutational and acquired. Penicillin, tetracycline and erythromycin are broad-spectrum drugs, effective against gram-positive and gram-negative microorganisms. Bacterial resistance to penicillin may occur due to diminished permeability of the bacterial cell to the antibiotic; alteration of the penicillin-binding proteins, or production of ß-lactamases. However, a very small proportion of the subgingival microbiota is resistant to penicillins. Bacteria become resistant to tetracyclines or macrolides by limiting their access to the cell, by altering the ribosome in order to prevent effective binding of the drug, or by producing tetracycline/macrolide-inactivating enzymes. Periodontal pathogens may become resistant to these drugs. Finally, metronidazole can be considered a prodrug in the sense that it requires metabolic activation by strict anaerobe microorganisms. Acquired resistance to this drug has rarely been reported. Due to these low rates of resistance and to its high activity against the gram-negative anaerobic bacterial species, metronidazole is a promising drug for treating periodontal infections.

Mechanisms of action of systemic antibiotics used in periodontal treatment and mechanisms of bacterial resistance to these drugs

Antibiotics are important adjuncts in the treatment of infectious diseases, including periodontitis. The most severe criticisms to the indiscriminate use of these drugs are their side effects and, especially, the development of bacterial resistance. The knowledge of the biological mechanisms involved with the antibiotic usage would help the medical and dental communities to overcome these two problems. Therefore, the aim of this manuscript was to review the mechanisms of action of the antibiotics most commonly used in the periodontal treatment (i.e. penicillin, tetracycline, macrolide and metronidazole) and the main mechanisms of bacterial resistance to these drugs. Antimicrobial resistance can be classified into three groups: intrinsic, mutational and acquired. Penicillin, tetracycline and erythromycin are broad-spectrum drugs, effective against gram-positive and gram-negative microorganisms. Bacterial resistance to penicillin may occur due to diminished permeability of the bacterial cell to the antibiotic; alteration of the penicillin-binding proteins, or production of β-lactamases. However, a very small proportion of the subgingival microbiota is resistant to penicillins. Bacteria become resistant to tetracyclines or macrolides by limiting their access to the cell, by altering the ribosome in order to prevent effective binding of the drug, or by producing tetracycline/macrolide-inactivating enzymes. Periodontal pathogens may become resistant to these drugs. Finally, metronidazole can be considered a prodrug in the sense that it requires metabolic activation by strict anaerobe microorganisms. Acquired resistance to this drug has rarely been reported. Due to these low rates of resistance and to its high activity against the gram-negative anaerobic bacterial species, metronidazole is a promising drug for treating periodontal infections.

An extracytoplasmic function sigma factor controls beta-lactamase gene expression in Bacillus anthracis and other Bacillus cereus group species.

The susceptibility of most Bacillus anthracis strains to beta-lactam antibiotics is intriguing considering that the closely related species Bacillus cereus and Bacillus thuringiensis typically produce beta-lactamases and the B. anthracis genome harbors two beta-lactamase genes, bla1 and bla2. We show that beta-lactamase activity associated with B. anthracis is affected by two genes, sigP (BA2502) and rsiP (BA2503), predicted to encode an extracytoplasmic function sigma factor and an anti-sigma factor, respectively. Deletion of the sigP-rsiP locus abolished beta-lactamase activity in a naturally occurring penicillin-resistant strain and had no effect on beta-lactamase activity in a prototypical penicillin-susceptible strain. Complementation with sigP and rsiP from the penicillin-resistant strain, but not with sigP and rsiP from the penicillin-susceptible strain, conferred constitutive beta-lactamase activity in both mutants. These results are attributed to a nucleotide deletion near the 5' end of rsiP in the penicillin-resistant strain that is predicted to result in a nonfunctional protein. B. cereus and B. thuringiensis sigP and rsiP homologues are required for inducible penicillin resistance in these species. Expression of the B. cereus or B. thuringiensis sigP and rsiP genes in a B. anthracis sigP-rsiP-null mutant confers inducible production of beta-lactamase activity, suggesting that while B. anthracis contains the genes necessary for sensing beta-lactam antibiotics, the B. anthracis sigP and rsiP gene products are not sufficient for bla induction.

Penicillin resistance in the intestinal spirochaete Brachyspira pilosicoli associated with OXA-136 and OXA-137, two new variants of the class D beta-lactamase OXA-63.

Penicillin resistance mediated by beta-lactamase activity has been reported previously in the anaerobic intestinal spirochaete Brachyspira pilosicoli, and a novel class D beta-lactamase (OXA-63) hydrolysing oxacillin was described recently in a resistant human strain from France. In the current study, 18 B. pilosicoli strains from Australia and Papua New Guinea were tested for ampicillin and oxacillin susceptibility, and investigated for the presence of the class D beta-lactamase gene blaOXA-63 using PCR. PCR products were amplified from seven human and four porcine strains that were penicillin resistant, but not from seven penicillin-sensitive strains. Sequence analysis of the whole gene amplified from seven of the resistant strains from humans and pigs revealed only minor nucleotide differences among them, but there were significant differences compared with blaOXA-63. The predicted amino acid sequence of the enzyme from all seven strains had the same key structural motifs as the previously reported OXA-63, but two variants with 94-95% identity with OXA-63 were identified. OXA-136 had an additional amino acid and 12 other consistent amino acid substitutions compared with OXA-63. OXA-137 had the same differences compared with OXA-63 as OXA-136, but had an additional amino acid substitution at position 16. No structures consistent with integrons or transposons were found in the nucleotide sequences in the vicinity of blaOXA-136 in partially sequenced B. pilosicoli strain 95/1000, and the GC content (25.2 mol%) of the gene was similar to that of the whole genome. The gene encoding OXA-136 from B. pilosicoli strain Cof-10 conferred penicillin resistance on Escherichia coli. This study shows that penicillin resistance in human and porcine B. pilosicoli strains from Australia is associated with the production of two variants of OXA-63, and that susceptible strains lack the genes encoding OXA-63 or the variants.

Beta-lactam activity against penicillin-resistant Streptococcus pneumoniae strains exhibiting higher amoxicillin versus penicillin minimum inhibitory concentration values: an in vitro pharmacodynamic simulation.

BACKGROUND: Activity of simulated serum concentrations after oral therapy with 400 mg cefditoren pivoxil b.i.d., 500 mg cefuroxime axetil b.i.d. and 875/125 mg amoxicillin/clavulanic acid b.i.d. and t.i.d. regimens was explored over 24 h against Streptococcus pneumoniae. METHODS: Computerized pharmacodynamic simulations were performed against strains with penicillin/amoxicillin/cefuroxime/cefditoren minimum inhibitory concentrations (MICs, microg/ml) and serotypes: strain 1 (0.25/0.12/1/0.12; serotype 6A), strain 2 (2/4/ 2/0.25; serotype 6B), strain 3 (4/16/4/0.5; serotype 14), and strain 4 (4/16/8/1; serotype 14). RESULTS: Bactericidal activity (> or =3 log(10) reduction) at 12 and 24 h was obtained against all strains with cefditoren, against strains 1 and 2 with cefuroxime and amoxicillin/clavulanic acid t.i.d., but only against strain 1 with amoxicillin/clavulanic acid b.i.d.. Bactericidal activity at 24 h was related to T > MIC of >30% dosing interval, 1.7-2.0 log(10) reductions with T > MIC of 20-30%, and <1 log(10) reduction or regrowth with T > MIC of 0%. CONCLUSIONS: It is difficult to achieve pharmacodynamic coverage and bactericidal activity by physiological concentrations of oral beta-lactams against penicillin-resistant pneumococcal strains exhibiting higher amoxicillin versus penicillin MICs. Cefditoren may offer alternatives.

Effects of EDP-420 on penicillin-resistant and quinolone- and penicillin-resistant pneumococci in the rabbit meningitis model.

OBJECTIVES: To test the efficacy of EDP-420, a new ketolide, in experimental pneumococcal meningitis and to determine its penetration into the CSF. METHODS: The experimental rabbit model was used in this study and EDP-420 was tested against a penicillin-resistant and a penicillin- and quinolone-resistant mutant. EDP-420 was also tested against both strains in time-killing assays over 8 h in vitro. RESULTS: In experimental meningitis, EDP-420 produced a bactericidal activity comparable to the standard regimen based on a combination of vancomycin with ceftriaxone against a penicillin-resistant Streptococcus pneumoniae and a penicillin- and quinolone-resistant S. pneumoniae isolate. The penetration of EDP-420 into inflamed meninges was 38% after an i.v. injection of 10 mg/kg. The bactericidal activity of EDP-420 was also confirmed in in vitro time-killing assays. CONCLUSIONS: EDP-420 is an efficacious alternative treatment in pneumococcal meningitis, especially when resistant strains are suspected.

[Streptococcus pneumoniae meningitis in Amiens Hospital between 1990 and 2005. Bacteriological characteristics of strains isolated]. / Les méningites à Streptococcus pneumoniae au CHU d'Amiens de 1990 à 2005. Aspects bactériologiques des souches isolées.

Streptococcus pneumoniae is actually the first most likely organism to cause meningitis in children 2 months to 2 years old and in adults older than 65 years. From January 1990 to December 2005, 72 cases of S. pneumoniae-positive cerebrospinal fluid culture were indexed in our hospital. Among the 72 cases, 25 came from children, and 60% of these came from children under two years of age and 47 came from adults whose the mean age was 55 years. The first penicillin-resistant S. pneumoniae (PNSP) meningitis was identified in 1993. The susceptibility to penicillin of pneumococcal isolates causing meningitis varied according to time; until 1995, 25% of the strains were PNSP, then from 1996 to 2005, 50% of strains were PNSP. The overall prevalence of non-susceptible was 34.7% (25/72). Among the 25 PNSP, 21 were intermediate to penicillin G and four of them were resistant. Among children, seven PNSP meningitis were indexed and one of them was resistant. The antimicrobial MICs of amoxicillin and cefotaxim varied from 0.064 to 1 mg/l and from 0.016 to 0.5 mg/l respectively. Among adults, 18 PNSP meningitis were indexed. Three strains were penicillin-resistant. The antimicrobial MICs of amoxicillin varied from 0.064 to 2 mg/l. Nine strains of 18 PNSP had cefotaxim MIC>/=0.5 mg/l and, four of them had MIC 1 mg/l. None amoxicillin and cefotaxim-resistant strain was isolated. Serotyping of all strains was performed in the Reference Center. Serotypes 6B, 9V and 19 were the most frequent in child and serotypes 6B, 23F, 19, 9, 4 were the most frequent in adult. So, all serotypes were represented.

Antibiotic resistance in the southeastern Mediterranean--preliminary results from the ARMed project.

Sporadic reports from centres in the south and east of the Mediterranean have suggested that the prevalence of antibiotic resistance in this region appears to be considerable, yet pan-regional studies using comparable methodology have been lacking in the past. Susceptibility test results from invasive isolates of Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli, Enterococcus faecium and faecalis routinely recovered from clinical samples of blood and cerebrospinal fluid within participating laboratories situated in Algeria, Cyprus, Egypt, Jordan, Lebanon, Malta, Morocco, Tunisia and Turkey were collected as part of the ARMed project. Preliminary data from the first two years of the project showed the prevalence of penicillin non-susceptibility in S. pneumoniae to range from 0% (Malta) to 36% (Algeria) [median: 29%] whilst methicillin resistance in Staphylococcus aureus varied from 10% in Lebanon to 65% in Jordan [median: 43%]. Significant country specific resistance in E. coli was also seen, with 72% of isolates from Egyptian hospitals reported to be resistant to third generation cephalosporins and 40% non-susceptible to fluoroquinolones in Turkey. Vancomycin non-susceptibility was only reported in 0.9% of E. faecalis isolates from Turkey and in 3.8% of E. faecium isolates from Cyprus. The preliminary results from the ARMed project appear to support previous sporadic reports suggesting high antibiotic resistance in the Mediterranean region. They suggest that this is particularly the case in the eastern Mediterranean region where resistance in S. aureus and E. coli seems to be higher than that reported in the other countries of the Mediterranean.

[Present situation of antibiotic resistances in tonsillar infections]. / Situación actual de las resistencias a antibióticos en infecciones amigdalares.

OBJECTIVE: To obtain the main responsible organisms, its sensitivity and resistances to antibiotics in tonsillitis. MATERIAL AND METHODS: We have studied the post-surgical tonsils, carrying out a microbiologic study, its culture and sensitivity. RESULTS: The most frequent isolated organisms were Staphylococcus aureus (29.3%), followed by Streptococcus pyogenes (23.4%), and Haemophilus influenzae (12.1%). The highest resistances were for the S. aureus (penicillin 91%, erythromycin 18% and 5% to the rest of the beta-lactams), followed by H. influenzae (50% clarithromycin, 30% amoxyciIlin and 2% cephalosporins) and S. pyogenes (28% erytromycin, 10% clindamycin and 3% penicillin). CONCLUSIONS: We noticed the minimal resistance found to cephalosporins, and for this reason they appear to be the safest option, except in children under five years old, in which amoxicillin is still the first line treatment, because the causative agent is S. pyogenes, sensitive to that antibiotic.

Situación actual de las resistencias a antibióticos en infecciones amigdalares / Present situation of antibiotic resistances in tonsillar infections

Objetivo: Obtener los principales microorganismos y resistencias a antibióticos en infecciones amigdalares. Material y métodos: Realizamos un estudio microbiológico con antibiograma de amígdalas palatinas postquirúrgicas. Resultados: Los microorganismos más aislados han sido el Staphylococcus aureus (29,3%) seguido del Streptococcus pyogenes (23,4%), y del Haemophilus influenzae (12,1%). Las mayores resistencias fueron para el S. aureus (91% a la penicilina, 18% a la eritromicina y un 5% al resto de β-lactámicos), seguido del H. influenzae (50% a la claritromicina, 30% a la amoxicilina y 2% a cefalosporinas) y por último el S. pyogenes (28% a la eritromicina, 10% a la clindamicina y 3% a la penicilina). Conclusiones: Destacamos la mínima resistencia encontrada a las cefalosporinas por lo que parece ser el grupo antibiótico más seguro, excepto en los niños menores de 5 años en los cuales la amoxicilina sigue siendo de primera elección dado que están provocadas por S. pyogenes sensibles a dicho antibiótico

Objective: To obtain the main responsible organisms, its sensitivity and resistances to antibiotics in tonsillitis. Material and methods: We have studied the post-surgical tonsils, carrying out a microbiologic study, its culture and sensitivity. Results: The most frequent isolated organisms were Staphylococcus aureus (29.3%), followed by Streptococcus pyogenes (23.4%), and Haemophilus influenzae (12.1%). The highest resistances were for the S. aureus (penicillin 91%, erythromycin 18% and 5% to the rest of the β-lactams), followed by H. influenzae (50% clarithromycin, 30% amoxycillin and 2% cephalosporins) and S. pyogenes (28% erytromycin, 10% clindamycin and 3% penicillin). Conclusions: We noticed the minimal resistance found to cephalosporins, and for this reason they appear to be the safest option, except in children under five years old, in which amoxicillin is still the first line treatment, because the causative agent is S. pyogenes, sensitive to that antibiotic

Serotype distribution and antibiotic susceptibility of invasive and nasopharyngeal isolates of Streptococcus pneumoniae among children in rural Mozambique.

OBJECTIVE: To describe and compare serotype distribution and antibiotic susceptibility of invasive and nasopharyngeal isolates of Streptococcus pneumoniae from children in rural Mozambique. METHODS: From August 2002 to July 2003, we prospectively obtained invasive pneumococcal isolates from children <15 years of age admitted to the paediatric ward of Manhiça District Hospital. During a cross-sectional study of children <5 years of age with mild illnesses, attending the outpatient department of the hospital in March and April 2003, we collected nasopharyngeal isolates. Serotypes and antibiotic susceptibilities were determined using standardized methods. RESULTS: The two most common pneumococcal serotypes among invasive isolates were types 1 (40% of 88 isolates serotyped) and 5 (10%), but these types were rare among nasopharyngeal isolates. Compared with invasive isolates, nasopharyngeal isolates were more likely to be serotypes in the licensed seven-valent conjugate vaccine (49%vs. 20%, P < 0.01), to have intermediate-level penicillin resistance (52%vs. 14%, P < 0.01) and to be non-susceptible to trimethoprim-sulfamethoxazole (61%vs. 45%, P < 0.01). Recent receipt of antibiotics or sulfadoxine/pyrimethamine were associated with carriage of antibiotic non-susceptible isolates. CONCLUSIONS: These data indicate that a pneumococcal conjugate vaccine containing serotypes 1 and 5 could substantially reduce pneumococcal invasive disease among young children in rural Mozambique. Carriage surveys can overestimate potential coverage of the seven-valent pneumococcal conjugate vaccine in settings where serotypes 1 and 5 predominate.

Beta-lactam resistance in Staphylococcus aureus cells that do not require a cell wall for integrity.

Staphylococcus aureus ATCC 9144 cells with defective cell walls were generated on a medium with elevated osmolality in the presence of sublethal levels of penicillin G. On removal of antibiotic pressure, the cells exhibited stable penicillin and methicillin resistance. The resistance was homogeneous and its acquisition was enhanced following transient cell wall-defective growth. The resistant cells were mecA negative, beta-lactamase negative and did not contain any mutations in the coding regions of pbp genes. When penicillin was added back to resistant cells, they continued to grow and produced a diffuse cell wall that was resistant to the action by lysostaphin but was very sensitive to lysis with Triton X-100. These data indicate that the resistant cells are not dependent upon an intact cell wall for osmotic stability and they are able to switch readily to this mode of growth in the presence of penicillin G.

Altered PBP 2A and its role in the development of penicillin, cefotaxime, and ceftriaxone resistance in a clinical isolate of Streptococcus pneumoniae.

We report the unusual involvement of altered PBP 2A in the development of beta-lactam resistance in Streptococcus pneumoniae. This was investigated amid three identical serotype 14 isolates (designated isolates 1, 2, and 3, respectively) of pneumococci cultured successfully from the blood of a human immunodeficiency virus-seropositive child with recurrent pneumonia. The passage of this strain through its human host induced several changes in the bacterium, which is typical of the adaptive and evolving nature of the pneumococcus. An efflux resistance mechanism, which conferred increased ciprofloxacin resistance, was induced in isolates 2 and 3. In addition, faster growth rates and larger capsules were also observed for these isolates, with respect to isolate 1. Notably, compared to isolates 1 and 2, isolate 3 showed a decrease in penicillin, cefotaxime, and ceftriaxone resistance. This change was associated with the replacement of an altered PBP 2A for an unaltered PBP 2A. In all likelihood, these events produced a strain which evolved into a fitter and more virulent type, isolate 3, that resulted in an aggravated pneumococcal infection and ultimately in the patient's death.