No abstract

We have identified an unusual group of viridans group streptococci that resemble Streptococcus pneumoniae. DNA-DNA homology studies suggested that a subset of these isolates represent a novel species that may be included in the S. oralis-S. mitis group of viridans group streptococci. We suggest that this novel species be termed Streptococcus pseudopneumoniae. A combination of phenotypic and genetic reactions allows its identification. S. pseudopneumoniae strains do not have pneumococcal capsules, are resistant to optochin (inhibition zones, less than 14 mm) when they are incubated under an atmosphere of increased CO 2 but are susceptible to optochin (inhibition zones, >14 mm) when they are incubated in ambient atmospheres, are not soluble in bile, and are positive by the GenProbe AccuProbe Pneumococcus test. The bile solubility test is more specific than the optochin test for identification of S. pneumoniae. Genetic tests for pneumolysin (ply) and manganesedependent superoxide dismutase (sodA) and identification tests with a commercial probe, AccuProbe Pneumococcus, do not discriminate between the new species and S. pneumoniae.Streptococcus pneumoniae is the most common cause of community-acquired pneumonia and is also associated with bacteremia, meningitis, otitis media, and sinusitis, accounting for approximately 3,000 cases of meningitis, 50,000 cases of bacteremia, 500,000 cases of pneumonia, and 7 million cases of otitis media each year in the United States (1). Clinical laboratories must be able to accurately differentiate S. pneumoniae from other viridans group streptococci commonly found in clinical samples. An inability to correctly identify S. pneumoniae may result in inappropriate antimicrobial therapy.S. pneumoniae is a member of the Streptococcus mitis-Streptococcus oralis group (the Smit group) of viridans group streptococci, which includes S. mitis, S. oralis, Streptococcus cristatus, Streptococcus infantis, and Streptococcus peroris. Differentiation of S. pneumoniae from other viridans group streptococci, including members of the Smit group, has conventionally been based on phenotypic characteristics, most commonly by demonstrating optochin (OPT) susceptibility and/or solubility in bile (sodium deoxycholate) (18). Identification by these two tests is satisfactory when isolates from sterile sites are tested (16). However, identification is often problematic when samples from nonsterile sites, such as respiratory samples, are tested. The results of phenotypic testing can result in ambiguous OPT susceptibility and bile solubility (BS) test results (18).Although they are uncommon, OPT resistance has been reported in S. pneumoniae and OPT-resistant subpopulations have also been reported, both of which may lead to problems in identification, especially in association with atypical colony morphologies (4,13,36,42,45,46,55,60). Gardam and Miller (21) reported that variances in OPT zone sizes are dependent on the test medium and incubation environment used, as some media and environments may result in f...

We report on amino acid substitutions in the quinolone resistance-determining region of type II topisomerases and the prevalence of reserpine-inhibited efflux for 70 clinical isolates of S. pneumoniae for which the ciprofloxacin MIC is >4 g/ml and 28 isolates for which the ciprofloxacin MIC is <2 g/ml.

Over the course of a 20-month period, in a hospital respiratory ward in which ciprofloxacin was often used as empirical antimicrobial therapy for lower respiratory tract infections (LRTIs), 16 patients with chronic bronchitis developed nosocomial LRTIs caused by penicillin- and ciprofloxacin-resistant Streptococcus pneumoniae (serotype 23 F). The minimum inhibitory concentration (MIC) of ciprofloxacin for all isolates from the first 9 patients was 4 microg/mL, in association with a parC mutation. Isolates from the subsequent 7 patients all had a ciprofloxacin MIC of 16 microg/mL, in association with an additional mutation in gyrA. The MICs for this isolate were 8 microg/mL of levofloxacin (resistant), 2 microg/mL of moxifloxacin and gatifloxacin (intermediately resistant), and 0.12 microg/mL of gemifloxacin. This outbreak demonstrates the ability of S. pneumoniae to acquire multiple mutations that result in increasing levels of resistance to the fluoroquinolones and to be transmitted from person to person.

DIBI, a purpose-designed hydroxypyridinone-containing iron-chelating antimicrobial polymer was studied for its anti-staphylococcal activities in vitro in comparison to deferiprone, the chemically related, small molecule hydroxypyridinone chelator. The sensitivities of 18 clinical isolates of Staphylococcus aureus from human, canine and bovine infections were determined. DIBI was strongly inhibitory to all isolates, displaying approximately 100-fold more inhibitory activity than deferiprone when compared on their molar iron-binding capacities. Sensitivity to DIBI was similar for both antibiotic-resistant and -sensitive isolates, including hospital- and community-acquired (United States 300) MRSA. DIBI inhibition was primarily bacteriostatic in nature at low concentration and was reversible by addition of Fe. DIBI also exhibited in vivo anti-infective activity in two distinct MRSA ATCC43300 infection and colonization models in mice. In a superficial skin wound infection model, topical application of DIBI provided a dose-dependent suppression of infection along with reduced wound inflammation. Intranasal DIBI reduced staphylococcal burden by >2 log in a MRSA nares carriage model. DIBI was also examined for its influence on antibiotic activities with a reference isolate ATCC6538, typically utilized to assess new antimicrobials. Sub-bacteriostatic concentrations of DIBI resulted in Fe-restricted growth and this physiological condition displayed increased sensitivity to GEN, CIP, and VAN. DIBI did not impair antibiotic activity but rather it enhanced overall killing. Importantly, recovery growth of survivors that typically followed an initial sub-MIC antibiotic killing phase was substantially suppressed by DIBI for each of the antibiotics examined. DIBI has promise for restricting staphylococcal infection on its own, regardless of the isolate’s animal source or antibiotic resistance profile. DIBI also has potential for use in combination with various classes of currently available antibiotics to improve their responses.

Streptococcus pyogenes is an important human pathogen worldwide. The identification of natural antibacterial phytochemicals has renewed interest due to the current scarcity of antibiotic development. Carvacrol is a monoterpenoid found in herbs. We evaluated carvacrol alone and combined with selected antibiotics against four strains of S. pyogenes in vitro. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of carvacrol against S. pyogenes were 125 µg/mL (0.53 mM) and 250 µg/mL (1.05 mM), respectively. Kill curve results showed that carvacrol exhibits instantaneous bactericidal activity against S. pyogenes. We also demonstrated the potential mechanism of action of carvacrol through compromising the cell membrane integrity. Carvacrol induced membrane integrity changes leading to leakage of cytoplasmic content such as lactate dehydrogenase enzymes and nucleic acids. We further confirmed dose-dependent rupturing of cells and cell deaths using transmission electron microscopy. The chequerboard assay results showed that carvacrol possesses an additive-synergistic effect with clindamycin or penicillin. Carvacrol alone, combined with clindamycin or penicillin, can be used as a safe and efficacious natural health product for managing streptococcal pharyngitis.

Legionella pneumophila expresses two catalase-peroxidase enzymes that exhibit strong peroxidatic but weak catalatic activities, suggesting that other enzymes participate in decomposition of hydrogen peroxide (H 2 O 2 ). Comparative genomics revealed that L. pneumophila and its close relative Coxiella burnetii each contain two peroxide-scavenging alkyl hydroperoxide reductase (AhpC) systems: AhpC1, which is similar to the Helicobacter pylori AhpC system, and AhpC2 AhpD (AhpC2D), which is similar to the AhpC AhpD system of Mycobacterium tuberculosis. To establish a catalatic function for these two systems, we expressed L. pneumophila ahpC1 or ahpC2 in a catalase/peroxidase mutant of Escherichia coli and demonstrated restoration of H 2 O 2 resistance by a disk diffusion assay. ahpC1::Km and ahpC2D::Km chromosomal deletion mutants were two-to eightfold more sensitive to H 2 O 2 , tert-butyl hydroperoxide, cumene hydroperoxide, and paraquat than the wild-type L. pneumophila, a phenotype that could be restored by trans-complementation. Reciprocal strategies to construct double mutants were unsuccessful. Mutant strains were not enfeebled for growth in vitro or in a U937 cell infection model. Green fluorescence protein reporter assays revealed expression to be dependent on the stage of growth, with ahpC1 appearing after the exponential phase and ahpC2 appearing during early exponential phase. Quantitative real-time PCR showed that ahpC1 mRNA levels were ϳ7-to 10-fold higher than ahpC2D mRNA levels. However, expression of ahpC2D was significantly increased in the ahpC1 mutant, whereas ahpC1 expression was unchanged in the ahpC2D mutant. These results indicate that AhpC1 or AhpC2D (or both) provide an essential hydrogen peroxide-scavenging function to L. pneumophila and that the compensatory activity of the ahpC2D system is most likely induced in response to oxidative stress.

Empirical treatment is best guided by current surveillance of local resistance patterns. The goal of this study is to characterize the prevalence of antimicrobial nonsusceptibility within pneumococcal isolates from Canada. The Canadian Bacterial Surveillance Network is comprised of laboratories from across Canada. Laboratories collected a defined number of consecutive clinical and all sterile site isolates of S. pneumoniae in 2002. In vitro susceptibility testing was performed by broth microdilution with NCCLS guidelines. Rates of nonsusceptibility were compared to previously published reports from the same network. A total of 2,539 isolates were tested. Penicillin nonsusceptibility increased to 15% (8.5% intermediate, 6.5% resistant) compared to 12.4% in 2000 (P < 0.025, 2 ). Only 32 (1.3%) isolates had an amoxicillin MIC of >4 g/ml and only 2 of 32 cerebrospinal fluid isolates had an intermediate susceptibility to ceftriaxone by meningeal interpretive criteria (MIC ‫؍‬ 1 g/ml). A total of 354 (13.9%) isolates were macrolide nonsusceptible (46.3% MLS B , 56.7% M phenotype), increasing from 11.4% in 2000 (P < 0.0075, 2 ). Only 13 (<1%) isolates had a telithromycin MIC of >1 g/ml. Ciprofloxacin nonsusceptibility (defined as an MIC of >4 g/ml) increased to 2.7% compared to 1.4% in 2000 (P < 0.0025, 2 ) and was primarily found in persons >18 years old (98.5%). Nonsusceptibility to penicillin, macrolides, and fluoroquinolones is increasing in Canada. Nonsusceptibility to amoxicillin and ceftriaxone remains uncommon. Newer antimicrobials such as telithromycin and respiratory fluoroquinolones have excellent in vitro activity.