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Biomedical subjects

G D Christensen

Publications and source records attributed to G D Christensen.

At least 19 recordsLinked to original sources
PubMed2001

Synergy between Staphylococcus aureus and Pseudomonas aeruginosa in a rat model of complex orthopaedic wounds.

BACKGROUND: We observed an interaction in animals inoculated concomitantly with Staphylococcus aureus and Pseudomonas aeruginosa during a study of the efficacy of surfactants for disinfection of orthopaedic wounds. This led us to investigate whether synergy could be demonstrated between Staphylococcus aureus and Pseudomonas aeruginosa in a rat model of complex orthopaedic wounds. METHODS: A wire was implanted into the spinous process of a lumbar vertebra of Sprague-Dawley rats through a dorsal incision. Animals were divided into two groups: group one was inoculated with either Staphylococcus aureus or Pseudomonas aeruginosa, and group two received a polymicrobial inoculation with both test organisms in varying concentrations. After inoculation, the wounds were irrigated and closed. On postoperative day 14, all animals were killed and specimens from the wounds were cultured. The number of colony-forming units (CFU) of Staphylococcus aureus or Pseudomonas aeruginosa needed to cause infection in 50% of the animals (ID50) was determined with use of the Reed-Muench method. The infection rate associated with each inoculum combination was calculated, and the two groups were compared. RESULTS: The ID50 was 2.8 x 10(4) CFU for Staphylococcus aureus and 4.8 x 10(5) CFU for Pseudomonas aeruginosa. The combination of 10(3) CFU of Staphylococcus aureus with low concentrations (10(2), 10(3), or 10(4) CFU) of Pseudomonas aeruginosa yielded infection rates that were higher than those found with either organism alone at the same concentrations. The combination of 10(3) CFU of Staphylococcus aureus and 10(3) CFU of Pseudomonas aeruginosa yielded a 75% infection rate, which was significantly higher (p = 0.004) than that associated with 10(3) CFU of either organism alone. As the Pseudomonas aeruginosa concentration was increased (to 10(5), 10(6), and 10(7) CFU), this trend reversed, and the infection rate decreased to 33% (p = 0.004). Low concentrations of Pseudomonas aeruginosa (0 to 10(5) CFU) combined with 10(6) CFU of Staphylococcus aureus yielded infection rates ranging from 83% to 100%. At the higher concentrations of Pseudomonas aeruginosa (10(6) and 10(7) CFU), however, the infection rate again decreased, to 33% (p = 0.005). Only Staphylococcus aureus was isolated from the cultures of the specimens from the animals that had received a polymicrobial inoculum. CONCLUSIONS: Synergy between Staphylococcus aureus and Pseudomonas aeruginosa was demonstrated when low levels of each organism were present in the wound. As the Pseudomonas aeruginosa concentration was increased, the infection rates fell well below what would be anticipated, suggesting that low concentrations of Pseudomonas aeruginosa enhance the ability of Staphylococcus aureus to cause infection in this orthopaedic wound model. At the same time, the presence of Staphylococcus aureus in the ratios tested decreased the rate of infection by Pseudomonas aeruginosa. CLINICAL RELEVANCE: Staphylococcus aureus is a pathogen commonly seen in orthopaedic patients. The pathogenicity of Staphylococcus aureus was shown to be increased in the presence of anaerobic bacteria. This study is the first one that we are aware of that demonstrated synergy between Staphylococcus aureus and Pseudomonas aeruginosa, at low concentrations, in a wound model while at the same time showing that Staphylococcus aureus lowers the rate of Pseudomonas aeruginosa infection.

Animals↗
PubMed1999

Sequential irrigation with common detergents: a promising new method for decontaminating orthopedic wounds.

This investigation sought to determine the capacity of irrigation solutions in decontaminating orthopedic wounds challenged with a polymicrobial inoculum. Rats were divided into two groups, a control group and a treatment group. After creation of a dorsolumbar incision and placement of a wire through the spinous process, rats were inoculated with Staphylococcus aureus and Pseudomonas aeruginosa. Wounds were irrigated with control or treated solutions. At 2 weeks, cultures were obtained. There were statistically significant differences between groups regarding total number of culture positive sites (P < 0.001), culture-positive animals (P = 0.02), and quantitative cultures (P < 0.02). Sequential irrigation with surfactants lowers bacteria counts recovered from polymicrobial wounds.

Analysis of Variance↗
PubMed1997

Expression of slime interferes with in vitro detection of host protein receptors of Staphylococcus epidermidis.

We hypothesized that slime may mask bacterial molecules important in the attachment of Staphylococcus epidermidis to inanimate surfaces. In support of this hypothesis, we found that slime-negative strains attached significantly better to fibrinogen or fibronectin than the parent strains and exhibited greater surface hydrophobicity. Comparable results were obtained with 53 clinical isolates.

Antigens, Bacterial↗
PubMed1996

Purification and characterization of the staphylococcal slime-associated antigen and its occurrence among Staphylococcus epidermis clinical isolates.

The Staphylococcus epidermidis slime-associated antigen (SAA) was purified and characterized. N-Acetyl-glucosamine accounted for 70% of the dry weight of SAA, which was immunolocalized on the ruthenium red-positive material produced by slime-positive strains. A total of 59% of slime-producing S. epidermidis clinical isolates expressed SAA, while the phenotype slime- SAA+ was never recovered.

Acetylglucosamine↗
PubMed1993

Variable fixation of staphylococcal slime by different histochemical fixatives.

A variety of histochemical fixatives were used to compare the fixation of bacterial films produced by a standard slime-producing strain of Staphylococcus epidermidis on plastic tissue culture plates. Some reagents were completely ineffective in fixing the slime layer, whereas others gave variable results. The best alternative to the fixative of the reference method, the potentially explosive Bouin's reagent, was air drying.

Bacteriological Techniques↗
PubMed1990

Colonial morphology of staphylococci on Memphis agar: phase variation of slime production, resistance to beta-lactam antibiotics, and virulence.

The growth of Staphylococcus epidermidis sensu stricto and Staphylococcus saprophyticus on Memphis agar yielded up to 6 morphotypes with each strain. With S. epidermidis, one morphotype produced slime (rho) but became non-slime-producing (epsilon) at a high frequency. The slime-producing rho variants were methicillin-resistant and more virulent than methicillin-susceptible epsilon variants in an endocarditis model. With S. saprophyticus, phase variation was of higher frequency. Nitrosoguanidine mutagenesis produced a stable blue epsilon form that was more virulent than the parent in a mouse model of urinary tract infection. Mutants with the blue epsilon phenotype differed from gold epsilon parents in a variety of phenotypic properties, including increased resistance to oxacillin. These staphylococcal species have a high frequency of phase variation: Phase variants differ in antibiotic resistance and virulence, which is only partially correlated with suggested virulence factors such as slime production.

Animals↗
PubMed1990

Identification of an antigenic marker of slime production for Staphylococcus epidermidis.

The pathogenic Staphylococcus epidermidis strain RP62A (ATCC 35984) adheres to smooth surfaces by forming a tenacious bacterial film known as slime. The mechanism of slime production is not known; however, workers in the laboratory of G. Pier (Harvard Medical School, Boston, Mass.) have isolated from RP62A a galactose-rich capsular polysaccharide adhesin (CPA) which mediates the attachment of the organism to smooth surfaces. We have obtained two daughter strains from RP62A that no longer produce slime. One daughter strain, H4A, was obtained by selection for a spontaneous variant; the other strain, HAM892, was obtained by treating growing cultures of RP62A with acriflavin. Using an antiserum generated against whole cells of RP62A, we have examined lysozyme-lysostaphin digests of RP62A, H4A, and HAM892 by double immunodiffusion. The two strains that no longer produced slime no longer produced a particular antigen, which we refer to as the slime-associated antigen (SAA). SAA was also produced by unrelated strains of slime-producing S. epidermidis. SAA was heat and protease stable, had a molecular weight of greater than 50,000, and could be partially purified by chromatographing trypsin-digested material over a Sephadex G-200 column. Chemical analysis of partially purified SAA by gas-liquid chromatography found SAA to be glucose rich (59%) and galactose poor (1.4%). This analysis chemically distinguished SAA from CPA. When tested together by double immunodiffusion with anti-RP62A and anti-CPA antisera, partially purified SAA did not cross-react with CPA. Kinetic studies suggested that SAA is a marker for surface accumulation whereas CPA mediates initial adherence.

Adhesins, Bacterial↗
PubMed1990

Differential production of slime under aerobic and anaerobic conditions.

A series of 37 clinical isolates of coagulase-negative staphylococci previously identified as negative for slime production by the tube test were reexamined by the tissue culture plate test under aerobic and anaerobic conditions. None of the strains produced slime under anaerobic conditions; however, five strains (13%) produced slime under aerobic conditions.

Aerobiosis↗
PubMed1990

Phenotypic variation of Staphylococcus epidermidis in infection of transvenous endocardial pacemaker electrodes.

Coagulase-negative staphylococci isolated from a patient with a pacemaker electrode infection were extensively evaluated by phenotypic and genotypic characterization. Findings from this evaluation were striking because different colony morphologic subtypes were recovered from blood and resected pacemaker electrodes. Staphylococci from each colony subtype (LBL, LBV, LBP, LBS) were identified as slime-producing strains of Staphylococcus epidermidis sensu stricto. Direct plating of isolates from a restricted electrode revealed a mixture of colony phenotypes when examined on a high-salt, low-glucose medium, Memphis agar. Bacteriophage typing employing 17 different phages and plasmid profile analysis were largely unsuccessful in further characterizing bacterial cells of each of the four colony morphotypes. On the other hand, restriction endonuclease analysis by EcoRI digestion of the chromosomal DNA demonstrated the probable common clonal origin of the four colony phenotypes.

Aged↗
PubMed1989

The effect of slime production on vancomycin efficacy in the treatment of experimental endocarditis due to Staphylococcus epidermidis.

We compared the efficacy of vancomycin in the treatment of experimental endocarditis caused by either a parent strain of Staphylococcus epidermidis that produced slime or a daughter strain that produced less slime. After subcutaneously administered vancomycin, we noted similar cure rates and similar microbiological characteristics of endocardial infections in rats challenged with these strains, regardless of slime produced.

Adhesiveness↗
PubMed1988

Characteristics of adherence to plastic tissue culture plates of coagulase-negative staphylococci exposed to subinhibitory concentrations of antimicrobial agents.

Adherence and hydrophobic properties characteristic of 6-h cultures of coagulase-negative staphylococci on plastic tissue culture plates were determined after the organisms had been treated for up to an additional 6 h with subinhibitory concentrations of antimicrobial agents. Clindamycin, erythromycin, norfloxacin, tunicamycin, and vancomycin had no effect. Cephalothin, chloramphenicol, gentamicin, imipenem, methicillin, novobiocin, polymyxin B, rifampin, and tobramycin had varied effects. Most changes induced by these agents resulted in differing degrees of inhibition of adherence. However, an increase in adherence of 65% was observed for one strain, RP14 (ATCC 35981), with rifampin treatment. Hydrophobicity of coagulase-negative staphylococci treated with antimicrobial agents measured by using a biphasic system with hexadecane showed excellent correlation with adherence (r = .958, P less than .0005), a result suggesting that adherence of these bacteria in this system depends heavily on hydrophobic surface moieties. Transmission electron microscopy of drug-treated coagulase-negative staphylococci revealed only an increase in cell-wall thickness, regardless of whether adherence was increased or decreased.

Anti-Bacterial Agents↗
PubMed1988

Phenotypic selection of small-colony variant forms of Staphylococcus epidermidis in the rat model of endocarditis.

Four pathogenic strains of Staphylococcus epidermidis (sensu strictu)-EC, RP62A, LW, and HBSN--exhibited a mixed population of colony phenotypes when plated onto a high-salt, low-glucose agar ("Memphis agar"). When compared with challenge inocula, significant shifts in colony populations to the small-colony variant forms occurred for all four strains for isolates recovered from infected vegetations of rats with catheter-induced endocarditis. Various colony phenotypes of the HBSN strain were compared in virulence studies by using the rat model of endocarditis. The infectivity rate of the small-colony variant forms was significantly less than that of either the normal parent form (P less than .05) or the mixed phenotypic inoculum (P less than .05). These data indicate that the small-colony variant forms may be selected for, once endocardial infections are established, and that the small-colony variant forms alone are much less able to initiate and/or sustain intracardiac infections in experimental endocarditis.

Animals↗
PubMed1988

Proposed virulence factors among coagulase-negative staphylococci isolated from two healthy populations.

Proposed virulence factors, including multiple antibiotic resistance and slime-mediated adherence, among coagulase-negative staphylococci colonizing healthy individuals from two different study populations were examined. Resistance to methicillin was more commonly seen than initially anticipated. In addition, adherence characteristics, as quantitated by a microtiter plate method, were very similar to those of strains of coagulase-negative staphylococci causing nosocomial infections.

Bacterial Adhesion↗
PubMed1987

Coagulase-negative staphylococci isolated from cerebrospinal fluid shunts: importance of slime production, species identification, and shunt removal to clinical outcome.

We collected and characterized 85 strains of coagulase-negative staphylococci (51 pathogens and 34 contaminants) from cerebrospinal fluid shunts. All isolates were classified by species and characterized by antimicrobial susceptibility and quantitative adherence to plastic tissue culture plates. There were more adherent organisms among pathogens than among contaminants (P less than .01). Species distribution was similar for both groups; however, 20% of the pathogens and none of the contaminants were phosphatase-negative Staphylococcus epidermidis (P less than .05). Resistance to four or more antimicrobial agents was detected in 45% of both groups. Neither species designation nor antimicrobial resistance correlated with clinical outcome. Five (83%) of six infections due to nonadherent (vs. 16 [41%] of 39 due to adherent; P less than .05) coagulase-negative staphylococci were, however, cured with antimicrobial therapy alone. Cure was highly associated with removal of the colonized shunt--38% of infected patients treated with antimicrobial therapy alone were cured, 75% treated with antimicrobial therapy and partial shunt removal were cured, and all treated with antimicrobial therapy and total shunt replacement were cured.

Bacterial Adhesion↗