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G D Christensen

Publications and source records attributed to G D Christensen.

At least 37 records · Page 2Linked to original sources
PubMed1987

Phenotypic variation of Staphylococcus epidermidis slime production in vitro and in vivo.

Clinical studies performed by us and others have found an association between slime production and strains of coagulase-negative staphylococci that infect indwelling medical devices. By serial low-speed centrifugation of broth cultures we have isolated a stable, weakly adherent strain (RP62A-NA) from a strongly adherent, slime-producing, pathogenic strain of Staphylococcus epidermidis sensu stricto (RP62A, ATCC 35984). We obtained a second strain from RP62A-NA (RP62A-NAR) by serial subculture of glass-adherent cells of RP62A-NA. All three strains had the same pattern of biochemical reactions, antimicrobial susceptibilities, and plasmid analysis. Transmission electron micrograph sections stained with the mucopolysaccharide-specific stain alcian blue demonstrated that the adherent strains RP62A and RP62A-NAR were covered with an extracellular coat of polysaccharide-rich material. In contrast, the nonadherent RP62A-NA strain lacked this external coat. All three strains were used in a mouse model of foreign body infection and a rat model of catheter-induced infective endocarditis. The adherence characteristics of isolates of RP62A and RP62A-NA recovered from experimental animals were relatively stable, although we noted a slight but a significant increase in the adherence of RP62A-NA isolates recovered from the foreign body model. The adherence characteristics of RP62A-NAR isolates recovered from infected animals were variable; in general these isolates were less adherent than the laboratory strain of RP62A-NAR. In both models the 50% infective dose (calculated by the Reed and Muench method) was three times greater for the RP62A-NA strain than for the RP62A strain. The phenotypic expression of slime production is subject to both in vitro and in vivo variation and could play a role in the pathogenesis of foreign body infection.

Animals↗
PubMed1987

Bacterial concentration correlations in experimental endocarditis caused by Staphylococcus epidermidis.

Using 13 strains of Staphylococcus epidermidis to produce catheter-induced experimental endocarditis in rats, we found that bacterial concentrations in blood cultures obtained at the time of sacrifice correlated significantly with the number of organisms per gram of endocardial vegetation (P less than 0.001) and the total number of organisms per vegetation (P less than 0.001). Furthermore, blood culture concentrations correlated with vegetation weights (P less than 0.001) and sizes of infecting inocula (P less than 0.0001). Mean bacterial concentrations in vegetations more than doubled as bacterial concentrations in blood rose from less than 10 to greater than 100 CFU/ml. Mean values for vegetation weights, total organisms per vegetation, and sizes of infecting inocula were also reflected by the intensity of bacteremia. Moreover, intracardiac catheters were more likely colonized as bacterial concentrations in blood cultures increased, with all catheters culture positive in the 25 animals that exhibited high-grade bacteremia (greater than or equal to 100 CFU/ml). Slime production by the bacteria did not influence the above-mentioned correlations. These data indicate that the blood concentration of bacteria reflects the microbiologic status of infected vegetations in experimental infective endocarditis.

Animals↗
PubMed1986

Comparison of microbiologic characteristics of pathogenic and saprophytic coagulase-negative staphylococci from patients on continuous ambulatory peritoneal dialysis.

Twenty-one microbiologically documented episodes of coagulase-negative staphylococcal peritonitis occurred in 21 continuous ambulatory peritoneal dialysis patients. All strains involved in these infections were tested for antimicrobial susceptibility and in vitro adherence assays. Twenty of the strains were species identified using two commercially available systems. For comparison, 20 saprophytic strains of coagulase-negative staphylococci obtained from the nares and axillae of 10 uninfected, peritoneal dialysis patients were included for in vitro characterization. Staphylococcus epidermidis was the species most often identified for both clinical and saprophytic strains. Eighteen of the 21 (86%) clinical strains were resistant to penicillin G. Methicillin resistance, which was present in five clinical strains, was not found in saprophytic strains. Adherence assay determinations showed marked differences between clinical versus colonization strains, with the clinical isolates significantly more adherent (p less than 0.025) than colonization strains. Electron microscopic examination of silastic catheter segments incubated with a strain of S. epidermidis in used and unused dialysis fluids demonstrated marked differences in attachment of bacteria to catheter material.

Bacterial Adhesion↗
PubMed1985

Adherence of coagulase-negative staphylococci to plastic tissue culture plates: a quantitative model for the adherence of staphylococci to medical devices.

The adherence of coagulase-negative staphylococci to smooth surfaces was assayed by measuring the optical densities of stained bacterial films adherent to the floors of plastic tissue culture plates. The optical densities correlated with the weight of the adherent bacterial film (r = 0.906; P less than 0.01). The measurements also agreed with visual assessments of bacterial adherence to culture tubes, microtiter plates, and tissue culture plates. Selected clinical strains were passed through a mouse model for foreign body infections and a rat model for catheter-induced endocarditis. The adherence measurements of animal passed strains remained the same as those of the laboratory-maintained parent strain. Spectrophotometric classification of coagulase-negative staphylococci into nonadherent and adherent categories according to these measurements had a sensitivity, specificity, and accuracy of 90.6, 80.8, and 88.4%, respectively. We examined a previously described collection of 127 strains of coagulase-negative staphylococci isolated from an outbreak of intravascular catheter-associated sepsis; strains associated with sepsis were more adherent than blood culture contaminants and cutaneous strains (P less than 0.001). We also examined a collection of 84 strains isolated from pediatric patients with cerebrospinal fluid (CSF) shunts; once again, pathogenic strains were more adherent than were CSF contaminants (P less than 0.01). Finally, we measured the adherence of seven endocarditis strains. As opposed to strains associated with intravascular catheters and CSF shunts, endocarditis strains were less adherent than were saprophytic strains of coagulase-negative staphylococci. The optical densities of bacterial films adherent to plastic tissue culture plates serve as a quantitative model for the study of the adherence of coagulase-negative staphylococci to medical devices, a process which may be important in the pathogenesis of foreign body infections.

Animals↗
PubMed1984

Production of experimental endocarditis by coagulase-negative staphylococci: variability in species virulence.

The abilities of 11 coagulase-negative staphylococcal isolates of human origin to establish infective endocarditis in a rat model were compared. Seven of the strains were Staphylococcus epidermidis, the species most commonly causing endocarditis in humans. The other four strains were Staphylococcus hominis, an infrequent cause of endocarditis. Four of the seven strains of S. epidermidis and two of the four strains of S. hominis elaborated surface slime. With an inoculum of 10(7) colony-forming units, endocarditis was established in all of 77 rats injected with S. epidermidis but in only five (12.5%) of 40 animals injected with S. hominis (P less than .001). Strains of S. epidermidis were significantly more resistant to phagocytic killing in vitro than were strains of S. hominis. These data indicate that there are major differences in the virulence of various species of coagulase-negative staphylococci, both in vivo and in vitro, and that these differences are reflected in the observed incidence of disease caused in humans by the respective species.

Animals↗
PubMed1983

Experimental foreign body infections in mice challenged with slime-producing Staphylococcus epidermidis.

The virulence of two previously described Staphylococcus epidermidis strains was examined in an experimental model of foreign body infection in mice. Animals challenged with the slime-producing strain developed three times as many infections as animals challenged with the strain that did not produce slime (P less than 0.001). Bacterial isolates recovered from the infected sites retained the characteristics of the inoculated strain. Animals without foreign bodies but challenged in a similar manner with either staphylococcal strain did not become infected. Thus, the presence of a foreign body predisposed the animals to S. epidermidis infection. These results indicate that the production of slime by S. epidermidis is a stable characteristic retained after animal passage and may be important in the pathogenesis of these infections.

Adhesiveness↗
PubMed1983

Characterization of clinically significant strains of coagulase-negative staphylococci.

On occasion, a patient may have two or more clinical cultures yielding a coagulase-negative staphylococcus If these multiple isolates have the same phenotype, one might conclude that the same strain was reisolated from the patient, indicating its persistent and pathological presence. We examined the validity of this conclusion when we applied a number of characterizing systems to a collection of 143 isolates of coagulase-negative staphylococci collected during an outbreak of intravascular catheter-associated sepsis. The probability of classifying two random isolates as the same phenotype or species was as follows: P = 0.356 for phage typing, P = 0.348 for Baird-Parker biotyping, P = 0.346 for the API STAPH-IDENT (Analytab Products) system, P = 0.327 for Bentley et al. biotyping, and P = 0.077 for antimicrobial susceptibility patterns. Although antimicrobial susceptibility patterns had the lowest probability, a variability in test results of 7.7% and a tendency for strains to have similar antibiograms effectively raised the probability to P = 0.897. The combination of the API STAPH-IDENT with antibiograms resulted in a probability of P = 0.037 to P = 0.147. When all of the above methods were used together a probability of P = 0.014 was achieved. Five patients had isolates from two or more blood cultures spaced more than 1 day apart that were identical by all of the above criteria, thus confirming prolonged bacteremia. The collection was also examined for the incidence of slime production. Slime production was not associated with any of the above groups, but was associated with symptomatic infections (P less than 0.05) and gentamicin resistance (P less than 0.01). Slime production was strain stable and was of assistance in typing strains of coagulase-negative staphylococci.

Bacteriological Techniques↗
PubMed1982

Adherence of slime-producing strains of Staphylococcus epidermidis to smooth surfaces.

Slime production is not a generally recognized feature of Staphylococcus epidermidis. In a recent outbreak of S. epidermidis intravascular catheter-associated sepsis, we noted that 63% of clinically implicated strains grew as a slimy film coating the culture tube walls when propagated in tryptic soy broth. Only 37% of randomly collected blood culture contaminants and skin isolates demonstrated a similar phenomenon (p less than 0.05). Transmission electron micrographs of these coating bacteria showed them to be encased in an extracellular matrix that stained with alcian blue. Slime production was most evident in autoclaved media containing Casamino Acids and glucose supplementation (0.25% wt/vol). There were strain and media preparation variability of slime production in the presence of other carbohydrates. Some strains were not able to produce slime under any of the tested conditions. The production or nonproduction of slime did not influence growth rate. When grown in vitro, slime producers accumulated on the surface of intravascular catheters as macrocolonies, whereas non-slime, producers did not. Transmission and scanning electron micrographs showed slime producers to be encased in an adhesive layer on the catheter surface, whereas nonproducers were not encased. These results suggest that slime-mediated adherence may be a critical factor in the pathogenesis of S. epidermidis infections of medical devices.

Adhesiveness↗
PubMed1982

Nosocomial septicemia due to multiply antibiotic-resistant Staphylococcus epidermidis.

Thirteen episodes of Staphylococcus epidermidis sepsis occurred over a 20-month period in 11 patients receiving general surgical and medical care. These episodes were characterized by fever, toxicity, multiple positive blood cultures, and uniformly colonized intravascular catheters. An additional 16 patients had possible sepsis. Four associated deaths occurred; all three patients autopsied had multiple pulmonary abscesses in which gram-positive cocci were profusely present. In individual patients, prolonged episodes of septicemia were confirmed by multiple blood culture isolates of S. epidermidis, identical in antibiotic resistance pattern, phage type, and biotype. A prominent feature of the S. epidermidis isolates was resistance to many commonly used antimicrobial agents. Case-control studies and review of laboratory records indicated a significant association between multiply resistant S. epidermidis blood isolates and prolonged hospitalization and parenteral hyperalimentation. Most of these patients were hospitalized in the intensive care unit; nose and hand cultures taken from the personnel showed frequent carriage of multiply resistant S. epidermidis Staphylococcus epidermidis associated with intravascular devices may produce life-threatening bloodstream infections.

Adult↗
PubMed1981

Clinical and laboratory evaluation of cefoperazone.

Cefoperazone, a third-generation cephalosporin derivative, has been reported to have excellent antibacterial activity against a wide range of gram-positive and gram-negative pathogens, including Pseudomonas aeruginosa. We treated 54 patients with a variety of clinical infections with cefoperazone and determined the susceptibilities of their 90 bacterial isolates. An additional 25 aerobic isolates obtained from patients treated with cefamandole in a comparison study were also tested for susceptibility to cefoperazone. Thus a total of 115 isolates were studied in vitro. One hundred nine (95%) of 115 bacterial isolates, including gram-positive and gram-negative aerobes and anaerobes, were susceptible to less than or equal to 32 microgram/ml. Only four isolates (three Escherichia coli and one Serratia marcescens) were highly resistant (minimal inhibitory concentration greater than or equal to 128 microgram/ml). We were able to assess clinical outcome of cefoperazone therapy in 53 patients; favorable responses (cure of improvement) were found in 48 (91%). P. aeruginosa was a major pathogen in three patients treated with cefoperazone; all three showed a favorable response. Side effects of cefoperazone therapy were noted in seven (13%) patients, and laboratory abnormalities were observed in 11 (20%) patients; all of these were mild and readily reversible. Cefoperazone thus appears to be safe, well tolerated, and suitable for use in a variety of human infections.

Bacterial Infections↗
PubMed1980

The role of opsonins in recovery from experimental pneumococcal pneumonia.

The opsonization of type 1 and type 25 pneumococci in the rabbit lung early in the course of experimental pneumonia was studied. Bacteria washed from the lungs of animals with type 1 pneumonia were coated with IgG, IgA, and complement within 24 hr of infection; these bacteria were not phagocytized. Both type 1 and type 25 pneumococci, when incubatd in concentrates of nonimmune bronchopulmonary washings (BPC), adsorbed IgG, IgA, and C3, but neither type of pneumococci was opsonized. Killing of pneumococci by surface phagocytosis, with or without the use of nonimmune BPC, was not demonstrated. When nonimmune serum was used, opsonization of type 25 pneumococci depended on the presence of heat-labile adsorbable factors, and when immune serum and immune BPC were used, opsonization was dependent on adsorbable factors. Depletion of serum complement with cobra venom factor before infection with type 25 pneumococci resulted in severe bacteremic pneumonia in the rabbit, but immunization before complement depletion allowed animals to clear type 25 pneumococci from the blood and lungs within 24 hr. Thus, opsonization is required for efficient clearance of pneumococci from the lung, and in the nonimmune animal, complement is also required for clearance.

Animals↗
PubMedDate not supplied

Epidemic Serratia marcescens in a neonatal intensive care unit: importance of the gastrointestinal tract as a reservoir.

Between a March and December of 1979, and outbreak of infections due to multiply antibiotic resistant Serratia marcescens took place in a 50-bed neonatal intensive care unit. Fifteen neonates suffered major infections (sepsis, meningitis and pneumonia) with one death, and 20 suffered minor infections (conjunctivitis, cystitis, wound infections). Epidemiologic investigation failed to reveal a common source; S. marcescens, however, ws isolated from an employee's hand, emollient skin cleanser, suction tubing, and three in-use manual infant resuscitation bags. The skin cleanser and equipment-cleaning agents were ineffective against S. marcescens. Asymptomatic, colonized infants were the major reservoir of S marcescens. These infants were identified by daily cultures of the nose, umbilicus and rectum. The rectal swab most commonly (76%) yielded first-positive cultures in previously uncolonized infants, and was ultimately positive in 92% of colonized infants. A control program was begun by: 1) removing all inanimate sources of S. marcescens; and 2) cohorting patients and staff into a S. marcescens-exposed group and a new patient group. The new patient group of infants was surveyed by daily triple-site cultures for colonization and subsequent transfer to the S. marcescens-exposed group. After four months, the epidemic was controlled and the organism eradicated from the neonatal intensive care unit.

Cross Infection↗