Log10 Colony Forming Units Reduction Research Articles

Rapid Antibacterial Activity of 2 Novel Hand Soaps: Evaluation of the Risk of Development of Bacterial Resistance to the Antibacterial Agents

To evaluate the antimicrobial efficacy of and risk of organisms developing resistance to 2 novel hand soaps: (1) a soap containing triclosan, polyhexamethylene biguanide, and benzethonium chloride added to a soap base (TPB soap); and (2) a soap containing farnesol, polyhexamethylene biguanide, and benzethonium chloride added to a soap base (FPB soap). Tests also included soaps containing only triclosan. The risk of emergence of resistant bacterial mutants was investigated by determining the susceptibility changes after repeated exposure of bacteria to the drugs and soaps in vitro. The effectiveness of the soaps was evaluated using an in vitro tube dilution method, a volunteer method (the ASTM standard), and 2 pig skin methods. The minimum inhibitory concentration and minimum bactericidal concentration of triclosan against Staphylococcus aureus increased 8- to 62.5-fold, whereas those of TPB and FPB (both alone and in soap) were unchanged. In vitro, TPB and FPB soaps produced higher log(10) reductions in colony-forming units of all tested organisms (4.95-8.58) than did soaps containing triclosan alone (0.29-4.86). In the test using the pig skin and volunteer methods, TPB soap produced a higher log(10) reduction in colony-forming units (3.1-3.3) than did the soap containing triclosan alone (2.6-2.8). The results indicate that TPB and FPB soaps may provide superior rapid and broad-spectrum efficacy with a lower risk of organisms developing resistance than do soaps containing triclosan alone. Pig skin methods may be used to predict the efficacy of antibacterial soaps in the rapid disinfection of contaminated hands. Hand washing with TPB and FPB soaps by healthcare workers and the general population may reduce the transmission of pathogens, with a lower risk of promoting the emergence of resistant organisms.

A comparison of two devices for the manual cleaning of flexible gastrointestinal endoscopes in a clinical setting

The ‘Pull Thru’ [Novapharm Research Aust. Pty Ltd], a new device designed for cleaning the biopsy/suction channel of flexible gastrointestinal endoscopes, was compared to reusable brushes in a clinical setting. A total of 53 endoscopes were tested with a microbiological assay. Directly after removing the endoscope from the patient, a sterile saline solution was flushed down the biopsy channel to provide a ‘before clean’ estimate of bioburden. Following a cleaning protocol with either of two manual cleaning devices – i.e. one pass with a Pull Thru or six passes with a reusable brush – a second volume of saline solution was used to provide an ‘after clean’ estimate. The protocols were compared for Log10Reduction in colony-forming units (cfu)/mL between the ‘before clean’ and ‘after clean’ samples. No significant difference was found between the two cleaning protocols (P=0.058) using a combined factorial analysis. The adjusted means for Log10Reduction (cfu/mL) were 3.003 (brush) and 3.302 (Pull Thru) with a standard error of difference of 0.154. It is concluded that the cleaning efficacy of one pass with the Pull Thru was as effective as six passes with a reusable brush.

Reduction of eggshell aerobic plate counts by ultraviolet irradiation

The effects of 254 nm ultraviolet light (UV) radiation on aerobic plate count (APC) of egg shells were investigated. In the first experiment, eggs were exposed to UV treatment (7.35 mW/cm2) for 0, 15, 30, and 60 s. Three eggs from each treatment were aseptically collected and placed into sterile plastic bags containing 50 mL of sterile phosphate-buffered solution. Serial dilutions of the phosphate-buffered solution were plated on aerobic plate count agar and incubated at 37 C for 48 h. Exposure of eggshells to 30 and 60 s UV significantly reduced aerobic plate counts compared to untreated eggs. Exposure to 60 s of UV resulted in a 2 to 3 log10 cfu/egg APC reduction and reduced counts below detectable levels. In the second experiment, UV lights were placed in a chamber equipped with a commercial-style egg conveyor. A UV treatment of 7.5 mW/cm2 and time intervals of 0, 12, 36, and 48 s were used. Three eggs were placed consecutively on the conveyor and passed through the chamber. The center egg was selected for APC evaluation. Sample size, dilution, plating, and incubation procedures were used as described for the first experiment. A significant 1 to 2 log10 reduction in colony-forming units per egg between the eggs treated 48 s to the untreated eggs was detected. The results of these studies show that UV light treatment at high intensities and low time intervals has the potential to reduce aerobic plate counts of eggshells.

Use of a one atmosphere uniform glow discharge plasma to kill a broad spectrum of microorganisms

The medical, industrial, and food processing industries are constantly in search of new technologies to provide improved methods of sterilization and pasteurization. Proposed techniques must deal with such problems as thermal sensitivity and destruction by heat, formation of toxic by-products, cost, and inefficiency in performance. We report results from a newly invented plasma source, a one atmosphere uniform glow discharge plasma (OAUGDP), which is capable of operating at atmospheric pressure in air and providing antimicrobial active species at room temperature. OAUGDP exposures have reduced log numbers of bacteria (Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa), bacterial endospores (Bacillus subtilis and Bacillus pumilus), and various yeast and bacterial viruses on a variety of surfaces. These surfaces included polypropylene, filter paper, paper strips, solid culture media, and glass. Experimental results showed at least a ⩾5 log10 colony forming units (CFU) reduction in bacteria within a range of 15–90 s of exposure, whether the samples were exposed in conventional sterilization bags or exposed directly to the plasma. An exception to these very short exposure times were experiments with solid culture media in which 5 min of plasma exposure was necessary to produce ⩾5 log10 CFU reduction in bacterial counts. The effects of plasma treatment on bacterial cell structures were investigated by exposing cells to plasma for various durations and examining them by transmission electron microscopy. The results showed that cell breakage (lysis) occurred with the release of cellular contents. These data were consistent with spectrophotometric results in which the release of cellular constituents was measured as a change in ultraviolet absorption at 260 nm. With all microorganisms tested, a biphasic survival curve (logarithmic number of survivors versus time) was observed in plots of dose-response data. Differences in susceptibilities of microorganisms observed on various surfaces suggested that the degree of lethality was dependent upon the time of diffusion of active species through the medium to the organism and the makeup of the microbial cellular surface.

Effective treatment of multidrug-resistant enterococcal experimental endocarditis with combinations of cell wall-active agents.

The efficacy of treatment with a combination of ampicillin, imipenem, and vancomycin was compared with that of two-drug combinations or monotherapy in a model of experimental endocarditis using a strain of Enterococcus faecium with high-level resistance to vancomycin and moderate intrinsic resistance to ampicillin and imipenem. In vitro time-kill synergy studies demonstrated bactericidal synergistic activity only for the triple combination. In vivo, monotherapy with vancomycin was not effective. Treatment with either ampicillin or imipenem alone or in combination with vancomycin resulted in <4 log10 reduction in colony-forming units (cfu) per gram of vegetation. The combination of ampicillin with imipenem was highly active (an additional 5 log10 reduction in cfu per gram of vegetation compared with the most active single agent), but efficacy was not increased by the addition of vancomycin to ampicillin and imipenem. Therapy with the combination of ampicillin and imipenem may be effective for some strains of multidrug-resistant enterococcal infections.

Effects of temperature and salinity on survival of toxigenic Vibrio cholerae O1 in seawater

In 1991 and 1992, the Latin American epidemic strain of Vibrio cholerae O1 was isolated from ballast water, bilge water, and sewage taken from cargo ships docked in Mobile Bay, Alabama. The findings raised questions regarding the organism's ability to survive long-term aboard ships and to withstand the exchange of ballast at sea. The effects of temperature (6, 18, and 30°C) and salinity (8, 16, and 32 ppt) on survival of V. cholerae O1 strains C6706 and C6707 and a ballast water isolate in sterile seawater were determined. The ballast water isolate, which had a D-value (number of days required to produce a 1 log10 reduction in colony-forming units per milliliter) of 240 days at 18°C, 32 ppt salinity, had the longest survival time. The range of D-values was 36-240 days at 18°C, 60-120 days at 30°C, and 5-20 days at 6°C. In sterile seawater short-term survival was temperature dependent, whereas long-term survival was salinity dependent. In raw seawater, survival time of the ballast water isolate was reduced to 12-27 days, implying the existence of biological influences. As also shown in our previous work, the organism appeared to be able to survive for several months under relatively stable conditions in ballast water aboard ships; however, viability may be reduced to only a few weeks after the organism is introduced into estuarine or marine environments.

Pharmacokinetics of DepoFoam Gentamicin Delivery System and Effect on Soft Tissue Infection

Infections of burn and soft tissue wounds are often difficult to treat with systemic antibiotics since drug delivery to the wound may be suboptimal and high doses may result in toxicity. DepoFoam particles, a novel lipid-based drug delivery system, are composed of phospholipid membranes, enclosing multiple aqueous chambers into which pharmacologic agents can be encapsulated for local drug delivery. We encapsulated gentamicin (GENT) in DepoFoam particles with an average yield of 81% ± 8 SD for 10 preparations. Encapsulated GENT was incubated in human plasma with t1/2 of 21 days, demonstrating stability in vitro. In vivo pharmacokinetics were determined by injecting CF-1 mice subcutaneously (sc) with a single dose of 0.5 mg of free (nonencapsulated drug) or DepoFoam GENT. At intervals postinjection the sc tissue was excised and blood was obtained by inferior cava puncture and both were assayed for GENT levels. At 0.5, 2, 6, and 24 hr following drug administration there was a significant difference between GENT levels in the tissue achieved with the encapsulated drug and free drug with n = 3-4 at each time point for each group (P < 0.01). By 24 hr following administration of free drug there was minimal detectable GENT in the tissues, while therapeutic levels of GENT remained in tissue at 24 hr following DepoFoam GENT injection. Serum GENT peaked at 30 min for both the DepoFoam (5 μg/ml) and free drug (10 μg/ml) and was undetectable by 2 hr (n = 3 each group). Other mice received sc pretreatment on the dorsum with DepoFoam GENT (n = 18) or free GENT (n = 13) followed 2 days later with inoculation of 107Staphylococcus aureus in the site where the antibiotic had been injected previously. At 48 hr postinfection, colony-forming units (CFU) of S. aureus per gram of tissue were determined. Animals which had received DepoFoam GENT had a fourfold log10 reduction in CFU compared to animals which received free GENT, sterile water, and nondrug containing DepoFoam. DepoFoam drug delivery offers a promising method of providing sustained, high concentrations of antibiotic to local tissues while avoiding prolonged exposure to toxic systemic levels.

Antigenic Specificity of Opsonophagocytic Antibodies in Rabbit Anti-Sera to Group B Streptococci

An opsonophagocytic assay has been developed which requires human polymorphonuclear leukocytes, immune serum, and complement for optimal killing of Group B streptococci. Only with all three of these components was killing of greater than 1.0 log10 of the initial inoculum achieved, using rabbit antisera directed to homologous strains of each of the five known serotypes of Group B streptococci. Titers of specific antisera which opsonized the strains and resulted in greater than 1 log 10 reduction of colony-forming units, ranged from 1:100 (serotype Ib) to 1:3200 (serotype Ia). Cross-reactions between serotype-specific sera and heterologous strains were seen in certain instances. Type Ic strain and serotype Ic antiserum demonstrated cross-reactions with types Ia and Ib which were explainable by known shared antigens among these types. The only other cross-reaction which resulted in greater than 1 log 10 reduction in colony-forming units was when unabsorbed antiserum to strain Ia was used to opsonize a strain of serotype III. Opsonization of 10 serotype III strains was demonstrated with a single type III antiserum. Killing of nine of these strains required polymorphonuclear leukocytes, complement, and antiserum, but one strain, D136C, the reference strain, could be killed (greater than 1 log 10 reduction in colony-forming units) without either complement or specific antiserum. Inhibition studies were performed utilizing large m.w. polysaccharide antigens extracted from each serotype. These antigens inhibited opsonization of homologous strains by homologous antisera with 50% inhibition points ranging between 0.5 and 4 mug.