Efficacy of high-level disinfectants for reprocessing GI endoscopes in simulated-use testing

BACKGROUND

There has been recent public concern regarding the adequacy of current practices for flexible endoscope reprocessing. High-level disinfection is defined by the Food and Drug Administration (FDA) as a minimum of 6-log reduction of mycobacteria under a worst-case scenario. Several agents are currently approved by the FDA, but published data on their relative efficacies against mycobacteria are lacking. The objective of this study was to determine the efficacy of these agents for high-level disinfection.

METHODS

In simulated-use testing, video endoscopes (5 colonoscopes and 5 duodenoscopes) were each inoculated with 9.0 x 10(7) colony-forming units of Mycobacterium chelonae. Cleaning was performed by using a standardized protocol. Each endoscope was then subjected to chemical disinfection with Cidex (2.0% glutaraldehyde) at 20 degrees C for 20 minutes, Sporox (7.5% hydrogen peroxide) at 20 degrees for 30 minutes, and Steris 20 (0.2% peracetic acid) at 50 degrees C to 56 degrees C for 12 minutes using the Steris System 1 processor. Although not FDA-approved, tests were also conducted by using 70% isopropyl alcohol at 20 degrees C for 20 minutes. These results were compared with disinfection with ethylene oxide gas. All channels were sampled for M chelonae before and after manual cleaning and after disinfection.

RESULTS

Cleaning alone resulted in an average log reduction of 3. Cidex, Sporox, Steris 20, ethylene oxide gas, and isopropyl alcohol, in combination with manual cleaning, each achieved a 6-log or greater reduction of the mycobacterial inoculum. No organisms were recovered from any channel after reprocessing with ethylene oxide and Steris 20.

CONCLUSIONS

Commercially available high-level disinfectants are equally efficacious for reprocessing flexible GI endoscopes when used in conjunction with cleaning and in accordance with recommended guidelines.

High-level disinfection of gastrointestinal endoscopes: are current guidelines adequate?

OBJECTIVE

For a germicide to obtain a high level disinfection (HLD) claim, FDA requires demonstration of a 6-log reduction of mycobacterial inoculum under worst case conditions. The purpose of this study was to assess the adequacy of current guidelines for high level disinfection of GI endoscopes using alkaline glutaraldehyde in simulated-use testing.

METHODS

Various gastrointestinal endoscopes were contaminated with Mycobacterium chelonae in 46 experiments. Quantitative cultures were obtained from each endoscope channel separately after each step: inoculation, standardized manual cleaning, immersion in 2% glutaraldehyde (Cidex) for 10, 20, or 45 min at room temperature, 70% isopropanol rinse, and drying.

RESULTS

Manual cleaning alone achieved a 4-log reduction. After 10 min of glutaraldehyde exposure, but before alcohol rinse, two of 10 experiments failed to achieve a 6-log reduction. However, after alcohol rinse, all 10 experiments achieved HLD. After 20 min of glutaraldehyde exposure, but before alcohol rinse, one of 18 experiments failed to achieve a 6-log reduction. After alcohol rinse, all 18 experiments achieved HLD. After 45 min of glutaraldehyde exposure, but before alcohol rinse, one of 18 experiments failed to achieve a 6-log reduction. After alcohol rinse, all 18 experiments achieved HLD. Thus, if the entire reprocessing protocol including manual cleaning, glutaraldehyde exposure, alcohol rinse, and drying was taken into account, the required 6-log reduction of mycobacteria was achieved with a minimum of 10 min of glutaraldehyde exposure at room temperature.

CONCLUSIONS

Current guidelines for high level disinfection using glutaraldehyde are appropriate. Alcohol rinse is a valuable adjunctive step for drying and for its bactericidal effects.

Efficacy of various disinfectants in killing a resistant strain of Pseudomonas aeruginosa by comparing zones of inhibition: implications for endoscopic equipment reprocessing

OBJECTIVE

Previous studies have shown that high-level disinfection of GI endoscopes may not be reliably achieved using glutaraldehyde at room temperature. In our laboratory, we have isolated a strain of Pseudomonas aeruginosa that is resistant to disinfection with glutaraldehyde. We compared the bactericidal activity of various disinfectants against this organism.

METHODS

One hundred microliters of an overnight culture of this organism was spread onto blood agar plates. Twenty microliters of a disinfectant was placed on a sterile 7-mm filter paper, placed on the blood agar plate, and incubated overnight at 37 degrees C to determine the zone of inhibition for each disinfectant tested. Disinfectants included Cidex, Dispatch, Virahol, OMNI II, Lysol, IodoFive, Lysol I.C. Spray, and Chlorox. The zone of inhibition (i.e., clearing) roughly correlates with the bactericidal strength of the disinfectant.

RESULTS

Compared with the glutaraldehyde-containing solution Cidex, the alcohol-containing disinfectants Lysol I.C. Spray and Virahol had the largest mean zones of inhibition (11.33 vs 20.60 and 20.55 mm; p = 0.0001). The hypochlorite compounds Chlorox (1:10 dilution) and Dispatch had mean zones of inhibition similar to that of Cidex (11.08 and 11.25 mm vs 11.33 mm; p = not significant). The phenolic compounds OMNI II and Lysol had mean zones of inhibition smaller than that of Cidex (10.50 and 10.35 mm vs 11.33 mm; p < 0.006), and the phosphoric acid and iodine-containing IodoFive had the smallest mean zone of inhibition (9.70 vs 11.33 mm; p = 0.0001).

CONCLUSIONS

The alcohol-containing disinfectants had the largest zones of inhibition against resistant P. aeruginosa. These compounds may be more effective than glutaraldehyde for endoscopic equipment reprocessing.

Rabbit Streptococcus pneumoniae keratitis model and topical therapy

PURPOSE

To develop a model for experimental Streptococcus pneumoniae keratitis and to evaluate the chemotherapeutic efficacy of 12 common topical antibiotics in vivo.

METHODS

Five-hundred (CFUs of log-phase S. pneumoniae were injected into the central corneal stroma of 36 eyes of 18 rabbits. After 0, 4, 8, 16, 24, and 48 hours, the in vivo growth was assayed as the CFU per cornea. Epithelial removal (to promote antibiotic entry and mimic human keratitis) was evaluated. Disc or tube dilution verification of the sensitivity or resistance of three S. pneumoniae strains was performed: a penicillin sensitive ("S"), an intermediate sensitive ("I"), and a resistant ("R") strain. Keratitis was established with S. pneumoniae "S" in 65 eyes, S. pneumoniae "I" in 107 eyes, and S. pneumoniae "R" in 78 eyes. Sixteen hours later, control corneas were harvested and the epithelium removed from treatment corneas. Every half hour saline, penicillin, gentamicin, bacitracin, ciprofloxacin, ofloxacin, erythromycin, vancomycin, ceftriaxone, cefotaxime, or chloramphenicol was applied for 5 hours. One hour later CFUs/cornea were assayed.

RESULTS

After 24 hours, S. pneumoniae "S" and "I" had proliferated to 9.18+/-6.65 x 10(6) CFUs and 9.26+/-6.90 x 10(6) CFUs. Epithelial removal at 16 hours was not significant. The in vitro antibiotic sensitivity was as expected. However, in vivo, penicillin, gentamicin, or cefazolin sterilized S. pneumoniae "S." S. pneumoniae "R" responded best to fortified gentamicin with or without vancomycin; all others antibiotics were significantly less effective (P < 0.001).

CONCLUSIONS

A small intracorneal S. pneumoniae inoculum in rabbit corneas grew and was maintained for 24 hours (with epithelial removal) to provide a model for testing antibiotic sensitivity in vivo. Topical penicillin is best for treating keratitis from penicillin-sensitive S. pneumoniae, whereas topical gentamicin or a combination of gentamicin and vancomycin was most effective against penicillin-resistant S. pneumoniae.

Lack of virus transmission by the excimer laser plume

PURPOSE

To test the possibility of pathogenic virus transmission into the operating suite during excimer laser treatment of corneal tissue. Such treatment vaporizes corneal tissue, which may put the surgeon at risk of infection from human immunodeficiency virus, hepatitis virus, or other viruses. We developed a model system to test the possibility of such virus transmission.

METHODS

Pseudorabies virus is a porcine enveloped herpesvirus similar in structure and life cycle to human immunodeficiency virus and herpes simplex virus. An excimer laser was used to ablate a virus-infected tissue culture plate while an uninfected tissue culture plate was in an inverted position over the infected plate. Six hundred laser pulses were applied. Pseudorabies virus in the excimer laser plume would, potentially, contact and infect the uninfected cells. The experiment was repeated 20 times with appropriate positive and negative controls.

RESULTS

None of the 20 uninfected plates was infected by the laser plume rising from ablation of infected tissue culture plates. Positive and negative controls performed as expected.

CONCLUSIONS

Even under conditions designed to maximize the likelihood of virus transmission, the excimer laser ablation plume does not appear capable of transmitting this particular live enveloped virus. Excimer laser ablation of the cornea of a human immunodeficiency virus (HIV)-infected or herpesvirus-infected patient is unlikely to pose a health hazard to the surgeon.

Comparison of topical ciprofloxacin to conventional antibiotic therapy in the treatment of experimental Pseudomonas aeruginosa keratitis

We evaluated the efficacy of topical ciprofloxacin (3.0 mg/ml) in the treatment of experimental Pseudomonas aeruginosa keratitis in 60 rabbits. We compared ciprofloxacin treatment with double drug therapy consisting of tobramycin (13.6 mg/ml) plus polymyxin B (25,000 U/ml) or carbenicillin (6 mg/L). Two strains of P. aeruginosa were used. One was a strain well characterized for use in experimental Pseudomonas keratitis (ATCC organism 27853); the second was an organism from a patient with a Pseudomonas corneal ulcer. Rabbits were treated for 16 h, after which the corneas were excised, homogenized, and plated serially for residual colony-forming units. Both organisms responded significantly better to topical off-the-shelf ciprofloxacin than to therapy with two conventional antipseudomonal fortified antibiotic drugs (p < or = 0.0001).

Effects of dietary fat and protein on DMH-induced tumor development and immune responses

Although in three different mouse tumor systems with corn oil as dietary fat we previously found that milk protein decreased tumor development compared with beef, the results were reversed in 1,2-dimethylhydrazine (DMH)-injected mice. The purpose of this study was to determine if the latter result was due to the protein source. BALB/c mice (n = 280) were divided into five diet groups and injected 10 times at weekly intervals with DMH (20 mg/kg wt) or saline. Four diets contained 11% protein (casein, milk, or beef) and 5% fat (corn oil or beef tallow), and the AIN-76A diet was used as a control diet. The source of fat was a significant modulator of tumor development. Corn oil markedly increased total tumor volume and the number of tumors per mouse compared with beef tallow. Its tumor-enhancing effects were evident when it was combined with milk but not with casein. In addition, significantly lower lymphoproliferation and T-cell cytotoxicity against colon tumor cell targets was associated with corn oil consumption, whereas nonfat milk as the protein source was related to normal oxidative burst capacity of phagocytes. These results demonstrate that the source of dietary fat, in addition to the protein source, has a profound effect on both tumor development and immune responsiveness in this animal tumor system.

Modification of a transplantable colon tumor and immune responses in mice fed different sources of protein, fat and carbohydrate

The effects of different sources of dietary protein, fat and carbohydrate on tumor development and on tests relating to cell-mediated immunity were investigated in male BALB/c mice after subcutaneous injection of 8 X 10(4) 1,2-dimethylhydrazine (DMH)-induced colon tumor (no. 51) cells. Results indicated that mice fed the milk protein source (especially at the low protein level) had smaller tumors, a higher spleen cell proliferative response to stimulation by phytohemagglutinin (PHA), and greater cytotoxic T-cell activity against the tumor cells than those fed the comparable diets containing protein from the other sources. Peripheral blood lymphocytes only from the milk-fed mice, regardless of tumor presence, exhibited a relatively low response to PHA stimulation, thereby suggesting a dietary effect on the migration pattern of PHA-responsive lymphocytes. The level of protein significantly affected both T-cell and natural killer cell cytotoxicity. The tumor-bearing mice fed the diet containing sucrose (table sugar) had a significantly lower spleen cell response to PHA stimulation than those fed the comparable diet containing dextrin. The level or source of fat did not significantly affect any of the parameters tested in this system.