Efficacy of ‘Nu-Cidex’ (0·35% peracetic acid) against mycobacteria and cryptosporidia

~OUYFMZ~

of Hospitul Itifertion

(1995) 31, 235-214

Letters

to the Editor

Sir, Efficacy

of ‘Nu-Cidex’

(0.35% peracetic acid) and cryptosporidia

against

mycobacteria

Glutaraldehyde is the primary disinfectant most often recommended for use with flexible endoscopes. However, it does have several drawbacks. It is a skin and respiratory irritant and its use requires expensive ventilation control in order to comply Lvith Control of Substances Hazardous to Health (COSHH) regulations. It has good activity against vegetative bacteria and Lriruses, variable yet poorer acti\.ity against mycobacteria and is only \‘er\ slowly sporicidal. Routine disinfection times vary from 4-20 mins, and if myocbacteria are thought to be contaminating the endoscope, a OO-min exposure time is generall>- recommended.‘-’ Notification rates for tuberculosis have recently increased and there have been several reported outbreaks of tuberculosis caused by multi-drugHIV-infected patients resistant IVlycobacterium tuberculosis.’ Additionally, frequently become colonized by A!. a~liunz-irztrucellulare lvhich may eventually lead to a fatal disseminated infection. Cryptosporidium is an enteric pathogen which generally gives rise to a self-limiting enteritis. Howe\rer, in immunocompromised AIDS patients it frequently leads to a prolonged illness that is difficult to treat and may prove ultimately fatal. The infective cyst stage is notably resistant to a \vide range of disinfectants. It is therefore increasingly important to ensure that endoscopes are decontaminated b? agents that ha\re a high degree of acti\rity against these infectious agents. Recently, Lvnam et al.’ have reported the activity of an equilibrium mixture of acetic acid, peracetic acid and hydrogen peroxide (‘Nu-Cidex’) against a number of mycobacterial species, lvhich included Ad. tuberculosis and glutaraldehyde-resistant LW. chelonae.’ 1T’e Lvish to report our experiences with ‘Nu-Cidex’ against both mycobacteria and cryptosporidia. Ilie evaluated ‘n‘u-Cidex’ in both suspension and surface tests \\:ith five strains of mycobacteria: 11,f. tubwczrlosis NCTC H37Ra; Af. bmis NCTC 10772; Al. mizm NCTC 10437; a laboratory-adapted clinical isolate of M. tubemdosis (strain 98) resistant to streptomycin, isoniazid and rifampicin and a clinical isolate of XI. arizun (strain 3051) subcultured twice prior to testing. .A clinical isolate of C. pnwunz w-as also used. The efficacy, of ‘NuCidex’ \\:as compared Lvith 2% activated glutaraldehyde (‘Cidex’); both disinfectants were a generous gift of Johnson & Johnson I\Iedical Ltd. Mycobacterial suspensions were prepared by growth for four weeks at 32°C

236

Letters

to the Editor

in Middlebrook’s 7H9 broth containing 0.5% Tween 80, vortexing in the presence of glass beads and dilution into fresh growth medium prior to inoculation into the disinfectant. A Ziehl-Neelsen stain confirmed the absence of any significant mycobacterial clumping in the suspension. A final concentration of approximately 10’ cfu/mL was used and confirmed by serial dilution and plating onto Middlebrook’s 7HlO agar. Cryptosporidial suspensions were prepared as described previouslyh and stored in potassium dichromate. Prior to exposure to the disinfectants the cysts were washed and suspended in RPM1 cell culture medium. Disinfectants were tested in the presence and absence of an organic load (lo”/, horse serum) at 23°C. Eight hundred microlitres of each bacterial suspension was added to 8 mL of disinfectant in glass bijous and samples removed at 5, 10, 30 and 60 min. At each time interval, 1 mL was removed and inoculated directly into 100 mL of Middlebrook’s broth and 1 mL was diluted into 20 mL of an inactivator (0.5% sodium bisulphite for ‘Cidex’ and 0.025% catalase + 5% sodium thiosulphate for ‘Nu-Cidex’), left for 10 min and filtered with excess broth through a 0.45ym membrane filter. The filter was then placed on the surface of Middlebrook’s agar. Incubation was at 32°C for six weeks. Surface tests were performed on sterile glass cover strips in the wells of a tissue culture plate. Ten microlitres of bacterial suspension was placed on the coverslip and dried overnight at 32°C. Disinfectants were added to the wells and left for the same times as the suspension tests, after which the disinfectant was aspirated, the well washed with inactivator and then filled with Middlebrook’s broth. The plates were incubated in a damp box at 32°C and growth was determined by turbidity and confirmed by ZiehlNeelsen staining. Suspensions of cryptosporidial cysts were exposed to ‘Nu-Cidex’ for similar time intervals, washed in RPM1 and then added to excystation medium (RPM1 +0.8% bovine bile salts) and left for 4.5 min at 37°C. The suspensions were examined microscopically for free sporozoites, oocyst shells and intact oocysts. The excystation index was calculated as described previously.7 The lower the index, the greater the activity of the disinfectant in preventing the release of sporozoites from the cysts. The results against mycobacteria are given in Table I. Our results confirm those of Lynam et al.” in showing that ‘Nu-Cidex’ is rapidly mycobactericidal, even against drug-resistant isolates of M. tuberculosis and M. avium-intracellulare after only 5 min exposure. We have also demonstrated exceptionally good activity of this disinfectant against cryptosporidia. ‘Nu-Cidex’ completely abrogated the viability of oocysts of C. parvum. Almost 40% of oocysts incubated in excystation medium without exposure to disinfectants released their sporozoites within 4.5 min. In complete contrast, no excystation at all occurred following treatment with ‘Nu-Cidex’ even after 5 min exposure giving an excystation index of zero compared to 0.02 for glutaraldehyde after 60 min exposure.

Letters ‘I’ahlc

I. Keszrlts

of s~tspemiorl

a17ti

to the Editor

237

SIII.~~C tests of disirzfxtmts load* absence o,f ovgurlic

ngclixst

Time

irr tlrr

(min)

‘Cides’

Suspension LITB lLIB iLIDRTB

~r~ycohncterin

‘Vu-Cides’

Inoculum (cfu/ml)

5

10

30

60

3

10

30

60

1,s 1.S 3.2 1.0 3.5

x x x x x

10‘ 10 10 10” 10”

SC SC 120 SC SC

68 12 17 120 136

0 0 0 C) 0

0 0 0 0 0

NC; NG NG svc; NG

sde and ‘Nu-Cidcs’ (0.3% paracetic acid) .7 Hasp Infect 1995; 30: 237-210. 6 RIcDonald V, Deer RSIA, Nina JRIS, \Vright 5, Chiodml PL, l\IcAdam Iptosporidia. J Hasp Itl/Cct 1994; 27: 105-l 15.