Antimicrobial action of nisin against Salmonella typhimurium lipopolysaccharide mutants.

The antimicrobial activity of nisin against outer membrane lipopolysaccharide mutants of Salmonella typhimurium LT2 was investigated. Nisin sensitivity was associated with the extent of saccharide deletions from the outer membrane core oligosaccharide. The results indicated that the core oligosaccharide in lipopolysaccharide plays a role in nisin sensitivity.

Nisin treatment for inactivation of Salmonella species and other gram-negative bacteria.

Nisin, produced by Lactococcus lactis subsp. lactis, has a broad spectrum of activity against gram-positive bacteria and is generally recognized as safe in the United States for use in selected pasteurized cheese spreads to control the outgrowth and toxin production of Clostridium botulinum. This study evaluated the inhibitory activity of nisin in combination with a chelating agent, disodium EDTA, against several Salmonella species and other selected gram-negative bacteria. After a 1-h exposure to 50 micrograms of nisin per ml and 20 mM disodium EDTA at 37 degrees C, a 3.2- to 6.9-log-cycle reduction in population was observed with the species tested. Treatment with disodium EDTA or nisin alone produced no significant inhibition (less than 1-log-cycle reduction) of the Salmonella and other gram-negative species tested. These results demonstrated that nisin is bactericidal to Salmonella species and that the observed inactivation can be demonstrated in other gram-negative bacteria. Applications involving the simultaneous treatment with nisin and chelating agents that alter the outer membrane may be of value in controlling food-borne salmonellae and other gram-negative bacteria.

Acute toxicity of the natural algicide, cyanobacterin, to Daphnia magna.

Cyanobacterin is a potent, photosynthetic inhibitor produced as a secondary metabolite by the filamentous, freshwater cyanobacterium Scytonema hofmanni. With a spectrum of activity encompassing species of cyanobacteria and eucaryotic algae as well as higher plants, cyanobacterin might be utilized as a commercial algicide for algae waterbloom control. As a component of the preliminary environmental risk/hazard evaluation of this proposed application, the acute toxicity of cyanobacterin to the planktonic crustacean, Daphnia magna, was assessed. Based on five trials, the 48-hr LC50 for D. magna was determined to be approximately 1.37 micrograms/ml (range: 0.78-2.58 micrograms/ml). In addition, a significant percentage of the surviving daphnids were completely immobile at the end of the 48-hr exposure period. These results give strong indication that cyanobacterin and/or its residues exhibit some nontarget organism lethality at projected use-concentration level. Furthermore, estimates of partition coefficients and bioconcentration factor, generated through quantitative structure-activity relationships, suggest that sediment, suspended particulates, and biota may serve as major compartments of cyanobacterin partitioning in an aquatic ecosystem. Before cyanobacterin should be further considered for application as a commercial algicide, a rigorous evaluation of nontarget organism lethality and environmental fate is required.

Hydrophobicity of Bacillus and Clostridium spores.

The hydrophobicities of spores and vegetative cells of several species of the genera Bacillus and Clostridium were measured by using the bacterial adherence to hexadecane assay and hydrophobic interaction chromatography. Although spore hydrophobicity varied among species and strains, the spores of each organism were more hydrophobic than the vegetative cells. The relative hydrophobicities determined by the two methods generally agreed. Sporulation media and conditions appeared to have little effect on spore hydrophobicity. However, exposure of spore suspensions to heat treatment caused a considerable increase in spore hydrophobicity. The hydrophobic nature of Bacillus and Clostridium spores suggests that hydrophobic interactions may play a role in the adhesion of these spores to surfaces.

Vapor-phase hydrogen peroxide as a surface decontaminant and sterilant.

The feasibility of utilizing vapor-phase hydrogen peroxide (VPHP) as a surface decontaminant and sterilant was evaluated in a centrifuge application. The prototype VPHP decontamination system, retrofitted into a Beckman L8-M ultracentrifuge, was designed to vaporize a 30% (wt/wt) solution of aqueous hydrogen peroxide continuously injecting and withdrawing VPHP in a deep-vacuum flow-through system. VPHP cycles of 4, 8, 16, and 32 min were examined for cidal activity against spores of Bacillus subtilis subsp. globigii and Bacillus stearothermophilus. Spore inocula (approximately 10(6)/coupon) were dried onto 0.5-in. (1.27-cm)-square stainless-steel coupons, and coupons were suspended in the centrifuge chamber, the space between the refrigeration can and the barrier ring (inner gap), and the space between the barrier ring and the vacuum ring (outer gap). At a chamber temperature of 4 degrees C, B. subtilis subsp. globigii spores were inactivated within 8 min, while inactivation of spores located in the outer gap at 27 degrees C required 32 min. The elevated temperature and high surface area/volume ratios in the outer gap may serve to decompose the gas more rapidly, thus reducing cidal efficacy. Of the two test spores, B. stearothermophilus was more resistant to VPHP. Nonetheless, VPHP was shown to possess significant sporicidal capability. For practical decontamination applications of the type described, VPHP shows promise as an effective and safer alternative to currently used ethylene oxide or formaldehyde vapors.

Microbial contamination associated with routine aseptic practice.

We have studied the rate of fortuitous contamination associated with routine aseptic technique under operational conditions. Stainless steel strips, as simulators of surgical instruments, were contained in sterilized surgical packs and assayed by nursing personnel during surgical and other invasive procedures at three different hospitals. The rates of contamination observed for the 36 investigators ranged from 0% to 11.3%, with an overall rate of 2.7%. Assays conducted in a clean room environment, under conditions approaching industrial sterility standards, showed a contamination rate of 0.16%. We concluded that aseptic practices, as routinely performed without any noticeable breaks or transgressions, do not guarantee sterility. The concept of surgical sterility implies low level, but measurable, microbial contamination.

Effect of long-term storage on sterile status of devices in surgical packs.

We investigated the effect of the following on the sterile integrity of surgical packs: four wrapping materials (two-ply reusable, nonbarrier wovens, both new and previously used; disposable, barrier nonwovens; and polypropylene peel pouches), dustcovers, two storage locations, and storage times ranging from 2 to 50 weeks. Two hundred sixty-three packs containing stainless steel coupons were prepared, wrapped, sterilized, and stored. Half of the packs were dustcovered prior to storage. At monthly intervals for a year, packs of each type were opened in a laminar flow hood, and the coupons inoculated into trypticase soy broth. The coupon contamination probabilities were 0.019 for reusable, woven packs; 0.017 for disposable, nonwoven packs; and 0.016 for peel pouches. These differences were not significant. The probability of finding a contaminated coupon in any pack after 50 weeks was 0.018. No trend toward increased probability of contamination over time was observed for any of the pack types studied.

Interhospital transportation. Monitoring sterility of instrument packs.

The Minneapolis-St Paul area is currently experiencing an increase in health care mergers among hospitals. As new facilities are acquired, whether through merger or the building of satellite hospitals, economic considerations often instigate the consolidation of certain departments and services. Thus, hospitals are confronted with a new set of management problems. One such problem might be determining if the probability of contamination increases when a sterile pack is transported from the central sterile supply department of one hospital to the operating room of another hospital. This study indicates that interhospital transport of surgical packs, using a specially designed transfer system, can be accomplished without compromising the sterile status to a significantly greater degree than that associated with transport within a hospital. Many more samples would have to be assayed before these results could be considered conclusive. This study proposes a simple, reproducible, microbiologically sensitive and statistically satisfactory test to monitor the sterile integrity of surgical packs. In the past, different sterility monitoring methods proposed have required either special equipment, specially trained personnel, or complicated procedures. The assay method described here can be easily used by central sterile supply department personnel to monitor the sterile status of transported or stored surgical packs.

Microbiological evaluation of wet and dry floor sanitization systems in hospital patient rooms.

A new system for sanitizing floors in hospital patient rooms has been developed. The method consists of dry dusting with a cotton-blend, chemically treated (10% by dry mop weight) dust mop. This method was compared with a conventional cleaning protocol consisting of an initial predusting with the same nongermicidal chemical (3% by dry mop weight) followed by wet mopping with a fresh solution of a quaternary ammonium disinfectant-detergent. Each of six rooms was sampled by using RODAC plates (Becton Dickinson Labware, Oxnard, Calif.) on 10 consecutive days for each of the two methods. The study was initially performed during the summer and then repeated during the winter. Results imply that there is no significant difference between the new dry method (81.9% CFU reduction) and the conventional method (83.1% CFU reduction). Furthermore, the initial dry dusting step in the conventional method accounted for virtually all of the reduction by that method. Thus, wet mopping with a germicidal chemical produced no additional significant reduction of natural microbial populations on environmental surfaces beyond that achieved by dry dusting with dust-suppressant chemicals.

Rapid assay for in situ identification of coagulase-positive staphylococci recovered by membrane filtration from swimming pool water.

A rapid, in situ thermonuclease test that identifies colonies of Staphylococcus aureus among staphylococci isolated from swimming pool water by membrane filtration recovery on various selective and differential media is described.

Comparison of Vogel-Johnson and Baird-Parker media for membrane filtration recovery of staphylococci in swimming pool water.

Previous studies have indicated that the coagulase-positive Staphylococcus (Staphylococcus aureus) has potential as a useful indicator of the infection hazard associated with the use of swimming pools and other recreational waters. However, before this indicator system can be used effectively, a recovery system that is sufficiently selective, accurate, and reliable for the enumeration of S. aureus must be developed. In this study, Vogel-Johnson (VJ) and Baird-Parker (BP) agars were compared for efficacy in the primary isolation and recovery of S. aureus from swimming pool water. For equal sample volumes of pool water containing adequate free chlorine residual, VJ agar was found to be more selective for staphylococcal species and less inhibitory to general cell growth than was BP agar. However, neither medium was found to be sufficiently differential to permit the accurate identification of S. aureus. In contrast, water samples obtained from a swimming pool containing very low levels of chlorine (none of which was in the free form) showed abundant growth of staphylococci on both test media, with both VJ and BP agars showing increased sensitivity for the detection of S. aureus. Thus, VJ and BP agars show increased sensitivity for the detection of coagulase-positive staphylococci from unchlorinated versus chlorinated waters.