Bacterial hand contamination and transfer after use of contaminated bulk-soap-refillable dispensers

Bulk-soap-refillable dispensers are prone to extrinsic bacterial contamination, and recent studies demonstrated that approximately one in four dispensers in public restrooms are contaminated. The purpose of this study was to quantify bacterial hand contamination and transfer after use of contaminated soap under controlled laboratory and in-use conditions in a community setting. Under laboratory conditions using liquid soap experimentally contaminated with 7.51 log(10) CFU/ml of Serratia marcescens, an average of 5.28 log(10) CFU remained on each hand after washing, and 2.23 log(10) CFU was transferred to an agar surface. In an elementary-school-based field study, Gram-negative bacteria on the hands of students and staff increased by 1.42 log(10) CFU per hand (26-fold) after washing with soap from contaminated bulk-soap-refillable dispensers. In contrast, washing with soap from dispensers with sealed refills significantly reduced bacteria on hands by 0.30 log(10) CFU per hand (2-fold). Additionally, the mean number of Gram-negative bacteria transferred to surfaces after washing with soap from dispensers with sealed-soap refills (0.06 log(10) CFU) was significantly lower than the mean number after washing with contaminated bulk-soap-refillable dispensers (0.74 log(10) CFU; P < 0.01). Finally, significantly higher levels of Gram-negative bacteria were recovered from students (2.82 log(10) CFU per hand) than were recovered from staff (2.22 log(10) CFU per hand) after washing with contaminated bulk soap (P < 0.01). These results demonstrate that washing with contaminated soap from bulk-soap-refillable dispensers can increase the number of opportunistic pathogens on the hands and may play a role in the transmission of bacteria in public settings.     

Influence of composition of diluent on populations of yeasts and moulds recovered from raw fruits

AIMS: The aims of this study were (i) to determine the retention of viability of mycoflora removed from raw fruits, and how this affected diluents used to prepare samples for enumeration of propagules, and (ii) to evaluate the performance of recovery media for supporting colony development. METHODS AND RESULTS: Yeasts and moulds removed from seven types of raw fruit were held in seven diluents for 1 h before plating on dichloran rose bengal chloramphenicol (DRBC) agar and plate count agar supplemented with chloramphenicol (100 micro g ml-1) (PCAC). Significant reductions (P=0.05) in populations of yeasts, moulds, and yeasts plus moulds occurred within the 1 h holding period, regardless of diluent composition. Overall, retention of viability was not influenced by diluent composition, and neither DRBC agar nor PCAC were superior in supporting colony development. CONCLUSIONS: The composition of diluents used to prepare food samples for mycological analysis has little affect on the number of yeasts and moulds recovered from seven types of naturally contaminated raw fruit. Both DRBC agar and PCAC are suitable as enumeration media. SIGNIFICANCE AND IMPACT OF THE STUDY: Diluents and media most often recommended for enumerating yeasts and moulds in foods are appropriate for raw fruits.     

Salmonella-TEK, a rapid screening method for Salmonella species in food.

A micro-enzyme-linked immunosorbent assay (micro-ELISA) using the Salmonella-TEK screen kit was tested for the detection of Salmonella spp. in pure cultures as well as in 30 artificially contaminated food samples and in 45 naturally contaminated food samples. Different raw, fleshy foods and processed foods were used as test products. The artificially contaminated minced meat samples were preenriched in buffered peptone water, and after incubation, different selective enrichment broths were tested. The micro-ELISA optical density values after enrichment and isolation of the different broths were very analogous. The quickest method to detect Salmonella spp. in different foods is to enrich them with Salmosyst broth, which reduces the total analysis time to 31 h. The Salmonella-TEK kit for Salmonella spp. provides a promising test for the detection of Salmonella antigens in food even when they are present at a low concentration (1 to 5 CFU/25 g). The cross-reaction of the anti-Salmonella antibodies, especially to other gram-negative bacteria, is nil.     

Salmonella-TEK, a rapid screening method for Salmonella species in food

A micro-enzyme-linked immunosorbent assay (micro-ELISA) using the Salmonella-TEK screen kit was tested for the detection of Salmonella spp. in pure cultures as well as in 30 artificially contaminated food samples and in 45 naturally contaminated food samples. Different raw, fleshy foods and processed foods were used as test products. The artificially contaminated minced meat samples were preenriched in buffered peptone water, and after incubation, different selective enrichment broths were tested. The micro-ELISA optical density values after enrichment and isolation of the different broths were very analogous. The quickest method to detect Salmonella spp. in different foods is to enrich them with Salmosyst broth, which reduces the total analysis time to 31 h. The Salmonella-TEK kit for Salmonella spp. provides a promising test for the detection of Salmonella antigens in food even when they are present at a low concentration (1 to 5 CFU/25 g). The cross-reaction of the anti-Salmonella antibodies, especially to other gram-negative bacteria, is nil.     

PCR-based detection of enterotoxigenic Staphylococcus aureus in the early stages of raw milk cheese making

AIMS: To define PCR-based detectability of Staphylococcus aureus in raw milk and intermediate products of raw milk cheese making in the presence of a complex background microflora by targetting different specific genes harboured by a single strain. METHODS AND RESULTS: The strain Staph. aureus FRI 137 harbouring nuc, sec, seg, seh and sei genes was used in this study. Raw milk artificially contaminated by different concentrations of Staph. aureus FRI 137 was employed in dairy processing resembling traditional raw milk cheese making. Samples of milk and curds were PCR-analysed after DNA extraction by targetting all the above genes. The pathogen was detected when the initial contamination was 10(4) CFU ml(-1) by amplification of nuc and seh genes. 10(5) and 10(7) CFU ml(-1) were needed when seg or sei and sec genes were targetted, respectively. Enrichment cultures from raw milk and curd samples proved to increase the detection limit of 1 log on average. CONCLUSIONS: The direct detection of the pathogen in the raw material and dairy intermediates of production can provide rapid results and highlight the presence of loads of Staph. aureus potentially representing the risk of intoxication. However, every target gene to be used in the analysis has to be studied in advance in a system similar to the real case in order to determine the level of contamination potentially predictable. SIGNIFICANCE AND IMPACT OF THE STUDY: The detection in real dairy systems of significant loads of Staph. aureus by multiple targets PCR can be more accurate.     

Comparative evaluation of the hygienic efficacy of an ultra-rapid hand dryer vs conventional warm air hand dryers

Aims: To compare an ultra‐rapid hand dryer against warm air dryers, with regard to: (A) bacterial transfer after drying and (B) the impact on bacterial numbers of rubbing hands during dryer use. Methods and Results: The Airblade? dryer (Dyson Ltd) uses two air ‘knives’ to strip water from still hands, whereas conventional dryers use warm air to evaporate moisture whilst hands are rubbed together. These approaches were compared using 14 volunteers; the Airblade? and two types of warm air dryer. In study (A), hands were contaminated by handling meat and then washed in a standardized manner. After dryer use, fingers were pressed onto foil and transfer of residual bacteria enumerated. Transfers of 0–10⁷ CFU per five fingers were observed. For a drying time of 10 s, the Airblade? led to significantly less bacterial transfer than the other dryers (P < 0·05; range 0·0003–0·0015). When the latter were used for 30–35 s, the trend was for the Airblade to still perform better, but differences were not significant (P > 0·05, range 0·1317–0·4099). In study (B), drying was performed ± hand rubbing. Contact plates enumerated bacteria transferred from palms, fingers and fingertips before and after drying. When keeping hands still, there was no statistical difference between dryers, and reduction in the numbers released was almost as high as with paper towels. Rubbing when using the warm air dryers inhibited an overall reduction in bacterial numbers on the skin (P < 0·05). Conclusions: Effective hand drying is important for reducing transfer of commensals or remaining contaminants to surfaces. Rubbing hands during warm air drying can counteract the reduction in bacterial numbers accrued during handwashing. Significance and Impact of the Study: The Airblade? was superior to the warm air dryers for reducing bacterial transfer. Its short, 10 s drying time should encourage greater compliance with hand drying and thus help reduce the spread of infectious agents via hands.     

Spread and control of mycoplasmal infection of cell cultures.

Environmental sampling was performed during trypsinization and passage of 3T-6 cell cultures that contained a mean of 4.3 X 10(7) colony forming units (CFU) per ml supernatant of A. laidlawii. The lip of the culture flask and the outside of the used pipet were always heavily contaminated. The outside of the culture flask (3/7), the work surface (8/12) and the outside of a pan of disinfectant (4/5) were regularly contaminated with mycoplasmas. Airborne mycoplasmas were detected eight of 32 times (25%) by settling plates; simultaneous forced-air samplers by two different methods were always negative. The technician's hands were contaminated two of 15 samples. When hands were contaminated, more contamination was detected in the environment. Droplets of A. laidlawii and M. orale inoculated onto work surfaces survived drying for a minimum of 3 days, even in laminar airflow cabinets. Twenty-five of 31 (80.6%) cell culture technicians carried M. salivarium in their throats; only two carried M. orale. It is concluded that mycoplasma-infected clltures are the most common source of further infection. Recommendations for prevention and control of mycoplasmal infection are listed.     

Bacterial species in biofilm cultivated from the end of the Seoul water distribution system

AIMS: To investigate changes in the bacterial population and the safety of the biofilm at the end of the drinking water distribution system in Seoul (Korea), selective media and bacterial community analyses were applied to a semi-pilot galvanized iron pipe (GIP) model. METHODS AND RESULTS: No total coliforms or faecal streptococci were detected on m-Endo or m-Enterococcus agar. No Salmonella spp. and Shigella spp. were detected on bismuth sulphite agar or Hektoen enteric agar, respectively. The latter two media detected coliforms, where m-Endo was negative. Biofilm formation started within 1 week (ca 104 CFU cm(-2)) and exceeded 105 CFU cm(-2) within 6 weeks. Although the fatty acid methyl ester analysis revealed dynamic changes in bacterial composition, Micrococcus, Bacillus, and Pseudomonas spp. were persistent members of the biofilm community. Micrococcus spp. was detected most frequently and in high numbers. CONCLUSIONS: Coliforms and Enterococcus species can be recovered from biofilms in water distribution systems. SIGNIFICANCE AND IMPACT OF THE STUDY: This study illustrates the role of biofilms in the chronic deterioration of the water-distribution system in Seoul (Korea).     

Prevalence and lineages of Listeria monocytogenes in Chinese food products

AIMS: This study was undertaken to investigate the prevalence and lineages of Listeria monocytogenes in different kinds of food products in local Chinese markets. METHODS AND RESULTS: A total of 2686 food samples and 645 water samples were collected and L. monocytogenes was isolated from 2.28% (76 of 3331) of all samples. The prevalence of L. monocytogenes (14 of 290, 4.83%) in raw meat products was significantly higher than that in other raw food products (P < 0.05). Among 844 ready-to-eat (RTE) food samples, 21 samples were positive for L. monocytogenes. RTE packaged food products from two supermarkets had a prevalence ranging from 0.00% to 25.00%. The prevalence of L. monocytogenes in meat products of freshly slaughtered hogs was 0.95% (four of 420), significantly lower than that in raw meat products in the retail markets (P < 0.05). Ten isolates were recovered from 645 water samples, which were collected after hands washing by shopkeepers or waiters. A total of 38 isolates were randomly selected for lineage classification based on the nucleotide variation of actA gene. Eighty percentage of isolates from RTE food products belonged to Lineage II while only 20% belonged to Lineage I. CONCLUSIONS: Food products in Chinese markets are contaminated with L. monocytogenes. Raw meat products have the highest contamination rates among all the raw food samples. RTE food products are more likely to be contaminated with Lineage II strains. SIGNIFICANCE AND IMPACT OF THE STUDY: The data presented here show the main contamination sources of L. monocytogenes in Chinese food products.     

The potential spread of infection caused by aerosol contamination of surfaces after flushing a domestic toilet

AIMS: To determine the level of aerosol formation and fallout within a toilet cubicle after flushing a toilet contaminated with indicator organisms at levels required to mimic pathogen shedding during infectious diarrhoea. METHODS AND RESULTS: A semisolid agar carrier containing either Serratia marcesens or MS2 bacteriophage was used to contaminate the sidewalls and bowl water of a domestic toilet to mimic the effects of soiling after an episode of acute diarrhoea. Viable counts were used to compare the numbers of Serratia adhering to the porcelain surfaces and those present in the bowl water before and after flushing the toilet. Air sampling and settle plates were used to determine the presence of bacteria or virus-laden aerosols within the toilet cubicle. After seeding there was a high level of contamination on the porcelain surfaces both under the rim and on the sides of the bowl. After a single flush there was a reduction of 2.0-3.0 log cycles cm(-2) for surface attached organisms. The number of micro-organisms in the bowl water was reduced by 2.0-3.0 log cycles ml(-1) after the first flush and following a second flush, a further reduction of c. 2.0 log cycles ml(-1) was achieved. Micro-organisms in the air were at the highest level immediately after the first flush (mean values, 1370 CFU m(-3) for Serratia and 2420 PFU m(-3) for MS2 page). Sequential flushing resulted in further distribution of micro-organisms into the air although the numbers declined after each flush. Serratia adhering to the sidewalls, as well as free-floating organisms in the toilet water, were responsible for the formation of bacterial aerosols. CONCLUSIONS: Although a single flush reduced the level of micro-organisms in the toilet bowl water when contaminated at concentrations reflecting pathogen shedding, large numbers of micro-organisms persisted on the toilet bowl surface and in the bowl water which were disseminated into the air by further flushes. SIGNIFICANCE AND IMPACT OF THE STUDY: Many individuals may be unaware of the risk of air-borne dissemination of microbes when flushing the toilet and the consequent surface contamination that may spread infection within the household, via direct surface-to-hand-to mouth contact. Some enteric viruses could persist in the air after toilet flushing and infection may be acquired after inhalation and swallowing.     

Achieving hygiene in the domestic kitchen: the effectiveness of commonly used cleaning procedures

AIMS: To quantify the transmission of Salmonella and Campylobacter to hands, cloths, and hand- and food-contact surfaces during the preparation of raw poultry in domestic kitchens, and to examine the impact on numbers of these bacteria of detergent-based cleaning alone, or in conjunction with thorough rising. METHODS AND RESULTS: Groups of volunteers prepared chickens for cooking. Surfaces were sampled either before cleaning or after cleaning using water and detergent with or without thorough rinsing. Although cleaning followed by rinsing consistently achieved decontamination of surfaces contaminated with Campylobacter, significant numbers of surfaces were still contaminated with low numbers of Salmonella. Where cloths contaminated with Salmonella were stored overnight, a reduction in the efficacy of detergent-based cleaning regimes was observed. CONCLUSIONS: Rinsing is the critical step in ensuring that bacteria are removed from surfaces during cleaning, but this may still leave residual contamination. Growth of Salmonella occurs in some contaminated cloths during overnight storage; Salmonella on cloths stored overnight are also more difficult to remove by washing. SIGNIFICANCE AND IMPACT OF THE STUDY: Rinsing, as part of the cleaning process, is a critical step in achieving hygiene in the kitchen. However, to achieve completely hygienic surfaces, the use of an antimicrobial agent may be necessary.     

Cytotoxic Bacillus spp. belonging to the B. cereus and B. subtilis groups in Norwegian surface waters

AIMS: To investigate the presence and numbers of Bacillus spp. spores in surface waters and examine isolates belonging to the B. cereus and B. subtilis groups for cytotoxicity, and to discuss the presence of cytotoxic Bacillus spp. in surface water as hazard identification in a risk assessment approach in the food industry. METHODS AND RESULTS: Samples from eight different rivers with variable degree of faecal pollution, and two drinking water sources, were heat shocked and examined for the presence of Bacillus spp. spores using membrane filtration followed by cultivation on bovine blood agar plates. Bacillus spp. was present in all samples. The numbers varied from 15 to 1400 CFU 100 ml(-1). Pure cultures of 86 Bacillus spp. isolates representing all sampling sites were characterized using colony morphology, atmospheric requirements, spore and sporangium morphology, and API 50 CHB and API 20E. Bacillus spp. representing the B. cereus and B. subtilis groups were isolated from all samples. Twenty-one isolates belonging to the B. cereus and B. subtilis groups, representing eight samples, were screened for cytotoxicity. Nine strains of B. cereus and five strains belonging to the B. subtilis group were cytotoxic. CONCLUSIONS: The presence of cytotoxic Bacillus spp. in surface water represents a possible source for food contamination. Filtration and chlorination of surface water, the most common drinking water treatment in Norway, do not remove Bacillus spores efficiently. This was confirmed by isolation of spores from tap water samples. SIGNIFICANCE AND IMPACT OF THE STUDY: Contamination of food with water containing low numbers of Bacillus spores implies a risk for bacterial growth in foods. Consequently, high numbers of Bacillus spp. may occur after growth in some products. High numbers of cytotoxic Bacillus spp. in foods may represent a risk for food poisoning.     

Evaluation of different growth media for the recovery of the species of Alicyclobacillus

AIMS: Five different isolation media, namely potato dextrose agar (PDA), orange serum agar (OSA), K agar, yeast-starch-glucose agar and Bacillus acidocaldarius medium were evaluated for the recovery of Alicyclobacillus spp. from inoculated diluted and undiluted fruit-juice concentrates. METHODS AND RESULTS: Plates of PDA (pH 3.7), spread with vegetative cells (3.9 x 10(6) CFU ml(-1)) of Alicyclobacillus acidoterrestris from single-strength pear juice, recovered 2.9 x 10(6 )CFU ml(-1) after 5 days at 50 degrees C (74% recovery). The recovery of endospores from single-strength pear juice, after a heat treatment at 80 degrees C for 10 min, was higher on spread plates of OSA (pH 5.5) at 50 degrees C for 5 days (97% recovery). CONCLUSIONS: PDA (pH 3.7) and OSA (pH 5.5) at 50 degrees C for 3-5 days recovered the highest numbers of vegative cells and endospores of Alicyclobacillus spp. from sterilized fruit juices and concentrates. SIGNIFICANCE AND IMPACT OF THE STUDY: The most appropriate synthetic media for the recovery of Alicyclobacillus species from inoculated fruit juices and concentrates are shown.     

Nonrecovery of varying proportions of viable bacteria during spread plating governed by the extent of spreader usage and proposal for an alternate spotting-spreading approach to maximize the CFU

Aims: To elucidate the cause of high variations and inconsistencies in bacterial CFU observed within and between different experiments while assessing viable bacterial counts through spread plating (SP). Methods and Results: Following the inconsistent results, CFU estimations were undertaken through conventional SP using the spreader, or a modified approach that did not use spreader employing four organisms. The latter approach involving spotting‐and‐tilt‐spreading of inoculum on agar surface [spotting spreading (SS)] yielded higher CFU by 11–120% over the weighted average depending on the organism and diluent. The adverse effect owing to the spreader was the most obvious in Escherichia coli followed by Staphylococcus epidermidis, Enterobacter cloacae and Bacillus pumilus. Plate attributes that determined the surface moisture levels of agar medium and the spreading practice adopted by the personnel formed two other major influencing factors. Plating for shorter periods (<60 s) using fresh 15/20 ml plates caused loss of 3–12% CFU owing to inoculum adhesion to spreader irrespective of glass or polypropylene make. On the other hand, prolonging the plating brought down the CFU significantly. Spreader movement on agar surface subsequent to the exhaustion of free moisture, which was marked by the experiencing of some friction to smooth spreader movement, was detrimental to vegetative cells, while Bacillus spores were less affected. Conclusions: The study brings out that the way SP is carried out exerts significant effects on CFU influenced by plate conditions. Prolonged use of spreader on dry agar surface could be highly detrimental to bacterial cells. A mild use of spreader accounting for spreader‐adhering inoculum or the practice of SS not involving the spreader is recommended. Significance and Impact of the Study: This study unravels the effects owing to the spreader on bacterial cells and the CFU and recommends an alternate approach of SS to minimize CFU inconsistencies and to maximize the viable bacterial counts.     

PCR detection of Listeria monocytogenes: a study of multiple factors affecting sensitivity

AIMS: To test, under comparable conditions, several parameters affecting sensitivity of PCR detection in order to establish a PCR procedure suitable for the routine detection of Listeria monocytogenes in food. METHODS AND RESULTS: Beef samples artificially inoculated were used to determine sensitivity of PCR detection under different parameters. As few as 1 CFU g(-1) were detected by DNA extraction using a DNeasy Tissue Kit (Qiagen GmhH, Hilden, Germany) of 1 ml aliquot and PCR amplification with primers directed to the hlyA gene. This PCR protocol was applied in 60 naturally contaminated foods, comparing two enrichment procedures with the traditional culture method. The highest number of positives was recorded by PCR following a 24-h pre-enrichment step at 30 degrees C and a 24-h enrichment step at 37 degrees C. Afterwards, it was applied in 217 naturally contaminated foods and 56 of them tested positive for L. monocytogenes in which only 17 tested positive using the culture method. CONCLUSIONS: The PCR procedure described has proved to be a rapid and sensitive method suitable for the routine analysis of different types of food. SIGNIFICANCE AND IMPACT OF THE STUDY: The method proposed for the detection of L. monocytogenes, has been validated in naturally contaminated food and is suitable to implement in the food industry.     

Prevalence and growth of Listeria monocytogenes in naturally contaminated cold-smoked salmon

AIM: To investigate Listeria monocytogenes contamination and behaviour in naturally contaminated French cold-smoked salmon (CSS). METHOD AND RESULTS: Between 2001 and 2004, L. monocytogenes was detected in 104 of 1010 CSS packs, produced by nine French plants, with different prevalence (from 0% to 41%). The initial contamination, measured with a sensitive filtration method, was low (92% of contaminated products below 1 CFU g(-1)) and growth was limited. CONCLUSION: Growth was consistent with results of a predictive model including microbial competition. SIGNIFICANCE AND IMPACT OF THE STUDY: To be included in a quantitative risk assessment.     

Enumeration of heterotrophs, fecal coliforms and Escherichia coli in water: comparison of 3M Petrifilm plates with standard plating procedures

A total of 177 naturally contaminated water samples were analyzed by membrane filtration according to the Standard Methods for the Examination of Water and Wastewater published by the American Public Health Association. Filters were incubated in parallel on mHPC-agar and 3M™ Petrifilm™ Aerobic Count Plates (Petrifilm™ AC plates) for heterotrophic counts. Fecal coliforms and Escherichia coli were enumerated on mFC-agar and 3M™ Petrifilm™ E. coli/Coliform Count Plates (Petrifilm™ EC plates). Typical colonies on each media type were confirmed following standard procedures. Heterotrophic counts were between 10³ and 10⁴ CFU/mL and the average log₁₀ counts obtained on Petrifilm™ AC plates were about two-fold lower than on mHPC-agar. Counts for fecal coliforms and E. coli were between 10² and 10³ CFU/mL. Average log₁₀ counts for confirmed fecal coliforms obtained on Petrifilm™ EC plates were slightly lower than on mFC agar with a correlation coefficient of 0.949. The average log₁₀ counts for confirmed E. coli on Petrifilm™ EC plates and on mFC agar were statistically not different (P=0.126) with a correlation coefficient of 0.879. Specificity of Petrifilm™ EC plates and mFC agar was evaluated by comparing typical colony counts with confirmed counts. On mFC agar, counts for typical colonies were by 2 log₁₀ CFU higher than the actual confirmed counts. In contrast, on Petrifilm™ EC plates typical colony counts were almost identical to confirmed colony counts for both fecal coliforms and E. coli. This comparison illustrates the high specificity of Petrifilm™ EC plates for enumeration of both fecal coliforms and E. coli in water.     

HANDS-FREE, "POP-UP," ADHESIVE TAPE METHOD FOR MICROBIAL SAMPLING OF MEAT SURFACES

Microbial contamination of food is a concern to both food producers and consumers. For the food production industry surface sampling of foods is one of the simplest ways to monitor the microbial load. The objective of this experiment was to investigate the feasibility of using the less expensive and quicker "Pop-up" tape method instead of the conventional swab/rinse method for the microbial sampling of meat surfaces. An analyst can place the unit on the wrist and then use both hands to lay out all the necessary materials and take the sample with one hand. The "Pop-up" tape method was able to measure microbial loads up to 2.2 log CFU/cm² on meat surfaces. The conventional swab/rinse method was able to measure up to 8.3 log CFU/cm² on meat surfaces. The correlation coefficient (R) between the two methods was 0.91 (n=42). These data show that the "Pop-up" tape method is a viable alternative to other methods for estimating microbial surface contamination.     

Massive fungal contamination in animal care facilities traced to bedding supply.

During the course of immunologic studies involving the gastrointestinal colonization of mice with Candida albicans, it became apparent that the animals were being exposed to large numbers of Aspergillus fumigatus spores which interfered with the C. albicans colonization. To determine the source of the A. fumigatus exposure and the extent of fungal contamination of the medical school vivarium and four satellite facilities, fungal analyses of feed, bedding, and air were undertaken. Initial samples from the air were collected with 3-h settle plates; air sampling following cleanup was done with an Anderson air sampler. The source of contamination in the mouse rooms was determined to be Beta Chip bedding, which came from the manufacturer highly contaminated. Beta Chip bedding (1 g) obtained from the manufacturer just prior to testing contained 10(4) CFU of A. fumigatus, 20 CFU of a zygomycete, and 10 CFU of a Penicillium sp. Coarse-grade Beta Chip had approximately one-half those levels of contamination. Pure Cob bedding was highly contaminated also, but with a Fusarium sp. and a Cladosporium sp. Untreated and heat-treated Sani-Chip as well as all other heat-treated preparations obtained from the manufacturer contained no detectable spores. Rodent chow direct from the manufacturer had no A. fumigatus, although it did contain 150 CFU of fungus per g, including 80 CFU of a Rhodotorula sp., 60 CFU of Cryptococcus uniguttulatus, and 1 CFU of a Penicillium sp.(ABSTRACT TRUNCATED AT 250 WORDS)