Microbiological quality of the fish species Trachurus murphyi, sold at the retail level in the town of Valdivia, Chile

A microbiological survey of 80 fish samples from the species Trachurus murphyi (common name ‘jurel’), sold at retail level in the town of Valdivia, Chile, was conducted. The aerobic plate count mean (geometric) was 1·91 × 10⁶ g⁻¹ with a range from 3·90 × 10⁴ g⁻¹ to 3·12 × 10⁸ g⁻¹. The average (geometric) coliform Most Probable Number (M.P.N.) was 411 g⁻¹ with a range from 15 g⁻¹ to over 1100 g⁻¹, while the fecal coliform M.P.N. showed an average (geometric) of 5·3 g⁻¹ with counts ranging between 3·6 g⁻¹ and more than 1100 g⁻¹. Bacteria from the genus Salmonella were not found in any of the samples tested.The average pH value of the fish meat was 6·29 fluctuating between 5·87 and 7·03. Taking as a basis the microbiological standards given for frozen fish, a high percentage of the samples did not meet with the requirements set by the Chilean Sanitary Food Regulations.     

An evaluation of street-vended sliced papaya (Carica papaya) for bacteria and indicator micro-organisms of public health significance

Thirty samples of ripe papaya (Carica papaya) slices, collected in Calcutta from the itinerant roadside vendors were collected over a 3-month period. The papaya were tested for total aerobic plate count (TPC), coliform and fecal coliform counts, and various foodborne pathogens. TPCs ranged from 3·3 to 6·52 log cfu g⁻¹ (average=5·96 log cfu g⁻¹). Eleven samples had counts >6 log cfu g⁻¹. Coliforms were detected in 70% of the samples with the average concentration being 13·5 g⁻¹. The presence ofEscherichia coli was confirmed in 48% of the samples positive for coliforms. Salmonella and Vibrio cholerae were detected in one sample each, and low levels of coagulase-positive Staphylococcus aureus were detected in 17% of the samples. An apparent relationship between high aerobic plate counts, detection of coliforms and the presence of enteric pathogens was observed.     

Evaluation of buoyant density centrifugation as a sample preparation method for NASBA-ELGA detection ofCampylobacter jejuni in foods

Buoyant densities of four Campylobacter jejuni strains were in the range of 1·084–1·087 g ml⁻¹. Milk (3% fat) and chicken skin homogenates had buoyant densities beneath 1·033 g ml⁻¹. Discontinuous buoyant density centrifugation (BDC) in 40% Standard Isotonic BactXTractor medium respectively succeeded in recovering C. jejuni (5×10³–5×10⁴cfu ml⁻¹) from spiked milk (3% fat) and chicken skin. NASBA–ELGA detection of C. jejuni (5×10²–5×10³cfu ml⁻¹) in 12 different food samples using four different sample preparation methods was performed: RNA extraction by heating (filter and non-filter stomacher bag), RNA extraction by BDC (non-filter stomacher bag), RNA extraction by GuSCN–Triton-X-100 lysis and silica-purification (non-filter stomacher bag). BDC succeeded in overcoming inhibition of the amplification reaction except for one of the soft cheese samples. It was noticed that for chicken skin, chicken meat, pork, chicken sausage, turkey meat, milk (3% fat) and skimmed milk a simple heat treatment at 96°C without any additional precautions to prevent inhibition accomplished NASBA–ELGA detection of the pathogen. The use of a filter stomacher bag improved the quality of the NASBA–ELGA detection signal for beef but did not prevent inhibition of the amplification reaction in the cases of ground beef, prepared minced meat, soft cheese and hard cheese. The silica purification of RNA (which was used as a control treatment) accomplished NASBA–ELGA detection of C. jejuni for all of the latter food homogenates.     

The occurrence of Staphylococcus aureus in fermented milk products (Fura and Manshanu) in Nigeria

Ninety-three samples of fermented milk cereal (Fura) and 79 of local butter (Manshanu) were collected from four different markets around Zaria. For Fura the mean content of Staphylococci for each of the four markets ranged from 4.5 × 10³ to 4.3 × 10⁴ cfu/ml and the mean aerobic mesophilic plate count from 5.6 × 10⁵ to 2.7 × 10⁶ cfu/ml. For Manshanu the mean staphylococcal count and aerobic mesophilic plate count ranged from 3.4 × 10² to 2.2 × 10³ cfu/ml and 6.7 × 10⁴ to 1.1 × 10⁶ cfu/ml respectively. Significant differences were seen between the different markets.     

Inhibition of Clostridium sporogenes growth in mascarpone cheese by co-inoculation with Streptococcus thermophilus under conditions of temperature abuse

The ability of a biological control system to inhibit the outgrowth of Clostridium sporogenes spores during storage of mascarpone cheese under temperature-abuse conditions was investigated. Challenge studies were carried out on mascarpone cheese artificially contaminated with spores of C. sporogenes (10 cfu g⁻¹), and with or without the coinoculum of a Streptococcus thermophilus strain (10⁵cfu g⁻¹). During storage at 4, 12, and 25°C, the outgrowth of clostridia spores, the growth of S. thermophilus, and the pH changes were evaluated at 10, 20, 30, and 40 days. In mascarpone cheese stored at 4° and 12°C, S. thermophilus and C. sporogenes did not show any growth. The initial pH (6·14) of the product also remained unchanged. During storage at 25°C S. thermophilus grew up to about 10⁷cfu g⁻¹after 10 days, resulting in a pH decrease of mascarpone cheese to values close to 4·5. The cell number decreased progressively during storage reaching values near to 10¹cfu g⁻¹after 40 days, whereas product acidity remained constant. C. sporogenes, when inoculated alone, also grew at 25°C. The cell number increased to levels of about 10⁷cfu g⁻¹after 20–40 days of storage according to the different mascarpone cheese lots used. No growth was found when C. sporogenes was co-inoculated in mascarpone cheese with S. thermophilus and stored at 25°C. The study on the behaviour of C. sporogenes, known as a non-toxigenic variant of Clostridium botulinum, allowed us to obtain useful information for setting up an effective biological control system to inhibit growth of the toxigenic species as well. The use of an additional barrier, besides refrigerated storage, may help to maintain the safety of mascarpone cheese in the event it was exposed to elevated temperatures.     

Microbial and color quality of fillets obtained from steam-pasteurized deheaded and eviscerated whole catfish

The present study reports on the microbiological quality and surface color of skinless catfish fillets obtained from steam-treated catfish. Total aerobic (APC), psychrotrophic (PPC), coliform (CPC) plate counts, and Hunter color analysis of fillets were performed after treatment and during 14 days of storage at 4°C. Results indicated that as steam treatment duration increased (15–120 s), greater reduction of fillet microflora population was achieved. Microbial counts on fillets obtained from steam-treated catfish were lower than controls at all sample times. Steam treatment for 120 s produced fillets with APC, PPC, and CPC that were 1·6, 1·7, and 1·9 log₁₀cfu g⁻¹lower than control fillets after 4 days at 4°C. Hunter color analysis of fillets revealed no color differences (L, a, b, and Whiteness) between steam-treated and control fillets. The reduction of skin microbial loads by steam prior to skinning of catfish resulted in fillets with superior microbiological quality and no Hunter surface color changes.     

Microbiological quality of foods packaged under modified atmospheres

The microbiological quality of various sandwiches and meats packaged under modified atmosphere was evaluated. Samples were analyzed both on the day of manufacture and at the end of shelf life. On day 0, around 60% of products examined contained ≤10⁵ total aerobic counts g⁻¹, while at the end of the shelf life approximately 63·3% of samples contained ≥10⁷ cfu g⁻¹.Listeria spp. were found in eight of the 58 lots examined, withL. monocytogenes being present in five of the eight samples. One lot was found to containAeromonas hydrophila, while another one containedStaphylococcus aureus. Clostridium botulinum andSalmonella spp. were not found in any of the samples.     

Destruction of acid- and non-adapted Listeria monocytogenes during drying and storage of beef jerky

Presence of Listeria monocytogenes in ready-to-eat meat products is not desired and strictly regulated in the US. Inactivation of acid- and non-adapted L. monocytogenes inoculated on beef slices was studied during drying and storage of jerky formulated with modified marinades. The inoculated (five-strain composite, c. 6·2 log cfu cm⁻²) slices were subjected to marinades (4°C, 24 h) prior to drying (60°C for 10 h) and aerobic storage (25°C for 60 days). The predrying marinade treatments tested were, first, no treatment, control (C); second, traditional marinade (TM); third, double amount of TM modified with 1·2% sodium lactate, 9% acetic acid, and 68% soy sauce containing 5% ethanol (MM); fourth, dipping into 5% acetic acid for 10 min and then applying the TM (AATM); and fifth dipping into 1% Tween 20 for 15 min and then into 5% acetic acid for 10 min followed by the TM (TWTM). Bacterial survivors on beef slices were determined during drying and storage using tryptic soy agar with 0·1% pyruvate (TSAP), and PALCAM agar. Results indicated that drying reduced bacterial populations in the order of pre-drying treatments TWTM (5·9–6·3 log cfucm⁻² in 10 h)≥AATM≥MM>TM≥C (3·8−4·6 log cfucm⁻² in 10 h). No significant (P≥0·05) difference was found in inactivation of acid-adapted and non-adapted inocula within individual treatments. Bacterial populations dropped below the detection limit (−0·4 log cfucm⁻²) as early as 4 h during drying or remained detectable even after 60 days of storage depending on acid-adaptation, predrying treatment, and agar media. These results indicated that acid-adaptation may not increase resistance to microbial hurdles involved in jerky processing and that use of modified marinades may improve the effectiveness of drying in inactivating L. monocytogenes.     

Migration of α-tocopherol from an active multilayer film into whole milk powder

Antioxidant active packaging is a promising technology for whole milk powder (WMP) protection. In this study, the migration of α-tocopherol from a multilayer active packaging (made of high density polyethylene, ethylene vinyl alcohol and a layer of low density polyethylene containing the antioxidant) to WMP was studied. A model based on the Fick’s diffusion equation was used to calculate the diffusion coefficients (D) of α-tocopherol as 2.34 × 10⁻¹¹, 3.06 × 10⁻¹¹, and 3.14 × 10⁻¹¹ cm² s⁻¹ at 20, 30 and 40 °C, respectively. The D at 20 °C was different from those at 30 and 40 °C (P < 0.05); but it was similar at 30 and 40 °C. This low influence of temperature on the migration of α-tocopherol from 20 to 40 °C assures the release at real storage and commercialization conditions in regions with warm/hot climate. The antioxidant delivering system delayed the lipid oxidation of WMP and it was more effective at 30 and 40 °C since the rate of oxidative reactions was higher at these temperatures than at 20 °C.     

Environmental factors affect efficacy of some essential oils and resveratrol to control growth and ochratoxin A production by Penicillium verrucosum and Aspergillus westerdijkiae on wheat grain

This study determined the efficacy of three essential oils (bay, clove and cinnamon oil) and the antioxidant resveratrol (0–500 μg g⁻¹) on the control of growth and ochratoxin A (OTA) production by Penicillium verrucosum and Aspergillus westerdijkiae (=A. ochraceus) under different water activity (a_w, 0.90, 0.95, 0.995), and temperature (15, 25 °C) conditions on irradiated wheat grain. The most effective treatment (resveratrol) was then tested on natural grain. The ED₅₀ values for growth inhibition by the oils were 200–300 μg g⁻¹ at the a_w and the temperatures tested. For resveratrol, this varied from <50 μg g⁻¹ at 0.90–0.95 a_w to >350 at 0.995a_w at both temperatures. The ED₅₀ values for the control of OTA were slightly lower than for control of growth, with approx. 200 μg g⁻¹ required for the oils and 50–100 μg g⁻¹ of the antioxidant, at 0.90/0.95a_w and both temperatures. In wet grain (0.995a_w), higher concentrations were required. For growth there were statistically significant effects of single-, two- and three-way interactions between treatments except for concentration×temperature and concentration×temperature×essential oil/antioxidant treatment. For OTA control, statistically significant treatments were a_w, temperature×a_w, concentration×temperature, treatment×concentration, and three-way interaction of concentration×a_w×treatment for P. verrucosum and A. westerdijkiae. Subsequent studies were done with the best treatment (resveratrol, 200 μg g⁻¹) on natural wheat grain with either P. verrucosum or A. westerdijkiae at 0.85–0.995a_w and 15/25 °C over 28 days storage. This showed that the populations of the mycotoxigenic species and OTA contamination could be reduced by >60% by this treatment at the end of the storage period.     

Inhibitory effect of clove oil on Listeria monocytogenes in meat and cheese

The antilisteric activity of clove oil was examined in meat and cheese at both 30°C and 7°C. At concentrations of 0·5% and 1% clove oil restricted the growth of Listeria monocytogenes in the food items at both temperatures. The inhibitory activity of clove oil was more pronounced at a concentration of 1%.Listeria counts in treated samples were 1–3 log₁₀cfu g⁻¹less compared to controls at different intervals during storage. The results revealed the potential of clove oil as a natural preservative in meat and cheese.     

Enumeration, isolation and characterization of Bacillus cereus strains from Spanish raw rice

Bacillus cereus was present in 61 samples of raw rice analysed representing unhusked, husked and commercial origins. B. cereus in husked and white rice samples did not reach 10² cfu g⁻¹, while in the unhusked rice B. cereus densities exceeded 10³ cfu g⁻¹. Processing steps such as drying, husking and polishing reduced the number of B. cereus in the final product. Eight strains with typical morphology of B. cereus on Polymyxin–Mannitol–Egg Yolk–Phenol Red Agar (PMYPA) were isolated. According to ISO confirmatory tests, the API System tests and supplementary tests of motility, oxidase activity and enterotoxin production, these isolates were characterized and identified as B. cereus. All strains were motile, oxidase-negative and produced diarrheal enterotoxin in TSB. D and z -values were used to characterize heat resistance of spores obtained from the eight strains ofB. cereus characterized. A large diversity in heat resistance was observed among the isolates. At 90°C, D -values ranged from 2·23 to 23·26 min, with five groups of D -value means significantly different at the 95% confidence level. D₉₅- and D₁₀₀ values calculated for the eight strains ranged from 0·69 to 5·17 min and from 0·43 to 1·09 min, respectively. Statistical analysis revealed that there was significant difference between the D -value means obtained for the strains at each temperature. The z -values for the eight strains of B. cereus tested in this study ranged from 7·42°C to 8·20°C with an average of 7·7°C.     

Quantification and characterization of microbial populations associated with naturally fermented Greek dry salami

The microbial flora associated with the natural fermentation and ripening of five batches of Greek dry salami was enumerated and characterized over time. Micrococci-staphylococci increased at a level of 10⁷ cfu g^-1 during early fermentation. By day 4, lactic acid bacteria outnumbered Micrococcaceae in all batches, since they exceeded — with the exception of batch III — 10⁸ cfu g^-1. Yeasts remained below 10⁶ cfu g^-1 during the whole process, but tended to increase at a late ripening stage. Almost all colonies grown on mannitol salt agar were catalase positive cocci. Nitrate-reducing micrococci were progressively replaced by less acid-sensitive staphylococci. A high proportion (62·5%) of 112 Staphylococcus isolates grew weakly under anaerobic conditions. Typical staphylococci were less capable of reducing nitrate. Yeast populations mainly comprised Debaryomyces strains. Characterization of 348 lactic isolates indicated that the salami microflora was dominated by homofermentative lactobacilli (61·4%) and leuconostoc-like bacteria (24·9%). Most lactobacilli (51·4%) belonged to the formerly-called ‘atypical' meat streptobacteria. Typical streptobacteria (10·0%), heterofermentative lactobacilli (10·0%) and homofermentative cocci (3·1%) were mainly isolated during the first days of fermentation and failed to compete with the other two groups. The microbial interactions as reflected by the distribution and succession of different general/subgenera in each batch and their possible effect on physicochemical and sensory characteristics of the sausages were discussed.     

Effect of lactic acid on Listeria monocytogenes and Edwardsiella tarda attached to catfish skin

This study evaluated the use of lactic acid to decontaminate Listeria monocytogenes andEdwardsiella tarda attached to catfish skin with or without mucus. At the highest inoculum levels (10⁴–10⁵cfu skin⁻¹), lactic acid (0·5–2·0%) exposure for 10 min reduced counts of L. monocytogenes firmly attached to catfish skin by 0·9–>1·9 log₁₀cfu skin⁻¹and cells loosely attached by 2·7–>3·7 logs. Counts of E. tarda firmly attached to catfish skin were reduced by 0·9–>3·0 logs and cells loosely attached by 1·5–>3·5 logs. Overall bacterial numbers of lactic acid-treated cells that were firmly attached to skin with mucus were higher than on skin without mucus. Firmly attached L. monocytogenes was more resistant to lactic acid than was firmly attached E. tarda. Catfish skin mucus decreased the antimicrobial effect of lactic acid against attached L. monocytogenes and E. tarda.     

Repair and growth of heat- and freeze-injured Escherichia coli O157:H7 in selective enrichment broths

Two Escherichia coli O157:H7 strains, ATCC 35150 and 43894, were heat injured in a beef infusion at 53°C for 40 and 50 min, respectively (1· 5–2·0 log₁₀cfu ml⁻¹of injury) and freeze injured at −25°C for 30 days (1 log₁₀cfu ml⁻¹of injury) as determined by plating on MacConkey agar with 0·60% bile salts #3 (Mac-BS) as the selective medium and on Brain Heart Infusion agar (BHIA) as the non-selective medium. Repair of injury was measured in five selective enrichment broths [buffered peptone water supplemented with vancomycin, cefsulodin, and cefixime (BPW-VCC), modified EC broth with novobiocin (mEC+n), enterohaemorrhagic E. coli enrichment broth (EEB), double modified TSB (dmTSB), and BCM^®E. coli enrichment broth (BCM^®-EB)] versus TSB as the non-selective control broth over 3 h incubation at 37°C and 42°C. Repair was measured as the increase in cfu ml⁻¹enumerated on Mac-BS with time vs the total cfu ml⁻¹(injured and uninjured cells) enumerated on BHIA. In mEC+n, EEB, and dmTSB some death of both heat- and freeze-injured cells occurred immediately during the 3 h incubation (decrease on BHIA plates), and there was either minimal or no repair of the injured cells at both temperatures. Efficient repair of heat injury was obtained with both BPW-VCC and BCM^®-EB, but the latter produced a growth rate and final cell concentration closer to TSB. In freeze-injury repair however, BPW-VCC gave poor results while repair in BCM^®-EB was equal to TSB. Both BCM^®-EB and BPW-VCC inhibited the growth of all Gram-positive and a select number of Gram-negative bacteria tested. The ability of the selective enrichment broth BCM^®-EB to resuscitate heat- and freeze-injured E. coli O157:H7 efficiently within 3 h, warrants further testing with other types of stress in both artificially and naturally contaminated foods.     

Nisin treatments to control Listeria monocytogenes post-processing contamination on Anthotyros, a traditional Greek whey cheese, stored at 4°C in vacuum packages

Post-processing contamination and growth of Listeria monocytogenes in whey cheeses stored under refrigeration is an important safety concern. This study evaluated commercially available nisin (Nisaplin^®) as a biopreservative to control L. monocytogenes introduced post-processing on Anthotyros, a traditional Greek whey cheese, stored at 4°C in vacuum packages for up to 45 days. The whey used (pH 6.5–6.7) was from Feta cheese manufacture, and it was subjected either to natural acidification (pH 5.3, readjusted to 6.2 with 10% NaOH) prior to heating, or to direct acidification (pH 6.0–6.2) at 80°C with 10% citric acid. Nisin was added either to the whey (100 or 500 IU g⁻¹) prior to heating, or to the cheese (500 IU g⁻¹) prior to packaging, also inoculated with ca. 10⁴ cfu g⁻¹ of L. monocytogenes strain Scott A. In cheese samples without nisin, L. monocytogenes (PALCAM agar) exceeded 7 log cfu g⁻¹ after the first 10 days of storage, irrespective of the whey acidification method. All nisin treatments had an immediate lethal effect (0.7–2.2 log reduction) on L. monocytogenes populations at inoculation (day 0), which was more pronounced with 500 IU g⁻¹ added to the whey. This treatment also suppressed L. monocytogenes growth below the inoculation level for 30 and 45 days in naturally and directly acidified samples, respectively. All other treatments had weak antilisterial effects. Nisin reversed the natural spoilage flora of Anthotyros cheese from Gram-positive to Gram-negative, and this ecological alteration was far more pronounced in the most effective antilisterial treatments.     

Microbiological and physicochemical characteristics of Cameros cheese

Eighteen samples of Cameros cheese, a fresh Spanish goat's cheese, were collected from the four different producers of this regional kind of cheese. Physicochemical and microbiological analyses were carried out to evaluate the sanitary quality and the physicochemical characteristics of the product. The influence of the season of the year and the elaboration conditions were also studied. Cameros cheese is a fat cheese (54·2±6·5% of total solids; TS), with a high pH close to the neutrality (6·35±0·14), high moisture (TS value of 42·5±4·7%) and low salt content (0·78±0·30% of TS). Listeria monocytogenes was found in 5·6% of samples. Staphylococcus aureus counts above 2 log cfu g⁻¹were found in 55% of the cheeses studied. Thirty-three percent of the April samples and 67% of the July samples reached microbiological levels above the legally established standards. None of the samples yieldedSalmonella spp. The dairy had a significant effect on salt content (P<0·001) because different salt application methods were applied. Also significant differences (P<0·01) of S. aureus counts were detected among the different dairies. Significant seasonal differences of non-protein nitrogen (P<0·01) were detected. The season significantly affected the counts of Enterobacteriaceae (P<0·01), mesophilic micro-organisms and psycrotrophs (P<0·05) and yeast and mould counts (P<0·05).     

The effect of oxygen and redox potential on growth of Clostridium botulinum type E from a spore inoculum

Small volumes of oxygen introduced into vials of medium at pH 7 prepared under anaerobic conditions reacted with the medium during sterilization by heating, and also raised the redox potential. The partial pressure of oxygen (pO₂) in the medium, and the redox potential (E_h) were measured and their effect on the number of spores of Clostridium botulinum type E required to produce growth, and hence on the probability of growth from single spore inocula, was determined.In the presence of a pO₂ of up to 4·5 × 10⁻³ atm resulting in an E_h of c. + 217 mV, the probability of growth from single spores within 5 days at 20°C was equal to that in strictly anaerobic conditions at an E_h of − 400 mV. At pO₂ values of between 5·3 × 10⁻³ atm and 8·4 × 10⁻³ atm corresponding to E_h values of between + 226 mV and + 254 mV an inoculum of between 10 and 1000 spores was required to produce growth and at pO₂ values of between 1·12 × 10⁻² atm,and 1·6 × 10⁻² atm, corresponding to redox potentials of between + 271 mV and + 294 mV, the number of spores required to produce growth was between 2 × 10⁴ and > 2 × 10⁵. The relationship between pO₂ and E_h depends on the chemical nature of a culture medium or food, and in order to assess the probable influence of these parameters on growth of C. botulinum in a medium or a food it is necessary to determine both the redox potential and the partial pressure of oxygen.     

Behaviour of Listeria monocytogenes in the presence of Listeria innocua during storage of minced beef under vacuum or in air at 0°C and 10°C

Minced beef was inoculated with low levels (1·2–1·7 log₁₀cfu g⁻¹) of Listeria monocytogenes or Listeria innocua, or a combination of the two strains. Inoculated samples were stored at 0 or 10°C under two packaging atmospheres (aerobic and vacuum) for up to 28 days and surviving organisms recovered on Palcam Agar. The only significant increases in numbers of Listeria spp. occurred in samples held at 10°C under aerobic conditions. In vacuum packs, growth of both strains was inhibited. Under aerobic conditions meat pH increased from an initial value of pH 5·85 to c. 8·85 within 28 days. The pH of vacuum packaged meat declined to c. 4·95 during the same period. These differences in pH may be related to differences in the nature and effects of different background microflora that were observed to develop under each of these packaging conditions.Pseudomonas spp. predominated in aerobically stored beef, whereas in vacuum packed beef lactic acid bacteria predominated. No significant differences were observed between the growth rates of Listeria spp. inoculated into beef mince in pure and mixed culture. This suggests that the more frequent prevalence of Listeria innocua than Listeria monocytogenes in meat and meat products is not due to overgrowth or inhibition of the pathogen (Listeria monocytogenes) by the non-pathogen(Listeria innocua) during low-temperature storage.     

Development of a membrane filtration method for enumeration of Listeria monocytogenes from soft cheese

A new and simple analytical method has been developed to quantify low levels (≤50 cfu g⁻¹) of Listeria monocytogenes in soft cheese. The technique allows the analysis of 1 g of cheese instead of 0·1 g or 0·01 g using the ISO 11290-2 standard method. The analysis protocol combines filtration of the decimally diluted cheese suspension through a 0·45-μm pore size cellulose ester membrane, and a culture of the filter on a Palcam agar. A tween 80–trypsin treatment used to increase filterability of cheese did not reduce L. monocytogenes counts. The tested method provided more precise results (nearer to the true value) compared to the ISO 11290-2 standard method in the enumeration of L. monocytogenes from artificially contaminated cheese. However, it improves neither repeatability nor reproducibility since the selected medium, Palcam, does not allow distinction between the different Listeria species.