Molecular characterization of extended-spectrum β-lactamases-producing Enterobacteriaceae species in ground beef and chicken meat

The objectives of this study were i) to characterize extended-spectrum β-lactamase-producing Enterobacteriaceae (ESBL-E) using pheno- and genotyping methods, ii) to evaluate the antimicrobial resistance pattern against 10 antibiotics, and iii) to investigate class 1 integron (intI1) in 80 Enterobacteriaceae isolates obtained from chicken meat (n = 40; 47 isolates) and ground beef (n = 40; 33 isolates) samples. Through the study, we found that 55 (68.7 %) of 80 Enterobacteriaceae isolates were capable of β-lactamase activity, and 38 (47.5 %) of them were multi-drug-resistant (MDR). The ground meat-origin isolates are 1.2 times more likely to produce imipenem resistance compared to chicken-meat-origin isolates (z = 2.1, p < 0.05, OR = 1.42). ESBL-E was found in 18 (22.5 %) of the isolates, 16.3 % of chicken meat and 6.3 % of ground beef origin. The bla genes were detected in 14 isolates [bla-_TEM (n = 10; 12.5 %); bla-_SHV (n = 4; 5.0 %); bla-_CTX-M (n = 0)], where the predominant species were Escherichia (E.) coli and Citrobacter braakii. The nine ESBL-E isolates were MDR. Twenty-eight (35.0 %) of 80 isolates were found to be resistant to at least one third-generation cephalosporin, and eight (28.6 %) of them were also ESBL-E. Eleven of 16 (48.5 %) carbapenem-resistant isolates were ESBL-E. The intI1 gene was found in 13 (16.3 %) isolates, five of which were ESBL-E, and four of which were MDR. Co-existing with bla-_TEM and the intI1 isolate was ESBL-E. coli, which was resistant to nine antibiotics. In conclusion, chicken meat and ground beef may pose a potential risk of containing ESBL-E, and bla genes which could be spread to the entire food chain.

Effects of dietary supplementation of quercetin on performance, egg quality, cecal microflora populations, and antioxidant status in laying hens

Plant polyphenols, especially flavonoids, are of great interest due to their wide range of biological activities. Quercetin, a ubiquitous flavonoid, is known to have antioxidant and antibacterial effects. In this study, we investigated the effect of quercetin on performance, egg quality, cecal microflora populations, and antioxidant status in laying hens. Two hundred forty 28-wk-old Hessian laying hens, with an average laying rate of lay 85% at the start, were randomly allotted to 4 treatments and fed 1 of 4 diets (negative control, 0.2, 0.4, and 0.6 g of quercetin/kg of diet) for 8 wk. Layer performance responses, egg quality parameters, cecal microflora populations and antioxidant status were measured at the end of the experiment. Results showed that feed conversion decreased as the quercetin level increased. Laying rate had a quadratic correlation with the level of quercetin (P = 0.056) and was maximized by the supplementation level of 0.2 g/kg of diet. However, no significant quercetin effect was observed on egg quality. Regression analysis showed that the population of total aerobes and coliforms decreased and the population of Bifidobacteria increased as the level of quercetin increased. Regression analysis also showed the activities of Cu-Zn-superoxide dismutase increased as the level of quercetin increased (P < 0.05). Results of the study suggest that the appropriate level of supplementation is 0.367 to 0.369 g of quercetin/kg of feed based on the improvement of laying rate (with 88.55 as maximum value) and feed conversion (with 2.0725 as minimum value). Our observations provided further evidence that dietary supplementation of quercetin improved performance by modulation of intestinal environment and liver superoxide dismutase content in laying hens. Quercetin has the potential as functional feed additive in animal production.

Effects of different molting procedures on incidence of Salmonella infection in flocks of naturally contaminated laying hens in a commercial egg-producing farm by detection of yolk antibodies to Salmonella in eggs

Indirect enzyme-linked immunosorbent assays (ELISAs) have been applied to detect immunoglobulin Y antibodies to different serotypes of Salmonella in the yolks of chicken eggs with heat-extracted antigens of Salmonella enterica serotypes Agona (SA), Cerro (SC), Enteritidis (SE), Montevideo (SM), and Putten (SP). The egg yolk samples examined were classified as positive if their ELISA absorbance values exceeded the value for eggs from specific-pathogen-free flocks by more than two standard deviations. Of 30 egg yolk samples from three flocks vaccinated with a killed SE vaccine, 29 were antibody positive by the ELISA assay for the SE antigen. Four to 29 of the 29 yolk samples showed positive results for the other serovars, although the absorbance values for SE were higher than those obtained for the other serotypes in each of the yolk samples. All 30 yolks from three flocks that were not administered any SE vaccines were found to be antibody negative for SE, and two samples were determined to be positive for SC. Thirty-nine or 40 eggs were obtained from each of four layer flocks in a commercial egg production farm where the laying houses were naturally contaminated with SA, SC, SM, SP, Salmonella serovar Infantis (SI), and untypeable strains. The ELISA absorbance values for SM in the egg yolks obtained from the two flocks molted through feed withdrawal when the birds restarted laying were significantly (P < 0.05) higher than those observed in the yolks obtained before the molt. In egg yolks from the two other flocks that were molted through a wheat bran diet, there was no significant difference between the absorbance values before and after the molt. The observations in the present study provide further evidence to suggest that a molt initiated through the administration of a wheat bran diet can reduce the risk for Salmonella problems in a commercial egg-producing setting.

Staphylococcus aureus growth and enterotoxin production during the manufacture of uncooked, semihard cheese from cows' raw milk

Staphylococcus aureus growth and enterotoxin production during the manufacture of model Saint-Nectaire, Registered Designation of Origin Saint-Nectaire, and Registered Designation of Origin Salers cheeses, three types of uncooked, semihard, raw milk cheese, were investigated. Coagulase-positive staphylococci (SC+) grew rapidly during the first 6 h. Between 6 and 24 h, counts increased by less than 0.5 log CFU/ml. Raw milk counts ranged from undetectable (<10 CFU/ml) to 3.03 log CFU/ml. Maximal levels reached in cheese on day 1 ranged from 2.82 to 6.84 log CFU/g. The level of SC+ after 24 h was mainly influenced by the milk baseline SC+ level (correlation coefficient, r > 0.80) but pH at 6 h influenced the SC+ growth observed between 6 and 24 h (r > 0.70). Thus, the initial level of SC+ in raw milk should be maintained below 100 CFU/ml and best below 40 CFU/ml. To limit growth, acidification should be managed to obtain pH values around or below 5.8 at 6 h in Saint-Nectaire cheeses and around or below 6.3 at 6 h in Salers cheeses. Enterotoxins were only detected in two Salers cheeses whose SC+ counts on day 1 were 5.55 log CFU/g and 5.06 log CFU/g, respectively, and whose pH values at 6 h were high (approximately 6.6 and 6.5, respectively).

Salmonella in Commercially Manufactured Feeds

We collected 886 samples (68 feed ingredient samples, 189 dust samples, and 629 feed samples) from 3 feed mills each of which produced between 100,000 and 400,000 tons of feed a year. Samples were collected on 3 d (Monday, Wednesday, and Friday), during 2 seasons (early spring and summer), and between 0700 and 1700 h approximately once per hour. Samples were collected from 5 locations within each mill: ingredient receiving, at the mixer, at the pellet mill, from pellet coolers, and at load-out. Temperatures were taken of the samples obtained at the pellet mill immediately following collection. All samples were analyzed for Enterobacteriaceae counts (EC) and Salmonella. The data confirm that feed ingredients and dust can be a major source of Salmonella contamination in feed mills. There were no differences (P < 0.05) in the Salmonella contamination rates of samples collected in spring as compared with samples collected in summer. Salmonella contamination rates were observed to be higher in samples collected on Friday compared with samples collected on Monday or Wednesday, an effect that may be management related. Data collected at the pellet mill clearly illustrate the uneven distribution of Salmonella contamination in feed as well as the need for control of dust around the pellet mill. Feed samples (both mash and pellets) contaminated with Salmonella contained significantly higher EC than samples not contaminated with Salmonella. Thus, EC may provide some indication of the likelihood of Salmonella contamination in feed samples.

Monitoring of chicken houses and an attached egg-processing facility in a laying farm for Salmonella contamination between 1994 and 1998

Two chicken houses and an attached egg-processing facility in a laying farm were sampled between 1994 and 1998 to investigate Salmonella contamination. Each of the houses was environmentally controlled and fitted with egg belts that transported eggs from the houses to the egg-processing facility. Four hundred twenty-eight Salmonella isolates were obtained from 904 environmental samples collected from the houses. Two hundred fifty-two of the 428 (58.9%) isolates yielded five serotypes as follows: Salmonella enterica subsp. enterica serovar Livingstone, Salmonella serovar Cerro, Salmonella serovar Montevideo, Salmonella serovar Mbandaka, and Salmonella serovar Corvallis. The remaining (41.1%, 176 of 428) isolates included four other serotypes and isolates that were untypeable. Salmonella isolates obtained from the drain water collected after the washing of the eggs in the egg-processing facility yielded the same serotypes as those found in the chicken houses. Strains having an identical pulsed-field gel electrophoresis (PFGE) pattern were continually recovered from a house for more than 1 year. Several strains of Salmonella Cerro, Salmonella Mbandaka, and Salmonella Montevideo obtained from both the houses and from the egg-processing facility were indistinguishable by PFGE, respectively. These results suggest that Salmonella organisms originating from a single clone colonized the chicken houses and that the egg belts are likely to be one of the means by which Salmonella organisms are spread from one house to the others.

Update on media for isolation of Enterobacteriaceae from foods

Testing for 'total' Enterobacteriaceae, coliforms and Escherichia coli as marker organisms in foods and detection of specific pathogens of the family Enterobacteriaceae, including pathogenic E. coli, Salmonella, Shigella and Yersinia spp. is widely applied in many food control laboratories. This review describes some recent developments in culture media for these organisms. Methods for enumeration of E. coli include the standard MPN technique, a membrane-filter method and the use of media containing chromogenic and fluorogenic indicators for beta-D-glucuronidase (GUD) activity. Shiga toxin-producing E. coli O157 strains usually do not ferment sorbitol and are GUD-negative. These characteristics are used in selective media for these organisms, such as cefixime tellurite sorbitol MacConkey agar. For the detection of salmonellae, motility enrichment in Modified Semisolid Rappaport-Vassiliadis (MSRV) medium shows equal or better results than the use of standard Rappaport-Vassiliadis broth. Addition of nitrofurantoin to diagnostic semisolid salmonella agar and to xylose lysine desoxycholate agar favours the isolation of S. enteritidis. Recently developed salmonella media use different selective and diagnostic properties, such as acid formation from propylene glycol, glucuronate fermentation, fermentation of glycerol and addition of Tergitol 4 as selective agent. The isolation of Shigella spp. from foods is rather difficult and further evaluation of suggested isolation systems and the development of more effective methods for the isolation of this pathogen are needed. Yersinia enterocolitica includes both pathogenic and nonpathogenic biotypes and serogroups. As no single procedure will recover all pathogenic strains of Y. enterocolitica, the use of two isolation procedures in parallel is recommended.

Media for 'total' Enterobacteriaceae, coliforms and Escherichia coli

Selective and enrichment media for the isolation and enumeration of 'total' Enterobacteriaceae, coliforms, faecal coliforms and E. coli from foods are described. The effects of time and temperature of incubation are discussed. Reports of some comparative studies of these media and factors to be considered in the selection of media for this group of organisms are noted and the difficulties associated with the isolation and enumeration of pathogenic serotypes of E. coli considered.

The enumeration of thermotrophic types amongst the Enterobacteriaceae colonizing perishable foods

A total of 41 pure cultures of Enterobacteriaceae, comprising 32 thermotrophic and nine psychrotrophic strains, pathogens or marker organisms, were examined for numbers of colony forming units obtained at 37 degrees and 42.5 degrees C (thermotrophs) and 30 degrees C (psychrotrophs), when surface-plated on a rich infusion agar and violet red bile agar. In addition 42 food and water samples, collected in a rural area of the Philippines, were examined by surface inoculating violet red bile AIPC (agar immersion plating and contact; 'dip') slides and incubating at 37 degrees and 42.5 degrees C. At 42.5 degrees C there was almost total recovery of the thermotrophic Enterobacteriaceae, whereas the psychrotrophic strains were completely suppressed. At 37 degrees C the psychrotrophs were only slightly inhibited. The Philippine foods, predominantly cooked meals, milk and drinking water, appeared to be significantly colonized by thermotrophic Enterobacteriaceae. It is concluded that incubation at 42.5 degrees C satisfactorily selects enteropathogenic and other enteric Enterobacteriaceae while suppressing the psychrotrophic types which are mainly of vegetable origin. It is emphasized that, regardless of the temperature used, a resuscitation procedure for Enterobacteriaceae populations that have incurred sublethal injury in food has to precede counts on or in the usual selective media.

Enterobacteriaceae as indicators of good manufacturing practices in rendering plants

Finished products and samples from the environment of the production line in rendering plants were checked for Enterobacteriaceae and salmonellae. Improvements in hygiene and measures taken to limit multiplication of microorganisms in the dry area of the production lines resulted in reduction of both numbers of Enterobacteriaceae in environmental samples and frequency of their occurrence in finished products. Simultaneously, there was an equivalent reduction of salmonellae positives in environmental samples and finished products. Consequently, the determination of Enterobacteriaceae can be used as an effective tool to assess the improvements in good manufacturing practices.

Quality assurance of selective culture media for bacteria, moulds and yeasts: an attempt at standardization at the international level

To facilitate monitoring of culture media, a simple quantitative streaking technique, implying ever-decreasing numbers of colony-forming units per surface area, as in spiral plating, was developed. The procedure evaluates, in quantitative terms, the ability of media (1) to support the formation of colonies by organisms that it was designed to grow and (2) to resist colonization by organisms that it is expected to suppress. The procedure was therefore termed ecometric evaluation. The ecometric results appeared to agree well with observations made on productivity and selectivity of the media studied during routine examination of specimens. These encouraging results prompted further, rigorous standardization of ecometry. A template was developed to standardize inoculation and the depth of the agar was controlled to within +/- 10%. Finally the attributes of the inocula used were accurately defined. The standardized ecometric technique has been found useful for the following purposes: (1) to assess the practical significance of the inhibitory effect of gentamicin observed in some moulds and yeasts (this was solved by replacing poorer basal media by one particular richer modification, viz, yeast morphology agar); (2) the development of a blood-free selective enumeration medium for Campylobacter jejuni, i.e. sulphide iron motility agar plus the combination of antibiotics suggested by Skirrow (1977); and (3) verification of the absence of antimicrobial activity of enzyme preparations, e.g. catalase, used in culture media to remedy sublethal damage in certain groups of bacteria. Ecometric evaluation can now be recommended for (1) routine monitoring of consignments of dehydrated or ready-to-use, purchased media; and (2) in-house checking of the functioning of medium preparation departments. Only occasionally is it necessary to use conventional counting techniques to confirm the results.

Enterobacteriaceae associated with meats and meat handling

The source of Enterobacteriaceae on meats was shown to be associated with the meat-handling work surfaces in two packing plants studies. A total of 2,343 Enterobacteriaceae were isolated and identified from meat samples and work surfaces at the packing plants and at the retail facilities. Escherichia coli biotype I and Serratia liquefaciens were detected at all stages of meat handling, indicating that they may be present in meats throughout the meat-handling system. Enterobacter agglomerans and S. liquefaciens were the predominant Enterobacteriaceae at the retail level, but they had limited indicator potential for sanitation and hygiene, Klebsiella pneumoniae was a frequent isolate among Enterobacteriaceae from meats and meat-handling surfaces in the packing plants but not at the retail level, indicating that this organism might signal unhygienic handling of meats at the retail level.

The reliability of the examination of foods, processed for safety, for enteric pathogens and Enterobacteriaceae: a mathematical and ecological study

Because of the paucity of quantitative data on numbers of other enteric pathogens in food, the reliability of the examination of processed foods for Enterobacteriaceae was estimated taking Salmonella as a model. For this purpose an assessment was carried out of the risk of accepting Salmonella contaminated consignments of foods, despite a negative outcome of (i) examination of 1.5 kg samples for Salmonella; (ii) examination of one or two 1 g samples for Enterobacteriaceae; (iii) simultaneous application of both tests. The computations were based on the results of the examination of 6830 samples of dried foods, processed for safety, out of a total of 18170 samples.Only 69 samples permitted the exact calculation of the epsilon-factor, defined as c.f.u./g of Enterobacteriaceae/c.f.u./g of Salmonella; 4642 were positive for the former group but ;free' from Salmonella, and the rest were negative in both tests. Numbers of c.f.u./g for both groups, and hence the epsilon-factors, varied widely between commodities and also between different consignments of the same food product. The average for epsilon amounted to 5.8 x 10(3), far from the base-line value of 0.75 x 10(3) assessed earlier. In only 0.1% of samples did the Enterobacteriaceae test fail to achieve the required consumer protection.This investigation therefore substantiates that testing foods processed for safety by examining accurately chosen quantities for ecologically well selected and taxonomically thoroughly defined index organisms is a most effective procedure in terms both of consumer protection and simplicity of examination without compelling the food industry to achieve hardly attainable microbiological quality standards.

Strontium chloride B and E.E. enrichment broth media for the isolation of Edwardsiella, Salmonella and Arizona species from tiger snakes

Strontium chloride B medium and E.E. broth have been found effective in the recovery of Edwardsiella, Salmonella and Arizona species from the cloacal contents of tiger snakes (Notechis scutatus). Strontium chloride B medium was superior to E.E. broth.At least one bacterial species was detected in each of the 60 reptiles examined, and all three organisms were recovered from each of 29 snakes on a single examination.Strontium chloride M, strontium selenite and Rappaport enrichment media and bismuth sulphite agar, although satisfactory for the isolation of Salmonella and Arizona species, were found unsuitable for Edwardsiella tarda.

Rapid detection of sublethally impaired cells of Enterobacteriaceae in dried foods

Samples of dried foods, feeds, and drugs were examined for Enterobacteriaceae by using buffered glucose-Brilliant Green-bile broth as the final enrichment medium and deep tubes of violet-red-bile-glucose-agar for confirmation. The pre-enrichment treatments used for the resuscitation of sublethally impaired cells were overnight incubation in lactose broth versus incubation for 1 to 6 hr at room temperature in shallow layers of tryptone soya peptone broth. The latter restoration treatment appeared to be significantly more productive.

Method for microbiological testing of nonsterile pharmaceuticals

A method for testing nonsterile pharmaceutical preparations for their microbial content is described. As far as possible, only solid culture media were used to obtain quantitative results. Aqueous and water-soluble products were tested with membrane-filter techniques. Nonfilterable products were first emulsified or suspended and the homogenate was used for examination. In both procedures, the total number of colonies is determined for aerobic bacteria and fungi. Tests for certain undesirable microbial groups were conducted with selected media. The method described is applicable for finished products, bulk products, raw materials, and active ingredients.