Prevalence of Salmonella enterica, Listeria monocytogenes, and Escherichia coli virulence factors in bulk tank milk and in-line filters from U.S. dairies

The zoonotic bacteria Salmonella enterica, Listeria monocytogenes, and Escherichia coli are known to infect dairy cows while not always causing clinical signs of disease. These pathogens are sometimes found in raw milk, and human disease outbreaks due to these organisms have been associated with the consumption of raw milk or raw milk products. Bulk tank milk (BTM) samples (536) and in-line milk filters (519) collected from dairy farms across the United States during the National Animal Health Monitoring System's Dairy 2007 study were analyzed by real-time PCR for the presence of S. enterica and pathogenic forms of E. coli and by culture techniques for the presence of L. monocytogenes. S. enterica was detected in samples from 28.1% of the dairy operations, primarily in milk filters. Salmonella was isolated from 36 of 75 PCR-positive BTM samples and 105 of 174 PCR-positive filter samples, and the isolates were serotyped. Cerro, Kentucky, Muenster, Anatum, and Newport were the most common serotypes. L. monocytogenes was isolated from 7.1% of the dairy operations, and the 1/2a complex was the most common serotype, followed by 1/2b and 4b (lineage 1). Shiga toxin genes were detected in enrichments from 15.2% of the BTM samples and from 51.0% of the filters by real-time PCR. In most cases, the cycle threshold values for the PCR indicated that toxigenic strains were not a major part of the enrichment populations. These data confirm those from earlier studies showing significant contamination of BTM by zoonotic bacterial pathogens and that the consumption of raw milk and raw milk products presents a health risk.     

Fecal shedding of Salmonella spp. by dairy cows on farm and at cull cow markets

As part of a national study of the U.S. dairy cow population, fecal samples were collected from representative cows on 91 dairies and 97 cull dairy cow markets in 19 states. Salmonella spp. were recovered from 5.4% of milk cows, 18.1% of milk cows expected to be culled within 7 days, and 14.9% of culled dairy cows at markets. On a premise basis, Salmonella shedding in milk cows was detected on 21.1% of dairies and 66% of cull dairy cow markets. The percentage of herds with at least one cow with detectable Salmonella fecal shedding was higher during the sampling period from May through July, in herds with at least 100 milk cows, and in herds in the South region. The most common Salmonella serogroups isolated were E (30.8% of isolates) and C1 (28.6%); the most common serotypes isolated were Salmonella Montevideo (21.5% of isolates), Salmonella Cerro (13.3%), and Salmonella Kentucky (8.5%). Fecal shedding of Salmonella Typhimurium or Salmonella Typhimurium var. copenhagen was infrequent (2.8% of isolates). Most isolates (88.9%) were susceptible to all 17 antimicrobials evaluated; multiple resistance was an infrequent occurrence. This study provides information describing the distribution of Salmonella fecal shedding from dairy cows on farm and at markets and will serve as a baseline for future studies.     

Prevalence of foodborne pathogens in bulk tank milk.

Bulk tank milk from 131 dairy herds in eastern South Dakota and western Minnesota was examined for the presence of for foodborne pathogens. Campylobacter jejuni, shiga-toxin producing Escherichia coli, Listeria monocytogenes, Salmonella spp., and Yersinia enterocolitica were detected in 9.2, 3.8, 4.6, 6.1, and 6.1% of bulk tank milk samples, respectively. Thirty-five of 131 (26.7%) bulk tank milk samples contained one or more species of pathogenic bacteria. Isolates of Salmonella belonged to group D (n = 4), B (n = 2), C (n = 1), and E (n = 1) "O" serogroups. All six isolates of Listeria monocytogenes were identified as O antigen type 1. Four of five isolates of E. coli encoded for the shiga-toxin 2 gene, while one strain encoded for the shiga-toxin 1 gene. Escherichia coli O157:H7 was not isolated from bulk tank milk samples. Based on autoagglutination testing, it was inferred that all eight isolates of Yersinia enterocolitica were likely to be virulent. Non A-grade (manufacturing grade) raw milk producers were at a higher risk (odd's ratio, 4.98; confidence interval, 1.96 to 12.22) of having one or more pathogens in their bulk tank milk than were Grade A producers. It was observed that 21 of 79 (26.6%) dairy producers who consumed raw milk had one or more pathogenic bacteria in their bulk tank milk. The findings of the study warrant the need for educational programs for dairy producers about the risks associated with consumption of raw milk.     

Molecular characterization of Salmonella spp. isolated from bulk tank milk and cull dairy cow fecal samples

The consumption of meat from cull dairy cows and of raw milk has been associated with foodborne salmonellosis. This survey was conducted to establish the prevalence of Salmonella in cull dairy cow fecal samples and bulk tank milk and to determine the proportion of Salmonella-positive dairy farms (n = 30) in east Tennessee. Food and Drug Administration bacteriological analytical protocols were generally used for Salmonella isolation. Primary enrichment was performed with lactose broth, and secondary enrichment was conducted with tetrathionate broth. Eosin methylene blue, hektoen enteric, xylose lysine desoxycholate, bismuth sulfite, and brilliant green (BG) were used as isolation agars. BG agars supplemented with individual antibiotics and/or sulfur compounds were also evaluated. Six of 268 (2.24%) bulk tank milk samples and 9 of 415 (2.17%) fecal samples from 7 of 30 (25.3%) dairy farms were Salmonella-positive. Most isolates (11 of 15) were obtained between September and December. Salmonella isolates were further characterized using polyvalent somatic O Salmonella antiserum, o-nitrophenyl-beta-D-galactopyranoside (ONPG), and Analytical Profile Index (API) 20E strips for Enterobacteriaceae. Serological evaluation of presumptive positive Salmonella isolates resulted in substantial numbers of false positives (41.2%). ONPG and API 20E tests enabled further biochemical distinction of the majority of Salmonella spp. from Salmonella Arizonae and closely related members of Enterobacteriaceae like Citrobacter youngae. Pulsed-field gel electrophoresis of SpeI-digested Salmonella DNA was used to subtype isolates. The isolates grouped into four clusters. The baseline information generated in this survey is being used to develop preharvest pathogen reduction programs on selected farms.     

Environmental sampling to predict fecal prevalence of Salmonella in an intensively monitored dairy herd

Although dairy cattle are known reservoirs for salmonellae, cattle that are shedding this organism are often asymptomatic and difficult to identify. A dairy herd that was experiencing a sustained, subclinical outbreak of Salmonella enterica subsp. enterica Cerro was monitored for 2 years. Fecal samples from the lactating cows were collected every 6 to 8 weeks and tested for the presence of Salmonella. Fecal prevalence of Salmonella fluctuated throughout the observation period and ranged from 8 to 88%. Manure composites and water trough samples were collected along with the fecal samples, and bulk milk and milk filters were cultured for the presence of Salmonella on a weekly basis. Over 90% of the manure composites--representing high-animal-traffic areas-were positive at each sampling. Salmonella was detected in 11% of milk samples and in 66% of the milk filters. Results of weekly bulk milk quality testing (i.e., bulk tank somatic cell score, standard plate count, preliminary incubation count) were typically well within acceptable ranges. Milk quality variables had low correlations with herd Salmonella fecal prevalence. When observed over time, sampling period average prevalence of Salmonella in milk filters closely paralleled fecal prevalence of Salmonella in the herd. Based on results of this study, milk filters appear to be an effective method for monitoring shedding prevalence at the herd level. In-line filter testing is also a more sensitive measure of Salmonella, and perhaps other pathogens, in raw milk than testing the milk alone.     

Destruction of Mycobacterium paratuberculosis, Salmonella spp., and Mycoplasma spp. in raw milk by a commercial on-farm high-temperature, short-time pasteurizer

The 2002 NAHM's Dairy Survey indicated that 87.2% of dairy farms in the United States feed waste milk to their neonatal calves. Although cost-effective, this practice can lead to increased calf morbidity and mortality due to ingestion of pathogenic agents. In an effort to reduce the risk of infection, dairy producers are implementing on-farm pasteurization of the waste milk as a control procedure before feeding the milk to calves. In the present study, the efficacy of a commercial high-temperature, short-time (HTST) on-farm pasteurizer unit to destroy Mycobacterium paratuberculosis, Salmonella enterica spp., and Mycoplasma spp. in raw milk was evaluated. Replicate experiments were run for 3 isolates of M. paratuberculosis, 3 serovars of Salmonella (derby, dublin, typhimurium); and 4 species of Mycoplasma (bovis, californicum, canadense, serogroup 7) at 2 different levels of experimental inoculation. In addition, HTST pasteurization experiments were performed on colostrum experimentally inoculated with M. paratuberculosis. After culture of the pasteurized milk samples, no viable M. paratuberculosis, Salmonella, or Mycoplasma were recovered, regardless of species, strain, or isolate. Pasteurization of colostrum was also effective in the destruction of M. paratuberculosis but resulted in an average 25% reduction in colostral immunoglobulin. These results suggest that HTST pasteurization is effective in generating a safer product to feed to young calves.     

A survey of foodborne pathogens in bulk tank milk and raw milk consumption among farm families in pennsylvania

A 2-part study was conducted to determine the risk of exposure to human pathogens from raw milk. The first part of the study focused on determining raw milk consumption habits of dairy producers. A total of 248 dairy producers from 16 counties in Pennsylvania were surveyed. Overall, 105 (42.3%) of the 248 dairy producers consumed raw milk and 170 (68.5%) of the 248 dairy producers were aware of foodborne pathogens in raw milk. Dairy producers who were not aware of foodborne pathogens in raw milk were 2-fold more likely to consume raw milk compared with dairy producers who were aware of foodborne pathogens. The majority of dairy producers who consumed raw milk indicated that taste (72%) and convenience (60%) were the primary factors for consuming raw milk. Dairy producers who resided on the dairy farm were nearly 3-fold more likely to consume raw milk compared with those who lived elsewhere. In the second part of the study, bulk tank milk from the 248 participating dairy herds was examined for foodborne pathogens. Campylobacter jejuni (2%), Shiga toxin-producing Escherichia coli (2.4%), Listeria monocytogenes (2.8%), Salmonella (6%), and Yersinia enterocolitica (1.2%) were detected in the milk samples. Salmonella isolates were identified as S. enterica serotype Typhimurium (n = 10) and S. enterica serotype Newport (n = 5). Of the 248 bulk tank milk samples, 32 (13%) contained ≥1 species of bacterial pathogens. The findings of the study could assist in developing farm community-based educational programs on the risks of consuming raw milk.     

Monitoring and identification of bacteria associated with safety concerns in the manufacture of São Jorge, a Portuguese traditional cheese from raw cow's milk

The aim of this study was to assess the hygienic quality of raw milk used in the manufacture of S?o Jorge, a Protected Denomination of Origin Portuguese semihard cheese, as well as to ascertain the sanitary conditions prevailing during its processing. Viable counts of Enterobacteriaceae and Micrococcaceae were accordingly obtained, pertaining to 21 independent batches (including samples of raw milk, curd, and cheeses after 1, 3, and 4 months of ripening), from 7 dairy farms. Standard plate counts (log CFU per milliliter or per gram) ranged from 6.1 to 8.6 in raw milk, whereas they ranged from 7.0 to 8.0 in 4-month-old cheeses. Viable counts of Enterobacteriaceae ranged between 5.9 and 7.0 in raw milk and between 0.0 and 1.3 in 4-month-old cheeses. Species identified within this family encompassed Klebsiella oxytoca, Klebsiella cloacae, Klebsiella pneumoniae, Enterobacter sakazakii, and Escherichia coli; Klebsiella ornithinolytica, Klebsiella terrigena, and Serratia odorifera were detected only in raw milk. No Salmonella whatsoever could be detected in any of the samples. Viable counts of Micrococcaceae ranged between 4.7 and 5.9 and between 1.3 and 3.3 in raw milk and 4-month-old cheeses, respectively. Species identified within this family encompassed Staphylococcus sciuri, Staphylococcus epidermidis, Staphylococcus saprophyticus (which was found mainly in ripened cheeses), and Staphylococcus aureus (which was not detected in 4-month-old cheeses). Accompanying physicochemical analyses included determination of moisture, salt, and pH. Statistical analyses revealed a negative correlation between salt content and viable numbers of Enterobacteriaceae in cheese, whereas in the case of Micrococcaceae, a more negative correlation was found between viable numbers and moisture content than between viable numbers and pH. The results of our study indicate, in general, poor milk handling conditions in all farms, given that the indicators total mesophile and Enterobacteriaceae counts were high, between 100- and 1,000-fold those enforced by international standards pertaining to the matrices in question. However, by the time of regular consumption (i.e., after 4 months of ripening), S?o Jorge cheeses exhibit low levels of contamination by Enterobacteriaceae and S. aureus, as well as absence of Salmonella.     

Effect of phage on survival of Salmonella enteritidis during manufacture and storage of cheddar cheese made from raw and pasteurized milk.

The ability of Salmonella Enteritidis to survive in the presence of phage, SJ2, during manufacture, ripening, and storage of Cheddar cheese produced from raw and pasteurized milk was investigated. Raw milk and pasteurized milk were inoculated to contain 10(4) CFU/ml of a luminescent strain of Salmonella Enteritidis (lux) and 10(8) PFU/ml SJ2 phage. The milks were processed into Cheddar cheese following standard procedures. Cheese samples were examined for Salmonella Enteritidis (lux), lactic acid bacteria, molds and yeasts, coliforms, and total counts, while moisture, fat, salt, and pH values were also measured. Salmonella Enteritidis (lux) was enumerated in duplicate samples by surface plating on MacConkey novobiocin agar. Bioluminescent colonies of Salmonella Enteritidis were identified in the NightOwl molecular imager. Samples were taken over a period of 99 days. Counts of Salmonella Enteritidis (lux) decreased by 1 to 2 log cycles in raw and pasteurized milk cheeses made from milk containing phage. In cheeses made from milks to which phage was not added, there was an increase in Salmonella counts of about 1 log cycle. Lower counts of Salmonella Enteritidis (lux) were observed after 24 h in pasteurized milk cheese containing phage compared to Salmonella counts in raw milk cheese with phage. Salmonella Enteritidis (lux) survived in raw milk and pasteurized milk cheese without phage, reaching a final concentration of 10(3) CFU/g after 99 days of storage at 8 degrees C. Salmonella did not survive in pasteurized milk cheese after 89 days in the presence of phage. However, Salmonella counts of approximately 50 CFU/g were observed in raw milk cheese containing phage even after 99 days of storage. In conclusion, this study demonstrates that the addition of phage may be a useful adjunct to reduce the ability of Salmonella to survive in Cheddar cheese made from both raw and pasteurized milk.     

Escherichia coli O157:H7, Campylobacter jejuni, and Salmonella Prevalence in cull dairy cows marketed in northeastern Ohio

Preharvest management factors are predicted to impact the prevalence of foodborne pathogens in cattle sent to slaughter. We simultaneously examined the prevalence and antibiotic resistance patterns of Campylobacter jejuni, Salmonella, and Escherichia coli O157:H7 isolated from cull dairy cattle at two livestock auctions in northeastern Ohio. Between April and September 2002, a total of 1,026 fecal samples were collected. C. jejuni was isolated from 48 of 686 (7%) fecal samples, Salmonella was isolated from 39 of 585 (6.7%) samples, and E. coli O157:H7 was isolated from 21 of 1,026 (2.1%) samples. Of the 585 samples tested for all three pathogens, at least one pathogen was identified in 86 of 585 (15%) samples. One sample was positive for both E. coli O157:H7 and C. jejuni, and five samples yielded both C. jejuni and Salmonella. Size of herd of origin could be traced for 75 to 85% of samples collected. Salmonella was isolated at higher frequencies from herds larger than 60 cattle than from smaller herds (9.0 versus 3.5%, P = 0.02). In contrast, size of herd of origin did not significantly affect the E. coli O157:H7 and C. jejuni prevalence. Approximately 90% of Salmonella and E. coli O157:H7 isolates were pansensitive to a panel of 16 antibiotics. Thirty-six percent of C. jejuni isolates were resistant to tetracycline. In this study, antibiotic resistance among the foodborne pathogens isolated from cull diary cattle was rare. Although size of dairy herd of origin was positively associated with Salmonella prevalence, herd size was not strongly associated with E. coli O157:H7 and C. jejuni prevalence in market dairy cattle. These results can be used to assess the food safety risks associated with the slaughter of cull dairy cattle.     

Salmonella in dairy operations in the United States: prevalence and antimicrobial drug susceptibility

Salmonella serotypes are important foodborne pathogens of humans that can be acquired through consumption of contaminated meat and dairy products. Salmonella infection also can be a significant animal health issue. As part of a national study of U.S. dairy operations conducted between March and September 2002, fecal samples were collected from representative cows in 97 dairy herds in 21 states and were cultured to determine the prevalence of Salmonella shedding. Salmonella was recovered from the feces of at least one cow in 30.9% of the herds. Overall, 7.3% of fecal samples were culture positive for Salmonella. The three most frequently recovered serotypes were Salmonella Meleagridis (24.1%), Salmonella Montevideo (11.9%), and Salmonella Typhimurium (9.9%). The susceptibilities of Salmonella isolates recovered were determined using a panel of 16 antimicrobial drugs. Salmonella isolates recovered from dairy cows had relatively little resistance to these antimicrobial agents; 83.0% of the isolates were susceptible to all antimicrobials tested. This study provides updated information on the prevalence and susceptibility patterns of Salmonella in dairy herds and on cow and herd characteristics. These data contribute to our understanding of the ecology of Salmonella in the dairy farm environment.     

A cross-sectional study on the prevalence of Listeria monocytogenes and Salmonella in New York dairy herds

As part of our long-term objective of assessing risk for Listeria monocytogenes and Salmonella spp. in dairy herds, we carried out a cross-sectional study to determine the prevalence of the two organisms. The study population consisted of a sample of dairy herds enrolled in the Quality Milk Promotion Services at Cornell during the period of April 1998 to March 1999. The sample was stratified by geographical region to assure representation. Four hundred and four dairy farms were enrolled in the study. In-line milk filters were collected from each farm for bacteriological examination of L. monocytogenes and Salmonella spp. Four hypothesized risk factors were evaluated for their association with the likelihood of the presence of each of the two organisms using logistic regression analysis. Listeria monocytogenes was isolated from 51 (12.6%) of the milk filters. We found region-specific differences in the rate of farms with positive milk filters for this pathogen. Salmonella spp. were isolated from 6 (1.5%) milk filters. One isolate was confirmed as Salmonella enterica Serotype Typhimurium DT 104. There was no significant association between any of the hypothetical risk factors and the likelihood of Salmonella spp. isolation. Our study demonstrated that both L. monocytogenes and Salmonella spp. were prevalent in milk filters in New York dairy herds and that Salmonella was isolated at a significantly lower rate then L. monocytogenes.     

Discrimination of Staphylococcus aureus strains from different species of Staphylococcus using Fourier transform infrared (FTIR) spectroscopy

Staphylococcus aureus is a widespread opportunistic pathogen that can cause food-borne illness and is sometimes associated with raw milk and raw milk cheese products. The traditional taxonomic procedures for classification of staphylococcal species are time consuming and often several tests are required. FTIR spectroscopy offers a rapid method for the discrimination and identification of S. aureus strains isolated from raw milk and raw milk cheeses. FTIR spectroscopy was used to discriminate S. aureus from other species of Staphylococcus. This was achieved by using a model composed of 39 species and subspecies of Staphylococcus. The model was validated using a set of spectra of strains isolated from raw milk and different varieties of French raw milk cheese. S. aureus was successfully discriminated from the other species of Staphylococcus and all the strains of S. aureus isolated from raw milk and different varieties of French raw milk cheese were also successfully identified as such. These results demonstrated that FTIR spectroscopy is a rapid (results obtained within 24 h starting from a pure strain or a single colony) and robust method for the identification of S. aureus isolates of dairy origin and food-borne origin in general.     

我国生牛乳蛋白质含量现状及影响因素调查

目的研究我国当前生牛乳的蛋白质含量和影响因素。方法分析覆盖17个省(市、自治区)18个乳品企业2014年1月—2015年2月连续12个月共30 531份生牛乳样品蛋白质含量数据,利用SPSS 19.0软件进行数据处理。结果生牛乳中蛋白质的平均含量为(3.14±0.15)g/100 g,规模化牧场、养殖小区和散户的生牛乳中蛋白质平均含量分别为(3.18±0.14)、(3.07±0.12)和(3.00±0.14)g/100 g,南方、西部、华北、东北内蒙古和大城市周边地区生牛乳蛋白质平均含量分别为(3.17±0.14)、(3.16±0.14)、(3.14±0.17)、(3.09±0.17)和(3.09±0.10)g/100 g,春、夏、秋、冬季生牛乳蛋白质平均含量分别为(3.09±0.13)、(3.07±0.13)、(3.21±0.13)、(3.20±0.14)g/100 g。结论我国生牛乳的蛋白质含量有八成以上达到3.0 g/100 g。养殖模式、养殖区域、季节和月份均会影响生牛乳中的蛋白质含量。乳脂肪、非脂乳固体、相对密度与乳蛋白含量呈正相关。     

Prevalence and risk factors for Bacillus cereus in raw milk in Inner Mongolia,Northern China

The prevalence of Bacillus cereus in raw milk from dairy herds in Inner Mongolia and associated risk factors were determined. In total, 160 raw milk samples collected from 2014 to 2015 and examined by culture methods to isolate B. cereus. Fifty‐five samples (34.38%) were positive. The prevalence of B. cereus in raw milk was significantly (P < 0.01) lower in winter (15%) than in summer (50%). The highest prevalence of B. cereus in raw milk was seen in samples collected from small‐ to medium‐sized dairy herds in summer. The results of this study indicated that B. cereus could be a common pathogen in Inner Mongolia because of its high prevalence. It is essential for dairy farmers and producers to strengthen hygienic practices in summer to control B. cereus contamination in raw milk. These results will be useful in establishing proper management procedures to reduce the prevalence of B. cereus in raw milk.     

Using a portable real-time PCR assay to detect Salmonella in raw milk

The purpose of this study was to determine the efficacy of a portable real-time PCR system in detecting Salmonella spp. in raw milk. The 200 bulk milk samples chosen for this study constituted a subset of the samples for a larger study; this subset contained 24 samples that were culture positive for Salmonella and 176 that were culture negative. Milk was both plated directly on selective agar and plated after enrichment in selective media. Presumptive Salmonella colonies were isolated by direct culturing of five samples, while Salmonella was isolated from the remaining 19 positive samples only after enrichment. Presumptive Salmonella isolates were serotyped, and isolates from 22 samples were confirmed to be Salmonella isolates. PCR assays of culture-positive milk prior to enrichment yielded no evidence of Salmonella. DNA extracts of bacterial pellets from the enriched samples were analyzed for Salmonella by real-time PCR with the Ruggedized Advanced Pathogen Identification Device (RAPID). Fifty-four samples from the enrichment pellets tested positive for Salmonella by real-time PCR. Two samples that tested positive for Salmonella by culture and serotyping tested Salmonella negative by real-time PCR. Serotyping identified isolates from these samples as Salmonella Montevideo. All DNA extracts of Salmonella Montevideo isolates tested positive for Salmonella by real-time PCR. Thirty-three samples tested negative by culture and positive by real-time PCR. These results indicate that the portable real-time PCR system appears to be a useful tool for detecting Salmonella in raw milk. Additionally, the combination of enrichment and real-time PCR techniques used in this study can yield results in 24 h, compared with the 48 to 72 h required for traditional culture.     

乳品生产链金黄色葡萄球菌的污染、耐药性分析及β-内酰胺类药物耐药基因的检测

为分析乳品生产链中金黄色葡萄球菌(Sa)的污染及耐药情况,从部分乳品生产企业采集乳样(生鲜牛乳、生产车间半成品牛乳、成品牛乳)523份,按照GB 4789.10-2010及PCR方法分离鉴定Sa菌株1;采用微量肉汤稀释法,测定Sa分离株对12种抗生素的药敏性,并利用多重PCR方法分析Sa对β-内酰胺类药物耐药性的产生与其耐药相关基因(mecA、blaZ)的关联性。结果显示,乳样Sa总分离率为24.9%(129株),其中生鲜牛乳、中间半成品牛乳及成品牛乳Sa污染率分别为37.5%、7.1%和0.0%;受试Sa分离株对青霉素的耐药率(97.7%)最高,其它依次是氨苄西林(95.4%)、甲氧苄啶/磺胺甲噁唑(61.9%)、阿莫西林/克拉维酸(61.7%)、红霉素(39.7%)、四环素(36.6%)、盐酸林可霉素(35.2%);所有菌株均对苯唑西林、头孢噻呋、氟苯尼考敏感;多重耐药Sa分离率为69.8%,主要对青霉素类、磺胺类、大环类脂类、林可胺类及四环素类表现出多重耐药;多重PCR检测结果显示,129株测试Sa的nuc、blaZ、mecA阳性率分别为100.0%、60.5%及0.0%;不同生产环节乳源Sa携带blaZ基因与其对β-内酰胺类药物的耐药表型有一定的对应关系。结果表明,乳品生产链Sa污染及耐药现状已不容乐观,应引起重视,避免食源性疾病的发生。     

A review of the microbiological hazards of dairy products made from raw milk

This review concentrates on information concerning microbiological hazards possibly present in raw milk dairy products, in particular cheese, butter, cream and buttermilk. The main microbiological hazards of raw milk cheeses (especially soft and fresh cheeses) are linked to Listeria monocytogenes, verocytotoxin-producing Escherichia coli (VTEC), Staphylococcus aureus, Salmonella and Campylobacter. L. monocytogenes, VTEC and S. aureus have been identified as microbiological hazards in raw milk butter and cream albeit to a lesser extent because of a reduced growth potential compared with cheese. In endemic areas, raw milk dairy products may also be contaminated with Brucella spp., Mycobacterium bovis and the tick-borne encephalitis virus (TBEV). Potential risks due to Coxiella burnetii and Mycobacterium avium subsp. paratuberculosis (MAP) are discussed. Pasteurisation ensures inactivation of vegetative pathogenic microorganisms, which increases the safety of products made thereof compared with dairy products made from raw milk. Several control measures from farm to fork are discussed.     

Evaluation of milk yield losses associated with Salmonella antibodies in bulk tank milk in bovine dairy herds

The effect of Salmonella on milk production is not well established in cattle. The objective of this study was to investigate whether introduction of Salmonella into dairy cattle herds was associated with reduced milk yield and determine the duration of any such effect. Longitudinal data from 2005 through 2009 were used, with data from 12 mo before until 18 mo after the estimated date of infection. Twenty-eight case herds were selected based on an increase in the level of Salmonella-specific antibodies in bulk-tank milk from <10 corrected optical density percentage (ODC%) to ≥70 ODC% between 2 consecutive three-monthly measurements in the Danish Salmonella surveillance program. All selected case herds were conventional Danish Holstein herds. Control herds (n=40) were selected randomly from Danish Holstein herds with Salmonella antibody levels consistently <10 ODC%. A date of herd infection was randomly allocated to the control herds. Hierarchical mixed effect models with the outcome test-day yield of energy-corrected milk (ECM)/cow were used to investigate daily milk yield before and after the estimated herd infection date for cows in parities 1, 2, and 3+. Control herds were used to evaluate whether the effects in the case herds could be reproduced in herds without Salmonella infection. Herd size, days in milk, somatic cell count, season, and year were included in the models. Yield in first-parity cows was reduced by a mean of 1.4kg (95% confidence interval: 0.5 to 2.3) of ECM/cow per day from 7 to 15 mo after the estimated herd infection date, compared with that of first-parity cows in the same herds in the 12 mo before the estimated herd infection date. Yield for parity 3+ cows was reduced by a mean of 3.0 kg (95% confidence interval: 1.3 to 4.8) of ECM/cow per day from 7 to 15 mo after herd infection compared with that of parity 3+ cows in the 12 mo before the estimated herd infection. We observed minor differences in yield in second-parity cows before and after herd infection and observed no difference between cows in control herds before and after the simulated infection date. Milk yield decreased significantly in affected herds and the reduction was detectable several months after the increase in bulk tank milk Salmonella antibodies. It took more than 1 yr for milk yield to return to preinfection levels.