Molecular characterization of antimicrobial resistance genes on farms and in commercial milk with emphasis on the effect of currently practiced heat treatments on viable but nonculturable formation

The Contribution of Dairy Bedding and Silage to the Dissemination of Genes Coding for Antimicrobial Resistance: A Narrative Review

Antimicrobial resistance (AMR) is a concern in the dairy industry. Recent studies have indicated that bedding serves as a reservoir for antimicrobial-resistant bacteria and antimicrobial-resistance genes (ARGs), while silage has been proposed as another possible source. The impact of AMR in dairy farming can be significant, resulting in decreased productivity and economic losses for farmers. Several studies have highlighted the safety implications of AMR bacteria and genes in bedding and silage, emphasizing the need for further research on how housing, bedding, and silage management affect AMR in farm environments. Exposure to sub-lethal concentrations of antibiotics, such as those from contaminated bedding and silage, can prompt bacteria to develop resistance mechanisms. Thus, even if antimicrobial usage is diminished, ARGs may be maintained in the dairy farm environment. By implementing proactive measures to tackle AMR in dairy farming, we can take steps to preserve the health and productivity of dairy cattle while also protecting public health. This involves addressing the prudent use of antibiotics during production and promoting animal welfare, hygiene, and management practices in bedding and farm environments to minimize the risk of AMR development and spread. This narrative review compiles the growing research, positioning the contribution of bedding and silage to the prevalence and dissemination of AMR, which can elicit insights for researchers and policymakers.

Epidemiology and antibiotic resistance of staphylococci on commercial pig farms in Cape Town, South Africa

Staphylococci are responsible for a wide range of infections in animals. The most common species infecting animals include Staphylococcus aureus, Staphylococcus epidermidis and Staphylococcus intermedius. Recent increases in antibiotic use and antibiotic resistance in animals highlight the need to understand the potential role of commercial livestock as a reservoir of staphylococci and antibiotic resistance genes. Nasal swabs were collected from 143 apparently healthy pigs and 21 pig farm workers, and 45 environmental swabs of feed and water troughs, from two commercial pig farms in the Western Cape, South Africa. Staphylococci were isolated, identified using mass-spectrometry, and antimicrobial susceptibility testing and Illumina whole genome sequencing were performed. One hundred and eighty-five (185) Staphylococcus spp. isolates were obtained, with Mammalicoccus sciuri (n = 57; 31%) being the most common, followed by S. hyicus (n = 40; 22%) and S. aureus (n = 29; 16%). S. epidermidis was predominantly identified in the farm workers (n = 18; 86%). Tetracycline resistance was observed across all species, with rates ranging from 67 to 100%. Majority of M. sciuri isolates (n = 40; 70%) were methicillin resistant, with 78% (n = 31) harbouring mecA. M. sciuri isolates had genes/elements which were associated with SCCmec_type_III (3A) and SCCmec_type_VIII(4A) and were mostly observed in ST61 strains. ST239 strains were associated with SCCmec_type_III(3A). High rates of tetracycline resistance were identified among staphylococci in the pig farms in Western Cape, South Africa. This highlights the need for policy makers to regulate the use of this antibiotic in pig farming.

Staphylococcal mastitis in dairy cows

Bovine mastitis is one of the most common diseases of dairy cattle. Even though different infectious microorganisms and mechanical injury can cause mastitis, bacteria are the most common cause of mastitis in dairy cows. Staphylococci, streptococci, and coliforms are the most frequently diagnosed etiological agents of mastitis in dairy cows. Staphylococci that cause mastitis are broadly divided into Staphylococcus aureus and non-aureus staphylococci (NAS). NAS is mainly comprised of coagulase-negative Staphylococcus species (CNS) and some coagulase-positive and coagulase-variable staphylococci. Current staphylococcal mastitis control measures are ineffective, and dependence on antimicrobial drugs is not sustainable because of the low cure rate with antimicrobial treatment and the development of resistance. Non-antimicrobial effective and sustainable control tools are critically needed. This review describes the current status of S. aureus and NAS mastitis in dairy cows and flags areas of knowledge gaps.

Lactoferrin's potential application in enhancing yoghurt's microbial and sensory qualities, with emphasis on the starter culture activity

This research paper aimed to examine the antibacterial activity of lactoferrin (LF) as a potential natural alternative in the dairy sector, by measuring its minimum inhibitory concentration (MIC) against a number of common food-borne pathogens as well as Pseudomonas aeruginosa, one of the major dairy product spoiling microorganisms. Additionally, a viability experiment was applied to laboratory-manufactured set yoghurt to assess its impact on the activity of starter culture, sensory properties and STEC survivability. The findings demonstrated that LF exhibited significant antimicrobial activity, particularly against E. coli and S. typhimurium with MIC values of 0.0001 and 0.01 mg/ml, respectively. However, P. aeruginosa and B. cereus were quite resistant to LF requiring higher concentrations for MIC (2.5 mg/ml). By the third day of storage, LF at 0.0001 and 0.001 mg/ml significantly reduced the survivability of Shiga toxin-producing E. coli STEC by 70 and 91.6%, respectively, in the lab-manufactured yoghurt. Furthermore, LF enhanced the sensory properties of fortified yoghurt with a statistically significant difference in comparison to the control yoghurt group. There was no interference with the activity of the starter culture throughout the manufacturing process and the storage period. In conclusion, the potent antimicrobial effect of LF opens a new avenue for the dairy industry's potential applications of LF as a natural preservative without negatively influencing the sensory properties and starter culture activity of fermented products.

Non-aureus staphylococci and mammaliicocci as a cause of mastitis in domestic ruminants: current knowledge, advances, biomedical applications, and future perspectives - a systematic review

Non-aureus staphylococci and mammaliicocci (NASM) are one of the most common causes of subclinical mastitis in dairy animals and the extent of damage by intramammary infections (IMI) caused by NASM is still under debate. The different effects of NASM on the mammary gland may be associated with differences between bacterial species. NASM are normal and abundant colonizers of humans and animals and become pathogenic only in certain situations. The veterinary interest in NASM has been intense for the last 25 years, due to the strongly increasing rate of opportunistic infections. Therefore, the objective of this review is to provide a general background of the NASM as a cause of mastitis and the most recent advances that exist to prevent and fight the biofilm formation of this group of bacteria, introduce new biomedical applications that could be used in dairy herds to reduce the risk of chronic and recurrent infections, potentially responsible for economic losses due to reduced milk production and quality. Effective treatment of biofilm infection requires a dual approach through a combination of antibiofilm and antimicrobial agents. Even though research on the development of biofilms is mainly focused on human medicine, this technology must be developed at the same time in veterinary medicine, especially in the dairy industry where IMI are extremely common.

Evaluating the antagonistic effect of Lactobacillus acidophilus against Shiga toxigenic and non-toxigenic Escherichia coli strains in bioyogurt

This study was conducted to determine the effect of acidophilus yoghurt (yoghurt fortified with Lactobacillus acidophilus) in comparison to traditional plain yoghurt (St. thermophilus and L. bulgaricus starter cultures) on the survival of three pathogenic Escherichia coli strains; Shiga toxigenic O157 (STx O157), non-toxigenic O157 (Non-STx O157) and Shiga toxigenic non-O157 (STx O145). After six days of refrigerated storage of laboratory-manufactured yoghurt inoculated with the three strains of E. coli separately, all were eliminated in acidophilus yoghurt, while their survival extended in the traditional yoghurt along the storage period (17 d). Reduction percentages of the tested strains in acidophilus yoghurt were 99.93, 99.93 and 99.86%, with log reduction of 3.176, 3.176, and 2.865 cfu/g for Stx O157, Non-Stx O157, and Stx O145 E. coli, respectively, in comparison to 91.67, 93.33 and 93.33%, with log reduction of 1.079, 1.176 and 1.176 cfu/g in traditional yoghurt. Statistical analysis showed a significant effect of acidophilus yoghurt in reducing the count of Stx E. coli O157 (P = 0.001), Non-Stx E. coli O157 (P < 0.01) and Stx E. coli O145 (P < 0.01) compared to the traditional yoghurt. These findings emphasize the potential use of acidophilus yoghurt as a biocontrol alternative method for eliminating pathogenic E. coli, as well as other similar applications in the dairy industry.

Characterization of Bacteria and Antibiotic Resistance in Commercially Produced Cheeses Sold in China

ABSTRACT

The consumption of cheese in the People's Republic of China is increasing rapidly. Little is known about the microbiota, the presence of antibiotic-resistant bacteria, or the distribution of antibiotic resistance genes (ARGs) in commercially produced cheeses sold in China. This information is important for evaluating quality and safety. This study was conducted using 16S rRNA gene sequencing to assess the metagenomics of 15 types of cheese. Fourteen bacterial genera were detected, and Lactococcus, Lactobacillus, and Streptococcus were dominant based on number of sequence reads. Multidrug-resistant lactic acid bacteria (i.e., resistant to two or more types of antibiotic) were isolated from most of the types of cheese. Of these isolates, 100 and 91.7% were resistant to streptomycin and sulfamethoxazole, respectively, and genes involved in acquired resistance to streptomycin (strB) and sulfonamides (sul2) were detected with high frequency. To analyze the distribution of ARGs in the cheeses overall, 309 ARGs from eight categories and nine transposase genes were profiled. A total of 169 ARGs were detected in the 15 cheeses; their occurrence and abundance varied significantly between cheeses. Our study revealed diverse bacteria and ARGs in cheeses sold in China. The risks associated with multidrug resistance among dominant lactic acid bacteria are of great concern.

HIGHLIGHTS

The Potential Benefits of N2 Gas Flushing Technology for Various Dairy Products: A Sustainable Approach That Proved to Be Multiadvantageous for Preserving the Quality and Safety of Raw Milk During Its Storage

Worldwide, food production systems are confronted with multifaceted challenges. In the context of global climate change, the necessity to feed an expanding population while addressing food insecurity and reducing the tremendous losses and wastage of food places all production steps under considerable pressure. In this context, dairies also face extensive pressure to reduce greenhouse gas emissions, wastewater, and sludge; here, as elsewhere, innovative technological solutions must meet sustainable criteria. To preserve the quality and safety of raw milk during its storage, N2 gas flushing technology was devised and implemented at laboratory and pilot plant scales: the treatment proved to be multiadvantageous considering microbiological, biochemical, and technological aspects. The proposed study aims to reconsider the benefits of the patented N2 flushing technology, applied at the “raw milk stage” and evaluate the potential advantages that the treatment would confer, in terms of quality and safety aspects, to various dairy products such as liquid milk products, butters, creams, ice creams, and cheeses, including local and traditional dairy products.

Assessing the Impact of Heat Treatment of Food on Antimicrobial Resistance Genes and Their Potential Uptake by Other Bacteria-A Critical Review

The dissemination of antibiotic resistance genes (ARGs) is a global health concern. This study identifies and critically reviews the published evidence on whether cooking (heating) food to eliminate bacterial contamination induces sufficient damage to the functionality of ARGs. Overall, the review found that there is evidence in the literature that Antimicrobial Resistant (AMR) bacteria are no more heat resistant than non-AMR bacteria. Consequently, recommended heat treatments sufficient to kill non-AMR bacteria in food (70 °C for at least 2 min, or equivalent) should be equally effective in killing AMR bacteria. The literature shows there are several mechanisms through which functional genes from AMR bacteria could theoretically persist in heat-treated food and be transferred to other bacteria. The literature search found sparce published evidence on whether ARGs may actually persist in food after effective heat treatments, and whether functional genes can be transferred to other bacteria. However, three publications have demonstrated that functional ARGs in plasmids may be capable of persisting in foods after effective heat treatments. Given the global impact of AMR, there is clearly a need for further practical research on this topic to provide sufficient evidence to fully assess whether there is a risk to human health from the persistence of functional ARGs in heat-treated and cooked foods.

Antimicrobials and Food-Related Stresses as Selective Factors for Antibiotic Resistance along the Farm to Fork Continuum

Antimicrobial resistance (AMR) is a global problem and there has been growing concern associated with its widespread along the animal-human-environment interface. The farm-to-fork continuum was highlighted as a possible reservoir of AMR, and a hotspot for the emergence and spread of AMR. However, the extent of the role of non-antibiotic antimicrobials and other food-related stresses as selective factors is still in need of clarification. This review addresses the use of non-antibiotic stressors, such as antimicrobials, food-processing treatments, or even novel approaches to ensure food safety, as potential drivers for resistance to clinically relevant antibiotics. The co-selection and cross-adaptation events are covered, which may induce a decreased susceptibility of foodborne bacteria to antibiotics. Although the available studies address the complexity involved in these phenomena, further studies are needed to help better understand the real risk of using food-chain-related stressors, and possibly to allow the establishment of early warnings of potential resistance mechanisms.