Molecular typing and distribution of Staphylococcus aureus isolates in Eastern Canadian dairy herds

Usefulness of molecular typing methods for epidemiological and evolutionary studies of Staphylococcus aureus isolated from bovine intramammary infections

In cattle, Staphylococcus aureus is a major pathogen of increasing importance due to its association with intramammary infections (IMIs), which are a primary cause of antibiotic use on farms and thus of the rise in antibiotic resistance. Methicillin-resistant S. aureus (MRSA), which are frequently isolated from cases of bovine mastitis, represent a public health problem worldwide. Understanding the epidemiology and the evolution of these strains relies on typing methods. Such methods were phenotypic at first, but more recently, molecular methods have been increasingly utilized. Multiple-locus variable number tandem repeat analysis (MLVA), a high-throughput molecular method for determining genetic diversity and the emergence of host- or udder-adapted clones, appears to be the most useful PCR-based method. Despite the difficulties present in reproducibility, interlaboratory reliability, and hard work, it is agreed that pulsed-field gel electrophoresis (PFGE) remains the gold standard, particularly for short-term surveillance. Multilocus sequence typing (MLST) is a good typing method for long-term and global epidemiological investigations, but it is not suitable for outbreak investigations. Staphylococcal protein A (spa) typing is the most widely used method today for first-line typing in the study of molecular evolution, and outbreaks investigations. Staphylococcal cassette chromosome mec (SCCmec) typing has gained popularity for the evolutionary analysis of MRSA strains. Whole-genome sequencing (WGS) and DNA microarrays that represent relatively new DNA-based technologies, provide more information for tracking antibioresistant and virulent outbreak strains. They offer a higher discriminatory power, but are not suitable for routine use in clinical veterinary medicine at this time. Descriptions of the evolution of these methods, their advantages, and limitations are given in this review.

Genetic diversity and virulence characteristics of Staphylococcus aureus isolates from cases of bovine mastitis

Staphylococcus aureus is one of the major bacterial mastitis pathogens with significant effects on animal and human health. Some studies showed that S. aureus strains that infect different host species are genetically distinct, although most strains can infect a wide range of host species. However, there are no clearly defined clonal patterns of S. aureus strains that are known to infect a specific host. The objectives of this study were to evaluate the clonal diversity and virulence characteristics of S. aureus isolates from cases of bovine mastitis. Bacteriological tests were conducted on milk samples from cases of bovine mastitis from 11 dairy farms including some milk samples from unknown farms in Eastern Tennessee. Overall, a total of 111 S. aureus were isolated and identified, and further evaluated for their genetic diversity by pulsed-field gel electrophoresis (PFGE) and virulence characteristics by PCR. Genotypic virulence factors including staphylococcal enterotoxins, and toxic shock syndrome toxin 1 (tsst-1) were tested by PCR. In addition, the association among several known virulence factors of these isolates based on our current and previous studies in our lab were evaluated. Previously generated data that were included in the analysis of association among virulence factors were the presence of biofilm production associated genes in the ica operon such as icaA, icaD and icaAB, and phenotypic virulence characteristics such as hemolysis on blood agar, slime production and resistance or susceptibility to ten commonly used antimicrobials in dairy farms. The PFGE results showed the presence of 16 PFGE types (designated A - P) throughout farms, of which three pulsotypes, I, M and O were the most frequently isolated PFGE types from most farms. The PFGE type M was the most prevalent of all 16 PFGE types, with 64 isolates being present among nine farms. The PCR results of enterotoxin genes showed that out of the total 111 tested 84 (75.7%) were negative whereas 13 (11.7%), 2 (1.8%), 3 (2.7%), 1 (0.9%) and 8 (7.2%) were positive for seb, seb and sec, sec, see, and tsst-1, respectively. All 111 isolates were negative for sea and sej. Results of the evaluation of I, M and O strains adhesion to and invasion into mammary epithelial cells showed that the total count of each strain of bacteria adhered to and invaded into mammary epithelial cell line (MAC-T cells) was not significantly different (P > 0.05). This may be an indication that there is no significant difference in their ability to establish early host-pathogen interaction and colonization of the host. There were no statistically significant associations among PFGE types and other known virulence factors of these strains. However, PFGE types O and M tend to cluster with β-hemolysin, absence of enterotoxins and susceptibility to antimicrobials. In conclusion, there was not any association between pulsotype and genotypic and phenotypic virulence factors. S. aureus isolates from cases of bovine mastitis had diverse genotypes that possessed variable virulence factors.

Prevalence of antibiotic resistant mastitis pathogens in dairy cows in Egypt and potential biological control agents produced from plant endophytic actinobacteria

Dairy production is threatened by antibiotic resistant pathogens worldwide, and alternative solutions to treat mastitis are not available. The prevalence of antibiotic resistant strains is not well known in less developed countries. The prevalence of pathogenic bacteria and their resistance to 21 commercial antibiotics were studied in milk samples taken from 122 dairy cows suffering from the symptoms of mastitis in Egypt. The bacterial species were identified with molecular methods, and antibiotic resistance was studied with disc diffusion method. The prevalence of Streptococcus aureus, Escherichia coli and Pseudomonas aeruginosa were 30%, 17% and 3.5%, respectively. Most (90%) of the S. aureus strains showed resistance to penicillin whereas only 10% of the strains were resistant to oxacillin. Nearly half (40%) of E. coli strains showed resistance to streptomycin. Six P. aeruginosa strains showed resistance to several antibiotics, including ceftriaxone, enrofloxacin and levofloxacin. This points out that despite P. aeruginosa was not common, it should be followed up carefully. Potential biocontrol agents against antibiotic resistant mastitis bacteria were searched among 30 endophytic actinobacterial strains derived from wild medicinal plants. Three plants, namely Mentha longifolia, Malva parviflora and Pulicaria undulata were chosen for a more detailed study; their endophytic actinobacteria were used to prepare metabolic extracts. The crude metabolites of the actinobacteria were extracted with ethyl acetate. All metabolic extracts inhibited the growth of S. aureus, methicillin-resistant Staphylococcus aureus (MRSA), E. coli and P. aeruginosa in vitro. The 16S rRNA sequence analysis revealed that the most efficient actinobacterial strains were two Micromonospora sp. and one Actinobacteria bacterium. We conclude that the combination of the metabolites of several endophytic actinobacteria derived from several medicinal plants would be the most efficient against pathogens. Different metabolite cocktails should be studied further in order to develop novel biocontrol agents to treat antibiotic resistant mastitis bacteria in dairy cows.

Phenolic Plant Extracts Versus Penicillin G: In Vitro Susceptibility of Staphylococcus aureus Isolated from Bovine Mastitis

Antibiotics are the elective drugs in bovine mastitis (BM) treatment, despite their low rates of efficiency and effectiveness and increasing risk of pathogen resistance. In this sense, it is urgent to discover new and effective antimicrobial agents to apply in BM control and even treatment. Plant extracts have been widely recognized as a rich source of phytochemicals with antimicrobial potential. Thus, the present work aims to compare the bioactivity of Eucalyptus globulus and Juglans regia extracts against Staphylococcus aureus bovine mastitis strains with penicillin G. At non-toxic concentrations, E. globulus exerted a bacteriostatic effect in planktonic cells and J. regia had no antimicrobial activity. Penicillin G, at minimum inhibitory concentration (MIC), demonstrated bactericidal activity, but just for S. aureus 3, 5, 6 and ATCC 25923, while the other strains seem to have acquired resistance. On the other hand, E. globulus and penicillin G in combination demonstrated synergy, being the most effective approach against S. aureus 1, 2 and 4. Thus, penicillin alone and in combination with E. globulus or J. regia seems to be promissory strategies to control bovine mastitis infections.

Identification and antimicrobial suceptibility profile of bacteria causing bovine mastitis from dairy farms in Pelotas, Rio Grande do Sul

Abstract Mastitis is an inflammatory process of the udder tissue caused mainly by the bacteria Staphylococcus aureus. The indiscriminate use of antibiotics fosters conditions that favor the selection of resistant microorganisms, suppressing at the same time susceptible forms, causing a serious problem in dairy cattle. Given the importance in performing an antibiogram to select the most adequate antimicrobial therapy, the aim of this study was to identify bacteria isolated from cow’s milk with mastitis, in dairy farms situated in the city of Pelotas, Rio Grande do Sul, and to determinate the susceptibility profile of these isolates against the antibiotics used to treat this illness. A total of 30 isolates of Staphylococcus spp., were selected from milk samples from the udder quarters with subclinical mastitis whose species were identified through the Vitek system. The susceptibility profile was performed by the disk diffusion assay, against: ampicillin, amoxicillin, bacitracin, cephalexin, ceftiofur, enrofloxacin, gentamicin, neomycin, norfloxacin, penicillin G, tetracycline and trimethoprim. In the antibiogram, 100.0% of the isolates were resistant to trimethoprim and 96.7% to tetracycline and neomycin, three strains of Staphylococcus spp., (10.0%) presented resistance to the 12 antibiotics tested and 24 (80.0%) to at least eight. These results showed the difficulty in treating mastitis, due to the pathogens’ resistance.

Multiple-Strain Approach and Probabilistic Modeling of Consumer Habits in Quantitative Microbial Risk Assessment: A Quantitative Assessment of Exposure to Staphylococcal Enterotoxin A in Raw Milk

Quantitative microbial risk assessment (QMRA) models are extensively applied to inform management of a broad range of food safety risks. Inevitably, QMRA modeling involves an element of simplification of the biological process of interest. Two features that are frequently simplified or disregarded are the pathogenicity of multiple strains of a single pathogen and consumer behavior at the household level. In this study, we developed a QMRA model with a multiple-strain approach and a consumer phase module (CPM) based on uncertainty distributions fitted from field data. We modeled exposure to staphylococcal enterotoxin A in raw milk in Lombardy; a specific enterotoxin production module was thus included. The model is adaptable and could be used to assess the risk related to other pathogens in raw milk as well as other staphylococcal enterotoxins. The multiplestrain approach, implemented as a multinomial process, allowed the inclusion of variability and uncertainty with regard to pathogenicity at the bacterial level. Data from 301 questionnaires submitted to raw milk consumers were used to obtain uncertainty distributions for the CPM. The distributions were modeled to be easily updatable with further data or evidence. The sources of uncertainty due to the multiple-strain approach and the CPM were identified, and their impact on the output was assessed by comparing specific scenarios to the baseline. When the distributions reflecting the uncertainty in consumer behavior were fixed to the 95th percentile, the risk of exposure increased up to 160 times. This reflects the importance of taking into consideration the diversity of consumers' habits at the household level and the impact that the lack of knowledge about variables in the CPM can have on the final QMRA estimates. The multiple-strain approach lends itself to use in other food matrices besides raw milk and allows the model to better capture the complexity of the real world and to be capable of geographical specificity.

Udder infections with Staphylococcus aureus, Streptococcus dysgalactiae, and Streptococcus uberis at calving in dairy herds with suboptimal udder health

Udder infections with Staphylococcus aureus, Streptococcus dysgalactiae, and Streptococcus uberis are common causes of bovine mastitis. To study these pathogens in early lactation, a 12-mo longitudinal, observational study was carried out in 13 herds with suboptimal udder health. The aims of the study were to investigate the occurrence of these pathogens and to identify if presence of the 3 pathogens, and of genotypes within the pathogens, differed with respect to herd, season, and parity. Quarter milk samples, collected at calving and 4 d in milk (DIM), were cultured for the 3 pathogens. Genotyping of staphylococcal and streptococcal isolates was performed using spa typing and pulsed-field gel electrophoresis, respectively. For each of the 3 pathogens, cows with an udder infection at calving or 4 DIM were allocated to 1 of 4 infection types: cleared (pathogen present only at calving), persistent (pathogen present in the same quarter at calving and 4 DIM), new (pathogen present only at 4 DIM), or cleared/new (pathogen present in 1 quarter at calving and in another quarter at 4 DIM). Associations between season or parity and overall occurrence of pathogens or infection types were determined using univariable mixed-effect logistic-regression models and the Fisher's exact test, respectively. The most commonly occurring pathogen was Staph. aureus, followed by Strep. dysgalactiae and Strep. uberis. Persistent infections were the most common infection type among Staph. aureus-infected cows, whereas cleared infections were the most common among Strep. dysgalactiae- and Strep. uberis-positive cows. The proportion of cows with persistent Staph. aureus infections and the proportion of cows having a Strep. uberis infection at calving or 4 DIM were higher in the multiparous cows than in primiparous cows. Infections with Strep. dysgalactiae were less common during the early housing season than during the late housing or pasture seasons, whereas persistent Strep. uberis infections were less common during the pasture season than during the late housing season. The relative occurrence of the 3 pathogens, infection types of each pathogen, and genotype diversity of each pathogen throughout the year or in different seasons and parities varied among the herds, indicating that underlying factors predisposing for udder infections at calving differ between herds. Genotyping of bacterial isolates gave important insight into how such infection patterns differed within and between herds. These findings emphasize the need to choose preventive strategies for each individual herd.

Clonal profile, virulence and resistance of Staphylococcus aureus isolated from sheep milk

The objective of this study was to characterize the clonal profile, virulence factors and antimicrobial resistance, particularly oxacillin resistance, of Staphylococcus aureus isolated from sheep milk. Milk samples were collected from all teats for the California Mastitis Test (CMT), somatic cell count, identification of S. aureus, investigation in these strains of genes encoding toxins (sea, seb, sec, sed, tst), biofilm (icaA, icaC, icaD, bap), leukocidin (luk-PV) oxacillin resistance by mecA gene detection and susceptibility testing (12 antibiotics). Messenger RNA expression was evaluated by RT-PCR in isolates carrying toxin and biofilm genes. Biofilm formation was also evaluated phenotypically by adherence to polystyrene plates. The clonal profile of S. aureus was investigated by pulsed-field gel electrophoresis. A total of 473 milk samples were collected from 242 animals on three farms and 20 S. aureus strains were isolated and none carried the mecA gene. The two sec gene-positive isolates and the isolates carrying the tst and luk-PV genes were positive by RT-PCR. Staphylococcus aureus isolated from the three flocks studied showed high susceptibility to the drugs tested and none was biofilm producer, indicating that biofilm formation was not a virulence factor causing infection by these strains. The typing of 17 S. aureus isolates revealed the presence of a common clone on the three farms studied, and the presence and expression of the sec and tst genes in one strain of this clone suggest the possible acquisition of virulence genes by this clone, a fact that is important for animal health and food hygiene.

Risk factors associated with the antimicrobial resistance of Staphylococcus aureus isolated from bovine mastitis

The objective of this study was to evaluate herd management practices and mastitis treatment procedures as risk factors associated with Staphylococcus aureus antimicrobial resistance. For this study, 13 herds were selected to participate in the study to evaluate the association between their management practices and mastitis treatment procedures and in vitro antimicrobial susceptibility. A total of 1069 composite milk samples were collected aseptically from the selected cows in four different periods over two years. The samples were used for microbiological culturing of S. aureus isolates and evaluation of their antimicrobial susceptibility. A total of 756 samples (70.7%) were culture-positive, and S. aureus comprised 27.77% (n=210) of the isolates. The S. aureus isolates were tested using the disk-diffusion susceptibility assay with the following antimicrobials: ampicillin 10mg; clindamycin 2μg; penicillin 1mg; ceftiofur 30μg; gentamicin 10mg; sulfa-trimethoprim 25μg; enrofloxacin 5μg; sulfonamide 300μg; tetracycline 30μg; oxacillin 1mg; cephalothin 30μg and erythromycin 5μg. The variables that were significantly associated with S. aureus resistance were as follows: the treatment of clinical mastitis for ampicillin (OR=2.18), dry cow treatment for enrofloxacin (OR=2.11) and not sending milk samples for microbiological culture and susceptibility tests, for ampicillin (OR=2.57) and penicillin (OR=4.69). In conclusion, the identification of risk factors for S. aureus resistance against various mastitis antimicrobials is an important information that may help in practical recommendations for prudent use of antimicrobial in milk production.

Atividade antibacteriana do extrato hidroalcoólico de Punica granatum Linn. sobre Staphylococcus spp. isolados de leite bovino

Mastite bovina é caraterizada por inflamação da glândula mamária, geralmente em resposta à infecção bacteriana, compromete quali-quantitativamente a produção leiteira. Este estudo objetivou verificar a atividade antibacteriana in vitro do extrato hidroalcoólico da casca da romã sobre bactérias isoladas de leite bovino. As colônias de Staphylococcus spp. foram ressuspendidas a escala 6 de MacFarland e ajustada a sua concentração por espectrofotometria UV visível na concentração de 10 mL-1. Os extratos foram avaliados em quintuplicata, em sete concentrações: de 4mg mL-1 até 0,0625 mg.mL-1. A sensibilidade dos isolados microbianos foi determinada utilizando o teste de difusão em disco e os resultados que apresentaram zonas de inibição correspondentes a valores a partir de 15 mm, foram considerados sensíveis. Os resultados foram avaliados pelo método ANOVA, teste de Tukey 5%, utilizando o SISVAR 5.3 -DEX/UFLA. Adicionalmente o extrato foi avaliado quanto à atividade antioxidante, teores de fenóis e flavonoides totais. Para tanto o extrato foi diluído em sete concentrações: de 25 a 1000µg.mL-1, e avaliado em triplicata. O crescimento bacteriano foi inibido a partir da concentração de 4mg.mL-1 e a ação antioxidante foi verificada a partir de 50µg.mL-1, com valores correspondentes a 4.62%, atingindo platô de 64,90% na concentração de 500µg.mL-1. Na avaliação da atividade captadora de radicais, empregando o radical livre DPPH, o extrato demonstrou atividade antioxidante (IC50%= 378,80µg/mL). Porém, não foi possível correlacionar a atividade antioxidante aos teores de fenóis e flavonoides. Talvez a presença de outras substâncias alcaloides e taninos presentes no extrato, possam ter sido as responsáveis pela atividade antioxidante encontrada. Conclui-se que o extrato hidroalcoólico de Punica granatum Linn. apresenta atividade antimicrobiana contra Staphylococcus spp., demonstrando potencial benefício para o controle da mastite bovina.

Associations between bacterial genotype and outcome of bovine clinical Staphylococcus aureus mastitis

BACKGROUND

Staphylococcus aureus is an important cause of clinical mastitis in dairy cows worldwide. The cure rate after antimicrobial treatment of clinical S. aureus mastitis is very variable due to both cow and bacterial factors. Studies have shown that bacterial genotype might affect short-term bacteriological and clinical cure, but the long-term outcome has been less studied. The objectives of this study were to investigate associations between bacterial genotype and long-term outcome of veterinary-treated clinical mastitis (VTCM) caused by S. aureus during a follow-up period of 120 days and to study genotype variation among Swedish S. aureus isolates. S. aureus isolates from cases of VTCM were genotyped by pulsed-field gel electrophoresis. Long-term outcome measurements used were somatic cell count (SCC), additional diagnoses of VTCM, milk yield and culling. Isolates were classified into clusters (>80% similarity) and pulsotypes (100% similarity). Clusters and pulsotypes were grouped according to occurrence. Multivariable mixed-effect linear regression models including cow and bacterial factors with possible influence on SCC or milk yield were used to calculate differences in SCC or milk yield between groups. Additional outcome measures were calculated using a test of proportions.

RESULTS

The isolates (n = 185) were divided into 18 clusters and 29 pulsotypes. Two pulsotypes were classified as common, and were found in 64% of the cases of VTCM. Remaining isolates were classified as less common or rare pulsotypes. The distribution was similar at cluster level. Outcome was calculated from follow-up data on 111 cows. Significantly lower SCC during the follow-up period was found in cows infected with common clusters compared to in cows infected with less common/rare clusters. The proportion of cows with SCC <200 000 cells/ml during the whole follow-up period was significantly higher in the group common clusters than in the group less common/rare clusters. Bacterial genotype did not influence the other outcome parameters.

CONCLUSIONS

In Sweden, two S. aureus pulsotypes, identified in about 64% of clinical S. aureus cases, were widespread. Cows infected with the common genotypes had significantly lower SCC during 120 days after treatment compared to cows infected with less common or rare genotypes.

Antimicrobial resistance profiles of common mastitis pathogens on Canadian dairy farms

Monitoring of antimicrobial resistance (AMR) in bacteria has clinical and public health significance. The present study determined prevalence of AMR in common mastitis pathogens Staphylococcus aureus, including methicillin-resistant Staph. aureus (MRSA; n=1,810), Escherichia coli (n=394), and Klebsiella species (n=139), including extended-spectrum β-lactamase (ESBL)-producing E. coli and Klebsiella species, isolated from milk samples on 89 dairy farms in 6 Canadian provinces. Minimum inhibitory concentrations (MIC) were determined using the Sensititer bovine mastitis plate (Trek Diagnostic Systems Inc., Cleveland, OH) and a National Antimicrobial Resistance Monitoring System gram-negative panel containing antimicrobials commonly used for mastitis treatment and control. Denim blue chromogenic agar and real-time PCR were used to screen and confirm MRSA, respectively. Resistance proportion estimates ranged from 0% for cephalothin and oxacillin to 8.8% for penicillin in Staph. aureus isolates, and 15% of the resistant Staph. aureus isolates were multidrug resistant. One MRSA isolate was confirmed (prevalence: 0.05%). Resistance proportion estimates ranged from 0% for ceftriaxone and ciprofloxacin to 14.8% for tetracycline in E. coli, and 0% for amikacin, ceftiofur, ciprofloxacin, and nalidixic acid to 18.6% for tetracycline in Klebsiella species isolates. Further, 62.8 and 55% of the resistant E. coli and Klebsiella species isolates were multidrug resistant, respectively. Resistance to >5 and >2 antimicrobials was most common in E. coli and Klebsiella species isolates, respectively, and no ESBL producers were found. Prevalence of AMR in bovine mastitis pathogens was low. Most gram-negative udder pathogens were multidrug resistant; MRSA was rarely found, and ESBL E. coli and Klebsiella species isolates were absent in Canadian milk samples.

Perfil de sensibilidade antimicrobiana in vitro de Staphylococcus aureus isolado de mastite subclínica bovina

Com o objetivo de determinar o perfil de sensibilidade antimicrobiana in vitro foram estudadas 83 amostras de Staphylococcus aureus isoladas de mastite subclínica bovina, em rebanhos leiteiros do município de Garanhuns, PE. Ao se utilizar a técnica de difusão em ágar, 79 (95%), amostras demonstraram resistência à penicilina G e 73 (88%) à ampicilina. Frente às demais drogas testadas, 100% das amostras foram sensíveis à cefalotina, 79 (95%) à enrofloxacina, 77 (93%) à tetraciclina, 76 (92%) à eritromicina e clindamicina, e 65 (78%) à gentamicina. Das amostras provenientes de animais com infecção intramamária recente, 91 e 87% foram resistentes à penicilina e ampicilina, enquanto 100 e 89% daquelas de infecção crônica foram resistentes àquelas drogas, nessa ordem. Dentro da categoria "infecção crônica", houve diferença significativa entre a eficácia de penicilina e ampicilina (P<0,01). A resistência a dois antimicrobianos simultaneamente foi a mais frequente, cujo perfil penicilina+ampicilina observado em 55 (66%) das amostras avaliadas. Os resultados deste trabalho demonstraram que a resistência às penicilinas é frequente em Staphylococcus aureus isolado de casos de mastite subclínica em rebanhos de bovinos leiteiros do município de Garanhuns, Pernambuco.

Characterization of contaminants from a sanitized milk processing plant

Milk processing lines offer a wide variety of microenvironments where a diversity of microorganisms can proliferate. We sampled crevices and junctions where, due to deficient reach by typical sanitizing procedures, bacteria can survive and establish biofilms. The sampling sites were the holding cell, cold storage tank, pasteurizer and storage tank - transfer pump junction. The culturable bacteria that were isolated after the sanitation procedure were predominantly Pseudomonas spp., Serratia spp, Staphylococcus sciuri and Stenotrophomonas maltophilia. We assayed several phenotypic characteristics such as the ability to secrete enzymes and siderophores, as well as the capacity of the strains to form biofilms that might contribute to their survival in a mixed species environment. The Pseudomonas spp. isolates were found to either produce proteases or lecithinases at high levels. Interestingly, protease production showed an inverse correlation with siderophore production. Furthermore, all of the Serratia spp. isolates were strong biofilm formers and spoilage enzymes producers. The organisms identified were not mere contaminants, but also producers of proteins with the potential to lower the quality and shelf-life of milk. In addition, we found that a considerable number of the Serratia and Pseudomonas spp. isolated from the pasteurizer were capable of secreting compounds with antimicrobial properties.

Molecular types and antibiotic resistance of Staphylococcus aureus isolates from bovine mastitis in a single herd in China

The molecular diversity, antibiotic resistance patterns and presence of resistance genes were determined in Staphylococcus aureus isolates from cases of bovine mastitis in a dairy cattle herd in China. Multiple locus variable number tandem repeat analysis was used for molecular typing. Resistance was determined through minimum inhibitory concentrations and resistance genes were detected by PCR. There was low molecular diversity; one predominant strain (type I) accounted for the majority of cases of S. aureus mastitis in the herd and this strain had a high frequency of resistance to penicillin and tetracycline. The most prevalent resistance genes were blaZ, ermC and tetM.

Characterization of Staphylococcus aureus strains isolated from raw milk utilized in small-scale artisan cheese production

Staphylococcus aureus is an important agent of bacterial mastitis in milking animals and of foodborne intoxication in humans. The purpose of this study was to examine the genetic and phenotypic diversity, enterotoxigenicity, and antimicrobial resistance of S. aureus strains isolated from raw milk used for the production of artisan cheese in Vermont. Cross-tabulations revealed that the 16 ribotypes identified among the 90 milk isolates examined were typically associated with a specific animal species and that more than half of these ribotypes were unique to individual farms. In general, specific EcoRI ribotypes were commonly associated with specific phenotypical characteristics, including staphylococcal enterotoxin production or the lack thereof. Limited antimicrobial resistance was observed among the isolates, with resistance to ampicillin (12.51%) or penicillin (17.04%) most common. Two isolates of the same ribotype obtained from the same farm were resistant to oxacillin with 2% NaCl. More than half (52.22%) of isolates produced toxin, and 31 of the 32 isolates solely produced staphylococcal enterotoxin type C. Although these data demonstrate that S. aureus strains found in raw milk intended for artisan cheese manufacture are capable of enterotoxin production, staphylococcal enterotoxin C is not typically linked to foodborne illness. Because S. aureus is a common contaminant of cheese, an understanding of the ecology of this pathogen and of the antimicrobial susceptibility and toxigenicity of various strains will ultimately contribute to the development of control practices needed to enhance the safety of artisan and farmstead cheese production.

Antibiotic resistance and pathogenicity factors in Staphylococcus aureus isolated from mastitic Sahiwal cattle

Methicillin-resistant Staphylococcus aureus (MRSA) poses a serious problem in dairy animals suffering from mastitis. In the present study, the distribution of mastitic MRSA and antibiotic resistance was studied in 107 strains of S. aureus isolated from milk samples from 195 infected udders. The characterizations pathogenic factors (adhesin and toxin genes) and antibiotic susceptibility of isolates were carried out using gene amplification and disc diffusion assays, respectively. A high prevalence of MRSA was observed in the tested isolates (13.1%). The isolates were also highly resistant to antibiotics, i.e. 36.4% were resistant to streptomycin, 33.6% to oxytetracycline, 29.9% to gentamicin and 26.2% each to chloramphenicol, pristinomycin and ciprofloxacin. A significant variation in the expression of pathogenic factors (Ig, coa and clf) was observed in these isolates. The overall distribution of adhesin genes ebp, fib, bbp, fnbB, cap5, cap8, map and cna in the isolates was found to be 69.1, 67.2, 6.5, 20.5, 60.7, 26.1, 81.3 and 8.4%, respectively. The presence of fib, fnbB, bbp and map genes was considerably greater in MRSA than in methicillin-susceptible S. aureus (MSSA) isolates. The proportions of toxin genes, namely, hlb, seb, sec, sed, seg and sei, in the isolates were found to be 94.3, 0.9, 8.4, 0.9, 10.2 and 49.5%, respectively. The proportions of agr genes I, II, III and IV were found to be 39.2, 27.1, 21.5 and 12.1%, respectively. A few isolates showed similar antibiotic-resistance patterns, which could be due to identical strains or the dissemination of the same strains among animals. These findings can be utilized in mastitis treatment programmes and antimicrobials strategies in organized herd.

Pulsed-field gel electrophoretic analysis and some characteristics of Staphylococcus aureus isolated from retail foods and human hands

This study investigates whether there is a predominant Staphylococcus aureus strain in retail foods and healthy human hands, and examines the relationship between pulsed-field gel electrophoresis (PFGE) banding patterns and the S. aureus characteristics of staphylococcal enterotoxin (SE) type, coagulase type, and β-lactamase activity. Ninety-four strains of S. aureus isolated from retail foods and healthy human hands were analyzed by PFGE. Several strains isolated from the same shop or a chain store showed identical patterns, indicating that the origins of these strains were identical. After excluding these strains showing identical patterns, 54 strains were used for the PFGE analysis. No spread of a particular clone in the environment surrounding the food was apparent. The PFGE analysis of these 54 strains was classified in 6 lineages (L1-L6). There was no relationship between the PFGE banding pattern and coagulase type or SE type. Eleven (84.6%) of the 13 isolates in PFGE banding pattern L5 did not produce β-lactamase, suggesting that the production of β-lactamase influenced a specific PFGE banding pattern.

Toxigenic status of Staphylococcus aureus isolated from bovine raw milk and Minas frescal cheese in Brazil

A group of 291 Staphylococcus aureus isolates from mastitic cow's milk (n = 125), bulk tank milk (n = 96), and Minas frescal cheese (n = 70) were screened for staphylococcal enterotoxin (SE) genes (sea, seb, sec, sed, see, seg, seh, sei, selj, and sell) and for the tst-1 gene encoding staphylococcal toxic shock syndrome toxin 1 by PCR assay. A total of 109 (37.5%) of the isolates were positive for at least one of these 11 genes, and 23 distinct genotypes of toxin genes were observed. Of the S. aureus isolates bearing SE genes, 17 (13.6%) were from mastitic cow's milk, 41 (41.7%) were from bulk tank milk, and 51 (72.9%) were from Minas frescal cheese. The occurrence of exclusively more recently described SE genes (seg through sell) was considerably higher (87 of 109 PCR-positive strains) than that of classical SE genes (sea through see, 15 strains). The SE genes most commonly detected were seg and sei; they were found alone or in different combinations with other toxin genes, but in 60.8% of the cases they were codetected. No strain possessed see. The tst-1 gene was found in eight isolates but none from mastitic cow's milk. Macrorestriction analysis of chromosomal DNA from 89 S. aureus isolates positive for SE gene(s) was conducted with the enzyme SmaI. Fifty-five distinct pulsed-field gel electrophoresis patterns were found, demonstrating a lack of predominance of any specific clone. A second enzyme, Apa I, used for some isolates was less discriminating than Sma I. The high genotype diversity of potential toxigenic S. aureus strains found in this study, especially from Minas frescal cheese, suggests various sources of contamination. Efforts from the entire production chain are required to improve consumer safety.

Prevalence, genetic diversity, and antimicrobial susceptibility profiles of Staphylococcus aureus isolated from bovine mastitis in Zhejiang Province, China

This study was conducted to determine genetic diversity and antimicrobial susceptibility profiles of Staphylococcus aureus recovered from bovine mastitis in Zhejiang Province, China. Out of 3178 quarter milk samples from 846 lactating cows, among which 459 cows (54.3%) were found HMT positive, 890 quarters (28%) were found having subclinical mastitis. From 75 representative S. aureus isolates, 16 distinct types were identified by pulsed-field gel electrophoresis (PFGE). Four major PFGE types (A, B, C, and D) accounted for 82.7% of all isolates, and type A (41.3%) was observed in multiple herds across the studied areas. Each region was found to have a predominant type: Hangzhou type A (64.1%), Ningbo type C (34.5%) and type B (23.1%), Jinhua type D (53.3%), and Taizhou type C (62.5%). Results of antimicrobial susceptibility tests showed that 90.7% of the isolates were resistant to at least one antimicrobial. Resistance to penicillin and ampicillin (77.3%), tetracycline (60.0%), or erythromycin (48.0%) was observed. The bacteria resistant to multiple antibiotics such as penicillin, ampicillin, tetracycline, and erythromycin were commonly found. The information obtained from this study is useful for designing specific control programs for bovine S. aureus mastitis in this region.

Genetic determinants of antibiotic resistance in Staphylococcus aureus isolates from milk of mastitic crossbred cattle

Staphylococcus aureus is one of the major causes of mastitis in dairy animals and its resistance against multiple antimicrobials always remains crucial concern. Present investigation was carried out to detect the distribution of antibiotic-resistant genes of S. aureus isolates. Isolates (128) of S. aureus from mastitic milk were collected, tested for antibiotics with disc-diffusion method, and resistant genes mecA, linA, msrA msrB, vatA, vatB, vatC ermA, ermC tetK, tetM and aacA-D were detected by PCR. The phenotypic antibiotics resistance percent in S. aureus isolates was classified as tetracycline (36.7), gentamycin (30.5), streptomycin (26.6), kanamycin (25.8) and penicillin G (22.7). All the isolates were susceptible to vancomycin. Among isolates, 10.2% were observed as methicillin-resistant. The distribution of antibiotic-resistant genes was linA (51.6) followed by msrB (46.1), tetK + M (34.4), msrA and aacA-D (26.6%). Different antibiotic-resistant genes combinations (mecA/linA-2; mecA/aacA-D/tetK/linA/msrB-3; mecA/linA/msrA/msrB-3; aacA-D/linA/msrA/msrB-4; aacA-D/linA/msrB-7; linA/msrA/msrB-10; tetK/linA/msrA/msrB-11; aacA/tetK/linA/msrB-12 isolates) were observed. All the isolates lacked amplification of vatA, vatB, ermA and ermC genes. Molecular typing resulted genetic variation in protein A (6-12 repeats) and coagulase genes (A-E patterns) were observed. Coagulase A and D genotypes were more prevalent in antibiotic-resistant isolates, while E, B and C in susceptible ones. The significant observation was the prevalence of methicillin-resistant S. aureus, which were resistant to multiple antibiotics. Findings revealed the status of resistant isolates in herd that might be helpful in treatment, controlling of resistant strains and culling of cows for mastitis reduction.

Regional profiling for determination of genotype diversity of mastitis-specific Staphylococcus aureus lineage in Canada by use of clumping factor A, pulsed-field gel electrophoresis, and spa typing

One of the major concerns in global public health and the dairy industry is the emergence of host-specific virulent Staphylococcus aureus strains. The high degree of stability of the species genome renders detection of genetic microvariations difficult. Thus, approaches for the rapid tracking of specialized lineages are urgently needed. We used clumping factor A (clfA) to profile 87 bovine mastitis isolates from four regions in Canada and compared the results to those obtained by pulsed-field gel electrophoresis (PFGE) and spa typing. Twenty-five pulsotypes were obtained by PFGE with an index of discrimination of 0.91. These were assigned to six PFGE lineage groups A to F and seven spa types, including two novel ones. Group A had 48.3% of the isolates and group D had 43.7% of the isolates, while only 8% of the isolates were variable. The results of antimicrobial susceptibility testing indicated that all isolates were sensitive to methicillin and the non-beta-lactam antibiotics, while three isolates were resistant to penicillin and one isolate was resistant to tetracycline. All isolates had the clfA gene and belonged to 20 clfA repeat types with an index of discrimination of 0.90. The dominant clfA types, types X, Q, C, and Z, formed 82% and 43% of PFGE groups A and D, respectively, and had copy numbers that varied only within a narrow range of between 46 and 52 copies, implying clonal selection. The rest were variable and region specific. Furthermore, the dominant groups contained subpopulations in different regions across Canada. Sequence information confirmed the relatedness obtained by the use of clfA repeat copy numbers and other methods and further revealed the occurrence of full-repeat deletions and conserved host-specific codon-triplet position biases at 18-bp units. Thus, concordant with the results of PFGE and spa typing, clfA typing proved useful for revealing the clonal nature of the mastitis isolate lineage and for the rapid profiling of subpopulations with comparable discriminatory powers.

Methicillin-resistant Staphylococcus aureus and Staphylococcus pseudintermedius in veterinary medicine

Staphylococci are important opportunistic pathogens in most animal species. Among the most relevant species are the coagulase positive species Staphylococcus aureus and Staphylococcus pseudintermedius. Methicillin resistance has emerged as an important problem in both of these organisms, with significant concerns about animal and public health. The relative importance of these staphylococci on different animal species varies, as do the concerns about zoonotic transmission, yet it is clear that both present a challenge to veterinary medicine.

Antimicrobial susceptibility of udder pathogens from cases of acute clinical mastitis in dairy cows

To investigate occurrence of acquired antimicrobial resistance in udder pathogens MICs in Staphylococcus aureus (n=211), coagulase-negative staphylococci (CNS) (n=56), Streptococcus uberis (n=113), Streptococcus dysgalactiae (n=152), Streptococcus agalactiae (n=6), Escherichia coli (n=163), and Klebsiella spp. (n=42) were determined using microdilution. Isolates were from a nation wide survey employing strict inclusion criteria. Presence of acquired resistance was evaluated by species-specific epidemiological cut-off values issued by EUCAST. Penicillin or methicillin resistance in staphylococci were however evaluated by beta-lactamase production or presence of the mecA gene, respectively. Staphylococci were mostly susceptible to antimicrobials tested but 7.1% of S. aureus and 12.5% of CNS were resistant to penicillin by beta-lactamase production. Methicillin resistance was not found in S. aureus. All Streptococcus dysgalactiae and S. agalactiae were susceptible to penicillin. Bimodal MIC distributions for tetracycline in S dysgalactiae and S. uberis indicate acquired resistance in some isolates. Among E. coli 12.3% of isolates were resistant to one or more antimicrobials. Resistance to streptomycin (11.0%), sulphametoxazole (8.6%), ampicillin (7.4%), or tetracycline (4.9%) were the most common traits. Klebsiella spp. were resistant to ampicillin and some isolates also to tetracycline (7.1%) or sulphonamide (9.5%). The study shows that in Sweden bacteria associated with acute clinical mastitis for the most part are susceptible to antimicrobials used in therapy but resistance to penicillin in S. aureus is not uncommon. Penicillin is recommended for treatment of mastitis caused by gram-positive pathogens and regular monitoring of beta-lactamase production in S. aureus is therefore recommended in herds with udder health problems.

Staphylococcus aureus strains in primiparous and multiparous cows in six herds with a high prevalence of Staph. aureus intramammary infections

The proportion of different strains of Staphylococcus aureus was tested in four groups of lactating dairy cows in six herds with a high overall prevalence of Staph. aureus using random amplified polymorphic DNA PCR. Group 1 included primiparous cows in early lactation (<50 days in milk, DIM). Group 2 consisted of primiparous cows in late lactation (>250 days in milk). Groups 3 and 4 were multiparous cows in the respective stages of lactation. Eight cows from each group on each farm were tested. Overall quarter prevalence of Staph. aureus ranged from 23.4 to 32.0% in the herds. Of the 130 isolates included in the analysis 86.9% were high prevalence strains (more than three isolates per herd), while 13.1% were strains that were only identified in one or two samples. Low prevalence strains were found in all six herds. The proportion of low prevalence strains was higher in multiparous than in primiparous cows (odds ratio, OR 4.4, 1.2-16.6). It is concluded that low prevalence Staph. aureus strains are common even in herds with a high prevalence of Staph. aureus and that their frequency is lower in primiparous cows than in older cows.

Mastite subclínica causada por Staphylococcus aureus: custo-benefício da antibioticoterapia de vacas em lactação

Avaliou-se a relação custo-benefício do tratamento da mastite subclínica bovina causada por Staphylococcus aureus. Foram selecionados 270 quartos mamários com mastite subclínica e sadios, divididos em quatro grupos de acordo com o estádio de lactação e o tratamento. O grupo 1 foi formado por animais entre 10 e 60 dias da lactação e tratados contra mastites; o grupo 2 incluiu animais entre 61 dias da lactação e dois meses antes da secagem e tratados contra mastite; o grupo 3 foi formado por animais entre 10 e 60 dias da lactação, não tratados contra mastite; e o grupo 4 foi formado por animais entre 61 dias em lactação e dois meses antes da secagem, não tratados. O tratamento foi realizado pela infusão intramamária de 150mg de gentamicina, uma vez ao dia. A reavaliação foi efetuada após 30 dias. Para os cálculos dos custos com o tratamento, foram considerados uma prevalência de S. aureus de 5% e os gastos com medicamento, descarte do leite, antibiograma e mão-de-obra. Observou-se redução de 2% e 14% das receitas nos grupos 1 e 2, respectivamente, quando comparada com as receitas obtidas antes do tratamento, demonstrando ser economicamente inviável o tratamento da mastite subclínica bovina causada por S. aureus, durante a lactação.

Efficacy and pharmacokinetics of bacteriophage therapy in treatment of subclinical Staphylococcus aureus mastitis in lactating dairy cattle

Bovine mastitis is an inflammation of the udder caused by microbial infection. Mastitis caused by Staphylococcus aureus is a major concern to the dairy industry due to its resistance to antibiotic treatment and its propensity to recur chronically. Growing concerns surrounding antibiotic resistance have spurred research into alternative treatment methods. The ability of lytic S. aureus bacteriophage K to eliminate bovine S. aureus intramammary infection during lactation was evaluated in a placebo-controlled, multisite trial. Twenty-four lactating Holstein cows with preexisting subclinical S. aureus mastitis were treated. Treatment consisted of 10-ml intramammary infusions of either 1.25 x 10(11) PFU of phage K or saline, administered once per day for 5 days. The cure rate was established by the assessment of four serial samples collected following treatment. The cure rate was 3 of 18 quarters (16.7%) in the phage-treated group, while none of the 20 saline-treated quarters were cured. This difference was not statistically significant. The effects of phage intramammary infusion on the bovine mammary gland were also studied. In healthy lactating cows, a single infusion of either filter-sterilized broth lysate or a CsCl gradient-purified phage preparation elicited a large increase in the milk somatic cell count. This response was not observed when phage was infused into quarters which were already infected with S. aureus. Phage-infused healthy quarters continued to shed viable bacteriophage into the milk for up to 36 h postinfusion. The phage concentration in the milk suggested that there was significant degradation or inactivation of the infused phage within the gland.

Genetic diversity and antimicrobial susceptibility profiles among mastitis-causingStaphylococcus aureusisolated from bovine milk samples

OBJECTIVE

To determine whether particular antimicrobial susceptibility profiles of bovine mastitis-causing Staphylococcus aureus isolates were associated with specific S aureus genotypes.

SAMPLE POPULATION

357 S aureus isolates recovered from milk samples submitted for diagnostic bacteriologic testing from 24 dairy herds.

PROCEDURES

Antimicrobial susceptibility of S aureus isolates was assessed by determining minimum inhibitory concentrations (MICs) to 14 antimicrobial agents. After digestion of S aureus genomic DNA by SmaI, electrophoretic patterns were obtained via pulsed-field gel electrophoresis (PFGE) and used to classify isolates into types. Gels were analyzed, and data were used to prepare dendrograms.

RESULTS

308 of 357 (86%) S aureus isolates were susceptible to all antimicrobials evaluated. Forty-nine S aureus isolates were resistant to 1 or more antimicrobials; of these isolates, 37 were resistant only to penicillin, 9 were resistant to penicillin and erythromycin, 2 were resistant to tetracycline, and 1 was resistant to erythromycin. Isolates were assigned to 7 PFGE types. An association was found between PFGE type and antimicrobial susceptibility profile. Organisms with resistance to at least one of the tested antimicrobial agents were identified in only 4 of the 7 types of S aureus.

CONCLUSIONS AND CLINICAL RELEVANCE

Antimicrobial resistance was uncommon among the mastitis-causing S aureus isolates identified in the milk samples. A limited number of genotypes were associated with mastitis in these herds. Antimicrobial resistance phenotypes were associated with particular S aureus PFGE types; this association may have implications for future treatment and control of S aureus-associated mastitis in cattle.

Molecular and phenotypic typing of Staphylococcus aureus isolates from rabbit meat

Twenty-six Staphylococcus aureus isolates were recovered from rabbit carcasses and cuts during a period of seven months. Samples from 51 different animals, flocks and farms were obtained from five establishments in four Spanish provinces. To determine their diversity and possible origin, isolates were typed by three molecular and three phenotypic methods. PFGE, with the highest discrimination index (D=0.966), identified 19 patterns (more than one band difference) and 10 types (more than three band differences). Based on > or = 90% similarity, RAPD (D=0.877) produced nine patterns while ribotyping (D=0.786) produced seven types. On the basis of biotyping (D=0.644), 11 isolates belonged to human ecovars and 15 to the non-host-specific crystal violet type C (NHS CV:C) biotypes. By direct phage typing (D=0.761), 17 isolates were lysed by human phages into groups II (8 isolates), III (5 isolates), I/III (2 isolates) and V (2 isolates). The overall resistance to antimicrobials (D=0.783) was 76.9%, with most isolates being resistant to tetracycline (61.5%) and penicillin G (26.9%). PFGE showed that samples from each processing plant carried different S. aureus types, some of them persisting over time. There also was evidence of interestablishment dissemination of genetically related clones, most of them belonging to the PFGE type A and phenotype "NHS CV:C biotypes-3A/3C/55/71 phage type", which is highly virulent for European commercial rabbitries. The ubiquity of the virulent phenotype, as well as the high incidence of resistance to antibiotics with application in human medicine, is a matter of concern in public and animal health.

Influence of the genotype of Staphylococcus aureus, determined by pulsed-field gel electrophoresis, on dry-period elimination of subclinical mastitis in Canadian dairy herds

By combining information from 2 databases, we investigated the possibility of an association between the genotype of Staphylococcus aureus causing bovine intramammary infection and dry-period cure of subclinical infection. The 1st database contained bacteriologic and cow data from a field study evaluating the efficacy in such infections of a new intramammary dry-cow therapy (DCT) containing tilmicosin phosphate, in comparison with a commercially available DCT containing benzathine cloxacillin. Isolates of S. aureus from that study were frozen and later independently analyzed by pulsed-field gel electrophoresis (PFGE) and macrorestriction DNA fingerprinting. The molecular information, summarized and published elsewhere, constituted the 2nd database. Data from 121 subclinically infected quarters of 92 cows from 40 herds were studied by univariate and multivariable regression analysis. Infection by an isolate of PFGE lineage group D was more likely than infection by an isolate of group A or F to be cured (P < 0.05). Cows infected by lineage group D had a higher linear somatic cell count score (LS) from the last Dairy Herd Improvement test before the dry period than did cows infected by the other lineage groups (P = 0.04). Although the probability of cure was significantly lower for cows with an LS at or above the mean of 5.7 for the study population (P = 0.05), when such a cow was infected with lineage group D, cure was significantly more likely (P < 0.001) than when it was infected by another lineage group. Significantly more (P = 0.02) of the infections treated with tilmicosin (74%) than of those treated with benzathine cloxacillin (53%) were cured, and significantly more (P = 0.05) of the infections by group D (81%) than of those by group A (57%) or group F (54%) were cured. However, there was no difference in cure rate for any PFGE genotype when tilmicosin phosphate was administered; when benzathine cloxacillin was administered, 87% of lineage group D isolates were eliminated, as compared with 46% of group A and 33% of group F isolates (P < 0.05). This research demonstrates that certain genotypes of S. aureus may naturally elicit a greater inflammatory response, yet be more susceptible to elimination by antibiotics in the dry period, than other genotypes.

Antimicrobial susceptibility and coagulase gene typing of Staphylococcus aureus isolated from bovine clinical mastitis cases in Turkey

The objectives of this study were to determine antimicrobial resistance patterns of Staphylococcus aureus strains isolated from bovine clinical mastitis cases and to subtype the strains by polymerase chain reaction (PCR) technique based on coagulase gene polymorphism. Two hundred sixty-five S. aureus isolates collected from individual animals in different herds (n = 235) from 1995 to 2004 were tested for susceptibility to penicillin, ampicillin, amoxicillin-clavulanate, oxacillin, oxytetracycline, enrofloxacin, kanamycin-cephalexin, and trimethoprim-sulfamethoxazole using the agar disc diffusion test. Strains were also tested for beta-lactamase production. A total of 29.8% of the strains were susceptible to all antimicrobial agents tested. The highest resistance was observed in 63.3% of the strains against beta-lactam antibiotics, penicillin and ampicillin. Oxytetracycline resistance was observed in 27.9% of the strains, either alone or in combination with beta-lactams. No resistance was detected for amoxicillin-clavulanate, oxacillin, enrofloxacin and kanamycin-cephalexin. beta-Lactamase production and resistance to beta-lactam antibiotics were usually correlated. Resistance against beta-lactams increased from 43.5% in 1995 to 58 to 77% from 1999 to 2004. One hundred twenty-five strains were examined for coagulase gene polymorphism. The isolates were subtyped into 4 types by coagulase gene-based PCR. A predominant 1000-bp PCR product was observed in 60.8% of the isolates typed. The results indicate that a few coagulase gene types of S. aureus are responsible for the majority of bovine clinical mastitis cases in one province of Central Anatolia region, Turkey.

Characteristics and Epidemiologic Genotyping of Staphylococcus aureus Isolates from Bovine Mastitic Milk in Hokkaido, Japan

Two hundred thirty one Staphylococcus aureus isolates from bovine mastitic milk were discriminated into 60 patterns and 16 lineages by pulsed-field gel electrophoresis (PFGE). The tested isolates were also investigated using coagulase and capsule serotyping and PCR for possession of genes that encode staphylococcal enterotoxins (sea to sei), enterotoxin-like toxins (selj to selr), and toxic shock syndrome toxin (tst). One hundred seventy three of the isolates (74.9%) possessed one or more toxin genes, while no egg-yolk factor was detected in most of them. The most common combinations of toxin genes possessed by the tested isolates were sec, seg, sei, sell, and tst, or seg and sei, or sec, seg, sei, sell, seln, and tst. Two hundred and ten of the isolates (91.0%) serotyped coagulase VI, and 207 of the isolates (89.6%) expressed serotype 5 or 8 capsules. These results suggested that isolates belonging to two major lineages have spread all over Hokkaido as bovine mastitic isolates. Additionally, no remarkable difference was recognized in the identification ratio of the isolates that belonged to the two major lineages between mastitis of subclinical origin and mastitis of clinical origin.

Genetic variation among Staphylococcus aureus strains from Norwegian bulk milk

Strains of Staphylococcus aureus obtained from bovine (n = 117) and caprine (n = 114) bulk milk were characterized and compared with S. aureus strains from raw-milk products (n = 27), bovine mastitis specimens (n = 9), and human blood cultures (n = 39). All isolates were typed by pulsed-field gel electrophoresis (PFGE). In addition, subsets of isolates were characterized using multilocus sequence typing (MLST), multiplex PCR (m-PCR) for genes encoding nine of the staphylococcal enterotoxins (SE), and the cloverleaf method for penicillin resistance. A variety of genotypes were observed, and greater genetic diversity was found among bovine than caprine bulk milk isolates. Certain genotypes, with a wide geographic distribution, were common to bovine and caprine bulk milk and may represent ruminant-specialized S. aureus. Isolates with genotypes indistinguishable from those of strains from ruminant mastitis were frequently found in bulk milk, and strains with genotypes indistinguishable from those from bulk milk were observed in raw-milk products. This indicates that S. aureus from infected udders may contaminate bulk milk and, subsequently, raw-milk products. Human blood culture isolates were diverse and differed from isolates from other sources. Genotyping by PFGE, MLST, and m-PCR for SE genes largely corresponded. In general, isolates with indistinguishable PFGE banding patterns had the same SE gene profile and isolates with identical SE gene profiles were placed together in PFGE clusters. Phylogenetic analyses agreed with the division of MLST sequence types into clonal complexes, and isolates within the same clonal complex had the same SE gene profile. Furthermore, isolates within PFGE clusters generally belonged to the same clonal complex.

ALTERAÇÕES DA COMPOSIÇÃO E DA PRODUÇÃO DE LEITE ORIUNDO DE QUARTOS MAMÁRIOS DE VACAS COM E SEM MASTITE SUBCLÍNICA DE ACORDO COM O ESTÁGIO E O NÚMERO DE LACTAÇÕES

RESUMO O presente trabalho teve por objetivo pesquisar diferenças na composição e na produção de leite ao serem estudadas as interações entre estágios de lactação, número de lactações e mastite subclínica. Quartos mamários foram distribuídos em 6 grupos: Grupo "A", animais com até 2 meses após o parto e até 5 lactações; Grupo "B", animais com até 2 meses após o parto e após a quinta lactação; Grupo "C", com vacas em meses intermediários do estágio de lactação e com até 5 lactações; Grupo "D", com animais em meses intermediários do estágio de lactação e após a quinta lactação; Grupo "E", com vacas nos 2 meses anteriores à secagem e até 5 lactações; e Grupo "F", composto por animais com até 2 meses antes da secagem e após a quinta lactação. Foram analisadas a produção láctea, a contagem de células somáticas (CCS), o teor de cloretos, a acidez titulável, a densidade, o extrato seco desengordurado (ESD) e a crioscopia. O estágio de lactação e o número de lactações influenciaram a produção láctea e o conteúdo de cloretos do leite de quartos sadios, devendo ser considerados quando estudada a influência da mastite subclínica sobre a composição e a produção de leite. Além disso, em conjunto com o período lactacional e o número de lactações, a etiologia infecciosa da mastite subclínica deve ser investigada pela possível variação do grau de acometimento da glândula mamária de acordo com os microrganismos envolvidos.

Prediction of penicillin resistance in Staphylococcus aureus isolates from dairy cows with mastitis, based on prior test results

AIM

To gauge how well prior laboratory test results predict in vitro penicillin resistance of Staphylococcus aureus isolates from dairy cows with mastitis.

METHODS

Population-based data on the farm of origin (n=79), genotype based on pulsed-field gel electrophoresis (PFGE) results, and the penicillin-resistance status of Staph. aureus isolates (n=115) from milk samples collected from dairy cows with mastitis submitted to two diagnostic laboratories over a 6-month period were used. Data were mined stochastically using the all-possible-pairs method, binomial modelling and bootstrap simulation, to test whether prior test results enhance the accuracy of prediction of penicillin resistance on farms.

RESULTS

Of all Staph. aureus isolates tested, 38% were penicillin resistant. A significant aggregation of penicillin-resistance status was evident within farms. The probability of random pairs of isolates from the same farm having the same penicillin-resistance status was 76%, compared with 53% for random pairings of samples across all farms. Thus, the resistance status of randomly selected isolates was 1.43 times more likely to correctly predict the status of other isolates from the same farm than the random population pairwise concordance probability (p=0.011). This effect was likely due to the clonal relationship of isolates within farms, as the predictive fraction attributable to prior test results was close to nil when the effect of within-farm clonal infections was withdrawn from the model.

CONCLUSIONS

Knowledge of the penicillin-resistance status of a prior Staph. aureus isolate significantly enhanced the predictive capability of other isolates from the same farm. In the time and space frame of this study, clinicians using previous information from a farm would have more accurately predicted the penicillin-resistance status of an isolate than they would by chance alone on farms infected with clonal Staph. aureus isolates, but not on farms infected with highly genetically heterogeneous bacterial strains.

Characterization of Staphylococcus aureus Isolated from Chronically Infected Dairy Goats

A herd of 88 Alpine goats in Northern Italy was monitored for a complete lactation. Milk samples were taken from each udder half during 8 monthly visits. Goats (n = 28) with > or =2 consecutive positive tests for Staphylococcus aureus in the same udder half were identified as chronically infected, and all of those had > or =4 positive tests of the 8 samples. Goats with no infections in either udder half during any visit were considered healthy (n = 26). Linear mixed models were used to examine the relationship between chronic infection by S. aureus and SCC and production traits. The bacteria isolated from one sample from each infected goat were genotyped on the basis of polymorphism in several genes and evaluated for the presence of genes encoding for enterotoxins. The bacteria isolated from each animal were also subject to a test for beta-lactamase production and to minimum inhibitory concentration tests for 11 antimicrobial agents. As expected, SCC (log2) was significantly higher in infected goats than in healthy goats (7.55 vs. 5.50). Also, mean log SCC from infected udder halves (8.02) was greater than that in uninfected udder halves from the same goats (6.44). No significant differences were observed in milk yield or for fat and protein percentages between infected and healthy goats. No genetic variability was observed among the bacteria isolated, suggesting that all were from the same strain, although isolates did vary in susceptibility to various antimicrobial agents. All S. aureus isolates were negative for the beta-lactamase production test. The most effective drugs when tested in vitro were benzylpenicillin, amoxicillin plus clavulanic acid, cloxacillin, and cephalosporins.