Characterization of Staphylococcus aureus strains isolated from bovine mastitis in Japan

Prevalence and characterization of Staphylococcus aureus isolated in raw milk from cows in Hokkaido, Japan

The aim of this study was to characterize the phenotypes and genotypes of Staphylococcus aureus isolated from raw bovine milk in Hokkaido, Japan. S. aureus isolates were identified in 135 of 436 milk samples from cows with and without signs of mastitis from three farms in Hokkaido. These clinical isolates were characterized for antimicrobial susceptibility patterns, molecular typing using phage-open-reading frame typing (POT), coagulase gene type, virulence genes, and biofilm-associated genes and were evaluated for biofilm-forming ability. Most isolates were susceptible to the antimicrobial agents tested. The highest rate of resistance was to ampicillin. Molecular typing of all S. aureus isolates indicated a predominance of coagulase type VI and 0-17-34 POT type, and virulence genes were highly prevalent in the isolates from all farms. Moreover, a high percentage of the 0-17-34 POT type isolates showed extensive formation of biofilm. These findings will help veterinarians and farmers to understand the epidemiology of S. aureus so that they can monitor the transmission and spread of this pathogen and control it more effectively.

Molecular epidemiology of mastitis pathogens of dairy cattle and comparative relevance to humans

Mastitis, inflammation of the mammary gland, can be caused by a wide range of organisms, including gram-negative and gram-positive bacteria, mycoplasmas and algae. Many microbial species that are common causes of bovine mastitis, such as Escherichia coli, Klebsiella pneumoniae, Streptococcus agalactiae and Staphylococcus aureus also occur as commensals or pathogens of humans whereas other causative species, such as Streptococcus uberis, Streptococcus dysgalactiae subsp. dysgalactiae or Staphylococcus chromogenes, are almost exclusively found in animals. A wide range of molecular typing methods have been used in the past two decades to investigate the epidemiology of bovine mastitis at the subspecies level. These include comparative typing methods that are based on electrophoretic banding patterns, library typing methods that are based on the sequence of selected genes, virulence gene arrays and whole genome sequencing projects. The strain distribution of mastitis pathogens has been investigated within individual animals and across animals, herds, countries and host species, with consideration of the mammary gland, other animal or human body sites, and environmental sources. Molecular epidemiological studies have contributed considerably to our understanding of sources, transmission routes, and prognosis for many bovine mastitis pathogens and to our understanding of mechanisms of host-adaptation and disease causation. In this review, we summarize knowledge gleaned from two decades of molecular epidemiological studies of mastitis pathogens in dairy cattle and discuss aspects of comparative relevance to human medicine.

Molecular typing of Staphylococcus aureus strains from ovine mastitis by pulsed-field gel electrophoresis and polymerase chain reaction based on coagulase and protein A gene polymorphisms

Staphylococcus aureus is one of the most important etiologic agents of ovine mastitis. To develop effective control measures for mastitis, it is important to type S. aureus strains that have considerable genetic heterogeneity. In the current study, 47 S. aureus strains isolated from ovine mastitis were typed by polymerase chain reaction (PCR) based on coagulase (coa) and protein A (spa) polymorphisms and by pulsed-field gel electrophoresis (PFGE). Eight different coa types and 4 spa types were identified by PCR. While the most prevalent coa type was CG2 (42.56%), the spa types S4 and S1 were the most commonly observed (44.68% and 38.29%, respectively). Nineteen different pulsotypes were identified, and 12 of these were represented by a single isolate. Pulsotypes J and K were predominant and each represented 9 isolates (19.14%). All isolates belonging to J and K pulsotypes were CG2. Although all 9 isolates belonging to the J pulsotype were S4, all isolates in the K pulsotype were S1. While PFGE was found to be the best discriminatory technique for distinguishing strains, coa and spa types were found to be in correlation with PFGE types and can be used for quick, preliminary epidemiologic studies for detecting strains that may cause mastitis.

Multiplex PCRs for assignment of Staphylocoagulase types and subtypes of type VI Staphylocoagulase

Staphylocoagulases (SCs) have been classified by the differences in antigenicity using a serological method. We have developed a system to classify them based on the nucleotide differences in SC genes (coa). The system was composed of three multiplex PCRs (M-PCRs): M-PCR:A, identifying types III, IV, VII, and VIII; M-PCR:B, identifying types I, II, V, and VI; M-PCR:C, identifying three subtypes of type VI. In this study, we found that coa genes of the serotype VI were not identical, but classified into three subtypes based on the nucleotide differences, especially in D2 and the central region: VIa, the coa gene carried by stp12 from human; and VIb and VIc, the coa genes carried by strains IFH556 and IFH514 isolated from bovine raw milk. The primer pair used in M-PCR:B was designed to identify all three subtypes of type VI coa. The results showed that coa types of 154 out of 155 Staphylococcus aureus strains from various origins assigned by M-PCR:A and B were identical to those obtained by serological methods, leaving a serotype IV strain unclassifiable. All 73 type VI strains were classified into one of three subtypes by M-PCR:C. Furthermore, we found that type VIa and VIb strains carried characteristic pyrogenic toxin superantigen genes, while no toxin genes were identified in type VIc strains, suggesting the correlation between the subtype of type VI coa gene and the carriage of genomic islands. Our results showed that these M-PCRs are convenient methods for SC typing that might be useful for epidemiological studies.

Occurrence of enterotoxic Staphylococcus aureus in raw milk from yaks and cattle in Mongolia

Staphylococcal food poisoning is considered one of the leading foodborne illnesses in humans worldwide and is associated with contaminated foods of animal origin, such as milk and dairy products. In this study, we investigated the occurrence of staphylococci and the enterotoxigenic properties of Staphylococcus aureus isolated from raw milk from yaks (Bos mutus) and cattle in Mongolia. Staphylococci were isolated from 72 (74%) of the 97 raw milk samples. Of the samples containing staphylococci, 69% (50 of 72) were from yaks and 30.5% (22 of 72) were from cattle. S. aureus was detected in 10% of yak (7 of 72) and 21% of cattle (15 of 72) milk samples. Staphylococcal enterotoxin C was detected in 23% (5 of 22) of the S. aureus strains investigated, based on the reverse passive latex agglutination technique. Three of the five enterotoxigenic strains were from yaks and two were from cattle. None of the S. aureus strains tested produced staphylococcal enterotoxins A, B, or D. To our knowledge, this is the first report of the occurrence of staphylococci and enterotoxigenic S. aureus in milk from yaks and cattle in Mongolia.

The impact of extrinsic sources on selected indicator organisms in a typical deboning room

Meat is a highly perishable product and the microbiological safety thereof is an extremely important issue for both the consumer and the meat industry. In this study, samples were randomly collected from various working surfaces, from raw meat and from the air in the deboning room of a high throughput red meat abattoir. The samples were analysed for the presence of total staphylococci counts as well as for total viable counts. The mean staphylococci counts from working surfaces were 19 CFU x cm(-2), and the staphylococci levels for the meat samples were well below the proposed maximum limit of 100 CFU x g(-1). Maximum staphylococcal bioaerosol counts of 10 CFU x m(-3) were also enumerated. Total viable counts from the workers' hands and working surfaces were high compared to the staphylococcal levels. Twelve staphylococci species were identified from the samples used in this study. Recontamination during the deboning process was identified as the major source of contamination, suggesting proper implementation of quality processing practices within the abattoir environment.

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.

Cytotoxin and pyrogenic toxin superantigen gene profiles of Staphylococcus aureus associated with subclinical mastitis in dairy cows and relationships with macrorestriction genomic profiles

A set of 84 Staphylococcus aureus isolates collected from the milk of cows with subclinical mastitis in Asturias (a cattle region of Spain) and six control strains were tested for sequences of genes encoding hemolysins (hla, hlb, hld, hlg, and hlg-2), leukotoxins (lukPV, lukM, and lukED), toxic shock syndrome toxin (tst), and enterotoxins (sea to see, seg to ser, and seu) by conventional and multiplex PCR. It was found that 84, 83, 11, and 39 isolates carried some type of hl, luk, tst, or se gene, respectively, which were arranged in 14 exotoxin genotypes. All of the isolates were negative for lukPV, hlg, sea, sed, see, sej, sek, sep, seq, and ser. Two gene groupings could be related with pathogenicity islands-[lukED, seg, sei, sem, sen, seo +/- seu] with Sabeta-1 and [tst, sec, sel] with SaPIbov, present in 45 and 13.1% of the isolates, respectively-while 11.9% of them carried both islands. Only one contained seb (together with upsilonSabeta-1), and another contained seh (together with lukED). The isolates were also analyzed by pulsed-field gel electrophoresis performed with SmaI. Thirty-nine SmaI profiles (similarity coefficient [S] = 0.94 to 0.21) were differentiated; 12, 1, and 10 of these, respectively, were generated by isolates presumptively carrying Sabeta-1, SaPIbov, or both. Five SmaI profiles (S > or = 0.8) formed a cluster, which contained 20 and 10 isolates carrying one (upsilonSabeta-1) or both islands. These data show the high frequency of genes encoding cytotoxins and pyrogenic toxin superantigens, their relationship with pathogenicity islands, and their distribution among a diversity of genetic types of S. aureus related to subclinical mastitis.

Molecular Typing of Enterotoxigenic Staphylococcus aureus Isolated from Bovine Mastitis in Korea

One hundred and sixty-six Staphylococcus aureus isolates from mastitic milk samples from different cows on 26 farms were investigated for staphylococcal enterotoxins(SEs) and toxic shock syndrome toxin-1(TSST-1) by polymerase chain reaction(PCR) and reverse passive latex agglutination assay(RPLA). SEs and the TSST-1 gene were detected in thirty-seven isolates based on a multiplex PCR; SEA was detected in 32 isolates, SEB in 3 isolates, SEC in 1 isolate, and SEA and the TSST-1 gene in 1 isolate. Of the 37 enterotoxigenic isolates, thirty-three isolates were enterotoxigenic according to RPLA, where 29 isolates produced SEA, 3 isolates produced SEB, and 1 isolate produced SEC. The enterotoxin-producing S. aureus isolates were further characterized by pulsed-field gel electrophoresis(PFGE). A macrorestriction analysis revealed 11 PFGE patterns. Among the 33 enterotoxigenic S. aureus isolates, 45.4% exhibited the same PFGE pattern I. Accordingly, although the enterotoxin-producing S. aureus isolates from bovine mastitis were genetically diverse, 1 common genotype prevailed on the farms, indicating that PFGE pattern I isolates may be the most disseminated in Korea.