Evaluation of salt concentrations, chromogenic media and anatomical sampling sites for detection of methicillin-resistant Staphylococcus aureus in pigs

Findings and measures to eradicate methicillin resistant Staphylococcus aureus clonal complex 7 spa-type t091 in two Norwegian pig farms: a case report

Background

The Norwegian LA-MRSA surveillance and control strategy in pig farms has been largely successful in preventing the establishment of MRSA in the pig population by identifying positive pig herds and eradicating MRSA from these. It can, however, be challenging to determine whether a particular type of MRSA is livestock-associated, particularly in cases where there is little evidence available to aid in classification.

Case presentation

In two Norwegian pig farms linked by trade of live pigs, MRSA CC7 t091 was found in samples from pigs and their environment. Longitudinal sampling, with a time interval of 25 days, in one farm demonstrated an increase in samples positive for MRSA CC7 t091, supporting a classification of the finding as livestock associated. Measures to eradicate MRSA from both farms were imposed by the National Food Safety Authority. Different measures of MRSA sanitation were applied in the two farms, and MRSA was successfully eradicated from both farms.

Conclusions

A high-cost, labor intensive and a lower-cost, less labor intensive MRSA eradication protocol, both including total depopulation and repopulation were successful in eradicating MRSA CC7 t091 from two case farms.

The presence of antibiotic-resistant Staphylococcus spp. and Escherichia coli in smallholder pig farms in Uganda

BACKGROUND

The development of antimicrobial resistance is of global concern, and is commonly monitored by the analysis of certain bacteria. The aim of the present study was to study the antibiotic susceptibility in isolates of Staphylococcus spp. and Escherichia (E.) coli obtained from healthy pigs originating from nineteen herds enrolled in a study on herd health management in Lira district, northern Uganda. Skin and nasal swabs were analyzed for the presence of Staphylococcus spp., and selectively cultivated to investigate the presence of methicillin-resistant Staphylococcus (S.) aureus (MRSA), and rectal swabs were analyzed for the presence of E. coli. Antibiotic susceptibility was tested by broth micro-dilution. Information on the antibiotic usage and treatment regimens during the previous year was gathered using structured interviews and longitudinal data.

RESULTS

In Staphylococcus spp., resistance to penicillin (10/19 isolates; 53%), fusidic acid (42%) and tetracycline (37%) were most commonly found. In E. coli, resistance to sulfamethoxazole (46/52 isolates; 88%), tetracycline (54%) and trimethoprim (17%) was most frequent. Methicillin-resistant S. aureus was found in one sample (1/50; 2%). Multi-drug resistant isolates of Staphylococcus spp. and E. coli were found in 54 and 47% of the herds, respectively. At the herd level, no associations could be made between antibiotic resistance and herd size or treatment regimens for either of the bacteria.

CONCLUSION

In conclusion, resistance to important antibiotics frequently used in animals in Uganda was common, and the presence of MRSA was demonstrated, in Ugandan pig herds.

Livestock-associated methicillin-resistant Staphylococcus aureus in slaughtered pigs in England

This study was performed to investigate the occurrence of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) in batches of pigs at slaughter and at different stages along the slaughter line. Nasal and ear skin swabs were collected from 105 batches of 10 pigs at six abattoirs. Cultures (pooled or individual) were performed for MRSA using selective media; presumptive MRSA were confirmed by mecA and nuc gene detection and a selection was spa-typed. MRSA was detected in 46 batches. All spa-types detected were those associated with LA-MRSA clonal complex 398. The proportion of positive batches varied among abattoirs (0–100%). Two abattoirs were subsequently further investigated, with samples taken at post-stunning, chiller and either at lairage or post-singe. Results suggested cross-contamination occurred between the lairage and point of post-stunning, but the slaughter processes appeared effective at reducing contamination before carcases entered the chiller. One abattoir provided only negative samples in the initial study and in the subsequent study along the slaughter line (26 batches in total), suggesting differences possibly in the MRSA status of pigs on arrival from supply farms or in its abattoir practices affecting the MRSA status of pigs at the sampling points. This study highlights that in the investigated abattoirs, MRSA was detected in 43.8% of batches of pigs at slaughter using sensitive selective culture methods.

Occurrence, antibiotic resistance and enteroxigenicity of Staphylococcus spp. in tonsils of slaughtered pigs in Greece

The aims of the present study were to examine the occurrence of Staphylococcus spp. in the tonsils of slaughtered pigs in a regional slaughterhouse in Greece, the antibiotic resistance of the Staphylococcus spp. isolates, and the enteroxigenicity of the S. aureus isolates. Staphylococcus spp. were isolated in 70 (48·61%) out of the total 144 tonsil samples. The predominant species was S. aureus in coagulase-positive staphylococci (CoPS), while the predominant species were Staphylococcus epidermidis and Staphylococcus saprophyticus in the coagulase-negative staphylococci (CoNS). Staphylococcus spp. isolates presented high antibiotic resistance frequencies to tetracycline (97·1%) or clindamycin (80·0%) and low antibiotic resistance frequencies to fusidic acid (14·3%). No methicillin-resistant S. aureus (MRSA) strains were identified, and all Staphylococcus spp. isolates were susceptible to vancomycin. Among the 26 S. aureus isolates, 21 (80·76%) possessed staphylococcal enterotoxin genes with seven different enterotoxin gene profiles. The predominant enterotoxin profile was seg, sei and sej with seven S. aureus isolates. The occurrence of multidrug resistant Staphylococcus spp. in pig tonsils indicate public health risk to pork consumers and handlers in developing antimicrobial resistance.

Identification and molecular characterization of Staphylococcus aureus and multi-drug resistant MRSA from monkey faeces in China

Staphylococcus aureus is a commensal bacterium and an important opportunistic pathogen in humans and animals. The increase in multi-drug resistant (MDR) strains of S. aureus is a growing concern due to their impact on animal health and potential for zoonotic transmission. Increasing evidence has shown that MRSA could be transmitted by faeces. The present study determined the prevalence, antibiotic resistance profile and genotypic characteristics of S. aureus isolated from monkey faecal samples in China. Thirty-eight out of 145 (26.21%) macaque faecal samples were S. aureus positive, which eight (5.5%) isolates were identified as MRSA. Antimicrobial susceptibility tests showed that most of the S. aureus isolates were resistant to tetracycline (TE, 44.74%), followed by penicillin (P, 21.05%), cefoxitin (FOX, 21.05%) and ciprofloxacin (CIP, 18.42%). The predominant spa types were t13638 (44.74%) and t189 (13.16%), which are reported to be closely associated with human infections in China. All MRSA isolates belonged to the SCCmecV type, which six of MRSA isolates were ST3268, while the other two isolates belonged to ST4981. This study for the first time describes the prevalence of S. aureus and MRSA in monkey faeces in China, indicating that faeces could be a potential factor of transmitting S. aureus between humans and monkeys.

Livestock-Associated Methicillin-Resistant Staphylococcus aureus From Animals and Animal Products in the UK

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) is an emerging problem in many parts of the world. Although animal-adapted LA-MRSA has been known for many years, recent reports suggest a possible increasing trend in the zoonotic transmission of LA-MRSA in Europe. Since its emergence in the early 2000's, several investigations have indicated that persons in prolonged, repeated contact with affected livestock are at a higher risk of becoming colonized with LA-MRSA. LA-MRSA monitoring in livestock is voluntary under current EU legislation, and not all member states, including the UK, participate. UK LA-MRSA isolates have been detected through scanning surveillance, where samples are submitted from clinically diseased livestock for diagnostic investigation, and research studies. Surveys conducted on retail beef, pig and poultry meat on sale in the UK have also detected LA-MRSA. Taken together these results suggest that LA-MRSA is present in the UK, possibly at low prevalence level, as suggested by available evidence. In this review, we examine the data available from UK livestock and animal products, and make recommendations for future. We also review the findings from whole genome sequencing (WGS) of the possible lineage of some UK livestock isolates.

Technical specifications on harmonised monitoring of antimicrobial resistance in zoonotic and indicator bacteria from food-producing animals and food

Proposals to update the harmonised monitoring and reporting of antimicrobial resistance (AMR) from a public health perspective in Salmonella, Campylobacter coli, Campylobacter jejuni, Escherichia coli, Enterococcus faecalis, Enterococcus faecium and methicillin-resistant Staphylococcus aureus (MRSA) from food-producing animals and derived meat in the EU are presented in this report, accounting for recent trends in AMR, data collection needs and new scientific developments. Phenotypic monitoring of AMR in bacterial isolates, using microdilution methods for testing susceptibility and interpreting resistance using epidemiological cut-off values is reinforced, including further characterisation of those isolates of E. coli and Salmonella showing resistance to extended-spectrum cephalosporins and carbapenems, as well as the specific monitoring of ESBL/AmpC/carbapenemase-producing E. coli. Combinations of bacterial species, food-producing animals and meat, as well as antimicrobial panels have been reviewed and adapted, where deemed necessary. Considering differing sample sizes, numerical simulations have been performed to evaluate the related statistical power available for assessing occurrence and temporal trends in resistance, with a predetermined accuracy, to support the choice of harmonised sample size. Randomised sampling procedures, based on a generic proportionate stratified sampling process, have been reviewed and reinforced. Proposals to improve the harmonisation of monitoring of prevalence, genetic diversity and AMR in MRSA are presented. It is suggested to complement routine monitoring with specific cross-sectional surveys on MRSA in pigs and on AMR in bacteria from seafood and the environment. Whole genome sequencing (WGS) of isolates obtained from the specific monitoring of ESBL/AmpC/carbapenemase-producing E. coli is strongly advocated to be implemented, on a voluntary basis, over the validity period of the next legislation, with possible mandatory implementation by the end of the period; the gene sequences encoding for ESBL/AmpC/carbapenemases being reported to EFSA. Harmonised protocols for WGS analysis/interpretation and external quality assurance programmes are planned to be provided by the EU-Reference Laboratory on AMR.

Transmission of highly virulent community-associated MRSA ST93 and livestock-associated MRSA ST398 between humans and pigs in Australia

Pigs have been recognised as a reservoir of livestock associated methicillin-resistant Staphylococcus aureus (LA-MRSA) in Europe, Asia and North America. However, little is known about the presence and distribution of MRSA in the Australian pig population and pig industry. This study describes the presence, distribution and molecular characteristics of the human adapted Australian CA-MRSA ST93 isolated from pigs, people, and the environment within a piggery. Isolates were subjected to antibiotic susceptibility testing, DNA microarray, whole genome sequencing, multi locus sequence typing, virulence and resistance gene characterization and phylogenetic analysis. MRSA were isolated from 60% (n = 52) of farm workers where 84% of isolates returned ST93 and the rest ST398. Of the thirty-one pig isolates tested further, an equal number of ST398 and ST93 (15 each) and one as ST30-V were identified. Four of six environmental isolates were identified as ST93 and two as ST398. This study has identified for the first time in Australia the occurrence of CA-MRSA ST93 and LA-MRSA ST398 amongst farm workers, pigs, and the farm environment. Comparative genome analysis indicates that ST398 is likely to have been introduced into Australia from Europe or North America. This study also reports the first linezolid resistant MRSA isolated in Australia.

Prevalence and Genetic Diversity of Livestock-Associated Methicillin-Resistant Staphylococcus aureus on Belgian Pork

Since the first description of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA), a high prevalence was observed in pigs. At present, questions remain about the transmission of LA-MRSA to the general human population through pork. The objectives of the present study were to determine the prevalence of LA-MRSA in Belgian pork and to determine the role of the pork production chain and butcheries in transmission of LA-MRSA to the human population. Pig meat samples (chops, bacon, minced pork, ribs, forelimbs, and ears; n = 137) originating from four butcheries (A through D) were spread plated on ChromID MRSA plates both before and after overnight enrichment culture. Suspect colonies were confirmed using a MRSA-specific triplex PCR assay and a CC398-specific PCR assay. The isolates (n = 147) were further characterized by SCCmec typing, multiple-locus variable number tandem repeat analysis, and antimicrobial susceptibility testing, a selection of isolates were subjected to pulsed-field gel electrophoresis and spa typing. Direct plating revealed a MRSA prevalence of 8%. After enrichment, MRSA was isolated from 98 (72%) of 137 samples of which the majority were from rib, ear, and forelimb. The majority (97%) of obtained isolates belonged to CC398, the main LA-MRSA type. A high level of genetic diversity was noted among the isolates from one butchery. Thirty antimicrobial susceptibility profiles were found; 13 and 9% of the isolates had Cip-Tet-Tri and Gen-Kan-Tet-Tob-Tri profiles, respectively. These results indicate the importance of enrichment for MRSA detection of pork. The observed genetic diversity of the isolates indicated that the pork production chain can be considered a source of multiple MRSA types that could be transmitted to the human population through cross-contaminated meat.

Large outbreak caused by methicillin resistant Staphylococcus pseudintermedius ST71 in a Finnish Veterinary Teaching Hospital--from outbreak control to outbreak prevention

Introduction

The purpose of this study was to describe a nosocomial outbreak caused by methicillin resistant Staphylococcus pseudintermedius (MRSP) ST71 SCCmec II-III in dogs and cats at the Veterinary Teaching Hospital of the University of Helsinki in November 2010 – January 2012, and to determine the risk factors for acquiring MRSP. In addition, measures to control the outbreak and current policy for MRSP prevention are presented.

Methods

Data of patients were collected from the hospital patient record software. MRSP surveillance data were acquired from the laboratory information system. Risk factors for MRSP acquisition were analyzed from 55 cases and 213 controls using multivariable logistic regression in a case-control study design. Forty-seven MRSP isolates were analyzed by pulsed field gel electrophoresis and three were further analyzed with multi-locus sequence and SCCmec typing.

Results

Sixty-three MRSP cases were identified, including 27 infections. MRSPs from the cases shared a specific multi-drug resistant antibiogram and PFGE-pattern indicated clonal spread. Four risk factors were identified; skin lesion (OR = 6.2; CI_95% 2.3–17.0, P = 0.0003), antimicrobial treatment (OR = 3.8, CI_95% 1.0–13.9, P = 0.0442), cumulative number of days in the intensive care unit (OR = 1.3, CI_95% 1.1–1.6, P = 0.0007) or in the surgery ward (OR = 1.1, CI_95% 1.0–1.3, P = 0.0401). Tracing and screening of contact patients, enhanced hand hygiene, cohorting and barrier nursing, as well as cleaning and disinfection were used to control the outbreak. To avoid future outbreaks and spread of MRSP a search-and-isolate policy was implemented. Currently nearly all new MRSP findings are detected in screening targeted to risk patients on admission.

Conclusion

Multidrug resistant MRSP is capable of causing a large outbreak difficult to control. Skin lesions, antimicrobial treatment and prolonged hospital stay increase the probability of acquiring MRSP. Rigorous control measures were needed to control the outbreak. We recommend the implementation of a search-and-isolate policy to reduce the burden of MRSP.

Genetic diversity of livestock-associated MRSA isolates obtained from piglets from farrowing until slaughter age on four farrow-to-finish farms

During a previous longitudinal study, performed on four farrow-to-finish farms (A to D), samples were taken from twelve sows, their offspring, and the environment on various occasions over six months to study the MRSA presence. During the present study, a selection of the obtained MRSA isolates were typed by multiple-locus variable-number tandem-repeat analysis (MLVA), Pulsed Field Gel Electrophoresis (PFGE), spa typing, and SCCmec typing to study the genetic diversity of LA-MRSA isolates and to determine possible MRSA sources for pig(let)s. PFGE, spa typing, and SCCmec typing revealed the presence of one or few dominant genotype(s) per farm. In contrast, 212 MLVA types were detected on the four farms, forming one cluster on farm A, three on farm B, four on farm C and two on farm D. The genotype, found on farm A was unique for this farm. Farms B, C and D shared one cluster. In general, MLVA types from these clusters were isolated from piglets, sows, and the environment on various sampling events. Piglets carried MLVA types both related and unrelated to their mother sows’ MLVA types at farrowing and onwards. In conclusion, molecular typing revealed that within a farm one or a few dominant strain(s) are widespread. Potential MRSA sources for piglets were mother sows, the environment and other piglets.

Recovery method development of sodium chloride-susceptible methicillin-resistant Staphylococcus aureus isolates from ground pork samples

The growth of certain methicillin-resistant Staphylococcus aureus (MRSA) isolates could be inhibited by NaCl higher than 2.5%. The objective of this study was to develop an enrichment method to recover NaCl-susceptible MRSA isolates from meat samples. The growth of 12 MRSA and 10 non-MRSA strains was measured in Mueller-Hinton (MH) broth supplemented with 2.5%, 4%, 6.5%, and 7.5% NaCl. Selective agents, including aztreonam, polymyxin B, NaCl, nalidixic acid, and NaN3, were determined for their inhibitory effect to MRSA and non-MRSA strains in MH broth. Based on these data, a two-step enrichment method was developed to recover both NaCl-susceptible and -resistant MRSA isolates in meat products. Comparing to the enrichment method that only used MH broth supplemented with 6.5% NaCl, five additional NaCl-susceptible MRSA isolates were recovered from 92 retail ground pork samples by this newly developed two-step enrichment method. To the best of our knowledge, this is the first study that considers NaCl-susceptible MRSA recovery from ground pork samples. The application of this new enrichment method might expand the diversity of MRSA isolates recovered from various samples.

Carriage of Staphylococcus aureus by free-living wild animals in Spain

The presence of methicillin-susceptible Staphylococcus aureus (MSSA) was analyzed in different free-living wild animals to assess the genetic diversity and predominant genotypes on each animal species. Samples were taken from the skin and/or nares, and isolates were characterized by spa typing, multilocus sequence typing (MLST) and antimicrobial susceptibility testing. The proportion of MSSA carriers were 5.00, 22.93, 19.78, and 17.67% in Eurasian griffon vulture, Iberian ibex, red deer, and wild boar, respectively (P = 0.057). A higher proportion of isolates (P = 0.000) were recovered from nasal samples (78.51%) than skin samples (21.49%), but the 9.26% of red deer and 18.25% of wild boar would have been undetected if only nasal samples had been tested. Sixty-three different spa types were identified, including 25 new spa types. The most common were t528 (43.59%) in Iberian ibex, t548 and t11212 (15.79% and 14.04%) in red deer, and t3750 (36.11%) in wild boar. By MLST, 27 STs were detected, of which 12 had not been described previously. The most frequent were ST581 for Iberian ibex (48.72%), ST425 for red deer (29.82%), and ST2328 for wild boar (42.36%). Isolates from Eurasian griffon vulture belong to ST133. Host specificity has been observed for the most frequent spa types and STs (P = 0.000). The highest resistance percentage was found against benzylpenicillin (average, 22.2%), although most of the S. aureus isolates were susceptible to all antimicrobial tested. Basically, MSSA isolates were different from those MRSA isolates previously detected in the same animal species.

Frequency of resistance to methicillin and other antimicrobial agents among Staphylococcus aureus strains isolated from pigs and their human handlers in Trinidad

Background

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged recently worldwide in production animals, particularly pigs and veal calves, which act as reservoirs for MRSA strains for human infection. The study determined the prevalence of MRSA and other resistant strains of S. aureus isolated from the anterior nares of pigs and human handlers on pig farms in Trinidad.

Methods

Isolation of S. aureus was done by concurrently inoculating Baird-Parker agar (BPA) and Chromagar MRSA (CHROM) with swab samples and isolates were identified using standard methods. Suspect MRSA isolates from Chromagar and BPA were subjected to confirmatory test using Oxoid PBP2 latex agglutination test. The disc diffusion method was used to determine resistance to antimicrobial agents.

Results

The frequency of isolation of MRSA was 2.1% (15 of 723) for pigs but 0.0% (0 of 72) for humans. Generally, for isolates of S. aureus from humans there was a high frequency of resistance compared with those from pigs, which had moderate resistance to the following antimicrobials: penicillin G (54.5%, 51.5%), ampicillin (59.1%, 49.5%), and streptomycin (59.1%, 37.1%), respectively. There was moderate resistance to tetracycline (36.4%, 41.2%) and gentamycin (27.2%, 23.7%) for human and pig S. aureus isolates, respectively, and low resistance to sulfamethoxazole-trimethoprim (4.5%, 6.2%) and norfloxacin (9.1%, 12.4%), respectively. The frequency of resistance to oxacillin by the disc method was 36.4 and 34.0% from S. aureus isolates from humans and pigs, respectively. Out of a total of 78 isolates of S. aureus from both human and pig sources that were resistant to oxacillin by the disc diffusion method, only 15 (19.2%) were confirmed as MRSA by the PBP'2 latex test kit.

Conclusions

The detection of MRSA strains in pigs, albeit at a low frequency, coupled with a high frequency of resistance to commonly used antimicrobial agents in pig and humans could have zoonotic and therapeutic implications. Finally, the diagnostic limitation of using CHROMagar and testing for oxacillin resistance by the disc diffusion method alone to determine MRSA strains without performing confirmatory tests cannot be overemphasized because the possibility of overdiagnosis of MRSA infections cannot be ignored.

Comparison of air samples, nasal swabs, ear-skin swabs and environmental dust samples for detection of methicillin-resistant Staphylococcus aureus (MRSA) in pig herds

To identify a cost-effective and practical method for detection of methicillin-resistant Staphylococcus aureus (MRSA) in pig herds, the relative sensitivity of four sample types: nasal swabs, ear-skin (skin behind the ears) swabs, environmental dust swabs and air was compared. Moreover, dependency of sensitivity on within-herd prevalence was estimated. spa-typing was applied in order to study strain diversity. The sensitivity of one air sample was equal to the sensitivity of ten pools of five nasal swabs and relatively independent of within-herd prevalence [predicted to be nearly perfect (99%) for within-herd prevalence ⩾25%]. The results indicate that taking swabs of skin behind the ears (ten pools of five) was even more sensitive than taking nasal swabs (ten pools of five) at the herd level and detected significantly more positive samples. spa types t011, t034 and t4208 were observed. In conclusion, MRSA detection by air sampling is easy to perform, reduces costs and analytical time compared to existing methods, and is recommended for initial testing of herds. Ear-skin swab sampling may be more sensitive for MRSA detection than air sampling or nasal swab sampling.

Effect of a disinfection strategy on the methicillin-resistant Staphylococcus aureus CC398 prevalence of sows, their piglets and the barn environment

AIMS

To assess, in a cleaned and disinfected barn environment, the efficacy of an animal disinfection strategy to reduce the livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) prevalence in sows, their offspring and the barn environment.

METHODS AND RESULTS

On each farm, six sow rounds were sampled; sows were divided into either a test or control group. Per round, 20 sows and 40 of their piglets were sampled at different time points together with the barn environment. The disinfection strategy of the test groups consisted of washing the sows with a shampoo followed by disinfection of the skin with a solution containing chlorhexidine digluconate and isopropanol. On the first day of disinfection and 6 days after stopping the disinfection, a significant decrease (P < 0·01) of on average 68 and 66% in sow MRSA prevalence was observed on both farms, whereas no decrease was seen in the control groups. Just before weaning, 21-28 days after the end of the disinfection strategy, the difference in MRSA prevalence between both groups was reduced to 4% and no longer significant (P = 0·20). The MRSA prevalence of the piglets in the test groups was significantly lower (26%; P < 0·01) 6 days after the end of disinfection. Just before weaning, this difference was reduced to 5% but still significant (P < 0·01). In the swine nursery unit, no significant difference (P = 0·99) was seen between both groups. Based on semi-quantitative counts, a relationship (r(2)  > 0·6; P < 0·01) was seen between MRSA contamination in the barn environment and the MRSA prevalence in pigs.

CONCLUSION

Results show that the tested disinfection strategy reduces temporarily the sow and piglet MRSA status, but does not result in a final reduction in MRSA at weaning or in the nursery unit.

SIGNIFICANCE AND IMPACT OF THE STUDY

First report on the efficacy of an animal disinfection strategy to reduce LA-MRSA prevalence in sows, their offspring and the barn environment.

Evaluation of different chromogenic media for the detection of methicillin-resistant Staphylococcus aureus CC398 in broilers

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) has emerged in a wide variety of animal species, including poultry. The objective of this study was to evaluate three different chromogenic media for MRSA clonal complex (CC) 398 detection in broilers. On three Belgian poultry farms, 50 broiler chickens were sampled per farm from both nose shell and cloaca. All swab specimens were enriched and inoculated the following day on three chromogenic media: chromID MRSA (bioMérieux), Brilliance MRSA 2 Agar (Oxoid) and MRSASelect (Bio-Rad). ChromID had the highest isolation rates, yet, Brilliance MRSA 2 Agar demonstrated the highest relative sensitivity, while MRSASelect and Brilliance MRSA 2 Agar showed the highest relative specificity. A subset of MRSA isolates was confirmed to be CC398 by the polymerase chain reaction (PCR) targeting sau1-hsdS1. In conclusion, Brilliance MRSA 2 Agar outperformed MRSASelect and chromID MRSA for the detection of MRSA in broilers.

Performance of culture media for the isolation and identification of Staphylococcus aureus from bovine mastitis

Rapid isolation and identification of pathogens is a major goal of diagnostic microbiology. In order to isolate and identify Staphylococcus aureus, a number of authors have used a variety of selective and/or differential culture media. However, to date, there are no reports comparing the efficacy of selective and differential culture media for S. aureus isolation from bovine mastitis cases using the 16S rRNA (rrs) gene sequence as a gold standard test. In the present study, we evaluated the efficacy of four selective and/or differential culture media for the isolation of S. aureus from milk samples collected from cows suffering from bovine mastitis. Four hundred and forty isolates were obtained using salt-mannitol agar (SMA, Bioxon), Staphylococcus-110 agar (S110, Bioxon), CHROMAgar Staph aureus (CSA, BD-BBL) and sheep's blood agar (SBA, BD-BBL). All bacterial isolates were identified by their typical colony morphology in the respective media, by secondary tests (for coagulase and β-haemolysis) and by partial 16S rRNA (rrs) gene sequencing as a gold standard test. Sensitivity, positive predictive and negative predictive values were higher for SMA (86.96, 52.63 and 95.95%, respectively) compared with S110 (70.00, 23.73 and 90.91%, respectively), CSA (69.23, 28.13 and 95.74%, respectively) and SBA (68.75, 37.93 and 89.58%, respectively) while specificity values were similar for all media. Data indicated that the use of culture media for S. aureus isolation combined with determination of coagulase activity and haemolysis as secondary tests improved accuracy of the identification and was in accordance with rrs gene sequence-analysis compared with the use of the culture media alone.