The staphylococci: an introduction

Modelling the growth of Staphylococcus aureus on cooked broccoli under isothermal conditions

In this study, we developed predictive models describing the growth of Staphylococcus aureus on cooked broccoli florets. A pool of 3.5 log CFU/g of five S. aureus strains were inoculated on 10 g broccoli portions. The samples were then stored at 10, 20, 30 and 37 °C, and colonies were enumerated at different time intervals. Baranyi and Roberts model was fitted to the data using a Bayesian Adaptive Markov Chain Monte Carlo for estimation of the growth parameters. S. aureus showed low growth at 10 °C on broccoli samples and at 20-37 °C interval, Baranyi and Roberts model fitted well to the experimental data (R²>0.97). Estimated growth parameters were correlated with the possibility of toxin production and indicate the potential presence of these biological hazards on contaminated broccoli after heat treatment. Additionally, linear regression was performed for growth rate as storage temperature function. This secondary model followed a linear tendency with R²=0.997 and was compared with two tertiary models (ComBase Predictor and Pathogen Modeling Program) and literature data, demonstrating similar growth rate values of both. These results can be helpful for food services and managers to establish food safety standards for S. aureus growth on cooked broccoli.

Comparative analysis of impact of human occupancy on indoor microbiomes

Educational facilities serve as community hubs and consequently hotspots for exposure to pathogenic microorganisms. Therefore, it is of critical importance to understand processes shaping the indoor microbiomes in educational facilities to protect public health by reducing potential exposure risks of students and the broader community. In this study, the indoor surface bacterial microbiomes were characterized in two multifunctional university buildings with contrasting levels of human occupancy, of which one was recently constructed with minimal human occupancy while the other had been in full operation for six years. Higher levels of human occupancy in the older building were shown to result in greater microbial abundance in the indoor environment and greater proportion of the indoor surface bacterial microbiomes contributed from human-associated microbiota, particularly the skin microbiota. It was further revealed that human-associated microbiota had greater influence on the indoor surface bacterial microbiomes in areas of high occupancy than areas of low occupancy. Consistent with minimal impact from human occupancy in a new construction, the indoor microbiomes in the new building exhibited significantly lower influence from human-associated microbiota than in the older building, with microbial taxa originating from soil and plants representing the dominant constituents of the indoor surface bacterial microbiomes. In contrast, microbial taxa in the older building with extensive human occupancy were represented by constituents of the human microbiota, likely from occupants. These findings provide insights into processes shaping the indoor microbiomes which will aid the development of effective strategies to control microbial exposure risks of occupants in educational facilities.

Effects of subzero saline chilling on broiler chilling efficiency, meat quality, and microbial safety

The poultry industry has attempted to improve carcass chilling efficiency, meat quality, and product safety. The purpose of this research was to investigate the effects of subzero saline chilling on carcass chilling, breast fillet tenderness, and microbial safety. After evisceration, broiler carcasses were chilled using ice slurry control (0% NaCl/0.5°C) or subzero saline solutions (3% NaCl/-1.8°C and 4% NaCl/-2.41°C). Broiler carcasses in the subzero saline solutions were chilled efficiently and reduced the chilling time by 11% in 3% NaCl/-1.8°C and 37% in 4% NaCl/-2.41°C over the ice slurry chilling. The breast fillets of broiler carcasses in 4% NaCl/-2.41°C were significantly tenderized than those in water control (P < 0.05), with an intermediate value observed in 3% NaCl/-1.8°C. Before chilling, broiler carcasses possessed mesophilic aerobic bacteria, Escherichia coli, and total coliforms for 3.81, 0.78, and 1.86 log cfu/g, respectively, which were significantly reduced after chilling in 3% NaCl/-1.8°C or 4% NaCl/-2.41°C solution over the water control (P < 0.05), except the mesophilic aerobic bacteria. Based on these results, chilling of boiler carcass in 4% NaCl/-1.8°C solution appears to improve carcass chilling efficiency, meat tenderness, and bacterial reduction for E. coli and total coliforms.

Growth of Staphylococcus aureus 2064 described by predictive microbiology: From primary to secondary models

The growth of Staphylococcus aureus 2064 isolate in model nutrient broth was studied as affected by temperature and water activity using principles and models of predictive microbiology. Specific rates resulting from growth curves fitted by the Baranyi model were modelled by the secondary Ratkowsky model for suboptimal temperature range (RTKsub) as well as the Ratkowsky extended model (RTKext) and cardinal model (CM) in the whole temperature range. With the biological background of the RTKext model, cardinal values of temperature T min = 6.06 °C and T max = 47.9 °C and water activity aw min = 0.859 were calculated and validated with cardinal values estimated by CM (T min = 7.72 °C, T max = 46.73 °C, aw min = 0.808). CM also provided other cardinal values, T opt = 40.63 °C, aw opt = 0.994, as well as optimal specific growth rate of 1.97 h–1 (at T opt and aw opt). To evaluate the goodness of fit of all models, mathematical and graphical validation was performed and the statistical indices proved appropriateness of all the secondary models used.

Methicillin-Resistant Staphylococcus aureus in Seafood: Prevalence, Laboratory Detection, Clonal Nature, and Control in Seafood Chain

Methicillin-resistant Staphylococcus aureus (MRSA), a versatile pathogen bearing multiple virulence determinants, is increasingly being detected in various food-producing animals, including fish. In addition, it is a potential food poisoning agent. MRSA is not an inherent microbiota of fish; its presence is attributed to pre- or postharvest contamination through fish handlers, water, ice, and processing equipment. Several reviews have been written on MRSA in clinical as well as the food animal-producing sector, but information specific to MRSA in seafood is scant. This review puts forth insights on MRSA detection in seafood, antibiotic resistance, diversity of clones in seafood, and possible control measures in seafood production chain. Emphasis has been given on assessing the variations in the protocols employed for isolation and identification in different food matrices and lay the foundation for researchers to develop optimized procedure.

Prevalence of Staphylococcus aureus and antibiotic resistant Staphylococcus aureus in public transport in Bratislava, Slovakia

There is evidence that the transmission of Staphylococcus aureus and methicillin-resistant S. aureus between the community and environmental surfaces still exists. Even the means of this transmission remain uncertain, the public transport system may serve as a potential source of different bacteria, and the contact with contaminated public surfaces may increase the risk for bacterial diseases emergence. This study aimed to investigate S. aureus contamination on Bratislava’s public transport vehicles. Forty samples of hand-touched surfaces were collected during December 2015 and March 2017 by using surface sampling method. S. aureus was detected in all analysed swabs. Simultaneously, antibiotic resistance of S. aureus from swabs was evaluated. Of 40 samples, only 23 % did not contain S. aureus resistant to some of 10 analysed antibiotics. On the other hand, the severe prevalence of highly resistant S. aureus to penicillin, methicillin, ampicillin, and cefoxitin was confirmed. 15 % of isolates displayed resistance to at least three antimicrobial classes. The amount of S. aureus was not significantly influenced by the lines or by the analysed surface (grabs rails or on-board stop buttons). However, there was a statistically significant effect of year period, both between samples from December and March and between samples from the same month but different year. The study confirmed the widespread occurrence of resistant S. aureus in public transport vehicles in Bratislava, Slovakia.

Effect of temperature and pH on the community dynamics of coagulase-negative staphylococci during spontaneous meat fermentation in a model system

Coagulase-negative staphylococci (CNS) contribute to the product quality of fermented meats. In spontaneously fermented meats, CNS communities are variable and difficult to predict, as their compositions depend on a superposed combination of different processing factors. To partially disentangle this superposition, a meat model system was used to study the influence of temperature and pH on the CNS community dynamics. Therefore, cured pork mince was prepared that was divided into three batches of different initial acidity levels, namely pH 5.7, pH 5.5, and pH 5.3. These three batches were incubated at three different temperatures, namely 23 °C, 30 °C, and 37 °C. Hence, the experimental set-up resulted in nine combinations of different temperature and initial pH values. Samples were analysed after 3 and 14 days to monitor pH, colony counts, and species diversity of the CNS communities, based on mannitol-salt-phenol-red agar (MSA) medium. At conditions of mild acidity (pH 5.7) and low temperature (23 °C), as often encountered during artisan-type meat fermentations, a co-prevalence of Staphylococcus xylosus, Staphylococcus equorum, and Staphylococcus saprophyticus occurred. At the same initial pH but higher incubation temperatures (30 °C and 37 °C), Staphylococcus lugdunensis became the prevailing CNS species, besides S. saprophyticus (30 °C) and the coagulase-positive species Staphylococcus aureus (37 °C). When the initial pH was set at 5.5, S. saprophyticus was the prevailing CNS species at both 23 °C and 30 °C, but it was replaced by Staphylococcus epidermidis and Staphylococcus simulans at 37 °C after 3 and 14 days, respectively. At the most acidic conditions (pH 5.3), CNS counts declined and many of the MSA isolates were of non-staphylococcal nature. Among others, Staphylococcus carnosus (23 °C), Staphylococcus warneri (30 °C), and S. epidermidis (37 °C) were found. Overall, the results of the present study indicated that the processing factors temperature and pH had a clear impact on the shaping of staphylococcal communities during meat fermentation.

Phenotypic and Molecular Aspects of Staphylococcus spp. Isolated from Hospitalized Patients and Beef in the Brazilian Amazon

The aim of this study was to characterize and compare Staphylococcus spp. isolated from hospitalized patients and beef marketed in the city of Porto Velho-RO, Brazil. The isolates were subjected to antibiogram tests, adherence capacity tests, detection of the mecA gene, and epidemiological investigation by the random amplified polymorphic DNA (RAPD) technique, using the primers M13 and H12. Among the 123 Staphylococcus spp. isolates, 50 were identified as S. aureus and 73 as coagulase-negative Staphylococcus; among the latter, 7 species were identified. It was observed that the coagulase-negative Staphylococcus isolates showed greater adhesion ability than S. aureus. The profile of antimicrobial susceptibility was different among isolates, all of which were susceptible to vancomycin and linezolid, and had high penicillin resistance rates, varying according to the bacterial class and the source. In this study, all strains were negative for mecA gene detection; however, 36% of S. aureus and 17% of coagulase-negative Staphylococcus were resistant to oxacillin. The genetic relationship of these bacteria, analyzed by RAPD, was able to discriminate the species of coagulase-negative Staphylococcus strains of S. aureus along its origin. It was concluded that the isolates of Staphylococcus spp. derived from beef and human infections differ genetically. Thus, it is suggested that isolates from beef, which were grouped within hospital isolates, were probably carried via contact with beef in hospital professionals or patients.

Composição química e eficácia do óleo essencial e do extrato etanólico de Alpinia zerumbet sobre Staphylococcus aureus

RESUMO: O presente trabalho descreve a atividade antibacteriana do óleo essencial e do extrato etanólico das folhas de Alpinia zerumbet (colônia) sobre cepas de Staphylococcus aureus isoladas de vacas com mastite subclínica e cepas padrão ATCC 29213 e ATCC 25923, por meio do método de difusão em ágar. Foram utilizados 10 tratamentos contendo diferentes concentrações do óleo essencial e do extrato etanólico (100,0; 50,0; 25,0; 12,5 e 6,3 mg.mL-1) e o grupo controle (álcool etílico a 50% e Tween a 1%). Os constituintes majoritários do óleo essencial foram p -cimeno (32,72%), 1,8-cineol (24,05%) e 4-terpineol (20,23%), sendo esses determinados por cromatografia a gás acoplada a espectrometria de massas e cromatografia a gás com detector de ionização de chama (CG-EM/DIC). No extrato etanólico foi detectado o ácido elágico e três flavonoides: rutina, quercetina e campferol, por meio de cromatografia a líquido de alta eficiência acoplada a detector de arranjo de diodo (CLAE-DAD). Todas as cepas apresentaram sensibilidade aos tratamentos com óleo essencial e extrato etanólico. A melhor resposta foi obtida com o óleo essencial de A. zerumbet que, na concentração de 100 mg.mL-1 proporcionou inibição total do crescimento bacteriano. Esses resultados sugerem o potencial antibacteriano do óleo essencial e do extrato etanólico de A. zerumbet no controle da mastite bovina.

Viabilidade de Staphylococcus aureus FRI S-6 e produção de SEB em queijo elaborado com adição de Lactobacillus rhamnosus e Lactococcus lactis

Staphylococcus aureus foi inoculado em queijos produzidos de forma estéril em laboratório, juntamente com Lactobacillus rhamnosus e Lactococcus lactis, isolados de queijo de coalho artesanal e identificados por PCR-ARDRA16S-23S. L. lactis foi capaz de reduzir a contagem de S. aureus no primeiro dia após produção (P<0,05) dos queijos de 3,3x10(7)UFC/g para 1,0x10(7)UFC/g. L. rhamnosus não impediu o crescimento de S. aureus. A presença das cepas acidoláticas, principalmente L. lactis, mostrou ainda potencial de inibição da produção de enterotoxina estafilocócica do tipo B, sendo que a concentração de enterotoxinas no 15° dia foi inferior ao limite de detecção pelo kit comercial utilizado. Concluiu-se que a presença das bactérias acidoláticas estudadas pode contribuir para a melhoria da qualidade sanitária de queijos artesanais.

ESTAFILOCOCOS EM ALIMENTOS

RESUMO Este artigo de revisão tem como objetivo descrever as principais características do Staphylocococus aureus e a relação deste micro-organismo com as doenças transmitidas por alimentos. S. aureus é a principal espécie do gênero e o homem e os animais são os reservatórios. Este micro-organismo se multiplica com facilidade em vários alimentos e produz enterotoxinas (EE) termorresistentes. Leite cru e derivados, creme, tortas recheadas com creme, salada de batata, atum, carne de frango, presunto, carnes e produtos a base de ovos já foram incriminados nos surtos alimentares envolvendo os estafilococos. Os principais sintomas são náuseas, vômito, cãibras abdominais e diarréia. O período de incubação varia de 2 a 4 horas. São conhecidos 20 tipos diferentes de EE e sua produção é influenciada pela temperatura, pH, atividade de água, tamanho do inóculo, fonte de carbono e nitrogênio, concentração de sal e condições atmosféricas do substrato. A maioria das intoxicações é produzida por EEA e EED. As EE são detectáveis nos alimentos que apresentam populações de S. aureus acima de 105 UFC/mL de alimento. A dose mínima de EE ingerida para causar intoxicação é 100 ng. Para detecção de EE, existem métodos como Sensibilidade Ótima em Placas (OSP- Optimun Sensitivity Place), microslide, Aglutinação Reversa Passiva em Látex (RPLA- Reversed Passive Latex Agglutination) e ELISA. A Reação em Cadeia pela Polimerase (PCR- Polimerase Chain Reaction), apesar de não diferenciar células viáveis de não viáveis, pode ser aplicada para detecção de diversos tipos de estafilococos enterotoxigênicos.

An immunomagnetic PCR signal amplification assay for sensitive detection of Staphylococcus aureus enterotoxins in foods

Enterotoxigenic strains of Staphylococcus aureus produce a variety of heat-stable staphylococcal enterotoxins (SEs) that are a prevalent cause of food poisoning in the United States and other countries. Many immunological and biochemical assays often work well in buffer systems but are hindered when tested in the complex chemical environment of foods. To overcome these biases and improve the limits of detection, we implemented an immunomagnetic PCR signal amplification assay (iPCR-SA) for recovery and detection of SEA and SEB in foods. Anti-SEA or anti-SEB primary antibodies were coated onto COOH-modified magnetic beads using 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide reagent. Secondary antibodies were covalently linked to amino-modified reporter DNA oligonucleotides (563 bp) via the linker molecule succinimidyl-4[N-maleimidomethyl]-cyclohexane-1-carboxylate. An internal 159-bp portion of the reporter DNA retained by the captured toxin molecule was then amplified by real-time PCR. A semiautomated Bead Retriever proved extremely helpful in both the application of the conjugation chemistries and required washes and the recovery and washing of bead-conjugated toxin from tested food samples. The procedure was simple, and analyses were completed in 5 to 6 h. The assay was sufficiently robust that we were able to detect SEA and SEB in tryptic soy broth, milk, lemon cream pie, tuna salad, deli turkey, and ground turkey at levels as low as 7.5 fg/ml. SE was still detected at high sensitivity after heating in food samples for typical pasteurization or cooking regimens. Sensitivity was diminished only when samples were subjected to extreme heating.

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

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

Growth and aroma production by Staphylococcus xylosus, S. carnosus and S. equorum--a comparative study in model systems

A laboratory medium inoculated with 20 different Staphylococcus strains was prepared in accordance with a full factorial experimental design investigating the effect of temperature, pH, NaCl and glucose on growth. The 12 strains most suited to growth in a fermented meat environment were inoculated in sausage minces together with Pediococcus pentosaceus, incubated at 25 degrees C for 1 week and the produced aroma compounds collected. The data were analysed by multiple linear regression and partial least squares regression analysis. The results showed that increasing pH and temperature from 4.6 to 6.0 and 10 to 26 degrees C, respectively, increased growth of all strains with strong synergy between temperature and pH. Increasing salt concentration from 5% to 15% w/v decreased growth of most strains, but the effect of pH and temperature was much stronger than the effect of salt. Strains of S. carnosus were more salt tolerant than strains of S. equorum and S. xylosus, especially at high pH and temperature. Addition of glucose up to 0.5% w/v had no significant influence on growth of any of the strains. With regard to aroma production, species characteristics were detected. S. carnosus and S. xylosus were quite different regarding the overall aroma profiles, whereas the profiles of S. equorum lied somewhere in-between. Contrary to S. carnosus, S. xylosus and S. equorum did not produce 2-methyl-1-butanol. On the other hand, in particular, S. xylosus produced more 3-methyl-1-butanol. Except for one of the strains of S. equorum, S. xylosus and S. equorum formed more diacetyl, 2-butanone and acetoin and also more of the methyl-branched ketones arising from degradation of leucine, isoleucine and valine. S. carnosus produced more methyl-branched aldehydes, acids and corresponding esters from leucine, isoleucine and valine compounds that have been correlated with fermented sausage maturity in former studies. S. equorum produced the least of the methyl-branched aldehydes.

Antimicrobial resistance of coagulase-negative staphylococci from a Kuwait hospital

This study investigated the incidence of antimicrobial resistance in clinically significant coagulase-negative staphylococci at the Mubarak Al Kabeer Hospital, Kuwait. A total of 104 isolates of coagulase-negative staphylococci consisting of S. epidermidis (67), S. haemolyticus (16), S. saprophyticus (6), S. simulans (2), S. hominis (4), S. albus (2), S. sciuri (3), S. warneri (2), S. capitis (1), and S. xylosus (1) were isolated from clinical specimens over a 6-7 month period and tested for resistance to 22 antibacterial agents and the ability to produce slime. They were all susceptible to vancomycin and mupirocin but intermediate resistance to teicoplanin was detected in seven isolates: 83 and 47.7% were resistant to penicillin G and methicillin, respectively, 57% were resistant to gentamicin, 49.5% to erythromycin, 50.4% to tetracycline, and 52.3% to trimethoprim. Resistance to heavy metals and the nucleic-acid binding compound was also detected. More than half of S. epidermidis, S. saprophyticus, S. simulans, S. hominis, and all of S. haemolyticus were multiply resistant to three or more groups of antibiotics and there was a significant association between slime production and resistance to multiple antimicrobial agents in S. epidermidis. The results revealed a high level of resistance to commonly used agents.