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Microbial biofilms in food environments: study approaches and intervention strategies
Full text linkThe main objective of this study was to examine in-depth the problems related to the for-mation of microbial biofilms in food plants. Although it has long been known that the ability to form biofilms is a common trend in natural environments including food processing environments, most of the studies in the literature concern the medical context, where microbial biofilms are often the cause of serious hospital infections. In the food field, however, the interest in biofilms has only recently arisen, even though the formation of microbial biofilms appears to be the major cause of cross-contamination in food products. Currently, data on microbial communities in the different food processing areas are only limited, and the influence of environmental parameters on the char-acteristics of biofilms have been studied for only a few microbial species. This knowledge is, how-ever, necessary for the development of intervention strategies for the prevention and removal of biofilms, which allows at the same time to obtain a high degree of hygienic-sanitary safety of the surfaces, as well as to reduce the impact conventional strategies have on the environment and on the safety of operators.
The study discussed in this thesis was carried out on specific groups of organisms known to be pathogenic or food spoilers, including Listeria monocytogenes, Staphylococcus aureus and Pseudomonas spp. The need for the availability of appropriate study models that allow to obtain, in as little time as possible, a high number of biofilm samples with homogeneous characteristics was addressed in Chapter 2, where the use of a microtiter plate system and a reactor able to grow mi-crobial biofilms was evaluated on materials widely used in the food industry. In addition, to facili-tate the microbiological laboratory activities, two techniques of plate counts were compared in or-der to highlight problems and benefits in the context of the study of biofilms for both. The micro-titer plate assay and the CDC biofilm reactor assay showed to be sufficiently reliable and repeatable tools to produce a number of samples large enough to provide sufficient information on the ability of food microorganisms to produce biofilms under different operating conditions. Moreover, the drop plate method has proved particularly suitable, sufficiently accurate and reliable, as well as ad-vantageous from the economic point of view, for the quantification of viable cells present in the biofilm.
The influence of environmental parameters on biofilm formation was studied in Chapter 3 and Chapter 4. In particular, in Chapter 3 the effect of the synergy of multiple parameters on the formation of biofilms in a static model system was studied, both in terms of quantification of total the biomass (dead and live cells and EPS matrix) and of the only evaluation of the cell count. The use of a Central Composite Design allowed to mimic the real environmental conditions in the food industry and to obtain the greatest amount of information limiting the number of experiments to be carried out. Therefore, useful data were obtained to increase the information in the literature about the synergistic effects of the environmental parameters on biofilm formation regarding the food sector. In Chapter 4 the effect of temperature on the adhesion and on the biofilm structure, as well as on resistance to disinfectants commonly used in the food industry sanitation plans was studied. The study showed that temperature significantly affects the kinetics of adhesion, but also the cell density and the amount of EPS produced, and consequently the resistance to biocides. The use of CLSM technique for microscopic observation allowed the study of biofilms in undisturbed condi-tions, and thus it is well suited to a possible use during the biofilm growth. The evaluation of dif-ferent strategies for the removal of biofilms was the subject of Chapter 5 and Chapter 6, in which conventional and non-conventional approaches were considered. A comparison between chemical, physical and biological treatments shows that a hurdle-approach, in which different strategies are used in sequence, could help in limiting the health and hygiene problems related to microbial bio-films in the production of foodstuffs. Finally, in Chapter 7 the gained knowledge was used to study the problem of biofilms in specific food contexts
Microbial biofilm: Bio-forming ability in Staphylococcus aureus in the dairy industry
No full textS. aureus is a major cause of contamination in milk and dairy products, representing a problem for the safety of the consumer. The ability to form biofilms, a pathogenic factor present in S. aureus, has been studied in a limited way in mastitic and food isolates. The purpose of this study was to investigate the ability to form biofilms and the peracetic acid resistance of dairy S. aureus isolates. The biofilm-forming ability was found to be widespread in S. aureus, and this trait may in part explain the presence and persistence of S. aureus in the dairy industry. The biofilm of S. aureus have been shown to be quite tolerant to peracetic acid, which highlights the need, in the development of a cleaning protocol, to keep in consideration the spread of microbial forms capable of forming biofilms in the dairy industry
Valutazione della resistenza a sanificanti utilizzati nell’industria alimentare in Staphylococcus aureus
No full textThe new trends in food production
lead to an increased need for efficient
sanitary practices and consequently
a more frequent use of chemical
disinfection. In this study 10
Staphylococcus aureus strains were tested
for resistance and adaptation responses
towards Quaternary Ammonium
Compounds (QAC). Minimum
Inhibitory Concentration (MIC)
determinations were performed in
order to evaluate the strains resistance
to each sanitizer. One strain showed
high resistance to QACs. Increasing
disinfecting concentration resulted
in the adaptation of Staphylococcus
aureus. The final MICs, however,
did not exceed the concentrations
used in working solutions in the food
processing plants. Most antimicrobials
were observed to cause crossadaptation
to other disinfectants.
Results obtained in this study may be
valuable when designing a rotation
of disinfectants in food processing
plants, since very little information is
available on how the rotation should
be performed and which disinfectants
to use
SANITIZERS SENSITIVITY OF LISTERIA MONOCYTOGENES BIOFILMS GROWN UNDER STATIC AND DYNAMIC CONDITIONS
No full textEffect of environmental factors on biofilm formation by Pseudomonas spp. of dairy origin
No full textResistenza agli antibiotici in batteri lattici di origine alimentare
No full textThe lactic acid bacteria have a
long history of “safe” use in food
technologies, even if there are some
studies about probable negative
activities of this microorganisms in
foods. The aim of this work was to
research the spread, among lactic
acid bacteria isolated from different
food matrices, of characteristics
potentially related with health and
security, such as the antibiotic
resistance. In this survey a high
occurrence of antibiotic multiresistance
has been evidenced,
mainly for strains isolated from
specific niches. This aspect has to be
deeply surveyed because the absence
of this characteristic is an important
selection standard for cultures used
as starters or probiotics
Crescita di Staphylococcus aureus, Escherichia coli e Listeria monocytogenes in formaggi a latte crudo
No full textNei formaggi a latte crudo la qualità microbiologica del latte, le tecniche di lavorazione e l’igiene di produzione rivestono un ruolo essenziale nel prevenire e/o arrestare la crescita dei microrganismi potenzialmente patogeni. Scopo di questo lavoro è stato quello di valutare l’efficacia delle pratiche di stoccaggio del latte e di caseificazione nel controllo di Staphylococcus aureus, Listeria monocytogenes ed Escherichia coli. I risultati delle prove di stoccaggio evidenziano come le temperature testate (da 8 a 12 C) permettano di arrestare la crescita di S. aureus ma non quella di L. monocytogenes e di E. coli, la cui carica aumenta dopo 24 ore a 10 e 12 C. Le pratiche effettuate durante la caseificazione (sosta del latte in caldaia, aggiunta di lattoinnesto e lisozima, cottura a 45 C) non creano le condizioni per la moltiplicazione dei patogeni, ma non causano nemmeno un abbattimento della loro carica. E’ quindi di fondamentale importanza la qualità igienico-sanitaria della materia prima e la temperatura di stoccaggio del latte prima della lavorazione, al fine di consentire l’utilizzo di pratiche casearie artigianali che permettano l’ottenimento di prodotti sicuri, oltre che di elevata qualità organolettica
Occurence and characterization of Staphylococcus aureus isolated from raw milk for cheesemaking
No full textFifty-four samples of raw milk for cheesemaking were tested for the presence of Staphylococcus aureus.
Multiplex polymerase chain reactions were performed to identify presumptive isolates and the presence
of enterotoxin-coding genes sea-see. The strains were tested for antibiotic resistance. Eighty strains were
identified as S. aureus and 31 of these carried one or more enterotoxin genes (sea-see). Resistance to eritromycin,
penicillin and ampicillin was widespread among isolates. Staphylococcus aureus in raw milk
for cheesemaking may constitute a risk with respect to staphylococcal food poisoning from raw milk
products
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