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The Bacillus cereus group is composed of eight species, including B. cereus sensu stricto (s. s.), Bacillus thuringiensis, Bacillus mycoides, Bacillus pseudomycoides, Bacillus anthracis, Bacillus weihenstephanensis, Bacillus cytotoxicus (GUINEBRETIÉRE et al., 2013) and Bacillus toyonensis (JIMÉNEZ et al., 2013). The bacteria belonging to this group are rod-shaped, gram-positive, facultatively anaerobe, spore-producers (allowing their survival to heat-treatment) and widespread on environment (FDA, 2012).
These bacteria are genomically similar besides their phonotypical differences, such as the ability to cause foodborne illness and anthrax, or to be used on biological pest control. The genetic differentiation on these species is possible. However, it still presents some difficulties due the high genetic similarity among these species and plasmids transfer (KOVAC et al., 2016).
The species B. cereus s. s. is highlighted in this group due its importance on food production chain considering its ability to cause emetic and diarrheal syndrome (FDA, 2012) and foodborne outbreaks (ZHOU et al., 2014). Yet, other species are also considered able to cause foodborne illness (GUINEBRETIÉRE et al., 2013). The dairy products are not often involved in these outbreaks (BENNET et al., 2013), but this group is important to dairy industries due its ability to form biofilms and result in food spoilage (KUMARI; SARKAR, 2016).
This group is reported as contaminant in several dairy products (KUMARI; SARKAR, 2016), but there are no studies published on literature reporting its presence on requeijão curd cheeses and especialidade láctea tipo requeijão, which are highly consumed in Brazil (ZACARCHENCO et al., 2012). Requeijão curd cheese is produced using acid coagulation of milk followed by a mass fusion (80ºC during 5 seconds), whey removal and washing, and the addition of fat milk is allowed (BRAZIL, 1997). Furthermore, a very similar dairy product (especialidade láctea tipo requeijão) is often consumed in Brazil, differing from the first product cited by the addition of cornstarch.
Thus, this study aimed to counting bacteria belonging to B. cereus group in requeijão curd cheeses and especialidade láctea tipo requeijão (regular and light) marketed in the state of São Paulo, Brazil, and verify if there is difference in relation to this occurrence among these categories. For this purpose, 200 samples of requeijão and especialidade láctea tipo requeijão were bought on supermarkets located in Jaboticabal, São Paulo, in 2015.
The samples were processed in groups of five unities each (one lot), as it follows:
50 samples of requeijão normal”, from five commercial brands and ten production lots;
50 samples of requeijão light”, from five brands and ten lots;
50 samples of especialidade láctea, from five brands and ten lots;
50 samples of especialidade láctea light, from three brands and ten production lots (Table 1).
Table 1: Average counts of bacteria from B. cereus group on requeijão, requeijão light, especialidade láctea tipo requeijão and especialidade láctea tipo requeijão light marketed in Jaboticabal municipality, state of São Paulo, Brazil, in 2015.
| Product | Brand | Lot | Bacillus cereus group (CFU/g) | Product | Brand | Lot | Bacillus cereus group (CFU/g) |
|---|---|---|---|---|---|---|---|
| Requeijão | A | 1 | 0.1 × 10 | Especialidade láctea | A | 1 | <0.1 × 10 |
| 2 | <0.1 × 10 | 2 | <0.1 × 10 | ||||
| B | 1 | 0.7 × 10 | B | 1 | <0.1 × 10 | ||
| 2 | 3.1 × 10 | 2 | 0.1 × 10 | ||||
| C | 1 | <0.5 × 10 | C | 1 | 2.5 × 10 | ||
| 2 | <0.5 × 10 | 2 | 0.1 × 10 | ||||
| D | 1 | <0.1 × 10 | D | 1 | <0.1 × 10 | ||
| 2 | <0.1 × 10 | 2 | <0.1 × 10 | ||||
| E | 1 | <0.1 × 10 | E | 1 | <0.1 × 10 | ||
| 2 | <0.1 × 10 | 2 | <0.1 × 10 | ||||
| Requeijão Light | A | 1 | 0.4 × 10 | Especialidade láctea light | A | 1 | 0.1 × 10 |
| 2 | <0.1 × 10 | 2 | <0.1 × 10 | ||||
| B | 1 | <0.1 × 10 | 3 | 0.7 × 10 | |||
| 2 | 0.2 × 10 | 4 | 1.8 × 10 | ||||
| C | 1 | <0.1 × 10 | B | 1 | 0.2 × 10 | ||
| 2 | <0.1 × 10 | 2 | <0.1 × 10 | ||||
| D | 1 | <0.1 × 10 | 3 | <0.1 × 10 | |||
| 2 | <0.1 × 10 | 4 | 0.2 × 10 | ||||
| E | 1 | <0.1 × 10 | C | 1 | <0.1 × 10 | ||
| 2 | 0.1 × 10 | 2 | <0.1 × 10 |
The asepsis of package was performed using ethanol 10%, and posteriorly 25 g of the samples were transferred to flasks containing sterile peptone water 0.1% to obtain the initial dilution (10-1). Following, 1 mL of this initial dilution was transferred to a tube containing 9 mL of sterile peptone water 0.1%, obtaining the dilution 10-2, and this step was repeated to obtain the dilution 10-3 (BRAZIL, 2003).
These dilutions were inoculated in duplicate on plates containing Agar-MYP and incubated on 30ºC during 18-40 hours. The colonies considered as suggestive of B. cereus group were those pink to red and lecithinase-positive (MOSSEL et al., 1967). Gram stain was performed using three to five suggestive colonies.
In order to verify if there were statistically significant differences on the counts between the different types of evaluated products, the radicalization of the counts values was carried out. When the requirements for the analysis were not a setback, the analysis was performed through non-parametric tests (Kruskal-Wallis). Data analysis was also performed through presence or absence in the products, to verify if there was a statistically significant difference. For this purpose, the products were divided into those with high and low fat (regular and light types), and with or without starch (requeijão and especialidade láctea tipo requeijão). Then, chi-square analysis was performed. These analyzes were carried out adopting the level of significance of 5% (p<0.05).
Among the 40 lots of dairy products, 14 (35%) showed contamination by bacteria from B. cereus group. REZENDE-LAGO et al. (2012) evaluated powdered, raw, pasteurized and ultra-high temperature processing (UHT) milks samples and isolated B. cereus in 73.3, 50.0, 96.7 and 13.3%, respectively, demonstrating the importance of bacteria from this group in dairy products. The result of bacterial counts belonging to the B. cereus group is shown in Table 1.
Although bacteria from the B. cereus group may be present in a wide variety of dairy products such as UHT milk, pasteurized milk, powdered milk, cheeses and fermented milks (WONG et al., 1998; REZENDE-LAGO et al., 2007), it can be observed in Table 1 that the counts of bacteria belonging to the B. cereus group in the evaluated dairy products were considered low. However, although low and unable to put consumers at risk, since the counts were above 105 CFU/g - value required to cause foodborne diseases (FDA, 2012) -, the action of their spoilage enzymes can reduce the shelf life of these products (KUMARI; SARKAR, 2016).
The low occurrence of these bacteria can be explained by the fact that the milk used as raw material has a satisfactory microbiological quality, since the contamination of raw milk by spores of B. cereus is dependent on management in dairy farms (VISSERS et al., 2007). Also, the temperature used during curd cheeses processing is able to inactivate most of the microorganisms, with the exception of the sporulating ones. In addition to composition, pH and water activity (Aw), the presence of flux salts and nisin may be inhibitory to sporulating microorganisms (JOHNSON, 2001).
Another factor that contributes to the low microbial load of these products is the bactofugation process, or Ultra-Fresh Bactofugation combines treatments that target the separation and removal of active, sporulating microorganisms and somatic cell with a subsequent heat treatment by direct injection of steam (PRATA et al., 2012). In addition, the use of preventive systems such as good manufacturing practices (GMP) and Hazard Analysis and Critical Control Points (HACCP), which are mandatory in Brazilian dairy industries, help to mitigate the risks (KUMARI; SARKAR, 2016).
The results of the B. cereus counts did not meet the requirements to be able to perform the analysis of variance. Then, the Kruskal-Wallis test was used. There were no statistically significant differences between the B. cereus counts (p>0.05) among the different evaluated product types. The results of chi-square analysis for the presence/absence of B. cereus did not reveal any statistically significant difference (p>0.05) between the different products. Thus, it is believed that the presence of starches or vegetable oils (requeijão × especialidade láctea) and fat (regular × light) in the products did not significantly influence the occurrence of B. cereus group.
Psychrotrophic strains of B. cereus present greater germination and multiplication capacity in high fat dairy products due to their hydrophobic spores (LARSEN; JORGENSEN, 1997). In addition, lipids confer a protective characteristic on the spores, since fat has low-thermal conductivity (MEER et al., 1991). Consequently, the presence of lipids in food could be an important factor in the microorganism adaptation to these conditions, but no influence was observed in this study.
The counts of the B. cereus group in requeijão and especialidade láctea tipo requeijão were low and unable to jeopardize the consumers of these products if proper conditions of refrigeration during storage and sale are adopted. However, the present study is the first one to report the presence of such group of microorganisms in these dairy products, which requires new studies to evaluate the impact of its spoilage on the shelf life of these products routinely consumed in Brazil.
