Abstract
Salmonella serotypes can develop biofilms in fresh food products. This study focused on determining the antimicrobial resistance profile and the effects of different growth media and environmental conditions on biofilm formation by multidrug-resistant serotypes of Salmonella. All 49.4% of the Salmonella strains (five serotypes) were multidrug resistant. Assessment of the ability to form biofilms using the crystal violet staining method revealed that 95.6% of the strains of Salmonella were strong biofilm producers in 96-well polystyrene microtiter plates. Overall, 59.3% of the Salmonella strains showed the rdar (red dry and rough colony) morphotype, 2.1% pdar (pink dry and rough colony), 27.4% bdar (brown dry and rough colony) and 10.9% saw (smooth and white colony), at two temperatures (22 and 35 °C). Mono-species biofilms of Salmonella serotypes showed a mean cell density of 8.78 log10 CFU/cm2 ± 0.053 in TSBS (1/20 diluted TSB (tryptic soy broth) + 1% strawberry residues) and 8.43 log10 CFU/cm2 ± 0.050 in TSBA (1/20 diluted TSB + 1% avocado residues) on polypropylene type B (PP) (p < 0.05). In addition, epifluorescence microscopy and scanning electron microscopy (SEM) enabled visualizing the bacteria and extracellular polymeric substances of biofilms on PP. Salmonella form biofilms depending on the serotype of the strains and the environmental conditions. Mono-species biofilms formed by Salmonella serotypes respond to nutrient limitation with the use of simplified culture media such as TSBA and TSBS.
Highlights
Salmonella spp. cause about 1.35 million infections, 26,500 hospitalizations, and 420 deaths annually in the United States; Enteritidis, Newport, Typhimurium, Javiana, 4,5,12:i: and Infantis were the top six Salmonella serotypes that caused foodborne infections in the United States in 2019 [1]
The objectives of this research were (i) to determine the antimicrobial resistance profile and morphotype of the Salmonella serotypes isolated from fresh fruits and (ii) to evaluate the effects of different growth media and environmental conditions on biofilm formation by multidrug-resistant serotypes of Salmonella on polypropylene food contact surfaces
On the basis of the obtained antibiotic resistance profiles, 49.4% of the Salmonella serotypes were multidrug resistant (Table 1)
Summary
Salmonella spp. cause about 1.35 million infections, 26,500 hospitalizations, and 420 deaths annually in the United States; Enteritidis, Newport, Typhimurium, Javiana, 4,5,12:i: and Infantis were the top six Salmonella serotypes that caused foodborne infections in the United States in 2019 [1]. According to the Centers for Disease Control and Prevention, from 2006 to 2019, foodborne outbreaks of the Salmonella serotypes Newport, Infantis, and Typhimurium were linked to the consumption of fresh products with maradol papaya, cucumber, cantaloupe, avocado, tomato, frozen raw tuna, and other products in the United States [2]. The ability of Salmonella serotypes to form biofilms has been demonstrated on stainless steel and polyethylene food contact surfaces or on polystyrene, glass, plastic, cement, and rubber [3,4]. Each year in the United States, there are an estimated USD 400 million of direct medical costs connected to the serotypes Salmonella typhi and Salmonella nontyphoidal [7]
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