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Phenotypic and Genotypic Characterization of S. aureus Isolated from Non-vegetarian and Vegetarian Ready-to-Eat Foods in Northern India

K
K. Seth1
P
Parul1,*
U
U. Jain1
B
B. Sharma2
R
R.P. Mishra2
V
V. Jeet1
R
R.P. Prajapati1
M
M. Goswami3
1Department of Veterinary Public Health, Uttar Pradesh Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam Go Anusandhan Sansthan, Mathura-281 001, Uttar Pradesh, India.
2Department of Veterinary Epidemiology, Uttar Pradesh Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam Go Anusandhan Sansthan, Mathura-281 001, Uttar Pradesh, India.
3Department of Livestock Product Technology, Uttar Pradesh Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam Go Anusandhan Sansthan, Mathura 281 001, Uttar Pradesh, India.

ABSTRACT

Background: Ready-to-eat foods are widely consumed due to their convenience; however, improper handling and unhygienic practices may predispose these foods to contamination by food-borne pathogens. The study investigated the prevalence, biofilm-forming ability, antimicrobial resistance and molecular characterization of S. aureus isolated from RTE foods and serving environment samples collected from Mathura and Delhi, India.

Method: A total of 264 samples comprising RTE vegetarian foods (n = 144), RTE non-vegetarian foods (n = 72) and serving environment samples including hand swabs and utensils (n = 48) were analyzed. Isolation and identification of S. aureus were performed using conventional bacteriological methods and confirmed by detection of the nuc gene. Biofilm production was evaluated using Congo Red Agar, tube method and tissue culture plate assay. Antimicrobial susceptibility testing was carried out against twelve antibiotics and minimum inhibitory concentrations (MICs) were determined for selected strong biofilm-forming isolates using E-test strips.

Result: Overall, S. aureus was detected in 20.45% of samples, with higher prevalence in RTE vegetarian foods (25.0%) compared to RTE non-vegetarian foods (15.27%) and serving environment samples (14.58%). All confirmed isolates harbored the nuc gene. The TCP assay revealed the highest proportion of biofilm-forming isolates (77.7%). High resistance was observed against penicillin, methicillin and oxacillin, while all isolates remained sensitive to vancomycin. Multidrug resistance was observed in 57.14% of biofilm-forming isolates. Phylogenetic analysis suggested possible cross-contamination between food handlers and RTE foods.

INTRODUCTION

India’s ready-to-eat (RTE) food industry has seen a tremendous surge in the recent years, driven by customary food habits, dynamic customer behaviour with growing demand for convenience (Zwe et al., 2025). These are ready for instant consumption very well adhering to the general norms of food safety and hygiene (Moges et al., 2024). The RTE food industry faces significant microbial contamination. The ability of S. aureus to form biofilm in vivo which greatly affects it’s pathogenicity is another important virulence factor and the biofilm producer bacteria exhibit high resistance to disinfectants, antibiotics and enhance their resistance to the antibiotics by gene transfer in food processing environments (Islam et al., 2019; Singh et al., 2026).
       
Whether through food handlers or improper sanitation of preparation surfaces, the serving environment remains a critical point in the food safety chain (Chen et al., 2022; Prajapati et al., 2025). Therefore, it becomes all the more imperative to ensure proper food safety and cleanliness protocols in the food service premises. This study investigates both phenotypic and genotypic characteristics, resistance profiles and biofilm-forming abilities of S. aureus isolated from RTE foods and associated environments.

MATERIALS AND METHODS

Sample collection and processing
 
A total of 264 samples were collected (RTE food items, hand swabs and utensils) from various food outlets across Mathura and Delhi during April,2025 to October 2025. This included 216 RTE items like samosa (36), paneer pakora (36), french fries (36), cake/pastry (36), fried chicken (24), chicken pakora (24), fried fish (24) with the food handler and utensil samples (48). Firstly, (10 g) each of food sample type were dissected and stored in small sterile zip lock pouches. All the collected samples were labeled, kept on ice, brought to the laboratory in chilled condition and processed within 24 hours of collection for isolation and identification of S. aureus using standard microbiological methods as per Xing et al., (2014) for RTE foods and Ballah et al., (2022) for hand swabs and utensil swabs.
 
Phenotypic detection of S. aureus
 
All the food samples (10 g each) were inoculated in the Buffered Peptone Water (BPW) (90 ml) and incubated overnight at 37°C for 24 hrs as per Xing et al., (2014). The loopful culture growth from TSB was streaked on Baird Parker Agar and incubated at 37°C for 24 hrs (Fig 1).               

Fig 1: Jet black colored colonies of Staphylococcus spp. on Baired-Parker Agar.

   

Staphylococcus spp. produced peculiar jetblack colored colonies and further single jet-black color colony was streaked on Mannitol salt agar (MSA) and incubated at 37°C for 24 hrs and produced golden yellow colonies surrounded by yellow zone (Fig 2).  All the S. aureus isolates were biochemically confirmed as per method described by Barrow and Feltham (1993).

Fig 2: Yellow colored colonies of Staphylococcus spp. on mannitol salt agar.


 
Molecular detection of S. aureus isolates
 
Biochemically confirmed isolates were further confirmed for S. aureus by using species-specific primer targeting nuc gene by using simplex-PCR as per the method given by Brakstad et al., (1992). The chromosomal DNA of studied organisms was obtained by using protocol given in kit (Machery Nagel). Primer details are shown in Table 1.

Table 1: Primers for nuc gene of S. aureus.


 
Phenotypic biofilm production
 
Phenotypically and genotypically confirmed isolates of S. aureus were subjected to the biofilm forming capacity in vitro by the following CRA, TP and TCP methods as given by Mathur et al., (2006). In Congo Red Agar method, black colonies with a dry crystalline consistency were biofilm producers, whereas pink colonies were non-biofilm producers. In Tube method, a visible film lined in the wall and bottom of the tube were considered positive for biofilm formation. Tubes were examined based on presence of visible film either on wall or bottom or at both the sites and the amount of biofilm formation was scored as weak, moderate (biofilm either on bottom or wall of tube) or strong (biofilm at bottom and wall of test tube).
       
In the TCP assays, the OD values were considered as an index of bacteria adhering to the surface and forming biofilms with the OD value less than 0.120 being considered as none adherence and weak biofilm former while mean OD values 0.120-0.24 showed moderate adherence and moderate biofilm former while OD≤0.240 showed strong adherence and categorized at strong biofilm former.
 
Antimicrobial resistance profile
 
Antibiotic sensitivity test (ABST)
 
Antimicrobial susceptibility of bacterial isolates was determined by Disc Diffusion method given by Bauer et al. (1966) and interpreted as per Clinical and Laboratory Standards Institute (CLSI, 2018).
 
Minimum inhibitory concentration by E-Test (Epsilometer Test)
 
Minimum inhibitory concentrations (MICs) are defined as the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation, which were determined as per the method given by Sharma et al., (2017).

RESULTS AND DISCUSSION

Out of the 264 samples, fifty-four S. aureus were isolated and all the phenotypically detected S. aureus were nuc gene bearers, with percentage positivity for this gene as 100.0% (Fig 3). The prevalence of S. aureus was 25.0%, 15.27% and 14.58% in RTE vegetarian, non-vegetarian foods and serving environment, respectively, with overall prevalence of 20.45% as shown in Table 2.

Fig 3: Species specific PCR amplicon (nuc) of S. aureus resolved after electrophoresis in 1.5 % agarose gel.



Table 2: Overall prevalence of S.aureus isolates in ready-to-eat vegetarian, non-vegetarian and environmental sources.


       
Within the RTE vegetarian foods, prevalence of S. aureus in samosa was 27.7%, similar and consistent to 17.0%, reported by Siddabathuni et al., (2019) from India. Higher prevalence had been reported as 46.67% by Khaledian et al., (2020) from Iran. Lower prevalence values had been reported by Urmi et al., (2021) at 6.67% .Paneer pakora samples showed S. aureus prevalence of 13.8%, similar to 12.5%  by Sabuj et al., (2018) from Bangladesh. While lower prevalence value reported by Tambekar et al., (2008) was 7.0%. French fries revealed S. aureus prevalence of 27.7 %, akin to 21.67% by Ballah et al., (2022). Higher prevalence value has been reported as 40.0% by Singh et al., (2025) from India. Cake/pastry samples showed S. aureus  prevalence of 30.5%, similar to 31.6%, reported by Oh et al., (2007) from Korea. The overall prevalence of S. aureus  in  RTE vegetarian foods was 25.0%, similar to 25.1%, reported by Yang et al., (2016) from China. The maximum prevalence of S. aureus was recorded in cake/pastry, followed by samosa and french fries, while panner pakora showed lowest prevalence. The reason behind the variation lies in the poor sanitation and food handling practices along with the post-frying contamination (for the fried items).
       
In RTE non-vegetarian foods, fried chicken samples showed a prevalence of 20.83%, similar  to 26.7% reported by Ghanem et al., (2025). Lower value to this was 6.42% by Madahi et al., (2014) from Iran. The higher prevalence reported was 38.82% by Thakur et al., (2023) in India. Chicken pakora samples revealed a lower prevalence (8.33%), similar to 6.8% reported by Mesbah et al., (2021) from Iran. Fried fish samples showed a prevalence of 16.6%, aligning with Sivaraman et al., (2022) from India at 17.74%. The overall prevalence of S. aureus in RTE non-vegetarian foods was 15.27%, quite similar to 13.6%, reported by Zwe et al., (2025) from Singapore. Higher prevalence of 40% was recorded by Thakur et al., (2023) from India. The variations across studies may be attributed to differences in cooking temperature, duration and post-cooking handling.
       
Within serving environment samples, hand swabs revealed a prevalence of 12.5%. The higher value with to this was 30.0% found by Saber et al., (2022) from Egypt. The utensil samples harbouring S. aureus contamination  showed a prevalence of 16.6%, which is absolutely the same as reported by Tasanapak et al., (2023) from Thailand. Higher prevalence value 50.62% was reported by Shahid et al., (2021) from Bangladesh.
       
The overall prevalence of S. aureus from RTE foods and serving environment was 20.45% , very similar and consistent with 21.67% from Ballah et al., (2022) in Bangladesh. In comparison to these results a higher prevalence of 58% was found within the findings of an Indian study reported by Kaur and Kahlon (2017), while the lowest prevalence found to be 15.42% in RTE foods of Iran in a study by Mesbah et al., (2021).
       
After careful assessment of the prevalence results of vegetarian and non- vegetarian food categories, noteworthy observations were made. S. aureus prevalence in RTE vegetarian foods (25.0%) was higher than that found in RTE non-vegetarian foods (15.27%). The underlying reason attributable to this variation lies in the customer behaviour and food culture dynamics (that varies from one place to the other). Moreover, the food service establishments catering non-vegetarian foods take utmost precautions in handling and processing of these non- vegetarian attributes to cater to a larger audience, preferred for invaluable taste and unique delicacy as a rich source of protein. The vegetarian items are generally more perishable by nature, due to poor handling practices and inadequate sanitation.
       
In the study, by CRA, total biofilm formers were 16.6%, similar to the findings of Ballah et al., (2022) from Bangladesh at 20%. Within Chicken products , the biofilm formers using CRA were 28.5%, which is dissimilar and inconsistent with the findings of the study by Thakur et al., (2024)  60.0%. In cake/pastry, biofilm formers were 9.09%. In food contact surfaces also, the biofilm formers using CRA were only 25.0%. Using this method, 29.6% isolates were characterized as strong which is consistent with 20.0% as studied by Ballah et al., (2022). Similarly, 48.1% isolates were regarded as moderate biofilm formers which is lower to and inconsistent with the findings of Ballah et al., (2022) 77.0% from Bangladesh. Moreover 22.2% isolates were regarded as weak biofilm formers, having dissimilarity and inconsistency with findings that are lower as in 3.0% as in Ballah et al., (2022).
       
More number of biofilm formers were found in RTE vegetarian foods (66.6%) as compared to that in RTE non-vegetarian foods (19.04%) , while the lowest number of biofilm formers were found in serving environment (14.28%). The reasons attributable to more biofilm formers in RTE vegetarian foods lies with the inadequate food handling practices (Fig 4 and Table 3).

Fig 4: Comparison of biofilm assays.



Table 3: Overall prevalence of biofilm Forming S. aureus isolates in ready-to-eat vegetarian, non-vegetarian foods and environmental sources.


 
Antibiotic sensitivity test (ABST)
 
The total biofilm formers (77.7%) were further subjected to ABST against 12 antibiotics as shown in Table 4. Penicillin recorded a high resistance of 81.0%. similar to that of  Mesbah et al., (2021) at 85.93% from Iran. Even higher resistance, reaching 93%, was reported by Esemu et al., (2023) in Cameroon. Resistance to ampicillin was also high at 66.7%. Extremely higher resistance value of  100.0% was observed by Sabuj et al., (2018) from Bangladesh. Lower resistance levels, around 31.0%, were found by Kaur and Kahlon (2017) from Mewar and Verma et al., (2023). The resistance to tetracycline was 40.5%. similar to 44.82% by Kaur and Kahlon (2017). Higher resistance to this value was recorded as 85.93% by Mesbah et al., (2021), while lower resistance at 40.6% was reported by Xing et al., (2014). For oxacillin, a resistance of 69.0% was observed, which is more than 5.56%  as reported by Esemu et al., (2023). Resistance to methicillin was 71.40%, lower values were reported as 12.2% by Shahid et al. (2021) and 23.4% by Saber et al., (2022) from Egypt.

Table 4: Antibiogram of biofilm forming S. aureus isolates from RTE vegetarian, non-vegetarian foods and serving environmental sources.


       
No resistance to vancomycin was detected, consistent with Esemu et al., (2023) from Cameroon. However, Puah et al., (2018) from Malaysia, showed a slightly higher resistance of 5.8% in his study. Chloramphenicol showed low resistance of 11.9%, similar to 10.5%, reported by Moges et al., (2024). Higher resistance to this finding was 20.83%, found by Esemu et al., (2023), while absolutely 0.0% resistance was reported by Urmi et al., (2021), from Bangladesh. Absolutely 0.0% resistance was found by Esemu et al., (2023). Resistance to gentamicin was 11.9%, consistent with 25.0%, reported by Urmi et al., (2021). Higher resistance to this value at 30.56% was observed by Esemu et al., (2023), while absolutely 0.0% was reported by Khaledian et al., (2020) from Iran. For cefotaxime, the resistance was 21.4%, which is very similar to the findings reported as 25.0% by Urmi et al., (2021) from Bangladesh. Higher resistance at 60.0% was reported by Siddabathuni et al., (2019), lower resistance value of  2.0% was reported by Zwe et al., (2025). Resistance to erythromycin was 35.7%, similar with 35.5%, as revealed by Alelign et al., (2023) from Ethiopia. Resistance of 100.0% was reported by Urmi et al., (2021).Resistance to ciprofloxacin was 11.9%, similar to 10.8%, by Moges et al., (2024). However, higher resistance at 44.82%, was recorded by Kaur and Kahlon (2017), whereas absolutely 0.0% was found by Urmi et al., (2021). Multi-drug resistant S. aureus revealed as 57.14%,were similar and consistent with the findings reported as 62% by Kaur and Kahlon (2017) from India. On the other side, lower value of 38.9% MDR S. aureus was identified by Li et al. (2019) from China.
       
Sixteen strong biofilm formers were subjected to E-Test for MIC determination against eight antibiotics. MIC for tetracycline (0.12-1.0 µg/ml), oxacillin (0.12-0.5 µg/ml), vancomycin (0.12-2.0 µg/ml), ofloxacin (0.12-1.0 µg/ml), gentamicin (0.12-1.0 µg/ml) were recorded. The highest MIC value was recorded with Chloramphenicol in the range (2-16 µg/ml). MIC for erythromycin was in the range (0.2-1.0 µg/ml) , which is lower than 16 µg/ml as per an Indian study by Kaur and Kahlon (2017) and also lower than 2 µg/ml as per study by Camellini et al., (2021). Ciprofloxacin showed the lowest MIC range (0.12-0.5 µg/ml), but somewhat similar to the range (0.25-1 mcg/ml) as per Camellini et al., (2021) from Italy.

CONCLUSION

S. aureus isolates from RTE foods display high resistance to beta-lactam antibiotics, moderate resistance to tetracyclines, macrolides and cephalosporins and low resistance to vancomycin and fluoroquinolones, underscoring the potential public health risks associated with contaminated RTE foods. The findings emphasize the need for strict implementation of good hygienic practices (GHP) along with the hygienic preparation of food, regular monitoring of food handlers and sanitation of food contact surfaces to minimize the risk of foodborne staphylococcal infections.

CONFLICT OF INTEREST

The authors declares no conflict of interest.

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    Full Research Article

    Phenotypic and Genotypic Characterization of S. aureus Isolated from Non-vegetarian and Vegetarian Ready-to-Eat Foods in Northern India

    K
    K. Seth1
    P
    Parul1,*
    U
    U. Jain1
    B
    B. Sharma2
    R
    R.P. Mishra2
    V
    V. Jeet1
    R
    R.P. Prajapati1
    M
    M. Goswami3
    1Department of Veterinary Public Health, Uttar Pradesh Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam Go Anusandhan Sansthan, Mathura-281 001, Uttar Pradesh, India.
    2Department of Veterinary Epidemiology, Uttar Pradesh Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam Go Anusandhan Sansthan, Mathura-281 001, Uttar Pradesh, India.
    3Department of Livestock Product Technology, Uttar Pradesh Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam Go Anusandhan Sansthan, Mathura 281 001, Uttar Pradesh, India.

    ABSTRACT

    Background: Ready-to-eat foods are widely consumed due to their convenience; however, improper handling and unhygienic practices may predispose these foods to contamination by food-borne pathogens. The study investigated the prevalence, biofilm-forming ability, antimicrobial resistance and molecular characterization of S. aureus isolated from RTE foods and serving environment samples collected from Mathura and Delhi, India.

    Method: A total of 264 samples comprising RTE vegetarian foods (n = 144), RTE non-vegetarian foods (n = 72) and serving environment samples including hand swabs and utensils (n = 48) were analyzed. Isolation and identification of S. aureus were performed using conventional bacteriological methods and confirmed by detection of the nuc gene. Biofilm production was evaluated using Congo Red Agar, tube method and tissue culture plate assay. Antimicrobial susceptibility testing was carried out against twelve antibiotics and minimum inhibitory concentrations (MICs) were determined for selected strong biofilm-forming isolates using E-test strips.

    Result: Overall, S. aureus was detected in 20.45% of samples, with higher prevalence in RTE vegetarian foods (25.0%) compared to RTE non-vegetarian foods (15.27%) and serving environment samples (14.58%). All confirmed isolates harbored the nuc gene. The TCP assay revealed the highest proportion of biofilm-forming isolates (77.7%). High resistance was observed against penicillin, methicillin and oxacillin, while all isolates remained sensitive to vancomycin. Multidrug resistance was observed in 57.14% of biofilm-forming isolates. Phylogenetic analysis suggested possible cross-contamination between food handlers and RTE foods.

    INTRODUCTION

    India’s ready-to-eat (RTE) food industry has seen a tremendous surge in the recent years, driven by customary food habits, dynamic customer behaviour with growing demand for convenience (Zwe et al., 2025). These are ready for instant consumption very well adhering to the general norms of food safety and hygiene (Moges et al., 2024). The RTE food industry faces significant microbial contamination. The ability of S. aureus to form biofilm in vivo which greatly affects it’s pathogenicity is another important virulence factor and the biofilm producer bacteria exhibit high resistance to disinfectants, antibiotics and enhance their resistance to the antibiotics by gene transfer in food processing environments (Islam et al., 2019; Singh et al., 2026).
           
    Whether through food handlers or improper sanitation of preparation surfaces, the serving environment remains a critical point in the food safety chain (Chen et al., 2022; Prajapati et al., 2025). Therefore, it becomes all the more imperative to ensure proper food safety and cleanliness protocols in the food service premises. This study investigates both phenotypic and genotypic characteristics, resistance profiles and biofilm-forming abilities of S. aureus isolated from RTE foods and associated environments.

    MATERIALS AND METHODS

    Sample collection and processing
     
    A total of 264 samples were collected (RTE food items, hand swabs and utensils) from various food outlets across Mathura and Delhi during April,2025 to October 2025. This included 216 RTE items like samosa (36), paneer pakora (36), french fries (36), cake/pastry (36), fried chicken (24), chicken pakora (24), fried fish (24) with the food handler and utensil samples (48). Firstly, (10 g) each of food sample type were dissected and stored in small sterile zip lock pouches. All the collected samples were labeled, kept on ice, brought to the laboratory in chilled condition and processed within 24 hours of collection for isolation and identification of S. aureus using standard microbiological methods as per Xing et al., (2014) for RTE foods and Ballah et al., (2022) for hand swabs and utensil swabs.
     
    Phenotypic detection of S. aureus
     
    All the food samples (10 g each) were inoculated in the Buffered Peptone Water (BPW) (90 ml) and incubated overnight at 37°C for 24 hrs as per Xing et al., (2014). The loopful culture growth from TSB was streaked on Baird Parker Agar and incubated at 37°C for 24 hrs (Fig 1).               

    Fig 1: Jet black colored colonies of Staphylococcus spp. on Baired-Parker Agar.

       

    Staphylococcus spp. produced peculiar jetblack colored colonies and further single jet-black color colony was streaked on Mannitol salt agar (MSA) and incubated at 37°C for 24 hrs and produced golden yellow colonies surrounded by yellow zone (Fig 2).  All the S. aureus isolates were biochemically confirmed as per method described by Barrow and Feltham (1993).

    Fig 2: Yellow colored colonies of Staphylococcus spp. on mannitol salt agar.


     
    Molecular detection of S. aureus isolates
     
    Biochemically confirmed isolates were further confirmed for S. aureus by using species-specific primer targeting nuc gene by using simplex-PCR as per the method given by Brakstad et al., (1992). The chromosomal DNA of studied organisms was obtained by using protocol given in kit (Machery Nagel). Primer details are shown in Table 1.

    Table 1: Primers for nuc gene of S. aureus.


     
    Phenotypic biofilm production
     
    Phenotypically and genotypically confirmed isolates of S. aureus were subjected to the biofilm forming capacity in vitro by the following CRA, TP and TCP methods as given by Mathur et al., (2006). In Congo Red Agar method, black colonies with a dry crystalline consistency were biofilm producers, whereas pink colonies were non-biofilm producers. In Tube method, a visible film lined in the wall and bottom of the tube were considered positive for biofilm formation. Tubes were examined based on presence of visible film either on wall or bottom or at both the sites and the amount of biofilm formation was scored as weak, moderate (biofilm either on bottom or wall of tube) or strong (biofilm at bottom and wall of test tube).
           
    In the TCP assays, the OD values were considered as an index of bacteria adhering to the surface and forming biofilms with the OD value less than 0.120 being considered as none adherence and weak biofilm former while mean OD values 0.120-0.24 showed moderate adherence and moderate biofilm former while OD≤0.240 showed strong adherence and categorized at strong biofilm former.
     
    Antimicrobial resistance profile
     
    Antibiotic sensitivity test (ABST)
     
    Antimicrobial susceptibility of bacterial isolates was determined by Disc Diffusion method given by Bauer et al. (1966) and interpreted as per Clinical and Laboratory Standards Institute (CLSI, 2018).
     
    Minimum inhibitory concentration by E-Test (Epsilometer Test)
     
    Minimum inhibitory concentrations (MICs) are defined as the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation, which were determined as per the method given by Sharma et al., (2017).

    RESULTS AND DISCUSSION

    Out of the 264 samples, fifty-four S. aureus were isolated and all the phenotypically detected S. aureus were nuc gene bearers, with percentage positivity for this gene as 100.0% (Fig 3). The prevalence of S. aureus was 25.0%, 15.27% and 14.58% in RTE vegetarian, non-vegetarian foods and serving environment, respectively, with overall prevalence of 20.45% as shown in Table 2.

    Fig 3: Species specific PCR amplicon (nuc) of S. aureus resolved after electrophoresis in 1.5 % agarose gel.



    Table 2: Overall prevalence of S.aureus isolates in ready-to-eat vegetarian, non-vegetarian and environmental sources.


           
    Within the RTE vegetarian foods, prevalence of S. aureus in samosa was 27.7%, similar and consistent to 17.0%, reported by Siddabathuni et al., (2019) from India. Higher prevalence had been reported as 46.67% by Khaledian et al., (2020) from Iran. Lower prevalence values had been reported by Urmi et al., (2021) at 6.67% .Paneer pakora samples showed S. aureus prevalence of 13.8%, similar to 12.5%  by Sabuj et al., (2018) from Bangladesh. While lower prevalence value reported by Tambekar et al., (2008) was 7.0%. French fries revealed S. aureus prevalence of 27.7 %, akin to 21.67% by Ballah et al., (2022). Higher prevalence value has been reported as 40.0% by Singh et al., (2025) from India. Cake/pastry samples showed S. aureus  prevalence of 30.5%, similar to 31.6%, reported by Oh et al., (2007) from Korea. The overall prevalence of S. aureus  in  RTE vegetarian foods was 25.0%, similar to 25.1%, reported by Yang et al., (2016) from China. The maximum prevalence of S. aureus was recorded in cake/pastry, followed by samosa and french fries, while panner pakora showed lowest prevalence. The reason behind the variation lies in the poor sanitation and food handling practices along with the post-frying contamination (for the fried items).
           
    In RTE non-vegetarian foods, fried chicken samples showed a prevalence of 20.83%, similar  to 26.7% reported by Ghanem et al., (2025). Lower value to this was 6.42% by Madahi et al., (2014) from Iran. The higher prevalence reported was 38.82% by Thakur et al., (2023) in India. Chicken pakora samples revealed a lower prevalence (8.33%), similar to 6.8% reported by Mesbah et al., (2021) from Iran. Fried fish samples showed a prevalence of 16.6%, aligning with Sivaraman et al., (2022) from India at 17.74%. The overall prevalence of S. aureus in RTE non-vegetarian foods was 15.27%, quite similar to 13.6%, reported by Zwe et al., (2025) from Singapore. Higher prevalence of 40% was recorded by Thakur et al., (2023) from India. The variations across studies may be attributed to differences in cooking temperature, duration and post-cooking handling.
           
    Within serving environment samples, hand swabs revealed a prevalence of 12.5%. The higher value with to this was 30.0% found by Saber et al., (2022) from Egypt. The utensil samples harbouring S. aureus contamination  showed a prevalence of 16.6%, which is absolutely the same as reported by Tasanapak et al., (2023) from Thailand. Higher prevalence value 50.62% was reported by Shahid et al., (2021) from Bangladesh.
           
    The overall prevalence of S. aureus from RTE foods and serving environment was 20.45% , very similar and consistent with 21.67% from Ballah et al., (2022) in Bangladesh. In comparison to these results a higher prevalence of 58% was found within the findings of an Indian study reported by Kaur and Kahlon (2017), while the lowest prevalence found to be 15.42% in RTE foods of Iran in a study by Mesbah et al., (2021).
           
    After careful assessment of the prevalence results of vegetarian and non- vegetarian food categories, noteworthy observations were made. S. aureus prevalence in RTE vegetarian foods (25.0%) was higher than that found in RTE non-vegetarian foods (15.27%). The underlying reason attributable to this variation lies in the customer behaviour and food culture dynamics (that varies from one place to the other). Moreover, the food service establishments catering non-vegetarian foods take utmost precautions in handling and processing of these non- vegetarian attributes to cater to a larger audience, preferred for invaluable taste and unique delicacy as a rich source of protein. The vegetarian items are generally more perishable by nature, due to poor handling practices and inadequate sanitation.
           
    In the study, by CRA, total biofilm formers were 16.6%, similar to the findings of Ballah et al., (2022) from Bangladesh at 20%. Within Chicken products , the biofilm formers using CRA were 28.5%, which is dissimilar and inconsistent with the findings of the study by Thakur et al., (2024)  60.0%. In cake/pastry, biofilm formers were 9.09%. In food contact surfaces also, the biofilm formers using CRA were only 25.0%. Using this method, 29.6% isolates were characterized as strong which is consistent with 20.0% as studied by Ballah et al., (2022). Similarly, 48.1% isolates were regarded as moderate biofilm formers which is lower to and inconsistent with the findings of Ballah et al., (2022) 77.0% from Bangladesh. Moreover 22.2% isolates were regarded as weak biofilm formers, having dissimilarity and inconsistency with findings that are lower as in 3.0% as in Ballah et al., (2022).
           
    More number of biofilm formers were found in RTE vegetarian foods (66.6%) as compared to that in RTE non-vegetarian foods (19.04%) , while the lowest number of biofilm formers were found in serving environment (14.28%). The reasons attributable to more biofilm formers in RTE vegetarian foods lies with the inadequate food handling practices (Fig 4 and Table 3).

    Fig 4: Comparison of biofilm assays.



    Table 3: Overall prevalence of biofilm Forming S. aureus isolates in ready-to-eat vegetarian, non-vegetarian foods and environmental sources.


     
    Antibiotic sensitivity test (ABST)
     
    The total biofilm formers (77.7%) were further subjected to ABST against 12 antibiotics as shown in Table 4. Penicillin recorded a high resistance of 81.0%. similar to that of  Mesbah et al., (2021) at 85.93% from Iran. Even higher resistance, reaching 93%, was reported by Esemu et al., (2023) in Cameroon. Resistance to ampicillin was also high at 66.7%. Extremely higher resistance value of  100.0% was observed by Sabuj et al., (2018) from Bangladesh. Lower resistance levels, around 31.0%, were found by Kaur and Kahlon (2017) from Mewar and Verma et al., (2023). The resistance to tetracycline was 40.5%. similar to 44.82% by Kaur and Kahlon (2017). Higher resistance to this value was recorded as 85.93% by Mesbah et al., (2021), while lower resistance at 40.6% was reported by Xing et al., (2014). For oxacillin, a resistance of 69.0% was observed, which is more than 5.56%  as reported by Esemu et al., (2023). Resistance to methicillin was 71.40%, lower values were reported as 12.2% by Shahid et al. (2021) and 23.4% by Saber et al., (2022) from Egypt.

    Table 4: Antibiogram of biofilm forming S. aureus isolates from RTE vegetarian, non-vegetarian foods and serving environmental sources.


           
    No resistance to vancomycin was detected, consistent with Esemu et al., (2023) from Cameroon. However, Puah et al., (2018) from Malaysia, showed a slightly higher resistance of 5.8% in his study. Chloramphenicol showed low resistance of 11.9%, similar to 10.5%, reported by Moges et al., (2024). Higher resistance to this finding was 20.83%, found by Esemu et al., (2023), while absolutely 0.0% resistance was reported by Urmi et al., (2021), from Bangladesh. Absolutely 0.0% resistance was found by Esemu et al., (2023). Resistance to gentamicin was 11.9%, consistent with 25.0%, reported by Urmi et al., (2021). Higher resistance to this value at 30.56% was observed by Esemu et al., (2023), while absolutely 0.0% was reported by Khaledian et al., (2020) from Iran. For cefotaxime, the resistance was 21.4%, which is very similar to the findings reported as 25.0% by Urmi et al., (2021) from Bangladesh. Higher resistance at 60.0% was reported by Siddabathuni et al., (2019), lower resistance value of  2.0% was reported by Zwe et al., (2025). Resistance to erythromycin was 35.7%, similar with 35.5%, as revealed by Alelign et al., (2023) from Ethiopia. Resistance of 100.0% was reported by Urmi et al., (2021).Resistance to ciprofloxacin was 11.9%, similar to 10.8%, by Moges et al., (2024). However, higher resistance at 44.82%, was recorded by Kaur and Kahlon (2017), whereas absolutely 0.0% was found by Urmi et al., (2021). Multi-drug resistant S. aureus revealed as 57.14%,were similar and consistent with the findings reported as 62% by Kaur and Kahlon (2017) from India. On the other side, lower value of 38.9% MDR S. aureus was identified by Li et al. (2019) from China.
           
    Sixteen strong biofilm formers were subjected to E-Test for MIC determination against eight antibiotics. MIC for tetracycline (0.12-1.0 µg/ml), oxacillin (0.12-0.5 µg/ml), vancomycin (0.12-2.0 µg/ml), ofloxacin (0.12-1.0 µg/ml), gentamicin (0.12-1.0 µg/ml) were recorded. The highest MIC value was recorded with Chloramphenicol in the range (2-16 µg/ml). MIC for erythromycin was in the range (0.2-1.0 µg/ml) , which is lower than 16 µg/ml as per an Indian study by Kaur and Kahlon (2017) and also lower than 2 µg/ml as per study by Camellini et al., (2021). Ciprofloxacin showed the lowest MIC range (0.12-0.5 µg/ml), but somewhat similar to the range (0.25-1 mcg/ml) as per Camellini et al., (2021) from Italy.

    CONCLUSION

    S. aureus isolates from RTE foods display high resistance to beta-lactam antibiotics, moderate resistance to tetracyclines, macrolides and cephalosporins and low resistance to vancomycin and fluoroquinolones, underscoring the potential public health risks associated with contaminated RTE foods. The findings emphasize the need for strict implementation of good hygienic practices (GHP) along with the hygienic preparation of food, regular monitoring of food handlers and sanitation of food contact surfaces to minimize the risk of foodborne staphylococcal infections.

    CONFLICT OF INTEREST

    The authors declares no conflict of interest.

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