Residues of antimicrobial agents have a potential hazard for the consumer and may cause allergic reactions, interference in the intestinal flora and to transfer of multiple antibiotic resistance to human and animal bacterial pathogens, thereby rendering antibiotic treatment ineffective. The control of antibiotic residues is necessary to ensure food safety and prevent exposure of the consumers to drug residues.
Public health risk assessment of fluoroquinolones residues
Detailed sample wise data provided in Table 1 and the highest antibiotic residue in bovine raw milk above the MRL values was noted in 20(25%) samples (n=80) than recommended limits for individual samples collected after treatment with specific antibiotics and cattle pooled, bulk (cattle and buffalo milk) and buffalo milk was noted as residue below maximum residue levels. The MRL recommended by EU and CAC for Fluoroqunilones Antibiotic residues is 100 μg/kg or L. The results of Fluoroquinolones residues analyzed in bovine raw milk in mean, median and interquartile range isreported in Table 1. The detection rate of Fluoroquinolones in milk (n=80) samples was 25% with a calculated mean residues value of 80.44 μg/kg or L. The maximum and minimum content of residues in milk was 4.22 and 329.14 μg/kg or L, respectively.
Zhang and Wang (2009) tested 19 milk samples in China and found 10 samples positive for quinolone residues. Other researchers have reported that quinolone residues in milk were extremely stable
(Fisher et al., 2010; Roca et al., 2010) that might be the reason for high detection rates of quinolone residues in milk.
In the present study, the highest Fluoroquinolones level (667.09 μg/kg or L) was detected, which exceeded the prescribed MRL value. While in another study
(Elizabeta et al., 2011), the MRL value was 149.1 μg/kg or L. These findings where mean residue values were higher than the values obtained in present study might be due to pooling effects of sample of the milk obtained. The higher rates for quinolones were reported in Mexico and China, were a maximum detected value for samples from Mexico was 5047.3 μg/kg or L, which was more than 8 times lower than the present study and 32 times higher than china (20.49 μg /kg or L).
In another study conducted by
Junza et al., (2010) in Spain for detection of quinolones and β-lactams in milk using Liquid chromatography (LC), 3% samples were found to be positive for quinolones out of 49 samples. A very high prevalence of 87.3% of Flouroquinolones was reported by
Navratilova et al., (2011) in bulk samples of raw cow’s milk from Czech Republic. Similarly,
Zhang et al., (2014) analyzed 120 samples in China and found 95.7% samples with detectable levels of quinolone residues. Another study conducted by
Bilandzic et al., (2011) in Croatia, total of 1259 raw milk samples were examined over a three-year period for various antibiotics. The contamination levels were lower than the maximum levels proposed by the European Legislation.
Public health risk assessment of Gentamicin residues
Detailed sample wise data of (n=80) bovine raw milk samples is summarized in Table 2 and the highest antibiotic residue in bovine raw milk above the MRL values was noted in 10 (12.5%) samples after treatment with specific antibiotics (n=20) and cattle pooled, mixing bulk cattle and buffalo and buffalo milk (n=0) was noted as residue below maximum residue levels. The MRL recommended by EU and CAC for Gentamicin antibiotic residues is 200 μg/kg or L. 70 milk samples did not exceed the MRLs of 200 μg/kg or L.
The analyzed samples resulted positive for Gentamicin in bovine raw milk with mean, median and interquartile range is reported in Table 2. The detection rate of Gentamicin in milk (n=10) samples was 12.5% with a calculated mean residues value of 47.92 μg/kg or L, respectively.
Gentamicin is potentially ototoxic and nephrotoxic and is known to cause immune deficiencies leading to drug resistant bacteria in animals and humans. Therefore, its residues in animal originated foods are of public concern
(Tan et al., 2009). Several studies were conducted to detect Gentamicin were
Fathalrhman et al., (2016) reported Gentamicin residues in 25% raw milk samples. In another study
Bilandzic et al., (2011) analyzed 119 samples collected from five counties for the detection of Gentamicin residues in raw milk and estimated mean value of Gentamicin residues to be 1.10 μg/kg or L, whereas in the present study, calculated mean value of residue was 47.92 μg/kg or L indicating higher contamination of Gentamicin.
In another study conducted by
Zeina et al., (2013) mean residual level of Gentamicin was 90 and 80 μg/kg or L, which was below the allowable maximum residue limit of 200 μg/kg or L as set by the FAO/WHO. Whereas in the present study, estimated mean value of Gentamicin residue below then the above study.
Gradinaru et al., (2011) studied antibiotic residues in milk samples collected from farms in the NE Romania (Moldavia). Out of 2785 total milk samples Gentamicin identified in 25% of samples, with average concentration of 198.68 μg/kg or L. In recent study,
Chauhan et al., (2019) analyzed 100 samples in Hisar for the detection of aminoglycosides residues in milk and found 10% samples contained average concentration of 65.06 μg/kg or L of Gentamicin which slightly higher than the above study.
A study reported by
Martins et al., (2016) in which total 180 milk samples of mammary quarter evaluated before and after mastitis treatment with Gentamicin and found 1440 milk samples (24.95%) contaminated to Gentamicin residues after the withdrawal period which higher than the values obtained in present study.
Public health risk assessment of Tetracycline residues
The (n=80) bovine raw milk samples from different dairy farms were collected and were quantified by c–ELISA. Detailed sample wise data presented in Table 3 indicated that overall exceeded Tetracycline antibiotic residues were observed in 79 (98.75%) samples than prescribed MRLs of 100 µg/kg or L, according to the regulations set by EU and CAC. The highest prescribed maximum residue levels were noted in cattle pooled (n=20), mix bulk of cattle and buffalo (n=20) and individual animal samples after treatment with tetracycline (n=20) following decreasing in buffalo pooled milk (n=19). Only one milk sample did not exceed the MRLs of 100 μg/kg or L.
The analyzed results of samples positive for Tetracycline with, mean, median and interquartile range is reported in Table 3. The detection rate of Tetracycline in milk (n=79) samples was 98.75% with a calculated mean residues value of 667.09 μg/kg or L.
Several studies were conducted to detect Tetracycline antibiotics in milk samples round the world.
Moghaddam et al., (2014), Noori et al., (2013) and
Aalipour et al., (2015), reported contamination rate of milk samples with Tetracyclines 33.39%, 17.5% and 34.75%, respectively.
Orwa et al., (2017) and
Gaurav et al., (2014) found highest contamination rate of milk samples with Tetracyclines residues to be 31.4% and 13.5%, respectively. Another study was conducted in Czech Republic indicated Tetracyclines in 50.6% of the samples with concentrations under the MRL value
(Navratilova et al., 2011). In the present study, Tetracycline level detected has exceeded the MRL value and it was 667.09 μg/kg or L. However
Elizabeta et al., 2011, reported the MRL value as 149.1 μg/kg or L. Which was lower than the values obtained in present study.
Monitoring of locally produced and imported milk and dairy products collected in different seasonal periods from farms and retail outlets in Kuwait indicated that 29.1% of the fresh milk samples were above the MRL
(Alomirah et al., 2007). The study conducted in Croatia
(Bilandzic et al., 2011), the highest tetracycline level detected was 49.5 μg/kg or L. However, the mean Tetracycline concentration (2.83 μg/kg or L) was more than 35 times lower than the MRL level.
A study conducted by
Zhang et al., 2014, with (n=94) samples of ultra-high temperature (UHT) milk and (n=26) samples of pasteurized in China, using the ELISA method were assessed for contamination with Tetracyclines. It was found that the percentage of UHT milk samples and pasteurized milk samples containing detectable levels of Tetracyclines were 0 and 7.7% respectively.
Due to the presence of reducing factors such as beta-lactams and milk microflora, antibiotics were decomposed during milk storage and in a high microbial population. Decomposition in processed milk is higher at room temperature and ready for spoilage samples
(Ahlberg et al., 2016). Therefore, due to high storage time and possibly high microbial populations, particularly in local raw milk samples, one or more antibiotic groups may have been decomposed and might not have detected in the milk samples in this study.