Safety Threat
5.4. Discussion
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Penicillin.Cefoxitin.Oxacillin.Ciprofloxacin.Gentamicin.Tetracycline.Trimethoprim-
Sulfamethoxazole were the most relevant profiles observed in S. haemolyticus in hand and nasal samples, respectively, in Cameroon. Similarly, the most relevant resistance patterns detected in S. haemolyticus in South Africa were Penicillin.Cefoxitin.Ciprofloxacin.
Erythromycin.Tetracycline.Trimethoprim-Sulfamethoxazole.Teicoplanin.Fusidic acid, Penicillin.Cefoxitin.Erythromycin.Tetracycline.Trimethoprim-Sulfamethoxazole and Penicillin.Cefoxitin.Oxacillin.Gentamicin.Tetracycline.Trimethoprim-
Sulfamethoxazole.Fusidic acid,
Penicillin.Cefoxitin.Oxacillin.Gentamicin.Ciprofloxacin.Erythromycin.Trimethoprim- Sulfamethoxazole in hand and nasal samples, respectively (Table 5.7).
5.3.8. Genotypic relatedness
All S. aureus and the most resistant S. lentus strains as the most prevalent CoPS and CoNS respectively, were genotyped by REP-PCR to determine their clonal relationships. REP-PCR allowed the differentiation of S. aureus strains into one major cluster and S. lentus into four clusters (Figure 5.2). One batch of S. aureus isolates (PN235B0, PN246B0, PN243B0 and PR243B0) detected in one South African abattoir (SH004) were closely related and share common ancestors as did a batch of S. lentus strains (PN085, PR226B0, and PR108) detected in pigs in two Cameroonian (SH002 and SH003) and one South African (SH004) abattoirs (Figure 5.2).
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humans was highly statistically significant in hand [72% (60/84), p=0.000] and nasal samples [73% (56/77), p=0.000]. The prevalence reported in our study is consistent with a study from Switzerland where 49.3% of MRCoNS were detected among exposed workers (Huber et al., 2011). Our results are however, higher than that reported by Gulani et al. (2016) where a 13.5%
prevalence of MRSA was detected in animal handlers in Nigeria. The prevalence of MRS carriage was significantly higher in Cameroonian workers than South African ones for both nasal (92.45% vs 29.17; p=0.000) and hand (100% vs 23.3%; p=0.000) samples. These discrepancies between both countries could be because that abattoir regulations, implementation of Hazard Analysis Critical Control Points (HACCP) plans and compliance with international food safety standard ISO 22000 are stringent in South Africa whereas Cameroonian slaughterhouses/markets were characterized by precarious hygienic conditions with minimal or non-existent biosecurity measures and absence of regulations. This has been confirmed by Ndebi et al. (2009) who already reported that the pig production industry in Cameroon is undermined by a mosaic of problems such as insufficient funds, poor sanitary and feeding requirements, sub-optimal transport conditions, lack of veterinarian control that leads to the emergence and spread of ABR in the farm-to-plate continuum. Our results therefore suggest that the implementation of effective food safety measures contributes to the containment of ABR dissemination.
The presence of MRS in nasal samples was highly statistically associated with hand colonization (31.58% vs 86.21%, p=0.000, OR=13.54; 95% CI 3.99-45.95; p=0.015). These findings reveal poor implementation of hygienic and sanitary conditions and suggest that these limited measures along with high prevalence of colonized food handlers represent an important food safety threat in both countries. It further suggests that food handlers represent a significant source of ABR dissemination for their relatives through person-to-person contact and for the general population through the contamination of food products occurring during food processing.
5.4.2. MRS in animals
The 75% and 70% positivity of all pooled nasal and rectal samples for MRS respectively, are higher than that reported from Nigeria where 31% and 52% of MRS were detected in pigs and pork, respectively (Ugwu et al., 2015; Igbinosa et al., 2016). They are however lower than that reported by Bhargava and Zhang (2012) where 100% of MRS were observed in nasal and rectal swabs of various food animals including pigs, sold during a livestock auction in Ohio. The high
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prevalence reported in our study could be associated with extensive use of antimicrobials in the food production industry.
When comparing the results at country-level, animals sampled in Cameroon were statistically significantly more colonized than those collected in South Africa with a maximum prevalence of MRS (100%) for both type of samples versus 50% and 81% MRS in nasal and rectal pooled samples, respectively, in South Africa (p=0.000). The elevated prevalence of MRS carriage detected in both type of pooled samples in South Africa and Cameroon is not surprising, as the use of antibiotics as growth promoters is legally approved in the former (Department of Agriculture, Forestry and Fisheries, 1996) and, policies promoting rational drug use are non- existent in both animals and humans in the latter. Ndebi et al. (2009) already revealed that antibiotics of human medicine are frequently use for the prevention and treatment of infectious diseases in pig husbandry in Cameroon, that the current state of knowledge of antibiotic use and antibiotic resistance (ABR) in humans, (food) animals, and environment is minimal or non- existent and that the debate about ABR-related consequences is neglected in the country.
Our results further indicate that MRS are widespread in food animals and abattoirs in both countries, can spread actively in the farm-to-plate continuum and pose a serious food safety threat for these nations. The rectal colonization reported in our study could be attributed to widespread antibiotic use on farms either for therapeutic, prophylactic or growth promotion purposes whereas the nasal MRS carriage is likely associated with environmental contamination.
5.4.3. MRS based on time points
The overall high MRS prevalence observed across time points in both countries suggests that measures implemented in both countries are suub-optimal for the effective eradication and containment of MRS. This has been confirmed by the maximum MRS prevalence recorded during the first (91%) and second (90%) time point for rectal sample in SH005 whereas 92%
and 86% of MRS was detected in SH004 at second and thrid time points for the same sample type in South Africa (Figure 1). Similarly, the high nasal MRS prevalence observed in both countries evidences the persistance of MRS not only in living food animals but also on environmental surfaces that leads to their dissemination across the animal-human- environmental interface. It further reveals that decontamination measures implemented in abattoirs should be updated and consider novel concepts that address environmental persistence of MRS.
5.4.4. Antimicrobial resistance patterns
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The analyses of resistance profiles revealed more than 80% resistance to β-lactams including penicillin, cefoxitin and oxacillin in both countries and for both populations. The phenotype P.FOX.OX.E.CLI.TET showing resistance to six antibiotics was the most common in MRSA strains isolated from rectal and nasal pooled samples in South Africa. One S. lentus strain isolated from rectal pooled sample in Cameroon displayed the profile P.FOX.OX.E.CLI.LIN.TEI.VAN.FA.RIF with resistance to ten antibiotics including the following last resort antibiotics; teicoplanin, vancomycin and linezolid. This confirms MRS as significant food contaminants, reservoir of and potential vectors for dissemination of ABR in the food chain.
Co-resistance to non-beta-lactam antibiotics, including trimethoprim-sulfamethoxazole, erythromycin, clindamycin, fusidic acid, gentamicin and ciprofloxacin, was also observed.
Such co-resistance to other antibiotic classes along with resistance to beta-lactams is frequent in MRS and could likely result from the indiscriminate and/or extensive antibiotic use in food animals in both countries (Asongalem et al., 2015). The presence of mobile genetic elements such as the Staphylococcal Cassette Chromosome (Scc) harbouring the mecA gene responsible for the methicillin resistance could also explained our results and be responsible of further resistance (Bhargava and Zhang, 2012). These results further reveal that MRS strains may transfer their resistance genes across susceptible species or genus through horizontal gene transfer in the farm-to-plate continuum.
5.4.5. Genotypic relatedness
REP-PCR analysis, demonstrated that isolates from pig origin exhibited varying levels of genetic variability and presented both related and unrelated patterns. The antibiotic resistance and REP patterns revealed relative association between animal and human strains within and across countries. Although no MRSA strains were detected in humans, some MRCoNS detected from humans share common ancestors with those isolated from pigs at the same or different abattoir. These results suggest that emergence of MRCoNS in humans may be of animal origin or vice-versa, and that these pathogens may be transferred to humans via the food chain, enabling them to subsequently enter community or healthcare settings. Similarly, MRSA strains detected in pigs revealed association within the same abattoir. Although not being an indication of MRS transmission dynamics, our results nonetheless show that some genetic relatedness exists between animal and human isolates due to similar clustering. This finding is of great concern as MRS originating from animals have been reported to be amongst the causative agents of clinical infections globally (Kluytmans, 2010).
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5.4.6. Association of MRS carriage in humans and risk factors
Twenty-one workers or their close relatives had been hospitalized within a year of the sample collection, leading to an overall 95.24% (p=0.007) and 85.71% (p=0.112) prevalence of nasal and hand MRS, respectively (Table 5.1). Likewise, 92.11% (p=0.000) and 92.11% (p=0.000) of workers who had consumed antibiotics the month preceding the sampling were colonized by MRS in nasal and hand samples, respectively (Table 5.1). Although the duration of MRS carriage and resistance genes involved were not investigated, the study reveals that no association between human MRS carriage and contact with MRS carrying pigs was observed for all type of samples, although not statistically significant (Table 5.2). In contrast, a clear association between human MRS carriage and contact with other animals, especially poultry, was observed and with high statistical significance (Table 5.2). We showed that when workers have been trained to practice their profession, convenient handwashing facilities were available and wearing of protective clothes was implemented, the odds of being colonized by MRS were significantly reduced. Our findings also reveal that the implementation of food safety measures is imperative to contain the dissemination of ABR in general and MRS in particular.
The scarcity of similar studies precluded robust comparison of results. We therefore discussed our findings with data considered most appropriate and as close as possible to our own results.
More research is required on MRS carriage in high risk human populations and other food animals such as poultry in order to improve our knowledge on the public health significance associated with the likely transmission of MRS through the farm-to-plate continuum.