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Foodborne infections due to Salmonella are still a major concern worldwide. Particularly contaminated egg and egg related products are the primary sources for human salmonellosis. It is necessary to determine the risk factors associated with Salmonella contamination of eggs within the scope of farm to table and environment. The objective of this study was to develop the "National Salmonella Control Program in Laying Hens" and report the prevalence and serotype distribution findings of Salmonella in laying hens and eggs in Turkey. A total of 2122 samples were collected and analysed according to ISO 6579:2002 after the isolation and identification procedures. All Salmonella isolates were serotyped including 726 eggs and 1396 farm specimens from 241 epidemiological units (EpUs) that were located in 9 different provinces between 2015 and 2017. Salmonella contamination was detected in 14.9% of 241 EpUs. The results indicated that almost half of the flocks have multiple contamination sources. The highest contamination rate was obtained from environmental (11%) followed by faeces (7.5%) and the lowest was from water samples (1.6%). The overall contamination rate was detected as 7.46% for farms and 3.3% for eggs. As S. Enteritidis and S. Typhimurium are the most frequently seen serotypes all over the world, in Turkey S. Typhimurium was not detected and S. Enteritidis was the 5th most common isolated serotype. According to our results it can be concluded that differences in various countries, particularly geographical and egg hatching systems, may affect the contamination rate and serotype distribution of Salmonella.

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Background: Drug resistance in Mycobacterium tuberculosis is primarily attributed to mutations in target genes. These mutations incur a fitness cost and result in bacterial generations that are less fit, which subsequently acquire compensatory mutations to restore fitness. We hypothesize that mutations in specific drug target genes influence bacterial metabolism and cellular function, which affects its ability to develop subsequent resistance to additional agents. We aim to determine whether the sequential acquisition of drug resistance and specific mutations in a well-defined clinical M. tuberculosis strain promotes or limits the development of additional resistance.Methods & Materials: In vitro mutants resistant to pretomanid, linezolid, moxifloxacin, rifampicin and kanamycin were generated from a pan-susceptible clinical strain from the Beijing lineage. The resistant phenotypes to the anti-TB agents were confirmed by the broth microdilution assay and genetic mutations were identified by targeted gene sequencing. Growth of mono-resistant mutants was done in enriched medium for 14 days to assess in vitro fitness. Double resistant mutants were generated against anti-TB drug combinations at concentrations 5x and 10x the MIC. Subsequently, mutation frequencies for these anti-TB drugs in the different monoresistant backgrounds were determined.Results: The initial level of resistance and the mutation frequencies observed for the mono-resistant mutants were comparable to those previously reported. Targeted gene sequencing revealed the presence of known and clinically relevant mutations in the mutants resistant to linezolid, rifampicin, kanamycin and moxifloxacin. Significant growth defects were observed for mutants grown under in vitro conditions compared to the sensitive progenitor. Mutation frequencies determination in the mono-resistant mutants revealed a significant increase in mutation frequency against rifampicin and kanamycin, but a significant decrease in mutation frequency against linezolid and sutezolid. This suggests that these mono-resistant mutants are more prone to develop resistance to rifampicin and kanamycin, but less prone to develop resistance against linezolid and sutezolid. Even though kanamycin and linezolid both inhibit protein synthesis, these compounds target different subunits of the ribosome, thereby leading to different outcomes in terms of fitness in the mutants with impaired cellular function.Conclusion: These observations showed that oxazolidinone treatment is instrumental in limiting the development of multidrug resistance in M. tuberculosis in vitro.