In this study the prevalence of Salmonella in apparently healthy lactating dairy cows is larger (10.76%) as compared to other studies, even though most of the reports are on slaughtered cattle from abattoirs and ready to eat food items [6, 8, 9]. Hence lactating cows could be potential sources of Salmonella infection for individuals working in dairy farms and for the community at large.
Alemayehu et al., 2003 (8) reported a prevalence of 7.1% from apparently healthy slaughtered cattle which is less than the present report. This difference may be attributed to the difference in the tests used, since pre-enrichment steps using buffered peptone water was employed in this study. On the other hand reports from England (0.2% and 4%) and from Northern Thailand (3%) are much lower than the current investigation [16–18]. But a report from Cameroon by Akoachere et al., 2009  indicated a very high prevalence (27%) of Salmonella among cattle. This may be due to the difference in the living condition, like housing conditions, feeding habits, types of feed given for the cattle, of the two cattle populations. A comparable result, 9.96%, was reported from four states of USA .
The prevalence of Salmonella among individuals working in dairy farms of Addis Ababa was 13.63%. The result is higher than a study conducted by Alemayehu et al., 2003  and Zewdu and Cornelius, 2009  who reported a prevalence of 6% and 7.6%, respectively. The difference may be due to different working environment, hence different hygienic status, of study subjects. This higher prevalence is a concern to the dairy farms that provide milk and milk products to the community since cross contamination from infected individuals could be a potential source of food borne infections.
Resistance for two or more of antimicrobials (83.3%) which was observed in this study was higher than other studies conducted in Ethiopia [5, 6, 8, 21] and elsewhere in the world [1, 2, 22, 23]. This difference may be due to the increasing rate of inappropriate utilization of antibiotics in the dairy farms which favors selection pressure that increased the advantage of maintaining resistance genes in bacteria [24, 25].
Zewdu and Cornelius (2009)  reported that the isolates of Salmonella from food items and personnel from Addis Ababa were resistant to the commonly used antibiotics including streptomycin, ampicillin, and tetracycline. The result of the current research also indicated resistance of Salmonella isolates to commonly used antimicrobials including ampicillin, streptomycin, nitrofurantoine, kanamycine and tetracycline, with resistance rate of 100%, 66.7%, 58.3% and 33.3%, respectively.
All the isolated Salmonella, in the current study, were 100% resistant to ampiciliin. This finding is in line with previous reports from South India , from Nigeria  and from Cameroon  which reported a similar 100%, over 90% and 100% resistance to ampicillin, respectively. Hghi et al. (2009)  reported a resistance rate of 60.3% and72.7% in different study periods among human isolates from Iran, which is slightly lower than the current finding.
Ciprofloxacin showed a good antimicrobial activity against both human and cow isolates. This is also comparable with the result reported by Akinyemia et al., 2005  from Nigeria, among human isolates and with that reported by Molla et al., 2006  from central part of Ethiopia among isolates of sheep and goat. Though no data has indicated this, the effectiveness of such drugs like ciprofloxacin may be because they are not widely used in countries like Ethiopia and other African countries.
In the current study cotrimoxazole (trimethoprim-sulfametoxazole) showed a good antimicrobial activity against all isolates and no resistant isolate against this drug was detected. This result is lower than the reports by Rotimi et al., 2008  from Kuwait and United Arab Emirates who reported a resistance rate of 26.1% and 8.9%, respectively. Even though cotrimoxazole has been widely available the reason of its effectiveness until this times need investigations.