THE EPIZOOTIOLOGICAL IMPORTANCE OF SALMONELLA SPP. ISOLATED IN VARIOUS ASPECTS OF POULTRY PRODUCTION IN THE SOUTHERN BAČKA AND SREM REGION*

Salmonella causes local and systemic infections of poultry, which may lead to substantial direct and indirect economic losses, presenting also si-gnifi cant risk to human health. Th e aim of this study was to monitor the occurrence of certain serotypes of Salmonella spp. isolated on poultry farms in Southern Bačka and Srem regions in the period from 2010 to 2014, as recommended by the Book of rules of early detection, diagnostic, prevention of spreading and eradication of Salmonella spp. We analyzed the results obtained from the laboratory for clinical bacteriology to determine number of salmonella cases. From all samples that have been submitted for bacte-riology analysis, salmonellas were isolated from 7.3% samples. Salmonella infantis was isolated from 50.3% of all salmonella-positive samples, mostly from materials supplied from broiler farms. Salmonella enteritidis was most frequently isolated in broiler chickens at the rate of 48.2%. Th ere is an increasing trend in the occurrence of Salmonella enteritidis and Salmonella in-fantis on poultry farms from year to year. Our research revealed the highest incidence of salmonella isolates in broilers that died during transportation or within the fi rst three days upon arrival of chickens. During the fi ve-year research period

Salmonella causes local and systemic infections of poultry, which may lead to substantial direct and indirect economic losses, presenting also signifi cant risk to human health. Th e aim of this study was to monitor the occurrence of certain serotypes of Salmonella spp. isolated on poultry farms in Southern Bačka and Srem regions in the period from 2010 to 2014, as recommended by the Book of rules of early detection, diagnostic, prevention of spreading and eradication of Salmonella spp. We analyzed the results obtained from the laboratory for clinical bacteriology to determine number of salmonella cases. From all samples that have been submitted for bacteriology analysis, salmonellas were isolated from 7.3% samples. Salmonella infantis was isolated from 50.3% of all salmonella-positive samples, mostly from materials supplied from broiler farms. Salmonella enteritidis was most frequently isolated in broiler chickens at the rate of 48.2%. Th ere is an increasing trend in the occurrence of Salmonella enteritidis and Salmonella infantis on poultry farms from year to year. Our research revealed the highest incidence of salmonella isolates in broilers that died during transportation or within the fi rst three days upon arrival of chickens. During the fi ve-year research period, 65 samples from parent fl ocks (63 from broiler breeders and 2 from parent fl ocks of layers) were salmonella positive, which ma-

INTRODUCTION
Salmonella does not cause clinical symptoms in poultry, but seldom may lead to increased mortality usually during rearing and induce a decrease in egg production. People become infected with salmonella by consuming contaminated food. Th ese infections may be manifested in humans through lighter or heavier clinical symptoms which may be accompanied with a long convalescing period (Dačić et al., 2004). Salmonella are a facultative Gram -negative aerobes, rod-shaped, and classifi ed as the Enterobacteriacae family. Th ey do not create spores and they do not encapsulate.
Salmonellas are excreted through feces, contaminating the environment so reinfections are frequent. Certain serotypes such as Salmonella Enteritidis (S. Enteritidis) and Salmonella Typhimurium (S. Typhimurium) persist inside parenchymal organs and ovaries which can cause vertical transmission (Ilić i sar., 2010). Salmonella can cause embryo death and early mortality in chickens (in the fi rst seven days of life). If the parent stock has been infected, incubators for hatching chickens may also be contaminated which may lead to a large number of hatched chickens to be infected. Th e process of animal feed pelleting can decrease the Salmonella contamination only to a certain extent therefore it is crucial to maintain cleanliness in animal feed factories. Since the Salmonella is so widespread and diffi cult to eliminate from the environment, it is on the eradication program priority list throughout the world. Th e goal of this research was to determine the prevalence of certain serotypes of Salmonella spp. in Srem and Southern Backa district from year 2010 -2014, specifi ed by the Book of Rules for poultry salmonellosis RS number 7/10, and to briefl y highlight control, prevention measures, and goals which should be achieved in order to eradicate these persistent infections.

MATERIAL AND METHODS
During the timeline from 2010 -2014, samples for Salmonella examination from the Srem and Southern Bačka district were delivered to the Veterinary Institute in Novi Sad. Th e following categories of poultry fl ocks were included in this research: -rearing broiler breeders and rearing layer breeder fl ocks -broiler breeders and layer breeders in production -hatcheries -Broilers -Turkey pullets -Layer chickens -Pheasants raised on farms In this research 11.044 samples from poultry were analyzed. Th ese samples were: parenchymatous organs, embryonated chicken eggs, unhatched eggs, mortality during transport, and paper pads. Salmonella spp. was isolated in a laboratory for clinical bacteriology, by using liquid media for enrichment, selective media, diff erential media, and for serological typing the slide aglutination test with specifi c serums (with poly-somatic and, fl agellar antigens) was done.
Th e results were processed by descriptive statistics and presented in percentages.

RESULTS
During the 2010 -2014 timeline, 11.044 samples were examined, 809 (7.32 %) tested positive for Salmonella. Most frequently detected were S. Enteritidis and Salmonella Infantis (S. Infantis). In a smaller number of samples, S. Typhimurium was isolated as well (Table 1).

DISCUSSION
Th e prevalence of Salmonella spp. in diagnostic materials is similar to reports from previous years (Stojanov et al., 2006). Most of the positive samples were from broilers, mortality during transportation, and mortality at three days old. From all of the positive samples, 521 were from broiler farms, which is 64.40% of the whole number of samples. Broiler breeders had 65 positive samples, which is 8.03% of all the positive samples. Sixty three positive samples were from rearing layer breeders and only two from fl ock of layer breeders. Samples that came from layer chickens were positive in 178 cases, which is 22.12% from the total number of Salmonella isolation. Salmonella was found in pheasants in seven samples, during this fi ve year run, and turkey pullets had 25 positive samples. Th e sampling was done during the whole year. Th e Salmonella spp infections were registered in 28 fl ocks (7.7%). In six farms S. Enteritidis (1.7%) was isolated while in 2 fl ocks S. Typhimurium (0.6%) was found. In the remaining 20 fl ocks: Salmonella Montevideo (4,1%), S. Infantis (0,6%), Salmonella Senft enberg, Salmonella Tennessee and S. Virchow (0.3%) were isolated. Data shows that the risk of horizontal transmission of Salmonella spp. to broiler chickens is very high. Th e study that was conducted by Rusul and associates (1996) in Malesia, in order to determine the prevalence of Salmonella in 230 samples from broiler chickens, has shown that the most prevalent are S. Enteritidis, Salmonella Muenchen, Salmonella Kentucky and Salmonella Blockley.
Salmonella are one of the most important bacteria which cause zoonoses. Worldwide, they are considered to be very signifi cant in epidemiology, and the program for eradication is mandatory in all the EU states. In order to eliminate salmonella from the food chain it is essential to minimize the incidence of Salmonella in breeder fl ocks and in other poultry farms as well (Velhner et al., 2011). Th e directive, EC number 1003/2005 has required that the incidence of S. Enteritidis and S. Typhimurium as well as other signifi cant serotypes of Salmonellas in breeder farms should not exceed an amount of ≤ 1% (EC, 1003/2005). For these reasons, Salmonella monitoring needs to be more comprehensive while better management practice on farms has to become one of the primary goals in the livestock industry in Serbia. In order to prevent salmonella infections in chickens, it is essential to apply the following measures: to purchase chickens only from farms that are free of salmonella; avoid mixing chickens from diff erent fl ocks; thermal processing of feed ingredients; to provide water not contaminated with salmonella; prevent wild birds and rodents from accessing farms; thoroughly clean and disinfect objects between poultry production cycles; disinfect by using fumigation for hatching eggs; disinfect incubators aft er every hatching. Farm workers need to wear protective clothing and regularly conduct personal hygiene. Treatment with antibiotics is not recommended in poultry, unless diarrhea and fever occur, when they can be used to reduce mortality. In laying hens antibiotics are contraindicated.

ACKNOWLEDGMENT
Th is work is supported by a grant from the Ministry of Education, Science and Technological Development, Republic of Serbia, Project number TR 31071.