Bacteria are known to be associated with a variety of poultry diseases. Escherichia coli is a common avian pathogen which contributes to enormous losses in poultry industry. Bacillus subtilis produces serine proteinase (trypsin and chymotrypsin) which contributes to causing mortality in affected birds [1] . Staphylococcus species cause acute death in laying birds and seem to be prevalent in tropical environment. E. coli and Staphylococcus species can also act as secondary bacteria to exacerbate clinical conditions leading to high mortality [2] . Klebsiella pneumoniae can occasionally cause embryonic mortality and severe losses in young chickens and turkeys [3] . Aeromonas hydrophila alone or concurrently with other organisms can cause localized and systemic infections in avian species including poultry [4] . Proteus species occasionally cause embryonic death, yolk sac infections, and mortality in young chickens, turkeys and ducks [5] .

Despite the established roles of bacteria in causing opportunistic infections in poultry, there is a paucity of information on the prevalent bacteria in the oropharynxs of chickens in Jos, Nigeria. This study is therefore aimed at determining the prevalent bacterial agents in the oropharynxs of apparently healthy chickens in Jos, Nigeria.

From the 400 oro-pharyngeal swabs collected, a total of 7 aerobic bacterial species were isolated from 250 (62.5%) samples, while the remaining 150 (37.5%) yielded no bacteria. Of the bacteria isolated, 3 (42.8%) were gram positive, while 4 (57.1%) gram negative. Bacterial isolated from the apparently healthy chickens indicated that Staphylococcus aureus 82 (20.5%) was the highest followed by Escherichia coli 53 (13.3%), Klebsiella pneumoniae 35 (8.8%) and Pasteurella multocida 5 (1.3%) was the least (Table 1). Microbact test identified Pasteurella multocida (1.0%) and Escherichia coli (7.5%) from the oro-pharyngeal swabs apparently healthy chickens.

Bacterial agents have been reported to contribute immensely to economic losses incurred in poultry production in Nigeria [12] . Some of the bacterial species isolated in the present study such as S. aureus and Proteus species are considered to be opportunistic invaders from environmental sources, while others (E. coli, Klebsiella species) are normal intestinal flora of poultry, but could cause infections whenever the immune system of affected bird is compromised [13] . It was observed that none of the chickens from which oro-pharyngeal swab was taken showed any clinical signs of disease, suggesting that the pathogens were present as subclinical infections, or as commensals in the chickens. Though the chickens appeared to be apparently healthy, the high prevalence of potentially pathogenic bacteria species isolated from their oro-pharynx could signify that they could possibly act as reservoirs for the bacterial species detected, with the potential risk of transmitting these pathogens to other poultry. The preponderance of these bacterial agents in apparently healthy poultry could possibly be responsible for their worldwide association with various disease conditions in a broad range of host including domestic and wild birds. This study also indicated that there were predominantly gram negative bacteria compared to gram positive. This finding is concurred to the report of [14] . The reflection of bacteria type identified in this study could have a significant impact on the chickens based on the severity of diseases they caused when the immune system was compromised. [2] reported that the activities of some aerobic bacteria, such as E. coli, Staphylococcus species and others could exacerbate clinical conditions leading to high mortality. The high isolation rate of E. coli in the oropharynx could probably be attributed to the ability of the organism to be acquired from the environment within the few days after hatching. This bacterium has also been reported to be one of the commonest bacteria that complicate both bacterial and viral diseases of poultry [15] .

Despite the fact that the isolation rate of P. multocida was low, the implication of the isolation of this organism was that it could act as secondary invader during other diseases. These findings have also revealed that apparently healthy chickens can be carriers of P. multocida. [16] reported that P. multocida had been consistently recovered in the upper respiratory tract of apparently and clinically sick birds. This suggests that this bacterium might have played a significant role in the fulminating and high mortality encountered during fowl cholera outbreaks. The finding of this study conformed to the previous report of [17] who opined that in their study on relationship of Pasteurella isolated from free ranging chickens and contact animals that healthy chickens could be carriers of P. multocida which caused clinical disease when the immune system was compromised. In a similar study conducted by [18] also indicated that carriers of P. multocida might exist within poultry flocks with no history of previous outbreaks of fowl cholera and they might play a dominant role in the transmission of the disease. [19] asserted that the pathogenicity P. multocida increased by bird-to-bird passage over a short period of time; this may indicate that natural passage of P. multocida between the birds may enhance the virulence of a normally avirulent strain, leading to clinical disease in a flock of carriers. The isolation of these micro-organisms in the present study suggests their probable role in the epizootiology and source of infections to susceptible domestic birds, since oro-pharyngeal carriage contribute to the shedding of these bacteria, which may add to the rapid spread of infections for other domestic poultry.

The finding of this study has shown that aerobic bacterial agents were present in the oro-pharynx of apparently healthy chickens in Jos metropolis. Further study to elucidate the role and associated economic impact of these organisms during outbreaks is recommended.

The authors acknowledge the assistance of the Executive Director Veterinary Research, Vom, staff of Molecular Biology Department, National Veterinary Research Institute, Vom and Central Diagnostic Laboratory.

Yakubu G. Dashe,Moshood A. Raji,Paul A. Abdu,Blessing S. Oladele,Lola Oluwadare, (2015) Bacteria Isolated from the Oropharynxs of Apparently Healthy Chickens in Jos, Nigeria. Open Access Library Journal,02,1-5. doi: 10.4236/oalib.1101808