| Formation and transmission of the bacterial aerosols of Staphylococcus aureus (S. aureus)in a chicken farming environment have gained relatively comprehensive understanding;however, a rather limited understanding of the antibiotic-resistance of the airborne S. aureusand the transmission of its antibiotic-resistant genes exists. In order to understand the drugresistance of Staphylococcus aureus in the chicken farm environment and reveal themechanisms for the dissemination of drug-resistant gene. We carried out the study aboutsuch problems.This research consists of four parts as follows:Part one: Isolation and identification of Staphylococcus aureusOne hundred forty-nine S. aureus strains were isolated from samples of feces, frominside the henhouse and from air in the external environment of6chicken farms. Baird-parkermedium culture was selected as air sampling media, and suspicious colonies were picked onthe Chromogenic culture medium.Then selected blue colonies and identification of149Staphylococcus aureus were based on the PCR of the heat-resistant nuclease gene (nuc).Part two: Transmission of the antibiotic-resistance of Staphylococcus aureusthe antibiotic-resistance research with15types of antibiotics. The results revealed thatfor the S. aureus isolated from the samples collected from the6chicken farms,5.37%strains(8/149)were resistant to methicillins (i.e. methicillin-resistant S. aureus),94%strains(140/149) were resistant to compound sulfamethoxazole,78.5%strains(117/149)wereresistant to penicillin,66.4%(99/149)strains were resistant to erythrocin,75.2%strains(112/149) were resistant to tetracycline, and they were also resistant to other antibiotics moreor less; But they were entirely sensitive to vancomycin. Most of them were resistant to4,5or6types of antibiotics, accounting for16.1%(24/149),32.9%(49/149)and14.8%(22/149)respectively. There were also3strains resistant to9antibiotics. In addition,these S. aureus strains indicated a resistance to multiple antibiotics. We should pay specialattention to the antibiotic-resistant of some strains isolated from the chicken feces, inside thehenhouse and the external environment(the air of the10m and50m upwind and10m,50m,100m and200m downwind) of the chicken farms was basically the same. Therefore, theresult can be described that the S. aureus that is antibiotic-resistance generated by thechickens can form aerosols, and spread to the environment outside the chickenhouse by airexchanges between the inside and outside of the chichenhouse. Part three: REP-PCR Identification of airborne staphylococcus aureus from the indoorand outdoor airIn order to study the transmission of S. aureus in poultry houses to their ambient air, theair samples, including indoor, upwind (10m,50m) and downwind air (10m,50m,100m,200m) of6chicken houses were collected. Feces samples were collected according to thestandard method and S. aureus was isolated. S. aureus was used as an indicator in thisstudy.The repetitive extragenic palindromic elements, PCR, REP-PCR method was applied togenerate genomic amplification products of S. aureus isolated from the chicken feces and theair. By analyzing the different concentration and genetic similarity of S. aureus in everysampling site, the transmission of bioaerosol from indoor houses to their ambient can beidentified.The fingerprints and the phylogenetic tree indicated that a part of the S. aureus (38.7%)isolated from indoor air had the same REP-PCR fingerprints with those isolated from feces,the most of S. aureus isolated (55.9%) from downwind10m,50m,100m,200m even400mhad the same REP-PCR fingerprints with those isolated from indoor air or feces too, whichindicated that some isolates isolated from downwind air and indoor air originated in thechicken feces. So, it was concluded that the isolates isolated from upwind air didn’t comefrom the feces or indoor air. In a word, the S. aureus in feces can be aerosolized andtransmitted into the indoor air and outdoor air, especially the downwind air of the houses withthe air exchange. This study can reveal the transmitting rule of airborne S. aureus bioaerosolto the ambience. Hygienic measures taking in animal farms have the significant meanings ofpublic hygiene and epidemiology.Part four: Formation and transmission of the aerosols of bacterial Staphylococcus aureuscarrying antibiotic-resistant genesThe detection rate of the tetM gene in the isolated149S. aureus strains from6chickenfarms was in the range of32.0-92.7%, The detection rate of the ermC gene was in the rangeof40.0-95.8%, with the highest rate in chicken farm B, and the lowest rate in chicken farm E.The detection rate of the aac(6’)-aph(2’’) gene was in the range of11.1-62.5%, The detectionrates of the ermC gene and its corresponding antibiotic-resistance were83.3%/100%,95.8%/91.7%,39.3%/53.6%,38.9%/44.4%,40%/28%and63.3%/76.7%, respectively. Thedetection rates of the aac(6’)-aph(2’’) gene and its corresponding antibiotic-resistance were62.5%/66.7%,20.8%/8.3%,10.7%/10.7%,11.1%/0%,20%/38.5%and16.7%/16.7%,respectively. The detection rates of the antibiotic-resistant phenotype of the mecA gene were8.3%,12.5%,3.6%,0%,0%and6.7%, respectively. In all6chicken farms, the differences in the detection rate between the mecA, tetM, ermC, and aac(6’)-aph(2’’) genes and theirrespective antibiotic-resistant phenotype were2%/5.4%,63.1%/75.2%,60.4%/66.4%,23.5%/20.8%, respectively. The100%homologous strains were selected to conduct furtherresearch on the carrying and transmission status of the antibiotic-resistant genes.The strains with the same REP-PCR trace identification result carried the same type ofantibiotic-resistant genes of tetM, mecA, ermC, ermA and aac (6’)-aph (2’’).(Discussion) Itwas observed that chicken-borne S. aureus that is antibiotic-resistant or that carried antibiotic-resistant genes could form aerosols and spread to the environment outside the henhouse (thetransmission distance depended on the meteorological conditions) by the exchange of airinside and outside of the henhouse. Transmission of such bacteria not only causes the spreadof epidemic diseases, but also exerts threats toward the public health of a community. |
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