[Genetic characterization and antimicrobial susceptibility analysis of methicillin-resistant Staphylococcus aureus isolated from ready-to-eat food and pig-related sources in China].
OBJECTIVE
To study the mecA gene distribution in 877 strains of Staphylococcus aureus isolated from the environment of pig farm and slaughter house, pig carcass and its iliac lymph nodes, and ready-to-eat foods in China as to screen the methicillin-resistant Staphylococcus aureus (MRSA), and to evaluate the antimicrobial susceptibility of MRSA.


METHODS
A total of 877 strains of S. aureus that had been phenotypically identified by Gram staining, catalase test, ability to coagulate rabbit plasma, API STAPH as well as analysis of nuc gene, encoding for a S. aureus specific thermonu-clease were screened for MRSA by characterizing the mecA gene. The antimicrobial susceptibility of MRSA was tested in accordance with the broth microdilution method recommended by the Clinical and Laboratory Standards Institute.


RESULTS
Of 877 S. aureus strains tested, 71 (8.1%, 71/887) were mecA positive and identified as MRSA, among which, 48 isolates were pig-associated and 23 isolates were ready-to-eat food-associated. The frequency of pig-associated MRSA was significantly higher than that of food-associated one (chi2 = 53.040, P < 0.01). All MRSA were susceptible to linezolid, vancomycin, tigecycline, and nitrofurantoin but resistant to cefoxitin, oxacillin and benzylpenicillin. Meanwhile, 98.6% (70 strains), 95.8% (68 strains), 88.7% (63 strains), 80.3% (57 strains), 80.3% (57 strains) and 32.4% (23 strains) MRSA exhibited the resistance to clindamycin, erythromycin, tetracycline, ciprofloxacin, trimethoprim/sulfamethoxazole, and gentamicin, respectively. Besides, one strain was resistant to each of antibiotics including levofloxacin, moxifloxacin, rifampicin, and quinupristin/dalfopristin. It was worth noting that the frequency of resistance to ciprofloxacin, tetracycline, and trimethoprim/sulfamethoxazole of pig-associated MRSA was significantly higher than that of food-associated MRSA (CIP: chi2 = 29.110, P < 0.01, TET: chi2 = 18.816, P < 0.01, TMP/ SMZ: chi2 = 36.394, P < 0.01). It should be pointed out that 70 (98.6%) strains of MRSA were multi-drug resistant and eight spectrums of antimicrobial susceptibility were observed.


CONCLUSIONS
The multi-drug resistant MRSA isolated from pig- and food-associated matrixin China is very serious.
Key Lab of Food Safety Risk Assessment, Ministry of Health, China National Centre for Food Safety Risk Assessment, Beijing 100021, China. wangweiwsw@cfsa.net.cn
Wei
W
Wang
Key Lab of Food Safety Risk Assessment, Ministry of Health, China National Centre for Food Safety Risk Assessment, Beijing 100021, China.
Yunchang
Y
Guo
Key Lab of Food Safety Risk Assessment, Ministry of Health, China National Centre for Food Safety Risk Assessment, Beijing 100021, China.
Xiaoyan
X
Pei
Key Lab of Food Safety Risk Assessment, Ministry of Health, China National Centre for Food Safety Risk Assessment, Beijing 100021, China.
Yujie
Y
Hu
Key Lab of Food Safety Risk Assessment, Ministry of Health, China National Centre for Food Safety Risk Assessment, Beijing 100021, China.
Li
L
Bai
Key Lab of Food Safety Risk Assessment, Ministry of Health, China National Centre for Food Safety Risk Assessment, Beijing 100021, China.
Aiping
A
Sun
Key Lab of Food Safety Risk Assessment, Ministry of Health, China National Centre for Food Safety Risk Assessment, Beijing 100021, China.
Jikai
J
Liu
Key Lab of Food Safety Risk Assessment, Ministry of Health, China National Centre for Food Safety Risk Assessment, Beijing 100021, China.
Ping
P
Fu
Key Lab of Food Safety Risk Assessment, Ministry of Health, China National Centre for Food Safety Risk Assessment, Beijing 100021, China.
Fengqin
F
Li
D000818:Animals; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D002681:China; D005516:Food Microbiology; D008460:Meat / Q000382:microbiology; D008461:Meat Products / Q000382:microbiology*; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D046915:Penicillin-Binding Proteins; D013552:Swine
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D046915:Penicillin-Binding Proteins; C487789:mecA protein, Staphylococcus aureus