Identification of swine influenza A virus and Stenotrophomonas maltophilia co-infection in Chinese pigs.
BACKGROUND
Influenza virus virulence can be exacerbated by bacterial co-infections. Swine influenza virus (SIV) infection together with some bacteria is found to enhance pathogenicity.


METHODS
SIV-positive samples suspected of containing bacteria were used for bacterial isolation and identification. Antimicrobial susceptibility testing was performed by disc diffusion methods. To investigate the interaction of SIV and the bacteria in vitro, guinea pigs were used as mammalian hosts to determine the effect on viral susceptibility and transmissibility. Differences in viral titers between groups were compared using Student's t-test.


RESULTS
During surveillance for SIV in China from 2006 to 2009, seven isolates (24.14%) of 29 influenza A viruses were co-isolated with Stenotrophomonas maltophilia from nasal and tracheal swab samples of pigs. Antimicrobial susceptibility testing showed that the bacteria possessed a high level of resistance towards clinically used antibiotics. To investigate the interaction between these two microorganisms in influencing viral susceptibility and transmission in humans, guinea pigs were used as an infection model. Animals were inoculated with SIV or S. maltophilia alone or co-infected with SIV and S. maltophilia. The results showed that although no transmission among guinea pigs was observed, virus-bacteria co-infections resulted in higher virus titers in nasal washes and trachea and a longer virus shedding period.


CONCLUSIONS
This is the first report of influenza virus co-infection with S. maltophilia in the Chinese swine population. Increased replication of virus by co-infection with multidrug resistant bacteria might increase the infection rate of SIV in humans. The control of S. maltophilia in clinics will contribute to reducing the spread of SIV in pigs and humans.
Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, Beijing 100193, People's Republic of China.
Dongjun
D
Hou
Yuhai
Y
Bi
Honglei
H
Sun
Jun
J
Yang
Guanghua
G
Fu
Yipeng
Y
Sun
Jinhua
J
Liu
Juan
J
Pu
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002681:China; D060085:Coinfection / Q000382:microbiology / Q000821:virology; D024881:Drug Resistance, Bacterial; D005260:Female; D016905:Gram-Negative Bacterial Infections / Q000150:complications / Q000382:microbiology / Q000662:veterinary*; D006168:Guinea Pigs; D009980:Influenza A virus / Q000302:isolation & purification* / Q000472:pathogenicity; D008826:Microbial Sensitivity Tests; D009297:Nasal Mucosa / Q000382:microbiology / Q000821:virology; D009976:Orthomyxoviridae Infections / Q000150:complications / Q000662:veterinary* / Q000821:virology; D020615:Stenotrophomonas maltophilia / Q000187:drug effects / Q000302:isolation & purification* / Q000472:pathogenicity; D013552:Swine; D013553:Swine Diseases / Q000382:microbiology* / Q000821:virology*; D014132:Trachea / Q000382:microbiology / Q000821:virology; D019562:Viral Load; D017201:Virus Shedding
D000900:Anti-Bacterial Agents