ABSTRACT
Objective:To identify 49 Aeromonas caviae strains isolated form foodborne and environmental samples and analyze their virulence and antibiotic resistance. Methods:All strains were identified by VITEK and API 20NE. Two housekeeping genes, gryB and rpoD, were amplified by PCR for phylogenetic analysis. Virulence genes including act, alt, ast, lip, ahp, aerA, hlyA, ompA1 and fla were detected by PCR. In vitro antimicrobial susceptibility of these strains was tested with AST-GN16 kit. Results:Fifty-four Aeromonas caviae/ Aeromonas hydrophila strains were identified by biochemical tests. Phylogenetic analysis revealed that there were 49 Aeromonas caviae strains, four Aeromonas hydrophila strains and one Aeromonas taiwanensis strain. The positive rates of alt, lip, ompA1, fla, act, aerA and hlyA genes were 100.00%, 100.00%, 79.59%, 14.29%, 2.04%, 2.04% and 2.04%, respectively. None of the isolates carried ast or ahp gene. A total of four virulence gene combination patterns were detected, and the predominant pattern was alt/ lip/ ompA1 (32/49). Antibiotic resistance rates of the Aeromonas caviae strains to ampicillin, cefazolin, cefoxitin, amoxicillin/clavulanic acid, ceftriaxone, trimethoprim/sulfamet hoxoazole and aztreonam were 79.59%, 14.29%, 10.20%, 6.12%, 4.08%, 4.08% and 2.04%, respectively. All strains were susceptible to piparacillin/tazobactam, imipenem, amikacin, gentamicin, levofloxacin, tigacycline and nitrofurantoin. Two multidrug-resistant strains were detected. Conclusions:Aeromonas caviae/ Aeromonas hydrophila can be effectively identified by the housekeeping genes gyrB and rpoD, and the closely related Aeromonas caviae and Aeromonas taiwanensis strains can be identified by rpoD. All Aeromonas caviae strains carried two or more virulence genes and one strain isolated from environment was positive for seven virulence genes. Aeromonas caviae strains were generally resistant to penicillin, which was mainly relate to the production of β-lactamase. No strain was resistant to carbapenems, aminoglycosides, fluoroquinolones, tetracyclines or furans. Multidrug-resistant strains were observed in food and drinking water.
ABSTRACT
Objective To analyze the antimicrobial resistance, distribution of resistance genes and staphylococcal cassette chromosome mec ( SCCmec) in 99 strains of mecA gene-positive Staphylococcus epi-dermidis strains isolated from early pregnancy cervical swabs and external environment in Beijing Chaoyang District from 2015 to 2016. Methods Kirby-Bauer disk diffusion method was performed to detect the sus-ceptibility of the 99 Staphylococcus epidermidis strains to cefoxitin. Microbroth dilution method was used to test their susceptibility to vancomycin, daptomycin, penicillin, erythromycin, compound sulfamethoxazole, tetracycline, ciprofloxacin, clindamycin, gentamicin and chloramphenicol. PCR was used to detect drug re-sistance genes of ermA, ermB, ermC, msrA, norA1, norA2, sul1, sul2, sul3, aac(6')/aph(2″), ant(4', 4″), ant(6) and tetM and to analyze the SCCmec types ofⅠ, Ⅱ, Ⅲ, Ⅳa, Ⅳb, Ⅳc, Ⅳd and Ⅴ. The results were compared with those of capillary electrophoresis. SPSS was used for data analysis. Results All of the 99 mecA-positive Staphylococcus epidermidis strains were sensitive to vancomycin and 93. 94％ of them were sensitive to datomycin. The resistance rates to penicillin, erythromycin, cefoxitin, compound sulfame-thoxazole, tetracycline, ciprofloxacin, clindamycin, gentamicin and chloramphenicol were 97. 98％, 85. 86％, 79. 80％, 52. 54％, 27. 27％, 43. 43％, 36. 36％, 23. 23％ and 11. 11％. The strains that car-ried the genes of norA1, norA2, ermA, ermB, ermC, msrA, sul1, sul2, sul3, aac(6')/aph(2″), ant(4', 4″), ant(6) and tetM accounted for 100％, 93. 94％, 0. 00％, 3. 03％, 17. 17％, 57. 58％, 50. 51％, 12. 12％, 4. 04％, 30. 30％, 8. 08％, 4. 04％ and 25. 26％, respectively. Among the 99 strains, 5. 05％, 0％, 43. 43％, 10. 10％, 0. 00％, 3. 03％, 3. 03％ and 19. 19％ belonged to SCCmecⅠ, Ⅱ, Ⅲ, Ⅳa,Ⅳb,Ⅳc,Ⅳd andⅤ, respectively, and 4. 04％ (4/99) were positive to two SCCmec types. The types of 12. 12％ (12/99) of the strains were unidentified. Conclusions All of the 99 strains of mecA-positive Staphylococcus epidermidis were sensitive to vancomycin. Among them, the strains carrying multidrug resist-ance genes accounted for 89. 90％. The main mechanisms of resistance to macrolides, sulfonamides and ami-noglycosides in local strains were related to the resistance genes of msrA, sul1 and aac ( 6')/aph ( 2″) . SCCmec Ⅲ was the prevalent type. There were 88. 37％ of SCCmec Ⅲ type strains and 75％ of unknown type strains carrying multiple resistance genes. Apart from that, the isolated strains of other SCCmecⅢtypes all carried multiple resistance genes.