Study on the minimum inhibitory concentration of β-lactam and β-lactam resistance molecular mechanism of Haemophilus influenzae isolates from neonates / 中国小儿急救医学

ABSTRACT

Objective:To study the changes of β-lactam resistance of Haemophilus influenzae (Hi) strain isolated from neonatal lower respiratory tract and the molecular mechanism of β-lactam resistance.Methods:Nineteen Hi strains isolated from neonatal lower respiratory tract infection in the previous multicenter prospective epidemiological study were re-identified, and the P6, fucK and Cap genes were detected by PCR.The minimum inhibitory concentration(MIC) of ampicillin, amoxicillin clavulanic acid and cefuroxime were detected by microdilution method, and tem-1 gene, rob-1 gene and ftsI gene were sequenced and analyzed.Results:(1) Nineteen strains of Hi were confirmed to be capsule-free type by P6 gene, fucK gene and cap gene, which was non-typeable Haemophilus influenzae(NTHi). (2)Compared with 2003-2004, the MIC values of ampicillin, amoxicillin clavulanic acid and cefuroxime of NTHi isolated from the lower respiratory tract of the newborn from 2013-2014 were significantly higher( P<0.05). (3)The rates of β-lactamase producing strains during 2003-2004 and 2013-2014 were 33.33% (3/9) and 30.00% (3/10), respectively.There was no significant difference between them during 10 years ( P>0.05). The detection of the β-lactamase gene showed that the β-lactamase of the all six strains were of the tem-1 type, and the rob-1 type was not detected.(4)Only one gBLNAR strain ( n=9) was found during 2003~2004, and gBLNAR 1, gBLNAI 3, gBLPAR 3, gBLPACR 1 ( n=10)appeared during 2013~2014.(5)There were 11 amino acid substitution patterns in ftsI gene during 2013~2014, but only five amino acid substitution patterns in 2003~2004.The mutation rate of the S357N, S385T, N526K and T532S of ftsI gene significantly increased during the past ten years ( P<0.05). One strain of gBLNAR/gBLNACR resistant to ampicillin, amoxicillin clavulanic acid and cefuroxime isolated in 2014 showed D350N, S357N, M377I, S385T, L389F, A502T and N526K variation at the same time. Conclusion:Neonatal patients with lower respiratory tract NTHi infection may rapidly face the severe challenge of multiple drug resistance of β-lactam antibiotics.