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Phenotypic Heterogeneity Affects Stenotrophomonas maltophilia K279a Colony Morphotypes and ?-Lactamase Expression.

ABSTRACT: Phenotypic heterogeneity at the cellular level in response to various stresses, e.g., antibiotic treatment has been reported for a number of bacteria. In a clonal population, cell-to-cell variation may result in phenotypic heterogeneity that is a mechanism to survive changing environments including antibiotic therapy. Stenotrophomonas maltophilia has been frequently isolated from cystic fibrosis patients, can cause numerous infections in other organs and tissues, and is difficult to treat due to antibiotic resistances. S. maltophilia K279a produces the L1 and L2 ?-lactamases in response to ?-lactam treatment. Here we report that the patient isolate S. maltophilia K279a diverges into cellular subpopulations with distinct but reversible morphotypes of small and big colonies when challenged with ampicillin. This observation is consistent with the formation of elongated chains of bacteria during exponential growth phase and the occurrence of mainly rod-shaped cells in liquid media. RNA-seq analysis of small versus big colonies revealed differential regulation of at least seven genes among the colony morphotypes. Among those, bla L1 and bla L2 were transcriptionally the most strongly upregulated genes. Promoter fusions of bla L1 and bla L2 genes indicated that expression of both genes is also subject to high levels of phenotypic heterogeneous expression on a single cell level. Additionally, the comE homolog was found to be differentially expressed in homogenously versus heterogeneously bla L2 expressing cells as identified by RNA-seq analysis. Overexpression of comE in S. maltophilia K279a reduced the level of cells that were in a bla L2-ON mode to 1% or lower. Taken together, our data provide strong evidence that S. maltophilia K279a populations develop phenotypic heterogeneity in an ampicillin challenged model. This cellular variability is triggered by regulation networks including bla L1, bla L2, and comE.

SUBMITTER: Abda EM

PROVIDER: S-EPMC4667094 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Project description:Intrinsic β-lactam resistance in Stenotrophomonas maltophilia is caused by bla L1 and/or bla L2, a kind of metallo-β-lactamase with a broad substrate spectrum including carbapenems. A rapid and sensitive molecular method for the detection of bla L1 in clinical samples is needed to guide therapeutic treatment. In present study, we first described a loop-mediated isothermal amplification (LAMP) method for the rapid detection of bla L1 in clinical samples by using two methods including a chromogenic method using calcein/Mn(2+) complex and the real-time turbidity monitoring to assess the reaction. Then dissemination of L1-producing S. maltophilia was investigated from ICU patients in three top hospital in Beijing, China. The results showed that both methods detected the target DNA within 60 min under isothermal conditions (65°C). The detection limit of LAMP was 3.79 pg/μl DNA, and its sensitivity 100-fold greater than that of conventional PCR. All 21 test strains except for S. maltophilia were negative for bla L1, indicative of the high-specificity of the primers for the bla L1. A total of 22 L1-positive isolates were identified for LAMP-based surveillance of bla L1 from 105 ICU patients with clinically suspected multi-resistant infections. The sequences of these bla L1 genes were conservative with only a few sites mutated, and the strains had highly resistant to β-lactam antibiotics. The MLST recovered that 22 strains belonged to seven different S. maltophilia sequence types (STs). Furthermore, co-occurrence of bla L1 and bla L2 genes were detected in all of isolates. Strikingly, S. maltophilia DCPS-01 was recovered to contain bla L1, bla L2, and bla NDM-1 genes, possessing an ability to hydrolyse all β-lactams antibiotics. Our data showed the diversity types of S. maltophilia carrying bla L1 and co-occurrence of many resistant genes in the clinical strains signal an ongoing and fast evolution of S. maltophilia resulting from their wide spread in the respiratory infections, and therefore will be difficult to control.

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Phenotypic Heterogeneity Affects Stenotrophomonas maltophilia K279a Colony Morphotypes and ?-Lactamase Expression.

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