Expression in Pseudomonas aeruginosa of an erythromycin-resistance determinant that encodes the mphA gene for macrolide 2'-phosphotransferase I from Escherichia coli

[Antimicrobial Resistance and Infection Control for Gram-positive Bacteria]

Antimicrobial resistance (AMR) is a serious problem worldwide. We searched for the AMR determinants of various bacteria isolated from clinical settings and studied their resistance mechanisms and molecular epidemiology. This review focuses on the AMR of Staphylococcus aureus, a major gram-positive pathogen, which has the ability to acquire resistance to antimicrobials. The resistance factors of S. aureus are frequently found on mobile elements, including plasmids and transposons. We determined the complete DNA sequence of the tetracycline-resistance plasmid and found that the inducible expression of tetK in S. aureus was regulated by a post-transcriptional attenuation mechanism. Furthermore, outbreaks of methicillin-resistant S. aureus (MRSA) in hospitals and communities have led us to study infection controls, including the antiseptic susceptibility evaluation and molecular epidemiology of MRSA. Various antiseptic resistance determinants, such as qacA/B and smr, were identified on plasmids and characterized. We demonstrated that the plasmid-mediated efflux pump QacB variant QacIII confers fluoroquinolone efflux ability to S. aureus. Studies on MRSA epidemiology had shown that community-acquired MRSA (CA-MRSA) was disseminated into hospitals and that an increased use of alcohol-based rubs could reduce the incidence of MRSA infections in such institutions. Additionally, the study of CA-MRSA collected from communities and hospitals showed an increase in Panton-Valentine leucocidin (PVL)-positive CA-MRSA, causing severe skin and soft tissue infections. Moreover, various PVL-positive CA-MRSA clones have disseminated in Japan, whereas the USA300 LV/J clone evolved in that country. Our study provides important information regarding MRSA infection control.

Comparative study between macrolide regulatory proteins MphR(A) and MphR(E) in ligand identification and DNA binding based on the rapid in vitro detection system

The macrolide regulatory protein MphR(A) has been widely studied and used in various aspects such as metabolism monitoring, exogenous gene expression, and in vivo and in vitro macrolide antibiotic screening. Another macrolide regulatory protein, MphR(E), has rarely been reported. In this study, in vitro ELISA-type systems were established for MphR(A) and MphR(E) to study their correlation. The reactivity of 14 macrolide antibiotics and pseudo-macrolide antibiotics was tested in the systems. The results indicated that the ligand identification spectra of MphR(A) and MphR(E) were basically consistent. The binding characteristics of MphR(A) and MphR(E) with three corresponding promoter DNA sequences were preliminarily studied. According to the ELISA-type analysis results, MphR(A) and MphR(E) have consistent DNA binding properties, which bind to A-DNA/B-DNA more easily than to C-DNA. This study has confirmed that MphR(E) can bind to the promoter DNA sequences mrx(E) and mph(E) in plasmid pRSB111, and different DNAs can affect the sensitivity of the in vitro detection systems.

Macrolide inactivation gene cluster mphA-mrx-mphR adjacent to a class 1 integron in Aeromonas hydrophila isolated from a diarrhoeic pig in Oklahoma

OBJECTIVES

To characterize a multidrug-resistant Aeromonas hydrophila isolate (CVM861) that possesses a high-level macrolide inactivation gene cluster (mphA-mrx-mphR), previously only reported in Escherichia coli.

METHODS

PCR fragment length mapping, gene sequencing and Southern blotting were used to map the mphA-mrx-mphR gene cluster and flanking elements in CVM861. Conjugation experiments were done to determine whether the multidrug resistance genetic element was mobile.

RESULTS

The mphA-mrx-mphR gene cluster mapped downstream of a class 1 integron and upstream of an aph(3') gene, and was present on a Tn21-like element. The gene order determined by sequencing was intI1-dhfrXII-orfF-aadA2-qacDeltaE-sul1-orf5Delta178-tnpA-mphR-mrx-mphA. Horizontal transmission of high-level macrolide resistance from CVM861 to E. coli 47011 was inconsistent; however, a composite plasmid possessing the mphA gene cluster was transferred at a conjugation frequency of 2.02 x 10(-5) per recipient.

CONCLUSIONS

An mphA-mrx-mphR gene cluster was present downstream of the In2 integron located on a Tn21-like transposon in an A. hydrophila isolate. Whether this recombination event resulted in the truncation of the orf5 sequence is unknown. The presence of other resistance genes downstream of the mphA-mrx-mphR gene cluster suggests that multiple recombination events have occurred on this genetic element. This is the first known report of the mphA-mrx-mphR gene cluster carried by A. hydrophila and the first known isolation of this cluster in the United States.