In the sequenced genome of Salmonella enterica serovar Typhimurium strain LT2, an open reading frame (STM0580) coding for a putative regulatory protein of the TetR family is found upstream of the ramA gene. Overexpression of ramA results in increased expression of the AcrAB efflux pump and, consequently, multidrug resistance (MDR) in several bacterial species. The inactivation of the putative regulatory protein gene upstream of ramA in a susceptible serovar Typhimurium strain resulted in an MDR phenotype with fourfold increases in the MICs of unrelated antibiotics, such as quinolones/fluoroquinolones, phenicols, and tetracycline. The inactivation of this gene also resulted in a fourfold increase in the expression of ramA and a fourfold increase in the expression of the AcrAB efflux pump. These results indicated that the gene encodes a local repressor of ramA and was thus named ramR. In contrast, the inactivation of marR, marA, soxR, and soxS did not affect the susceptibilities of the strain. In quinolone-or fluoroquinolone-resistant strains of serovar Typhimurium overexpressing AcrAB, several point mutations which resulted in amino acid changes or an in-frame shift were identified in ramR; in addition, mutations interrupting ramR with an IS1 element were identified in high-level fluoroquinolone-resistant serovar Typhimurium DT204 strains. One serovar Typhimurium DT104 isolate had a 2-nucleotide deletion in the putative RamR binding site found upstream of ramA. These mutations were confirmed to play a role in the MDR phenotype by complementing the isolates with an intact ramR gene or by inactivating their respective ramA gene. No mutations in the mar or sox region were found in the strains studied. In conclusion, mutations in ramR appear to play a major role in the upregulation of RamA and AcrAB and, consequently, in the efflux-mediated MDR phenotype of serovar Typhimurium.

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Background: Methicillin-resistant staphylococci (MRS) are an emerging global problem with serious public health concern.Aims: This study investigated the prevalence and antimicrobial susceptibility of commensal Staphylococcus species isolated from healthy and clinical cats and dogs.Methods: Nasal swab samples were collected from animals and processed using selective and semi-selective mediums. Presumptive isolates were subjected to biochemical testing and analyzed using the Phoenix automated identification and susceptibility testing system. PCRs protocols were used to screen for mecA and pvl genes.Results: In total, 151 pets (103 cats and 48 dogs) were enrolled, of which 14 dogs (29%) and 24 cats (23%) were colonized with various Staphylococcus species mainly originated from healthy animals. A total of 38 staphylococci isolates were collected and distributed between 24 coagulase-negative and 14 coagulase-positive staphylococci. Only 13 staphylococci strains were identified as MRS, out of which only five isolates expressed that the mecA gene exclusively originated from healthy pets.Conclusion: This is the first study reporting the prevalence and colonization status of staphylococci species and MRS strains isolated from cats and dogs in Libya. The study reports important information of medical and clinical importance on antimicrobial and multidrug resistance of different staphylococci strains, particularly the coagulase negative species.

This is the largest Libyan study to date to investigate the prevalence and antimicrobial susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) among health care workers in Tripoli, Libya. A total of 569 doctors and nurses from 4 main hospitals were screened for MRSA with specimens collected from the anterior nares. Isolates from 109 of the 569 subjects (19%) were confirmed as MRSA by polymerase chain reaction assay; the majority (98/109) were from a general hospital. Antimicrobial resistance patterns tested by disk diffusion were as follows: erythromycin (74%), ciprofloxacin (77%), clindamycin (20%), trimethoprim/sulfamethoxazole (50%), quinuprisin/dalfopristin (19%), vancomycin (12%) and mupirocin (5%). Eighteen isolates exhibited macrolide-lincosamide-streptogramin B resistance (MLSB): 6 were MLSBi and 12 were MLSBc. The results provide evidence that Libyan health care workers could serve as MRSA carriers and play a role in the dissemination of MRSA to the public and other workers.

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) is a nosocomial (hospital-acquired) pathogen of exceptional concern. It is responsible for life-threatening infections in both the hospital and the community.AimsTo determine the frequency of MRSA misidentification in hospitals in Tripoli, Libya using current testing methods.MethodsOne hundred and seventy S. aureus isolates previously identified as MRSA were obtained from three hospitals in Tripoli. All isolates were reidentified by culturing on mannitol salt agar, API 20 Staph System and retested for resistance to methicillin using the cefoxitin disk diffusion susceptibility test and PBP2a. D-tests and vancomycin E-tests (Van-E-tests) were also performed for vancomycin-resistant isolates.ResultsOf the 170 isolates examined, 86 (51%) were confirmed as MRSA (i.e. 49% were misidentified as MRSA). Fifteen (17%) of the confirmed MRSA strains exhibited inducible clindamycin resistance. Of the 86 confirmed MRSA isolates, 13 (15%) were resistant to mupirocin, 53 (62%) were resistant to ciprofloxacin, 41 (48%) were resistant to trimethoprim-sulfamethoxazole, and none were resistant to linezolid. Although disc-diffusion testing indicated that 23 (27%) of the isolates were resistant to vancomycin, none of the isolates were vancomycin-resistant by Van-E-test.ConclusionsMisidentification of nosocomial S. aureus as MRSA is a serious problem in Libyan hospitals. There is an urgent need for the proper training of microbiology laboratory technicians in standard antimicrobial susceptibility procedures and the implementation of quality control programs in microbiology laboratories of Libyan hospitals.