Difference in epidemiology and antibiotic susceptibility of methicillin resistant and methicillin susceptible Staphylococcus aureus isolates

Antimicrobial resistance of Staphylococcus aureus especially methicillin resistant S. aureus [MRSA] continues to be a problem for clinicians worldwide. Although difference in epidemiology and antibiotic susceptibility of methicillin resistant S. aureus [MRSA] and methicillin susceptible S. aureus [MSSA] isolates has been proposed by investigators, few data have been reported to now. Disk diffusion method was used for determination of in vitro susceptibility of S. aureus isolates to 15 antibiotics. Susceptibility pattern of 192 non-duplicates S. aureus isolated from clinical specimens in four university hospitals in Tehran, from November 2007 to August 2008, were compared. In addition, distribution of MRSA and MSSA isolates were investigated in different specimens, on various wards, and in different age groups. MRSA isolates were constituted 49% of all isolates. While only 1.7% of the MSSA isolates were multidrug resistant, all of MRSA were shown resistance to at least five antibiotics. Majority of isolates from patients >/= 65 years old were MRSA and prevalence of methicillin resistance was highest among S. aureus isolated from respiratory specimens. Also, MRSA appeared to be more prevalent in intensive care units and operation wards than in other departments. This study has shown a relationship between methicillin resistance and resistance to other antibiotics in S. aureus isolates. Also, considerable differences were observed in epidemiology of MRSA and MSSA isolates

[Antibiotic resistance patterns of isolated pseudomonas aeruginosa strains from infections of burned patients]

Pseudomonas aeruginosa is one of the most important pathogens, particularly in immunocompromised hosts, and remains a prominent gram-negative bacterium that causes hospital-associated infections. The aim of this study was to evaluate the susceptibility of 110 clinical isolates of Pseudomonas aeruginosa to routine antibiotics and antibiotyping of these strains. One hundred and ten bacterial isolates of Pseudomonas aeruginosa were isolated from 99 burned patients [Shahid Motahary Burn Hospital, Tehran, Iran, during March to April 2006] with different types of infections. Antibiotic susceptibility test was performed by disc diffusion method and clones of bacteria were determined by antibiotyping. Demographic data of patients were recorded too. The frequency of Pseudomonas aeruginosa resistant to imipenem, amikacin, gentamicin, trimethoprim, tetracycline, carbenicillin, piperacillin, ceftazidime ceftriaxone and ciprofloxacin were 32.1%, 47.2%, 89%, 100%, 70%, 90%, 88.1%, 91.8%, 93.6% and 77.2%, respectively. Antibiotyping showed that 110 isolates were distributed in 33 patterns, but 19 isolates were resistant to all antibiotics and 65 isolates belonged to 7 patterns of antibiotyping. Other isolates [45 isolates] created 26 patterns. The results showed that most of isolates were resistant to routine antibiotics and it is necessary to introduce urgent measures for restriction of the spread of Pseudomonas aeruginosa infection in Shahid Motahary Burn Hospital. It is possible that most infections were carried by special clones and it is probable that the source of these clones is environmental