الفهرس 
Title pageOnly 14 pages are availabe for public view
 |  | from | 104 |  |  |
| | | from | 104 | | |
Abstract
Staphylococcus aureus (S. aureus) is a principle human pathogen that causes different types of infections. The bacterium is known to be resistant to diverse antibiotics. Methicillin-resistant S. aureus (MRSA) plays an important role in public health especially due to its high mortality and morbidity. MRSA strain generates an altered penicillin binding protein (PBP2a) encoded by mecA gene which is located on SCCmec mobile genomic island. This makes the bacteria resistant to beta-lactam antibiotics.
Thirteen SCCmec types designated types I-XIII have been detected till now.
The aim of this study was to detect the prevalence of different SCCmec types of MRSA isolated in the Microbiology department of the Medical Research Institute from September 2019 to March 2021. This study was carried out on 100 MRSA strains isolated from clinical samples.
Identification of S.aureus was done by inoculation on blood and MacConkey agar. S aureus isolates were identified by their microscopic appearance and colonies morphology followed by biochemical tests. MRSA was identified by disc diffusion for cefoxitin antibiotic and screening on ORSAB. Susceptibility testing was done using Kirby-Bauer disc diffusion method and vancomycin screening agar.
Staphylococcal Cassette chromosome mec typing was done using conventional PCR and confirmed by Sybr green Real time PCR with melting curve analysis.
Among the 100 MRSA isolates 72% were isolated from inpatients and 28% from out patients. The majority (60%) were isolated from pyogenic skin and soft tissue infections including 31% from abscesses and 29% from wound swabs, with a higher proportion among inpatients (46/72,63%) compared to outpatients (14/28,50%).
Fourteen % of the MRSA isolates were sensitive to all tested antibiotics. The highest resistance was to gentamicin 71%, followed by tetracycline 44%, while the highest sensitivity was to linezolid 97% and rifampicin 93%. All MRSA isolates were sensitive to vancomycin.
Sensitive isolates to clindamycin were 85 %, while 8% were constitutively resistant and 4 % showed induced resistance with a positive D-test.
The resistance to the majority of antibiotics was slightly higher among inpatients than outpatients. Only resistance to tetracycline and rifampicin was higher among out patients.
Among the inpatient and outpatient MRSA isolates, nearly 14% in each were sensitive to all antibiotics. The most prominent resistance pattern among inpatients was to gentamicin only (14/72, 19.4%), followed by resistance to gentamicin, doxycycline and tetracycline (13/72, 18%). Similarly, among outpatients, the most prominent resistance
patterns were to gentamicin, doxycycline and tetracycline and resistance to gentamicin and tetracycline only (4/28, 14.2%) each.
Out of the 100MRSA isolates, only (75%) were successfully typed. Among the 75 typed MRSA isolates,34 (45.3%) were identified as SCCmec type V, followed by 12 (16%) were SCCmec type VI, SCCmec types II and III were found each in 10 (13.3%) isolates, and SCCmec type IV in 9 (12%).
Among the 16 outpatient SCCmec typed isolates, 5(31.3%) were SCCmec type V, followed by 4(25%) SCCmec type VI. SCCmec types IV and III were found each in 3(18.8%) isolates. And the 59 inpatient SCCmec typed isolates were distributed as, 29 (49.2%) belonged to SCCmec type V followed by 9 (15.3%) SCCmec type II, 8(13.6%) were SCCmec type VI and 7(11.9%) SCCmec type III.
Among the 22 abscess isolates 11(50%) were SCCmec type V, followed by 5(22.7%) SCCmec type VI. While SCCmec type V constituted 13(56%)of the 23 wound swabs, followed by 5(21.7%) SCCmec type III.
SCCmec type II was the highest prevalent type 4(33%)among the 12 blood isolates, followed by 3(25%) were of SCCmec type V. Among the 6 nasal swabs 3(50%) were SCCmec type IV. No significant relation was found between the source of infection and the SCCmec types except for nasal swabs where SCCmec type IV is significantly higher (p=0.049).
SCCmec types II and III had the highest resistance to antibiotics. SCCmec type II was resistant mainly to gentamicin, macrolides followed by flouroquinolones. While SCCmec type III showed resistance to flouroquinolones followed by gentamicin and tetracyclines. On the other hand, SCCmec IV showed the least resistance to antibiotics followed by SCCmec type V and VI and this was statistically significant (p=0.02-0.001).
Most of the isolates with the same SCCmec type displayed the same pattern of resistance to antibiotics. For instance, simultaneous resistance to gentamicin and tetracycline was displayed by 8 isolates typed as SCCmec type V,also resistance to gentamicin, doxycycline and tetracycline was displayed by 5 isolates of SCCmec type V and 7 isolates of SCCmec type VI.