As strains of SA with reduced susceptibility to many antibiotics continue to emerge, with increasing the rates of morbidity and death in the hospitals and community, there is a clinical need to fully characterize them and conduct a well-designed research and epidemiological studies. The current MRSA strains in hospitals and community are alarming condition to the clinicians¹⁹.

Development of resistance to antibiotics in developing countries, like ours, seems to be mainly related to the unreasonable usage of antibiotics due to their easy availability without prescription at the drug stores, non-optimal use in hospitals, animal husbandry, fisheries and agriculture²⁰.

The accurate and rapid diagnosis of MRSA infections is of major importance. Susceptibility testing of MRSA may be problematic owing to the phenotypic heterogeneous resistance (heteroresistance) displayed by many isolates to anti-Staphylococcal b-lactams. Consequently, many laboratory methods have been developed to increase the resistance expression, including prolonging the incubation period to 24 hours and the supplementation of media with NaCl²¹.

This study aimed to estimate the role of MRSA as a causative agent of nosocomial infections in MUHs. During the study period, a total of 642 SA isolates were isolated. One hundred and thirty MRSA isolates were isolated representing 20% of all SA nosocomial infections. This result is nearly like the result of Viswanathan et al.²² who have reported that MRSA accounts for 20-40 % of all SA infections, and of Saunders and Holmes²³ who reported that this percentage reached up to 30%.

Also, it was stated by Dhanalakshmi, et al.²⁴ that methicillin resistance represented 31.3% of SA isolates. Moreover, Abd El-Baky et al.²⁰ found that methicillin resistance represented 25.4% of SA isolates in the study conducted for documentation of VRSA in the Minia University, Egypt.

Higher rates were reported in U.S.A. hospitals by Diekema et al.²⁵ who mentioned that MRSA accounts for 30-50% of all nosocomial SA isolates and Wisplinghoff et al.²⁶, who found that the proportion of MRSA increased from 22% in 1995 to 57% in 2001.

Higher rates were reported in the Kingdom of Saudi Arabia by Baddour et al.²⁷ who reported that MRSA accounted for 77.5% of all SA nosocomial infections in a study conducted in several hospitals in Riyadh, and by Alzolibani et al.²⁸ who reported that 90% of SA strains were resistant to methicillin in a study conducted in the Qassim region for documentation of VRSA among children with atopic dermatitis. These higher rates could be attributed to the vulnerable study group.

In this study, MRSA constituted 6.48% of the total nosocomial infections. This result is not coming with the higher rates that were reported by Hsueh et al.²⁹ who stated that a rapid emergence of nosocomial MRSA infection (from 26.3% in 1986 to 77% in 2001) was found in a university hospital in Taiwan.

The prevalence of MRSA infection shows marked variation. The difference in the MRSA rates is likely related to differences in the populations of the studies and variations in the infection control measures applied. Some investigators used active surveillance cultures, and others used only culture of clinical specimens. In addition, infection control measures for patients with MRSA colonization or infection in some hospitals are stricter than in other hospitals.

Out of the 130 MRSA isolates, MRSA was isolated alone from 77 cultures (59.2%) while MRSA was isolated with another organism from 53 cultures (40.8%). Gram negative bacilli were common co-pathogens that are resistant to VA required for the MRSA treatment, so they may need to be treated by b-lactam antibiotics which may induce VA resistance among MRSA isolates^30,31.

SSIs were by far the commonest sites for MRSA infections in this study, followed by blood stream infections. Similar results have been obtained by Carla et al.³² who found that the most common sites infected by MRSA were surgical wounds (21%), intra venous sites (18%), and bacteremia (13%).

These results do not agree with the results coming from United Kingdom, Ireland and Greece that reported one of the highest rates of MRSA from bloodstream isolates (44%) in 2004³³.

In the present study, MRSA was noticed to be more prevalent in surgical patients (58.46%) than in medical patients (41.54%). In agreement with our results, Gordon and Lowy³⁴ reported that MRSA was isolated from surgical patients, ICU patients and from medical patients represented (40%, 27%, 33% respectively).

Regarding the risk factors, it was revealed that recent antibiotic therapy (especially b-lactam antibiotics) and prolonged hospital stay for > 7 days are important risk factors for the expansion of MRSA infections (90.0% & 84.6% of cases, respectively). This was supported by many reports^35-37. This may be owing, in part, to the more likelihood over time of becoming colonized with MRSA from either horizontal nosocomial transmission or endogenous emergence of resistance.

Similarly, Raygada and Levine³⁸ have demonstrated a close association between recent antibiotic usage and the development of subsequent antibiotic resistance in both Gram positive and negative bacteria.

In the current study, b-lactams alone were the antibiotics prescribed for 73.1% of patients. Other drugs prescribed ranged among fluoroquinolones, monobactams, macrolides and aminoglycosides. These findings are consistent with Borg et al.³⁹ who stated that mecA expression is either constitutive or inducible by some b-lactam antibiotics. Also, extensive antibiotics usage within a hospital may partly explain differences among hospitals in transmission rates of resistant organisms⁴⁰.

During the study, it was noticed that invasive indwelling devices (such as IV lines, urinary catheters and wound drains), ICU admission and presence of surgical sutures were also important risk factors for the emergence of MRSA infections. This agreed with data mentioned by Ricarda et al.⁴¹

Moreover, the greatest incidence of acquisition of MRSA infections occurred when³ 2 different devices were used for the same patient. Likewise, Sadoyama and Gontijo-Filho⁴² concluded that most nosocomial MRSA infections occur in persons with multiple risk factors for infection.

Concerning the antibiotics sensitivity patterns of the MRSA isolates, it was noticed that, all isolates were resistant to penicillin, ampicillin and cephradine antibiotics. These findings agreed with Noto et al.⁴³ who stated that more than 95% of patients with SA infections worldwide do not respond to first-line antibiotics such as penicillin or ampicillin.

During the study, MRSA was found to be resistance to ciprofloxacin (65%), trimethoprim-sulfamethoxazole (71%), clindamycin (89%) and erythromycin (88%). Similarly, Adwan et al.⁴⁴ reported that up to 82.1% of nosocomial MRSA isolates were resistant to erythromycin and therefore, the macrolides cannot be considered first line therapy for serious Staphylococcal infections.

However, in a study done by Al-Tawfiq⁴⁵, nosocomial MRSA isolates showed lower rates of resistance to trimethoprim-sulfamethoxazole (68%), clindamycin (76.6%) and erythromycin (68%) but showed higher rates of ciprofloxacin resistance (76.6%).

In studying sensitivity to gentamicin, MRSA isolates were resistant in 80% of cases. This does not correlate with results obtained in Cyprus by Gourni et al.⁴⁶, who found that MRSA were gentamicin resistant in 18.75 only.

In this study, thirteen MRSA isolates were found to be resistant to rifampicin (10%). This agreed with the Turkish study that reported the emergence of rifampicin-resistant MRSA in 3 wards of a university hospital in Turkey⁴⁷.

All MRSA isolates detected by Colakoglu et al.⁴⁸ were found to be sensitive to fusidic acid, rifampicin and tetracycline, but, some of the isolates that were detected in our study were resistant to these antibiotics.; for fusidic acid (64%), rifampicin (10%) and for tetracycline (92%) were resistant.

The variations in the antibiotics resistance patterns among different studies can be explained by selection pressure of certain drugs used according to the local hospital policy.

Glycopeptides antibiotics are the treatment of choice of MRSA infections. Appearance of different degrees of VA resistance occurred due to its widespread use to treat MRSA and other Gram-positive infections. The first strain of SA with reduced susceptibility to VA and teicoplanin (glycopeptide-intermediate SA [GISA]) was reported in the 1997 from Japan, whereas VRSA isolates were first reported in the 2002 from the USA, Jordan and Brazil¹⁰.

The reasons for decreased VA susceptibility may be owing to non-optimal utilization of VA and other antibiotics or due to use of antimicrobial agents in food-producing animals as documented in Saudi Arabia in Qassim area²⁸. These strains represent a crucial challenge for antimicrobial therapy, testing antimicrobial susceptibility and infection control in hospitals²⁰.

Fortunately, one hundred and twenty-nine of MRSA (99.2%) in the current study, were VA sensitive, which agreed with Sievert et al.⁴⁹ and Antonanzas et al.⁵⁰ who included VA in antibiotic susceptibility testing of MRSA.

The present study encountered one VRSA strain (0.8%) with VA MIC 32µg/ml. Many studies encountered VRSA strains at higher frequencies than that reported in our study; Saderi et al.⁵¹ reported that 3.5% of SA isolates were VRSA and Hakim et al.⁵² reported VISA (13%). On the other hand, Dhanalakshmi, et al.²⁴ reported that no VISA or VRSA were found among MRSA strains.

The VRSA case reported in our study³¹ showed multi-drug resistance to penicillin, amoxicillin/clavulanic, ampicillin/sulbactam, cefazolin, cefuroxime, gentamicin and ciprofloxacin but showed susceptibility to linezolid. Multi-drug resistance of VRSA was also reported by many studies^3,28,53.