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A comparative study of antibiotic profile of community acquired and hospital acquired isolates of staphylococcus aureus in a tertiary care hospital, Kashmir

Introduction: Staphylococcus aureus is a virulent pathogen in humans capable of surviving in the hospital environment as a saprophyte and in the human body as a normal commensal. It is a gram positive cocci which is capable of causing serious and life threatening infections like bacteremia and pneumonia with high morbidity and mortality. Presence in the blood increases its chances of metastasis and the risk of fatality. The choice of antibiotic therapy has conventionally relied to a large extent on the susceptibility of the pathogen to methicillin. In our study we intend to analyze the cases of different infections caused by Staphylococcus aureus both from the community and hospital environment with main focus on methicillin resistant strains.


Introduction
Staphylococcus aureus is the most important human pathogen among the Staphylococci. It has developed resistance against most of the therapeutic agents. Being a versatile human pathogen it causes infections ranging from a mild involvement of the skin and the soft tissue, to lifethreating sepsis and pneumonia. The capability of this pathogenic gram positive cocci to produce numerous cell surface and secreted virulence factors as well as the propensity to develop resistance to multiple antibiotics leads to an increase in its propensity to cause systemic and invasive diseases. The ubiquity of these bacteria in nature makes the interpretation of their recovery from patient specimens occasionally difficult, unless the clinical manifestations of disease are apparent. Staphylococcus aureus may reside in approximately 20-40% of healthy adults in the anterior nares followed by the axillae, the vagina, the perineum and lower gut as other sites of colonization. 1 Originally, penicillin was the drug of choice for the Staphylococcus aureus infections. Most of the penicillinresistant strains of Staphylococcus aureus produce β lactamase, which hydrolyzes the β-lactam ring of the antibiotic. Soon after methicillin was introduced into the clinical use in 1961, resistance to methicillin and other β lactamase resistant penicillins was first observed in Staphylococcus aureus. 2 The first case of an MRSA infection recorded in Australia, was in Sydney in 1965. 3,4 The first case of a community associated MRSA (CAMRSA) infection in the United States was reported in 1980.
The HA-MRSA isolates do circulate in the community, especially among adults. Additionally, many reports have demonstrated that the MRSA clones bear Staphyloccocal Cassette Chromosome (mec type IV gene).
The CA-MRSA strains are genetically and phenotypically distinct from the HA-MRSA strains. They typically resemble some strains of methicillin-susceptible S. aureus (MSSA) in being susceptible to a wider range of anti-staphylococcal antibiotics (some are resistant only to β lactams), and they often produce panton valentine leucocidine (PVL), a toxin that destroys the white blood cells and is a staphylococcal virulence factor. 5,6 Many of the MRSA isolates are becoming multidrug resistant and they are susceptible only to the glycopeptide antibiotics such as vancomycin. A low level resistance, even to vancomycin, is emerging. A prolonged hospital stay and the indiscriminate use of antibiotics before hospitalization are the common factors responsible for emergence of MRSA infections globally. These affected patients act as the root cause for the spread of the infections to the hospital staff who may act as carriers adding more complications to the treatment.
Aims and Objectives 1. To determine the incidence of occurrence of community acquired and hospital acquired Staphylococcus aureus infection. 2. To study the antibiotic sensitivity pattern of these infections.

Materials and Methods
The present study was carried out in the department of Microbiology, in a tertiary care hospital in Srinagar for a period of two years (Jan 2017-Dec 2018).
The study material consisted of 573 non-repetitive isolates of Staphylococcus aureus which were obtained from various clinical samples of the out-patients and the inpatients treated in various clinical departments.

Methodology
1. All clinical samples were properly collected under strict aseptic precautions and appropriately delivered to the microbiology laboratory. 2. After an initial direct gram staining technique, all samples were inoculated on the routine laboratory media like nutrient agar, blood agar, MacConkey agar and chocolate agar following the standard microbiological techniques. 7 3. Any growth obtained after overnight incubation at 37⁰C was put to confirmation by various spot tests like catalase, coagulase and modified oxidase or biochemical tests and hemolytic pattern. 8

Detection of methicillin resistant Staphylococcus aureus
The detection of MRSA was done phenotypically by using cefoxitin (30µg) disc. A zone of inhibition equal to or more than 21mm was considered as susceptible.

Categorization of Staphylococcus aureus isolates into hospital acquired and community acquired.
Based on the history of the patient, the MRSA isolates were categorized into Community acquired or Hospital acquired. An infection occurring among the in-patients with a Staphylococcus aureus isolate earlier than 48 hours of hospitalization or among out-patients is considered as community acquired, and that occurring after 48 hours of hospitalization or from a patient with a history of hospitalization for surgery or dialysis, intervention, or of an admission in day-care is considered as hospital acquired.

Results
A year-wise prevalence of Staphylococcus aureus infection was studied among various samples. Highest prevalence was observed among exudates during these two years whereas very low prevalence was observed among blood and urine samples. All blood samples with positive growth of Staphylococcus aureus were collected from IPD (Table  1).  A comparison of antibiotic sensitivity pattern among Staphylococcus aureus isolates from hospital and community revealed a higher resistance to most of the drugs among isolates from hospital samples. However, more isolates from community samples were resistant to drugs like penicillin, erythromycin and ciprofloxacin. The difference in sensitivity was however observed to be of less significance to most drugs except co-trimoxazole where 60% of the isolates from community samples were observed sensitive compared to 41.76% of sensitive isolates from hospitalized patients. Highest sensitivities were observed for teicoplanin, vancomycin and linezolid among isolates from both OPD and IPD (Table3). An overall higher percentage of Staphylococcus aureus isolates were cultured from exudates and blood samples collected from male patients. However among the urine samples, Staphylococcus aureus was isolated from 7 urine samples belonging to female patients in comparison to just 2 urine samples from male patients (Table 4).

Discussion
Among the gram-positive pathogens, Staphylococcus aureus is a common cause of skin and soft tissue infection in hospitalized as well as community-acquired infections.
Of the 580 total non-repetitive isolates of S aureus detected from January 2017 to December 2018, 234(40.34%) were isolated in 2017 and 346(59.65%) were isolated in 2018. Majority of the patients were referred from Dermatology department followed by departments of General surgery, Orthopedics, Gynaecology and Obstretics and Medicine. The prevalence of CAMRSA was found to be 346(62.53%) and that of HAMRSA was 234(37.46%). This is in concordance with a study made by D'Souza et al 10 in 2010 where prevalence of MRSA amongst the outpatient was 54% and study by Avneet Kaur et al 11 in 2017 where 49% prevalence rate was reported. This may partly be attributed to the fact that a large percentage (60%) of samples from skin and soft tissue infections were reported to be Staphylococcus aureus as in case of study by Sangeeta Joshi et al 12 and study by D'Souza et al. 10 CAMRSA is increasing, even in USA, where 50% or more of Staphylococcus aureus infections presenting to the emergency department may be methicillin resistant. These occur in otherwise healthy individuals with no recent healthcare contacts. 13 CAMRSA strains cause the same range of infections as HAMRSA strains and these may include blood stream infections (BSI), skin and soft tissue infections and severe pneumonia. 13 This could be partly attributed to the fact that the CAMRSA strains produced skin disease whereas HAMRSA are associated with risk factors including recent hospitalization or surgery.
In our study we observed that the percentage of males (65%) was significantly more than females (35%) and this number was 377 and 203 respectively. This was in contrast to study by Abbas et al 14 where no significant difference was found. A total of 355(61.20%) MRSA strains were detected from various clinical samples using cefoxitin disc diffusion technique. This is significantly higher than other studies in India by Mittal et al [15] (40.38%) and Mohanasoundaram et al 17  Highest isolation of MRSA among different clinical samples was observed from pus samples (88.62%), followed by Blood (9.8%) and Urine (1.55%). This is in concordance with a study done by Tiwari et al which showed 71.20% MRSA from pus samples. 21 The present study revealed that 99.58% of HAMRSA were sensitive to linezolid, vancomycin and teicoplanin. One isolate among the HAMRSA isolated from an orthopedic implant was found to be pan-drug resistant which is in contrast to study by Abbas et al 14 where 100% MRSA isolates were found to be sensitive to vancomycin, linezolid and teicoplanin. About 79.70% isolates of hospital acquired Staphylococcus aureus were sensitive to amikacin followed by clindamycin (71.4%), gentamycin (62.05%), erythromycin (55.8%), amoxiclav (53.75%), cefoxitin (44.59%) and cotrimoxazole (41.76%). Among the community acquired Staphylococcus aureus, 100% isolates were sensitive to vancomycin, linezolid and teicoplanin, 85% isolates were sensitive to amikacin followed by clindamycin (75.88%), gentamycin (70.5%), amoxiclav (60%), cotrimaxazole (60%) and cefoxitin (34.71%).

Conclusion
This study demonstrates that MRSA is a common cause of therapeutic problem in health care facilities. Injudicious use of over-the-counter antibiotics is the major cause behind this trend. The current challenging problem is the spread of MRSA among the community. There is a need to study epidemiology of such infections as this appears to be a changing trend. Robust antimicrobial stewardship, strengthened infection control measures most importantly hand hygiene practices are required to prevent spread and reduce emergence of resistance. Glycopeptides and linezolid continues to remain the mainstay for treatment for MRSA infections. However de-escalation of vancomycin to β lactams once the culture sensitivity results reveal a MSSA isolate should be encouraged. Cephalosporins are the drugs of choice for the treatment of MSSA infection. Amikacin, chloramphenicol, clindamycin and teicoplanin are to be kept as reserved drugs and drugs like vancomycin and linezolid which should be used for life-threatening infections.

Source of Funding
None.