Bacterial isolates & their resistance patterns from blood cultures,KIMS

Introduction

Bloodstream infections (BSI) remain one of the important causes of morbidity and mortality worldwide.^[1] Bacteremia refers to the presence of bacteria in the blood and Septicemia is a condition where bacteria circulate, multiply, form toxic products and cause high fever.^[2] Several mechanisms play a role in the removal of microorganisms from the bloodstream. Patients who are debilitated, immunocompromised/ immunodeficient are at increased risk because circulating bacteria may not be cleared from blood due to impairment in defense mechanisms.^[3] A variety of bacteria have been recovered from the bloodstream, both Gram-positive and Gram-negative. The most common ones are members of Enterobacteriaceae, Staphylococcus aureus, Streptococcus pneumoniae, Enterococci, Pseudomonas aeruginosa.^[3]

Microorganisms present in the circulating blood -whether continuously, intermittently, or transiently are a threat to every organ in the body.^[2] The major categories of BSI are intravascular i.e, they originate within CVS. eg: infective endocarditis, catheter-associated bacteremia, and extravascular where the organisms multiply at the primary site and are drained by lymphatics reaching the bloodstream, eg: genitourinary tract (25%), respiratory tract (20%), abscess (10%), surgical site infections (5%), biliary tract (5%).^[4] The usual presentation of septicemia is fever, chills, malaise, tachycardia, hyperventilation, prostration, and hypertension. ^[5]

Major complications are the development of shock, disseminated intravascular coagulation, and acute renal failure.^[5] Early diagnosis plays a crucial role in managing BSI and hence, prompt detection of such infections is a critical function of the microbiology laboratory.^[6] Blood culture is a vital tool for the detection of BSI and remains the gold standard for bacteremia detection.^[6] Prompt initiation of appropriate antimicrobial therapy is demonstrably important for preventing morbidity and mortality.^[3] Empiric antimicrobial therapy is based on knowledge of the microbial profile and their antimicrobial sensitivity patterns, clinical and epidemiological data.^[6] Irrational use of drugs has led to an increase of MDR bugs and thus worsened the condition.^[7] Hence, the present study was undertaken to describe the bacteriological profile and drug resistance pattern from blood culture specimen to guide clinicians to initiate empiric antibiotic therapy.

Materials and Methods

The present study is a retrospective analysis of blood culture isolates received in the Department of Microbiology, KIMS & RF, Amalapuram, Andhra Pradesh from August 2019 to January 2020.

Results

A total of 380 blood culture samples were processed. Out of 380 samples processed, 57 samples (15%) showed bacterial growth. Rest 323 (83%) samples showed no growth.

Out of 57 culture-positive blood samples, isolates of Gram-positive cocci were 27 (47.3%) and those of Gram-negative Bacteria were 30 (52.7%).

S.aureus is predominant organism, isolated in 20 samples (35.08%) followed by Klebsiella in 19 samples (33.3%), Pseudomonas in 7 cases (12.28%), CONS in 7 cases (12.28%), E.coli in 3 cases (5.26%) and Acinetobacter in 1 case (1.75%).

Antibiotic susceptibility patterns for Gram-positive cocci and Gram-negative bacilli were interpreted according to CLSI Guidelines. Both S.aureus and CONS were highly resistant to Penicillin, Ampicillin, Amoxyclav, and Ciprofloxacin. All S.aureus isolates were highly sensitive to Methicillin, Vancomycin, Teicoplanin, Linezolid, Clindamycin, and Cefoperazone-sulbactam.

Among Gram negative bacteria, Klebsiella and E.coli showed high resistance to Cefixime (95% &67%) amoxycillin/clavulanic acid (84% & 100%) and Ceftazidime (79% & 67%). Klebsiella isolates also exhibited high resistance to third generation cephalosporins (74%) and low resistance to piperacillin tazobactum (31%) and cefoperazone sulbactum (26%). Pseudomonas isolates showed high resistance to cefixime (100%), cefoperazone (86%) and amoxyclav (86%). Acinetobacter showed resistance to ciprofloxacin and cefixime.

Discussion

The present study was conducted to demonstrate the distribution of microbial isolates causing bloodstream infections and their drug resistance patterns to the commonly used oral and parenteral antimicrobial agents.

The susceptibility to antimicrobials and the bacteriological profile is a constantly evolving feature. This necessitates the need for effective management of bloodstream infections.

In our study, the rate of positive blood culture was found to be 15%. This finding is comparable to studies conducted by Qureshi et al,^[10] Mehta MP et al,^[11] and Vijaya Devi et al ^[4] who reported a culture-positive rate of 16.6%, 16.4%, and 16.8% respectively. The low rate of isolation could be due to prior antibiotic therapy before reaching the tertiary center and the other reason could be self-medication and availability of antibiotics without any prescripition. However slight higher rate (27.9%) of positive blood culture was reported by Latif et al^[12] Such differences in the prevalence of bloodstream infections could be due to blood culture systems. geographical location and difference in infection control practices.

In the present analysis, Gram-negative bacteremia accounted for 52.7% while 47.3% isolates were Gram-Positive bacteria. It was by the study conducted by A.Vijaya Devi et al^[4] and Fatima Fasih et al^[5] in which the Gram-negative isolates were higher as compared to Gram-Positive isolates. Kalantar et al^[13] documented an increased number of Gram-positive isolates (65%) compared to Gram-negative (42%). The differences in the pattern of bacterial isolates could be differences in the study plan, variation in etiological agents, and seasonal variations.

Staphylococcus aureus was the predominant Gram-positive isolate (47.3%) and Klebsiella species was the predominant Gram-negative isolate (33.3%) in our study. Several studies like Laxmikant et al^[14] revealed that S.aureus is the common cause of bacteremia and septicemia particularly in Post-op Surgical Site Infections, CVP lines, etc.

In our study, Coagulase Negative Staphylococcus was isolated from 7 cases (12.28%). CONS, the usual skin commensals, are being increasingly considered as bloodstream pathogens over the past two decades.^[5] Presence of long-standing intravascular catheters, increasing use of medical devices like prosthetic heart valves, vascular grafts could be the mode of spread of bloodstream infections by CONS. Two studies, Valencia et al^[15] and Wattal et al^[16] have reported CONS as the most common isolate causing Bloodstream infections in ICU patients.

The most common Gram-negative organism isolated in the present study is the Klebsiella species. Similar findings were observed by Fatima Fasih et al (2019) and Tariq et al in 2014.^[5], ^[17] However, E coli followed by Klebsiella sps was found to be the most common among Gram-negative bacteria in a study by Fayyaz et al and N Vasu deva et al. ^[7], ^[18]

Few studies like Amit Banik et al (2018)^[6] and Laxmikant et al (2020)^[14] have documented Acinetobacter baumanii as the predominant Gram-negative isolate. In contrast, Acinetobacter sps (1.75%) was isolated from only one case in our study.

Antibiotic susceptibility testing in the present study showed high resistance towards Penicillin (85%), Ampicillin (85%) in S.aureus isolates. CONS isolates were highly resistant to ciprofloxacin (71.4%) and ampicillin (71.4%). All Gram-positive cocci isolates were susceptible to Methicillin, Vancomycin, Teicoplanin, Linezolid, and Cefaperazone-sulbactam. Out of 20 Staphylococcus species, none were Methicillin-resistant which is comparable to the study done by Sweta et al[20] in 2016. However, the incidence of MRSA was between 29-57% in other studies Sheshta et al 2014,^[1] Banik et al (2018).^[6]

Among the Gram-negative isolates, all Klebsiella isolates exhibited high resistance to Cefixime (95%), Ceftazidime (79%), and Amoxycillin/Clavulanic Acid (84%), lowest resistance against Cefoperazone -Sulbactam (26%), Piperacillin-Tazobactum (32%), and no resistance to Imipenem. Out of 30 Gram-Negative isolates,^[12] were ESBL producers (40%). Out of 19 Klebsiella pneumoniae isolates, 9 were ESBL producers. The prevalence of ESBL producer GNB was 32% in a study done by Prabhu et al (2010).^[19]

The isolation of Non-Fermenters like Pseudomonas aeruginosa (12.28%) and Acinetobacter (1.75%) is of concern in the present study. These bacteria are associated with a high degree of resistance to antibiotics. In the current scenario, constant antibiotic surveillance and cautious use of antibiotics are the need of the hour.

Conclusion

Early commencement of antimicrobial therapy can play a vital role in reducing mortality and morbidity in bloodstream infections. Appropriate empirical treatment is based on continuous knowledge of causative agents and their resistance patterns. Our study has provided information about likely pathogens in bloodstream infections and their resistance patterns in the rural setup. This can help in formulating Antibiotic policy and can avoid indiscriminate antibiotic use.

Acknowledgments

Technical and material resource support was provided by the Dept of Microbiology, KIMS&RF.

Conflict of Interest

The authors declare no relevant conflicts of interest.

Source of Funding

None.