Antibiotic Susceptibility Patterns of Biofilm-Producing Nosocomial Non-Coagulase Staphylococcus Isolates from Clinical Sources in Iraq

Coagulase-negative staphylococci (CoNS) are commonly found on the skin and mucous membranes of humans and animals. Many of them, such as Staphylococcus epidermidis, Staphylococcus haemolyticus, and Staphylococcus petrasii, are significant causes of various diseases. Staphylococcus spp. is typically a commensal microorganism that can exist in the human body and often does not cause any illness. A bacterium possessing virulence factors, such as biofilm formation, is significant because these factors enhance its ability to cause disease. As biofilms shield bacteria from opsonophagocytosis and antimicrobial agents, they can cause persistent or chronic infections. This study aimed to examine biofilm formation in coagulase-negative Staphylococcus as a strategy to prevent and manage infection, thereby supporting public health maintenance and improvement. It focused on characterizing local S. epidermidis and S. haemolyticus isolates using molecular techniques, particularly multilocus sequence typing (MLST), with the goal of advancing epidemiological understanding and surveillance efforts.

In this study, samples were collected, and the species were identified using the VITEK 2 Compact system. A Kirby-Bauer disc diffusion test was carried out to detect antimicrobial susceptibility, and the biofilm production was tested with a microtiter plate. Multilocus sequence typing (MLST) was performed, followed by data processing using the Oxford scheme to categorize the isolates.

The isolates included 13.3% (n=20) S.epidermidis, 20% (n=30) S. haemolyticus, 23.3% (n=35) coagulase-positive staphylococci, 26% (n=39) Gram-negative bacteria, and 17.3% (n=26) showed no growth. Coagulase-negative Staphylococcus (CoNS) isolates exhibited 100% resistance to amoxiclav, cefoxitin, methicillin, amoxicillin, and ceftriaxone. High resistance was observed against piperacillin (96%), ceftazidime (96%), fusidic acid (76%), tobramycin (68%), tetracycline (68%), gentamicin (66%), and azithromycin (66%). Moderate resistance was noted for vancomycin (52%), clindamycin (46%), lincomycin (42%), ciprofloxacin (42%), and levofloxacin (40%). Lower resistance rates were recorded for trimethoprim-sulfamethoxazole (38%), rifampicin (38%), nitrofurantoin (18%), meropenem (10%), and chloramphenicol (2%). Notably, 76% of isolates were classified as multidrug-resistant (MDR). Biofilm formation was observed in 100% of isolates, with 58% showing strong, 30% moderate, and 12% weak biofilm production. MLST analysis revealed genetic diversity among local S. epidermidis and S. hemolyticus isolates, identifying several sequence types (STs), including STs (23, 59, 89, 35, 1183) for S. epidermidis and STs (24, 35, 109, 173, 146) for S. hemolyticus, some of which were reported for the first time in Iraq.

This study offers significant insights into the prevalence, antibiotic resistance patterns, and genotypic variation of S.epidermidis and S.haemolyticus strains in Anbar, Iraq. Additionally, it identifies several strains with novel MLST data, marking the first instance of such findings in Iraq, including strain S.epidermidis with IDs (46590, 46588, 46587, 46591, 46592) and S.haemolyticus with IDs (240, 241, 242, 243, 244).